diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index 2c198f14..ba2f21e4 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -1,4045 +1,4052 @@
 <?php
 
 /**
  * Calendar plugin for Roundcube webmail
  *
  * @author Lazlo Westerhof <hello@lazlo.me>
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2010, Lazlo Westerhof <hello@lazlo.me>
  * Copyright (C) 2014-2015, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
+#[AllowDynamicProperties]
 class calendar extends rcube_plugin
 {
     const FREEBUSY_UNKNOWN   = 0;
     const FREEBUSY_FREE      = 1;
     const FREEBUSY_BUSY      = 2;
     const FREEBUSY_TENTATIVE = 3;
     const FREEBUSY_OOF       = 4;
 
     const SESSION_KEY = 'calendar_temp';
 
     public $task = '?(?!logout).*';
     public $rc;
     public $lib;
     public $resources_dir;
     public $home;  // declare public to be used in other classes
     public $urlbase;
     public $timezone;
     public $timezone_offset;
     public $gmt_offset;
+    public $dst_active;
     public $ui;
 
     public $defaults = [
         'calendar_default_view' => "agendaWeek",
         'calendar_timeslots'    => 2,
         'calendar_work_start'   => 6,
         'calendar_work_end'     => 18,
         'calendar_agenda_range' => 60,
         'calendar_show_weekno'  => 0,
         'calendar_first_day'    => 1,
         'calendar_first_hour'   => 6,
         'calendar_time_format'  => null,
         'calendar_event_coloring'      => 0,
         'calendar_time_indicator'      => true,
         'calendar_allow_invite_shared' => false,
         'calendar_itip_send_option'    => 3,
         'calendar_itip_after_action'   => 0,
     ];
 
     // These are implemented with __get()
     //  private $ical;
     //  private $itip;
     //  private $driver;
 
 
     /**
      * Plugin initialization.
      */
     function init()
     {
         $this->rc = rcube::get_instance();
 
         $this->register_task('calendar', 'calendar');
 
         // load calendar configuration
         $this->load_config();
 
         // catch iTIP confirmation requests that don're require a valid session
         if ($this->rc->action == 'attend' && !empty($_REQUEST['_t'])) {
             $this->add_hook('startup', [$this, 'itip_attend_response']);
         }
         else if ($this->rc->action == 'feed' && !empty($_REQUEST['_cal'])) {
             $this->add_hook('startup', [$this, 'ical_feed_export']);
         }
         else if ($this->rc->task != 'login') {
             // default startup routine
             $this->add_hook('startup', [$this, 'startup']);
         }
 
         $this->add_hook('user_delete', [$this, 'user_delete']);
     }
 
     /**
      * Setup basic plugin environment and UI
      */
     protected function setup()
     {
         $this->require_plugin('libcalendaring');
         $this->require_plugin('libkolab');
 
         $this->lib             = libcalendaring::get_instance();
         $this->timezone        = $this->lib->timezone;
         $this->gmt_offset      = $this->lib->gmt_offset;
         $this->dst_active      = $this->lib->dst_active;
         $this->timezone_offset = $this->gmt_offset / 3600 - $this->dst_active;
 
         // load localizations
         $this->add_texts('localization/', $this->rc->task == 'calendar' && (!$this->rc->action || $this->rc->action == 'print'));
 
         require($this->home . '/lib/calendar_ui.php');
         $this->ui = new calendar_ui($this);
     }
 
     /**
      * Startup hook
      */
     public function startup($args)
     {
         // the calendar module can be enabled/disabled by the kolab_auth plugin
         if ($this->rc->config->get('calendar_disabled', false)
             || !$this->rc->config->get('calendar_enabled', true)
         ) {
             return;
         }
 
         $this->setup();
 
         // load Calendar user interface
         if (!$this->rc->output->ajax_call
             && (empty($this->rc->output->env['framed']) || $args['action'] == 'preview')
         ) {
             $this->ui->init();
 
             // settings are required in (almost) every GUI step
             if ($args['action'] != 'attend') {
                 $this->rc->output->set_env('calendar_settings', $this->load_settings());
             }
         }
 
         if ($args['task'] == 'calendar' && $args['action'] != 'save-pref') {
             if ($args['action'] != 'upload') {
                 $this->load_driver();
             }
 
             // register calendar actions
             $this->register_action('index', [$this, 'calendar_view']);
             $this->register_action('event', [$this, 'event_action']);
             $this->register_action('calendar', [$this, 'calendar_action']);
             $this->register_action('count', [$this, 'count_events']);
             $this->register_action('load_events', [$this, 'load_events']);
             $this->register_action('export_events', [$this, 'export_events']);
             $this->register_action('import_events', [$this, 'import_events']);
             $this->register_action('upload', [$this, 'attachment_upload']);
             $this->register_action('get-attachment', [$this, 'attachment_get']);
             $this->register_action('freebusy-status', [$this, 'freebusy_status']);
             $this->register_action('freebusy-times', [$this, 'freebusy_times']);
             $this->register_action('randomdata', [$this, 'generate_randomdata']);
             $this->register_action('print', [$this,'print_view']);
             $this->register_action('mailimportitip', [$this, 'mail_import_itip']);
             $this->register_action('mailimportattach', [$this, 'mail_import_attachment']);
             $this->register_action('dialog-ui', [$this, 'mail_message2event']);
             $this->register_action('check-recent', [$this, 'check_recent']);
             $this->register_action('itip-status', [$this, 'event_itip_status']);
             $this->register_action('itip-remove', [$this, 'event_itip_remove']);
             $this->register_action('itip-decline-reply', [$this, 'mail_itip_decline_reply']);
             $this->register_action('itip-delegate', [$this, 'mail_itip_delegate']);
             $this->register_action('resources-list', [$this, 'resources_list']);
             $this->register_action('resources-owner', [$this, 'resources_owner']);
             $this->register_action('resources-calendar', [$this, 'resources_calendar']);
             $this->register_action('resources-autocomplete', [$this, 'resources_autocomplete']);
             $this->register_action('talk-room-create', [$this, 'talk_room_create']);
 
             $this->add_hook('refresh', [$this, 'refresh']);
 
             // remove undo information...
             if (!empty($_SESSION['calendar_event_undo'])) {
                 $undo = $_SESSION['calendar_event_undo'];
                 // ...after timeout
                 $undo_time = $this->rc->config->get('undo_timeout', 0);
                 if ($undo['ts'] < time() - $undo_time) {
                     $this->rc->session->remove('calendar_event_undo');
                     // @TODO: do EXPUNGE on kolab objects?
                 }
             }
         }
         else if ($args['task'] == 'settings') {
             // add hooks for Calendar settings
             $this->add_hook('preferences_sections_list', [$this, 'preferences_sections_list']);
             $this->add_hook('preferences_list', [$this, 'preferences_list']);
             $this->add_hook('preferences_save', [$this, 'preferences_save']);
         }
         else if ($args['task'] == 'mail') {
             // hooks to catch event invitations on incoming mails
             if ($args['action'] == 'show' || $args['action'] == 'preview') {
                 $this->add_hook('template_object_messagebody', [$this, 'mail_messagebody_html']);
             }
 
             // add 'Create event' item to message menu
             if ($this->api->output->type == 'html' && (empty($_GET['_rel']) || $_GET['_rel'] != 'event')) {
                 $this->api->output->add_label('calendar.createfrommail');
                 $this->api->add_content(
                     html::tag('li', ['role' => 'menuitem'],
                         $this->api->output->button([
                             'command'  => 'calendar-create-from-mail',
                             'label'    => 'calendar.createfrommail',
                             'type'     => 'link',
                             'classact' => 'icon calendarlink active',
                             'class'    => 'icon calendarlink disabled',
                             'innerclass' => 'icon calendar',
                         ])
                     ),
                     'messagemenu'
                 );
             }
 
             $this->add_hook('messages_list', [$this, 'mail_messages_list']);
             $this->add_hook('message_compose', [$this, 'mail_message_compose']);
         }
         else if ($args['task'] == 'addressbook') {
             if ($this->rc->config->get('calendar_contact_birthdays')) {
                 $this->add_hook('contact_update', [$this, 'contact_update']);
                 $this->add_hook('contact_create', [$this, 'contact_update']);
             }
         }
 
         // add hooks to display alarms
         $this->add_hook('pending_alarms', [$this, 'pending_alarms']);
         $this->add_hook('dismiss_alarms', [$this, 'dismiss_alarms']);
     }
 
     /**
      * Helper method to load the backend driver according to local config
      */
     private function load_driver()
     {
         if (!empty($this->driver)) {
             return;
         }
 
         $driver_name = $this->rc->config->get('calendar_driver', 'database');
         $driver_class = $driver_name . '_driver';
 
         require_once($this->home . '/drivers/calendar_driver.php');
         require_once($this->home . '/drivers/' . $driver_name . '/' . $driver_class . '.php');
 
         $this->driver = new $driver_class($this);
 
         if ($this->driver->undelete) {
             $this->driver->undelete = $this->rc->config->get('undo_timeout', 0) > 0;
         }
     }
 
     /**
      * Load iTIP functions
      */
     private function load_itip()
     {
         if (empty($this->itip)) {
             require_once($this->home . '/lib/calendar_itip.php');
             $this->itip = new calendar_itip($this);
 
             if ($this->rc->config->get('kolab_invitation_calendars')) {
                 $this->itip->set_rsvp_actions(['accepted','tentative','declined','delegated','needs-action']);
             }
         }
 
         return $this->itip;
     }
 
     /**
      * Load iCalendar functions
      */
     public function get_ical()
     {
         if (empty($this->ical)) {
             $this->ical = libcalendaring::get_ical();
         }
 
         return $this->ical;
     }
 
     /**
      * Get properties of the calendar this user has specified as default
      */
     public function get_default_calendar($calendars = null)
     {
         if ($calendars === null) {
             $filter    = calendar_driver::FILTER_PERSONAL | calendar_driver::FILTER_WRITEABLE;
             $calendars = $this->driver->list_calendars($filter);
         }
 
         $default_id = $this->rc->config->get('calendar_default_calendar');
         $calendar   = !empty($calendars[$default_id]) ? $calendars[$default_id] : null;
         $first      = null;
 
         if (!$calendar) {
             foreach ($calendars as $cal) {
                 if (!empty($cal['default']) && $cal['editable']) {
                     $calendar = $cal;
                 }
                 if ($cal['editable']) {
                     $first = $cal;
                 }
             }
         }
 
         return $calendar ?: $first;
     }
 
     /**
      * Render the main calendar view from skin template
      */
     function calendar_view()
     {
         $this->rc->output->set_pagetitle($this->gettext('calendar'));
 
         // Add JS files to the page header
         $this->ui->addJS();
 
         $this->ui->init_templates();
         $this->rc->output->add_label('lowest','low','normal','high','highest','delete',
             'cancel','uploading','noemailwarning','close'
         );
 
         // initialize attendees autocompletion
         $this->rc->autocomplete_init();
 
         $this->rc->output->set_env('timezone', $this->timezone->getName());
         $this->rc->output->set_env('calendar_driver', $this->rc->config->get('calendar_driver'), false);
         $this->rc->output->set_env('calendar_resources', (bool)$this->rc->config->get('calendar_resources_driver'));
         $this->rc->output->set_env('identities-selector', $this->ui->identity_select([
                 'id'         => 'edit-identities-list',
                 'aria-label' => $this->gettext('roleorganizer'),
                 'class'      => 'form-control custom-select',
         ]));
 
         $view = rcube_utils::get_input_value('view', rcube_utils::INPUT_GPC);
         if (in_array($view, ['agendaWeek', 'agendaDay', 'month', 'list'])) {
             $this->rc->output->set_env('view', $view);
         }
 
         if ($date = rcube_utils::get_input_value('date', rcube_utils::INPUT_GPC)) {
             $this->rc->output->set_env('date', $date);
         }
 
         if ($msgref = rcube_utils::get_input_value('itip', rcube_utils::INPUT_GPC)) {
             $this->rc->output->set_env('itip_events', $this->itip_events($msgref));
         }
 
         $this->rc->output->send('calendar.calendar');
     }
 
     /**
      * Handler for preferences_sections_list hook.
      * Adds Calendar settings sections into preferences sections list.
      *
      * @param array Original parameters
      *
      * @return array Modified parameters
      */
     function preferences_sections_list($p)
     {
         $p['list']['calendar'] = [
             'id'      => 'calendar',
             'section' => $this->gettext('calendar'),
         ];
 
         return $p;
     }
 
     /**
      * Handler for preferences_list hook.
      * Adds options blocks into Calendar settings sections in Preferences.
      *
      * @param array Original parameters
      *
      * @return array Modified parameters
      */
     function preferences_list($p)
     {
         if ($p['section'] != 'calendar') {
             return $p;
         }
 
         $no_override = array_flip((array) $this->rc->config->get('dont_override'));
 
         $p['blocks']['view']['name'] = $this->gettext('mainoptions');
 
         if (!isset($no_override['calendar_default_view'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             $field_id = 'rcmfd_default_view';
             $view = $this->rc->config->get('calendar_default_view', $this->defaults['calendar_default_view']);
 
             $select = new html_select(['name' => '_default_view', 'id' => $field_id]);
             $select->add($this->gettext('day'), "agendaDay");
             $select->add($this->gettext('week'), "agendaWeek");
             $select->add($this->gettext('month'), "month");
             $select->add($this->gettext('agenda'), "list");
 
             $p['blocks']['view']['options']['default_view'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('default_view'))),
                 'content' => $select->show($view == 'table' ? 'list' : $view),
             ];
         }
 
         if (!isset($no_override['calendar_timeslots'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             $field_id  = 'rcmfd_timeslots';
             $choices   = ['1', '2', '3', '4', '6'];
             $timeslots = $this->rc->config->get('calendar_timeslots', $this->defaults['calendar_timeslots']);
 
             $select = new html_select(['name' => '_timeslots', 'id' => $field_id]);
             $select->add($choices, $choices);
 
             $p['blocks']['view']['options']['timeslots'] = [
                 'title' => html::label($field_id, rcube::Q($this->gettext('timeslots'))),
                 'content' => $select->show(strval($timeslots)),
             ];
         }
 
         if (!isset($no_override['calendar_first_day'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             $field_id  = 'rcmfd_firstday';
             $first_day = $this->rc->config->get('calendar_first_day', $this->defaults['calendar_first_day']);
 
             $select = new html_select(['name' => '_first_day', 'id' => $field_id]);
             $select->add($this->gettext('sunday'), '0');
             $select->add($this->gettext('monday'), '1');
             $select->add($this->gettext('tuesday'), '2');
             $select->add($this->gettext('wednesday'), '3');
             $select->add($this->gettext('thursday'), '4');
             $select->add($this->gettext('friday'), '5');
             $select->add($this->gettext('saturday'), '6');
 
             $p['blocks']['view']['options']['first_day'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('first_day'))),
                 'content' => $select->show(strval($first_day)),
             ];
         }
 
         if (!isset($no_override['calendar_first_hour'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             $first_hour  = $this->rc->config->get('calendar_first_hour', $this->defaults['calendar_first_hour']);
             $time_format = $this->rc->config->get('calendar_time_format', $this->defaults['calendar_time_format']);
             $time_format = $this->rc->config->get('time_format', libcalendaring::to_php_date_format($time_format));
             $field_id    = 'rcmfd_firsthour';
 
             $select_hours = new html_select(['name' => '_first_hour', 'id' => $field_id]);
             for ($h = 0; $h < 24; $h++) {
                 $select_hours->add(date($time_format, mktime($h, 0, 0)), $h);
             }
 
             $p['blocks']['view']['options']['first_hour'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('first_hour'))),
                 'content' => $select_hours->show($first_hour),
             ];
         }
 
         if (!isset($no_override['calendar_work_start'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             $field_id   = 'rcmfd_workstart';
             $work_start = $this->rc->config->get('calendar_work_start', $this->defaults['calendar_work_start']);
             $work_end   = $this->rc->config->get('calendar_work_end', $this->defaults['calendar_work_end']);
 
             $p['blocks']['view']['options']['workinghours'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('workinghours'))),
                 'content' => html::div('input-group',
                     $select_hours->show($work_start, ['name' => '_work_start', 'id' => $field_id])
                     . html::span('input-group-append input-group-prepend', html::span('input-group-text',' &mdash; '))
                     . $select_hours->show($work_end, ['name' => '_work_end', 'id' => $field_id])
                 )
             ];
         }
 
         if (!isset($no_override['calendar_event_coloring'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             $field_id = 'rcmfd_coloring';
             $mode     = $this->rc->config->get('calendar_event_coloring', $this->defaults['calendar_event_coloring']);
 
             $select_colors = new html_select(['name' => '_event_coloring', 'id' => $field_id]);
             $select_colors->add($this->gettext('coloringmode0'), 0);
             $select_colors->add($this->gettext('coloringmode1'), 1);
             $select_colors->add($this->gettext('coloringmode2'), 2);
             $select_colors->add($this->gettext('coloringmode3'), 3);
 
             $p['blocks']['view']['options']['eventcolors'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('eventcoloring'))),
                 'content' => $select_colors->show($mode),
             ];
         }
 
         // loading driver is expensive, don't do it if not needed
         $this->load_driver();
 
         if (!isset($no_override['calendar_default_alarm_type']) || !isset($no_override['calendar_default_alarm_offset'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             $alarm_type = $alarm_offset = '';
 
             if (!isset($no_override['calendar_default_alarm_type'])) {
                 $field_id    = 'rcmfd_alarm';
                 $select_type = new html_select(['name' => '_alarm_type', 'id' => $field_id]);
                 $select_type->add($this->gettext('none'), '');
 
                 foreach ($this->driver->alarm_types as $type) {
                     $select_type->add($this->rc->gettext(strtolower("alarm{$type}option"), 'libcalendaring'), $type);
                 }
 
                 $alarm_type = $select_type->show($this->rc->config->get('calendar_default_alarm_type', ''));
             }
 
             if (!isset($no_override['calendar_default_alarm_offset'])) {
                 $field_id      = 'rcmfd_alarm';
                 $input_value   = new html_inputfield(['name' => '_alarm_value', 'id' => $field_id . 'value', 'size' => 3]);
                 $select_offset = new html_select(['name' => '_alarm_offset', 'id' => $field_id . 'offset']);
 
                 foreach (['-M','-H','-D','+M','+H','+D'] as $trigger) {
                     $select_offset->add($this->rc->gettext('trigger' . $trigger, 'libcalendaring'), $trigger);
                 }
 
                 $preset = libcalendaring::parse_alarm_value($this->rc->config->get('calendar_default_alarm_offset', '-15M'));
                 $alarm_offset = $input_value->show($preset[0]) . ' ' . $select_offset->show($preset[1]);
             }
 
             $p['blocks']['view']['options']['alarmtype'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('defaultalarmtype'))),
                 'content' => html::div('input-group', $alarm_type . ' ' . $alarm_offset),
             ];
         }
 
         if (!isset($no_override['calendar_default_calendar'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             // default calendar selection
             $field_id   = 'rcmfd_default_calendar';
             $filter     = calendar_driver::FILTER_PERSONAL | calendar_driver::FILTER_ACTIVE | calendar_driver::FILTER_INSERTABLE;
             $select_cal = new html_select(['name' => '_default_calendar', 'id' => $field_id, 'is_escaped' => true]);
 
             $default_calendar = null;
             foreach ((array) $this->driver->list_calendars($filter) as $id => $prop) {
                 $select_cal->add($prop['name'], strval($id));
                 if (!empty($prop['default'])) {
                     $default_calendar = $id;
                 }
             }
 
             $p['blocks']['view']['options']['defaultcalendar'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('defaultcalendar'))),
                 'content' => $select_cal->show($this->rc->config->get('calendar_default_calendar', $default_calendar)),
             ];
         }
 
         if (!isset($no_override['calendar_show_weekno'])) {
             if (empty($p['current'])) {
                 $p['blocks']['view']['content'] = true;
                 return $p;
             }
 
             $field_id   = 'rcmfd_show_weekno';
             $select = new html_select(['name' => '_show_weekno', 'id' => $field_id]);
             $select->add($this->gettext('weeknonone'), -1);
             $select->add($this->gettext('weeknodatepicker'), 0);
             $select->add($this->gettext('weeknoall'), 1);
 
             $p['blocks']['view']['options']['show_weekno'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('showweekno'))),
                 'content' => $select->show(intval($this->rc->config->get('calendar_show_weekno'))),
             ];
         }
 
         $p['blocks']['itip']['name'] = $this->gettext('itipoptions');
 
         // Invitations handling
         if (!isset($no_override['calendar_itip_after_action'])) {
             if (empty($p['current'])) {
                 $p['blocks']['itip']['content'] = true;
                 return $p;
             }
 
             $field_id = 'rcmfd_after_action';
             $select   = new html_select([
                     'name'     => '_after_action',
                     'id'       => $field_id,
                     'onchange' => "\$('#{$field_id}_select')[this.value == 4 ? 'show' : 'hide']()"
             ]);
 
             $select->add($this->gettext('afternothing'), '');
             $select->add($this->gettext('aftertrash'), 1);
             $select->add($this->gettext('afterdelete'), 2);
             $select->add($this->gettext('afterflagdeleted'), 3);
             $select->add($this->gettext('aftermoveto'), 4);
 
             $val    = $this->rc->config->get('calendar_itip_after_action', $this->defaults['calendar_itip_after_action']);
             $folder = null;
 
             if ($val !== null && $val !== '' && !is_int($val)) {
                 $folder = $val;
                 $val    = 4;
             }
 
             $folders = $this->rc->folder_selector([
                     'id'            => $field_id . '_select',
                     'name'          => '_after_action_folder',
                     'maxlength'     => 30,
                     'folder_filter' => 'mail',
                     'folder_rights' => 'w',
                     'style'         => $val !== 4 ? 'display:none' : '',
             ]);
 
             $p['blocks']['itip']['options']['after_action'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('afteraction'))),
                 'content' => html::div(
                     'input-group input-group-combo',
                     $select->show($val) . $folders->show($folder)
                 ),
             ];
         }
 
         // category definitions
         if (empty($this->driver->nocategories) && !isset($no_override['calendar_categories'])) {
             $p['blocks']['categories']['name'] = $this->gettext('categories');
 
             if (empty($p['current'])) {
                 $p['blocks']['categories']['content'] = true;
                 return $p;
             }
 
             $categories      = (array) $this->driver->list_categories();
             $categories_list = '';
 
             foreach ($categories as $name => $color) {
                 $key = md5($name);
                 $field_class = 'rcmfd_category_' . str_replace(' ', '_', $name);
                 $category_remove = html::span('input-group-append',
                     html::a([
                             'class'   => 'button icon delete input-group-text',
                             'onclick' => '$(this).parent().parent().remove()',
                             'title'   => $this->gettext('remove_category'),
                             'href'    => '#rcmfd_new_category',
                         ],
                         html::span('inner', $this->gettext('delete'))
                     )
                 );
 
                 $category_name  = new html_inputfield(array('name' => "_categories[$key]", 'class' => $field_class, 'size' => 30, 'disabled' => $this->driver->categoriesimmutable));
                 $category_color = new html_inputfield(array('name' => "_colors[$key]", 'class' => "$field_class colors", 'size' => 6));
                 $hidden         = '';
 
                 if (!empty($this->driver->categoriesimmutable)) {
                     $hidden =  html::tag('input', ['type' => 'hidden', 'name' => "_categories[$key]", 'value' => $name]);
                 }
 
                 $categories_list .= $hidden
                     . html::div('input-group', $category_name->show($name) . $category_color->show($color) . $category_remove);
             }
 
             $p['blocks']['categories']['options']['category_' . $name] = [
                 'content' => html::div(['id' => 'calendarcategories'], $categories_list),
             ];
 
             $field_id = 'rcmfd_new_category';
             $new_category = new html_inputfield(['name' => '_new_category', 'id' => $field_id, 'size' => 30]);
             $add_category = html::span('input-group-append',
                 html::a(
                     [
                         'type'    => 'button',
                         'class'   => 'button create input-group-text',
                         'title'   => $this->gettext('add_category'),
                         'onclick' => 'rcube_calendar_add_category()',
                         'href'    => '#rcmfd_new_category',
                     ],
                     html::span('inner', $this->gettext('add_category'))
                 )
             );
 
             $p['blocks']['categories']['options']['categories'] = [
                 'content' => html::div('input-group', $new_category->show('') . $add_category),
             ];
 
             $this->rc->output->add_label('delete', 'calendar.remove_category');
             $this->rc->output->add_script('
 function rcube_calendar_add_category() {
     var name = $("#rcmfd_new_category").val();
     if (name.length) {
         var button_label = rcmail.gettext("calendar.remove_category");
         var input = $("<input>").attr({type: "text", name: "_categories[]", size: 30, "class": "form-control"}).val(name);
         var color = $("<input>").attr({type: "text", name: "_colors[]", size: 6, "class": "colors form-control"}).val("000000");
         var button = $("<a>").attr({"class": "button icon delete input-group-text", title: button_label, href: "#rcmfd_new_category"})
             .click(function() { $(this).parent().parent().remove(); })
             .append($("<span>").addClass("inner").text(rcmail.gettext("delete")));
 
         $("<div>").addClass("input-group").append(input).append(color).append($("<span class=\'input-group-append\'>").append(button))
             .appendTo("#calendarcategories");
         color.minicolors(rcmail.env.minicolors_config || {});
         $("#rcmfd_new_category").val("");
     }
 }',
                 'foot'
             );
 
             $this->rc->output->add_script('
 $("#rcmfd_new_category").keypress(function(event) {
     if (event.which == 13) {
         rcube_calendar_add_category();
         event.preventDefault();
     }
 });',
                 'docready'
             );
 
             // load miniColors js/css files
             jqueryui::miniColors();
         }
 
         // virtual birthdays calendar
         if (!isset($no_override['calendar_contact_birthdays'])) {
             $p['blocks']['birthdays']['name'] = $this->gettext('birthdayscalendar');
 
             if (empty($p['current'])) {
                 $p['blocks']['birthdays']['content'] = true;
                 return $p;
             }
 
             $field_id = 'rcmfd_contact_birthdays';
             $input    = new html_checkbox([
                     'name'    => '_contact_birthdays',
                     'id'      => $field_id,
                     'value'   => 1,
                     'onclick' => '$(".calendar_birthday_props").prop("disabled",!this.checked)'
             ]);
 
             $p['blocks']['birthdays']['options']['contact_birthdays'] = [
                 'title'   => html::label($field_id, $this->gettext('displaybirthdayscalendar')),
                 'content' => $input->show($this->rc->config->get('calendar_contact_birthdays') ? 1 : 0),
             ];
 
             $input_attrib = [
                 'class'    => 'calendar_birthday_props',
                 'disabled' => !$this->rc->config->get('calendar_contact_birthdays'),
             ];
 
             $sources  = [];
             $checkbox = new html_checkbox(['name' => '_birthday_adressbooks[]'] + $input_attrib);
 
             foreach ($this->rc->get_address_sources(false, true) as $source) {
                 // Roundcube >= 1.5, Ignore Collected Recipients and Trusted Senders sources
                 if ((defined('rcube_addressbook::TYPE_RECIPIENT') && $source['id'] == (string) rcube_addressbook::TYPE_RECIPIENT)
                     || (defined('rcube_addressbook::TYPE_TRUSTED_SENDER') && $source['id'] == (string) rcube_addressbook::TYPE_TRUSTED_SENDER)
                 ) {
                     continue;
                 }
 
                 $active = in_array($source['id'], (array) $this->rc->config->get('calendar_birthday_adressbooks')) ? $source['id'] : '';
                 $sources[] = html::tag('li', null,
                     html::label(null,
                         $checkbox->show($active, ['value' => $source['id']])
                         . rcube::Q(!empty($source['realname']) ? $source['realname'] : $source['name'])
                     )
                 );
             }
 
             $p['blocks']['birthdays']['options']['birthday_adressbooks'] = [
                 'title'   => rcube::Q($this->gettext('birthdayscalendarsources')),
                 'content' => html::tag('ul', 'proplist', implode("\n", $sources)),
             ];
 
             $field_id = 'rcmfd_birthdays_alarm';
             $select_type = new html_select(['name' => '_birthdays_alarm_type', 'id' => $field_id] + $input_attrib);
             $select_type->add($this->gettext('none'), '');
 
             foreach ($this->driver->alarm_types as $type) {
                 $select_type->add($this->rc->gettext(strtolower("alarm{$type}option"), 'libcalendaring'), $type);
             }
 
             $input_value   = new html_inputfield(['name' => '_birthdays_alarm_value', 'id' => $field_id . 'value', 'size' => 3] + $input_attrib);
             $select_offset = new html_select(['name' => '_birthdays_alarm_offset', 'id' => $field_id . 'offset'] + $input_attrib);
 
             foreach (['-M','-H','-D'] as $trigger) {
                 $select_offset->add($this->rc->gettext('trigger' . $trigger, 'libcalendaring'), $trigger);
             }
 
             $preset      = libcalendaring::parse_alarm_value($this->rc->config->get('calendar_birthdays_alarm_offset', '-1D'));
             $preset_type = $this->rc->config->get('calendar_birthdays_alarm_type', '');
 
             $p['blocks']['birthdays']['options']['birthdays_alarmoffset'] = [
                 'title'   => html::label($field_id, rcube::Q($this->gettext('showalarms'))),
                 'content' => html::div('input-group',
                     $select_type->show($preset_type)
                     . $input_value->show($preset[0]) . ' ' . $select_offset->show($preset[1])
                 ),
             ];
         }
 
         return $p;
     }
 
     /**
      * Handler for preferences_save hook.
      * Executed on Calendar settings form submit.
      *
      * @param array Original parameters
      *
      * @return array Modified parameters
      */
     function preferences_save($p)
     {
         if ($p['section'] == 'calendar') {
             $this->load_driver();
 
             // compose default alarm preset value
             $alarm_offset  = rcube_utils::get_input_value('_alarm_offset', rcube_utils::INPUT_POST);
             $alarm_value   = rcube_utils::get_input_value('_alarm_value', rcube_utils::INPUT_POST);
             $default_alarm = $alarm_offset[0] . intval($alarm_value) . $alarm_offset[1];
 
             $birthdays_alarm_offset = rcube_utils::get_input_value('_birthdays_alarm_offset', rcube_utils::INPUT_POST);
             $birthdays_alarm_value  = rcube_utils::get_input_value('_birthdays_alarm_value', rcube_utils::INPUT_POST);
             $birthdays_alarm_value  = $birthdays_alarm_offset[0] . intval($birthdays_alarm_value) . $birthdays_alarm_offset[1];
 
             $p['prefs'] = [
                 'calendar_default_view' => rcube_utils::get_input_value('_default_view', rcube_utils::INPUT_POST),
                 'calendar_timeslots'    => intval(rcube_utils::get_input_value('_timeslots', rcube_utils::INPUT_POST)),
                 'calendar_first_day'    => intval(rcube_utils::get_input_value('_first_day', rcube_utils::INPUT_POST)),
                 'calendar_first_hour'   => intval(rcube_utils::get_input_value('_first_hour', rcube_utils::INPUT_POST)),
                 'calendar_work_start'   => intval(rcube_utils::get_input_value('_work_start', rcube_utils::INPUT_POST)),
                 'calendar_work_end'     => intval(rcube_utils::get_input_value('_work_end', rcube_utils::INPUT_POST)),
                 'calendar_show_weekno'  => intval(rcube_utils::get_input_value('_show_weekno', rcube_utils::INPUT_POST)),
                 'calendar_event_coloring'       => intval(rcube_utils::get_input_value('_event_coloring', rcube_utils::INPUT_POST)),
                 'calendar_default_alarm_type'   => rcube_utils::get_input_value('_alarm_type', rcube_utils::INPUT_POST),
                 'calendar_default_alarm_offset' => $default_alarm,
                 'calendar_default_calendar'     => rcube_utils::get_input_value('_default_calendar', rcube_utils::INPUT_POST),
                 'calendar_date_format'          => null,  // clear previously saved values
                 'calendar_time_format'          => null,
                 'calendar_contact_birthdays'      => (bool) rcube_utils::get_input_value('_contact_birthdays', rcube_utils::INPUT_POST),
                 'calendar_birthday_adressbooks'   => (array) rcube_utils::get_input_value('_birthday_adressbooks', rcube_utils::INPUT_POST),
                 'calendar_birthdays_alarm_type'   => rcube_utils::get_input_value('_birthdays_alarm_type', rcube_utils::INPUT_POST),
                 'calendar_birthdays_alarm_offset' => $birthdays_alarm_value ?: null,
                 'calendar_itip_after_action'      => intval(rcube_utils::get_input_value('_after_action', rcube_utils::INPUT_POST)),
             ];
 
             if ($p['prefs']['calendar_itip_after_action'] == 4) {
                 $p['prefs']['calendar_itip_after_action'] = rcube_utils::get_input_value('_after_action_folder', rcube_utils::INPUT_POST, true);
             }
 
             // categories
             if (empty($this->driver->nocategories)) {
                 $old_categories = $new_categories = [];
 
                 foreach ($this->driver->list_categories() as $name => $color) {
                     $old_categories[md5($name)] = $name;
                 }
 
                 $categories = (array) rcube_utils::get_input_value('_categories', rcube_utils::INPUT_POST);
                 $colors     = (array) rcube_utils::get_input_value('_colors', rcube_utils::INPUT_POST);
 
                 foreach ($categories as $key => $name) {
                     if (!isset($colors[$key])) {
                         continue;
                     }
 
                     $color = preg_replace('/^#/', '', strval($colors[$key]));
 
                     // rename categories in existing events -> driver's job
                     if (!empty($old_categories[$key])) {
                         $oldname = $old_categories[$key];
                         $this->driver->replace_category($oldname, $name, $color);
                         unset($old_categories[$key]);
                     }
                     else {
                         $this->driver->add_category($name, $color);
                     }
 
                     $new_categories[$name] = $color;
                 }
 
                 // these old categories have been removed, alter events accordingly -> driver's job
                 foreach ((array) $old_categories as $key => $name) {
                     $this->driver->remove_category($name);
                 }
 
                 $p['prefs']['calendar_categories'] = $new_categories;
             }
         }
 
         return $p;
     }
 
     /**
      * Dispatcher for calendar actions initiated by the client
      */
     function calendar_action()
     {
         $action  = rcube_utils::get_input_value('action', rcube_utils::INPUT_GPC);
         $cal     = rcube_utils::get_input_value('c', rcube_utils::INPUT_GPC);
         $success = false;
         $reload  = false;
 
         if (isset($cal['showalarms'])) {
             $cal['showalarms'] = intval($cal['showalarms']);
         }
 
         switch ($action) {
         case "form-new":
         case "form-edit":
             echo $this->ui->calendar_editform($action, $cal);
             exit;
 
         case "new":
             $success = $this->driver->create_calendar($cal);
             $reload  = true;
             break;
 
         case "edit":
             $success = $this->driver->edit_calendar($cal);
             $reload  = true;
             break;
 
         case "delete":
             if ($success = $this->driver->delete_calendar($cal)) {
                 $this->rc->output->command('plugin.destroy_source', ['id' => $cal['id']]);
             }
             break;
 
         case "subscribe":
             if (!$this->driver->subscribe_calendar($cal)) {
                 $this->rc->output->show_message($this->gettext('errorsaving'), 'error');
             }
             else {
                 $calendars = $this->driver->list_calendars();
                 $calendar  = !empty($calendars[$cal['id']]) ? $calendars[$cal['id']] : null;
 
                 // find parent folder and check if it's a "user calendar"
                 // if it's also activated we need to refresh it (#5340)
                 while (!empty($calendar['parent'])) {
                     if (isset($calendars[$calendar['parent']])) {
                         $calendar = $calendars[$calendar['parent']];
                     }
                     else {
                         break;
                     }
                 }
 
                 if ($calendar && $calendar['id'] != $cal['id']
                     && !empty($calendar['active'])
                     && $calendar['group'] == "other user"
                 ) {
                     $this->rc->output->command('plugin.refresh_source', $calendar['id']);
                 }
             }
             return;
 
         case "search":
             $results    = [];
             $color_mode = $this->rc->config->get('calendar_event_coloring', $this->defaults['calendar_event_coloring']);
             $query      = rcube_utils::get_input_value('q', rcube_utils::INPUT_GPC);
             $source     = rcube_utils::get_input_value('source', rcube_utils::INPUT_GPC);
 
             foreach ((array) $this->driver->search_calendars($query, $source) as $id => $prop) {
                 $editname = $prop['editname'];
                 unset($prop['editname']);  // force full name to be displayed
                 $prop['active'] = false;
 
                 // let the UI generate HTML and CSS representation for this calendar
                 $html = $this->ui->calendar_list_item($id, $prop, $jsenv);
                 $cal  = $jsenv[$id];
                 $cal['editname'] = $editname;
                 $cal['html']     = $html;
 
                 if (!empty($prop['color'])) {
                     $cal['css'] = $this->ui->calendar_css_classes($id, $prop, $color_mode);
                 }
 
                 $results[] = $cal;
             }
 
             // report more results available
             if (!empty($this->driver->search_more_results)) {
                 $this->rc->output->show_message('autocompletemore', 'notice');
             }
 
             $reqid = rcube_utils::get_input_value('_reqid', rcube_utils::INPUT_GPC);
             $this->rc->output->command('multi_thread_http_response', $results, $reqid);
             return;
         }
 
         if ($success) {
             $this->rc->output->show_message('successfullysaved', 'confirmation');
         }
         else {
             $error_msg = $this->gettext('errorsaving');
             if (!empty($this->driver->last_error)) {
                 $error_msg .= ': ' . $this->driver->last_error;
             }
             $this->rc->output->show_message($error_msg, 'error');
         }
 
         $this->rc->output->command('plugin.unlock_saving');
 
         if ($success && $reload) {
             $this->rc->output->command('plugin.reload_view');
         }
     }
 
     /**
      * Dispatcher for event actions initiated by the client
      */
     function event_action()
     {
         $action  = rcube_utils::get_input_value('action', rcube_utils::INPUT_GPC);
         $event   = rcube_utils::get_input_value('e', rcube_utils::INPUT_POST, true);
         $success = $reload = $got_msg = false;
         $old     = null;
 
         // read old event data in order to find changes
         if ((!empty($event['_notify']) || !empty($event['_decline'])) && $action != 'new') {
             $old = $this->driver->get_event($event);
 
             // load main event if savemode is 'all' or if deleting 'future' events
-            if (($event['_savemode'] == 'all' || ($event['_savemode'] == 'future' && $action == 'remove' && empty($event['_decline'])))
-                && !empty($old['recurrence_id'])
+            if (!empty($old['recurrence_id'])
+                && !empty($event['_savemode'])
+                && ($event['_savemode'] == 'all' || ($event['_savemode'] == 'future' && $action == 'remove' && empty($event['_decline'])))
             ) {
                 $old['id'] = $old['recurrence_id'];
                 $old = $this->driver->get_event($old);
             }
         }
 
         switch ($action) {
         case "new":
             // create UID for new event
             $event['uid'] = $this->generate_uid();
             if (!$this->write_preprocess($event, $action)) {
                 $got_msg = true;
             }
             else if ($success = $this->driver->new_event($event)) {
                 $event['id']        = $event['uid'];
                 $event['_savemode'] = 'all';
 
                 $this->cleanup_event($event);
                 $this->event_save_success($event, null, $action, true);
                 $this->talk_room_update($event);
             }
 
             $reload = $success && !empty($event['recurrence']) ? 2 : 1;
             break;
 
         case "edit":
             if (!$this->write_preprocess($event, $action)) {
                 $got_msg = true;
             }
             else if ($success = $this->driver->edit_event($event)) {
                 $this->cleanup_event($event);
                 $this->event_save_success($event, $old, $action, $success);
                 $this->talk_room_update($event);
             }
 
             $reload = $success && (!empty($event['recurrence']) || !empty($event['_savemode']) || !empty($event['_fromcalendar'])) ? 2 : 1;
             break;
 
         case "resize":
             if (!$this->write_preprocess($event, $action)) {
                 $got_msg = true;
             }
             else if ($success = $this->driver->resize_event($event)) {
                 $this->event_save_success($event, $old, $action, $success);
             }
 
             $reload = !empty($event['_savemode']) ? 2 : 1;
             break;
 
         case "move":
             if (!$this->write_preprocess($event, $action)) {
                 $got_msg = true;
             }
             else if ($success = $this->driver->move_event($event)) {
                 $this->event_save_success($event, $old, $action, $success);
             }
 
             $reload = $success && !empty($event['_savemode']) ? 2 : 1;
             break;
 
         case "remove":
             // remove previous deletes
             $undo_time = $this->driver->undelete ? $this->rc->config->get('undo_timeout', 0) : 0;
 
             // search for event if only UID is given
             if (!isset($event['calendar']) && !empty($event['uid'])) {
                 if (!($event = $this->driver->get_event($event, calendar_driver::FILTER_WRITEABLE))) {
                     break;
                 }
                 $undo_time = 0;
             }
 
             // Note: the driver is responsible for setting $_SESSION['calendar_event_undo']
             //       containing 'ts' and 'data' elements
             $success = $this->driver->remove_event($event, $undo_time < 1);
             $reload = (!$success || !empty($event['_savemode'])) ? 2 : 1;
 
             if ($undo_time > 0 && $success) {
                 // display message with Undo link.
                 $onclick = sprintf("%s.http_request('event', 'action=undo', %s.display_message('', 'loading'))",
                     rcmail_output::JS_OBJECT_NAME,
                     rcmail_output::JS_OBJECT_NAME
                 );
                 $msg = html::span(null, $this->gettext('successremoval'))
                     . ' ' . html::a(['onclick' => $onclick], $this->gettext('undo'));
 
                 $this->rc->output->show_message($msg, 'confirmation', null, true, $undo_time);
                 $got_msg = true;
             }
             else if ($success) {
                 $this->rc->output->show_message('calendar.successremoval', 'confirmation');
                 $got_msg = true;
             }
 
             // send cancellation for the main event
             if ($event['_savemode'] == 'all') {
                 unset($old['_instance'], $old['recurrence_date'], $old['recurrence_id']);
             }
             // send an update for the main event's recurrence rule instead of a cancellation message
             else if ($event['_savemode'] == 'future' && $success !== false && $success !== true) {
                 $event['_savemode'] = 'all';  // force event_save_success() to load master event
                 $action  = 'edit';
                 $success = true;
             }
 
             // send iTIP reply that participant has declined the event
             if ($success && !empty($event['_decline'])) {
                 $emails    = $this->get_user_emails();
                 $organizer = null;
 
                 foreach ($old['attendees'] as $i => $attendee) {
                     if ($attendee['role'] == 'ORGANIZER') {
                         $organizer = $attendee;
                     }
                     else if (!empty($attendee['email']) && in_array(strtolower($attendee['email']), $emails)) {
                         $old['attendees'][$i]['status'] = 'DECLINED';
                         $reply_sender = $attendee['email'];
                     }
                 }
 
                 if ($event['_savemode'] == 'future' && $event['id'] != $old['id']) {
                     $old['thisandfuture'] = true;
                 }
 
                 $itip = $this->load_itip();
                 $itip->set_sender_email($reply_sender);
 
                 if ($organizer && $itip->send_itip_message($old, 'REPLY', $organizer, 'itipsubjectdeclined', 'itipmailbodydeclined')) {
                     $mailto = !empty($organizer['name']) ? $organizer['name'] : $organizer['email'];
                     $msg    = $this->gettext(['name' => 'sentresponseto', 'vars' => ['mailto' => $mailto]]);
 
                     $this->rc->output->command('display_message', $msg, 'confirmation');
                 }
                 else {
                     $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
                 }
             }
             else if ($success) {
                 $this->event_save_success($event, $old, $action, $success);
             }
 
             break;
 
         case "undo":
             // Restore deleted event
             if (!empty($_SESSION['calendar_event_undo']['data'])) {
                 $event   = $_SESSION['calendar_event_undo']['data'];
                 $success = $this->driver->restore_event($event);
             }
 
             if ($success) {
                 $this->rc->session->remove('calendar_event_undo');
                 $this->rc->output->show_message('calendar.successrestore', 'confirmation');
                 $got_msg = true;
                 $reload  = 2;
             }
 
             break;
 
         case "rsvp":
             $itip_sending  = $this->rc->config->get('calendar_itip_send_option', $this->defaults['calendar_itip_send_option']);
             $status        = rcube_utils::get_input_value('status', rcube_utils::INPUT_POST);
             $attendees     = rcube_utils::get_input_value('attendees', rcube_utils::INPUT_POST);
             $reply_comment = $event['comment'];
 
             $this->write_preprocess($event, 'edit');
             $ev = $this->driver->get_event($event);
             $ev['attendees'] = $event['attendees'];
             $ev['free_busy'] = $event['free_busy'];
             $ev['_savemode'] = $event['_savemode'];
             $ev['comment']   = $reply_comment;
 
             // send invitation to delegatee + add it as attendee
             if ($status == 'delegated' && !empty($event['to'])) {
                 $itip = $this->load_itip();
                 if ($itip->delegate_to($ev, $event['to'], !empty($event['rsvp']), $attendees)) {
                     $this->rc->output->show_message('calendar.itipsendsuccess', 'confirmation');
                     $noreply = false;
                 }
             }
 
             $event = $ev;
 
             // compose a list of attendees affected by this change
             $updated_attendees = array_filter(array_map(function($j) use ($event) {
                     return $event['attendees'][$j];
                 },
                 $attendees
             ));
 
             if ($success = $this->driver->edit_rsvp($event, $status, $updated_attendees)) {
                 $noreply = rcube_utils::get_input_value('noreply', rcube_utils::INPUT_GPC);
                 $noreply = intval($noreply) || $status == 'needs-action' || $itip_sending === 0;
                 $reload  = $event['calendar'] != $ev['calendar'] || !empty($event['recurrence']) ? 2 : 1;
                 $emails  = $this->get_user_emails();
                 $ownedResourceEmails = $this->owned_resources_emails();
                 $organizer = null;
                 $resourceConfirmation = false;
 
                 foreach ($event['attendees'] as $i => $attendee) {
                     if ($attendee['role'] == 'ORGANIZER') {
                         $organizer = $attendee;
                     }
                     else if (!empty($attendee['email']) && in_array_nocase($attendee['email'], $emails)) {
                         $reply_sender = $attendee['email'];
                     }
                     else if (!empty($attendee['cutype']) && $attendee['cutype'] == 'RESOURCE' && !empty($attendee['email']) && in_array_nocase($attendee['email'], $ownedResourceEmails)) {
                         $resourceConfirmation = true;
                         // Note on behalf of which resource this update is going to be sent out
                         $event['_resource'] = $attendee['email'];
                     }
                 }
 
                 if (!$noreply) {
                     $itip = $this->load_itip();
                     $itip->set_sender_email($reply_sender);
                     $event['thisandfuture'] = $event['_savemode'] == 'future';
                     $bodytextprefix = $resourceConfirmation ? 'itipmailbodyresource' : 'itipmailbody';
 
                     if ($organizer && $itip->send_itip_message($event, 'REPLY', $organizer, 'itipsubject' . $status, $bodytextprefix . $status)) {
                         $mailto = !empty($organizer['name']) ? $organizer['name'] : $organizer['email'];
                         $msg    = $this->gettext(['name' => 'sentresponseto', 'vars' => ['mailto' => $mailto]]);
 
                         $this->rc->output->command('display_message', $msg, 'confirmation');
                     }
                     else {
                         $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
                     }
                 }
 
                 // refresh all calendars
                 if ($event['calendar'] != $ev['calendar']) {
                     $this->rc->output->command('plugin.refresh_calendar', ['source' => null, 'refetch' => true]);
                     $reload = 0;
                 }
             }
 
             break;
 
         case "dismiss":
             $event['ids'] = explode(',', $event['id']);
             $plugin  = $this->rc->plugins->exec_hook('dismiss_alarms', $event);
             $success = $plugin['success'];
 
             foreach ($event['ids'] as $id) {
                 if (strpos($id, 'cal:') === 0) {
                     $success |= $this->driver->dismiss_alarm(substr($id, 4), $event['snooze']);
                 }
             }
 
             break;
 
         case "changelog":
             $data = $this->driver->get_event_changelog($event);
             if (is_array($data) && !empty($data)) {
                 $lib = $this->lib;
                 $dtformat = $this->rc->config->get('date_format') . ' ' . $this->rc->config->get('time_format');
                 array_walk($data, function(&$change) use ($lib, $dtformat) {
                     if (!empty($change['date'])) {
                         $dt = $lib->adjust_timezone($change['date']);
 
                         if ($dt instanceof DateTimeInterface) {
                             $change['date'] = $this->rc->format_date($dt, $dtformat, false);
                         }
                     }
                 });
 
                 $this->rc->output->command('plugin.render_event_changelog', $data);
             }
             else {
                 $this->rc->output->command('plugin.render_event_changelog', false);
             }
 
             $got_msg = true;
             $reload  = false;
 
             break;
 
         case "diff":
             $data = $this->driver->get_event_diff($event, $event['rev1'], $event['rev2']);
             if (is_array($data)) {
                 // convert some properties, similar to self::_client_event()
                 $lib = $this->lib;
                 array_walk($data['changes'], function(&$change, $i) use ($event, $lib) {
                     // convert date cols
                     foreach (['start', 'end', 'created', 'changed'] as $col) {
                         if ($change['property'] == $col) {
                             $change['old'] = $lib->adjust_timezone($change['old'], strlen($change['old']) == 10)->format('c');
                             $change['new'] = $lib->adjust_timezone($change['new'], strlen($change['new']) == 10)->format('c');
                         }
                     }
                     // create textual representation for alarms and recurrence
                     if ($change['property'] == 'alarms') {
                         if (is_array($change['old'])) {
                             $change['old_'] = libcalendaring::alarm_text($change['old']);
                         }
                         if (is_array($change['new'])) {
                             $change['new_'] = libcalendaring::alarm_text(array_merge((array)$change['old'], $change['new']));
                         }
                     }
                     if ($change['property'] == 'recurrence') {
                         if (is_array($change['old'])) {
                             $change['old_'] = $lib->recurrence_text($change['old']);
                         }
                         if (is_array($change['new'])) {
                             $change['new_'] = $lib->recurrence_text(array_merge((array)$change['old'], $change['new']));
                         }
                     }
                     if ($change['property'] == 'attachments') {
                         if (is_array($change['old'])) {
                             $change['old']['classname'] = rcube_utils::file2class($change['old']['mimetype'], $change['old']['name']);
                         }
                         if (is_array($change['new'])) {
                             $change['new']['classname'] = rcube_utils::file2class($change['new']['mimetype'], $change['new']['name']);
                         }
                     }
                     // compute a nice diff of description texts
                     if ($change['property'] == 'description') {
                         $change['diff_'] = libkolab::html_diff($change['old'], $change['new']);
                     }
                 });
 
                 $this->rc->output->command('plugin.event_show_diff', $data);
             }
             else {
                 $this->rc->output->command('display_message', $this->gettext('objectdiffnotavailable'), 'error');
             }
 
             $got_msg = true;
             $reload  = false;
 
             break;
 
         case "show":
             if ($event = $this->driver->get_event_revison($event, $event['rev'])) {
                 $this->rc->output->command('plugin.event_show_revision', $this->_client_event($event));
             }
             else {
                 $this->rc->output->command('display_message', $this->gettext('objectnotfound'), 'error');
             }
 
             $got_msg = true;
             $reload  = false;
             break;
 
         case "restore":
             if ($success = $this->driver->restore_event_revision($event, $event['rev'])) {
                 $_event = $this->driver->get_event($event);
                 $reload = $_event['recurrence'] ? 2 : 1;
                 $msg = $this->gettext(['name' => 'objectrestoresuccess', 'vars' => ['rev' => $event['rev']]]);
                 $this->rc->output->command('display_message', $msg, 'confirmation');
                 $this->rc->output->command('plugin.close_history_dialog');
             }
             else {
                 $this->rc->output->command('display_message', $this->gettext('objectrestoreerror'), 'error');
                 $reload = 0;
             }
 
             $got_msg = true;
             break;
         }
 
         // show confirmation/error message
         if (!$got_msg) {
             if ($success) {
                 $this->rc->output->show_message('successfullysaved', 'confirmation');
             }
             else {
                 $this->rc->output->show_message('calendar.errorsaving', 'error');
             }
         }
 
         // unlock client
         $this->rc->output->command('plugin.unlock_saving', $success);
 
         // update event object on the client or trigger a complete refresh if too complicated
         if ($reload && empty($_REQUEST['_framed'])) {
             $args = ['source' => $event['calendar']];
             if ($reload > 1) {
                 $args['refetch'] = true;
             }
             else if ($success && $action != 'remove') {
                 $args['update'] = $this->_client_event($this->driver->get_event($event), true);
             }
             $this->rc->output->command('plugin.refresh_calendar', $args);
         }
     }
 
     /**
      * Helper method sending iTip notifications after successful event updates
      */
     private function event_save_success(&$event, $old, $action, $success)
     {
         // $success is a new event ID
         if ($success !== true) {
             // send update notification on the main event
-            if ($event['_savemode'] == 'future' && !empty($event['_notify'])
+            if (!empty($event['_savemode']) && $event['_savemode'] == 'future' && !empty($event['_notify'])
                 && !empty($old['attendees']) && !empty($old['recurrence_id'])
             ) {
                 $master = $this->driver->get_event(['id' => $old['recurrence_id'], 'calendar' => $old['calendar']], 0, true);
                 unset($master['_instance'], $master['recurrence_date']);
 
                 $sent = $this->notify_attendees($master, null, $action, $event['_comment'], false);
                 if ($sent < 0) {
                     $this->rc->output->show_message('calendar.errornotifying', 'error');
                 }
 
                 $event['attendees'] = $master['attendees'];  // this tricks us into the next if clause
             }
 
             // delete old reference if saved as new
-            if ($event['_savemode'] == 'future' || $event['_savemode'] == 'new') {
+            if (!empty($event['_savemode']) && ($event['_savemode'] == 'future' || $event['_savemode'] == 'new')) {
                 $old = null;
             }
 
             $event['id']        = $success;
             $event['_savemode'] = 'all';
         }
 
         // send out notifications
         if (!empty($event['_notify']) && (!empty($event['attendees']) || !empty($old['attendees']))) {
-            $_savemode = $event['_savemode'];
+            $_savemode = $event['_savemode'] ?? null;
 
             // send notification for the main event when savemode is 'all'
             if ($action != 'remove' && $_savemode == 'all'
                 && (!empty($event['recurrence_id']) || !empty($old['recurrence_id']) || ($old && $old['id'] != $event['id']))
             ) {
                 if (!empty($event['recurrence_id'])) {
                     $event['id'] = $event['recurrence_id'];
                 }
                 else if (!empty($old['recurrence_id'])) {
                     $event['id'] = $old['recurrence_id'];
                 }
                 else {
                     $event['id'] = $old['id'];
                 }
                 $event = $this->driver->get_event($event, 0, true);
                 unset($event['_instance'], $event['recurrence_date']);
             }
             else {
                 // make sure we have the complete record
                 $event = $action == 'remove' ? $old : $this->driver->get_event($event, 0, true);
             }
 
             $event['_savemode'] = $_savemode;
 
             if ($old) {
                 $old['thisandfuture'] = $_savemode == 'future';
             }
 
             // only notify if data really changed (TODO: do diff check on client already)
             if (!$old || $action == 'remove' || self::event_diff($event, $old)) {
                 $comment = isset($event['_comment']) ? $event['_comment'] : null;
                 $sent    = $this->notify_attendees($event, $old, $action, $comment);
 
                 if ($sent > 0) {
                     $this->rc->output->show_message('calendar.itipsendsuccess', 'confirmation');
                 }
                 else if ($sent < 0) {
                     $this->rc->output->show_message('calendar.errornotifying', 'error');
                 }
             }
         }
     }
 
     /**
      * Handler for load-requests from fullcalendar
      * This will return pure JSON formatted output
      */
     function load_events()
     {
         $start  = $this->input_timestamp('start', rcube_utils::INPUT_GET);
         $end    = $this->input_timestamp('end', rcube_utils::INPUT_GET);
         $query  = rcube_utils::get_input_value('q', rcube_utils::INPUT_GET);
         $source = rcube_utils::get_input_value('source', rcube_utils::INPUT_GET);
 
         $events = $this->driver->load_events($start, $end, $query, $source);
         echo $this->encode($events, !empty($query));
         exit;
     }
 
     /**
      * Handler for requests fetching event counts for calendars
      */
     public function count_events()
     {
         // don't update session on these requests (avoiding race conditions)
         $this->rc->session->nowrite = true;
 
         $start  = rcube_utils::get_input_value('start', rcube_utils::INPUT_GET);
         $source = rcube_utils::get_input_value('source', rcube_utils::INPUT_GET);
         $end    = rcube_utils::get_input_value('end', rcube_utils::INPUT_GET);
 
         if (!$start) {
             $start = new DateTime('today 00:00:00', $this->timezone);
             $start = $start->format('U');
         }
 
         $counts = $this->driver->count_events($source, $start, $end);
 
         $this->rc->output->command('plugin.update_counts', ['counts' => $counts]);
     }
 
     /**
      * Load event data from an iTip message attachment
      */
     public function itip_events($msgref)
     {
         $path = explode('/', $msgref);
         $msg  = array_pop($path);
         $mbox = join('/', $path);
         list($uid, $mime_id) = explode('#', $msg);
         $events = [];
 
         if ($event = $this->lib->mail_get_itip_object($mbox, $uid, $mime_id, 'event')) {
             $partstat = 'NEEDS-ACTION';
 
             $event['id']        = $event['uid'];
             $event['temporary'] = true;
             $event['readonly']  = true;
             $event['calendar']  = '--invitation--itip';
             $event['className'] = 'fc-invitation-' . strtolower($partstat);
             $event['_mbox']     = $mbox;
             $event['_uid']      = $uid;
             $event['_part']     = $mime_id;
 
             $events[] = $this->_client_event($event, true);
 
             // add recurring instances
             if (!empty($event['recurrence'])) {
                 // Some installations can't handle all occurrences (aborting the request w/o an error in log)
                 $freq = !empty($event['recurrence']['FREQ']) ? $event['recurrence']['FREQ'] : null;
                 $end  = clone $event['start'];
                 $end->add(new DateInterval($freq == 'DAILY' ? 'P1Y' : 'P10Y'));
 
                 foreach ($this->driver->get_recurring_events($event, $event['start'], $end) as $recurring) {
                     $recurring['temporary'] = true;
                     $recurring['readonly']  = true;
                     $recurring['calendar']  = '--invitation--itip';
 
                     $events[] = $this->_client_event($recurring, true);
                 }
             }
         }
 
         return $events;
     }
 
     /**
      * Handler for keep-alive requests
      * This will check for updated data in active calendars and sync them to the client
      */
     public function refresh($attr)
     {
         // refresh the entire calendar every 10th time to also sync deleted events
         if (rand(0, 10) == 10) {
             $this->rc->output->command('plugin.refresh_calendar', ['refetch' => true]);
             return;
         }
 
         $counts = [];
 
         foreach ($this->driver->list_calendars(calendar_driver::FILTER_ACTIVE) as $cal) {
             $events = $this->driver->load_events(
                 rcube_utils::get_input_value('start', rcube_utils::INPUT_GPC),
                 rcube_utils::get_input_value('end', rcube_utils::INPUT_GPC),
                 rcube_utils::get_input_value('q', rcube_utils::INPUT_GPC),
                 $cal['id'],
                 1,
                 $attr['last']
             );
 
             foreach ($events as $event) {
                 $this->rc->output->command(
                     'plugin.refresh_calendar',
                     ['source' => $cal['id'], 'update' => $this->_client_event($event)]
                 );
             }
 
             // refresh count for this calendar
             if (!empty($cal['counts'])) {
                 $today = new DateTime('today 00:00:00', $this->timezone);
                 $counts += $this->driver->count_events($cal['id'], $today->format('U'));
             }
         }
 
         if (!empty($counts)) {
             $this->rc->output->command('plugin.update_counts', ['counts' => $counts]);
         }
     }
 
     /**
      * Handler for pending_alarms plugin hook triggered by the calendar module on keep-alive requests.
      * This will check for pending notifications and pass them to the client
      */
     public function pending_alarms($p)
     {
         $this->load_driver();
 
         $time = !empty($p['time']) ? $p['time'] : time();
 
         if ($alarms = $this->driver->pending_alarms($time)) {
             foreach ($alarms as $alarm) {
                 $alarm['id'] = 'cal:' . $alarm['id'];  // prefix ID with cal:
                 $p['alarms'][] = $alarm;
             }
         }
 
         // get alarms for birthdays calendar
         if (
             $this->rc->config->get('calendar_contact_birthdays')
             && $this->rc->config->get('calendar_birthdays_alarm_type') == 'DISPLAY'
         ) {
             $cache = $this->rc->get_cache('calendar.birthdayalarms', 'db');
 
             foreach ($this->driver->load_birthday_events($time, $time + 86400 * 60) as $e) {
                 $alarm = libcalendaring::get_next_alarm($e);
 
                 // overwrite alarm time with snooze value (or null if dismissed)
                 if ($dismissed = $cache->get($e['id'])) {
                     $alarm['time'] = $dismissed['notifyat'];
                 }
 
                 // add to list if alarm is set
                 if ($alarm && !empty($alarm['time']) && $alarm['time'] <= $time) {
                     $e['id']       = 'cal:bday:' . $e['id'];
                     $e['notifyat'] = $alarm['time'];
                     $p['alarms'][] = $e;
                 }
             }
         }
 
         return $p;
     }
 
     /**
      * Handler for alarm dismiss hook triggered by libcalendaring
      */
     public function dismiss_alarms($p)
     {
         $this->load_driver();
 
         foreach ((array) $p['ids'] as $id) {
             if (strpos($id, 'cal:bday:') === 0) {
                 $p['success'] |= $this->driver->dismiss_birthday_alarm(substr($id, 9), $p['snooze']);
             }
             else if (strpos($id, 'cal:') === 0) {
                 $p['success'] |= $this->driver->dismiss_alarm(substr($id, 4), $p['snooze']);
             }
         }
 
         return $p;
     }
 
     /**
      * Handler for check-recent requests which are accidentally sent to calendar
      */
     function check_recent()
     {
         // NOP
         $this->rc->output->send();
     }
 
     /**
      * Hook triggered when a contact is saved
      */
     function contact_update($p)
     {
         // clear birthdays calendar cache
         if (!empty($p['record']['birthday'])) {
             $cache = $this->rc->get_cache('calendar.birthdays', 'db');
             $cache->remove();
         }
     }
 
     /**
      *
      */
     function import_events()
     {
         // Upload progress update
         if (!empty($_GET['_progress'])) {
             $this->rc->upload_progress();
         }
 
         @set_time_limit(0);
 
         // process uploaded file if there is no error
         $err = $_FILES['_data']['error'];
 
         if (!$err && !empty($_FILES['_data']['tmp_name'])) {
             $calendar   = rcube_utils::get_input_value('calendar', rcube_utils::INPUT_GPC);
             $rangestart = !empty($_REQUEST['_range']) ? date_create("now -" . intval($_REQUEST['_range']) . " months") : 0;
 
             // extract zip file
             if ($_FILES['_data']['type'] == 'application/zip') {
                 $count = 0;
                 if (class_exists('ZipArchive', false)) {
                     $zip = new ZipArchive();
                     if ($zip->open($_FILES['_data']['tmp_name'])) {
                         $randname = uniqid('zip-' . session_id(), true);
                         $tmpdir = slashify($this->rc->config->get('temp_dir', sys_get_temp_dir())) . $randname;
                         mkdir($tmpdir, 0700);
 
                         // extract each ical file from the archive and import it
                         for ($i = 0; $i < $zip->numFiles; $i++) {
                             $filename = $zip->getNameIndex($i);
                             if (preg_match('/\.ics$/i', $filename)) {
                                 $tmpfile = $tmpdir . '/' . basename($filename);
                                 if (copy('zip://' . $_FILES['_data']['tmp_name'] . '#'.$filename, $tmpfile)) {
                                     $count += $this->import_from_file($tmpfile, $calendar, $rangestart, $errors);
                                     unlink($tmpfile);
                                 }
                             }
                         }
 
                         rmdir($tmpdir);
                         $zip->close();
                     }
                     else {
                         $errors = 1;
                         $msg = 'Failed to open zip file.';
                     }
                 }
                 else {
                     $errors = 1;
                     $msg = 'Zip files are not supported for import.';
                 }
             }
             else {
                 // attempt to import teh uploaded file directly
                 $count = $this->import_from_file($_FILES['_data']['tmp_name'], $calendar, $rangestart, $errors);
             }
 
             if ($count) {
                 $this->rc->output->command('display_message', $this->gettext(['name' => 'importsuccess', 'vars' => ['nr' => $count]]), 'confirmation');
                 $this->rc->output->command('plugin.import_success', ['source' => $calendar, 'refetch' => true]);
             }
             else if (!$errors) {
                 $this->rc->output->command('display_message', $this->gettext('importnone'), 'notice');
                 $this->rc->output->command('plugin.import_success', ['source' => $calendar]);
             }
             else {
                 $this->rc->output->command('plugin.import_error', ['message' => $this->gettext('importerror') . ($msg ? ': ' . $msg : '')]);
             }
         }
         else {
             if ($err == UPLOAD_ERR_INI_SIZE || $err == UPLOAD_ERR_FORM_SIZE) {
                 $max = $this->rc->show_bytes(parse_bytes(ini_get('upload_max_filesize')));
                 $msg = $this->rc->gettext(['name' => 'filesizeerror', 'vars' => ['size' => $max]]);
             }
             else {
                 $msg = $this->rc->gettext('fileuploaderror');
             }
 
             $this->rc->output->command('plugin.import_error', ['message' => $msg]);
         }
 
         $this->rc->output->send('iframe');
     }
 
     /**
      * Helper function to parse and import a single .ics file
      */
     private function import_from_file($filepath, $calendar, $rangestart, &$errors)
     {
         $user_email = $this->rc->user->get_username();
         $ical       = $this->get_ical();
         $errors     = !$ical->fopen($filepath);
 
         $count = $i = 0;
 
         foreach ($ical as $event) {
             // keep the browser connection alive on long import jobs
             if (++$i > 100 && $i % 100 == 0) {
                 echo "<!-- -->";
                 ob_flush();
             }
 
             // TODO: correctly handle recurring events which start before $rangestart
             if ($rangestart && $event['end'] < $rangestart
                 && (empty($event['recurrence']) || (!empty($event['recurrence']['until']) && $event['recurrence']['until'] < $rangestart))
             ) {
                 continue;
             }
 
             $event['_owner']   = $user_email;
             $event['calendar'] = $calendar;
 
             if ($this->driver->new_event($event)) {
                 $count++;
             }
             else {
                 $errors++;
             }
         }
 
         return $count;
     }
 
     /**
      * Construct the ics file for exporting events to iCalendar format;
      */
     function export_events($terminate = true)
     {
         $start       = rcube_utils::get_input_value('start', rcube_utils::INPUT_GET);
         $end         = rcube_utils::get_input_value('end', rcube_utils::INPUT_GET);
         $event_id    = rcube_utils::get_input_value('id', rcube_utils::INPUT_GET);
         $attachments = rcube_utils::get_input_value('attachments', rcube_utils::INPUT_GET);
         $calid       = rcube_utils::get_input_value('source', rcube_utils::INPUT_GET);
 
         if (!isset($start)) {
             $start = 'today -1 year';
         }
         if (!is_numeric($start)) {
             $start = strtotime($start . ' 00:00:00');
         }
         if (!$end) {
             $end = 'today +10 years';
         }
         if (!is_numeric($end)) {
             $end = strtotime($end . ' 23:59:59');
         }
 
         $filename  = $calid;
         $calendars = $this->driver->list_calendars();
         $events    = [];
 
         if (!empty($calendars[$calid])) {
             $filename = !empty($calendars[$calid]['name']) ? $calendars[$calid]['name'] : $calid;
             $filename = asciiwords(html_entity_decode($filename));  // to 7bit ascii
 
             if (!empty($event_id)) {
                 if ($event = $this->driver->get_event(['calendar' => $calid, 'id' => $event_id], 0, true)) {
                     if (!empty($event['recurrence_id'])) {
                         $event = $this->driver->get_event(['calendar' => $calid, 'id' => $event['recurrence_id']], 0, true);
                     }
 
                     $events   = [$event];
                     $filename = asciiwords($event['title']);
 
                     if (empty($filename)) {
                         $filename = 'event';
                     }
                 }
             }
             else {
                 $events = $this->driver->load_events($start, $end, null, $calid, 0);
                 if (empty($filename)) {
                     $filename = $calid;
                 }
             }
         }
 
         header("Content-Type: text/calendar");
         header("Content-Disposition: inline; filename=".$filename.'.ics');
 
         $this->get_ical()->export($events, '', true, $attachments ? [$this->driver, 'get_attachment_body'] : null);
 
         if ($terminate) {
             exit;
         }
     }
 
     /**
      * Handler for iCal feed requests
      */
     function ical_feed_export()
     {
         $session_exists = !empty($_SESSION['user_id']);
 
         // process HTTP auth info
         if (!empty($_SERVER['PHP_AUTH_USER']) && isset($_SERVER['PHP_AUTH_PW'])) {
             $_POST['_user'] = $_SERVER['PHP_AUTH_USER']; // used for rcmail::autoselect_host()
             $auth = $this->rc->plugins->exec_hook('authenticate', [
                 'host' => $this->rc->autoselect_host(),
                 'user' => trim($_SERVER['PHP_AUTH_USER']),
                 'pass' => $_SERVER['PHP_AUTH_PW'],
                 'cookiecheck' => true,
                 'valid'       => true,
             ]);
 
             if ($auth['valid'] && !$auth['abort']) {
                 $this->rc->login($auth['user'], $auth['pass'], $auth['host']);
             }
         }
 
         // require HTTP auth
         if (empty($_SESSION['user_id'])) {
             header('WWW-Authenticate: Basic realm="Kolab Calendar"');
             header('HTTP/1.0 401 Unauthorized');
             exit;
         }
 
         // decode calendar feed hash
         $format  = 'ics';
         $calhash = rcube_utils::get_input_value('_cal', rcube_utils::INPUT_GET);
 
         if (preg_match(($suff_regex = '/\.([a-z0-9]{3,5})$/i'), $calhash, $m)) {
             $format  = strtolower($m[1]);
             $calhash = preg_replace($suff_regex, '', $calhash);
         }
 
         if (!strpos($calhash, ':')) {
             $calhash = base64_decode($calhash);
         }
 
         list($user, $_GET['source']) = explode(':', $calhash, 2);
 
         // sanity check user
         if ($this->rc->user->get_username() == $user) {
             $this->setup();
             $this->load_driver();
             $this->export_events(false);
         }
         else {
             header('HTTP/1.0 404 Not Found');
         }
 
         // don't save session data
         if (!$session_exists) {
             session_destroy();
         }
 
         exit;
     }
 
     /**
      *
      */
     function load_settings()
     {
         $this->lib->load_settings();
         $this->defaults += $this->lib->defaults;
 
         $settings = [];
 
         // configuration
         $settings['default_view']     = (string) $this->rc->config->get('calendar_default_view', $this->defaults['calendar_default_view']);
         $settings['timeslots']        = (int) $this->rc->config->get('calendar_timeslots', $this->defaults['calendar_timeslots']);
         $settings['first_day']        = (int) $this->rc->config->get('calendar_first_day', $this->defaults['calendar_first_day']);
         $settings['first_hour']       = (int) $this->rc->config->get('calendar_first_hour', $this->defaults['calendar_first_hour']);
         $settings['work_start']       = (int) $this->rc->config->get('calendar_work_start', $this->defaults['calendar_work_start']);
         $settings['work_end']         = (int) $this->rc->config->get('calendar_work_end', $this->defaults['calendar_work_end']);
         $settings['agenda_range']     = (int) $this->rc->config->get('calendar_agenda_range', $this->defaults['calendar_agenda_range']);
         $settings['event_coloring']   = (int) $this->rc->config->get('calendar_event_coloring', $this->defaults['calendar_event_coloring']);
         $settings['time_indicator']   = (int) $this->rc->config->get('calendar_time_indicator', $this->defaults['calendar_time_indicator']);
         $settings['invite_shared']    = (int) $this->rc->config->get('calendar_allow_invite_shared', $this->defaults['calendar_allow_invite_shared']);
         $settings['itip_notify']      = (int) $this->rc->config->get('calendar_itip_send_option', $this->defaults['calendar_itip_send_option']);
         $settings['show_weekno']      = (int) $this->rc->config->get('calendar_show_weekno', $this->defaults['calendar_show_weekno']);
         $settings['default_calendar'] = $this->rc->config->get('calendar_default_calendar');
         $settings['invitation_calendars'] = (bool) $this->rc->config->get('kolab_invitation_calendars', false);
 
         // 'table' view has been replaced by 'list' view
         if ($settings['default_view'] == 'table') {
             $settings['default_view'] = 'list';
         }
 
         // get user identity to create default attendee
         if ($this->ui->screen == 'calendar') {
             foreach ($this->rc->user->list_emails() as $rec) {
                 if (empty($identity)) {
                     $identity = $rec;
                 }
 
                 $identity['emails'][] = $rec['email'];
                 $settings['identities'][$rec['identity_id']] = $rec['email'];
             }
 
             $identity['emails'][] = $this->rc->user->get_username();
             $identity['ownedResources'] = $this->owned_resources_emails();
             $settings['identity'] = [
                 'name'   => $identity['name'],
                 'email'  => strtolower($identity['email']),
                 'emails' => ';' . strtolower(join(';', $identity['emails'])),
                 'ownedResources' => ';' . strtolower(join(';', $identity['ownedResources']))
             ];
         }
 
         // freebusy token authentication URL
         if (($url = $this->rc->config->get('calendar_freebusy_session_auth_url'))
             && ($uniqueid = $this->rc->config->get('kolab_uniqueid'))
         ) {
             if ($url === true) {
                 $url = '/freebusy';
             }
             $url = rtrim(rcube_utils::resolve_url($url), '/ ');
             $url .= '/' . urlencode($this->rc->get_user_name());
             $url .= '/' . urlencode($uniqueid);
 
             $settings['freebusy_url'] = $url;
         }
 
         return $settings;
     }
 
     /**
      * Encode events as JSON
      *
      * @param array Events as array
      * @param bool  Add CSS class names according to calendar and categories
      *
      * @return string JSON encoded events
      */
     function encode($events, $addcss = false)
     {
         $json = [];
         foreach ($events as $event) {
             $json[] = $this->_client_event($event, $addcss);
         }
         return rcube_output::json_serialize($json);
     }
 
     /**
      * Convert an event object to be used on the client
      */
     private function _client_event($event, $addcss = false)
     {
         // compose a human readable strings for alarms_text and recurrence_text
         if (!empty($event['valarms'])) {
             $event['alarms_text'] = libcalendaring::alarms_text($event['valarms']);
             $event['valarms'] = libcalendaring::to_client_alarms($event['valarms']);
         }
 
         if (!empty($event['recurrence'])) {
             $event['recurrence_text'] = $this->lib->recurrence_text($event['recurrence']);
             $event['recurrence'] = $this->lib->to_client_recurrence($event['recurrence'], $event['allday']);
             unset($event['recurrence_date']);
         }
 
         if (!empty($event['attachments'])) {
             foreach ($event['attachments'] as $k => $attachment) {
                 $event['attachments'][$k]['classname'] = rcube_utils::file2class($attachment['mimetype'], $attachment['name']);
 
                 unset($event['attachments'][$k]['data'], $event['attachments'][$k]['content']);
 
                 if (empty($attachment['id'])) {
                     $event['attachments'][$k]['id'] = $k;
                 }
             }
         }
 
         // convert link URIs references into structs
         if (array_key_exists('links', $event)) {
             foreach ((array) $event['links'] as $i => $link) {
                 if (strpos($link, 'imap://') === 0 && ($msgref = $this->driver->get_message_reference($link))) {
                     $event['links'][$i] = $msgref;
                 }
             }
         }
 
         // check for organizer in attendees list
         $organizer = null;
         foreach ((array) $event['attendees'] as $i => $attendee) {
             if ($attendee['role'] == 'ORGANIZER') {
                 $organizer = $attendee;
             }
             if (!empty($attendee['status']) && $attendee['status'] == 'DELEGATED' && empty($attendee['rsvp'])) {
                 $event['attendees'][$i]['noreply'] = true;
             }
             else {
                 unset($event['attendees'][$i]['noreply']);
             }
         }
 
         if ($organizer === null && !empty($event['organizer'])) {
             $organizer = $event['organizer'];
             $organizer['role'] = 'ORGANIZER';
             if (!is_array($event['attendees'])) {
                 $event['attendees'] = [$organizer];
             }
         }
 
         // Convert HTML description into plain text
         if ($this->is_html($event)) {
             $h2t = new rcube_html2text($event['description'], false, true, 0);
             $event['description'] = trim($h2t->get_text());
         }
 
         // mapping url => vurl, allday => allDay because of the fullcalendar client script
-        $event['vurl']   = $event['url'];
+        $event['vurl']   = $event['url'] ?? null;
         $event['allDay'] = !empty($event['allday']);
         unset($event['url']);
         unset($event['allday']);
 
         $event['className'] = !empty($event['className']) ? explode(' ', $event['className']) : [];
 
         if ($event['allDay']) {
             $event['end'] = $event['end']->add(new DateInterval('P1D'));
         }
 
         if (!empty($_GET['mode']) && $_GET['mode'] == 'print') {
             $event['editable'] = false;
         }
 
         return [
             '_id'     => $event['calendar'] . ':' . $event['id'],  // unique identifier for fullcalendar
             'start'   => $this->lib->adjust_timezone($event['start'], $event['allDay'])->format('c'),
             'end'     => $this->lib->adjust_timezone($event['end'], $event['allDay'])->format('c'),
             // 'changed' might be empty for event recurrences (Bug #2185)
             'changed' => !empty($event['changed']) ? $this->lib->adjust_timezone($event['changed'])->format('c') : null,
             'created' => !empty($event['created']) ? $this->lib->adjust_timezone($event['created'])->format('c') : null,
-            'title'       => strval($event['title']),
-            'description' => strval($event['description']),
-            'location'    => strval($event['location']),
+            'title'       => strval($event['title'] ?? null),
+            'description' => strval($event['description'] ?? null),
+            'location'    => strval($event['location'] ?? null),
         ] + $event;
     }
 
     /**
      * Generate a unique identifier for an event
      */
     public function generate_uid()
     {
         return strtoupper(md5(time() . uniqid(rand())) . '-' . substr(md5($this->rc->user->get_username()), 0, 16));
     }
 
     /**
      * TEMPORARY: generate random event data for testing
      * Create events by opening http://<roundcubeurl>/?_task=calendar&_action=randomdata&_num=500&_date=2014-08-01&_dev=120
      */
     public function generate_randomdata()
     {
         @set_time_limit(0);
 
         $num   = !empty($_REQUEST['_num']) ? intval($_REQUEST['_num']) : 100;
         $date  = !empty($_REQUEST['_date']) ? $_REQUEST['_date'] : 'now';
         $dev   = !empty($_REQUEST['_dev']) ? $_REQUEST['_dev'] : 30;
         $cats  = array_keys($this->driver->list_categories());
         $cals  = $this->driver->list_calendars(calendar_driver::FILTER_ACTIVE);
         $count = 0;
 
         while ($count++ < $num) {
             $spread   = intval($dev) * 86400; // days
             $refdate  = strtotime($date);
             $start    = round(($refdate + rand(-$spread, $spread)) / 600) * 600;
             $duration = round(rand(30, 360) / 30) * 30 * 60;
             $allday   = rand(0,20) > 18;
             $alarm    = rand(-30,12) * 5;
             $fb       = rand(0,2);
 
             if (date('G', $start) > 23) {
                 $start -= 3600;
             }
 
             if ($allday) {
                 $start    = strtotime(date('Y-m-d 00:00:00', $start));
                 $duration = 86399;
             }
 
             $title = '';
             $len = rand(2, 12);
             $words = explode(" ", "The Hough transform is named after Paul Hough who patented the method in 1962."
                 . " It is a technique which can be used to isolate features of a particular shape within an image."
                 . " Because it requires that the desired features be specified in some parametric form, the classical"
                 . " Hough transform is most commonly used for the de- tection of regular curves such as lines, circles,"
                 . " ellipses, etc. A generalized Hough transform can be employed in applications where a simple"
                 . " analytic description of a feature(s) is not possible. Due to the computational complexity of"
                 . " the generalized Hough algorithm, we restrict the main focus of this discussion to the classical"
                 . " Hough transform. Despite its domain restrictions, the classical Hough transform (hereafter"
                 . " referred to without the classical prefix ) retains many applications, as most manufac- tured"
                 . " parts (and many anatomical parts investigated in medical imagery) contain feature boundaries"
                 . " which can be described by regular curves. The main advantage of the Hough transform technique"
                 . " is that it is tolerant of gaps in feature boundary descriptions and is relatively unaffected"
                 . " by image noise.");
             // $chars = "!# abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ 1234567890";
             for ($i = 0; $i < $len; $i++) {
                 $title .= $words[rand(0,count($words)-1)] . " ";
             }
 
             $this->driver->new_event([
                 'uid'        => $this->generate_uid(),
                 'start'      => new DateTime('@'.$start),
                 'end'        => new DateTime('@'.($start + $duration)),
                 'allday'     => $allday,
                 'title'      => rtrim($title),
                 'free_busy'  => $fb == 2 ? 'outofoffice' : ($fb ? 'busy' : 'free'),
                 'categories' => $cats[array_rand($cats)],
                 'calendar'   => array_rand($cals),
                 'alarms'     => $alarm > 0 ? "-{$alarm}M:DISPLAY" : '',
                 'priority'   => rand(0,9),
             ]);
         }
 
         $this->rc->output->redirect('');
     }
 
     /**
      * Handler for attachments upload
      */
     public function attachment_upload()
     {
         $handler = new kolab_attachments_handler();
         $handler->attachment_upload(self::SESSION_KEY, 'cal-');
     }
 
     /**
      * Handler for attachments download/displaying
      */
     public function attachment_get()
     {
         $handler = new kolab_attachments_handler();
 
         // show loading page
         if (!empty($_GET['_preload'])) {
             return $handler->attachment_loading_page();
         }
 
         $event_id = rcube_utils::get_input_value('_event', rcube_utils::INPUT_GPC);
         $calendar = rcube_utils::get_input_value('_cal', rcube_utils::INPUT_GPC);
         $id       = rcube_utils::get_input_value('_id', rcube_utils::INPUT_GPC);
         $rev      = rcube_utils::get_input_value('_rev', rcube_utils::INPUT_GPC);
 
         $event = ['id' => $event_id, 'calendar' => $calendar, 'rev' => $rev];
 
         if ($calendar == '--invitation--itip') {
             $uid  = rcube_utils::get_input_value('_uid', rcube_utils::INPUT_GPC);
             $part = rcube_utils::get_input_value('_part', rcube_utils::INPUT_GPC);
             $mbox = rcube_utils::get_input_value('_mbox', rcube_utils::INPUT_GPC);
 
             $event      = $this->lib->mail_get_itip_object($mbox, $uid, $part, 'event');
             $attachment = $event['attachments'][$id];
             $attachment['body'] = &$attachment['data'];
         }
         else {
             $attachment = $this->driver->get_attachment($id, $event);
         }
 
         // show part page
         if (!empty($_GET['_frame'])) {
             $handler->attachment_page($attachment);
         }
         // deliver attachment content
         else if ($attachment) {
             if ($calendar != '--invitation--itip') {
                 $attachment['body'] = $this->driver->get_attachment_body($id, $event);
             }
 
             $handler->attachment_get($attachment);
         }
 
         // if we arrive here, the requested part was not found
         header('HTTP/1.1 404 Not Found');
         exit;
     }
 
     /**
      * Determine whether the given event description is HTML formatted
      */
     private function is_html($event)
     {
           // check for opening and closing <html> or <body> tags
         return preg_match('/<(html|body)(\s+[a-z]|>)/', $event['description'], $m)
             && strpos($event['description'], '</'.$m[1].'>') > 0;
     }
 
     /**
      * Prepares new/edited event properties before save
      */
     private function write_preprocess(&$event, $action)
     {
         // Remove double timezone specification (T2313)
         $event['start'] = preg_replace('/\s*\(.*\)/', '', $event['start']);
         $event['end']   = preg_replace('/\s*\(.*\)/', '', $event['end']);
 
         // convert dates into DateTime objects in user's current timezone
         $event['start']  = new DateTime($event['start'], $this->timezone);
         $event['end']    = new DateTime($event['end'], $this->timezone);
         $event['allday'] = !empty($event['allDay']);
         unset($event['allDay']);
 
         // start/end is all we need for 'move' action (#1480)
         if ($action == 'move') {
             return true;
         }
 
         // convert the submitted recurrence settings
         if (!empty($event['recurrence'])) {
             $event['recurrence'] = $this->lib->from_client_recurrence($event['recurrence'], $event['start']);
 
             // align start date with the first occurrence
             if (!empty($event['recurrence']) && !empty($event['syncstart'])
                 && (empty($event['_savemode']) || $event['_savemode'] == 'all')
             ) {
                 $next = $this->find_first_occurrence($event);
 
                 if (!$next) {
                     $this->rc->output->show_message('calendar.recurrenceerror', 'error');
                     return false;
                 }
                 else if ($event['start'] != $next) {
                     $diff = $event['start']->diff($event['end'], true);
 
                     $event['start'] = $next;
                     $event['end']   = clone $next;
                     $event['end']->add($diff);
                 }
             }
         }
 
         // convert the submitted alarm values
         if (!empty($event['valarms'])) {
             $event['valarms'] = libcalendaring::from_client_alarms($event['valarms']);
         }
 
         $attachments = [];
         $eventid     = 'cal-' . (!empty($event['id']) ? $event['id'] : 'new');
 
         if (!empty($_SESSION[self::SESSION_KEY]) && $_SESSION[self::SESSION_KEY]['id'] == $eventid) {
             if (!empty($_SESSION[self::SESSION_KEY]['attachments'])) {
                 foreach ($_SESSION[self::SESSION_KEY]['attachments'] as $id => $attachment) {
                     if (!empty($event['attachments']) && in_array($id, $event['attachments'])) {
                         $attachments[$id] = $this->rc->plugins->exec_hook('attachment_get', $attachment);
                     }
                 }
             }
         }
 
         $event['attachments'] = $attachments;
 
         // convert link references into simple URIs
         if (array_key_exists('links', $event)) {
             $event['links'] = array_map(function($link) {
                     return is_array($link) ? $link['uri'] : strval($link);
                 },
                 (array) $event['links']
             );
         }
 
         // check for organizer in attendees
         if ($action == 'new' || $action == 'edit') {
             if (empty($event['attendees'])) {
                 $event['attendees'] = [];
             }
 
             $emails = $this->get_user_emails();
             $organizer = $owner = false;
 
             foreach ((array) $event['attendees'] as $i => $attendee) {
                 if ($attendee['role'] == 'ORGANIZER') {
                     $organizer = $i;
                 }
                 if (!empty($attendee['email']) && in_array(strtolower($attendee['email']), $emails)) {
                     $owner = $i;
                 }
                 if (!isset($attendee['rsvp'])) {
                     $event['attendees'][$i]['rsvp'] = true;
                 }
                 else if (is_string($attendee['rsvp'])) {
                     $event['attendees'][$i]['rsvp'] = $attendee['rsvp'] == 'true' || $attendee['rsvp'] == '1';
                 }
             }
 
             if (!empty($event['_identity'])) {
                 $identity = $this->rc->user->get_identity($event['_identity']);
             }
 
             // set new organizer identity
             if ($organizer !== false && !empty($identity)) {
                 $event['attendees'][$organizer]['name']  = $identity['name'];
                 $event['attendees'][$organizer]['email'] = $identity['email'];
             }
             // set owner as organizer if yet missing
             else if ($organizer === false && $owner !== false) {
                 $event['attendees'][$owner]['role'] = 'ORGANIZER';
                 unset($event['attendees'][$owner]['rsvp']);
             }
             // fallback to the selected identity
             else if ($organizer === false && !empty($identity)) {
                 $event['attendees'][] = [
                     'role'  => 'ORGANIZER',
                     'name'  => $identity['name'],
                     'email' => $identity['email'],
                 ];
             }
         }
 
         // mapping url => vurl because of the fullcalendar client script
         if (array_key_exists('vurl', $event)) {
             $event['url'] = $event['vurl'];
             unset($event['vurl']);
         }
 
         return true;
     }
 
     /**
      * Releases some resources after successful event save
      */
     private function cleanup_event(&$event)
     {
         // remove temp. attachment files
         if (!empty($_SESSION[self::SESSION_KEY]) && ($eventid = $_SESSION[self::SESSION_KEY]['id'])) {
             $this->rc->plugins->exec_hook('attachments_cleanup', ['group' => $eventid]);
             $this->rc->session->remove(self::SESSION_KEY);
         }
     }
 
     /**
      * Send out an invitation/notification to all event attendees
      */
     private function notify_attendees($event, $old, $action = 'edit', $comment = null, $rsvp = null)
     {
         $is_cancelled = false;
         if ($action == 'remove' || ($event['status'] == 'CANCELLED' && $old['status'] != $event['status'])) {
             $event['cancelled'] = true;
             $is_cancelled = true;
         }
 
         if ($rsvp === null) {
-            $rsvp = !$old || $event['sequence'] > $old['sequence'];
+            $rsvp = !$old || ($event['sequence'] ?? 0) > ($old['sequence'] ?? 0);
         }
 
         $itip        = $this->load_itip();
         $emails      = $this->get_user_emails();
         $itip_notify = (int) $this->rc->config->get('calendar_itip_send_option', $this->defaults['calendar_itip_send_option']);
 
         // add comment to the iTip attachment
         $event['comment'] = $comment;
 
         // set a valid recurrence-id if this is a recurrence instance
         libcalendaring::identify_recurrence_instance($event);
 
         // compose multipart message using PEAR:Mail_Mime
         $method  = $action == 'remove' ? 'CANCEL' : 'REQUEST';
         $message = $itip->compose_itip_message($event, $method, $rsvp);
 
         // list existing attendees from $old event
         $old_attendees = [];
         if (!empty($old['attendees'])) {
             foreach ((array) $old['attendees'] as $attendee) {
                 $old_attendees[] = $attendee['email'];
             }
         }
 
         // send to every attendee
         $sent    = 0;
         $current = [];
         foreach ((array) $event['attendees'] as $attendee) {
             // skip myself for obvious reasons
             if (empty($attendee['email']) || in_array(strtolower($attendee['email']), $emails)) {
                 continue;
             }
 
             $current[] = strtolower($attendee['email']);
 
             // skip if notification is disabled for this attendee
             if (!empty($attendee['noreply']) && $itip_notify & 2) {
                 continue;
             }
 
             // skip if this attendee has delegated and set RSVP=FALSE
             if ($attendee['status'] == 'DELEGATED' && $attendee['rsvp'] === false) {
                 continue;
             }
 
             // which template to use for mail text
             $is_new   = !in_array($attendee['email'], $old_attendees);
             $is_rsvp  = $is_new || $event['sequence'] > $old['sequence'];
             $bodytext = $is_cancelled ? 'eventcancelmailbody' : ($is_new ? 'invitationmailbody' : 'eventupdatemailbody');
             $subject  = $is_cancelled ? 'eventcancelsubject'  : ($is_new ? 'invitationsubject' : ($event['title'] ? 'eventupdatesubject' : 'eventupdatesubjectempty'));
 
             $event['comment'] = $comment;
 
             // finally send the message
             if ($itip->send_itip_message($event, $method, $attendee, $subject, $bodytext, $message, $is_rsvp)) {
                 $sent++;
             }
             else {
                 $sent = -100;
             }
         }
 
         // TODO: on change of a recurring (main) event, also send updates to differing attendess of recurrence exceptions
 
         // send CANCEL message to removed attendees
         if (!empty($old['attendees'])) {
             foreach ($old['attendees'] as $attendee) {
                 if ($attendee['role'] == 'ORGANIZER'
                     || empty($attendee['email'])
                     || in_array(strtolower($attendee['email']), $current)
                 ) {
                     continue;
                 }
 
                 $vevent = $old;
                 $vevent['cancelled'] = $is_cancelled;
                 $vevent['attendees'] = [$attendee];
                 $vevent['comment']   = $comment;
 
                 if ($itip->send_itip_message($vevent, 'CANCEL', $attendee, 'eventcancelsubject', 'eventcancelmailbody')) {
                     $sent++;
                 }
                 else {
                     $sent = -100;
                 }
             }
         }
 
         return $sent;
     }
 
     /**
      * Echo simple free/busy status text for the given user and time range
      */
     public function freebusy_status()
     {
         $email = rcube_utils::get_input_value('email', rcube_utils::INPUT_GPC);
         $start = $this->input_timestamp('start', rcube_utils::INPUT_GPC);
         $end   = $this->input_timestamp('end', rcube_utils::INPUT_GPC);
 
         if (!$start) $start = time();
         if (!$end) $end = $start + 3600;
 
         $status = 'UNKNOWN';
         $fbtypemap = [
             calendar::FREEBUSY_UNKNOWN   => 'UNKNOWN',
             calendar::FREEBUSY_FREE      => 'FREE',
             calendar::FREEBUSY_BUSY      => 'BUSY',
             calendar::FREEBUSY_TENTATIVE => 'TENTATIVE',
             calendar::FREEBUSY_OOF       => 'OUT-OF-OFFICE'
         ];
 
         // if the backend has free-busy information
         $fblist = $this->driver->get_freebusy_list($email, $start, $end);
 
         if (is_array($fblist)) {
             $status = 'FREE';
 
             foreach ($fblist as $slot) {
                 list($from, $to, $type) = $slot;
                 if ($from < $end && $to > $start) {
                     $status = isset($type) && !empty($fbtypemap[$type]) ? $fbtypemap[$type] : 'BUSY';
                     break;
                 }
             }
         }
 
         // let this information be cached for 5min
         $this->rc->output->future_expire_header(300);
 
         echo $status;
         exit;
     }
 
     /**
      * Return a list of free/busy time slots within the given period
      * Echo data in JSON encoding
      */
     public function freebusy_times()
     {
         $email = rcube_utils::get_input_value('email', rcube_utils::INPUT_GPC);
         $start = $this->input_timestamp('start', rcube_utils::INPUT_GPC);
         $end   = $this->input_timestamp('end', rcube_utils::INPUT_GPC);
         $interval  = intval(rcube_utils::get_input_value('interval', rcube_utils::INPUT_GPC));
         $strformat = $interval > 60 ? 'Ymd' : 'YmdHis';
 
         if (!$start) $start = time();
         if (!$end)   $end = $start + 86400 * 30;
         if (!$interval) $interval = 60;  // 1 hour
 
         if (!$dte) {
             $dts = new DateTime('@'.$start);
             $dts->setTimezone($this->timezone);
         }
 
         $fblist = $this->driver->get_freebusy_list($email, $start, $end);
         $slots  = '';
 
         // prepare freebusy list before use (for better performance)
         if (is_array($fblist)) {
             foreach ($fblist as $idx => $slot) {
                 list($from, $to, ) = $slot;
 
                 // check for possible all-day times
                 if (gmdate('His', $from) == '000000' && gmdate('His', $to) == '235959') {
                     // shift into the user's timezone for sane matching
                     $fblist[$idx][0] -= $this->gmt_offset;
                     $fblist[$idx][1] -= $this->gmt_offset;
                 }
             }
         }
 
         // build a list from $start till $end with blocks representing the fb-status
         for ($s = 0, $t = $start; $t <= $end; $s++) {
             $t_end = $t + $interval * 60;
             $dt = new DateTime('@'.$t);
             $dt->setTimezone($this->timezone);
 
             // determine attendee's status
             if (is_array($fblist)) {
                 $status = self::FREEBUSY_FREE;
 
                 foreach ($fblist as $slot) {
                     list($from, $to, $type) = $slot;
 
                     if ($from < $t_end && $to > $t) {
                         $status = isset($type) ? $type : self::FREEBUSY_BUSY;
                         if ($status == self::FREEBUSY_BUSY) {
                             // can't get any worse :-)
                             break;
                         }
                     }
                 }
             }
             else {
                 $status = self::FREEBUSY_UNKNOWN;
             }
 
             // use most compact format, assume $status is one digit/character
             $slots .= $status;
             $t = $t_end;
         }
 
         $dte = new DateTime('@'.$t_end);
         $dte->setTimezone($this->timezone);
 
         // let this information be cached for 5min
         $this->rc->output->future_expire_header(300);
 
         echo rcube_output::json_serialize([
             'email' => $email,
             'start' => $dts->format('c'),
             'end'   => $dte->format('c'),
             'interval' => $interval,
             'slots' => $slots,
         ]);
         exit;
     }
 
     /**
      * Handler for printing calendars
      */
     public function print_view()
     {
         $title = $this->gettext('print');
 
         $view = rcube_utils::get_input_value('view', rcube_utils::INPUT_GPC);
         if (!in_array($view, ['agendaWeek', 'agendaDay', 'month', 'list'])) {
             $view = 'agendaDay';
         }
 
         $this->rc->output->set_env('view', $view);
 
         if ($date = rcube_utils::get_input_value('date', rcube_utils::INPUT_GPC)) {
             $this->rc->output->set_env('date', $date);
         }
 
         if ($range = rcube_utils::get_input_value('range', rcube_utils::INPUT_GPC)) {
             $this->rc->output->set_env('listRange', intval($range));
         }
 
         if ($search = rcube_utils::get_input_value('search', rcube_utils::INPUT_GPC)) {
             $this->rc->output->set_env('search', $search);
             $title .= ' "' . $search . '"';
         }
 
         // Add JS to the page
         $this->ui->addJS();
 
         $this->register_handler('plugin.calendar_css', [$this->ui, 'calendar_css']);
         $this->register_handler('plugin.calendar_list', [$this->ui, 'calendar_list']);
 
         $this->rc->output->set_pagetitle($title);
         $this->rc->output->send('calendar.print');
     }
 
     /**
      * Compare two event objects and return differing properties
      *
      * @param array Event A
      * @param array Event B
      *
      * @return array List of differing event properties
      */
     public static function event_diff($a, $b)
     {
         $diff   = [];
         $ignore = ['changed' => 1, 'attachments' => 1];
 
         foreach (array_unique(array_merge(array_keys($a), array_keys($b))) as $key) {
             if (empty($ignore[$key]) && $key[0] != '_') {
                 $av = isset($a[$key]) ? $a[$key] : null;
                 $bv = isset($b[$key]) ? $b[$key] : null;
 
                 if ($av != $bv) {
                     $diff[] = $key;
                 }
             }
         }
 
         // only compare number of attachments
         $ac = !empty($a['attachments']) ? count($a['attachments']) : 0;
         $bc = !empty($b['attachments']) ? count($b['attachments']) : 0;
 
         if ($ac != $bc) {
             $diff[] = 'attachments';
         }
 
         return $diff;
     }
 
     /**
      * Update attendee properties on the given event object
      *
      * @param array The event object to be altered
      * @param array List of hash arrays each represeting an updated/added attendee
      */
     public static function merge_attendee_data(&$event, $attendees, $removed = null)
     {
         if (!empty($attendees) && !is_array($attendees[0])) {
             $attendees = [$attendees];
         }
 
         foreach ($attendees as $attendee) {
             $found = false;
 
             foreach ($event['attendees'] as $i => $candidate) {
                 if ($candidate['email'] == $attendee['email']) {
                     $event['attendees'][$i] = $attendee;
                     $found = true;
                     break;
                 }
             }
 
             if (!$found) {
                 $event['attendees'][] = $attendee;
             }
         }
 
         // filter out removed attendees
         if (!empty($removed)) {
             $event['attendees'] = array_filter($event['attendees'], function($attendee) use ($removed) {
                 return !in_array($attendee['email'], $removed);
             });
         }
     }
 
     /****  Resource management functions  ****/
 
     /**
      * Getter for the configured implementation of the resource directory interface
      */
     private function resources_directory()
     {
         if (!empty($this->resources_dir)) {
             return $this->resources_dir;
         }
 
         if ($driver_name = $this->rc->config->get('calendar_resources_driver')) {
             $driver_class = 'resources_driver_' . $driver_name;
 
             require_once($this->home . '/drivers/resources_driver.php');
             require_once($this->home . '/drivers/' . $driver_name . '/' . $driver_class . '.php');
 
             $this->resources_dir = new $driver_class($this);
         }
 
         return $this->resources_dir;
     }
 
     /**
      * Handler for resoruce autocompletion requests
      */
     public function resources_autocomplete()
     {
         $search  = rcube_utils::get_input_value('_search', rcube_utils::INPUT_GPC, true);
         $sid     = rcube_utils::get_input_value('_reqid', rcube_utils::INPUT_GPC);
         $maxnum  = (int)$this->rc->config->get('autocomplete_max', 15);
         $results = [];
 
         if ($directory = $this->resources_directory()) {
             foreach ($directory->load_resources($search, $maxnum) as $rec) {
                 $results[]  = [
                     'name'  => $rec['name'],
                     'email' => $rec['email'],
                     'type'  => $rec['_type'],
                 ];
             }
         }
 
         $this->rc->output->command('ksearch_query_results', $results, $search, $sid);
         $this->rc->output->send();
     }
 
     /**
      * Handler for load-requests for resource data
      */
     function resources_list()
     {
         $data = [];
 
         if ($directory = $this->resources_directory()) {
             foreach ($directory->load_resources() as $rec) {
                 $data[] = $rec;
             }
         }
 
         $this->rc->output->command('plugin.resource_data', $data);
         $this->rc->output->send();
     }
 
     /**
      * Handler for requests loading resource owner information
      */
     function resources_owner()
     {
         if ($directory = $this->resources_directory()) {
             $id   = rcube_utils::get_input_value('_id', rcube_utils::INPUT_GPC);
             $data = $directory->get_resource_owner($id);
         }
 
         $this->rc->output->command('plugin.resource_owner', $data);
         $this->rc->output->send();
     }
 
     /**
      * Deliver event data for a resource's calendar
      */
     function resources_calendar()
     {
         $events = [];
 
         if ($directory = $this->resources_directory()) {
             $id    = rcube_utils::get_input_value('_id', rcube_utils::INPUT_GPC);
             $start = $this->input_timestamp('start', rcube_utils::INPUT_GET);
             $end   = $this->input_timestamp('end', rcube_utils::INPUT_GET);
 
             $events = $directory->get_resource_calendar($id, $start, $end);
         }
 
         echo $this->encode($events);
         exit;
     }
 
     /**
      * List email addressed of owned resources
      */
     private function owned_resources_emails()
     {
         $results = [];
         if ($directory = $this->resources_directory()) {
             foreach ($directory->load_resources($_SESSION['kolab_dn'], 5000, 'owner') as $rec) {
                 $results[] = $rec['email'];
             }
         }
         return $results;
     }
 
 
     /****  Event invitation plugin hooks ****/
 
     /**
      * Find an event in user calendars
      */
     protected function find_event($event, &$mode)
     {
         $this->load_driver();
 
         // We search for writeable calendars in personal namespace by default
         $mode   = calendar_driver::FILTER_WRITEABLE | calendar_driver::FILTER_PERSONAL;
         $result = $this->driver->get_event($event, $mode);
         // ... now check shared folders if not found
         if (!$result) {
             $result = $this->driver->get_event($event, calendar_driver::FILTER_WRITEABLE | calendar_driver::FILTER_SHARED);
             if ($result) {
                 $mode |= calendar_driver::FILTER_SHARED;
             }
         }
 
         return $result;
     }
 
     /**
      * Handler for calendar/itip-status requests
      */
     function event_itip_status()
     {
         $data = rcube_utils::get_input_value('data', rcube_utils::INPUT_POST, true);
 
         $this->load_driver();
 
         // find local copy of the referenced event (in personal namespace)
         $existing  = $this->find_event($data, $mode);
         $is_shared = $mode & calendar_driver::FILTER_SHARED;
         $itip      = $this->load_itip();
         $response  = $itip->get_itip_status($data, $existing);
 
         // get a list of writeable calendars to save new events to
         if (
             (!$existing || $is_shared)
             && empty($data['nosave'])
             && ($response['action'] == 'rsvp' || $response['action'] == 'import')
         ) {
             $calendars       = $this->driver->list_calendars($mode);
             $calendar_select = new html_select([
                 'name'       => 'calendar',
                 'id'         => 'itip-saveto',
                 'is_escaped' => true,
                 'class'      => 'form-control custom-select'
             ]);
 
             $calendar_select->add('--', '');
             $numcals = 0;
             foreach ($calendars as $calendar) {
                 if (!empty($calendar['editable'])) {
                     $calendar_select->add($calendar['name'], $calendar['id']);
                     $numcals++;
                 }
             }
             if ($numcals < 1) {
                 $calendar_select = null;
             }
         }
 
         if (!empty($calendar_select)) {
             $default_calendar   = $this->get_default_calendar($calendars);
             $response['select'] = html::span('folder-select', $this->gettext('saveincalendar')
                 . '&nbsp;'
                 . $calendar_select->show($is_shared ? $existing['calendar'] : $default_calendar['id'])
             );
         }
         else if (!empty($data['nosave'])) {
             $response['select'] = html::tag('input', ['type' => 'hidden', 'name' => 'calendar', 'id' => 'itip-saveto', 'value' => '']);
         }
 
         // render small agenda view for the respective day
         if ($data['method'] == 'REQUEST' && !empty($data['date']) && $response['action'] == 'rsvp') {
             $event_start = rcube_utils::anytodatetime($data['date']);
             $day_start   = new Datetime(gmdate('Y-m-d 00:00', $data['date']), $this->lib->timezone);
             $day_end     = new Datetime(gmdate('Y-m-d 23:59', $data['date']), $this->lib->timezone);
 
             // get events on that day from the user's personal calendars
             $calendars = $this->driver->list_calendars(calendar_driver::FILTER_PERSONAL);
             $events    = $this->driver->load_events($day_start->format('U'), $day_end->format('U'), null, array_keys($calendars));
 
             usort($events, function($a, $b) { return $a['start'] > $b['start'] ? 1 : -1; });
 
             $before = $after = [];
             foreach ($events as $event) {
                 // TODO: skip events with free_busy == 'free' ?
                 if ($event['uid'] == $data['uid']
                     || $event['end'] < $day_start || $event['start'] > $day_end
                     || $event['status'] == 'CANCELLED'
                     || (!empty($event['className']) && strpos($event['className'], 'declined') !== false)
                 ) {
                     continue;
                 }
 
                 if ($event['start'] < $event_start) {
                     $before[] = $this->mail_agenda_event_row($event);
                 }
                 else {
                     $after[] = $this->mail_agenda_event_row($event);
                 }
             }
 
             $response['append'] = [
                 'selector' => '.calendar-agenda-preview',
                 'replacements' => [
                     '%before%' => !empty($before) ? join("\n", array_slice($before,  -3)) : html::div('event-row no-event', $this->gettext('noearlierevents')),
                     '%after%'  => !empty($after)  ? join("\n", array_slice($after, 0, 3)) : html::div('event-row no-event', $this->gettext('nolaterevents')),
                 ],
             ];
         }
 
         $this->rc->output->command('plugin.update_itip_object_status', $response);
     }
 
     /**
      * Handler for calendar/itip-remove requests
      */
     function event_itip_remove()
     {
         $uid      = rcube_utils::get_input_value('uid', rcube_utils::INPUT_POST);
         $instance = rcube_utils::get_input_value('_instance', rcube_utils::INPUT_POST);
         $savemode = rcube_utils::get_input_value('_savemode', rcube_utils::INPUT_POST);
         $listmode = calendar_driver::FILTER_WRITEABLE | calendar_driver::FILTER_PERSONAL;
         $success  = false;
 
         // search for event if only UID is given
         if ($event = $this->driver->get_event(['uid' => $uid, '_instance' => $instance], $listmode)) {
             $event['_savemode'] = $savemode;
             $success = $this->driver->remove_event($event, true);
         }
 
         if ($success) {
             $this->rc->output->show_message('calendar.successremoval', 'confirmation');
         }
         else {
             $this->rc->output->show_message('calendar.errorsaving', 'error');
         }
     }
 
     /**
      * Handler for URLs that allow an invitee to respond on his invitation mail
      */
     public function itip_attend_response($p)
     {
         $this->setup();
 
         if ($p['action'] == 'attend') {
             $this->ui->init();
 
             $this->rc->output->set_env('task', 'calendar');  // override some env vars
             $this->rc->output->set_env('refresh_interval', 0);
             $this->rc->output->set_pagetitle($this->gettext('calendar'));
 
             $itip  = $this->load_itip();
             $token = rcube_utils::get_input_value('_t', rcube_utils::INPUT_GPC);
 
             // read event info stored under the given token
             if ($invitation = $itip->get_invitation($token)) {
                 $this->token = $token;
                 $this->event = $invitation['event'];
 
                 // show message about cancellation
                 if (!empty($invitation['cancelled'])) {
                     $this->invitestatus = html::div('rsvp-status declined', $itip->gettext('eventcancelled'));
                 }
                 // save submitted RSVP status
                 else if (!empty($_POST['rsvp'])) {
                     $status = null;
                     foreach (['accepted', 'tentative', 'declined'] as $method) {
                         if ($_POST['rsvp'] == $itip->gettext('itip' . $method)) {
                             $status = $method;
                             break;
                         }
                     }
 
                     // send itip reply to organizer
                     $invitation['event']['comment'] = rcube_utils::get_input_value('_comment', rcube_utils::INPUT_POST);
                     if ($status && $itip->update_invitation($invitation, $invitation['attendee'], strtoupper($status))) {
                         $this->invitestatus = html::div('rsvp-status ' . strtolower($status), $itip->gettext('youhave'.strtolower($status)));
                     }
                     else {
                         $this->rc->output->command('display_message', $this->gettext('errorsaving'), 'error', -1);
                     }
 
                     // if user is logged in...
                     // FIXME: we should really consider removing this functionality
                     //        it's confusing that it creates/updates an event only for logged-in user
                     //        what if the logged-in user is not the same as the attendee?
                     if ($this->rc->user->ID) {
                         $this->load_driver();
 
                         $invitation = $itip->get_invitation($token);
                         $existing   = $this->driver->get_event($this->event);
 
                         // save the event to his/her default calendar if not yet present
                         if (!$existing && ($calendar = $this->get_default_calendar())) {
                             $invitation['event']['calendar'] = $calendar['id'];
                             if ($this->driver->new_event($invitation['event'])) {
                                 $msg = $this->gettext(['name' => 'importedsuccessfully', 'vars' => ['calendar' => $calendar['name']]]);
                                 $this->rc->output->command('display_message', $msg, 'confirmation');
                             }
                             else {
                                 $this->rc->output->command('display_message', $this->gettext('errorimportingevent'), 'error');
                             }
                         }
                         else if ($existing
                             && ($this->event['sequence'] >= $existing['sequence']
                                 || $this->event['changed'] >= $existing['changed'])
                             && ($calendar = $this->driver->get_calendar($existing['calendar']))
                         ) {
                             $this->event       = $invitation['event'];
                             $this->event['id'] = $existing['id'];
 
                             unset($this->event['comment']);
 
                             // merge attendees status
                             // e.g. preserve my participant status for regular updates
                             $this->lib->merge_attendees($this->event, $existing, $status);
 
                             // update attachments list
                             $event['deleted_attachments'] = true;
 
                             // show me as free when declined (#1670)
                             if ($status == 'declined') {
                                 $this->event['free_busy'] = 'free';
                             }
 
                             if ($this->driver->edit_event($this->event)) {
                                 $msg = $this->gettext(['name' => 'updatedsuccessfully', 'vars' => ['calendar' => $calendar->get_name()]]);
                                 $this->rc->output->command('display_message', $msg, 'confirmation');
                             }
                             else {
                                 $this->rc->output->command('display_message', $this->gettext('errorimportingevent'), 'error');
                             }
                         }
                     }
                 }
 
                 $this->register_handler('plugin.event_inviteform', [$this, 'itip_event_inviteform']);
                 $this->register_handler('plugin.event_invitebox', [$this->ui, 'event_invitebox']);
 
                 if (empty($this->invitestatus)) {
                     $this->itip->set_rsvp_actions(['accepted', 'tentative', 'declined']);
                     $this->register_handler('plugin.event_rsvp_buttons', [$this->ui, 'event_rsvp_buttons']);
                 }
 
                 $this->rc->output->set_pagetitle($itip->gettext('itipinvitation') . ' ' . $this->event['title']);
             }
             else {
                 $this->rc->output->command('display_message', $this->gettext('itipinvalidrequest'), 'error', -1);
             }
 
             $this->rc->output->send('calendar.itipattend');
         }
     }
 
     /**
      *
      */
     public function itip_event_inviteform($attrib)
     {
         $hidden = new html_hiddenfield(['name' => "_t", 'value' => $this->token]);
 
         return html::tag('form', [
                 'action' => $this->rc->url(['task' => 'calendar', 'action' => 'attend']),
                 'method' => 'post',
                 'noclose' => true
             ] + $attrib
         ) . $hidden->show();
     }
 
     /**
      *
      */
     private function mail_agenda_event_row($event, $class = '')
     {
         if (!empty($event['allday'])) {
             $time = $this->gettext('all-day');
         }
         else {
             $start = is_object($event['start']) ? clone $event['start'] : $event['start'];
             $end = is_object($event['end']) ? clone $event['end'] : $event['end'];
 
             $time = $this->rc->format_date($start, $this->rc->config->get('time_format'))
                 . ' - ' . $this->rc->format_date($end, $this->rc->config->get('time_format'));
         }
 
         return html::div(rtrim('event-row ' . ($class ?: $event['className'])),
             html::span('event-date', $time)
             . html::span('event-title', rcube::Q($event['title']))
         );
     }
 
     /**
      *
      */
     public function mail_messages_list($p)
     {
         if (!empty($p['cols']) && in_array('attachment', (array) $p['cols']) && !empty($p['messages'])) {
             foreach ($p['messages'] as $header) {
                 $part = new StdClass;
                 $part->mimetype = $header->ctype;
 
                 if (libcalendaring::part_is_vcalendar($part)) {
                     $header->list_flags['attachmentClass'] = 'ical';
                 }
                 else if (in_array($header->ctype, ['multipart/alternative', 'multipart/mixed'])) {
                     // TODO: fetch bodystructure and search for ical parts. Maybe too expensive?
                     if (!empty($header->structure) && !empty($header->structure->parts)) {
                         foreach ($header->structure->parts as $part) {
                             if (libcalendaring::part_is_vcalendar($part)
                                 && !empty($part->ctype_parameters['method'])
                             ) {
                                 $header->list_flags['attachmentClass'] = 'ical';
                                 break;
                             }
                         }
                     }
                 }
             }
         }
     }
 
     /**
      * Add UI element to copy event invitations or updates to the calendar
      */
     public function mail_messagebody_html($p)
     {
         // load iCalendar functions (if necessary)
         if (!empty($this->lib->ical_parts)) {
             $this->get_ical();
             $this->load_itip();
         }
 
         $html = '';
         $has_events = false;
         $ical_objects = $this->lib->get_mail_ical_objects();
 
         // show a box for every event in the file
         foreach ($ical_objects as $idx => $event) {
             if ($event['_type'] != 'event') {
                 // skip non-event objects (#2928)
                 continue;
             }
 
             $has_events = true;
 
             // get prepared inline UI for this event object
             if ($ical_objects->method) {
                 $append   = '';
                 $date_str = $this->rc->format_date(clone $event['start'], $this->rc->config->get('date_format'), empty($event['start']->_dateonly));
                 $date     = new DateTime($event['start']->format('Y-m-d') . ' 12:00:00', new DateTimeZone('UTC'));
 
                 // prepare a small agenda preview to be filled with actual event data on async request
                 if ($ical_objects->method == 'REQUEST') {
                     $append = html::div('calendar-agenda-preview',
                         html::tag('h3', 'preview-title', $this->gettext('agenda') . ' ' . html::span('date', $date_str))
                         . '%before%' . $this->mail_agenda_event_row($event, 'current') . '%after%'
                     );
                 }
 
                 $html .= html::div('calendar-invitebox invitebox boxinformation',
                     $this->itip->mail_itip_inline_ui(
                         $event,
                         $ical_objects->method,
                         $ical_objects->mime_id . ':' . $idx,
                         'calendar',
                         rcube_utils::anytodatetime($ical_objects->message_date),
                         $this->rc->url(['task' => 'calendar']) . '&view=agendaDay&date=' . $date->format('U')
                     ) . $append
                 );
             }
 
             // limit listing
             if ($idx >= 3) {
                 break;
             }
         }
 
         // prepend event boxes to message body
         if ($html) {
             $this->ui->init();
             $p['content'] = $html . $p['content'];
             $this->rc->output->add_label('calendar.savingdata','calendar.deleteventconfirm','calendar.declinedeleteconfirm');
         }
 
         // add "Save to calendar" button into attachment menu
         if ($has_events) {
             $this->add_button([
                     'id'         => 'attachmentsavecal',
                     'name'       => 'attachmentsavecal',
                     'type'       => 'link',
                     'wrapper'    => 'li',
                     'command'    => 'attachment-save-calendar',
                     'class'      => 'icon calendarlink disabled',
                     'classact'   => 'icon calendarlink active',
                     'innerclass' => 'icon calendar',
                     'label'      => 'calendar.savetocalendar',
                 ],
                 'attachmentmenu'
             );
         }
 
         return $p;
     }
 
     /**
      * Handler for POST request to import an event attached to a mail message
      */
     public function mail_import_itip()
     {
         $itip_sending = $this->rc->config->get('calendar_itip_send_option', $this->defaults['calendar_itip_send_option']);
 
         $uid     = rcube_utils::get_input_value('_uid', rcube_utils::INPUT_POST);
         $mbox    = rcube_utils::get_input_value('_mbox', rcube_utils::INPUT_POST);
         $mime_id = rcube_utils::get_input_value('_part', rcube_utils::INPUT_POST);
         $status  = rcube_utils::get_input_value('_status', rcube_utils::INPUT_POST);
         $delete  = intval(rcube_utils::get_input_value('_del', rcube_utils::INPUT_POST));
         $noreply = intval(rcube_utils::get_input_value('_noreply', rcube_utils::INPUT_POST));
         $noreply = $noreply || $status == 'needs-action' || $itip_sending === 0;
         $instance = rcube_utils::get_input_value('_instance', rcube_utils::INPUT_POST);
         $savemode = rcube_utils::get_input_value('_savemode', rcube_utils::INPUT_POST);
         $comment  = rcube_utils::get_input_value('_comment', rcube_utils::INPUT_POST);
 
         $error_msg = $this->gettext('errorimportingevent');
         $success   = false;
         $deleted   = false;
 
         if ($status == 'delegated') {
             $to = rcube_utils::get_input_value('_to', rcube_utils::INPUT_POST, true);
             $delegates = rcube_mime::decode_address_list($to, 1, false);
             $delegate  = reset($delegates);
 
             if (empty($delegate) || empty($delegate['mailto'])) {
                 $this->rc->output->command('display_message', $this->rc->gettext('libcalendaring.delegateinvalidaddress'), 'error');
                 return;
             }
         }
 
         // successfully parsed events?
         if ($event = $this->lib->mail_get_itip_object($mbox, $uid, $mime_id, 'event')) {
             // forward iTip request to delegatee
             if (!empty($delegate)) {
                 $rsvpme = rcube_utils::get_input_value('_rsvp', rcube_utils::INPUT_POST);
                 $itip   = $this->load_itip();
 
                 $event['comment'] = $comment;
 
                 if ($itip->delegate_to($event, $delegate, !empty($rsvpme))) {
                     $this->rc->output->show_message('calendar.itipsendsuccess', 'confirmation');
                 }
                 else {
                     $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
                 }
 
                 unset($event['comment']);
 
                 // the delegator is set to non-participant, thus save as non-blocking
                 $event['free_busy'] = 'free';
             }
 
             $mode = calendar_driver::FILTER_PERSONAL
                 | calendar_driver::FILTER_SHARED
                 | calendar_driver::FILTER_WRITEABLE;
 
             // find writeable calendar to store event
             $cal_id    = rcube_utils::get_input_value('_folder', rcube_utils::INPUT_POST);
             $dontsave  = $cal_id === '' && $event['_method'] == 'REQUEST';
             $calendars = $this->driver->list_calendars($mode);
             $calendar  = isset($calendars[$cal_id]) ? $calendars[$cal_id] : null;
 
             // select default calendar except user explicitly selected 'none'
             if (!$calendar && !$dontsave) {
                 $calendar = $this->get_default_calendar($calendars);
             }
 
             $metadata = [
                 'uid'       => $event['uid'],
                 '_instance' => isset($event['_instance']) ? $event['_instance'] : null,
                 'changed'   => is_object($event['changed']) ? $event['changed']->format('U') : 0,
                 'sequence'  => intval($event['sequence']),
                 'fallback'  => strtoupper($status),
                 'method'    => $event['_method'],
                 'task'      => 'calendar',
             ];
 
             // update my attendee status according to submitted method
             if (!empty($status)) {
                 $organizer = null;
                 $emails = $this->get_user_emails();
                 foreach ($event['attendees'] as $i => $attendee) {
                     if ($attendee['role'] == 'ORGANIZER') {
                         $organizer = $attendee;
                     }
                     else if (!empty($attendee['email']) && in_array(strtolower($attendee['email']), $emails)) {
                         $event['attendees'][$i]['status'] = strtoupper($status);
                         if (!in_array($event['attendees'][$i]['status'], ['NEEDS-ACTION', 'DELEGATED'])) {
                             $event['attendees'][$i]['rsvp'] = false;  // unset RSVP attribute
                         }
 
                         $metadata['attendee'] = $attendee['email'];
                         $metadata['rsvp']     = $attendee['role'] != 'NON-PARTICIPANT';
 
                         $reply_sender   = $attendee['email'];
                         $event_attendee = $attendee;
                     }
                 }
 
                 // add attendee with this user's default identity if not listed
                 if (!$reply_sender) {
                     $sender_identity = $this->rc->user->list_emails(true);
                     $event['attendees'][] = [
                         'name'   => $sender_identity['name'],
                         'email'  => $sender_identity['email'],
                         'role'   => 'OPT-PARTICIPANT',
                         'status' => strtoupper($status),
                     ];
                     $metadata['attendee'] = $sender_identity['email'];
                 }
             }
 
             // save to calendar
             if ($calendar && !empty($calendar['editable'])) {
                 // check for existing event with the same UID
                 $existing = $this->find_event($event, $mode);
 
                 // we'll create a new copy if user decided to change the calendar
                 if ($existing && $cal_id && $calendar && $calendar['id'] != $existing['calendar']) {
                     $existing = null;
                 }
 
                 if ($existing) {
                     $calendar = $calendars[$existing['calendar']];
 
                     // forward savemode for correct updates of recurring events
                     $existing['_savemode'] = $savemode ?: (!empty($event['_savemode']) ? $event['_savemode'] : null);
 
                     // only update attendee status
                     if ($event['_method'] == 'REPLY') {
                         $existing_attendee_index  = -1;
 
                         $event_attendee   = null;
                         $update_attendees = [];
 
                         if ($attendee = $this->itip->find_reply_attendee($event)) {
                             $event_attendee       = $attendee;
                             $update_attendees[]   = $attendee;
                             $metadata['fallback'] = $attendee['status'];
                             $metadata['attendee'] = $attendee['email'];
                             $metadata['rsvp']     = !empty($attendee['rsvp']) || $attendee['role'] != 'NON-PARTICIPANT';
 
                             $existing_attendee_emails = [];
 
                             // Find the attendee to update
                             foreach ($existing['attendees'] as $i => $existing_attendee) {
                                 $existing_attendee_emails[] = $existing_attendee['email'];
                                 if ($this->itip->compare_email($existing_attendee['email'], $attendee['email'])) {
                                     $existing_attendee_index = $i;
                                 }
                             }
 
                             if ($attendee['status'] == 'DELEGATED') {
                                 //Also find and copy the delegatee
                                 $delegatee_email = $attendee['email'];
                                 $delegatees = array_filter($event['attendees'], function($attendee) use ($delegatee_email){ return $attendee['role'] != 'ORGANIZER' && $this->itip->compare_email($attendee['delegated-from'], $delegatee_email); });
 
                                 if ($delegatee = $this->itip->find_attendee_by_email($event['attendees'], 'delegated-from', $attendee['email'])) {
                                     $update_attendees[] = $delegatee;
                                     if (!in_array_nocase($delegatee['email'], $existing_attendee_emails)) {
                                         $existing['attendees'][] = $delegated_attendee;
                                     }
                                 }
                             }
                         }
 
                         // if delegatee has declined, set delegator's RSVP=True
                         if ($event_attendee
                             && $event_attendee['status'] == 'DECLINED'
                             && !empty($event_attendee['delegated-from'])
                         ) {
                             foreach ($existing['attendees'] as $i => $attendee) {
                                 if ($attendee['email'] == $event_attendee['delegated-from']) {
                                     $existing['attendees'][$i]['rsvp'] = true;
                                     break;
                                 }
                             }
                         }
 
                         // found matching attendee entry in both existing and new events
                         if ($existing_attendee_index >= 0 && $event_attendee) {
                             $existing['attendees'][$existing_attendee_index] = $event_attendee;
                             $success = $this->driver->update_attendees($existing, $update_attendees);
                         }
                         // update the entire attendees block
                         else if (
                             ($event['sequence'] >= $existing['sequence'] || $event['changed'] >= $existing['changed'])
                             && $event_attendee
                         ) {
                             $existing['attendees'][] = $event_attendee;
                             $success = $this->driver->update_attendees($existing, $update_attendees);
                         }
                         else if (!$event_attendee) {
                             $error_msg = $this->gettext('errorunknownattendee');
                         }
                         else {
                             $error_msg = $this->gettext('newerversionexists');
                         }
                     }
                     // delete the event when declined (#1670)
                     else if ($status == 'declined' && $delete) {
                         $deleted = $this->driver->remove_event($existing, true);
                         $success = true;
                     }
                     // import the (newer) event
                     else if ($event['sequence'] >= $existing['sequence'] || $event['changed'] >= $existing['changed']) {
                         $event['id']       = $existing['id'];
                         $event['calendar'] = $existing['calendar'];
 
                         // merge attendees status
                         // e.g. preserve my participant status for regular updates
                         $this->lib->merge_attendees($event, $existing, $status);
 
                         // set status=CANCELLED on CANCEL messages
                         if ($event['_method'] == 'CANCEL') {
                             $event['status'] = 'CANCELLED';
                         }
 
                         // update attachments list, allow attachments update only on REQUEST (#5342)
                         if ($event['_method'] == 'REQUEST') {
                             $event['deleted_attachments'] = true;
                         }
                         else {
                             unset($event['attachments']);
                         }
 
                         // show me as free when declined (#1670)
                         if ($status == 'declined'
                             || (!empty($event['status']) && $event['status'] == 'CANCELLED')
                             || $event_attendee['role'] == 'NON-PARTICIPANT'
                         ) {
                             $event['free_busy'] = 'free';
                         }
 
                         $success = $this->driver->edit_event($event);
                     }
                     else if (!empty($status)) {
                         $existing['attendees'] = $event['attendees'];
                         if ($status == 'declined' || $event_attendee['role'] == 'NON-PARTICIPANT') {
                             // show me as free when declined (#1670)
                             $existing['free_busy'] = 'free';
                         }
                         $success = $this->driver->edit_event($existing);
                     }
                     else {
                         $error_msg = $this->gettext('newerversionexists');
                     }
                 }
                 else if (!$existing && ($status != 'declined' || $this->rc->config->get('kolab_invitation_calendars'))) {
                     if ($status == 'declined'
                         || $event['status'] == 'CANCELLED'
                         || $event_attendee['role'] == 'NON-PARTICIPANT'
                     ) {
                         $event['free_busy'] = 'free';
                     }
 
                     // if the RSVP reply only refers to a single instance:
                     // store unmodified master event with current instance as exception
                     if (!empty($instance) && !empty($savemode) && $savemode != 'all') {
                         $master = $this->lib->mail_get_itip_object($mbox, $uid, $mime_id, 'event');
                         if ($master['recurrence'] && empty($master['_instance'])) {
                             // compute recurring events until this instance's date
                             if ($recurrence_date = rcube_utils::anytodatetime($instance, $master['start']->getTimezone())) {
                                 $recurrence_date->setTime(23,59,59);
 
                                 foreach ($this->driver->get_recurring_events($master, $master['start'], $recurrence_date) as $recurring) {
                                     if ($recurring['_instance'] == $instance) {
                                         // copy attendees block with my partstat to exception
                                         $recurring['attendees'] = $event['attendees'];
                                         $master['recurrence']['EXCEPTIONS'][] = $recurring;
                                         $event = $recurring;  // set reference for iTip reply
                                         break;
                                     }
                                 }
 
                                 $master['calendar'] = $event['calendar'] = $calendar['id'];
                                 $success = $this->driver->new_event($master);
                             }
                             else {
                                 $master = null;
                             }
                         }
                         else {
                             $master = null;
                         }
                     }
 
                     // save to the selected/default calendar
                     if (!$master) {
                         $event['calendar'] = $calendar['id'];
                         $success = $this->driver->new_event($event);
                     }
                 }
                 else if ($status == 'declined') {
                     $error_msg = null;
                 }
             }
             else if ($status == 'declined' || $dontsave) {
                 $error_msg = null;
             }
             else {
                 $error_msg = $this->gettext('nowritecalendarfound');
             }
         }
 
         if ($success) {
             if ($event['_method'] == 'REPLY') {
                 $message = 'attendeupdateesuccess';
             }
             else {
                 $message = $deleted ? 'successremoval' : ($existing ? 'updatedsuccessfully' : 'importedsuccessfully');
             }
 
             $msg = $this->gettext(['name' => $message, 'vars' => ['calendar' => $calendar['name']]]);
             $this->rc->output->command('display_message', $msg, 'confirmation');
         }
 
         if ($success || $dontsave) {
             $metadata['calendar'] = isset($event['calendar']) ? $event['calendar'] : null;
             $metadata['nosave']   = $dontsave;
             $metadata['rsvp']     = !empty($metadata['rsvp']);
 
             $metadata['after_action'] = $this->rc->config->get('calendar_itip_after_action', $this->defaults['calendar_itip_after_action']);
             $this->rc->output->command('plugin.itip_message_processed', $metadata);
             $error_msg = null;
         }
         else if ($error_msg) {
             $this->rc->output->command('display_message', $error_msg, 'error');
         }
 
         // send iTip reply
         if ($event['_method'] == 'REQUEST' && !empty($organizer) && !$noreply
             && !in_array(strtolower($organizer['email']), $emails) && !$error_msg
         ) {
             $event['comment'] = $comment;
             $itip = $this->load_itip();
             $itip->set_sender_email($reply_sender);
 
             if ($itip->send_itip_message($event, 'REPLY', $organizer, 'itipsubject' . $status, 'itipmailbody' . $status)) {
                 $mailto = $organizer['name'] ? $organizer['name'] : $organizer['email'];
                 $msg    = $this->gettext(['name' => 'sentresponseto', 'vars' => ['mailto' => $mailto]]);
                 $this->rc->output->command('display_message', $msg, 'confirmation');
             }
             else {
                 $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
             }
         }
 
         $this->rc->output->send();
     }
 
     /**
      * Handler for calendar/itip-remove requests
      */
     function mail_itip_decline_reply()
     {
         $uid     = rcube_utils::get_input_value('_uid', rcube_utils::INPUT_POST);
         $mbox    = rcube_utils::get_input_value('_mbox', rcube_utils::INPUT_POST);
         $mime_id = rcube_utils::get_input_value('_part', rcube_utils::INPUT_POST);
 
         if (($event = $this->lib->mail_get_itip_object($mbox, $uid, $mime_id, 'event'))
             && $event['_method'] == 'REPLY'
         ) {
             $event['comment'] = rcube_utils::get_input_value('_comment', rcube_utils::INPUT_POST);
 
             foreach ($event['attendees'] as $_attendee) {
                 if ($_attendee['role'] != 'ORGANIZER') {
                     $attendee = $_attendee;
                     break;
                 }
             }
 
             $itip = $this->load_itip();
 
             if ($itip->send_itip_message($event, 'CANCEL', $attendee, 'itipsubjectcancel', 'itipmailbodycancel')) {
                 $mailto = !empty($attendee['name']) ? $attendee['name'] : $attendee['email'];
                 $msg    = $this->gettext(['name' => 'sentresponseto', 'vars' => ['mailto' => $mailto]]);
                 $this->rc->output->command('display_message', $msg, 'confirmation');
             }
             else {
                 $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
             }
         }
         else {
             $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
         }
     }
 
     /**
      * Handler for calendar/itip-delegate requests
      */
     function mail_itip_delegate()
     {
         // forward request to mail_import_itip() with the right status
         $_POST['_status'] = $_REQUEST['_status'] = 'delegated';
         $this->mail_import_itip();
     }
 
     /**
      * Import the full payload from a mail message attachment
      */
     public function mail_import_attachment()
     {
         $uid     = rcube_utils::get_input_value('_uid', rcube_utils::INPUT_POST);
         $mbox    = rcube_utils::get_input_value('_mbox', rcube_utils::INPUT_POST);
         $mime_id = rcube_utils::get_input_value('_part', rcube_utils::INPUT_POST);
         $charset = RCUBE_CHARSET;
 
         // establish imap connection
         $imap = $this->rc->get_storage();
         $imap->set_folder($mbox);
 
         if ($uid && $mime_id) {
             $part = $imap->get_message_part($uid, $mime_id);
             // $headers = $imap->get_message_headers($uid);
 
             if ($part) {
                 if (!empty($part->ctype_parameters['charset'])) {
                     $charset = $part->ctype_parameters['charset'];
                 }
                 $events = $this->get_ical()->import($part, $charset);
             }
         }
 
         $success = $existing = 0;
 
         if (!empty($events)) {
             // find writeable calendar to store event
             $cal_id = !empty($_REQUEST['_calendar']) ? rcube_utils::get_input_value('_calendar', rcube_utils::INPUT_POST) : null;
             $calendars = $this->driver->list_calendars(calendar_driver::FILTER_PERSONAL);
 
             foreach ($events as $event) {
                 // save to calendar
                 $calendar = !empty($calendars[$cal_id]) ? $calendars[$cal_id] : $this->get_default_calendar();
                 if ($calendar && $calendar['editable'] && $event['_type'] == 'event') {
                     $event['calendar'] = $calendar['id'];
 
                     if (!$this->driver->get_event($event['uid'], calendar_driver::FILTER_WRITEABLE)) {
                         $success += (bool)$this->driver->new_event($event);
                     }
                     else {
                         $existing++;
                     }
                 }
             }
         }
 
         if ($success) {
             $msg = $this->gettext(['name' => 'importsuccess', 'vars' => ['nr' => $success]]);
             $this->rc->output->command('display_message', $msg, 'confirmation');
         }
         else if ($existing) {
             $this->rc->output->command('display_message', $this->gettext('importwarningexists'), 'warning');
         }
         else {
             $this->rc->output->command('display_message', $this->gettext('errorimportingevent'), 'error');
         }
     }
 
     /**
      * Read email message and return contents for a new event based on that message
      */
     public function mail_message2event()
     {
         $this->ui->init();
         $this->ui->addJS();
         $this->ui->init_templates();
         $this->ui->calendar_list([], true); // set env['calendars']
 
         $uid   = rcube_utils::get_input_value('_uid', rcube_utils::INPUT_GET);
         $mbox  = rcube_utils::get_input_value('_mbox', rcube_utils::INPUT_GET);
         $event = [];
 
         // establish imap connection
         $imap    = $this->rc->get_storage();
         $message = new rcube_message($uid, $mbox);
 
         if ($message->headers) {
             $event['title']       = trim($message->subject);
             $event['description'] = trim($message->first_text_part());
 
             $this->load_driver();
 
             // add a reference to the email message
             if ($msgref = $this->driver->get_message_reference($message->headers, $mbox)) {
                 $event['links'] = [$msgref];
             }
             // copy mail attachments to event
             else if ($message->attachments) {
                 $eventid = 'cal-';
                 if (empty($_SESSION[self::SESSION_KEY]) || $_SESSION[self::SESSION_KEY]['id'] != $eventid) {
                     $_SESSION[self::SESSION_KEY] = [
                         'id'          => $eventid,
                         'attachments' => [],
                     ];
                 }
 
                 foreach ((array) $message->attachments as $part) {
                     $attachment = [
                         'data' => $imap->get_message_part($uid, $part->mime_id, $part),
                         'size' => $part->size,
                         'name' => $part->filename,
                         'mimetype' => $part->mimetype,
                         'group' => $eventid,
                     ];
 
                     $attachment = $this->rc->plugins->exec_hook('attachment_save', $attachment);
 
                     if (!empty($attachment['status']) && !$attachment['abort']) {
                         $id = $attachment['id'];
                         $attachment['classname'] = rcube_utils::file2class($attachment['mimetype'], $attachment['name']);
 
                         // store new attachment in session
                         unset($attachment['status'], $attachment['abort'], $attachment['data']);
                         $_SESSION[self::SESSION_KEY]['attachments'][$id] = $attachment;
 
                         $attachment['id'] = 'rcmfile' . $attachment['id'];  // add prefix to consider it 'new'
                         $event['attachments'][] = $attachment;
                     }
                 }
             }
 
             $this->rc->output->set_env('event_prop', $event);
         }
         else {
             $this->rc->output->command('display_message', $this->gettext('messageopenerror'), 'error');
         }
 
         $this->rc->output->send('calendar.dialog');
     }
 
     /**
      * Handler for the 'message_compose' plugin hook. This will check for
      * a compose parameter 'calendar_event' and create an attachment with the
      * referenced event in iCal format
      */
     public function mail_message_compose($args)
     {
         // set the submitted event ID as attachment
         if (!empty($args['param']['calendar_event'])) {
             $this->load_driver();
 
             list($cal, $id) = explode(':', $args['param']['calendar_event'], 2);
 
             if ($event = $this->driver->get_event(['id' => $id, 'calendar' => $cal])) {
                 $filename = asciiwords($event['title']);
                 if (empty($filename)) {
                     $filename = 'event';
                 }
 
                 // save ics to a temp file and register as attachment
                 $tmp_path = tempnam($this->rc->config->get('temp_dir'), 'rcmAttmntCal');
                 $export   = $this->get_ical()->export([$event], '', false, [$this->driver, 'get_attachment_body']);
 
                 file_put_contents($tmp_path, $export);
 
                 $args['attachments'][] = [
                     'path'     => $tmp_path,
                     'name'     => $filename . '.ics',
                     'mimetype' => 'text/calendar',
                     'size'     => filesize($tmp_path),
                 ];
                 $args['param']['subject'] = $event['title'];
             }
         }
 
         return $args;
     }
 
     /**
      * Create a Nextcould Talk room
      */
     public function talk_room_create()
     {
         require_once __DIR__ . '/lib/calendar_nextcloud_api.php';
 
         $api = new calendar_nextcloud_api();
 
         $name = (string) rcube_utils::get_input_value('_name', rcube_utils::INPUT_POST);
 
         $room_url = $api->talk_room_create($name);
 
         if ($room_url) {
             $this->rc->output->command('plugin.talk_room_created', ['url' => $room_url]);
         }
         else {
             $this->rc->output->command('display_message', $this->gettext('talkroomcreateerror'), 'error');
         }
     }
 
     /**
      * Update a Nextcould Talk room
      */
     public function talk_room_update($event)
     {
         // If a room is assigned to the event...
         if (
             ($talk_url = $this->rc->config->get('calendar_nextcloud_url'))
             && isset($event['attendees'])
             && !empty($event['location'])
             && strpos($event['location'], unslashify($talk_url) . '/call/') === 0
         ) {
             $participants = [];
             $organizer = null;
 
             // ollect participants' and organizer's email addresses
             foreach ($event['attendees'] as $attendee) {
                 if (!empty($attendee['email'])) {
                     if ($attendee['role'] == 'ORGANIZER') {
                         $organizer = $attendee['email'];
                     }
                     else if ($attendee['cutype'] == 'INDIVIDUAL') {
                         $participants[] = $attendee['email'];
                     }
                 }
             }
 
             // If the event is owned by the current user update the room
             if ($organizer && in_array($organizer, $this->get_user_emails())) {
                 require_once __DIR__ . '/lib/calendar_nextcloud_api.php';
 
                 $api = new calendar_nextcloud_api();
 
                 $api->talk_room_update($event['location'], $participants);
             }
         }
     }
 
     /**
      * Get a list of email addresses of the current user (from login and identities)
      */
     public function get_user_emails()
     {
         return $this->lib->get_user_emails();
     }
 
     /**
      * Build an absolute URL with the given parameters
      */
     public function get_url($param = [])
     {
         $param += ['task' => 'calendar'];
         return $this->rc->url($param, true, true);
     }
 
     public function ical_feed_hash($source)
     {
         return base64_encode($this->rc->user->get_username() . ':' . $source);
     }
 
     /**
      * Handler for user_delete plugin hook
      */
     public function user_delete($args)
     {
          // delete itipinvitations entries related to this user
          $db = $this->rc->get_dbh();
          $table_itipinvitations = $db->table_name('itipinvitations', true);
 
          $db->query("DELETE FROM $table_itipinvitations WHERE `user_id` = ?", $args['user']->ID);
 
         $this->setup();
         $this->load_driver();
 
         return $this->driver->user_delete($args);
     }
 
     /**
      * Find first occurrence of a recurring event excluding start date
      *
      * @param array $event Event data (with 'start' and 'recurrence')
      *
      * @return DateTime Date of the first occurrence
      */
     public function find_first_occurrence($event)
     {
-        // Make sure libkolab plugin is loaded in case of Kolab driver
+        // Make sure libkolab/libcalendaring plugins are loaded
         $this->load_driver();
 
-        // Use libkolab to compute recurring events (and libkolab plugin)
-        if (class_exists('kolabformat') && class_exists('kolabcalendaring') && class_exists('kolab_date_recurrence')) {
+        $driver_name = $this->rc->config->get('calendar_driver', 'database');
+
+        // Use kolabcalendaring/kolabformat to compute recurring events only with the Kolab driver
+        if ($driver_name == 'kolab' && class_exists('kolabformat') && class_exists('kolabcalendaring')
+            && class_exists('kolab_date_recurrence')
+        ) {
             $object = kolab_format::factory('event', 3.0);
             $object->set($event);
 
             $recurrence = new kolab_date_recurrence($object);
         }
         else {
             // fallback to libcalendaring recurrence implementation
             $recurrence = new libcalendaring_recurrence($this->lib, $event);
         }
 
         return $recurrence->first_occurrence();
     }
 
     /**
      * Get date-time input from UI and convert to unix timestamp
      */
     protected function input_timestamp($name, $type)
     {
         $ts = rcube_utils::get_input_value($name, $type);
 
         if ($ts && (!is_numeric($ts) || strpos($ts, 'T'))) {
             $ts = new DateTime($ts, $this->timezone);
             $ts = $ts->getTimestamp();
         }
 
         return $ts;
     }
 
     /**
      * Magic getter for public access to protected members
      */
     public function __get($name)
     {
         switch ($name) {
         case 'ical':
             return $this->get_ical();
 
         case 'itip':
             return $this->load_itip();
 
         case 'driver':
             $this->load_driver();
             return $this->driver;
         }
 
         return null;
     }
 }
diff --git a/plugins/calendar/drivers/caldav/caldav_calendar.php b/plugins/calendar/drivers/caldav/caldav_calendar.php
index 742e9dac..7d4e94f7 100644
--- a/plugins/calendar/drivers/caldav/caldav_calendar.php
+++ b/plugins/calendar/drivers/caldav/caldav_calendar.php
@@ -1,899 +1,878 @@
 <?php
 
 /**
  * CalDAV calendar storage class
  *
  * @author Aleksander Machniak <machniak@apheleia-it.ch>
  *
  * Copyright (C) 2012-2022, Apheleia IT AG <contact@apheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class caldav_calendar extends kolab_storage_dav_folder
 {
     public $ready         = false;
     public $rights        = 'lrs';
     public $editable      = false;
     public $attachments   = false; // TODO
     public $alarms        = false;
     public $history       = false;
     public $subscriptions = false;
     public $categories    = [];
     public $storage;
 
     public $type = 'event';
 
     protected $cal;
     protected $events = [];
     protected $search_fields = ['title', 'description', 'location', 'attendees', 'categories'];
 
     /**
      * Factory method to instantiate a caldav_calendar object
      *
      * @param string $id       Calendar ID (encoded IMAP folder name)
      * @param object $calendar Calendar plugin object
      *
      * @return caldav_calendar Self instance
      */
     public static function factory($id, $calendar)
     {
         return new caldav_calendar($id, $calendar);
     }
 
     /**
      * Default constructor
      */
     public function __construct($folder_or_id, $calendar)
     {
         if ($folder_or_id instanceof kolab_storage_dav_folder) {
             $this->storage = $folder_or_id;
         }
         else {
             // $this->storage = kolab_storage_dav::get_folder($folder_or_id, 'event');
         }
 
         $this->cal        = $calendar;
         $this->id         = $this->storage->id;
         $this->attributes = $this->storage->attributes;
         $this->ready      = true;
         $this->alarms     = !isset($this->storage->attributes['alarms']) || $this->storage->attributes['alarms'];
 
         // Set writeable and alarms flags according to folder permissions
         if ($this->ready) {
             if ($this->storage->get_namespace() == 'personal') {
                 $this->editable = true;
                 $this->rights = 'lrswikxteav';
             }
             else {
                 $rights = $this->storage->get_myrights();
                 if ($rights) {
                     $this->rights = $rights;
                     if (strpos($rights, 't') !== false || strpos($rights, 'd') !== false) {
                         $this->editable = strpos($rights, 'i');;
                     }
                 }
             }
         }
 
         $this->default = $this->storage->default;
         $this->subtype = $this->storage->subtype;
     }
 
     /**
      * Getter for the folder name
      *
      * @return string Name of the folder
      */
     public function get_realname()
     {
         return $this->get_name();
     }
 
     /**
      * Return color to display this calendar
      */
     public function get_color($default = null)
     {
         if ($color = $this->storage->get_color()) {
             return $color;
         }
 
         return $default ?: 'cc0000';
     }
 
     /**
      * Compose an URL for CalDAV access to this calendar (if configured)
      */
     public function get_caldav_url()
     {
 /*
         if ($template = $this->cal->rc->config->get('calendar_caldav_url', null)) {
             return strtr($template, [
                     '%h' => $_SERVER['HTTP_HOST'],
                     '%u' => urlencode($this->cal->rc->get_user_name()),
                     '%i' => urlencode($this->storage->get_uid()),
                     '%n' => urlencode($this->name),
             ]);
         }
 */
         return false;
     }
 
     /**
      * Update properties of this calendar folder
      *
      * @see caldav_driver::edit_calendar()
      */
     public function update(&$prop)
     {
         return false; // NOP
     }
 
     /**
      * Getter for a single event object
      */
     public function get_event($id)
     {
         // remove our occurrence identifier if it's there
         $master_id = preg_replace('/-\d{8}(T\d{6})?$/', '', $id);
 
         // directly access storage object
         if (empty($this->events[$id]) && $master_id == $id && ($record = $this->storage->get_object($id))) {
             $this->events[$id] = $record = $this->_to_driver_event($record, true);
         }
 
         // maybe a recurring instance is requested
         if (empty($this->events[$id]) && $master_id != $id) {
             $instance_id = substr($id, strlen($master_id) + 1);
 
             if ($record = $this->storage->get_object($master_id)) {
                 $master = $record = $this->_to_driver_event($record);
             }
 
             if (!empty($master)) {
-                // check for match in top-level exceptions (aka loose single occurrences)
-                if (!empty($master['_formatobj']) && ($instance = $master['_formatobj']->get_instance($instance_id))) {
-                    $this->events[$id] = $this->_to_driver_event($instance, false, true, $master);
-                }
                 // check for match on the first instance already
-                else if (!empty($master['_instance']) && $master['_instance'] == $instance_id) {
+                if (!empty($master['_instance']) && $master['_instance'] == $instance_id) {
                     $this->events[$id] = $master;
                 }
                 else if (!empty($master['recurrence'])) {
                     $start_date = $master['start'];
                     // For performance reasons we'll get only the specific instance
                     if (($date = substr($id, strlen($master_id) + 1, 8)) && strlen($date) == 8 && is_numeric($date)) {
                         $start_date = new DateTime($date . 'T000000', $master['start']->getTimezone());
                     }
 
                     $this->get_recurring_events($record, $start_date, null, $id, 1);
                 }
             }
         }
 
         return $this->events[$id];
     }
 
     /**
      * Get attachment body
      * @see calendar_driver::get_attachment_body()
      */
     public function get_attachment_body($id, $event)
     {
         if (!$this->ready) {
             return false;
         }
 
         $data = $this->storage->get_attachment($event['id'], $id);
 
         if ($data == null) {
             // try again with master UID
             $uid = preg_replace('/-\d+(T\d{6})?$/', '', $event['id']);
             if ($uid != $event['id']) {
                 $data = $this->storage->get_attachment($uid, $id);
             }
         }
 
         return $data;
     }
 
     /**
      * @param int    Event's new start (unix timestamp)
      * @param int    Event's new end (unix timestamp)
      * @param string Search query (optional)
      * @param bool   Include virtual events (optional)
      * @param array  Additional parameters to query storage
      * @param array  Additional query to filter events
      *
      * @return array A list of event records
      */
     public function list_events($start, $end, $search = null, $virtual = 1, $query = [], $filter_query = null)
     {
         // convert to DateTime for comparisons
         // #5190: make the range a little bit wider
         // to workaround possible timezone differences
         try {
             $start = new DateTime('@' . ($start - 12 * 3600));
         }
         catch (Exception $e) {
             $start = new DateTime('@0');
         }
         try {
             $end = new DateTime('@' . ($end + 12 * 3600));
         }
         catch (Exception $e) {
             $end = new DateTime('today +10 years');
         }
 
         // get email addresses of the current user
         $user_emails = $this->cal->get_user_emails();
 
         // query Kolab storage
         $query[] = ['dtstart', '<=', $end];
         $query[] = ['dtend',   '>=', $start];
 
         if (is_array($filter_query)) {
             $query = array_merge($query, $filter_query);
         }
 
         $words = [];
         $partstat_exclude = [];
         $events = [];
 
         if (!empty($search)) {
             $search = mb_strtolower($search);
             $words  = rcube_utils::tokenize_string($search, 1);
             foreach (rcube_utils::normalize_string($search, true) as $word) {
                 $query[] = ['words', 'LIKE', $word];
             }
         }
 
         // set partstat filter to skip pending and declined invitations
         if (empty($filter_query)
             && $this->cal->rc->config->get('kolab_invitation_calendars')
             && $this->get_namespace() != 'other'
         ) {
             $partstat_exclude = ['NEEDS-ACTION', 'DECLINED'];
         }
 
         foreach ($this->storage->select($query) as $record) {
             $event = $this->_to_driver_event($record, !$virtual, false);
 
             // remember seen categories
             if (!empty($event['categories'])) {
                 $cat = is_array($event['categories']) ? $event['categories'][0] : $event['categories'];
                 $this->categories[$cat]++;
             }
 
             // list events in requested time window
             if ($event['start'] <= $end && $event['end'] >= $start) {
                 unset($event['_attendees']);
                 $add = true;
 
                 // skip the first instance of a recurring event if listed in exdate
                 if ($virtual && !empty($event['recurrence']['EXDATE'])) {
                     $event_date = $event['start']->format('Ymd');
                     $event_tz   = $event['start']->getTimezone();
 
                     foreach ((array) $event['recurrence']['EXDATE'] as $exdate) {
                         $ex = clone $exdate;
                         $ex->setTimezone($event_tz);
 
                         if ($ex->format('Ymd') == $event_date) {
                             $add = false;
                             break;
                         }
                     }
                 }
 
                 // find and merge exception for the first instance
                 if ($virtual && !empty($event['recurrence']) && !empty($event['recurrence']['EXCEPTIONS'])) {
                     foreach ($event['recurrence']['EXCEPTIONS'] as $exception) {
                         if ($event['_instance'] == $exception['_instance']) {
                             unset($exception['calendar'], $exception['className'], $exception['_folder_id']);
                             // clone date objects from main event before adjusting them with exception data
                             if (is_object($event['start'])) {
                                 $event['start'] = clone $record['start'];
                             }
                             if (is_object($event['end'])) {
                                 $event['end'] = clone $record['end'];
                             }
                             kolab_driver::merge_exception_data($event, $exception);
                         }
                     }
                 }
 
                 if ($add) {
                     $events[] = $event;
                 }
             }
 
             // resolve recurring events
             if (!empty($event['recurrence']) && $virtual == 1) {
                 $events = array_merge($events, $this->get_recurring_events($event, $start, $end));
             }
             // add top-level exceptions (aka loose single occurrences)
             else if (!empty($record['exceptions'])) {
                 foreach ($record['exceptions'] as $ex) {
                     $component = $this->_to_driver_event($ex, false, false, $record);
                     if ($component['start'] <= $end && $component['end'] >= $start) {
                         $events[] = $component;
                     }
                 }
             }
         }
 
         // post-filter all events by fulltext search and partstat values
         $me = $this;
         $events = array_filter($events, function($event) use ($words, $partstat_exclude, $user_emails, $me) {
             // fulltext search
             if (count($words)) {
                 $hits = 0;
                 foreach ($words as $word) {
                     $hits += $me->fulltext_match($event, $word, false);
                 }
                 if ($hits < count($words)) {
                     return false;
                 }
             }
 
             // partstat filter
             if (count($partstat_exclude) && !empty($event['attendees'])) {
                 foreach ($event['attendees'] as $attendee) {
                     if (
                         in_array($attendee['email'], $user_emails)
                         && in_array($attendee['status'], $partstat_exclude)
                     ) {
                         return false;
                     }
                 }
             }
 
             return true;
         });
 
         // Apply event-to-mail relations
         // $config = kolab_storage_config::get_instance();
         // $config->apply_links($events);
 
         // Avoid session race conditions that will loose temporary subscriptions
         // $this->cal->rc->session->nowrite = true;
 
         return $events;
     }
 
     /**
      * Get number of events in the given calendar
      *
      * @param int   Date range start (unix timestamp)
      * @param int   Date range end (unix timestamp)
      * @param array Additional query to filter events
      *
      * @return int Number of events
      */
     public function count_events($start, $end = null, $filter_query = null)
     {
         // convert to DateTime for comparisons
         try {
             $start = new DateTime('@'.$start);
         }
         catch (Exception $e) {
             $start = new DateTime('@0');
         }
         if ($end) {
             try {
                 $end = new DateTime('@'.$end);
             }
             catch (Exception $e) {
                 $end = null;
             }
         }
 
         // query Kolab storage
         $query[] = ['dtend',   '>=', $start];
 
         if ($end) {
             $query[] = ['dtstart', '<=', $end];
         }
 
         // add query to exclude pending/declined invitations
         if (empty($filter_query)) {
             foreach ($this->cal->get_user_emails() as $email) {
                 $query[] = ['tags', '!=', 'x-partstat:' . $email . ':needs-action'];
                 $query[] = ['tags', '!=', 'x-partstat:' . $email . ':declined'];
             }
         }
         else if (is_array($filter_query)) {
             $query = array_merge($query, $filter_query);
         }
 
         return $this->storage->count($query);
     }
 
     /**
      * Create a new event record
      *
      * @see calendar_driver::new_event()
      *
      * @return array|false The created record ID on success, False on error
      */
     public function insert_event($event)
     {
         if (!is_array($event)) {
             return false;
         }
 
         // email links are stored separately
         // $links = !empty($event['links']) ? $event['links'] : [];
         // unset($event['links']);
 
         // generate new event from RC input
         $object = $this->_from_driver_event($event);
         $saved  = $this->storage->save($object, 'event');
 
         if (!$saved) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error saving event object to DAV server"
                 ],
                 true, false
             );
             return false;
         }
 
         // save links in configuration.relation object
         // if ($this->save_links($event['uid'], $links)) {
         //    $object['links'] = $links;
         // }
 
         $this->events = [$event['uid'] => $this->_to_driver_event($object, true)];
 
         return true;
     }
 
     /**
      * Update a specific event record
      *
      * @return bool True on success, False on error
      */
     public function update_event($event, $exception_id = null)
     {
         $updated = false;
         $old = $this->storage->get_object(!empty($event['uid']) ? $event['uid'] : $event['id']);
 
         if (!$old || PEAR::isError($old)) {
             return false;
         }
 
         // email links are stored separately
         // $links = !empty($event['links']) ? $event['links'] : [];
         // unset($event['links']);
 
         $object = $this->_from_driver_event($event, $old);
         $saved  = $this->storage->save($object, 'event', $old['uid']);
 
         if (!$saved) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error saving event object to CalDAV server"
                 ],
                 true, false
             );
         }
         else {
             // save links in configuration.relation object
             // if ($this->save_links($event['uid'], $links)) {
             //     $object['links'] = $links;
             // }
 
             $updated = true;
             $this->events = [$event['uid'] => $this->_to_driver_event($object, true)];
 
             // refresh local cache with recurring instances
             if ($exception_id) {
                 $this->get_recurring_events($object, $event['start'], $event['end'], $exception_id);
             }
         }
 
         return $updated;
     }
 
     /**
      * Delete an event record
      *
      * @see calendar_driver::remove_event()
      *
      * @return bool True on success, False on error
      */
     public function delete_event($event, $force = true)
     {
         $uid = !empty($event['uid']) ? $event['uid'] : $event['id'];
         $deleted = $this->storage->delete($uid, $force);
 
         if (!$deleted) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error deleting event '{$uid}' from CalDAV server"
                 ],
                 true, false
             );
         }
 
         return $deleted;
     }
 
     /**
      * Restore deleted event record
      *
      * @see calendar_driver::undelete_event()
      *
      * @return bool True on success, False on error
      */
     public function restore_event($event)
     {
         // TODO
         return false;
     }
 
     /**
      * Find messages linked with an event
      */
     protected function get_links($uid)
     {
         return []; // TODO
         $storage = kolab_storage_config::get_instance();
         return $storage->get_object_links($uid);
     }
 
     /**
      * Save message references (links) to an event
      */
     protected function save_links($uid, $links)
     {
         return false; // TODO
         $storage = kolab_storage_config::get_instance();
         return $storage->save_object_links($uid, (array) $links);
     }
 
     /**
      * Create instances of a recurring event
      *
      * @param array    $event    Hash array with event properties
      * @param DateTime $start    Start date of the recurrence window
      * @param DateTime $end      End date of the recurrence window
      * @param string   $event_id ID of a specific recurring event instance
      * @param int      $limit    Max. number of instances to return
      *
      * @return array List of recurring event instances
      */
     public function get_recurring_events($event, $start, $end = null, $event_id = null, $limit = null)
     {
-        $object = $event['_formatobj'];
-
-        if (!is_object($object)) {
-            return [];
-        }
-
         // determine a reasonable end date if none given
         if (!$end) {
             $end = clone $event['start'];
             $end->add(new DateInterval('P100Y'));
         }
 
         // read recurrence exceptions first
         $events = [];
         $exdata = [];
         $futuredata = [];
         $recurrence_id_format = libcalendaring::recurrence_id_format($event);
 
         if (!empty($event['recurrence'])) {
             // copy the recurrence rule from the master event (to be used in the UI)
             $recurrence_rule = $event['recurrence'];
             unset($recurrence_rule['EXCEPTIONS'], $recurrence_rule['EXDATE']);
 
             if (!empty($event['recurrence']['EXCEPTIONS'])) {
                 foreach ($event['recurrence']['EXCEPTIONS'] as $exception) {
                     if (empty($exception['_instance'])) {
                         $exception['_instance'] = libcalendaring::recurrence_instance_identifier($exception, !empty($event['allday']));
                     }
 
                     $rec_event = $this->_to_driver_event($exception, false, false, $event);
                     $rec_event['id'] = $event['uid'] . '-' . $exception['_instance'];
                     $rec_event['isexception'] = 1;
 
                     // found the specifically requested instance: register exception (single occurrence wins)
                     if (
                         $rec_event['id'] == $event_id
                         && (empty($this->events[$event_id]) || !empty($this->events[$event_id]['thisandfuture']))
                     ) {
                         $rec_event['recurrence'] = $recurrence_rule;
                         $rec_event['recurrence_id'] = $event['uid'];
                         $this->events[$rec_event['id']] = $rec_event;
                     }
 
                     // remember this exception's date
                     $exdate = substr($exception['_instance'], 0, 8);
                     if (empty($exdata[$exdate]) || !empty($exdata[$exdate]['thisandfuture'])) {
                         $exdata[$exdate] = $rec_event;
                     }
                     if (!empty($rec_event['thisandfuture'])) {
                         $futuredata[$exdate] = $rec_event;
                     }
                 }
             }
         }
 
         // found the specifically requested instance, exiting...
         if ($event_id && !empty($this->events[$event_id])) {
             return [$this->events[$event_id]];
         }
 
         // Check first occurrence, it might have been moved
-        if ($first = $exdata[$event['start']->format('Ymd')]) {
+        if (!empty($exdata[$event['start']->format('Ymd')])) {
+            $first = $exdata[$event['start']->format('Ymd')];
             // return it only if not already in the result, but in the requested period
             if (!($event['start'] <= $end && $event['end'] >= $start)
                 && ($first['start'] <= $end && $first['end'] >= $start)
             ) {
                 $events[] = $first;
             }
         }
 
         if ($limit && count($events) >= $limit) {
             return $events;
         }
 
         // use libkolab to compute recurring events
-        $recurrence = new kolab_date_recurrence($object);
+        $recurrence = libcalendaring::get_recurrence($event);
 
         $i = 0;
         while ($next_event = $recurrence->next_instance()) {
             $datestr     = $next_event['start']->format('Ymd');
             $instance_id = $next_event['start']->format($recurrence_id_format);
 
             // use this event data for future recurring instances
-            if (!empty($futuredata[$datestr])) {
-                $overlay_data = $futuredata[$datestr];
-            }
+            $overlay_data = $futuredata[$datestr] ?? null;
 
             $rec_id      = $event['uid'] . '-' . $instance_id;
             $exception   = !empty($exdata[$datestr]) ? $exdata[$datestr] : $overlay_data;
             $event_start = $next_event['start'];
             $event_end   = $next_event['end'];
 
             // copy some event from exception to get proper start/end dates
             if ($exception) {
                 $event_copy = $next_event;
                 caldav_driver::merge_exception_dates($event_copy, $exception);
                 $event_start = $event_copy['start'];
                 $event_end   = $event_copy['end'];
             }
 
             // add to output if in range
             if (($event_start <= $end && $event_end >= $start) || ($event_id && $rec_id == $event_id)) {
                 $rec_event = $this->_to_driver_event($next_event, false, false, $event);
                 $rec_event['_instance'] = $instance_id;
                 $rec_event['_count'] = $i + 1;
 
                 if ($exception) {
                     // copy data from exception
                     caldav_driver::merge_exception_data($rec_event, $exception);
                 }
 
                 $rec_event['id'] = $rec_id;
                 $rec_event['recurrence_id'] = $event['uid'];
                 $rec_event['recurrence'] = $recurrence_rule;
                 unset($rec_event['_attendees']);
                 $events[] = $rec_event;
 
                 if ($rec_id == $event_id) {
                     $this->events[$rec_id] = $rec_event;
                     break;
                 }
 
                 if ($limit && count($events) >= $limit) {
                     return $events;
                 }
             }
             else if ($next_event['start'] > $end) {
                 // stop loop if out of range
                 break;
             }
 
             // avoid endless recursion loops
             if (++$i > 100000) {
                 break;
             }
         }
 
         return $events;
     }
 
     /**
      * Convert from storage format to internal representation
      */
     private function _to_driver_event($record, $noinst = false, $links = true, $master_event = null)
     {
         $record['calendar'] = $this->id;
 
         // remove (possibly outdated) cached parameters
         unset($record['_folder_id'], $record['className']);
 
         // if ($links && !array_key_exists('links', $record)) {
         //    $record['links'] = $this->get_links($record['uid']);
         // }
 
         $ns = $this->get_namespace();
 
         if ($ns == 'other') {
             $record['className'] = 'fc-event-ns-other';
         }
 
         if ($ns == 'other' || !$this->cal->rc->config->get('kolab_invitation_calendars')) {
             $record = caldav_driver::add_partstat_class($record, ['NEEDS-ACTION', 'DECLINED'], $this->get_owner());
 
             // Modify invitation status class name, when invitation calendars are disabled
             // we'll use opacity only for declined/needs-action events
             $record['className'] = !empty($record['className']) ? str_replace('-invitation', '', $record['className']) : '';
         }
 
         // add instance identifier to first occurrence (master event)
         $recurrence_id_format = libcalendaring::recurrence_id_format($master_event ? $master_event : $record);
         if (!$noinst && !empty($record['recurrence']) && !empty($record['start'])
             && empty($record['recurrence_id']) && empty($record['_instance'])
         ) {
             $record['_instance'] = $record['start']->format($recurrence_id_format);
         }
         else if (isset($record['recurrence_date']) && $record['recurrence_date'] instanceof DateTimeInterface) {
             $record['_instance'] = $record['recurrence_date']->format($recurrence_id_format);
         }
 
         // clean up exception data
         if (!empty($record['recurrence']) && !empty($record['recurrence']['EXCEPTIONS'])) {
             array_walk($record['recurrence']['EXCEPTIONS'], function(&$exception) {
-                unset($exception['_mailbox'], $exception['_msguid'], $exception['_formatobj'], $exception['_attachments']);
+                unset($exception['_attachments']);
             });
         }
 
-        // Load the given event data into a libkolabxml container
-        // it's needed for recurrence resolving, which uses libcalendaring
-        // TODO: Drop dependency on libkolabxml?
-        $event_xml = new kolab_format_event();
-        $event_xml->set($record);
-        $record['_formatobj'] = $event_xml;
-
         return $record;
     }
 
     /**
      * Convert the given event record into a data structure that can be passed to the storage backend for saving
      * (opposite of self::_to_driver_event())
      */
     private function _from_driver_event($event, $old = [])
     {
         // set current user as ORGANIZER
         if ($identity = $this->cal->rc->user->list_emails(true)) {
             $event['attendees'] = !empty($event['attendees']) ? $event['attendees'] : [];
             $found = false;
 
             // there can be only resources on attendees list (T1484)
             // let's check the existence of an organizer
             foreach ($event['attendees'] as $attendee) {
                 if (!empty($attendee['role']) && $attendee['role'] == 'ORGANIZER') {
                     $found = true;
                     break;
                 }
             }
 
             if (!$found) {
                 $event['attendees'][] = ['role' => 'ORGANIZER', 'name' => $identity['name'], 'email' => $identity['email']];
             }
 
             $event['_owner'] = $identity['email'];
         }
 
         // remove EXDATE values if RDATE is given
         if (!empty($event['recurrence']['RDATE'])) {
             $event['recurrence']['EXDATE'] = [];
         }
 
         // remove recurrence information (e.g. EXDATES and EXCEPTIONS) entirely
         if (!empty($event['recurrence']) && empty($event['recurrence']['FREQ']) && empty($event['recurrence']['RDATE'])) {
             $event['recurrence'] = [];
         }
 
         // keep 'comment' from initial itip invitation
         if (!empty($old['comment'])) {
             $event['comment'] = $old['comment'];
         }
 
         // remove some internal properties which should not be cached
         $cleanup_fn = function(&$event) {
             unset($event['_savemode'], $event['_fromcalendar'], $event['_identity'], $event['_folder_id'],
                 $event['calendar'], $event['className'], $event['recurrence_id'],
                 $event['attachments'], $event['deleted_attachments']);
         };
 
         $cleanup_fn($event);
 
         // clean up exception data
         if (!empty($event['exceptions'])) {
-            array_walk($event['exceptions'], function(&$exception) use ($cleanup_fn) {
-                unset($exception['_mailbox'], $exception['_msguid'], $exception['_formatobj']);
-                $cleanup_fn($exception);
-            });
+            array_walk($event['exceptions'], $cleanup_fn);
         }
 
         // copy meta data (starting with _) from old object
         foreach ((array) $old as $key => $val) {
             if (!isset($event[$key]) && $key[0] == '_') {
                 $event[$key] = $val;
             }
         }
 
         return $event;
     }
 
     /**
      * Match the given word in the event contents
      */
     public function fulltext_match($event, $word, $recursive = true)
     {
         $hits = 0;
         foreach ($this->search_fields as $col) {
             if (empty($event[$col])) {
                 continue;
             }
 
             $sval = is_array($event[$col]) ? self::_complex2string($event[$col]) : $event[$col];
             if (empty($sval)) {
                 continue;
             }
 
             // do a simple substring matching (to be improved)
             $val = mb_strtolower($sval);
             if (strpos($val, $word) !== false) {
                 $hits++;
                 break;
             }
         }
 
         return $hits;
     }
 
     /**
      * Convert a complex event attribute to a string value
      */
     private static function _complex2string($prop)
     {
         static $ignorekeys = ['role', 'status', 'rsvp'];
 
         $out = '';
         if (is_array($prop)) {
             foreach ($prop as $key => $val) {
                 if (is_numeric($key)) {
                     $out .= self::_complex2string($val);
                 }
                 else if (!in_array($key, $ignorekeys)) {
                     $out .= $val . ' ';
                 }
             }
         }
         else if (is_string($prop) || is_numeric($prop)) {
             $out .= $prop . ' ';
         }
 
         return rtrim($out);
     }
 }
diff --git a/plugins/calendar/drivers/caldav/caldav_driver.php b/plugins/calendar/drivers/caldav/caldav_driver.php
index 3ca6bfdd..f5f91c31 100644
--- a/plugins/calendar/drivers/caldav/caldav_driver.php
+++ b/plugins/calendar/drivers/caldav/caldav_driver.php
@@ -1,608 +1,692 @@
 <?php
 
 /**
  * CalDAV driver for the Calendar plugin.
  *
  * @author Aleksander Machniak <machniak@apheleia-it.ch>
  *
  * Copyright (C) 2012-2022, Apheleia IT AG <contact@apheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 require_once(__DIR__ . '/../kolab/kolab_driver.php');
 
 class caldav_driver extends kolab_driver
 {
     // features this backend supports
     public $alarms              = true;
     public $attendees           = true;
     public $freebusy            = true;
     public $attachments         = false; // TODO
     public $undelete            = false; // TODO
     public $alarm_types         = ['DISPLAY', 'AUDIO'];
     public $categoriesimmutable = true;
 
+    protected $scheduling_properties = ['start', 'end', 'location'];
+
     /**
      * Default constructor
      */
     public function __construct($cal)
     {
         $cal->require_plugin('libkolab');
 
         // load helper classes *after* libkolab has been loaded (#3248)
         require_once(__DIR__ . '/caldav_calendar.php');
         // require_once(__DIR__ . '/kolab_user_calendar.php');
         // require_once(__DIR__ . '/caldav_invitation_calendar.php');
 
         $this->cal = $cal;
         $this->rc  = $cal->rc;
 
         // Initialize the CalDAV storage
         $url = $this->rc->config->get('calendar_caldav_server', 'http://localhost');
         $this->storage = new kolab_storage_dav($url);
 
         $this->cal->register_action('push-freebusy', [$this, 'push_freebusy']);
         $this->cal->register_action('calendar-acl', [$this, 'calendar_acl']);
 
         // $this->freebusy_trigger = $this->rc->config->get('calendar_freebusy_trigger', false);
 
         if (!$this->rc->config->get('kolab_freebusy_server', false)) {
             $this->freebusy = false;
         }
 
         // TODO: get configuration for the Bonnie API
         // $this->bonnie_api = libkolab::get_bonnie_api();
     }
 
     /**
      * Read available calendars from server
      */
     protected function _read_calendars()
     {
         // already read sources
         if (isset($this->calendars)) {
             return $this->calendars;
         }
 
         // get all folders that support VEVENT, sorted by namespace/name
         $folders = $this->storage->get_folders('event');
             // + $this->storage->get_user_folders('event', true);
 
         $this->calendars = [];
 
         foreach ($folders as $folder) {
             $calendar = $this->_to_calendar($folder);
             if ($calendar->ready) {
                 $this->calendars[$calendar->id] = $calendar;
                 if ($calendar->editable) {
                     $this->has_writeable = true;
                 }
             }
         }
 
         return $this->calendars;
     }
 
     /**
      * Convert kolab_storage_folder into caldav_calendar
      */
     protected function _to_calendar($folder)
     {
         if ($folder instanceof caldav_calendar) {
             return $folder;
         }
 
         if ($folder instanceof kolab_storage_folder_user) {
             $calendar = new kolab_user_calendar($folder, $this->cal);
             $calendar->subscriptions = count($folder->children) > 0;
         }
         else {
             $calendar = new caldav_calendar($folder, $this->cal);
         }
 
         return $calendar;
     }
 
     /**
      * Get a list of available calendars from this source.
      *
      * @param int    $filter Bitmask defining filter criterias
      * @param object $tree   Reference to hierarchical folder tree object
      *
      * @return array List of calendars
      */
     public function list_calendars($filter = 0, &$tree = null)
     {
         $this->_read_calendars();
 
         $folders   = $this->filter_calendars($filter);
         $calendars = [];
         $prefs     = $this->rc->config->get('kolab_calendars', []);
 
         // include virtual folders for a full folder tree
 /*
         if (!is_null($tree)) {
             $folders = $this->storage->folder_hierarchy($folders, $tree);
         }
 */
         $parents = array_keys($this->calendars);
 
         foreach ($folders as $id => $cal) {
             $parent_id = null;
 /*
             $path = explode('/', $cal->name);
 
             // find parent
             do {
                 array_pop($path);
                 $parent_id = $this->storage->folder_id(implode('/', $path));
             }
             while (count($path) > 1 && !in_array($parent_id, $parents));
 
             // restore "real" parent ID
             if ($parent_id && !in_array($parent_id, $parents)) {
                 $parent_id = $this->storage->folder_id($cal->get_parent());
             }
 
             $parents[] = $cal->id;
 
             if ($cal->virtual) {
                 $calendars[$cal->id] = [
                     'id'       => $cal->id,
                     'name'     => $cal->get_name(),
                     'listname' => $cal->get_foldername(),
                     'editname' => $cal->get_foldername(),
                     'virtual'  => true,
                     'editable' => false,
                     'group'    => $cal->get_namespace(),
                 ];
             }
             else {
 */
                 // additional folders may come from kolab_storage_dav::folder_hierarchy() above
                 // make sure we deal with caldav_calendar instances
                 $cal = $this->_to_calendar($cal);
                 $this->calendars[$cal->id] = $cal;
 
                 $is_user = ($cal instanceof caldav_user_calendar);
 
                 $calendars[$cal->id] = [
                     'id'        => $cal->id,
                     'name'      => $cal->get_name(),
                     'listname'  => $cal->get_foldername(),
                     'editname'  => $cal->get_foldername(),
                     'title'     => '', // $cal->get_title(),
                     'color'     => $cal->get_color(),
                     'editable'  => $cal->editable,
                     'group'     => $is_user ? 'other user' : $cal->get_namespace(),
                     'active'    => !isset($prefs[$cal->id]['active']) || !empty($prefs[$cal->id]['active']),
                     'owner'     => $cal->get_owner(),
                     'removable' => !$cal->default,
                     // extras to hide some elements in the UI
                     'subscriptions' => $cal->subscriptions,
                     'driver' => 'caldav',
                 ];
 
                 if (!$is_user) {
                     $calendars[$cal->id] += [
                         'default'    => $cal->default,
                         'rights'     => $cal->rights,
                         'showalarms' => $cal->alarms,
                         'history'    => !empty($this->bonnie_api),
                         'children'   => true,  // TODO: determine if that folder indeed has child folders
                         'parent'     => $parent_id,
                         'subtype'    => $cal->subtype,
                         'caldavurl'  => '', // $cal->get_caldav_url(),
                     ];
                 }
 /*
             }
 */
             if ($cal->subscriptions) {
                 $calendars[$cal->id]['subscribed'] = $cal->is_subscribed();
             }
         }
 /*
         // list virtual calendars showing invitations
         if ($this->rc->config->get('kolab_invitation_calendars') && !($filter & self::FILTER_INSERTABLE)) {
             foreach ([self::INVITATIONS_CALENDAR_PENDING, self::INVITATIONS_CALENDAR_DECLINED] as $id) {
                 $cal = new caldav_invitation_calendar($id, $this->cal);
                 if (!($filter & self::FILTER_ACTIVE) || $cal->is_active()) {
                     $calendars[$id] = [
                         'id'         => $cal->id,
                         'name'       => $cal->get_name(),
                         'listname'   => $cal->get_name(),
                         'editname'   => $cal->get_foldername(),
                         'title'      => $cal->get_title(),
                         'color'      => $cal->get_color(),
                         'editable'   => $cal->editable,
                         'rights'     => $cal->rights,
                         'showalarms' => $cal->alarms,
                         'history'    => !empty($this->bonnie_api),
                         'group'      => 'x-invitations',
                         'default'    => false,
                         'active'     => $cal->is_active(),
                         'owner'      => $cal->get_owner(),
                         'children'   => false,
                         'counts'     => $id == self::INVITATIONS_CALENDAR_PENDING,
                     ];
 
 
                     if (is_object($tree)) {
                         $tree->children[] = $cal;
                     }
                 }
             }
         }
 */
         // append the virtual birthdays calendar
         if ($this->rc->config->get('calendar_contact_birthdays', false) && !($filter & self::FILTER_INSERTABLE)) {
             $id    = self::BIRTHDAY_CALENDAR_ID;
             $prefs = $this->rc->config->get('kolab_calendars', []);  // read local prefs
 
             if (!($filter & self::FILTER_ACTIVE) || !empty($prefs[$id]['active'])) {
                 $calendars[$id] = [
                     'id'         => $id,
                     'name'       => $this->cal->gettext('birthdays'),
                     'listname'   => $this->cal->gettext('birthdays'),
                     'color'      => !empty($prefs[$id]['color']) ? $prefs[$id]['color'] : '87CEFA',
                     'active'     => !empty($prefs[$id]['active']),
                     'showalarms' => (bool) $this->rc->config->get('calendar_birthdays_alarm_type'),
                     'group'      => 'x-birthdays',
                     'editable'   => false,
                     'default'    => false,
                     'children'   => false,
                     'history'    => false,
                 ];
             }
         }
 
         return $calendars;
     }
 
     /**
      * Get the caldav_calendar instance for the given calendar ID
      *
      * @param string Calendar identifier
      *
      * @return ?caldav_calendar Object nor null if calendar doesn't exist
      */
     public function get_calendar($id)
     {
         $this->_read_calendars();
 
         // create calendar object if necessary
         if (empty($this->calendars[$id])) {
             if (in_array($id, [self::INVITATIONS_CALENDAR_PENDING, self::INVITATIONS_CALENDAR_DECLINED])) {
                 return new caldav_invitation_calendar($id, $this->cal);
             }
 
             // for unsubscribed calendar folders
             if ($id !== self::BIRTHDAY_CALENDAR_ID) {
                 $calendar = caldav_calendar::factory($id, $this->cal);
                 if ($calendar->ready) {
                     $this->calendars[$calendar->id] = $calendar;
                 }
             }
         }
 
         return !empty($this->calendars[$id]) ? $this->calendars[$id] : null;
     }
 
     /**
      * Create a new calendar assigned to the current user
      *
      * @param array Hash array with calendar properties
      *    name: Calendar name
      *   color: The color of the calendar
      *
      * @return mixed ID of the calendar on success, False on error
      */
     public function create_calendar($prop)
     {
         $prop['type']   = 'event';
         $prop['alarms'] = !empty($prop['showalarms']);
 
         $id = $this->storage->folder_update($prop);
 
         if ($id === false) {
             return false;
         }
 
         $prefs['kolab_calendars'] = $this->rc->config->get('kolab_calendars', []);
         $prefs['kolab_calendars'][$id]['active'] = true;
 
         $this->rc->user->save_prefs($prefs);
 
         return $id;
     }
 
     /**
      * Update properties of an existing calendar
      *
      * @see calendar_driver::edit_calendar()
      */
     public function edit_calendar($prop)
     {
         $id = $prop['id'];
 
         if (!in_array($id, [self::BIRTHDAY_CALENDAR_ID, self::INVITATIONS_CALENDAR_PENDING, self::INVITATIONS_CALENDAR_DECLINED])) {
             $prop['type']   = 'event';
             $prop['alarms'] = !empty($prop['showalarms']);
 
             return $this->storage->folder_update($prop) !== false;
         }
 
         // fallback to local prefs for special calendars
         $prefs['kolab_calendars'] = $this->rc->config->get('kolab_calendars', []);
         unset($prefs['kolab_calendars'][$id]['showalarms']);
 
         if (isset($prop['showalarms']) && $id == self::BIRTHDAY_CALENDAR_ID) {
             $prefs['calendar_birthdays_alarm_type'] = $prop['showalarms'] ? $this->alarm_types[0] : '';
         }
         else if (isset($prop['showalarms'])) {
             $prefs['kolab_calendars'][$id]['showalarms'] = !empty($prop['showalarms']);
         }
 
         if (!empty($prefs['kolab_calendars'][$id])) {
             $this->rc->user->save_prefs($prefs);
         }
 
         return true;
     }
 
     /**
      * Set active/subscribed state of a calendar
      *
      * @see calendar_driver::subscribe_calendar()
      */
     public function subscribe_calendar($prop)
     {
         if (empty($prop['id'])) {
             return false;
         }
 
         // save state in local prefs
         if (isset($prop['active'])) {
             $prefs['kolab_calendars'] = $this->rc->config->get('kolab_calendars', []);
             $prefs['kolab_calendars'][$prop['id']]['active'] = !empty($prop['active']);
 
             $this->rc->user->save_prefs($prefs);
         }
 
         return true;
     }
 
     /**
      * Delete the given calendar with all its contents
      *
      * @see calendar_driver::delete_calendar()
      */
     public function delete_calendar($prop)
     {
         if (!empty($prop['id'])) {
             if ($this->storage->folder_delete($prop['id'], 'event')) {
                 // remove folder from user prefs
                 $prefs['kolab_calendars'] = $this->rc->config->get('kolab_calendars', []);
                 if (isset($prefs['kolab_calendars'][$prop['id']])) {
                     unset($prefs['kolab_calendars'][$prop['id']]);
                     $this->rc->user->save_prefs($prefs);
                 }
 
                 return true;
             }
         }
 
         return false;
     }
 
     /**
      * Search for shared or otherwise not listed calendars the user has access
      *
      * @param string Search string
      * @param string Section/source to search
      *
      * @return array List of calendars
      */
     public function search_calendars($query, $source)
     {
         $this->calendars = [];
         $this->search_more_results = false;
 /*
         // find unsubscribed IMAP folders that have "event" type
         if ($source == 'folders') {
             foreach ((array) $this->storage->search_folders('event', $query, ['other']) as $folder) {
                 $calendar = new kolab_calendar($folder->name, $this->cal);
                 $this->calendars[$calendar->id] = $calendar;
             }
         }
         // find other user's virtual calendars
         else if ($source == 'users') {
             // we have slightly more space, so display twice the number
             $limit = $this->rc->config->get('autocomplete_max', 15) * 2;
 
             foreach ($this->storage->search_users($query, 0, [], $limit, $count) as $user) {
                 $calendar = new caldav_user_calendar($user, $this->cal);
                 $this->calendars[$calendar->id] = $calendar;
 
                 // search for calendar folders shared by this user
                 foreach ($this->storage->list_user_folders($user, 'event', false) as $foldername) {
                     $cal = new caldav_calendar($foldername, $this->cal);
                     $this->calendars[$cal->id] = $cal;
                     $calendar->subscriptions = true;
                 }
             }
 
             if ($count > $limit) {
                 $this->search_more_results = true;
             }
         }
 
         // don't list the birthday calendar
         $this->rc->config->set('calendar_contact_birthdays', false);
         $this->rc->config->set('kolab_invitation_calendars', false);
 */
         return $this->list_calendars();
     }
 
     /**
      * Get events from source.
      *
      * @param int    Event's new start (unix timestamp)
      * @param int    Event's new end (unix timestamp)
      * @param string Search query (optional)
      * @param mixed  List of calendar IDs to load events from (either as array or comma-separated string)
      * @param bool   Include virtual events (optional)
      * @param int    Only list events modified since this time (unix timestamp)
      *
      * @return array A list of event records
      */
     public function load_events($start, $end, $search = null, $calendars = null, $virtual = 1, $modifiedsince = null)
     {
         if ($calendars && is_string($calendars)) {
             $calendars = explode(',', $calendars);
         }
         else if (!$calendars) {
             $this->_read_calendars();
             $calendars = array_keys($this->calendars);
         }
 
         $query      = [];
         $events     = [];
         $categories = [];
 
         if ($modifiedsince) {
             $query[] = ['changed', '>=', $modifiedsince];
         }
 
         foreach ($calendars as $cid) {
             if ($storage = $this->get_calendar($cid)) {
                 $events = array_merge($events, $storage->list_events($start, $end, $search, $virtual, $query));
                 $categories += $storage->categories;
             }
         }
 
         // add events from the address books birthday calendar
         if (in_array(self::BIRTHDAY_CALENDAR_ID, $calendars)) {
             $events = array_merge($events, $this->load_birthday_events($start, $end, $search, $modifiedsince));
         }
 
         // add new categories to user prefs
         $old_categories = $this->rc->config->get('calendar_categories', $this->default_categories);
         $newcats = array_udiff(
             array_keys($categories),
             array_keys($old_categories),
             function($a, $b) { return strcasecmp($a, $b); }
         );
 
         if (!empty($newcats)) {
             foreach ($newcats as $category) {
                 $old_categories[$category] = '';  // no color set yet
             }
             $this->rc->user->save_prefs(['calendar_categories' => $old_categories]);
         }
 
         array_walk($events, 'caldav_driver::to_rcube_event');
 
         return $events;
     }
 
     /**
      * Create instances of a recurring event
      *
      * @param array    Hash array with event properties
      * @param DateTime Start date of the recurrence window
      * @param DateTime End date of the recurrence window
      *
      * @return array List of recurring event instances
      */
     public function get_recurring_events($event, $start, $end = null)
     {
-        // load the given event data into a libkolabxml container
-        $event_xml = new kolab_format_event();
-        $event_xml->set($event);
-        $event['_formatobj'] = $event_xml;
-
         $this->_read_calendars();
         $storage = reset($this->calendars);
 
         return $storage->get_recurring_events($event, $start, $end);
     }
 
     /**
      *
      */
     protected function get_recurrence_count($event, $dtstart)
     {
-        // load the given event data into a libkolabxml container
-        $event_xml = new kolab_format_event();
-        $event_xml->set($event);
-        $event['_formatobj'] = $event_xml;
-
         // use libkolab to compute recurring events
-        $recurrence = new kolab_date_recurrence($event['_formatobj']);
+        $recurrence = libcalendaring::get_recurrence($event);
 
         $count = 0;
         while (($next_event = $recurrence->next_instance()) && $next_event['start'] <= $dtstart && $count < 1000) {
             $count++;
         }
 
         return $count;
     }
 
+    /**
+     * Determine whether the current change affects scheduling and reset attendee status accordingly
+     */
+    protected function check_scheduling(&$event, $old, $update = true)
+    {
+        // skip this check when importing iCal/iTip events
+        if (isset($event['sequence']) || !empty($event['_method'])) {
+            return false;
+        }
+
+        // iterate through the list of properties considered 'significant' for scheduling
+        $reschedule = $this->is_rescheduling_needed($event, $old);
+
+        // reset all attendee status to needs-action (#4360)
+        if ($update && $reschedule && !empty($event['attendees'])) {
+            $is_organizer = false;
+            $emails       = $this->cal->get_user_emails();
+            $attendees    = $event['attendees'];
+
+            foreach ($attendees as $i => $attendee) {
+                if ($attendee['role'] == 'ORGANIZER'
+                    && !empty($attendee['email'])
+                    && in_array(strtolower($attendee['email']), $emails)
+                ) {
+                    $is_organizer = true;
+                }
+                else if ($attendee['role'] != 'ORGANIZER'
+                    && $attendee['role'] != 'NON-PARTICIPANT'
+                    && $attendee['status'] != 'DELEGATED'
+                ) {
+                    $attendees[$i]['status'] = 'NEEDS-ACTION';
+                    $attendees[$i]['rsvp'] = true;
+                }
+            }
+
+            // update attendees only if I'm the organizer
+            if ($is_organizer || (!empty($event['organizer']) && in_array(strtolower($event['organizer']['email']), $emails))) {
+                $event['attendees'] = $attendees;
+            }
+        }
+
+        return $reschedule;
+    }
+
+    /**
+     * Identify changes considered relevant for scheduling
+     * 
+     * @param array Hash array with NEW object properties
+     * @param array Hash array with OLD object properties
+     *
+     * @return bool True if changes affect scheduling, False otherwise
+     */
+    protected function is_rescheduling_needed($object, $old = null)
+    {
+        $reschedule = false;
+
+        foreach ($this->scheduling_properties as $prop) {
+            $a = $old[$prop] ?? null;
+            $b = $object[$prop] ?? null;
+
+            if (!empty($object['allday'])
+                && ($prop == 'start' || $prop == 'end')
+                && $a instanceof DateTimeInterface
+                && $b instanceof DateTimeInterface
+            ) {
+                $a = $a->format('Y-m-d');
+                $b = $b->format('Y-m-d');
+            }
+
+            if ($prop == 'recurrence' && is_array($a) && is_array($b)) {
+                unset($a['EXCEPTIONS'], $b['EXCEPTIONS']);
+                $a = array_filter($a);
+                $b = array_filter($b);
+
+                // advanced rrule comparison: no rescheduling if series was shortened
+                if ($a['COUNT'] && $b['COUNT'] && $b['COUNT'] < $a['COUNT']) {
+                    unset($a['COUNT'], $b['COUNT']);
+                }
+                else if ($a['UNTIL'] && $b['UNTIL'] && $b['UNTIL'] < $a['UNTIL']) {
+                    unset($a['UNTIL'], $b['UNTIL']);
+                }
+            }
+
+            if ($a != $b) {
+                $reschedule = true;
+                break;
+            }
+        }
+
+        return $reschedule;
+    }
+
     /**
      * Callback function to produce driver-specific calendar create/edit form
      *
      * @param string Request action 'form-edit|form-new'
      * @param array  Calendar properties (e.g. id, color)
      * @param array  Edit form fields
      *
      * @return string HTML content of the form
      */
     public function calendar_form($action, $calendar, $formfields)
     {
         $special_calendars = [
             self::BIRTHDAY_CALENDAR_ID,
             self::INVITATIONS_CALENDAR_PENDING,
             self::INVITATIONS_CALENDAR_DECLINED
         ];
 
         // show default dialog for birthday calendar
         if (in_array($calendar['id'], $special_calendars)) {
             if ($calendar['id'] != self::BIRTHDAY_CALENDAR_ID) {
                 unset($formfields['showalarms']);
             }
 
             // General tab
             $form['props'] = [
                 'name'   => $this->rc->gettext('properties'),
                 'fields' => $formfields,
             ];
 
             return kolab_utils::folder_form($form, '', 'calendar');
         }
 
         $form['props'] = [
             'name'   => $this->rc->gettext('properties'),
             'fields' => [
                 'location' => $formfields['name'],
                 'color'    => $formfields['color'],
                 'alarms'   => $formfields['showalarms'],
             ],
         ];
 
         return kolab_utils::folder_form($form, $folder, 'calendar', [], true);
     }
 }
diff --git a/plugins/calendar/drivers/kolab/kolab_calendar.php b/plugins/calendar/drivers/kolab/kolab_calendar.php
index e0129c0a..408e4d7f 100644
--- a/plugins/calendar/drivers/kolab/kolab_calendar.php
+++ b/plugins/calendar/drivers/kolab/kolab_calendar.php
@@ -1,958 +1,957 @@
 <?php
 
 /**
  * Kolab calendar storage class
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  * @author Aleksander Machniak <machniak@kolabsys.com>
  *
  * Copyright (C) 2012-2015, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 
 class kolab_calendar extends kolab_storage_folder_api
 {
     public $ready         = false;
     public $rights        = 'lrs';
     public $editable      = false;
     public $attachments   = true;
     public $alarms        = false;
     public $history       = false;
     public $subscriptions = true;
     public $categories    = [];
     public $storage;
 
     public $type = 'event';
 
     protected $cal;
     protected $events = [];
     protected $search_fields = ['title', 'description', 'location', 'attendees', 'categories'];
 
     /**
      * Factory method to instantiate a kolab_calendar object
      *
      * @param string  Calendar ID (encoded IMAP folder name)
      * @param object  Calendar plugin object
      *
      * @return kolab_calendar Self instance
      */
     public static function factory($id, $calendar)
     {
         $imap = $calendar->rc->get_storage();
         $imap_folder = kolab_storage::id_decode($id);
         $info = $imap->folder_info($imap_folder, true);
 
         if (
             empty($info)
             || !empty($info['noselect'])
             || strpos(kolab_storage::folder_type($imap_folder), 'event') !== 0
         ) {
             return new kolab_user_calendar($imap_folder, $calendar);
         }
 
         return new kolab_calendar($imap_folder, $calendar);
     }
 
     /**
      * Default constructor
      */
     public function __construct($imap_folder, $calendar)
     {
         $this->cal  = $calendar;
         $this->imap = $calendar->rc->get_storage();
         $this->name = $imap_folder;
 
         // ID is derrived from folder name
         $this->id = kolab_storage::folder_id($this->name, true);
         $old_id   = kolab_storage::folder_id($this->name, false);
 
         // fetch objects from the given IMAP folder
         $this->storage = kolab_storage::get_folder($this->name);
         $this->ready   = $this->storage && $this->storage->valid;
 
         // Set writeable and alarms flags according to folder permissions
         if ($this->ready) {
             if ($this->storage->get_namespace() == 'personal') {
                 $this->editable = true;
                 $this->rights = 'lrswikxteav';
                 $this->alarms = true;
             }
             else {
                 $rights = $this->storage->get_myrights();
                 if ($rights && !PEAR::isError($rights)) {
                     $this->rights = $rights;
                     if (strpos($rights, 't') !== false || strpos($rights, 'd') !== false) {
                         $this->editable = strpos($rights, 'i');;
                     }
                 }
             }
 
             // user-specific alarms settings win
             $prefs = $this->cal->rc->config->get('kolab_calendars', []);
             if (isset($prefs[$this->id]['showalarms'])) {
                 $this->alarms = $prefs[$this->id]['showalarms'];
             }
             else if (isset($prefs[$old_id]['showalarms'])) {
                 $this->alarms = $prefs[$old_id]['showalarms'];
             }
         }
 
         $this->default = $this->storage->default;
         $this->subtype = $this->storage->subtype;
     }
 
     /**
      * Getter for the IMAP folder name
      *
      * @return string Name of the IMAP folder
      */
     public function get_realname()
     {
         return $this->name;
     }
 
     /**
      *
      */
     public function get_title()
     {
         return null;
     }
 
     /**
      * Return color to display this calendar
      */
     public function get_color($default = null)
     {
         // color is defined in folder METADATA
         if ($color = $this->storage->get_color()) {
             return $color;
         }
 
         // calendar color is stored in user prefs (temporary solution)
         $prefs = $this->cal->rc->config->get('kolab_calendars', []);
 
         if (!empty($prefs[$this->id]) && !empty($prefs[$this->id]['color'])) {
             return $prefs[$this->id]['color'];
         }
 
         return $default ?: 'cc0000';
     }
 
     /**
      * Compose an URL for CalDAV access to this calendar (if configured)
      */
     public function get_caldav_url()
     {
         if ($template = $this->cal->rc->config->get('calendar_caldav_url', null)) {
             return strtr($template, [
                     '%h' => $_SERVER['HTTP_HOST'],
                     '%u' => urlencode($this->cal->rc->get_user_name()),
                     '%i' => urlencode($this->storage->get_uid()),
                     '%n' => urlencode($this->name),
             ]);
         }
 
         return false;
     }
 
     /**
      * Update properties of this calendar folder
      *
      * @see calendar_driver::edit_calendar()
      */
     public function update(&$prop)
     {
         $prop['oldname'] = $this->get_realname();
         $newfolder = kolab_storage::folder_update($prop);
 
         if ($newfolder === false) {
             $this->cal->last_error = $this->cal->gettext(kolab_storage::$last_error);
             return false;
         }
 
         // create ID
         return kolab_storage::folder_id($newfolder);
     }
 
     /**
      * Getter for a single event object
      */
     public function get_event($id)
     {
         // remove our occurrence identifier if it's there
         $master_id = preg_replace('/-\d{8}(T\d{6})?$/', '', $id);
 
         // directly access storage object
         if (empty($this->events[$id]) && $master_id == $id && ($record = $this->storage->get_object($id))) {
             $this->events[$id] = $this->_to_driver_event($record, true);
         }
 
         // maybe a recurring instance is requested
         if (empty($this->events[$id]) && $master_id != $id) {
             $instance_id = substr($id, strlen($master_id) + 1);
 
             if ($record = $this->storage->get_object($master_id)) {
                 $master = $this->_to_driver_event($record);
             }
 
             if ($master) {
                 // check for match in top-level exceptions (aka loose single occurrences)
                 if (!empty($master['_formatobj']) && ($instance = $master['_formatobj']->get_instance($instance_id))) {
                     $this->events[$id] = $this->_to_driver_event($instance, false, true, $master);
                 }
                 // check for match on the first instance already
                 else if (!empty($master['_instance']) && $master['_instance'] == $instance_id) {
                     $this->events[$id] = $master;
                 }
                 else if (!empty($master['recurrence'])) {
                     $start_date = $master['start'];
                     // For performance reasons we'll get only the specific instance
                     if (($date = substr($id, strlen($master_id) + 1, 8)) && strlen($date) == 8 && is_numeric($date)) {
                         $start_date = new DateTime($date . 'T000000', $master['start']->getTimezone());
                     }
 
                     $this->get_recurring_events($record, $start_date, null, $id, 1);
                 }
             }
         }
 
         return $this->events[$id];
     }
 
     /**
      * Get attachment body
      * @see calendar_driver::get_attachment_body()
      */
     public function get_attachment_body($id, $event)
     {
         if (!$this->ready) {
             return false;
         }
 
         $data = $this->storage->get_attachment($event['id'], $id);
 
         if ($data == null) {
             // try again with master UID
             $uid = preg_replace('/-\d+(T\d{6})?$/', '', $event['id']);
             if ($uid != $event['id']) {
                 $data = $this->storage->get_attachment($uid, $id);
             }
         }
 
         return $data;
     }
 
     /**
      * @param  int    Event's new start (unix timestamp)
      * @param  int    Event's new end (unix timestamp)
      * @param  string Search query (optional)
      * @param  bool   Include virtual events (optional)
      * @param  array  Additional parameters to query storage
      * @param  array  Additional query to filter events
      *
      * @return array A list of event records
      */
     public function list_events($start, $end, $search = null, $virtual = 1, $query = [], $filter_query = null)
     {
         // convert to DateTime for comparisons
         // #5190: make the range a little bit wider
         // to workaround possible timezone differences
         try {
             $start = new DateTime('@' . ($start - 12 * 3600));
         }
         catch (Exception $e) {
             $start = new DateTime('@0');
         }
         try {
             $end = new DateTime('@' . ($end + 12 * 3600));
         }
         catch (Exception $e) {
             $end = new DateTime('today +10 years');
         }
 
         // get email addresses of the current user
         $user_emails = $this->cal->get_user_emails();
 
         // query Kolab storage
         $query[] = ['dtstart', '<=', $end];
         $query[] = ['dtend',   '>=', $start];
 
         if (is_array($filter_query)) {
             $query = array_merge($query, $filter_query);
         }
 
         $words = [];
         $partstat_exclude = [];
         $events = [];
 
         if (!empty($search)) {
             $search = mb_strtolower($search);
             $words  = rcube_utils::tokenize_string($search, 1);
             foreach (rcube_utils::normalize_string($search, true) as $word) {
                 $query[] = ['words', 'LIKE', $word];
             }
         }
 
         // set partstat filter to skip pending and declined invitations
         if (empty($filter_query)
             && $this->cal->rc->config->get('kolab_invitation_calendars')
             && $this->get_namespace() != 'other'
         ) {
             $partstat_exclude = ['NEEDS-ACTION', 'DECLINED'];
         }
 
         foreach ($this->storage->select($query) as $record) {
             $event = $this->_to_driver_event($record, !$virtual, false);
 
             // remember seen categories
             if (!empty($event['categories'])) {
                 $cat = is_array($event['categories']) ? $event['categories'][0] : $event['categories'];
                 $this->categories[$cat]++;
             }
 
             // list events in requested time window
             if ($event['start'] <= $end && $event['end'] >= $start) {
                 unset($event['_attendees']);
                 $add = true;
 
                 // skip the first instance of a recurring event if listed in exdate
                 if ($virtual && !empty($event['recurrence']['EXDATE'])) {
                     $event_date = $event['start']->format('Ymd');
                     $event_tz   = $event['start']->getTimezone();
 
                     foreach ((array) $event['recurrence']['EXDATE'] as $exdate) {
                         $ex = clone $exdate;
                         $ex->setTimezone($event_tz);
 
                         if ($ex->format('Ymd') == $event_date) {
                             $add = false;
                             break;
                         }
                     }
                 }
 
                 // find and merge exception for the first instance
                 if ($virtual && !empty($event['recurrence']) && !empty($event['recurrence']['EXCEPTIONS'])) {
                     foreach ($event['recurrence']['EXCEPTIONS'] as $exception) {
                         if ($event['_instance'] == $exception['_instance']) {
                             unset($exception['calendar'], $exception['className'], $exception['_folder_id']);
                             // clone date objects from main event before adjusting them with exception data
                             if (is_object($event['start'])) {
                                 $event['start'] = clone $record['start'];
                             }
                             if (is_object($event['end'])) {
                                 $event['end'] = clone $record['end'];
                             }
                             kolab_driver::merge_exception_data($event, $exception);
                         }
                     }
                 }
 
                 if ($add) {
                     $events[] = $event;
                 }
             }
 
             // resolve recurring events
             if (!empty($record['recurrence']) && $virtual == 1) {
                 $events = array_merge($events, $this->get_recurring_events($record, $start, $end));
             }
             // add top-level exceptions (aka loose single occurrences)
             else if (!empty($record['exceptions'])) {
                 foreach ($record['exceptions'] as $ex) {
                     $component = $this->_to_driver_event($ex, false, false, $record);
                     if ($component['start'] <= $end && $component['end'] >= $start) {
                         $events[] = $component;
                     }
                 }
             }
         }
 
         // post-filter all events by fulltext search and partstat values
         $me = $this;
         $events = array_filter($events, function($event) use ($words, $partstat_exclude, $user_emails, $me) {
             // fulltext search
             if (count($words)) {
                 $hits = 0;
                 foreach ($words as $word) {
                     $hits += $me->fulltext_match($event, $word, false);
                 }
                 if ($hits < count($words)) {
                     return false;
                 }
             }
 
             // partstat filter
             if (count($partstat_exclude) && !empty($event['attendees'])) {
                 foreach ($event['attendees'] as $attendee) {
                     if (
                         in_array($attendee['email'], $user_emails)
                         && in_array($attendee['status'], $partstat_exclude)
                     ) {
                         return false;
                     }
                 }
             }
 
             return true;
         });
 
         // Apply event-to-mail relations
         $config = kolab_storage_config::get_instance();
         $config->apply_links($events);
 
         // avoid session race conditions that will loose temporary subscriptions
         $this->cal->rc->session->nowrite = true;
 
         return $events;
     }
 
     /**
      * Get number of events in the given calendar
      *
      * @param int   Date range start (unix timestamp)
      * @param int   Date range end (unix timestamp)
      * @param array Additional query to filter events
      *
      * @return int Count
      */
     public function count_events($start, $end = null, $filter_query = null)
     {
         // convert to DateTime for comparisons
         try {
             $start = new DateTime('@'.$start);
         }
         catch (Exception $e) {
             $start = new DateTime('@0');
         }
         if ($end) {
             try {
                 $end = new DateTime('@'.$end);
             }
             catch (Exception $e) {
                 $end = null;
             }
         }
 
         // query Kolab storage
         $query[] = ['dtend',   '>=', $start];
 
         if ($end) {
             $query[] = ['dtstart', '<=', $end];
         }
 
         // add query to exclude pending/declined invitations
         if (empty($filter_query)) {
             foreach ($this->cal->get_user_emails() as $email) {
                 $query[] = ['tags', '!=', 'x-partstat:' . $email . ':needs-action'];
                 $query[] = ['tags', '!=', 'x-partstat:' . $email . ':declined'];
             }
         }
         else if (is_array($filter_query)) {
             $query = array_merge($query, $filter_query);
         }
 
         // we rely the Kolab storage query (no post-filtering)
         return $this->storage->count($query);
     }
 
     /**
      * Create a new event record
      *
      * @see calendar_driver::new_event()
      *
      * @return array|false The created record ID on success, False on error
      */
     public function insert_event($event)
     {
         if (!is_array($event)) {
             return false;
         }
 
         // email links are stored separately
         $links = !empty($event['links']) ? $event['links'] : [];
         unset($event['links']);
 
         //generate new event from RC input
         $object = $this->_from_driver_event($event);
         $saved  = $this->storage->save($object, 'event');
 
         if (!$saved) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error saving event object to Kolab server"
                 ],
                 true, false
             );
             $saved = false;
         }
         else {
             // save links in configuration.relation object
             if ($this->save_links($event['uid'], $links)) {
                 $object['links'] = $links;
             }
 
             $this->events = [$event['uid'] => $this->_to_driver_event($object, true)];
         }
 
         return $saved;
     }
 
     /**
      * Update a specific event record
      *
      * @see calendar_driver::new_event()
      *
      * @return bool True on success, False on error
      */
     public function update_event($event, $exception_id = null)
     {
         $updated = false;
         $old = $this->storage->get_object(!empty($event['uid']) ? $event['uid'] : $event['id']);
 
         if (!$old || PEAR::isError($old)) {
             return false;
         }
 
         // email links are stored separately
         $links = !empty($event['links']) ? $event['links'] : [];
         unset($event['links']);
 
         $object = $this->_from_driver_event($event, $old);
         $saved  = $this->storage->save($object, 'event', $old['uid']);
 
         if (!$saved) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error saving event object to Kolab server"
                 ],
                 true, false
             );
         }
         else {
             // save links in configuration.relation object
             if ($this->save_links($event['uid'], $links)) {
                 $object['links'] = $links;
             }
 
             $updated = true;
             $this->events = [$event['uid'] => $this->_to_driver_event($object, true)];
 
             // refresh local cache with recurring instances
             if ($exception_id) {
                 $this->get_recurring_events($object, $event['start'], $event['end'], $exception_id);
             }
         }
 
         return $updated;
     }
 
     /**
      * Delete an event record
      *
      * @see calendar_driver::remove_event()
      *
      * @return bool True on success, False on error
      */
     public function delete_event($event, $force = true)
     {
         $deleted = $this->storage->delete(!empty($event['uid']) ? $event['uid'] : $event['id'], $force);
 
         if (!$deleted) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => sprintf("Error deleting event object '%s' from Kolab server", $event['id'])
                 ],
                 true, false
             );
         }
 
         return $deleted;
     }
 
     /**
      * Restore deleted event record
      *
      * @see calendar_driver::undelete_event()
      *
      * @return bool True on success, False on error
      */
     public function restore_event($event)
     {
         // Make sure this is not an instance identifier
         $uid = preg_replace('/-\d{8}(T\d{6})?$/', '', $event['id']);
 
         if ($this->storage->undelete($uid)) {
             return true;
         }
 
         rcube::raise_error([
                 'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                 'message' => sprintf("Error undeleting the event object '%s' from the Kolab server", $event['id'])
             ],
             true, false
         );
 
         return false;
     }
 
     /**
      * Find messages linked with an event
      */
     protected function get_links($uid)
     {
         $storage = kolab_storage_config::get_instance();
         return $storage->get_object_links($uid);
     }
 
     /**
      *
      */
     protected function save_links($uid, $links)
     {
         $storage = kolab_storage_config::get_instance();
         return $storage->save_object_links($uid, (array) $links);
     }
 
     /**
      * Create instances of a recurring event
      *
      * @param array    $event    Hash array with event properties
      * @param DateTime $start    Start date of the recurrence window
      * @param DateTime $end      End date of the recurrence window
      * @param string   $event_id ID of a specific recurring event instance
      * @param int      $limit    Max. number of instances to return
      *
      * @return array List of recurring event instances
      */
     public function get_recurring_events($event, $start, $end = null, $event_id = null, $limit = null)
     {
         if (empty($event['_formatobj'])) {
             $rec    = $this->storage->get_object(!empty($event['uid']) ? $event['uid'] : $event['id']);
             $object = $rec['_formatobj'];
         }
         else {
             $object = $event['_formatobj'];
         }
 
         if (!is_object($object)) {
             return [];
         }
 
         // determine a reasonable end date if none given
         if (!$end) {
             $end = clone $event['start'];
             $end->add(new DateInterval('P100Y'));
         }
 
         // read recurrence exceptions first
         $events = [];
         $exdata = [];
         $futuredata = [];
         $recurrence_id_format = libcalendaring::recurrence_id_format($event);
 
         if (!empty($event['recurrence'])) {
             // copy the recurrence rule from the master event (to be used in the UI)
             $recurrence_rule = $event['recurrence'];
             unset($recurrence_rule['EXCEPTIONS'], $recurrence_rule['EXDATE']);
 
             if (!empty($event['recurrence']['EXCEPTIONS'])) {
                 foreach ($event['recurrence']['EXCEPTIONS'] as $exception) {
                     if (empty($exception['_instance'])) {
                         $exception['_instance'] = libcalendaring::recurrence_instance_identifier($exception, !empty($event['allday']));
                     }
 
                     $rec_event = $this->_to_driver_event($exception, false, false, $event);
                     $rec_event['id'] = $event['uid'] . '-' . $exception['_instance'];
                     $rec_event['isexception'] = 1;
 
                     // found the specifically requested instance: register exception (single occurrence wins)
                     if (
                         $rec_event['id'] == $event_id
                         && (empty($this->events[$event_id]) || !empty($this->events[$event_id]['thisandfuture']))
                     ) {
                         $rec_event['recurrence'] = $recurrence_rule;
                         $rec_event['recurrence_id'] = $event['uid'];
                         $this->events[$rec_event['id']] = $rec_event;
                     }
 
                     // remember this exception's date
                     $exdate = substr($exception['_instance'], 0, 8);
                     if (empty($exdata[$exdate]) || !empty($exdata[$exdate]['thisandfuture'])) {
                         $exdata[$exdate] = $rec_event;
                     }
                     if (!empty($rec_event['thisandfuture'])) {
                         $futuredata[$exdate] = $rec_event;
                     }
                 }
             }
         }
 
         // found the specifically requested instance, exiting...
         if ($event_id && !empty($this->events[$event_id])) {
             return [$this->events[$event_id]];
         }
 
         // Check first occurrence, it might have been moved
-        if ($first = $exdata[$event['start']->format('Ymd')]) {
+        if (!empty($exdata[$event['start']->format('Ymd')])) {
+            $first = $exdata[$event['start']->format('Ymd')];
             // return it only if not already in the result, but in the requested period
             if (!($event['start'] <= $end && $event['end'] >= $start)
                 && ($first['start'] <= $end && $first['end'] >= $start)
             ) {
                 $events[] = $first;
             }
         }
 
         if ($limit && count($events) >= $limit) {
             return $events;
         }
 
         // use libkolab to compute recurring events
         $recurrence = new kolab_date_recurrence($object);
 
         $i = 0;
         while ($next_event = $recurrence->next_instance()) {
             $datestr     = $next_event['start']->format('Ymd');
             $instance_id = $next_event['start']->format($recurrence_id_format);
 
             // use this event data for future recurring instances
-            if (!empty($futuredata[$datestr])) {
-                $overlay_data = $futuredata[$datestr];
-            }
+            $overlay_data = $futuredata[$datestr] ?? null;
 
             $rec_id      = $event['uid'] . '-' . $instance_id;
             $exception   = !empty($exdata[$datestr]) ? $exdata[$datestr] : $overlay_data;
             $event_start = $next_event['start'];
             $event_end   = $next_event['end'];
 
             // copy some event from exception to get proper start/end dates
             if ($exception) {
                 $event_copy = $next_event;
                 kolab_driver::merge_exception_dates($event_copy, $exception);
                 $event_start = $event_copy['start'];
                 $event_end   = $event_copy['end'];
             }
 
             // add to output if in range
             if (($event_start <= $end && $event_end >= $start) || ($event_id && $rec_id == $event_id)) {
                 $rec_event = $this->_to_driver_event($next_event, false, false, $event);
                 $rec_event['_instance'] = $instance_id;
                 $rec_event['_count'] = $i + 1;
 
                 if ($exception) {
                     // copy data from exception
                     kolab_driver::merge_exception_data($rec_event, $exception);
                 }
 
                 $rec_event['id'] = $rec_id;
                 $rec_event['recurrence_id'] = $event['uid'];
                 $rec_event['recurrence'] = $recurrence_rule;
                 unset($rec_event['_attendees']);
                 $events[] = $rec_event;
 
                 if ($rec_id == $event_id) {
                     $this->events[$rec_id] = $rec_event;
                     break;
                 }
 
                 if ($limit && count($events) >= $limit) {
                     return $events;
                 }
             }
             else if ($next_event['start'] > $end) {
                 // stop loop if out of range
                 break;
             }
 
             // avoid endless recursion loops
             if (++$i > 100000) {
                 break;
             }
         }
 
         return $events;
     }
 
     /**
      * Convert from Kolab_Format to internal representation
      */
     private function _to_driver_event($record, $noinst = false, $links = true, $master_event = null)
     {
         $record['calendar'] = $this->id;
 
         // remove (possibly outdated) cached parameters
         unset($record['_folder_id'], $record['className']);
 
         if ($links && !array_key_exists('links', $record)) {
             $record['links'] = $this->get_links($record['uid']);
         }
 
         $ns = $this->get_namespace();
 
         if ($ns == 'other') {
             $record['className'] = 'fc-event-ns-other';
         }
 
         if ($ns == 'other' || !$this->cal->rc->config->get('kolab_invitation_calendars')) {
             $record = kolab_driver::add_partstat_class($record, ['NEEDS-ACTION', 'DECLINED'], $this->get_owner());
 
             // Modify invitation status class name, when invitation calendars are disabled
             // we'll use opacity only for declined/needs-action events
             $record['className'] = str_replace('-invitation', '', $record['className']);
         }
 
         // add instance identifier to first occurrence (master event)
         $recurrence_id_format = libcalendaring::recurrence_id_format($master_event ? $master_event : $record);
         if (!$noinst && !empty($record['recurrence']) && empty($record['recurrence_id']) && empty($record['_instance'])) {
             $record['_instance'] = $record['start']->format($recurrence_id_format);
         }
         else if (isset($record['recurrence_date']) && $record['recurrence_date'] instanceof DateTimeInterface) {
             $record['_instance'] = $record['recurrence_date']->format($recurrence_id_format);
         }
 
         // clean up exception data
         if (!empty($record['recurrence']) && !empty($record['recurrence']['EXCEPTIONS'])) {
             array_walk($record['recurrence']['EXCEPTIONS'], function(&$exception) {
                 unset($exception['_mailbox'], $exception['_msguid'], $exception['_formatobj'], $exception['_attachments']);
             });
         }
 
         return $record;
     }
 
     /**
      * Convert the given event record into a data structure that can be passed to Kolab_Storage backend for saving
      * (opposite of self::_to_driver_event())
      */
     private function _from_driver_event($event, $old = [])
     {
         // set current user as ORGANIZER
         if ($identity = $this->cal->rc->user->list_emails(true)) {
             $event['attendees'] = !empty($event['attendees']) ? $event['attendees'] : [];
             $found = false;
 
             // there can be only resources on attendees list (T1484)
             // let's check the existence of an organizer
             foreach ($event['attendees'] as $attendee) {
                 if (!empty($attendee['role']) && $attendee['role'] == 'ORGANIZER') {
                     $found = true;
                     break;
                 }
             }
 
             if (!$found) {
                 $event['attendees'][] = ['role' => 'ORGANIZER', 'name' => $identity['name'], 'email' => $identity['email']];
             }
 
             $event['_owner'] = $identity['email'];
         }
 
         // remove EXDATE values if RDATE is given
         if (!empty($event['recurrence']['RDATE'])) {
             $event['recurrence']['EXDATE'] = [];
         }
 
         // remove recurrence information (e.g. EXDATES and EXCEPTIONS) entirely
         if (!empty($event['recurrence']) && empty($event['recurrence']['FREQ']) && empty($event['recurrence']['RDATE'])) {
             $event['recurrence'] = [];
         }
 
         // keep 'comment' from initial itip invitation
         if (!empty($old['comment'])) {
             $event['comment'] = $old['comment'];
         }
 
         // remove some internal properties which should not be cached
         $cleanup_fn = function(&$event) {
             unset($event['_savemode'], $event['_fromcalendar'], $event['_identity'], $event['_folder_id'],
                 $event['calendar'], $event['className'], $event['recurrence_id'],
                 $event['attachments'], $event['deleted_attachments']);
         };
 
         $cleanup_fn($event);
 
         // clean up exception data
         if (!empty($event['exceptions'])) {
             array_walk($event['exceptions'], function(&$exception) use ($cleanup_fn) {
                 unset($exception['_mailbox'], $exception['_msguid'], $exception['_formatobj']);
                 $cleanup_fn($exception);
             });
         }
 
         // copy meta data (starting with _) from old object
         foreach ((array) $old as $key => $val) {
             if (!isset($event[$key]) && $key[0] == '_') {
                 $event[$key] = $val;
             }
         }
 
         return $event;
     }
 
     /**
      * Match the given word in the event contents
      */
     public function fulltext_match($event, $word, $recursive = true)
     {
         $hits = 0;
         foreach ($this->search_fields as $col) {
             if (empty($event[$col])) {
                 continue;
             }
 
             $sval = is_array($event[$col]) ? self::_complex2string($event[$col]) : $event[$col];
             if (empty($sval)) {
                 continue;
             }
 
             // do a simple substring matching (to be improved)
             $val = mb_strtolower($sval);
             if (strpos($val, $word) !== false) {
                 $hits++;
                 break;
             }
         }
 
         return $hits;
     }
 
     /**
      * Convert a complex event attribute to a string value
      */
     private static function _complex2string($prop)
     {
         static $ignorekeys = ['role', 'status', 'rsvp'];
 
         $out = '';
         if (is_array($prop)) {
             foreach ($prop as $key => $val) {
                 if (is_numeric($key)) {
                     $out .= self::_complex2string($val);
                 }
                 else if (!in_array($key, $ignorekeys)) {
                     $out .= $val . ' ';
                 }
             }
         }
         else if (is_string($prop) || is_numeric($prop)) {
             $out .= $prop . ' ';
         }
 
         return rtrim($out);
     }
 }
diff --git a/plugins/calendar/drivers/kolab/kolab_driver.php b/plugins/calendar/drivers/kolab/kolab_driver.php
index 4062bb61..31ac42eb 100644
--- a/plugins/calendar/drivers/kolab/kolab_driver.php
+++ b/plugins/calendar/drivers/kolab/kolab_driver.php
@@ -1,2650 +1,2652 @@
 <?php
 
 /**
  * Kolab driver for the Calendar plugin
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  * @author Aleksander Machniak <machniak@kolabsys.com>
  *
  * Copyright (C) 2012-2015, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_driver extends calendar_driver
 {
     const INVITATIONS_CALENDAR_PENDING  = '--invitation--pending';
     const INVITATIONS_CALENDAR_DECLINED = '--invitation--declined';
 
     // features this backend supports
     public $alarms              = true;
     public $attendees           = true;
     public $freebusy            = true;
     public $attachments         = true;
     public $undelete            = true;
     public $alarm_types         = ['DISPLAY', 'AUDIO'];
     public $categoriesimmutable = true;
 
     protected $rc;
     protected $cal;
     protected $calendars;
     protected $storage;
     protected $has_writeable    = false;
     protected $freebusy_trigger = false;
     protected $bonnie_api       = false;
 
     /**
      * Default constructor
      */
     public function __construct($cal)
     {
         $cal->require_plugin('libkolab');
 
         // load helper classes *after* libkolab has been loaded (#3248)
         require_once(__DIR__ . '/kolab_calendar.php');
         require_once(__DIR__ . '/kolab_user_calendar.php');
         require_once(__DIR__ . '/kolab_invitation_calendar.php');
 
         $this->cal     = $cal;
         $this->rc      = $cal->rc;
         $this->storage = new kolab_storage();
 
         $this->cal->register_action('push-freebusy', [$this, 'push_freebusy']);
         $this->cal->register_action('calendar-acl', [$this, 'calendar_acl']);
 
         $this->freebusy_trigger = $this->rc->config->get('calendar_freebusy_trigger', false);
 
         if (!$this->rc->config->get('kolab_freebusy_server', false)) {
             $this->freebusy = false;
         }
 
         if (kolab_storage::$version == '2.0') {
             $this->alarm_types    = ['DISPLAY'];
             $this->alarm_absolute = false;
         }
 
         // get configuration for the Bonnie API
         $this->bonnie_api = libkolab::get_bonnie_api();
 
         // calendar uses fully encoded identifiers
         kolab_storage::$encode_ids = true;
     }
 
     /**
      * Read available calendars from server
      */
     protected function _read_calendars()
     {
         // already read sources
         if (isset($this->calendars)) {
             return $this->calendars;
         }
 
         // get all folders that have "event" type, sorted by namespace/name
         $folders = $this->storage->sort_folders(
             $this->storage->get_folders('event') + kolab_storage::get_user_folders('event', true)
         );
 
         $this->calendars = [];
 
         foreach ($folders as $folder) {
             $calendar = $this->_to_calendar($folder);
             if ($calendar->ready) {
                 $this->calendars[$calendar->id] = $calendar;
                 if ($calendar->editable) {
                     $this->has_writeable = true;
                 }
             }
         }
 
         return $this->calendars;
     }
 
     /**
      * Convert kolab_storage_folder into kolab_calendar
      */
     protected function _to_calendar($folder)
     {
         if ($folder instanceof kolab_calendar) {
             return $folder;
         }
 
         if ($folder instanceof kolab_storage_folder_user) {
             $calendar = new kolab_user_calendar($folder, $this->cal);
             $calendar->subscriptions = count($folder->children) > 0;
         }
         else {
             $calendar = new kolab_calendar($folder->name, $this->cal);
         }
 
         return $calendar;
     }
 
     /**
      * Get a list of available calendars from this source
      *
      * @param int    $filter Bitmask defining filter criterias
      * @param object $tree   Reference to hierarchical folder tree object
      *
      * @return array List of calendars
      */
     public function list_calendars($filter = 0, &$tree = null)
     {
         $this->_read_calendars();
 
         // attempt to create a default calendar for this user
         if (!$this->has_writeable) {
             if ($this->create_calendar(['name' => 'Calendar', 'color' => 'cc0000'])) {
                 unset($this->calendars);
                 $this->_read_calendars();
             }
         }
 
         $delim     = $this->rc->get_storage()->get_hierarchy_delimiter();
         $folders   = $this->filter_calendars($filter);
         $calendars = [];
 
         // include virtual folders for a full folder tree
         if (!is_null($tree)) {
             $folders = $this->storage->folder_hierarchy($folders, $tree);
         }
 
         $parents = array_keys($this->calendars);
 
         foreach ($folders as $id => $cal) {
             $imap_path = explode($delim, $cal->name);
 
             // find parent
             do {
                 array_pop($imap_path);
                 $parent_id = $this->storage->folder_id(join($delim, $imap_path));
             }
             while (count($imap_path) > 1 && !in_array($parent_id, $parents));
 
             // restore "real" parent ID
             if ($parent_id && !in_array($parent_id, $parents)) {
                 $parent_id = $this->storage->folder_id($cal->get_parent());
             }
 
             $parents[] = $cal->id;
 
             if ($cal->virtual) {
                 $calendars[$cal->id] = [
                     'id'       => $cal->id,
                     'name'     => $cal->get_name(),
                     'listname' => $cal->get_foldername(),
                     'editname' => $cal->get_foldername(),
                     'virtual'  => true,
                     'editable' => false,
                     'group'    => $cal->get_namespace(),
                 ];
             }
             else {
                 // additional folders may come from kolab_storage::folder_hierarchy() above
                 // make sure we deal with kolab_calendar instances
                 $cal = $this->_to_calendar($cal);
                 $this->calendars[$cal->id] = $cal;
 
                 $is_user = ($cal instanceof kolab_user_calendar);
 
                 $calendars[$cal->id] = [
                     'id'        => $cal->id,
                     'name'      => $cal->get_name(),
                     'listname'  => $cal->get_foldername(),
                     'editname'  => $cal->get_foldername(),
                     'title'     => $cal->get_title(),
                     'color'     => $cal->get_color(),
                     'editable'  => $cal->editable,
                     'group'     => $is_user ? 'other user' : $cal->get_namespace(),
                     'active'    => $cal->is_active(),
                     'owner'     => $cal->get_owner(),
                     'removable' => !$cal->default,
                 ];
 
                 if (!$is_user) {
                     $calendars[$cal->id] += [
                         'default'    => $cal->default,
                         'rights'     => $cal->rights,
                         'showalarms' => $cal->alarms,
                         'history'    => !empty($this->bonnie_api),
                         'children'   => true,  // TODO: determine if that folder indeed has child folders
                         'parent'     => $parent_id,
                         'subtype'    => $cal->subtype,
                         'caldavurl'  => $cal->get_caldav_url(),
                     ];
                 }
             }
 
             if ($cal->subscriptions) {
                 $calendars[$cal->id]['subscribed'] = $cal->is_subscribed();
             }
         }
 
         // list virtual calendars showing invitations
         if ($this->rc->config->get('kolab_invitation_calendars') && !($filter & self::FILTER_INSERTABLE)) {
             foreach ([self::INVITATIONS_CALENDAR_PENDING, self::INVITATIONS_CALENDAR_DECLINED] as $id) {
                 $cal = new kolab_invitation_calendar($id, $this->cal);
                 if (!($filter & self::FILTER_ACTIVE) || $cal->is_active()) {
                     $calendars[$id] = [
                         'id'         => $cal->id,
                         'name'       => $cal->get_name(),
                         'listname'   => $cal->get_name(),
                         'editname'   => $cal->get_foldername(),
                         'title'      => $cal->get_title(),
                         'color'      => $cal->get_color(),
                         'editable'   => $cal->editable,
                         'rights'     => $cal->rights,
                         'showalarms' => $cal->alarms,
                         'history'    => !empty($this->bonnie_api),
                         'group'      => 'x-invitations',
                         'default'    => false,
                         'active'     => $cal->is_active(),
                         'owner'      => $cal->get_owner(),
                         'children'   => false,
                         'counts'     => $id == self::INVITATIONS_CALENDAR_PENDING,
                     ];
 
 
                     if (is_object($tree)) {
                         $tree->children[] = $cal;
                     }
                 }
             }
         }
 
         // append the virtual birthdays calendar
         if ($this->rc->config->get('calendar_contact_birthdays', false) && !($filter & self::FILTER_INSERTABLE)) {
             $id    = self::BIRTHDAY_CALENDAR_ID;
             $prefs = $this->rc->config->get('kolab_calendars', []);  // read local prefs
 
             if (!($filter & self::FILTER_ACTIVE) || !empty($prefs[$id]['active'])) {
                 $calendars[$id] = [
                     'id'         => $id,
                     'name'       => $this->cal->gettext('birthdays'),
                     'listname'   => $this->cal->gettext('birthdays'),
                     'color'      => !empty($prefs[$id]['color']) ? $prefs[$id]['color'] : '87CEFA',
                     'active'     => !empty($prefs[$id]['active']),
                     'showalarms' => (bool) $this->rc->config->get('calendar_birthdays_alarm_type'),
                     'group'      => 'x-birthdays',
                     'editable'   => false,
                     'default'    => false,
                     'children'   => false,
                     'history'    => false,
                 ];
             }
         }
 
         return $calendars;
     }
 
     /**
      * Get list of calendars according to specified filters
      *
      * @param int Bitmask defining restrictions. See FILTER_* constants for possible values.
      *
      * @return array List of calendars
      */
     protected function filter_calendars($filter)
     {
         $this->_read_calendars();
 
         $calendars = [];
 
         $plugin = $this->rc->plugins->exec_hook('calendar_list_filter', [
             'list'      => $this->calendars,
             'calendars' => $calendars,
             'filter'    => $filter,
         ]);
 
         if ($plugin['abort']) {
             return $plugin['calendars'];
         }
 
         $personal = $filter & self::FILTER_PERSONAL;
         $shared   = $filter & self::FILTER_SHARED;
 
         foreach ($this->calendars as $cal) {
             if (!$cal->ready) {
                 continue;
             }
             if (($filter & self::FILTER_WRITEABLE) && !$cal->editable) {
                 continue;
             }
             if (($filter & self::FILTER_INSERTABLE) && !$cal->editable) {
                 continue;
             }
             if (($filter & self::FILTER_ACTIVE) && !$cal->is_active()) {
                 continue;
             }
             if (($filter & self::FILTER_PRIVATE) && $cal->subtype != 'private') {
                 continue;
             }
             if (($filter & self::FILTER_CONFIDENTIAL) && $cal->subtype != 'confidential') {
                 continue;
             }
             if ($personal || $shared) {
                 $ns = $cal->get_namespace();
                 if (!(($personal && $ns == 'personal') || ($shared && $ns == 'shared'))) {
                     continue;
                 }
             }
 
             $calendars[$cal->id] = $cal;
         }
 
         return $calendars;
     }
 
     /**
      * Get the kolab_calendar instance for the given calendar ID
      *
      * @param string Calendar identifier (encoded imap folder name)
      *
      * @return kolab_calendar Object nor null if calendar doesn't exist
      */
     public function get_calendar($id)
     {
         $this->_read_calendars();
 
         // create calendar object if necesary
         if (empty($this->calendars[$id])) {
             if (in_array($id, [self::INVITATIONS_CALENDAR_PENDING, self::INVITATIONS_CALENDAR_DECLINED])) {
                 return new kolab_invitation_calendar($id, $this->cal);
             }
 
             // for unsubscribed calendar folders
             if ($id !== self::BIRTHDAY_CALENDAR_ID) {
                 $calendar = kolab_calendar::factory($id, $this->cal);
                 if ($calendar->ready) {
                     $this->calendars[$calendar->id] = $calendar;
                 }
             }
         }
 
         return !empty($this->calendars[$id]) ? $this->calendars[$id] : null;
     }
 
     /**
      * Create a new calendar assigned to the current user
      *
      * @param array Hash array with calendar properties
      *    name: Calendar name
      *   color: The color of the calendar
      *
      * @return mixed ID of the calendar on success, False on error
      */
     public function create_calendar($prop)
     {
         $prop['type']       = 'event';
         $prop['active']     = true;
         $prop['subscribed'] = true;
 
         $folder = $this->storage->folder_update($prop);
 
         if ($folder === false) {
             $this->last_error = $this->cal->gettext($this->storage->last_error);
             return false;
         }
 
         // create ID
         $id = $this->storage->folder_id($folder);
 
         // save color in user prefs (temp. solution)
         $prefs['kolab_calendars'] = $this->rc->config->get('kolab_calendars', []);
 
         if (isset($prop['color'])) {
             $prefs['kolab_calendars'][$id]['color'] = $prop['color'];
         }
 
         if (isset($prop['showalarms'])) {
             $prefs['kolab_calendars'][$id]['showalarms'] = !empty($prop['showalarms']);
         }
 
         if (!empty($prefs['kolab_calendars'][$id])) {
             $this->rc->user->save_prefs($prefs);
         }
 
         return $id;
     }
 
     /**
      * Update properties of an existing calendar
      *
      * @see calendar_driver::edit_calendar()
      */
     public function edit_calendar($prop)
     {
         if (!empty($prop['id']) && ($cal = $this->get_calendar($prop['id']))) {
             $id = $cal->update($prop);
         }
         else {
             $id = $prop['id'];
         }
 
         // fallback to local prefs
         $prefs['kolab_calendars'] = $this->rc->config->get('kolab_calendars', []);
         unset($prefs['kolab_calendars'][$prop['id']]['color'], $prefs['kolab_calendars'][$prop['id']]['showalarms']);
 
         if (isset($prop['color'])) {
             $prefs['kolab_calendars'][$id]['color'] = $prop['color'];
         }
 
         if (isset($prop['showalarms']) && $id == self::BIRTHDAY_CALENDAR_ID) {
             $prefs['calendar_birthdays_alarm_type'] = $prop['showalarms'] ? $this->alarm_types[0] : '';
         }
         else if (isset($prop['showalarms'])) {
             $prefs['kolab_calendars'][$id]['showalarms'] = !empty($prop['showalarms']);
         }
 
         if (!empty($prefs['kolab_calendars'][$id])) {
             $this->rc->user->save_prefs($prefs);
         }
 
         return true;
     }
 
     /**
      * Set active/subscribed state of a calendar
      *
      * @see calendar_driver::subscribe_calendar()
      */
     public function subscribe_calendar($prop)
     {
         if (!empty($prop['id']) && ($cal = $this->get_calendar($prop['id'])) && !empty($cal->storage)) {
             $ret = false;
             if (isset($prop['permanent'])) {
                 $ret |= $cal->storage->subscribe(intval($prop['permanent']));
             }
             if (isset($prop['active'])) {
                 $ret |= $cal->storage->activate(intval($prop['active']));
             }
 
             // apply to child folders, too
             if (!empty($prop['recursive'])) {
                 foreach ((array) $this->storage->list_folders($cal->storage->name, '*', 'event') as $subfolder) {
                     if (isset($prop['permanent'])) {
                         if ($prop['permanent']) {
                             $this->storage->folder_subscribe($subfolder);
                         }
                         else {
                             $this->storage->folder_unsubscribe($subfolder);
                         }
                     }
 
                     if (isset($prop['active'])) {
                         if ($prop['active']) {
                             $this->storage->folder_activate($subfolder);
                         }
                         else {
                             $this->storage->folder_deactivate($subfolder);
                         }
                     }
                 }
             }
             return $ret;
         }
         else {
             // save state in local prefs
             $prefs['kolab_calendars'] = $this->rc->config->get('kolab_calendars', []);
             $prefs['kolab_calendars'][$prop['id']]['active'] = !empty($prop['active']);
             $this->rc->user->save_prefs($prefs);
             return true;
         }
 
         return false;
     }
 
     /**
      * Delete the given calendar with all its contents
      *
      * @see calendar_driver::delete_calendar()
      */
     public function delete_calendar($prop)
     {
         if (!empty($prop['id']) && ($cal = $this->get_calendar($prop['id']))) {
             $folder = $cal->get_realname();
 
             // TODO: unsubscribe if no admin rights
             if ($this->storage->folder_delete($folder)) {
                 // remove color in user prefs (temp. solution)
                 $prefs['kolab_calendars'] = $this->rc->config->get('kolab_calendars', []);
                 unset($prefs['kolab_calendars'][$prop['id']]);
 
                 $this->rc->user->save_prefs($prefs);
                 return true;
             }
             else {
                 $this->last_error = $this->storage->last_error;
             }
         }
 
         return false;
     }
 
     /**
      * Search for shared or otherwise not listed calendars the user has access
      *
      * @param string Search string
      * @param string Section/source to search
      *
      * @return array List of calendars
      */
     public function search_calendars($query, $source)
     {
         if (!$this->storage->setup()) {
             return [];
         }
 
         $this->calendars = [];
         $this->search_more_results = false;
 
         // find unsubscribed IMAP folders that have "event" type
         if ($source == 'folders') {
             foreach ((array) $this->storage->search_folders('event', $query, ['other']) as $folder) {
                 $calendar = new kolab_calendar($folder->name, $this->cal);
                 $this->calendars[$calendar->id] = $calendar;
             }
         }
         // find other user's virtual calendars
         else if ($source == 'users') {
             // we have slightly more space, so display twice the number
             $limit = $this->rc->config->get('autocomplete_max', 15) * 2;
 
             foreach ($this->storage->search_users($query, 0, [], $limit, $count) as $user) {
                 $calendar = new kolab_user_calendar($user, $this->cal);
                 $this->calendars[$calendar->id] = $calendar;
 
                 // search for calendar folders shared by this user
                 foreach ($this->storage->list_user_folders($user, 'event', false) as $foldername) {
                     $cal = new kolab_calendar($foldername, $this->cal);
                     $this->calendars[$cal->id] = $cal;
                     $calendar->subscriptions = true;
                 }
             }
 
             if ($count > $limit) {
                 $this->search_more_results = true;
             }
         }
 
         // don't list the birthday calendar
         $this->rc->config->set('calendar_contact_birthdays', false);
         $this->rc->config->set('kolab_invitation_calendars', false);
 
         return $this->list_calendars();
     }
 
     /**
      * Fetch a single event
      *
      * @see calendar_driver::get_event()
      * @return array Hash array with event properties, false if not found
      */
     public function get_event($event, $scope = 0, $full = false)
     {
         if (is_array($event)) {
             $id  = !empty($event['id']) ? $event['id'] : $event['uid'];
             $cal = $event['calendar'];
 
             // we're looking for a recurring instance: expand the ID to our internal convention for recurring instances
             if (empty($event['id']) && !empty($event['_instance'])) {
                 $id .= '-' . $event['_instance'];
             }
         }
         else {
             $id = $event;
         }
 
         if (!empty($cal)) {
             if ($storage = $this->get_calendar($cal)) {
                 $result = $storage->get_event($id);
                 return self::to_rcube_event($result);
             }
 
             // get event from the address books birthday calendar
             if ($cal == self::BIRTHDAY_CALENDAR_ID) {
                 return $this->get_birthday_event($id);
             }
         }
         // iterate over all calendar folders and search for the event ID
         else {
             foreach ($this->filter_calendars($scope) as $calendar) {
                 if ($result = $calendar->get_event($id)) {
                     return self::to_rcube_event($result);
                 }
             }
         }
 
         return false;
     }
 
     /**
      * Add a single event to the database
      *
      * @see calendar_driver::new_event()
      */
     public function new_event($event)
     {
         if (!$this->validate($event)) {
             return false;
         }
 
         $event = self::from_rcube_event($event);
 
         if (!$event['calendar']) {
             $this->_read_calendars();
             $cal_ids = array_keys($this->calendars);
             $event['calendar'] = reset($cal_ids);
         }
 
         if ($storage = $this->get_calendar($event['calendar'])) {
             // if this is a recurrence instance, append as exception to an already existing object for this UID
             if (!empty($event['recurrence_date']) && ($master = $storage->get_event($event['uid']))) {
                 self::add_exception($master, $event);
                 $success = $storage->update_event($master);
             }
             else {
                 $success = $storage->insert_event($event);
             }
 
             if ($success && $this->freebusy_trigger) {
                 $this->rc->output->command('plugin.ping_url', ['action' => 'calendar/push-freebusy', 'source' => $storage->id]);
                 $this->freebusy_trigger = false; // disable after first execution (#2355)
             }
 
             return $success;
         }
 
         return false;
     }
 
     /**
      * Update an event entry with the given data
      *
      * @see calendar_driver::new_event()
      * @return bool True on success, False on error
      */
     public function edit_event($event)
     {
         if (!($storage = $this->get_calendar($event['calendar']))) {
             return false;
         }
 
         return $this->update_event(self::from_rcube_event($event, $storage->get_event($event['id'])));
     }
 
     /**
      * Extended event editing with possible changes to the argument
      *
      * @param array  Hash array with event properties
      * @param string New participant status
      * @param array  List of hash arrays with updated attendees
      *
      * @return bool True on success, False on error
      */
     public function edit_rsvp(&$event, $status, $attendees)
     {
         $update_event = $event;
 
         // apply changes to master (and all exceptions)
         if ($event['_savemode'] == 'all' && !empty($event['recurrence_id'])) {
             if ($storage = $this->get_calendar($event['calendar'])) {
                 $update_event = $storage->get_event($event['recurrence_id']);
                 $update_event['_savemode'] = $event['_savemode'];
                 $update_event['id'] = $update_event['uid'];
                 unset($update_event['recurrence_id']);
                 calendar::merge_attendee_data($update_event, $attendees);
             }
         }
 
         if ($ret = $this->update_attendees($update_event, $attendees)) {
             // replace with master event (for iTip reply)
             $event = self::to_rcube_event($update_event);
 
             // re-assign to the according (virtual) calendar
             if ($this->rc->config->get('kolab_invitation_calendars')) {
                 if (strtoupper($status) == 'DECLINED') {
                     $event['calendar'] = self::INVITATIONS_CALENDAR_DECLINED;
                 }
                 else if (strtoupper($status) == 'NEEDS-ACTION') {
                     $event['calendar'] = self::INVITATIONS_CALENDAR_PENDING;
                 }
                 else if (!empty($event['_folder_id'])) {
                     $event['calendar'] = $event['_folder_id'];
                 }
             }
         }
 
         return $ret;
     }
 
     /**
      * Update the participant status for the given attendees
      *
      * @see calendar_driver::update_attendees()
      */
     public function update_attendees(&$event, $attendees)
     {
         // for this-and-future updates, merge the updated attendees onto all exceptions in range
         if (
             ($event['_savemode'] == 'future' && !empty($event['recurrence_id']))
             || (!empty($event['recurrence']) && empty($event['recurrence_id']))
         ) {
             if (!($storage = $this->get_calendar($event['calendar']))) {
                 return false;
             }
 
             // load master event
             $master = !empty($event['recurrence_id']) ? $storage->get_event($event['recurrence_id']) : $event;
 
             // apply attendee update to each existing exception
             if (!empty($master['recurrence']) && !empty($master['recurrence']['EXCEPTIONS'])) {
                 $saved = false;
                 foreach ($master['recurrence']['EXCEPTIONS'] as $i => $exception) {
                     // merge the new event properties onto future exceptions
                     if ($exception['_instance'] >= strval($event['_instance'])) {
                         calendar::merge_attendee_data($master['recurrence']['EXCEPTIONS'][$i], $attendees);
                     }
                     // update a specific instance
                     if ($exception['_instance'] == $event['_instance'] && $exception['thisandfuture']) {
                         $saved = true;
                     }
                 }
 
                 // add the given event as new exception
                 if (!$saved && $event['id'] != $master['id']) {
                     $event['thisandfuture'] = true;
                     $master['recurrence']['EXCEPTIONS'][] = $event;
                 }
 
                 // set link to top-level exceptions
                 $master['exceptions'] = &$master['recurrence']['EXCEPTIONS'];
 
                 return $this->update_event($master);
             }
         }
 
         // just update the given event (instance)
         return $this->update_event($event);
     }
 
     /**
      * Move a single event
      *
      * @see calendar_driver::move_event()
      * @return boolean True on success, False on error
      */
     public function move_event($event)
     {
         if (($storage = $this->get_calendar($event['calendar'])) && ($ev = $storage->get_event($event['id']))) {
             unset($ev['sequence']);
             self::clear_attandee_noreply($ev);
 
             return $this->update_event($event + $ev);
         }
 
         return false;
     }
 
     /**
      * Resize a single event
      *
      * @see calendar_driver::resize_event()
      * @return boolean True on success, False on error
      */
     public function resize_event($event)
     {
         if (($storage = $this->get_calendar($event['calendar'])) && ($ev = $storage->get_event($event['id']))) {
             unset($ev['sequence']);
             self::clear_attandee_noreply($ev);
 
             return $this->update_event($event + $ev);
         }
 
         return false;
     }
 
     /**
      * Remove a single event
      *
      * @param array Hash array with event properties:
      *      id: Event identifier
      * @param bool  Remove record(s) irreversible (mark as deleted otherwise)
      *
      * @return bool True on success, False on error
      */
     public function remove_event($event, $force = true)
     {
         $ret      = true;
         $success  = false;
         $savemode = isset($event['_savemode']) ? $event['_savemode'] : null;
 
         if (!$force) {
             unset($event['attendees']);
             $this->rc->session->remove('calendar_event_undo');
             $this->rc->session->remove('calendar_restore_event_data');
             $sess_data = $event;
         }
 
         if (($storage = $this->get_calendar($event['calendar'])) && ($event = $storage->get_event($event['id']))) {
             $event['_savemode'] = $savemode;
             $decline  = $event['_decline'];
             $savemode = 'all';
             $master   = $event;
 
             // read master if deleting a recurring event
             if (!empty($event['recurrence']) || !empty($event['recurrence_id']) || !empty($event['isexception'])) {
                 $master = $storage->get_event($event['uid']);
 
                 if (!empty($event['_savemode'])) {
                     $savemode = $event['_savemode'];
                 }
                 else if (!empty($event['_instance']) || !empty($event['isexception'])) {
                     $savemode = 'current';
                 }
 
                 // force 'current' mode for single occurrences stored as exception
                 if (empty($event['recurrence']) && empty($event['recurrence_id']) && !empty($event['isexception'])) {
                     $savemode = 'current';
                 }
             }
 
             // removing an exception instance
             if ((!empty($event['recurrence_id']) || !empty($event['isexception'])) && !empty($master['exceptions'])) {
                 foreach ($master['exceptions'] as $i => $exception) {
                     if ($exception['_instance'] == $event['_instance']) {
                         unset($master['exceptions'][$i]);
                         // set event date back to the actual occurrence
                         if (!empty($exception['recurrence_date'])) {
                             $event['start'] = $exception['recurrence_date'];
                         }
                     }
                 }
 
                 if (!empty($master['recurrence'])) {
                     $master['recurrence']['EXCEPTIONS'] = &$master['exceptions'];
                 }
             }
 
             switch ($savemode) {
             case 'current':
                 $_SESSION['calendar_restore_event_data'] = $master;
 
                 // remove the matching RDATE entry
                 if (!empty($master['recurrence']['RDATE'])) {
                     foreach ($master['recurrence']['RDATE'] as $j => $rdate) {
                         if ($rdate->format('Ymd') == $event['start']->format('Ymd')) {
                             unset($master['recurrence']['RDATE'][$j]);
                             break;
                         }
                     }
                 }
 
                 // add exception to master event
                 $master['recurrence']['EXDATE'][] = $event['start'];
 
                 $success = $storage->update_event($master);
                 break;
 
             case 'future':
                 $master['_instance'] = libcalendaring::recurrence_instance_identifier($master);
                 if ($master['_instance'] != $event['_instance']) {
                     $_SESSION['calendar_restore_event_data'] = $master;
 
                     // set until-date on master event
                     $master['recurrence']['UNTIL'] = clone $event['start'];
                     $master['recurrence']['UNTIL']->sub(new DateInterval('P1D'));
                     unset($master['recurrence']['COUNT']);
 
                     // if all future instances are deleted, remove recurrence rule entirely (bug #1677)
                     if ($master['recurrence']['UNTIL']->format('Ymd') == $master['start']->format('Ymd')) {
                         $master['recurrence'] = [];
                     }
                     // remove matching RDATE entries
                     else if (!empty($master['recurrence']['RDATE'])) {
                         foreach ($master['recurrence']['RDATE'] as $j => $rdate) {
                             if ($rdate->format('Ymd') == $event['start']->format('Ymd')) {
                                 $master['recurrence']['RDATE'] = array_slice($master['recurrence']['RDATE'], 0, $j);
                                 break;
                             }
                         }
                     }
 
                     $success = $storage->update_event($master);
                     $ret = $master['uid'];
                     break;
                 }
 
             default:  // 'all' is default
                 // removing the master event with loose exceptions (not recurring though)
                 if (!empty($event['recurrence_date']) && empty($master['recurrence']) && !empty($master['exceptions'])) {
                     // make the first exception the new master
                     $newmaster = array_shift($master['exceptions']);
                     $newmaster['exceptions']   = $master['exceptions'];
                     $newmaster['_attachments'] = $master['_attachments'];
                     $newmaster['_mailbox']     = $master['_mailbox'];
                     $newmaster['_msguid']      = $master['_msguid'];
 
                     $success = $storage->update_event($newmaster);
                 }
                 else if ($decline && $this->rc->config->get('kolab_invitation_calendars')) {
                     // don't delete but set PARTSTAT=DECLINED
                     if ($this->cal->lib->set_partstat($master, 'DECLINED')) {
                         $success = $storage->update_event($master);
                     }
                 }
 
                 if (!$success) {
                     $success = $storage->delete_event($master, $force);
                 }
                 break;
             }
         }
 
         if ($success && !$force) {
             if (!empty($master['_folder_id'])) {
                 $sess_data['_folder_id'] = $master['_folder_id'];
             }
             $_SESSION['calendar_event_undo'] = ['ts' => time(), 'data' => $sess_data];
         }
 
         if ($success && $this->freebusy_trigger) {
             $this->rc->output->command('plugin.ping_url', [
                     'action' => 'calendar/push-freebusy',
                     // _folder_id may be set by invitations calendar
                     'source' => !empty($master['_folder_id']) ? $master['_folder_id'] : $storage->id,
             ]);
         }
 
         return $success ? $ret : false;
     }
 
     /**
      * Restore a single deleted event
      *
      * @param array Hash array with event properties:
      *                    id: Event identifier
      *              calendar: Event calendar
      *
      * @return bool True on success, False on error
      */
     public function restore_event($event)
     {
         if ($storage = $this->get_calendar($event['calendar'])) {
             if (!empty($_SESSION['calendar_restore_event_data'])) {
                 $success = $storage->update_event($event = $_SESSION['calendar_restore_event_data']);
             }
             else {
                 $success = $storage->restore_event($event);
             }
 
             if ($success && $this->freebusy_trigger) {
                 $this->rc->output->command('plugin.ping_url', [
                         'action' => 'calendar/push-freebusy',
                         // _folder_id may be set by invitations calendar
                         'source' => !empty($event['_folder_id']) ? $event['_folder_id'] : $storage->id,
                 ]);
             }
 
             return $success;
         }
 
         return false;
     }
 
     /**
      * Wrapper to update an event object depending on the given savemode
      */
     protected function update_event($event)
     {
         if (!($storage = $this->get_calendar($event['calendar']))) {
             return false;
         }
 
         // move event to another folder/calendar
         if (!empty($event['_fromcalendar']) && $event['_fromcalendar'] != $event['calendar']) {
             if (!($fromcalendar = $this->get_calendar($event['_fromcalendar']))) {
                 return false;
             }
 
             $old = $fromcalendar->get_event($event['id']);
 
             if ($event['_savemode'] != 'new') {
                 if (!$fromcalendar->storage->move($old['uid'], $storage->storage)) {
                     return false;
                 }
 
                 $fromcalendar = $storage;
             }
         }
         else {
             $fromcalendar = $storage;
         }
 
         $success     = false;
         $savemode    = 'all';
         $attachments = [];
         $old = $master = $storage->get_event($event['id']);
 
         if (!$old || empty($old['start'])) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Failed to load event object to update: id=" . $event['id']
                 ],
                 true, false
             );
             return false;
         }
 
         // modify a recurring event, check submitted savemode to do the right things
         if (!empty($old['recurrence']) || !empty($old['recurrence_id']) || !empty($old['isexception'])) {
             $master = $storage->get_event($old['uid']);
 
             if (!empty($event['_savemode'])) {
                 $savemode = $event['_savemode'];
             }
             else {
                 $savemode = (!empty($old['recurrence_id']) || !empty($old['isexception'])) ? 'current' : 'all';
             }
 
             // this-and-future on the first instance equals to 'all'
             if ($savemode == 'future' && !empty($master['start'])
                 && $old['_instance'] == libcalendaring::recurrence_instance_identifier($master)
             ) {
                 $savemode = 'all';
             }
             // force 'current' mode for single occurrences stored as exception
             else if (empty($old['recurrence']) && empty($old['recurrence_id']) && !empty($old['isexception'])) {
                 $savemode = 'current';
             }
 
             // Stick to the master timezone for all occurrences (Bifrost#T104637)
             $master_tz = $master['start']->getTimezone();
             $event_tz  = $event['start']->getTimezone();
 
             if ($master_tz->getName() != $event_tz->getName()) {
                 $event['start']->setTimezone($master_tz);
                 $event['end']->setTimezone($master_tz);
             }
         }
 
         // check if update affects scheduling and update attendee status accordingly
         $reschedule = $this->check_scheduling($event, $old, true);
 
         // keep saved exceptions (not submitted by the client)
         if (!empty($old['recurrence']['EXDATE']) && !isset($event['recurrence']['EXDATE'])) {
             $event['recurrence']['EXDATE'] = $old['recurrence']['EXDATE'];
         }
 
         if (isset($event['recurrence']['EXCEPTIONS'])) {
             // exceptions already provided (e.g. from iCal import)
             $with_exceptions = true;
         }
         else if (!empty($old['recurrence']['EXCEPTIONS'])) {
             $event['recurrence']['EXCEPTIONS'] = $old['recurrence']['EXCEPTIONS'];
         }
         else if (!empty($old['exceptions'])) {
             $event['exceptions'] = $old['exceptions'];
         }
 
         // remove some internal properties which should not be saved
         unset($event['_savemode'], $event['_fromcalendar'], $event['_identity'], $event['_owner'],
             $event['_notify'], $event['_method'], $event['_sender'], $event['_sender_utf'], $event['_size']
         );
 
         switch ($savemode) {
         case 'new':
             // save submitted data as new (non-recurring) event
             $event['recurrence'] = [];
             $event['_copyfrom']  = $master['_msguid'];
             $event['_mailbox']   = $master['_mailbox'];
             $event['uid']        = $this->cal->generate_uid();
 
             unset($event['recurrence_id'], $event['recurrence_date'], $event['_instance'], $event['id']);
 
             // copy attachment metadata to new event
             $event = self::from_rcube_event($event, $master);
 
             self::clear_attandee_noreply($event);
             if ($success = $storage->insert_event($event)) {
                 $success = $event['uid'];
             }
             break;
 
         case 'future':
             // create a new recurring event
             $event['_copyfrom'] = $master['_msguid'];
             $event['_mailbox']  = $master['_mailbox'];
             $event['uid']       = $this->cal->generate_uid();
 
             unset($event['recurrence_id'], $event['recurrence_date'], $event['_instance'], $event['id']);
 
             // copy attachment metadata to new event
             $event = self::from_rcube_event($event, $master);
 
             // remove recurrence exceptions on re-scheduling
             if ($reschedule) {
                 unset($event['recurrence']['EXCEPTIONS'], $event['exceptions'], $master['recurrence']['EXDATE']);
             }
             else if (isset($event['recurrence']['EXCEPTIONS']) && is_array($event['recurrence']['EXCEPTIONS'])) {
                 // only keep relevant exceptions
                 $event['recurrence']['EXCEPTIONS'] = array_filter(
                     $event['recurrence']['EXCEPTIONS'],
                     function($exception) use ($event) {
                         return $exception['start'] > $event['start'];
                     }
                 );
                 if (isset($event['recurrence']['EXDATE']) && is_array($event['recurrence']['EXDATE'])) {
                     $event['recurrence']['EXDATE'] = array_filter(
                         $event['recurrence']['EXDATE'],
                         function($exdate) use ($event) {
                             return $exdate > $event['start'];
                         }
                     );
                 }
                 // set link to top-level exceptions
                 $event['exceptions'] = &$event['recurrence']['EXCEPTIONS'];
             }
 
             // compute remaining occurrences
             if ($event['recurrence']['COUNT']) {
                 if (empty($old['_count'])) {
                     $old['_count'] = $this->get_recurrence_count($master, $old['start']);
                 }
                 $event['recurrence']['COUNT'] -= intval($old['_count']);
             }
 
             // remove fixed weekday when date changed
             if ($old['start']->format('Y-m-d') != $event['start']->format('Y-m-d')) {
                 if (!empty($event['recurrence']['BYDAY']) && strlen($event['recurrence']['BYDAY']) == 2) {
                     unset($event['recurrence']['BYDAY']);
                 }
                 if (!empty($old['recurrence']['BYMONTH']) && $old['recurrence']['BYMONTH'] == $old['start']->format('n')) {
                     unset($event['recurrence']['BYMONTH']);
                 }
             }
 
             // set until-date on master event
             $master['recurrence']['UNTIL'] = clone $old['start'];
             $master['recurrence']['UNTIL']->sub(new DateInterval('P1D'));
             unset($master['recurrence']['COUNT']);
 
             // remove all exceptions after $event['start']
             if (isset($master['recurrence']['EXCEPTIONS']) && is_array($master['recurrence']['EXCEPTIONS'])) {
                 $master['recurrence']['EXCEPTIONS'] = array_filter(
                     $master['recurrence']['EXCEPTIONS'],
                     function($exception) use ($event) {
                         return $exception['start'] < $event['start'];
                     }
                 );
                 // set link to top-level exceptions
                 $master['exceptions'] = &$master['recurrence']['EXCEPTIONS'];
             }
 
             if (isset($master['recurrence']['EXDATE']) && is_array($master['recurrence']['EXDATE'])) {
                 $master['recurrence']['EXDATE'] = array_filter(
                     $master['recurrence']['EXDATE'],
                     function($exdate) use ($event) {
                         return $exdate < $event['start'];
                     }
                 );
             }
 
             // save new event
             if ($success = $storage->insert_event($event)) {
                 $success = $event['uid'];
 
                 // update master event (no rescheduling!)
                 self::clear_attandee_noreply($master);
                 $storage->update_event($master);
             }
             break;
 
         case 'current':
             // recurring instances shall not store recurrence rules and attachments
             $event['recurrence']    = [];
             $event['thisandfuture'] = $savemode == 'future';
             unset($event['attachments'], $event['id']);
 
             // increment sequence of this instance if scheduling is affected
             if ($reschedule) {
                 $event['sequence'] = max($old['sequence'], $master['sequence']) + 1;
             }
             else if (!isset($event['sequence'])) {
                 $event['sequence'] = !empty($old['sequence']) ? $old['sequence'] : $master['sequence'];
             }
 
             // save properties to a recurrence exception instance
             if (!empty($old['_instance']) && isset($master['recurrence']['EXCEPTIONS'])) {
                 if ($this->update_recurrence_exceptions($master, $event, $old, $savemode)) {
                     $success = $storage->update_event($master, $old['id']);
                     break;
                 }
             }
 
             $add_exception = true;
 
             // adjust matching RDATE entry if dates changed
             if (
                 !empty($master['recurrence']['RDATE'])
                 && ($old_date = $old['start']->format('Ymd')) != $event['start']->format('Ymd')
             ) {
                 foreach ($master['recurrence']['RDATE'] as $j => $rdate) {
                     if ($rdate->format('Ymd') == $old_date) {
                         $master['recurrence']['RDATE'][$j] = $event['start'];
                         sort($master['recurrence']['RDATE']);
                         $add_exception = false;
                         break;
                     }
                 }
             }
 
             // save as new exception to master event
             if ($add_exception) {
                 self::add_exception($master, $event, $old);
             }
 
             $success = $storage->update_event($master);
             break;
 
         default:  // 'all' is the default
             $event['id']  = $master['uid'];
             $event['uid'] = $master['uid'];
 
             // use start date from master but try to be smart on time or duration changes
             $old_start_date = $old['start']->format('Y-m-d');
             $old_start_time = !empty($old['allday']) ? '' : $old['start']->format('H:i');
             $old_duration   = self::event_duration($old['start'], $old['end'], !empty($old['allday']));
 
             $new_start_date = $event['start']->format('Y-m-d');
             $new_start_time = !empty($event['allday']) ? '' : $event['start']->format('H:i');
             $new_duration   = self::event_duration($event['start'], $event['end'], !empty($event['allday']));
 
             $diff = $old_start_date != $new_start_date || $old_start_time != $new_start_time || $old_duration != $new_duration;
             $date_shift = $old['start']->diff($event['start']);
 
             // shifted or resized
             if ($diff && ($old_start_date == $new_start_date || $old_duration == $new_duration)) {
                 $event['start'] = $master['start']->add($date_shift);
                 $event['end'] = clone $event['start'];
                 $event['end']->add(new DateInterval($new_duration));
 
                 // remove fixed weekday, will be re-set to the new weekday in kolab_calendar::update_event()
                 if ($old_start_date != $new_start_date && !empty($event['recurrence'])) {
                     if (!empty($event['recurrence']['BYDAY']) && strlen($event['recurrence']['BYDAY']) == 2)
                         unset($event['recurrence']['BYDAY']);
                     if (!empty($old['recurrence']['BYMONTH']) && $old['recurrence']['BYMONTH'] == $old['start']->format('n'))
                         unset($event['recurrence']['BYMONTH']);
                 }
             }
             // dates did not change, use the ones from master
             else if ($new_start_date . $new_start_time == $old_start_date . $old_start_time) {
                 $event['start'] = $master['start'];
                 $event['end'] = $master['end'];
             }
 
             // when saving an instance in 'all' mode, copy recurrence exceptions over
             if (!empty($old['recurrence_id'])) {
-                $event['recurrence']['EXCEPTIONS'] = $master['recurrence']['EXCEPTIONS'];
-                $event['recurrence']['EXDATE']     = $master['recurrence']['EXDATE'];
+                $event['recurrence']['EXCEPTIONS'] = $master['recurrence']['EXCEPTIONS'] ?? [];
+                $event['recurrence']['EXDATE']     = $master['recurrence']['EXDATE'] ?? [];
             }
             else if (!empty($master['_instance'])) {
                 $event['_instance']       = $master['_instance'];
                 $event['recurrence_date'] = $master['recurrence_date'];
             }
 
             // TODO: forward changes to exceptions (which do not yet have differing values stored)
             if (!empty($event['recurrence']) && !empty($event['recurrence']['EXCEPTIONS']) && !$with_exceptions) {
                 // determine added and removed attendees
                 $old_attendees = $current_attendees = $added_attendees = [];
 
                 if (!empty($old['attendees'])) {
                     foreach ((array) $old['attendees'] as $attendee) {
                         $old_attendees[] = $attendee['email'];
                     }
                 }
 
                 if (!empty($event['attendees'])) {
                     foreach ((array) $event['attendees'] as $attendee) {
                         $current_attendees[] = $attendee['email'];
                         if (!in_array($attendee['email'], $old_attendees)) {
                             $added_attendees[] = $attendee;
                         }
                     }
                 }
 
                 $removed_attendees = array_diff($old_attendees, $current_attendees);
 
                 foreach ($event['recurrence']['EXCEPTIONS'] as $i => $exception) {
                     calendar::merge_attendee_data($event['recurrence']['EXCEPTIONS'][$i], $added_attendees, $removed_attendees);
                 }
 
                 // adjust recurrence-id when start changed and therefore the entire recurrence chain changes
                 if ($old_start_date != $new_start_date || $old_start_time != $new_start_time) {
                     $recurrence_id_format = libcalendaring::recurrence_id_format($event);
 
                     foreach ($event['recurrence']['EXCEPTIONS'] as $i => $exception) {
                         if (isset($exception['recurrence_date']) && $exception['recurrence_date'] instanceof DateTimeInterface) {
                             $recurrence_id = $exception['recurrence_date'];
                         }
                         else {
                             $recurrence_id = rcube_utils::anytodatetime($exception['_instance'], $old['start']->getTimezone());
                         }
 
                         if ($recurrence_id instanceof DateTimeInterface) {
                             $recurrence_id->add($date_shift);
                             $event['recurrence']['EXCEPTIONS'][$i]['recurrence_date'] = $recurrence_id;
                             $event['recurrence']['EXCEPTIONS'][$i]['_instance'] = $recurrence_id->format($recurrence_id_format);
                         }
                     }
                 }
 
                 // set link to top-level exceptions
                 $event['exceptions'] = &$event['recurrence']['EXCEPTIONS'];
             }
 
             // unset _dateonly flags in (cached) date objects
             unset($event['start']->_dateonly, $event['end']->_dateonly);
 
             $success = $storage->update_event($event) ? $event['id'] : false;  // return master UID
             break;
         }
 
         if ($success && $this->freebusy_trigger) {
             $this->rc->output->command('plugin.ping_url', [
                     'action' => 'calendar/push-freebusy',
                     'source' => $storage->id
             ]);
         }
 
         return $success;
     }
 
     /**
      * Calculate event duration, returns string in DateInterval format
      */
     protected static function event_duration($start, $end, $allday = false)
     {
         if ($allday) {
             $diff = $start->diff($end);
             return 'P' . $diff->days . 'D';
         }
 
         return 'PT' . ($end->format('U') - $start->format('U')) . 'S';
     }
 
     /**
      * Determine whether the current change affects scheduling and reset attendee status accordingly
      */
-    public function check_scheduling(&$event, $old, $update = true)
+    protected function check_scheduling(&$event, $old, $update = true)
     {
         // skip this check when importing iCal/iTip events
         if (isset($event['sequence']) || !empty($event['_method'])) {
             return false;
         }
 
         // iterate through the list of properties considered 'significant' for scheduling
         $kolab_event = !empty($old['_formatobj']) ? $old['_formatobj'] : new kolab_format_event();
         $reschedule  = $kolab_event->check_rescheduling($event, $old);
 
         // reset all attendee status to needs-action (#4360)
         if ($update && $reschedule && !empty($event['attendees'])) {
             $is_organizer = false;
             $emails       = $this->cal->get_user_emails();
             $attendees    = $event['attendees'];
 
             foreach ($attendees as $i => $attendee) {
                 if ($attendee['role'] == 'ORGANIZER'
                     && !empty($attendee['email'])
                     && in_array(strtolower($attendee['email']), $emails)
                 ) {
                     $is_organizer = true;
                 }
                 else if ($attendee['role'] != 'ORGANIZER'
                     && $attendee['role'] != 'NON-PARTICIPANT'
                     && $attendee['status'] != 'DELEGATED'
                 ) {
                     $attendees[$i]['status'] = 'NEEDS-ACTION';
                     $attendees[$i]['rsvp'] = true;
                 }
             }
 
             // update attendees only if I'm the organizer
             if ($is_organizer || (!empty($event['organizer']) && in_array(strtolower($event['organizer']['email']), $emails))) {
                 $event['attendees'] = $attendees;
             }
         }
 
         return $reschedule;
     }
 
     /**
      * Apply the given changes to already existing exceptions
      */
     protected function update_recurrence_exceptions(&$master, $event, $old, $savemode)
     {
         $saved    = false;
         $existing = null;
 
         // determine added and removed attendees
         $added_attendees = $removed_attendees = [];
 
         if ($savemode == 'future') {
             $old_attendees = $current_attendees = [];
 
             if (!empty($old['attendees'])) {
                 foreach ((array) $old['attendees'] as $attendee) {
                     $old_attendees[] = $attendee['email'];
                 }
             }
 
             if (!empty($event['attendees'])) {
                 foreach ((array) $event['attendees'] as $attendee) {
                     $current_attendees[] = $attendee['email'];
                     if (!in_array($attendee['email'], $old_attendees)) {
                         $added_attendees[] = $attendee;
                     }
                 }
             }
 
             $removed_attendees = array_diff($old_attendees, $current_attendees);
         }
 
         foreach ($master['recurrence']['EXCEPTIONS'] as $i => $exception) {
             // update a specific instance
             if ($exception['_instance'] == $old['_instance']) {
                 $existing = $i;
 
                 // check savemode against existing exception mode.
                 // if matches, we can update this existing exception
                 $thisandfuture = !empty($exception['thisandfuture']);
                 if ($thisandfuture === ($savemode == 'future')) {
                     $event['_instance']       = $old['_instance'];
                     $event['thisandfuture']   = $old['thisandfuture'];
                     $event['recurrence_date'] = $old['recurrence_date'];
                     $master['recurrence']['EXCEPTIONS'][$i] = $event;
                     $saved = true;
                 }
             }
 
             // merge the new event properties onto future exceptions
             if ($savemode == 'future' && $exception['_instance'] >= $old['_instance']) {
                 unset($event['thisandfuture']);
                 self::merge_exception_data($master['recurrence']['EXCEPTIONS'][$i], $event, ['attendees']);
 
                 if (!empty($added_attendees) || !empty($removed_attendees)) {
                     calendar::merge_attendee_data($master['recurrence']['EXCEPTIONS'][$i], $added_attendees, $removed_attendees);
                 }
             }
         }
 /*
         // we could not update the existing exception due to savemode mismatch...
         if (!$saved && isset($existing) && !empty($master['recurrence']['EXCEPTIONS'][$existing]['thisandfuture'])) {
             // ... try to move the existing this-and-future exception to the next occurrence
             foreach ($this->get_recurring_events($master, $existing['start']) as $candidate) {
                 // our old this-and-future exception is obsolete
                 if (!empty($candidate['thisandfuture'])) {
                     unset($master['recurrence']['EXCEPTIONS'][$existing]);
                     $saved = true;
                     break;
                 }
                 // this occurrence doesn't yet have an exception
                 else if (empty($candidate['isexception'])) {
                     $event['_instance'] = $candidate['_instance'];
                     $event['recurrence_date'] = $candidate['recurrence_date'];
                     $master['recurrence']['EXCEPTIONS'][$i] = $event;
                     $saved = true;
                     break;
                 }
             }
         }
 */
 
         // set link to top-level exceptions
         $master['exceptions'] = &$master['recurrence']['EXCEPTIONS'];
 
         // returning false here will add a new exception
         return $saved;
     }
 
     /**
      * Add or update the given event as an exception to $master
      */
     public static function add_exception(&$master, $event, $old = null)
     {
         if ($old) {
             $event['_instance'] = $old['_instance'];
             if (empty($event['recurrence_date'])) {
                 $event['recurrence_date'] = !empty($old['recurrence_date']) ? $old['recurrence_date'] : $old['start'];
             }
         }
         else if (empty($event['recurrence_date'])) {
             $event['recurrence_date'] = $event['start'];
         }
 
         if (empty($event['_instance']) && $event['recurrence_date'] instanceof DateTimeInterface) {
             $event['_instance'] = libcalendaring::recurrence_instance_identifier($event, !empty($master['allday']));
         }
 
         if (!is_array($master['exceptions']) && isset($master['recurrence']['EXCEPTIONS'])) {
             $master['exceptions'] = &$master['recurrence']['EXCEPTIONS'];
         }
 
         $existing = false;
         foreach ((array) $master['exceptions'] as $i => $exception) {
             if ($exception['_instance'] == $event['_instance']) {
                 $master['exceptions'][$i] = $event;
                 $existing = true;
             }
         }
 
         if (!$existing) {
             $master['exceptions'][] = $event;
         }
 
         return true;
     }
 
     /**
      * Remove the noreply flags from attendees
      */
     public static function clear_attandee_noreply(&$event)
     {
         if (!empty($event['attendees'])) {
             foreach ((array) $event['attendees'] as $i => $attendee) {
                 unset($event['attendees'][$i]['noreply']);
             }
         }
     }
 
     /**
      * Merge certain properties from the overlay event to the base event object
      *
      * @param array The event object to be altered
      * @param array The overlay event object to be merged over $event
      * @param array List of properties not allowed to be overwritten
      */
     public static function merge_exception_data(&$event, $overlay, $blacklist = null)
     {
         $forbidden = ['id','uid','recurrence','recurrence_date','thisandfuture','organizer','_attachments'];
 
         if (is_array($blacklist)) {
             $forbidden = array_merge($forbidden, $blacklist);
         }
 
         foreach ($overlay as $prop => $value) {
             if ($prop == 'start' || $prop == 'end') {
                 // handled by merge_exception_dates() below
             }
             else if ($prop == 'thisandfuture' && $overlay['_instance'] == $event['_instance']) {
                 $event[$prop] = $value;
             }
             else if ($prop[0] != '_' && !in_array($prop, $forbidden)) {
                 $event[$prop] = $value;
             }
         }
 
         self::merge_exception_dates($event, $overlay);
     }
 
     /**
      * Merge start/end date from the overlay event to the base event object
      *
      * @param array The event object to be altered
      * @param array The overlay event object to be merged over $event
      */
     public static function merge_exception_dates(&$event, $overlay)
     {
         // compute date offset from the exception
         if ($overlay['start'] instanceof DateTimeInterface && $overlay['recurrence_date'] instanceof DateTimeInterface) {
             $date_offset = $overlay['recurrence_date']->diff($overlay['start']);
         }
 
         foreach (['start', 'end'] as $prop) {
             $value = $overlay[$prop];
             if (isset($event[$prop]) && $event[$prop] instanceof DateTimeInterface) {
                 // set date value if overlay is an exception of the current instance
                 if (substr($overlay['_instance'], 0, 8) == substr($event['_instance'], 0, 8)) {
                     $event[$prop]->setDate(intval($value->format('Y')), intval($value->format('n')), intval($value->format('j')));
                 }
                 // apply date offset
                 else if (!empty($date_offset)) {
                     $event[$prop]->add($date_offset);
                 }
                 // adjust time of the recurring event instance
                 $event[$prop]->setTime($value->format('G'), intval($value->format('i')), intval($value->format('s')));
             }
         }
     }
 
     /**
      * Get events from source.
      *
      * @param int    Event's new start (unix timestamp)
      * @param int    Event's new end (unix timestamp)
      * @param string Search query (optional)
      * @param mixed  List of calendar IDs to load events from (either as array or comma-separated string)
      * @param bool   Include virtual events (optional)
      * @param int    Only list events modified since this time (unix timestamp)
      *
      * @return array A list of event records
      */
     public function load_events($start, $end, $search = null, $calendars = null, $virtual = 1, $modifiedsince = null)
     {
         if ($calendars && is_string($calendars)) {
             $calendars = explode(',', $calendars);
         }
         else if (!$calendars) {
             $this->_read_calendars();
             $calendars = array_keys($this->calendars);
         }
 
         $query      = [];
         $events     = [];
         $categories = [];
 
         if ($modifiedsince) {
             $query[] = ['changed', '>=', $modifiedsince];
         }
 
         foreach ($calendars as $cid) {
             if ($storage = $this->get_calendar($cid)) {
                 $events = array_merge($events, $storage->list_events($start, $end, $search, $virtual, $query));
                 $categories += $storage->categories;
             }
         }
 
         // add events from the address books birthday calendar
         if (in_array(self::BIRTHDAY_CALENDAR_ID, $calendars)) {
             $events = array_merge($events, $this->load_birthday_events($start, $end, $search, $modifiedsince));
         }
 
         // add new categories to user prefs
         $old_categories = $this->rc->config->get('calendar_categories', $this->default_categories);
         $newcats = array_udiff(
             array_keys($categories),
             array_keys($old_categories),
             function($a, $b) { return strcasecmp($a, $b); }
         );
 
         if (!empty($newcats)) {
             foreach ($newcats as $category) {
                 $old_categories[$category] = '';  // no color set yet
             }
             $this->rc->user->save_prefs(['calendar_categories' => $old_categories]);
         }
 
         array_walk($events, 'kolab_driver::to_rcube_event');
 
         return $events;
     }
 
     /**
      * Get number of events in the given calendar
      *
      * @param mixed List of calendar IDs to count events (either as array or comma-separated string)
      * @param int   Date range start (unix timestamp)
      * @param int   Date range end (unix timestamp)
      *
      * @return array Hash array with counts grouped by calendar ID
      */
     public function count_events($calendars, $start, $end = null)
     {
         $counts = [];
 
         if ($calendars && is_string($calendars)) {
             $calendars = explode(',', $calendars);
         }
         else if (!$calendars) {
             $this->_read_calendars();
             $calendars = array_keys($this->calendars);
         }
 
         foreach ($calendars as $cid) {
             if ($storage = $this->get_calendar($cid)) {
                 $counts[$cid] = $storage->count_events($start, $end);
             }
         }
 
          return $counts;
     }
 
     /**
      * Get a list of pending alarms to be displayed to the user
      *
      * @see calendar_driver::pending_alarms()
      */
     public function pending_alarms($time, $calendars = null)
     {
         $interval = 300;
         $time -= $time % 60;
 
         $slot = $time;
         $slot -= $slot % $interval;
 
         $last = $time - max(60, $this->rc->config->get('refresh_interval', 0));
         $last -= $last % $interval;
 
         // only check for alerts once in 5 minutes
         if ($last == $slot) {
             return [];
         }
 
         if ($calendars && is_string($calendars)) {
             $calendars = explode(',', $calendars);
         }
 
         $time = $slot + $interval;
 
         $alarms     = [];
         $candidates = [];
         $query      = [['tags', '=', 'x-has-alarms']];
 
         $this->_read_calendars();
 
         foreach ($this->calendars as $cid => $calendar) {
             // skip calendars with alarms disabled
             if (!$calendar->alarms || ($calendars && !in_array($cid, $calendars))) {
                 continue;
             }
 
             foreach ($calendar->list_events($time, $time + 86400 * 365, null, 1, $query) as $e) {
                 // add to list if alarm is set
                 $alarm = libcalendaring::get_next_alarm($e);
                 if ($alarm && !empty($alarm['time']) && $alarm['time'] >= $last
                     && in_array($alarm['action'], $this->alarm_types)
                 ) {
                     $id = $alarm['id'];  // use alarm-id as primary identifier
                     $candidates[$id] = [
                         'id'       => $id,
                         'title'    => $e['title'],
                         'location' => $e['location'],
                         'start'    => $e['start'],
                         'end'      => $e['end'],
                         'notifyat' => $alarm['time'],
                         'action'   => $alarm['action'],
                     ];
                 }
             }
         }
 
         // get alarm information stored in local database
         if (!empty($candidates)) {
             $dbdata = [];
             $alarm_ids = array_map([$this->rc->db, 'quote'], array_keys($candidates));
 
             $result = $this->rc->db->query("SELECT *"
                 . " FROM " . $this->rc->db->table_name('kolab_alarms', true)
                 . " WHERE `alarm_id` IN (" . join(',', $alarm_ids) . ")"
                     . " AND `user_id` = ?",
                 $this->rc->user->ID
             );
 
             while ($result && ($e = $this->rc->db->fetch_assoc($result))) {
                 $dbdata[$e['alarm_id']] = $e;
             }
 
             foreach ($candidates as $id => $alarm) {
                 // skip dismissed alarms
                 if ($dbdata[$id]['dismissed']) {
                     continue;
                 }
 
                 // snooze function may have shifted alarm time
                 $notifyat = $dbdata[$id]['notifyat'] ? strtotime($dbdata[$id]['notifyat']) : $alarm['notifyat'];
                 if ($notifyat <= $time) {
                     $alarms[] = $alarm;
                 }
             }
         }
 
         return $alarms;
     }
 
     /**
      * Feedback after showing/sending an alarm notification
      *
      * @see calendar_driver::dismiss_alarm()
      */
     public function dismiss_alarm($alarm_id, $snooze = 0)
     {
         $alarms_table = $this->rc->db->table_name('kolab_alarms', true);
 
         // delete old alarm entry
         $this->rc->db->query("DELETE FROM $alarms_table"
             . " WHERE `alarm_id` = ? AND `user_id` = ?",
             $alarm_id,
             $this->rc->user->ID
         );
 
         // set new notifyat time or unset if not snoozed
         $notifyat = $snooze > 0 ? date('Y-m-d H:i:s', time() + $snooze) : null;
 
         $query = $this->rc->db->query("INSERT INTO $alarms_table"
             . " (`alarm_id`, `user_id`, `dismissed`, `notifyat`)"
             . " VALUES (?, ?, ?, ?)",
             $alarm_id,
             $this->rc->user->ID,
             $snooze > 0 ? 0 : 1,
             $notifyat
         );
 
         return $this->rc->db->affected_rows($query);
     }
 
     /**
      * List attachments from the given event
      */
     public function list_attachments($event)
     {
         if (!($storage = $this->get_calendar($event['calendar']))) {
             return false;
         }
 
         $event = $storage->get_event($event['id']);
 
         return $event['attachments'];
     }
 
     /**
      * Get attachment properties
      */
     public function get_attachment($id, $event)
     {
         if (!($storage = $this->get_calendar($event['calendar']))) {
             return false;
         }
 
         // get old revision of event
         if (!empty($event['rev'])) {
             $event = $this->get_event_revison($event, $event['rev'], true);
         }
         else {
             $event = $storage->get_event($event['id']);
         }
 
         if ($event) {
             $attachments = isset($event['_attachments']) ? $event['_attachments'] : $event['attachments'];
             foreach ((array) $attachments as $att) {
                 if ($att['id'] == $id) {
                     return $att;
                 }
             }
         }
     }
 
     /**
      * Get attachment body
      * @see calendar_driver::get_attachment_body()
      */
     public function get_attachment_body($id, $event)
     {
         if (!($cal = $this->get_calendar($event['calendar']))) {
             return false;
         }
 
         // get old revision of event
         if (!empty($event['rev'])) {
             if (empty($this->bonnie_api)) {
                 return false;
             }
 
             $cid = substr($id, 4);
 
             // call Bonnie API and get the raw mime message
             list($uid, $mailbox, $msguid) = $this->_resolve_event_identity($event);
             if ($msg_raw = $this->bonnie_api->rawdata('event', $uid, $event['rev'], $mailbox, $msguid)) {
                 // parse the message and find the part with the matching content-id
                 $message = rcube_mime::parse_message($msg_raw);
                 foreach ((array) $message->parts as $part) {
                     if (!empty($part->headers['content-id']) && trim($part->headers['content-id'], '<>') == $cid) {
                         return $part->body;
                     }
                 }
             }
 
             return false;
         }
 
         return $cal->get_attachment_body($id, $event);
     }
 
     /**
      * Build a struct representing the given message reference
      *
      * @see calendar_driver::get_message_reference()
      */
     public function get_message_reference($uri_or_headers, $folder = null)
     {
         if (is_object($uri_or_headers)) {
             $uri_or_headers = kolab_storage_config::get_message_uri($uri_or_headers, $folder);
         }
 
         if (is_string($uri_or_headers)) {
             return kolab_storage_config::get_message_reference($uri_or_headers, 'event');
         }
 
         return false;
     }
 
     /**
      * List availabale categories
      * The default implementation reads them from config/user prefs
      */
     public function list_categories()
     {
         // FIXME: complete list with categories saved in config objects (KEP:12)
         return $this->rc->config->get('calendar_categories', $this->default_categories);
     }
 
     /**
      * Create instances of a recurring event
      *
      * @param array    Hash array with event properties
      * @param DateTime Start date of the recurrence window
      * @param DateTime End date of the recurrence window
      *
      * @return array List of recurring event instances
      */
     public function get_recurring_events($event, $start, $end = null)
     {
         // load the given event data into a libkolabxml container
         if (empty($event['_formatobj'])) {
             $event_xml = new kolab_format_event();
             $event_xml->set($event);
             $event['_formatobj'] = $event_xml;
         }
 
         $this->_read_calendars();
         $storage = reset($this->calendars);
 
         return $storage->get_recurring_events($event, $start, $end);
     }
 
     /**
      *
      */
     protected function get_recurrence_count($event, $dtstart)
     {
         // load the given event data into a libkolabxml container
         if (empty($event['_formatobj'])) {
             $event_xml = new kolab_format_event();
             $event_xml->set($event);
             $event['_formatobj'] = $event_xml;
         }
 
         // use libkolab to compute recurring events
         $recurrence = new kolab_date_recurrence($event['_formatobj']);
 
         $count = 0;
         while (($next_event = $recurrence->next_instance()) && $next_event['start'] <= $dtstart && $count < 1000) {
             $count++;
         }
 
         return $count;
     }
 
     /**
      * Fetch free/busy information from a person within the given range
      */
     public function get_freebusy_list($email, $start, $end)
     {
         if (empty($email)/* || $end < time()*/) {
             return false;
         }
 
         // map vcalendar fbtypes to internal values
         $fbtypemap = [
             'FREE'            => calendar::FREEBUSY_FREE,
             'BUSY-TENTATIVE'  => calendar::FREEBUSY_TENTATIVE,
             'X-OUT-OF-OFFICE' => calendar::FREEBUSY_OOF,
             'OOF'             => calendar::FREEBUSY_OOF
         ];
 
         // ask kolab server first
         try {
             $request_config = [
                 'store_body'       => true,
                 'follow_redirects' => true,
             ];
 
             $request  = libkolab::http_request($this->storage->get_freebusy_url($email), 'GET', $request_config);
             $response = $request->send();
 
             // authentication required
             if ($response->getStatus() == 401) {
                 $request->setAuth($this->rc->user->get_username(), $this->rc->decrypt($_SESSION['password']));
                 $response = $request->send();
             }
 
             if ($response->getStatus() == 200) {
                 $fbdata = $response->getBody();
             }
 
             unset($request, $response);
         }
         catch (Exception $e) {
             PEAR::raiseError("Error fetching free/busy information: " . $e->getMessage());
         }
 
         // get free-busy url from contacts
         if (empty($fbdata)) {
             $fburl = null;
             foreach ((array) $this->rc->config->get('autocomplete_addressbooks', 'sql') as $book) {
                 $abook = $this->rc->get_address_book($book);
 
                 if ($result = $abook->search(['email'], $email, true, true, true/*, 'freebusyurl'*/)) {
                     while ($contact = $result->iterate()) {
                         if (!empty($contact['freebusyurl'])) {
                             $fbdata = @file_get_contents($contact['freebusyurl']);
                             break;
                         }
                     }
                 }
 
                 if (!empty($fbdata)) {
                     break;
                 }
             }
         }
 
         // parse free-busy information using Horde classes
         if (!empty($fbdata)) {
             $ical = $this->cal->get_ical();
             $ical->import($fbdata);
             if ($fb = $ical->freebusy) {
                 $result = [];
                 foreach ($fb['periods'] as $tuple) {
                     list($from, $to, $type) = $tuple;
                     $result[] = [
                         $from->format('U'),
                         $to->format('U'),
                         isset($fbtypemap[$type]) ? $fbtypemap[$type] : calendar::FREEBUSY_BUSY
                     ];
                 }
 
                 // we take 'dummy' free-busy lists as "unknown"
                 if (empty($result) && !empty($fb['comment']) && stripos($fb['comment'], 'dummy')) {
                     return false;
                 }
 
                 // set period from $start till the begin of the free-busy information as 'unknown'
                 if (!empty($fb['start']) && ($fbstart = $fb['start']->format('U')) && $start < $fbstart) {
                     array_unshift($result, [$start, $fbstart, calendar::FREEBUSY_UNKNOWN]);
                 }
                 // pad period till $end with status 'unknown'
                 if (!empty($fb['end']) && ($fbend = $fb['end']->format('U')) && $fbend < $end) {
                     $result[] = [$fbend, $end, calendar::FREEBUSY_UNKNOWN];
                 }
 
                 return $result;
             }
         }
 
         return false;
     }
 
     /**
      * Handler to push folder triggers when sent from client.
      * Used to push free-busy changes asynchronously after updating an event
      */
     public function push_freebusy()
     {
         // make shure triggering completes
         set_time_limit(0);
         ignore_user_abort(true);
 
         $cal = rcube_utils::get_input_value('source', rcube_utils::INPUT_GPC);
         if (!($cal = $this->get_calendar($cal))) {
             return false;
         }
 
         // trigger updates on folder
         $trigger = $cal->storage->trigger();
         if (is_object($trigger) && is_a($trigger, 'PEAR_Error')) {
             rcube::raise_error([
                     'code' => 900, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Failed triggering folder. Error was " . $trigger->getMessage()
                 ],
                 true, false
             );
         }
 
         exit;
     }
 
     /**
      * Convert from driver format to external caledar app data
      */
     public static function to_rcube_event(&$record)
     {
         if (!is_array($record)) {
             return $record;
         }
 
         $record['id'] = $record['uid'];
 
         if (!empty($record['_instance'])) {
             $record['id'] .= '-' . $record['_instance'];
 
             if (empty($record['recurrence_id']) && !empty($record['recurrence'])) {
                 $record['recurrence_id'] = $record['uid'];
             }
         }
 
         // all-day events go from 12:00 - 13:00
         if ($record['start'] instanceof DateTimeInterface && $record['end'] <= $record['start'] && !empty($record['allday'])) {
             $record['end'] = clone $record['start'];
             $record['end']->add(new DateInterval('PT1H'));
         }
 
         // translate internal '_attachments' to external 'attachments' list
         if (!empty($record['_attachments'])) {
             foreach ($record['_attachments'] as $key => $attachment) {
                 if ($attachment !== false) {
                     if (empty($attachment['name'])) {
                         $attachment['name'] = $key;
                     }
 
                     unset($attachment['path'], $attachment['content']);
                     $attachments[] = $attachment;
                 }
             }
 
             $record['attachments'] = $attachments;
         }
 
         if (!empty($record['attendees'])) {
             foreach ((array) $record['attendees'] as $i => $attendee) {
                 if (isset($attendee['delegated-from']) && is_array($attendee['delegated-from'])) {
                     $record['attendees'][$i]['delegated-from'] = join(', ', $attendee['delegated-from']);
                 }
                 if (isset($attendee['delegated-to']) && is_array($attendee['delegated-to'])) {
                     $record['attendees'][$i]['delegated-to'] = join(', ', $attendee['delegated-to']);
                 }
             }
         }
 
         // Roundcube only supports one category assignment
         if (!empty($record['categories']) && is_array($record['categories'])) {
             $record['categories'] = $record['categories'][0];
         }
 
         // the cancelled flag transltes into status=CANCELLED
         if (!empty($record['cancelled'])) {
             $record['status'] = 'CANCELLED';
         }
 
         // The web client only supports DISPLAY type of alarms
         if (!empty($record['alarms'])) {
             $record['alarms'] = preg_replace('/:[A-Z]+$/', ':DISPLAY', $record['alarms']);
         }
 
         // remove empty recurrence array
         if (empty($record['recurrence'])) {
             unset($record['recurrence']);
         }
         // clean up exception data
         else if (!empty($record['recurrence']['EXCEPTIONS'])) {
             array_walk($record['recurrence']['EXCEPTIONS'], function(&$exception) {
                 unset($exception['_mailbox'], $exception['_msguid'],
                     $exception['_formatobj'], $exception['_attachments']
                 );
             });
         }
 
         unset($record['_mailbox'], $record['_msguid'], $record['_type'], $record['_size'],
             $record['_formatobj'], $record['_attachments'], $record['exceptions'], $record['x-custom']
         );
 
         return $record;
     }
 
     /**
      *
      */
     public static function from_rcube_event($event, $old = [])
     {
         kolab_format::merge_attachments($event, $old);
 
         return $event;
     }
 
 
     /**
      * Set CSS class according to the event's attendde partstat
      */
     public static function add_partstat_class($event, $partstats, $user = null)
     {
         // set classes according to PARTSTAT
         if (!empty($event['attendees'])) {
             $user_emails = libcalendaring::get_instance()->get_user_emails($user);
             $partstat = 'UNKNOWN';
 
             foreach ($event['attendees'] as $attendee) {
                 if (in_array($attendee['email'], $user_emails)) {
-                    $partstat = $attendee['status'];
+                    if (!empty($attendee['status'])) {
+                        $partstat = $attendee['status'];
+                    }
                     break;
                 }
             }
 
             if (in_array($partstat, $partstats)) {
                 $event['className'] = trim($event['className'] . ' fc-invitation-' . strtolower($partstat));
             }
         }
 
         return $event;
     }
 
     /**
      * Provide a list of revisions for the given event
      *
      * @param array $event Hash array with event properties
      *
      * @return array List of changes, each as a hash array
      * @see calendar_driver::get_event_changelog()
      */
     public function get_event_changelog($event)
     {
         if (empty($this->bonnie_api)) {
             return false;
         }
 
         list($uid, $mailbox, $msguid) = $this->_resolve_event_identity($event);
 
         $result = $this->bonnie_api->changelog('event', $uid, $mailbox, $msguid);
         if (is_array($result) && $result['uid'] == $uid) {
             return $result['changes'];
         }
 
         return false;
     }
 
     /**
      * Get a list of property changes beteen two revisions of an event
      *
      * @param array $event Hash array with event properties
      * @param mixed $rev1  Old Revision
      * @param mixed $rev2  New Revision
      *
      * @return array List of property changes, each as a hash array
      * @see calendar_driver::get_event_diff()
      */
     public function get_event_diff($event, $rev1, $rev2)
     {
         if (empty($this->bonnie_api)) {
             return false;
         }
 
         list($uid, $mailbox, $msguid) = $this->_resolve_event_identity($event);
 
         // get diff for the requested recurrence instance
         $instance_id = $event['id'] != $uid ? substr($event['id'], strlen($uid) + 1) : null;
 
         // call Bonnie API
         $result = $this->bonnie_api->diff('event', $uid, $rev1, $rev2, $mailbox, $msguid, $instance_id);
 
         if (is_array($result) && $result['uid'] == $uid) {
             $result['rev1'] = $rev1;
             $result['rev2'] = $rev2;
 
             $keymap = [
                 'dtstart'  => 'start',
                 'dtend'    => 'end',
                 'dstamp'   => 'changed',
                 'summary'  => 'title',
                 'alarm'    => 'alarms',
                 'attendee' => 'attendees',
                 'attach'   => 'attachments',
                 'rrule'    => 'recurrence',
                 'transparency' => 'free_busy',
                 'lastmodified-date' => 'changed',
             ];
 
             $prop_keymaps = [
                 'attachments' => ['fmttype' => 'mimetype', 'label' => 'name'],
                 'attendees'   => ['partstat' => 'status'],
             ];
 
             $special_changes = [];
 
             // map kolab event properties to keys the client expects
             array_walk($result['changes'], function(&$change, $i) use ($keymap, $prop_keymaps, $special_changes) {
                 if (array_key_exists($change['property'], $keymap)) {
                     $change['property'] = $keymap[$change['property']];
                 }
                 // translate free_busy values
                 if ($change['property'] == 'free_busy') {
                     $change['old'] = !empty($old['old']) ? 'free' : 'busy';
                     $change['new'] = !empty($old['new']) ? 'free' : 'busy';
                 }
 
                 // map alarms trigger value
                 if ($change['property'] == 'alarms') {
                     if (!empty($change['old']['trigger'])) {
                         $change['old']['trigger'] = $change['old']['trigger']['value'];
                     }
                     if (!empty($change['new']['trigger'])) {
                         $change['new']['trigger'] = $change['new']['trigger']['value'];
                     }
                 }
 
                 // make all property keys uppercase
                 if ($change['property'] == 'recurrence') {
                     $special_changes['recurrence'] = $i;
                     foreach (['old', 'new'] as $m) {
                         if (!empty($change[$m])) {
                             $props = [];
                             foreach ($change[$m] as $k => $v) {
                                 $props[strtoupper($k)] = $v;
                             }
                             $change[$m] = $props;
                         }
                     }
                 }
 
                 // map property keys names
                 if (!empty($prop_keymaps[$change['property']])) {
                     foreach ($prop_keymaps[$change['property']] as $k => $dest) {
                         if (!empty($change['old']) && array_key_exists($k, $change['old'])) {
                             $change['old'][$dest] = $change['old'][$k];
                             unset($change['old'][$k]);
                         }
                         if (!empty($change['new']) && array_key_exists($k, $change['new'])) {
                             $change['new'][$dest] = $change['new'][$k];
                             unset($change['new'][$k]);
                         }
                     }
                 }
 
                 if ($change['property'] == 'exdate') {
                     $special_changes['exdate'] = $i;
                 }
                 else if ($change['property'] == 'rdate') {
                     $special_changes['rdate'] = $i;
                 }
             });
 
             // merge some recurrence changes
             foreach (['exdate', 'rdate'] as $prop) {
                 if (array_key_exists($prop, $special_changes)) {
                     $exdate = $result['changes'][$special_changes[$prop]];
                     if (array_key_exists('recurrence', $special_changes)) {
                         $recurrence = &$result['changes'][$special_changes['recurrence']];
                     }
                     else {
                         $i = count($result['changes']);
                         $result['changes'][$i] = ['property' => 'recurrence', 'old' => [], 'new' => []];
                         $recurrence = &$result['changes'][$i]['recurrence'];
                     }
                     $key = strtoupper($prop);
                     $recurrence['old'][$key] = $exdate['old'];
                     $recurrence['new'][$key] = $exdate['new'];
                     unset($result['changes'][$special_changes[$prop]]);
                 }
             }
 
             return $result;
         }
 
         return false;
     }
 
     /**
      * Return full data of a specific revision of an event
      *
      * @param array Hash array with event properties
      * @param mixed $rev Revision number
      *
      * @return array Event object as hash array
      * @see calendar_driver::get_event_revison()
      */
     public function get_event_revison($event, $rev, $internal = false)
     {
         if (empty($this->bonnie_api)) {
             return false;
         }
 
         $eventid = $event['id'];
         $calid   = $event['calendar'];
 
         list($uid, $mailbox, $msguid) = $this->_resolve_event_identity($event);
 
         // call Bonnie API
         $result = $this->bonnie_api->get('event', $uid, $rev, $mailbox, $msguid);
         if (is_array($result) && $result['uid'] == $uid && !empty($result['xml'])) {
             $format = kolab_format::factory('event');
             $format->load($result['xml']);
             $event = $format->to_array();
             $format->get_attachments($event, true);
 
             // get the right instance from a recurring event
             if ($eventid != $event['uid']) {
                 $instance_id = substr($eventid, strlen($event['uid']) + 1);
 
                 // check for recurrence exception first
                 if ($instance = $format->get_instance($instance_id)) {
                     $event = $instance;
                 }
                 else {
                     // not a exception, compute recurrence...
                     $event['_formatobj'] = $format;
                     $recurrence_date = rcube_utils::anytodatetime($instance_id, $event['start']->getTimezone());
                     foreach ($this->get_recurring_events($event, $event['start'], $recurrence_date) as $instance) {
                         if ($instance['id'] == $eventid) {
                             $event = $instance;
                             break;
                         }
                     }
                 }
             }
 
             if ($format->is_valid()) {
                 $event['calendar'] = $calid;
                 $event['rev']      = $result['rev'];
 
                 return $internal ? $event : self::to_rcube_event($event);
             }
         }
 
         return false;
     }
 
     /**
      * Command the backend to restore a certain revision of an event.
      * This shall replace the current event with an older version.
      *
      * @param mixed $event UID string or hash array with event properties:
      *              id: Event identifier
      *        calendar: Calendar identifier
      * @param mixed $rev   Revision number
      *
      * @return bool True on success, False on failure
      */
     public function restore_event_revision($event, $rev)
     {
         if (empty($this->bonnie_api)) {
             return false;
         }
 
         list($uid, $mailbox, $msguid) = $this->_resolve_event_identity($event);
 
         $calendar = $this->get_calendar($event['calendar']);
         $success  = false;
 
         if ($calendar && $calendar->storage && $calendar->editable) {
             if ($raw_msg = $this->bonnie_api->rawdata('event', $uid, $rev, $mailbox)) {
                 $imap = $this->rc->get_storage();
 
                 // insert $raw_msg as new message
                 if ($imap->save_message($calendar->storage->name, $raw_msg, null, false)) {
                     $success = true;
 
                     // delete old revision from imap and cache
                     $imap->delete_message($msguid, $calendar->storage->name);
                     $calendar->storage->cache->set($msguid, false);
                 }
             }
         }
 
         return $success;
     }
 
     /**
      * Helper method to resolved the given event identifier into uid and folder
      *
      * @return array (uid,folder,msguid) tuple
      */
     protected function _resolve_event_identity($event)
     {
         $mailbox = $msguid = null;
 
         if (is_array($event)) {
             $uid = !empty($event['uid']) ? $event['uid'] : $event['id'];
 
             if (($cal = $this->get_calendar($event['calendar'])) && !($cal instanceof kolab_invitation_calendar)) {
                 $mailbox = $cal->get_mailbox_id();
 
                 // get event object from storage in order to get the real object uid an msguid
                 if ($ev = $cal->get_event($event['id'])) {
                     $msguid = $ev['_msguid'];
                     $uid = $ev['uid'];
                 }
             }
         }
         else {
             $uid = $event;
 
             // get event object from storage in order to get the real object uid an msguid
             if ($ev = $this->get_event($event)) {
                 $mailbox = $ev['_mailbox'];
                 $msguid  = $ev['_msguid'];
                 $uid     = $ev['uid'];
             }
         }
 
         return array($uid, $mailbox, $msguid);
     }
 
     /**
      * Callback function to produce driver-specific calendar create/edit form
      *
      * @param string Request action 'form-edit|form-new'
      * @param array  Calendar properties (e.g. id, color)
      * @param array  Edit form fields
      *
      * @return string HTML content of the form
      */
     public function calendar_form($action, $calendar, $formfields)
     {
         $special_calendars = [
             self::BIRTHDAY_CALENDAR_ID,
             self::INVITATIONS_CALENDAR_PENDING,
             self::INVITATIONS_CALENDAR_DECLINED
         ];
 
         // show default dialog for birthday calendar
         if (in_array($calendar['id'], $special_calendars)) {
             if ($calendar['id'] != self::BIRTHDAY_CALENDAR_ID) {
                 unset($formfields['showalarms']);
             }
 
             // General tab
             $form['props'] = [
                 'name'   => $this->rc->gettext('properties'),
                 'fields' => $formfields,
             ];
 
             return kolab_utils::folder_form($form, '', 'calendar');
         }
 
         $this->_read_calendars();
 
         if (!empty($calendar['id']) && ($cal = $this->calendars[$calendar['id']])) {
             $folder = $cal->get_realname(); // UTF7
             $color  = $cal->get_color();
         }
         else {
             $folder = '';
             $color  = '';
         }
 
         $hidden_fields[] = ['name' => 'oldname', 'value' => $folder];
 
         $storage = $this->rc->get_storage();
         $delim   = $storage->get_hierarchy_delimiter();
         $form    = [];
 
         if (strlen($folder)) {
             $path_imap = explode($delim, $folder);
             array_pop($path_imap);  // pop off name part
             $path_imap = implode($delim, $path_imap);
 
             $options = $storage->folder_info($folder);
         }
         else {
             $path_imap = '';
         }
 
         // General tab
         $form['props'] = [
             'name'   => $this->rc->gettext('properties'),
             'fields' => [],
         ];
 
         $protected = !empty($options) && (!empty($options['norename']) || !empty($options['protected']));
         // Disable folder name input
         if ($protected) {
             $input_name = new html_hiddenfield(['name' => 'name', 'id' => 'calendar-name']);
             $formfields['name']['value'] = $this->storage->object_name($folder)
                 . $input_name->show($folder);
         }
 
         // calendar name (default field)
         $form['props']['fields']['location'] = $formfields['name'];
 
         if ($protected) {
             // prevent user from moving folder
             $hidden_fields[] = ['name' => 'parent', 'value' => $path_imap];
         }
         else {
             $select = $this->storage->folder_selector('event', ['name' => 'parent', 'id' => 'calendar-parent'], $folder);
 
             $form['props']['fields']['path'] = [
                 'id'    => 'calendar-parent',
                 'label' => $this->cal->gettext('parentcalendar'),
                 'value' => $select->show(strlen($folder) ? $path_imap : ''),
             ];
         }
 
         // calendar color (default field)
         $form['props']['fields']['color']  = $formfields['color'];
         $form['props']['fields']['alarms'] = $formfields['showalarms'];
 
         return kolab_utils::folder_form($form, $folder, 'calendar', $hidden_fields);
     }
 
     /**
      * Handler for user_delete plugin hook
      */
     public function user_delete($args)
     {
         $db = $this->rc->get_dbh();
         foreach (['kolab_alarms', 'itipinvitations'] as $table) {
             $db->query("DELETE FROM " . $this->rc->db->table_name($table, true)
                 . " WHERE `user_id` = ?", $args['user']->ID);
         }
     }
 }
diff --git a/plugins/calendar/lib/calendar_itip.php b/plugins/calendar/lib/calendar_itip.php
index 4f7f382f..4940fc32 100644
--- a/plugins/calendar/lib/calendar_itip.php
+++ b/plugins/calendar/lib/calendar_itip.php
@@ -1,258 +1,258 @@
 <?php
 
-require_once realpath(__DIR__ . '/../../libcalendaring/lib/libcalendaring_itip.php');
-
 /**
  * iTIP functions for the Calendar plugin
  *
  * Class providing functionality to manage iTIP invitations
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  * @package @package_name@
  *
  * Copyright (C) 2011, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 class calendar_itip extends libcalendaring_itip
 {
+    protected $db_itipinvitations;
+
     /**
      * Constructor to set text domain to calendar
      */
     function __construct($plugin, $domain = 'calendar')
     {
         parent::__construct($plugin, $domain);
 
         $this->db_itipinvitations = $this->rc->db->table_name('itipinvitations', true);
     }
 
     /**
      * Handler for calendar/itip-status requests
      */
     public function get_itip_status($event, $existing = null)
     {
         $status = parent::get_itip_status($event, $existing);
 
         // don't ask for deleting events when declining
         if ($this->rc->config->get('kolab_invitation_calendars')) {
             $status['saved'] = false;
         }
 
         return $status;
     }
 
     /**
      * Find invitation record by token
      *
      * @param string $token Invitation token
      *
      * @return mixed Invitation record as hash array or False if not found
      */
     public function get_invitation($token)
     {
         if ($parts = $this->decode_token($token)) {
             $result = $this->rc->db->query("SELECT * FROM $this->db_itipinvitations WHERE `token` = ?", $parts['base']);
             if ($result && ($rec = $this->rc->db->fetch_assoc($result))) {
                 $rec['event']    = unserialize($rec['event']);
                 $rec['attendee'] = $parts['attendee'];
 
                 return $rec;
             }
         }
 
         return false;
     }
 
     /**
      * Update the attendee status of the given invitation record
      *
      * @param array  $invitation Invitation record as fetched with calendar_itip::get_invitation()
      * @param string $email      Attendee email address
      * @param string $newstatus  New attendee status
      */
     public function update_invitation($invitation, $email, $newstatus)
     {
         if (is_string($invitation)) {
             $invitation = $this->get_invitation($invitation);
         }
 
         if (!empty($invitation['token']) && !empty($invitation['event'])) {
             // update attendee record in event data
             foreach ($invitation['event']['attendees'] as $i => $attendee) {
                 if ($attendee['role'] == 'ORGANIZER') {
                     $organizer = $attendee;
                 }
                 else if ($attendee['email'] == $email) {
                     // nothing to be done here
                     if ($attendee['status'] == $newstatus) {
                         return true;
                     }
 
                     $invitation['event']['attendees'][$i]['status'] = $newstatus;
                     $this->sender = $attendee;
                 }
             }
 
             $invitation['event']['changed'] = new DateTime();
 
             // send iTIP REPLY message to organizer
             if (!empty($organizer)) {
                 $status = strtolower($newstatus);
                 if ($this->send_itip_message($invitation['event'], 'REPLY', $organizer, 'itipsubject' . $status, 'itipmailbody' . $status)) {
                     $mailto = !empty($organizer['name']) ? $organizer['name'] : $organizer['email'];
                     $message = $this->plugin->gettext([
                             'name' => 'sentresponseto',
                             'vars' => ['mailto' => $mailto]
                     ]);
                     $this->rc->output->command('display_message', $message, 'confirmation');
                 }
                 else {
                     $this->rc->output->command('display_message', $this->plugin->gettext('itipresponseerror'), 'error');
                 }
             }
 
             // update record in DB
             $query = $this->rc->db->query(
                 "UPDATE $this->db_itipinvitations SET `event` = ? WHERE `token` = ?",
                 self::serialize_event($invitation['event']),
                 $invitation['token']
             );
 
             if ($this->rc->db->affected_rows($query)) {
                 return true;
             }
         }
 
         return false;
     }
 
     /**
      * Create iTIP invitation token for later replies via URL
      *
      * @param array  $event    Hash array with event properties
      * @param string $attendee Attendee email address
      *
      * @return string Invitation token
      */
     public function store_invitation($event, $attendee)
     {
         static $stored = [];
 
         if (empty($event['uid']) || !$attendee) {
             return false;
         }
 
         // generate token for this invitation
         $token = $this->generate_token($event, $attendee);
         $base = substr($token, 0, 40);
 
         // already stored this
         if (!empty($stored[$base])) {
             return $token;
         }
 
         // delete old entry
         $this->rc->db->query("DELETE FROM $this->db_itipinvitations WHERE `token` = ?", $base);
 
         $event_uid = $event['uid'] . (!empty($event['_instance']) ? '-' . $event['_instance'] : '');
 
         $query = $this->rc->db->query(
             "INSERT INTO $this->db_itipinvitations"
             . " (`token`, `event_uid`, `user_id`, `event`, `expires`)"
             . " VALUES(?, ?, ?, ?, ?)",
             $base,
             $event_uid,
             $this->rc->user->ID,
             self::serialize_event($event),
             date('Y-m-d H:i:s', $event['end']->format('U') + 86400 * 2)
         );
 
         if ($this->rc->db->affected_rows($query)) {
             $stored[$base] = 1;
             return $token;
         }
 
         return false;
     }
 
     /**
      * Mark invitations for the given event as cancelled
      *
      * @param array $event Hash array with event properties
      */
     public function cancel_itip_invitation($event)
     {
         $event_uid = $event['uid'] . (!empty($event['_instance']) ? '-' . $event['_instance'] : '');
 
         // flag invitation record as cancelled
         $this->rc->db->query(
             "UPDATE $this->db_itipinvitations SET `cancelled` = 1"
             . " WHERE `event_uid` = ? AND `user_id` = ?",
            $event_uid,
            $this->rc->user->ID
         );
     }
 
     /**
      * Generate an invitation request token for the given event and attendee
      *
      * @param array  $event    Event hash array
      * @param string $attendee Attendee email address
      */
     public function generate_token($event, $attendee)
     {
         $event_uid = $event['uid'] . (!empty($event['_instance']) ? '-' . $event['_instance'] : '');
         $base = sha1($event_uid . ';' . $this->rc->user->ID);
         $mail = base64_encode($attendee);
         $hash = substr(md5($base . $mail . $this->rc->config->get('des_key')), 0, 6);
 
         return "$base.$mail.$hash";
     }
 
     /**
      * Decode the given iTIP request token and return its parts
      *
      * @param string $token Request token to decode
      *
      * @return mixed Hash array with parts or False if invalid
      */
     public function decode_token($token)
     {
         list($base, $mail, $hash) = explode('.', $token);
 
         // validate and return parts
         if ($mail && $hash && $hash == substr(md5($base . $mail . $this->rc->config->get('des_key')), 0, 6)) {
             return ['base' => $base, 'attendee' => base64_decode($mail)];
         }
 
         return false;
     }
 
     /**
      * Helper method to serialize the given event for storing in invitations table
      */
     private static function serialize_event($event)
     {
         $ev = $event;
 
         if (!empty($ev['description'])) {
             $ev['description'] = abbreviate_string($ev['description'], 100);
         }
 
         unset($ev['attachments']);
 
         return serialize($ev);
     }
 }
diff --git a/plugins/kolab_addressbook/drivers/carddav/carddav_contacts.php b/plugins/kolab_addressbook/drivers/carddav/carddav_contacts.php
index 9ec2d117..b815064c 100644
--- a/plugins/kolab_addressbook/drivers/carddav/carddav_contacts.php
+++ b/plugins/kolab_addressbook/drivers/carddav/carddav_contacts.php
@@ -1,1269 +1,1271 @@
 <?php
 
 /**
  * Backend class for a custom address book using CardDAV service.
  *
  * This part of the Roundcube+Kolab integration and connects the
  * rcube_addressbook interface with the kolab_storage_dav wrapper from libkolab
  *
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  * @author Aleksander Machniak <machniak@apheleia-it.chm>
  *
  * Copyright (C) 2011-2022, Kolab Systems AG <contact@apheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  *
  * @see rcube_addressbook
  */
 class carddav_contacts extends rcube_addressbook
 {
     public $primary_key = 'ID';
     public $rights   = 'lrs';
     public $readonly = true;
     public $undelete = false;
     public $groups   = true;
 
     public $coltypes = [
         'name'         => ['limit' => 1],
         'firstname'    => ['limit' => 1],
         'surname'      => ['limit' => 1],
         'middlename'   => ['limit' => 1],
         'prefix'       => ['limit' => 1],
         'suffix'       => ['limit' => 1],
         'nickname'     => ['limit' => 1],
         'jobtitle'     => ['limit' => 1],
         'organization' => ['limit' => 1],
         'department'   => ['limit' => 1],
         'email'        => ['subtypes' => ['home','work','other']],
         'phone'        => [],
         'address'      => ['subtypes' => ['home','work','office']],
         'website'      => ['subtypes' => ['homepage','blog']],
         'im'           => ['subtypes' => null],
         'gender'       => ['limit' => 1],
         'birthday'     => ['limit' => 1],
         'anniversary'  => ['limit' => 1],
         'manager'      => ['limit' => null],
         'assistant'    => ['limit' => null],
         'spouse'       => ['limit' => 1],
         'notes'        => ['limit' => 1],
         'photo'        => ['limit' => 1],
     ];
 
     public $vcard_map = [
     //    'profession'     => 'X-PROFESSION',
     //    'officelocation' => 'X-OFFICE-LOCATION',
     //    'initials'       => 'X-INITIALS',
     //    'children'       => 'X-CHILDREN',
     //    'freebusyurl'    => 'X-FREEBUSY-URL',
     //    'pgppublickey'   => 'KEY',
         'uid'            => 'UID',
     ];
 
     /**
      * List of date type fields
      */
     public $date_cols = ['birthday', 'anniversary'];
 
     public $fulltext_cols  = ['name', 'firstname', 'surname', 'middlename', 'email'];
 
     private $gid;
     private $storage;
     private $dataset;
     private $sortindex;
     private $contacts;
     private $distlists;
     private $groupmembers;
     private $filter;
     private $result;
     private $namespace;
     private $action;
 
     // list of fields used for searching in "All fields" mode
     private $search_fields = [
         'name',
         'firstname',
         'surname',
         'middlename',
         'prefix',
         'suffix',
         'nickname',
         'jobtitle',
         'organization',
         'department',
         'email',
         'phone',
         'address',
 //        'profession',
         'manager',
         'assistant',
         'spouse',
 //        'children',
         'notes',
     ];
 
 
     /**
      * Object constructor
      */
     public function __construct($dav_folder = null)
     {
         $this->storage = $dav_folder;
         $this->ready   = !empty($this->storage);
 
         // Set readonly and rights flags according to folder permissions
         if ($this->ready) {
             if ($this->storage->get_owner() == $_SESSION['username']) {
                 $this->readonly = false;
                 $this->rights = 'lrswikxtea';
             }
             else {
                 $rights = $this->storage->get_myrights();
                 if ($rights && !PEAR::isError($rights)) {
                     $this->rights = $rights;
                     if (strpos($rights, 'i') !== false && strpos($rights, 't') !== false) {
                         $this->readonly = false;
                     }
                 }
             }
         }
 
         $this->action = rcube::get_instance()->action;
     }
 
     /**
      * Getter for the address book name to be displayed
      *
      * @return string Name of this address book
      */
     public function get_name()
     {
         return $this->storage->get_name();
     }
 
     /**
      * Wrapper for kolab_storage_folder::get_foldername()
      */
     public function get_foldername()
     {
         return $this->storage->get_foldername();
     }
 
     /**
      * Getter for the folder name
      *
      * @return string Name of the folder
      */
     public function get_realname()
     {
         return $this->get_name();
     }
 
     /**
      * Getter for the name of the namespace to which the IMAP folder belongs
      *
      * @return string Name of the namespace (personal, other, shared)
      */
     public function get_namespace()
     {
         if ($this->namespace === null && $this->ready) {
             $this->namespace = $this->storage->get_namespace();
         }
 
         return $this->namespace;
     }
 
     /**
      * Getter for parent folder path
      *
      * @return string Full path to parent folder
      */
     public function get_parent()
     {
         return $this->storage->get_parent();
     }
 
     /**
      * Check subscription status of this folder
      *
      * @return boolean True if subscribed, false if not
      */
     public function is_subscribed()
     {
         return true;
     }
 
     /**
      * Compose an URL for CardDAV access to this address book (if configured)
      */
     public function get_carddav_url()
     {
 /*
         $rcmail = rcmail::get_instance();
         if ($template = $rcmail->config->get('kolab_addressbook_carddav_url', null)) {
             return strtr($template, [
                     '%h' => $_SERVER['HTTP_HOST'],
                     '%u' => urlencode($rcmail->get_user_name()),
                     '%i' => urlencode($this->storage->get_uid()),
                     '%n' => urlencode($this->imap_folder),
             ]);
         }
 */
         return false;
     }
 
     /**
      * Setter for the current group
      */
     public function set_group($gid)
     {
         $this->gid = $gid;
     }
 
     /**
      * Save a search string for future listings
      *
      * @param mixed Search params to use in listing method, obtained by get_search_set()
      */
     public function set_search_set($filter)
     {
         $this->filter = $filter;
     }
 
     /**
      * Getter for saved search properties
      *
      * @return mixed Search properties used by this class
      */
     public function get_search_set()
     {
         return $this->filter;
     }
 
     /**
      * Reset saved results and search parameters
      */
     public function reset()
     {
         $this->result = null;
         $this->filter = null;
     }
 
     /**
      * List all active contact groups of this source
      *
      * @param string Optional search string to match group name
      * @param int    Search mode. Sum of self::SEARCH_*
      *
      * @return array Indexed list of contact groups, each a hash array
      */
     function list_groups($search = null, $mode = 0)
     {
         $this->_fetch_groups();
         $groups = [];
 
         foreach ((array)$this->distlists as $group) {
             if (!$search || strstr(mb_strtolower($group['name']), mb_strtolower($search))) {
                 $groups[$group['ID']] = ['ID' => $group['ID'], 'name' => $group['name']];
             }
         }
 
         // sort groups by name
         uasort($groups, function($a, $b) { return strcoll($a['name'], $b['name']); });
 
         return array_values($groups);
     }
 
     /**
      * List the current set of contact records
      *
      * @param array List of cols to show
      * @param int   Only return this number of records, use negative values for tail
      * @param bool  True to skip the count query (select only)
      *
      * @return array Indexed list of contact records, each a hash array
      */
     public function list_records($cols = null, $subset = 0, $nocount = false)
     {
         $this->result = new rcube_result_set(0, ($this->list_page-1) * $this->page_size);
 
         $fetch_all = false;
         $fast_mode = !empty($cols) && is_array($cols);
 
         // list member of the selected group
         if ($this->gid) {
             $this->_fetch_groups();
 
             $this->sortindex = [];
             $this->contacts  = [];
             $local_sortindex = [];
             $uids            = [];
 
             // get members with email specified
             foreach ((array)$this->distlists[$this->gid]['member'] as $member) {
                 // skip member that don't match the search filter
                 if (!empty($this->filter['ids']) && array_search($member['ID'], $this->filter['ids']) === false) {
                     continue;
                 }
 
                 if (!empty($member['uid'])) {
                     $uids[] = $member['uid'];
                 }
                 else if (!empty($member['email'])) {
                     $this->contacts[$member['ID']] = $member;
                     $local_sortindex[$member['ID']] = $this->_sort_string($member);
                     $fetch_all = true;
                 }
             }
 
             // get members by UID
             if (!empty($uids)) {
                 $this->_fetch_contacts($query = [['uid', '=', $uids]], $fetch_all ? false : count($uids), $fast_mode);
                 $this->sortindex = array_merge($this->sortindex, $local_sortindex);
             }
         }
-        else if (is_array($this->filter['ids'])) {
+        else if (isset($this->filter['ids']) && is_array($this->filter['ids'])) {
             $ids = $this->filter['ids'];
             if (count($ids)) {
                 $uids = array_map([$this, 'id2uid'], $this->filter['ids']);
                 $this->_fetch_contacts($query = [['uid', '=', $uids]], count($ids), $fast_mode);
             }
         }
         else {
             $this->_fetch_contacts($query = 'contact', true, $fast_mode);
         }
 
         if ($fetch_all) {
             // sort results (index only)
             asort($this->sortindex, SORT_LOCALE_STRING);
             $ids = array_keys($this->sortindex);
 
             // fill contact data into the current result set
             $this->result->count = count($ids);
             $start_row = $subset < 0 ? $this->result->first + $this->page_size + $subset : $this->result->first;
             $last_row = min($subset != 0 ? $start_row + abs($subset) : $this->result->first + $this->page_size, $this->result->count);
 
             for ($i = $start_row; $i < $last_row; $i++) {
                 if (array_key_exists($i, $ids)) {
                     $idx = $ids[$i];
                     $this->result->add($this->contacts[$idx] ?: $this->_to_rcube_contact($this->dataset[$idx]));
                 }
             }
         }
         else if (!empty($this->dataset)) {
             // get all records count, skip the query if possible
             if (!isset($query) || count($this->dataset) < $this->page_size) {
                 $this->result->count = count($this->dataset) + $this->page_size * ($this->list_page - 1);
             }
             else {
                 $this->result->count = $this->storage->count($query);
             }
 
             $start_row = $subset < 0 ? $this->page_size + $subset : 0;
             $last_row  = min($subset != 0 ? $start_row + abs($subset) : $this->page_size, $this->result->count);
 
             for ($i = $start_row; $i < $last_row; $i++) {
                 $this->result->add($this->_to_rcube_contact($this->dataset[$i]));
             }
         }
 
         return $this->result;
     }
 
     /**
      * Search records
      *
      * @param mixed $fields   The field name of array of field names to search in
      * @param mixed $value    Search value (or array of values when $fields is array)
      * @param int   $mode     Matching mode:
      *                        0 - partial (*abc*),
      *                        1 - strict (=),
      *                        2 - prefix (abc*)
      *                        4 - include groups (if supported)
      * @param bool  $select   True if results are requested, False if count only
      * @param bool  $nocount  True to skip the count query (select only)
      * @param array $required List of fields that cannot be empty
      *
      * @return rcube_result_set List of contact records and 'count' value
      */
     public function search($fields, $value, $mode = 0, $select = true, $nocount = false, $required = [])
     {
         // search by ID
         if ($fields == $this->primary_key) {
             $ids    = !is_array($value) ? explode(',', $value) : $value;
             $result = new rcube_result_set();
 
             foreach ($ids as $id) {
                 if ($rec = $this->get_record($id, true)) {
                     $result->add($rec);
                     $result->count++;
                 }
             }
             return $result;
         }
         else if ($fields == '*') {
             $fields = $this->search_fields;
         }
 
         if (!is_array($fields)) {
             $fields = [$fields];
         }
         if (!is_array($required) && !empty($required)) {
             $required = [$required];
         }
 
         // advanced search
         if (is_array($value)) {
             $advanced = true;
             $value = array_map('mb_strtolower', $value);
         }
         else {
             $value = mb_strtolower($value);
         }
 
         $scount = count($fields);
         // build key name regexp
         $regexp = '/^(' . implode('|', $fields) . ')(?:.*)$/';
 
         // pass query to storage if only indexed cols are involved
         // NOTE: this is only some rough pre-filtering but probably includes false positives
         $squery = $this->_search_query($fields, $value, $mode);
 
         // add magic selector to select contacts with birthday dates only
         if (in_array('birthday', $required)) {
             $squery[] = ['tags', '=', 'x-has-birthday'];
         }
 
         $squery[] = ['type', '=', 'contact'];
 
         // get all/matching records
         $this->_fetch_contacts($squery);
 
         // save searching conditions
         $this->filter = ['fields' => $fields, 'value' => $value, 'mode' => $mode, 'ids' => []];
 
         // search by iterating over all records in dataset
         foreach ($this->dataset as $record) {
             $contact = $this->_to_rcube_contact($record);
             $id = $contact['ID'];
 
             // check if current contact has required values, otherwise skip it
             if ($required) {
                 foreach ($required as $f) {
                     // required field might be 'email', but contact might contain 'email:home'
                     if (!($v = rcube_addressbook::get_col_values($f, $contact, true)) || empty($v)) {
                         continue 2;
                     }
                 }
             }
 
             $found    = [];
             $contents = '';
 
             foreach (preg_grep($regexp, array_keys($contact)) as $col) {
                 $pos     = strpos($col, ':');
                 $colname = $pos ? substr($col, 0, $pos) : $col;
 
                 foreach ((array)$contact[$col] as $val) {
                     if ($advanced) {
                         $found[$colname] = $this->compare_search_value($colname, $val, $value[array_search($colname, $fields)], $mode);
                     }
                     else {
                         $contents .= ' ' . join(' ', (array)$val);
                     }
                 }
             }
 
             // compare matches
             if (($advanced && count($found) >= $scount) ||
                 (!$advanced && rcube_utils::words_match(mb_strtolower($contents), $value))) {
                 $this->filter['ids'][] = $id;
             }
         }
 
         // dummy result with contacts count
         if (!$select) {
             return new rcube_result_set(count($this->filter['ids']), ($this->list_page-1) * $this->page_size);
         }
 
         // list records (now limited by $this->filter)
         return $this->list_records();
     }
 
     /**
      * Refresh saved search results after data has changed
      */
     public function refresh_search()
     {
         if ($this->filter) {
             $this->search($this->filter['fields'], $this->filter['value'], $this->filter['mode']);
         }
 
         return $this->get_search_set();
     }
 
     /**
      * Count number of available contacts in database
      *
      * @return rcube_result_set Result set with values for 'count' and 'first'
      */
     public function count()
     {
         if ($this->gid) {
             $this->_fetch_groups();
             $count = count($this->distlists[$this->gid]['member']);
         }
         else if (is_array($this->filter['ids'])) {
             $count = count($this->filter['ids']);
         }
         else {
             $count = $this->storage->count('contact');
         }
 
         return new rcube_result_set($count, ($this->list_page-1) * $this->page_size);
     }
 
     /**
      * Return the last result set
      *
      * @return rcube_result_set Current result set or NULL if nothing selected yet
      */
     public function get_result()
     {
         return $this->result;
     }
 
     /**
      * Get a specific contact record
      *
      * @param mixed Record identifier(s)
      * @param bool  True to return record as associative array, otherwise a result set is returned
      *
      * @return mixed Result object with all record fields or False if not found
      */
     public function get_record($id, $assoc = false)
     {
         $rec = null;
         $uid = $this->id2uid($id);
         $rev = rcube_utils::get_input_value('_rev', rcube_utils::INPUT_GPC);
 
         if (strpos($uid, 'mailto:') === 0) {
             $this->_fetch_groups(true);
             $rec = $this->contacts[$id];
             $this->readonly = true;  // set source to read-only
         }
 /*
         else if (!empty($rev)) {
             $rcmail = rcube::get_instance();
             $plugin = $rcmail->plugins->get_plugin('kolab_addressbook');
             if ($plugin && ($object = $plugin->get_revision($id, kolab_storage::id_encode($this->imap_folder), $rev))) {
                 $rec = $this->_to_rcube_contact($object);
                 $rec['rev'] = $rev;
             }
             $this->readonly = true;  // set source to read-only
         }
 */
         else if ($object = $this->storage->get_object($uid)) {
             $rec = $this->_to_rcube_contact($object);
         }
 
         if ($rec) {
             $this->result = new rcube_result_set(1);
             $this->result->add($rec);
             return $assoc ? $rec : $this->result;
         }
 
         return false;
     }
 
     /**
      * Get group assignments of a specific contact record
      *
      * @param mixed Record identifier
      *
      * @return array List of assigned groups as ID=>Name pairs
      */
     public function get_record_groups($id)
     {
         $out = [];
         $this->_fetch_groups();
 
         if (!empty($this->groupmembers[$id])) {
             foreach ((array) $this->groupmembers[$id] as $gid) {
                 if (!empty($this->distlists[$gid])) {
                     $group = $this->distlists[$gid];
                     $out[$gid] = $group['name'];
                 }
             }
         }
 
         return $out;
     }
 
     /**
      * Create a new contact record
      *
      * @param array Associative array with save data
      *  Keys:   Field name with optional section in the form FIELD:SECTION
      *  Values: Field value. Can be either a string or an array of strings for multiple values
      * @param bool  True to check for duplicates first
      *
      * @return mixed The created record ID on success, False on error
      */
     public function insert($save_data, $check = false)
     {
         if (!is_array($save_data)) {
             return false;
         }
 
         $insert_id = $existing = false;
 
         // check for existing records by e-mail comparison
         if ($check) {
             foreach ($this->get_col_values('email', $save_data, true) as $email) {
                 if (($res = $this->search('email', $email, true, false)) && $res->count) {
                     $existing = true;
                     break;
                 }
             }
         }
 
         if (!$existing) {
             // Unset contact ID (e.g. when copying/moving from another addressbook)
             unset($save_data['ID'], $save_data['uid'], $save_data['_type']);
 
             // generate new Kolab contact item
             $object = $this->_from_rcube_contact($save_data);
             $saved  = $this->storage->save($object, 'contact');
 
             if (!$saved) {
                 rcube::raise_error([
                         'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                         'message' => "Error saving contact object to CardDAV server"
                     ],
                     true, false);
             }
             else {
                 $insert_id = $object['uid'];
             }
         }
 
         return $insert_id;
     }
 
     /**
      * Update a specific contact record
      *
      * @param mixed Record identifier
      * @param array Associative array with save data
      *  Keys:   Field name with optional section in the form FIELD:SECTION
      *  Values: Field value. Can be either a string or an array of strings for multiple values
      *
      * @return bool True on success, False on error
      */
     public function update($id, $save_data)
     {
         $updated = false;
         if ($old = $this->storage->get_object($this->id2uid($id))) {
             $object = $this->_from_rcube_contact($save_data, $old);
 
             if (!$this->storage->save($object, 'contact', $old['uid'])) {
                 rcube::raise_error([
                         'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                         'message' => "Error saving contact object to CardDAV server"
                     ],
                     true, false
                 );
             }
             else {
                 $updated = true;
 
                 // TODO: update data in groups this contact is member of
             }
         }
 
         return $updated;
     }
 
     /**
      * Mark one or more contact records as deleted
      *
      * @param array Record identifiers
      * @param bool  Remove record(s) irreversible (mark as deleted otherwise)
      *
      * @return int Number of records deleted
      */
     public function delete($ids, $force = true)
     {
         $this->_fetch_groups();
 
         if (!is_array($ids)) {
             $ids = explode(',', $ids);
         }
 
         $count = 0;
         foreach ($ids as $id) {
             if ($uid = $this->id2uid($id)) {
                 $is_mailto = strpos($uid, 'mailto:') === 0;
                 $deleted = $is_mailto || $this->storage->delete($uid, $force);
 
                 if (!$deleted) {
                     rcube::raise_error([
                             'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                             'message' => "Error deleting a contact object $uid from the CardDAV server"
                         ],
                         true, false
                     );
                 }
                 else {
                     // remove from distribution lists
                     foreach ((array) $this->groupmembers[$id] as $gid) {
                         if (!$is_mailto || $gid == $this->gid) {
                             $this->remove_from_group($gid, $id);
                         }
                     }
 
                     // clear internal cache
                     unset($this->groupmembers[$id]);
                     $count++;
                 }
             }
         }
 
         return $count;
     }
 
     /**
      * Undelete one or more contact records.
      * Only possible just after delete (see 2nd argument of delete() method).
      *
      * @param array Record identifiers
      *
      * @return int Number of records restored
      */
     public function undelete($ids)
     {
         if (!is_array($ids)) {
             $ids = explode(',', $ids);
         }
 
         $count = 0;
         foreach ($ids as $id) {
             $uid = $this->id2uid($id);
             if ($this->storage->undelete($uid)) {
                 $count++;
             }
             else {
                 rcube::raise_error([
                         'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                         'message' => "Error undeleting a contact object $uid from the CardDav server"
                     ],
                     true, false
                 );
             }
         }
 
         return $count;
     }
 
     /**
      * Remove all records from the database
      *
      * @param bool $with_groups Remove also groups
      */
     public function delete_all($with_groups = false)
     {
         if ($this->storage->delete_all()) {
             $this->contacts  = [];
             $this->sortindex = [];
             $this->dataset   = null;
             $this->result    = null;
         }
     }
 
     /**
      * Close connection to source
      * Called on script shutdown
      */
     public function close()
     {
         // NOP
     }
 
     /**
      * Create a contact group with the given name
      *
      * @param string The group name
      *
      * @return mixed False on error, array with record props in success
      */
     function create_group($name)
     {
         $this->_fetch_groups();
 
         $rcube = rcube::get_instance();
 
         $list = [
             'uid'    => strtoupper(md5(time() . uniqid(rand())) . '-' . substr(md5($rcube->user->get_username()), 0, 16)),
             'name'   => $name,
             'kind'   => 'group',
             'member' => [],
         ];
 
         $saved = $this->storage->save($list, 'contact');
 
         if (!$saved) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error saving a contact group to CardDAV server"
                 ],
                 true, false
             );
 
             return false;
         }
 
         $id = $this->uid2id($list['uid']);
 
         $this->distlists[$id] = $list;
 
         return ['id' => $id, 'name' => $name];
     }
 
     /**
      * Delete the given group and all linked group members
      *
      * @param string Group identifier
      *
      * @return bool True on success, false if no data was changed
      */
     function delete_group($gid)
     {
         $this->_fetch_groups();
 
         $list = $this->distlists[$gid];
 
         if (!$list) {
             return false;
         }
 
         $deleted = $this->storage->delete($list['uid']);
 
         if (!$deleted) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error deleting a contact group from the CardDAV server"
                 ],
                 true, false
             );
         }
 
         return $deleted;
     }
 
     /**
      * Rename a specific contact group
      *
      * @param string Group identifier
      * @param string New name to set for this group
      * @param string New group identifier (if changed, otherwise don't set)
      *
      * @return string|false New name on success, false if no data was changed
      */
     function rename_group($gid, $newname, &$newid)
     {
         $this->_fetch_groups();
 
         $list = $this->distlists[$gid];
 
         if (!$list) {
             return false;
         }
 
         if ($newname === $list['name']) {
             return $newname;
         }
 
         $list['name'] = $newname;
         $saved = $this->storage->save($list, 'contact', $list['uid']);
 
         if (!$saved) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error saving a contact group to CardDAV server"
                 ],
                 true, false
             );
 
             return false;
         }
 
         return $newname;
     }
 
     /**
      * Add the given contact records the a certain group
      *
      * @param string Group identifier
      * @param array  List of contact identifiers to be added
      *
      * @return int Number of contacts added
      */
     function add_to_group($gid, $ids)
     {
         if (!is_array($ids)) {
             $ids = explode(',', $ids);
         }
 
         $this->_fetch_groups(true);
 
         $list = $this->distlists[$gid];
 
         if (!$list) {
             return 0;
         }
 
         $added  = 0;
         $uids   = [];
         $exists = [];
 
         foreach ((array) $list['member'] as $member) {
             $exists[] = $member['ID'];
         }
 
         // substract existing assignments from list
         $ids = array_unique(array_diff($ids, $exists));
 
         // add mailto: members
         foreach ($ids as $contact_id) {
             $uid = $this->id2uid($contact_id);
             if (strpos($uid, 'mailto:') === 0 && ($contact = $this->contacts[$contact_id])) {
                 $list['member'][] = [
                     'email' => $contact['email'],
                     'name'  => $contact['name'],
                 ];
                 $this->groupmembers[$contact_id][] = $gid;
                 $added++;
             }
             else {
                 $uids[$uid] = $contact_id;
             }
         }
 
         // add members with UID
         if (!empty($uids)) {
             foreach ($uids as $uid => $contact_id) {
                 $list['member'][] = ['uid' => $uid];
                 $this->groupmembers[$contact_id][] = $gid;
                 $added++;
             }
         }
 
         if ($added) {
             $saved = $this->storage->save($list, 'contact', $list['uid']);
         }
         else {
             $saved = true;
         }
 
         if (!$saved) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error saving a contact-group to CardDAV server"
                 ],
                 true, false
             );
 
             $added = false;
             $this->set_error(self::ERROR_SAVING, 'errorsaving');
         }
         else {
             $this->distlists[$gid] = $list;
         }
 
         return $added;
     }
 
     /**
      * Remove the given contact records from a certain group
      *
      * @param string Group identifier
      * @param array  List of contact identifiers to be removed
      *
      * @return bool
      */
     function remove_from_group($gid, $ids)
     {
         $this->_fetch_groups();
 
         $list = $this->distlists[$gid];
 
         if (!$list) {
             return false;
         }
 
         if (!is_array($ids)) {
             $ids = explode(',', $ids);
         }
 
         $new_member = [];
         foreach ((array) $list['member'] as $member) {
             if (!in_array($member['ID'], $ids)) {
                 $new_member[] = $member;
             }
         }
 
         // write distribution list back to server
         $list['member'] = $new_member;
         $saved = $this->storage->save($list, 'contact', $list['uid']);
 
         if (!$saved) {
             rcube::raise_error([
                     'code' => 600, 'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Error saving a contact group to CardDAV server"
                 ],
                 true, false
             );
         }
         else {
             // remove group assigments in local cache
             foreach ($ids as $id) {
                 $j = array_search($gid, $this->groupmembers[$id]);
                 unset($this->groupmembers[$id][$j]);
             }
 
             $this->distlists[$gid] = $list;
 
             return true;
         }
 
         return false;
     }
 
     /**
      * Check the given data before saving.
      * If input not valid, the message to display can be fetched using get_error()
      *
      * @param array Associative array with contact data to save
      * @param bool  Attempt to fix/complete data automatically
      *
      * @return bool True if input is valid, False if not.
      */
     public function validate(&$save_data, $autofix = false)
     {
         // validate e-mail addresses
         $valid = parent::validate($save_data);
 
         // require at least one e-mail address if there's no name
         // (syntax check is already done)
         if ($valid) {
             if (!strlen($save_data['name'])
                 && !strlen($save_data['organization'])
                 && !array_filter($this->get_col_values('email', $save_data, true))
             ) {
                 $this->set_error('warning', 'kolab_addressbook.noemailnamewarning');
                 $valid = false;
             }
         }
 
         return $valid;
     }
 
     /**
      * Query storage layer and store records in private member var
      */
     private function _fetch_contacts($query = [], $limit = false, $fast_mode = false)
     {
         if (!isset($this->dataset) || !empty($query)) {
             if ($limit) {
                 $size = is_int($limit) && $limit < $this->page_size ? $limit : $this->page_size;
                 $this->storage->set_order_and_limit($this->_sort_columns(), $size, ($this->list_page-1) * $this->page_size);
             }
 
             $this->sortindex = [];
             $this->dataset   = $this->storage->select($query, $fast_mode);
 
             foreach ($this->dataset as $idx => $record) {
                 $contact = $this->_to_rcube_contact($record);
                 $this->sortindex[$idx] = $this->_sort_string($contact);
             }
         }
     }
 
     /**
      * Extract a string for sorting from the given contact record
      */
     private function _sort_string($rec)
     {
         $str = '';
 
         switch ($this->sort_col) {
         case 'name':
-            $str = $rec['name'] . $rec['prefix'];
+            $str = ($rec['name'] ?? '') . ($rec['prefix'] ?? '');
         case 'firstname':
-            $str .= $rec['firstname'] . $rec['middlename'] . $rec['surname'];
+            $str .= ($rec['firstname'] ?? '') . ($rec['middlename'] ?? '') . ($rec['surname'] ?? '');
             break;
 
         case 'surname':
-            $str = $rec['surname'] . $rec['firstname'] . $rec['middlename'];
+            $str = ($rec['surname'] ?? '') . ($rec['firstname'] ?? '') . ($rec['middlename'] ?? '');
             break;
 
         default:
-            $str = $rec[$this->sort_col];
+            $str = $rec[$this->sort_col] ?? '';
             break;
         }
 
-        $str .= is_array($rec['email']) ? $rec['email'][0] : $rec['email'];
+        if (!empty($rec['email'])) {
+            $str .= is_array($rec['email']) ? $rec['email'][0] : $rec['email'];
+        }
 
         return mb_strtolower($str);
     }
 
     /**
      * Return the cache table columns to order by
      */
     private function _sort_columns()
     {
         $sortcols = [];
 
         switch ($this->sort_col) {
         case 'name':
             $sortcols[] = 'name';
 
         case 'firstname':
             $sortcols[] = 'firstname';
             break;
 
         case 'surname':
             $sortcols[] = 'surname';
             break;
         }
 
         $sortcols[] = 'email';
         return $sortcols;
     }
 
     /**
      * Read contact groups from server
      */
     private function _fetch_groups($with_contacts = false)
     {
         if (!isset($this->distlists)) {
             $this->distlists = $this->groupmembers = [];
 
             // Set order (and LIMIT to skip the count(*) select)
             $this->storage->set_order_and_limit(['name'], 200, 0);
 
             foreach ($this->storage->select('group', true) as $record) {
                 $record['ID'] = $this->uid2id($record['uid']);
                 foreach ((array)$record['member'] as $i => $member) {
                     $mid = $this->uid2id($member['uid'] ? $member['uid'] : 'mailto:' . $member['email']);
                     $record['member'][$i]['ID'] = $mid;
                     $record['member'][$i]['readonly'] = empty($member['uid']);
                     $this->groupmembers[$mid][] = $record['ID'];
 
                     if ($with_contacts && empty($member['uid'])) {
                         $this->contacts[$mid] = $record['member'][$i];
                     }
                 }
 
                 $this->distlists[$record['ID']] = $record;
             }
 
             $this->storage->set_order_and_limit($this->_sort_columns(), null, 0);
         }
     }
 
     /**
      * Encode object UID into a safe identifier
      */
     public function uid2id($uid)
     {
         return rtrim(strtr(base64_encode($uid), '+/', '-_'), '=');
     }
 
     /**
      * Convert Roundcube object identifier back into the original UID
      */
     public function id2uid($id)
     {
         return base64_decode(str_pad(strtr($id, '-_', '+/'), strlen($id) % 4, '=', STR_PAD_RIGHT));
     }
 
     /**
      * Build SQL query for fulltext matches
      */
     private function _search_query($fields, $value, $mode)
     {
         $query = [];
         $cols  = [];
 
         $cols = array_intersect($fields, $this->fulltext_cols);
 
         if (count($cols)) {
             if ($mode & rcube_addressbook::SEARCH_STRICT) {
                 $prefix = '^'; $suffix = '$';
             }
             else if ($mode & rcube_addressbook::SEARCH_PREFIX) {
                 $prefix = '^'; $suffix = '';
             }
             else {
                 $prefix = ''; $suffix = '';
             }
 
             $search_string = is_array($value) ? join(' ', $value) : $value;
             foreach (rcube_utils::normalize_string($search_string, true) as $word) {
                 $query[] = ['words', 'LIKE', $prefix . $word . $suffix];
             }
         }
 
         return $query;
     }
 
     /**
      * Map fields from internal Kolab_Format to Roundcube contact format
      */
     private function _to_rcube_contact($record)
     {
         $record['ID'] = $this->uid2id($record['uid']);
 
         // remove empty fields
         $record = array_filter($record);
 
         // Set _type for proper icon on the list
         $record['_type'] = 'person';
 
         return $record;
     }
 
     /**
      * Map fields from Roundcube format to internal kolab_format_contact properties
      */
     private function _from_rcube_contact($contact, $old = [])
     {
         if (empty($contact['uid']) && !empty($contact['ID'])) {
             $contact['uid'] = $this->id2uid($contact['ID']);
         }
         else if (empty($contact['uid']) && !empty($old['uid'])) {
             $contact['uid'] = $old['uid'];
         }
         else if (empty($contact['uid'])) {
             $rcube = rcube::get_instance();
             $contact['uid'] = strtoupper(md5(time() . uniqid(rand())) . '-' . substr(md5($rcube->user->get_username()), 0, 16));
         }
 
         // When importing contacts 'vcard' data might be added, we don't need it (Bug #1711)
         unset($contact['vcard']);
 
         return $contact;
     }
 }
diff --git a/plugins/kolab_addressbook/kolab_addressbook.php b/plugins/kolab_addressbook/kolab_addressbook.php
index 4a60c755..8a6f0729 100644
--- a/plugins/kolab_addressbook/kolab_addressbook.php
+++ b/plugins/kolab_addressbook/kolab_addressbook.php
@@ -1,1141 +1,1142 @@
 <?php
 
 /**
  * Kolab address book
  *
  * Sample plugin to add a new address book source with data from Kolab storage
  * It provides also a possibilities to manage contact folders
  * (create/rename/delete/acl) directly in Addressbook UI.
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  * @author Aleksander Machniak <machniak@kolabsys.com>
  *
  * Copyright (C) 2011-2015, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_addressbook extends rcube_plugin
 {
     public $task = '?(?!logout).*';
 
     public $driver;
     public $bonnie_api = false;
 
     private $sources;
     private $rc;
     private $ui;
+    private $recurrent = false;
 
     const GLOBAL_FIRST = 0;
     const PERSONAL_FIRST = 1;
     const GLOBAL_ONLY = 2;
     const PERSONAL_ONLY = 3;
 
     /**
      * Startup method of a Roundcube plugin
      */
     public function init()
     {
         $this->rc = rcube::get_instance();
 
         // load required plugin
         $this->require_plugin('libkolab');
 
         $this->load_config();
 
         $driver       = $this->rc->config->get('kolab_addressbook_driver') ?: 'kolab';
         $driver_class = "{$driver}_contacts_driver";
 
         require_once dirname(__FILE__) . "/drivers/{$driver}/{$driver}_contacts_driver.php";
         require_once dirname(__FILE__) . "/drivers/{$driver}/{$driver}_contacts.php";
 
         $this->driver = new $driver_class($this);
 
         // register hooks
         $this->add_hook('addressbooks_list', array($this, 'address_sources'));
         $this->add_hook('addressbook_get', array($this, 'get_address_book'));
         $this->add_hook('config_get', array($this, 'config_get'));
 
         if ($this->rc->task == 'addressbook') {
             $this->add_texts('localization');
 
             if ($this->driver instanceof kolab_contacts_driver) {
                 $this->add_hook('contact_form', array($this, 'contact_form'));
                 $this->add_hook('contact_photo', array($this, 'contact_photo'));
             }
 
             $this->add_hook('template_object_directorylist', array($this, 'directorylist_html'));
 
             // Plugin actions
             $this->register_action('plugin.book', array($this, 'book_actions'));
             $this->register_action('plugin.book-save', array($this, 'book_save'));
             $this->register_action('plugin.book-search', array($this, 'book_search'));
             $this->register_action('plugin.book-subscribe', array($this, 'book_subscribe'));
 
             $this->register_action('plugin.contact-changelog', array($this, 'contact_changelog'));
             $this->register_action('plugin.contact-diff', array($this, 'contact_diff'));
             $this->register_action('plugin.contact-restore', array($this, 'contact_restore'));
 
             // get configuration for the Bonnie API
             $this->bonnie_api = libkolab::get_bonnie_api();
 
             // Load UI elements
             if ($this->api->output->type == 'html') {
                 require_once $this->home . '/lib/kolab_addressbook_ui.php';
                 $this->ui = new kolab_addressbook_ui($this);
 
                 if ($this->bonnie_api) {
                     $this->add_button(array(
                         'command'    => 'contact-history-dialog',
                         'class'      => 'history contact-history disabled',
                         'classact'   => 'history contact-history active',
                         'innerclass' => 'icon inner',
                         'label'      => 'kolab_addressbook.showhistory',
                         'type'       => 'link-menuitem'
                     ), 'contactmenu');
                 }
             }
         }
         else if ($this->rc->task == 'settings') {
             $this->add_texts('localization');
             $this->add_hook('preferences_list', array($this, 'prefs_list'));
             $this->add_hook('preferences_save', array($this, 'prefs_save'));
         }
 
         if ($this->driver instanceof kolab_contacts_driver) {
             $this->add_hook('folder_delete', array($this, 'prefs_folder_delete'));
             $this->add_hook('folder_rename', array($this, 'prefs_folder_rename'));
             $this->add_hook('folder_update', array($this, 'prefs_folder_update'));
         }
     }
 
     /**
      * Handler for the addressbooks_list hook.
      *
      * This will add all instances of available Kolab-based address books
      * to the list of address sources of Roundcube.
      * This will also hide some addressbooks according to kolab_addressbook_prio setting.
      *
      * @param array $p Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function address_sources($p)
     {
         $abook_prio = $this->addressbook_prio();
 
         // Disable all global address books
         // Assumes that all non-kolab_addressbook sources are global
         if ($abook_prio == self::PERSONAL_ONLY) {
             $p['sources'] = array();
         }
 
         $sources = array();
         foreach ($this->_list_sources() as $abook_id => $abook) {
             // register this address source
             $sources[$abook_id] = $this->driver->abook_prop($abook_id, $abook);
 
             // flag folders with 'i' right as writeable
             if ($this->rc->action == 'add' && strpos($abook->rights, 'i') !== false) {
                 $sources[$abook_id]['readonly'] = false;
             }
         }
 
         // Add personal address sources to the list
         if ($abook_prio == self::PERSONAL_FIRST) {
             // $p['sources'] = array_merge($sources, $p['sources']);
             // Don't use array_merge(), because if you have folders name
             // that resolve to numeric identifier it will break output array keys
             foreach ($p['sources'] as $idx => $value) {
                 $sources[$idx] = $value;
             }
             $p['sources'] = $sources;
         }
         else {
             // $p['sources'] = array_merge($p['sources'], $sources);
             foreach ($sources as $idx => $value) {
                 $p['sources'][$idx] = $value;
             }
         }
 
         return $p;
     }
 
     /**
      *
      */
     public function directorylist_html($args)
     {
         $out     = '';
         $spec    = '';
         $kolab   = '';
         $jsdata  = [];
         $sources = (array) $this->rc->get_address_sources();
 
         // list all non-kolab sources first (also exclude hidden sources), special folders will go last
         foreach ($sources  as $j => $source) {
             $id = strval(strlen($source['id']) ? $source['id'] : $j);
             if (!empty($source['kolab']) || !empty($source['hidden'])) {
                 continue;
             }
 
             // Roundcube >= 1.5, Collected Recipients and Trusted Senders sources will be listed at the end
             if ((defined('rcube_addressbook::TYPE_RECIPIENT') && $source['id'] == (string) rcube_addressbook::TYPE_RECIPIENT)
                 || (defined('rcube_addressbook::TYPE_TRUSTED_SENDER') && $source['id'] == (string) rcube_addressbook::TYPE_TRUSTED_SENDER)
             ) {
                 $spec .= $this->addressbook_list_item($id, $source, $jsdata) . '</li>';
             }
             else {
                 $out .= $this->addressbook_list_item($id, $source, $jsdata) . '</li>';
             }
         }
 
         // render a hierarchical list of kolab contact folders
         // TODO: Move this to the drivers
         if ($this->driver instanceof kolab_contacts_driver) {
             $folders = kolab_storage::sort_folders(kolab_storage::get_folders('contact'));
             kolab_storage::folder_hierarchy($folders, $tree);
             if ($tree && !empty($tree->children)) {
                 $kolab .= $this->folder_tree_html($tree, $sources, $jsdata);
             }
         }
         else {
             $filter = function($source) { return !empty($source['kolab']) && empty($source['hidden']); };
             foreach (array_filter($sources, $filter) as $j => $source) {
                 $id = strval(strlen($source['id']) ? $source['id'] : $j);
                 $kolab .= $this->addressbook_list_item($id, $source, $jsdata) . '</li>';
             }
         }
 
         $out .= $kolab . $spec;
 
-        $this->rc->output->set_env('contactgroups', array_filter($jsdata, function($src){ return $src['type'] == 'group'; }));
-        $this->rc->output->set_env('address_sources', array_filter($jsdata, function($src){ return $src['type'] != 'group'; }));
+        $this->rc->output->set_env('contactgroups', array_filter($jsdata, function($src){ return isset($src['type']) && $src['type'] == 'group'; }));
+        $this->rc->output->set_env('address_sources', array_filter($jsdata, function($src){ return !isset($src['type']) || $src['type'] != 'group'; }));
 
         $args['content'] = html::tag('ul', $args, $out, html::$common_attrib);
         return $args;
     }
 
     /**
      * Return html for a structured list <ul> for the folder tree
      */
     protected function folder_tree_html($node, $data, &$jsdata)
     {
         $out = '';
         foreach ($node->children as $folder) {
             $id = $folder->id;
             $source = $data[$id];
             $is_collapsed = strpos($this->rc->config->get('collapsed_abooks',''), '&'.rawurlencode($id).'&') !== false;
 
             if ($folder->virtual) {
                 $source = $this->driver->abook_prop($folder->id, $folder);
             }
             else if (empty($source)) {
                 $this->sources[$id] = new kolab_contacts($folder->name);
                 $source = $this->driver->abook_prop($id, $this->sources[$id]);
             }
 
             $content = $this->addressbook_list_item($id, $source, $jsdata);
 
             if (!empty($folder->children)) {
                 $child_html = $this->folder_tree_html($folder, $data, $jsdata);
 
                 // copy group items...
                 if (preg_match('!<ul[^>]*>(.*)</ul>\n*$!Ums', $content, $m)) {
                     $child_html = $m[1] . $child_html;
                     $content = substr($content, 0, -strlen($m[0]) - 1);
                 }
                 // ... and re-create the subtree
                 if (!empty($child_html)) {
                     $content .= html::tag('ul', array('class' => 'groups', 'style' => ($is_collapsed ? "display:none;" : null)), $child_html);
                 }
             }
 
             $out .= $content . '</li>';
         }
 
         return $out;
     }
 
     /**
      *
      */
     protected function addressbook_list_item($id, $source, &$jsdata, $search_mode = false)
     {
         $current = rcube_utils::get_input_value('_source', rcube_utils::INPUT_GPC);
 
-        if (!$source['virtual']) {
+        if (empty($source['virtual'])) {
             $jsdata[$id] = $source;
             $jsdata[$id]['name'] = html_entity_decode($source['name'], ENT_NOQUOTES, RCUBE_CHARSET);
         }
 
         // set class name(s)
         $classes = array('addressbook');
-        if ($source['group'])
+        if (!empty($source['group']))
             $classes[] = $source['group'];
         if ($current === $id)
             $classes[] = 'selected';
-        if ($source['readonly'])
+        if (!empty($source['readonly']))
             $classes[] = 'readonly';
-        if ($source['virtual'])
+        if (!empty($source['virtual']))
             $classes[] = 'virtual';
-        if ($source['class_name'])
+        if (!empty($source['class_name']))
             $classes[] = $source['class_name'];
 
         $name = !empty($source['listname']) ? $source['listname'] : (!empty($source['name']) ? $source['name'] : $id);
         $label_id = 'kabt:' . $id;
-        $inner = ($source['virtual'] ?
+        $inner = (!empty($source['virtual']) ?
             html::a(array('tabindex' => '0'), $name) :
             html::a(array(
                     'href' => $this->rc->url(array('_source' => $id)),
                     'rel' => $source['id'],
                     'id' => $label_id,
                     'onclick' => "return " . rcmail_output::JS_OBJECT_NAME.".command('list','" . rcube::JQ($id) . "',this)",
                 ), $name)
         );
 
         if ($this->driver instanceof kolab_contacts_driver && isset($source['subscribed'])) {
             $inner .= html::span(array(
                 'class' => 'subscribed',
                 'title' => $this->gettext('foldersubscribe'),
                 'role' => 'checkbox',
                 'aria-checked' => $source['subscribed'] ? 'true' : 'false',
             ), '');
         }
 
         // don't wrap in <li> but add a checkbox for search results listing
         if ($search_mode) {
             $jsdata[$id]['group'] = join(' ', $classes);
 
             if (!$source['virtual']) {
                 $inner .= html::tag('input', array(
                     'type' => 'checkbox',
                     'name' => '_source[]',
                     'value' => $id,
                     'checked' => false,
                     'aria-labelledby' => $label_id,
                 ));
             }
             return html::div(null, $inner);
         }
 
-        $out .= html::tag('li', array(
+        $out = html::tag('li', array(
                 'id' => 'rcmli' . rcube_utils::html_identifier($id, true),
                 'class' => join(' ', $classes), 
                 'noclose' => true,
             ),
-            html::div($source['subscribed'] ? 'subscribed' : null, $inner)
+            html::div(!empty($source['subscribed']) ? 'subscribed' : null, $inner)
         );
 
         $groupdata = array('out' => '', 'jsdata' => $jsdata, 'source' => $id);
         if ($source['groups']) {
             if (function_exists('rcmail_contact_groups')) {
                 $groupdata = rcmail_contact_groups($groupdata);
             }
             else {
                 // Roundcube >= 1.5
                 $groupdata = rcmail_action_contacts_index::contact_groups($groupdata);
             }
         }
 
         $jsdata = $groupdata['jsdata'];
         $out .= $groupdata['out'];
 
         return $out;
     }
 
     /**
      * Sets autocomplete_addressbooks option according to
      * kolab_addressbook_prio setting extending list of address sources
      * to be used for autocompletion.
      */
     public function config_get($args)
     {
         if ($args['name'] != 'autocomplete_addressbooks' || $this->recurrent) {
             return $args;
         }
 
         $abook_prio = $this->addressbook_prio();
 
         // Get the original setting, use temp flag to prevent from an infinite recursion
         $this->recurrent = true;
         $sources = $this->rc->config->get('autocomplete_addressbooks');
         $this->recurrent = false;
 
         // Disable all global address books
         // Assumes that all non-kolab_addressbook sources are global
         if ($abook_prio == self::PERSONAL_ONLY) {
             $sources = array();
         }
 
         if (!is_array($sources)) {
             $sources = array();
         }
 
         $kolab_sources = array();
         foreach (array_keys($this->_list_sources()) as $abook_id) {
             if (!in_array($abook_id, $sources))
                 $kolab_sources[] = $abook_id;
         }
 
         // Add personal address sources to the list
         if (!empty($kolab_sources)) {
             if ($abook_prio == self::PERSONAL_FIRST) {
                 $sources = array_merge($kolab_sources, $sources);
             }
             else {
                 $sources = array_merge($sources, $kolab_sources);
             }
         }
 
         $args['result'] = $sources;
 
         return $args;
     }
 
     /**
      * Getter for the rcube_addressbook instance
      *
      * @param array $p Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function get_address_book($p)
     {
         if ($p['id']) {
             if ($source = $this->driver->get_address_book($p['id'])) {
                 $p['instance'] = $source;
 
                 // flag source as writeable if 'i' right is given
                 if ($p['writeable'] && $this->rc->action == 'save' && strpos($p['instance']->rights, 'i') !== false) {
                     $p['instance']->readonly = false;
                 }
                 else if ($this->rc->action == 'delete' && strpos($p['instance']->rights, 't') !== false) {
                     $p['instance']->readonly = false;
                 }
             }
         }
 
         return $p;
     }
 
     /**
      * List addressbook sources list
      */
     private function _list_sources()
     {
         // already read sources
         if (isset($this->sources)) {
             return $this->sources;
         }
 
         $this->sources = [];
 
         $abook_prio = $this->addressbook_prio();
 
         // Personal address source(s) disabled?
         if ($abook_prio == kolab_addressbook::GLOBAL_ONLY) {
             return $this->sources;
         }
 
         $folders = $this->driver->list_folders();
 
         // get all folders that have "contact" type
         foreach ($folders as $id => $source) {
             $this->sources[$id] = $source;
         }
 
         return $this->sources;
     }
 
     /**
      * Plugin hook called before rendering the contact form or detail view
      *
      * @param array $p Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function contact_form($p)
     {
         // none of our business
         if (!is_object($GLOBALS['CONTACTS']) || !is_a($GLOBALS['CONTACTS'], 'kolab_contacts')) {
             return $p;
         }
 
         // extend the list of contact fields to be displayed in the 'personal' section
         if (is_array($p['form']['personal'])) {
             $p['form']['personal']['content']['profession']    = array('size' => 40);
             $p['form']['personal']['content']['children']      = array('size' => 40);
             $p['form']['personal']['content']['freebusyurl']   = array('size' => 40);
             $p['form']['personal']['content']['pgppublickey']  = array('size' => 70);
             $p['form']['personal']['content']['pkcs7publickey'] = array('size' => 70);
 
             // re-order fields according to the coltypes list
             $p['form']['contact']['content']  = $this->_sort_form_fields($p['form']['contact']['content'], $GLOBALS['CONTACTS']);
             $p['form']['personal']['content'] = $this->_sort_form_fields($p['form']['personal']['content'], $GLOBALS['CONTACTS']);
 
             /* define a separate section 'settings'
             $p['form']['settings'] = array(
                 'name'    => $this->gettext('settings'),
                 'content' => array(
                     'freebusyurl'  => array('size' => 40, 'visible' => true),
                     'pgppublickey' => array('size' => 70, 'visible' => true),
                     'pkcs7publickey' => array('size' => 70, 'visible' => false),
                 )
             );
             */
         }
 
         if ($this->bonnie_api && $this->rc->action == 'show' && empty($p['record']['rev'])) {
             $this->rc->output->set_env('kolab_audit_trail', true);
         }
 
         return $p;
     }
 
     /**
      * Plugin hook for the contact photo image
      */
     public function contact_photo($p)
     {
         // add photo data from old revision inline as data url
         if (!empty($p['record']['rev']) && !empty($p['data'])) {
             $p['url'] = 'data:image/gif;base64,' . base64_encode($p['data']);
         }
 
         return $p;
     }
 
     /**
      * Handler for contact audit trail changelog requests
      */
     public function contact_changelog()
     {
         if (empty($this->bonnie_api)) {
             return false;
         }
 
         $contact = rcube_utils::get_input_value('cid', rcube_utils::INPUT_POST, true);
         $source = rcube_utils::get_input_value('source', rcube_utils::INPUT_POST);
 
         list($uid, $mailbox, $msguid) = $this->_resolve_contact_identity($contact, $source);
 
         $result = $uid && $mailbox ? $this->bonnie_api->changelog('contact', $uid, $mailbox, $msguid) : null;
         if (is_array($result) && $result['uid'] == $uid) {
             if (is_array($result['changes'])) {
                 $rcmail = $this->rc;
                 $dtformat = $this->rc->config->get('date_format') . ' ' . $this->rc->config->get('time_format');
                 array_walk($result['changes'], function(&$change) use ($rcmail, $dtformat) {
                   if ($change['date']) {
                       $dt = rcube_utils::anytodatetime($change['date']);
                       if ($dt instanceof DateTime) {
                           $change['date'] = $rcmail->format_date($dt, $dtformat);
                       }
                   }
                 });
             }
             $this->rc->output->command('contact_render_changelog', $result['changes']);
         }
         else {
             $this->rc->output->command('contact_render_changelog', false);
         }
 
         $this->rc->output->send();
     }
 
     /**
      * Handler for audit trail diff view requests
      */
     public function contact_diff()
     {
         if (empty($this->bonnie_api)) {
             return false;
         }
 
         $contact = rcube_utils::get_input_value('cid', rcube_utils::INPUT_POST, true);
         $source = rcube_utils::get_input_value('source', rcube_utils::INPUT_POST);
         $rev1 = rcube_utils::get_input_value('rev1', rcube_utils::INPUT_POST);
         $rev2 = rcube_utils::get_input_value('rev2', rcube_utils::INPUT_POST);
 
         list($uid, $mailbox, $msguid) = $this->_resolve_contact_identity($contact, $source);
 
         $result = $this->bonnie_api->diff('contact', $uid, $rev1, $rev2, $mailbox, $msguid);
         if (is_array($result) && $result['uid'] == $uid) {
             $result['rev1'] = $rev1;
             $result['rev2'] = $rev2;
             $result['cid'] = $contact;
 
             // convert some properties, similar to kolab_contacts::_to_rcube_contact()
             $keymap = array(
                 'lastmodified-date' => 'changed',
                 'additional' => 'middlename',
                 'fn' => 'name',
                 'tel' => 'phone',
                 'url' => 'website',
                 'bday' => 'birthday',
                 'note' => 'notes',
                 'role' => 'profession',
                 'title' => 'jobtitle',
             );
 
             $propmap = array('email' => 'address', 'website' => 'url', 'phone' => 'number');
             $date_format = $this->rc->config->get('date_format', 'Y-m-d');
 
             // map kolab object properties to keys and values the client expects
             array_walk($result['changes'], function(&$change, $i) use ($keymap, $propmap, $date_format) {
                 if (array_key_exists($change['property'], $keymap)) {
                     $change['property'] = $keymap[$change['property']];
                 }
 
                 // format date-time values
                 if ($change['property'] == 'created' || $change['property'] == 'changed') {
                     if ($old_ = rcube_utils::anytodatetime($change['old'])) {
                         $change['old_'] = $this->rc->format_date($old_);
                     }
                     if ($new_ = rcube_utils::anytodatetime($change['new'])) {
                         $change['new_'] = $this->rc->format_date($new_);
                     }
                 }
                 // format dates
                 else if ($change['property'] == 'birthday' || $change['property'] == 'anniversary') {
                     if ($old_ = rcube_utils::anytodatetime($change['old'])) {
                         $change['old_'] = $this->rc->format_date($old_, $date_format);
                     }
                     if ($new_ = rcube_utils::anytodatetime($change['new'])) {
                         $change['new_'] = $this->rc->format_date($new_, $date_format);
                     }
                 }
                 // convert email, website, phone values
                 else if (array_key_exists($change['property'], $propmap)) {
                     $propname = $propmap[$change['property']];
                     foreach (array('old','new') as $k) {
                         $k_ = $k . '_';
                         if (!empty($change[$k])) {
                             $change[$k_] = html::quote($change[$k][$propname] ?: '--');
                             if ($change[$k]['type']) {
                                 $change[$k_] .= '&nbsp;' . html::span('subtype', $this->get_type_label($change[$k]['type']));
                             }
                             $change['ishtml'] = true;
                         }
                     }
                 }
                 // serialize address structs
                 if ($change['property'] == 'address') {
                     foreach (array('old','new') as $k) {
                         $k_ = $k . '_';
                         $change[$k]['zipcode'] = $change[$k]['code'];
                         $template = $this->rc->config->get('address_template', '{'.join('} {', array_keys($change[$k])).'}');
                         $composite = array();
                         foreach ($change[$k] as $p => $val) {
                             if (strlen($val))
                                 $composite['{'.$p.'}'] = $val;
                         }
                         $change[$k_] = preg_replace('/\{\w+\}/', '', strtr($template, $composite));
                         if ($change[$k]['type']) {
                             $change[$k_] .= html::div('subtype', $this->get_type_label($change[$k]['type']));
                         }
                         $change['ishtml'] = true;
                     }
 
                     $change['diff_'] = libkolab::html_diff($change['old_'], $change['new_'], true);
                 }
                 // localize gender values
                 else if ($change['property'] == 'gender') {
                     if ($change['old']) $change['old_'] = $this->rc->gettext($change['old']);
                     if ($change['new']) $change['new_'] = $this->rc->gettext($change['new']);
                 }
                 // translate 'key' entries in individual properties
                 else if ($change['property'] == 'key') {
                     $p = $change['old'] ?: $change['new'];
                     $t = $p['type'];
                     $change['property'] = $t . 'publickey';
                     $change['old'] = $change['old'] ? $change['old']['key'] : '';
                     $change['new'] = $change['new'] ? $change['new']['key'] : '';
                 }
                 // compute a nice diff of notes
                 else if ($change['property'] == 'notes') {
                     $change['diff_'] = libkolab::html_diff($change['old'], $change['new'], false);
                 }
             });
 
             $this->rc->output->command('contact_show_diff', $result);
         }
         else {
             $this->rc->output->command('display_message', $this->gettext('objectdiffnotavailable'), 'error');
         }
 
         $this->rc->output->send();
     }
 
     /**
      * Handler for audit trail revision restore requests
      */
     public function contact_restore()
     {
         if (empty($this->bonnie_api)) {
             return false;
         }
 
         $success = false;
         $contact = rcube_utils::get_input_value('cid', rcube_utils::INPUT_POST, true);
         $source = rcube_utils::get_input_value('source', rcube_utils::INPUT_POST);
         $rev = rcube_utils::get_input_value('rev', rcube_utils::INPUT_POST);
 
         list($uid, $mailbox, $msguid) = $this->_resolve_contact_identity($contact, $source, $folder);
 
         if ($folder && ($raw_msg = $this->bonnie_api->rawdata('contact', $uid, $rev, $mailbox))) {
             $imap = $this->rc->get_storage();
 
             // insert $raw_msg as new message
             if ($imap->save_message($folder->name, $raw_msg, null, false)) {
                 $success = true;
 
                 // delete old revision from imap and cache
                 $imap->delete_message($msguid, $folder->name);
                 $folder->cache->set($msguid, false);
                 $this->cache = array();
             }
         }
 
         if ($success) {
             $this->rc->output->command('display_message', $this->gettext(array('name' => 'objectrestoresuccess', 'vars' => array('rev' => $rev))), 'confirmation');
             $this->rc->output->command('close_contact_history_dialog', $contact);
         }
         else {
             $this->rc->output->command('display_message', $this->gettext('objectrestoreerror'), 'error');
         }
 
         $this->rc->output->send();
     }
 
     /**
      * Get a previous revision of the given contact record from the Bonnie API
      */
     public function get_revision($cid, $source, $rev)
     {
         if (empty($this->bonnie_api)) {
             return false;
         }
 
         list($uid, $mailbox, $msguid) = $this->_resolve_contact_identity($cid, $source);
 
         // call Bonnie API
         $result = $this->bonnie_api->get('contact', $uid, $rev, $mailbox, $msguid);
         if (is_array($result) && $result['uid'] == $uid && !empty($result['xml'])) {
             $format = kolab_format::factory('contact');
             $format->load($result['xml']);
             $rec = $format->to_array();
 
             if ($format->is_valid()) {
                 $rec['rev'] = $result['rev'];
                 return $rec;
             }
         }
 
         return false;
     }
 
     /**
      * Helper method to resolved the given contact identifier into uid and mailbox
      *
      * @return array (uid,mailbox,msguid) tuple
      */
     private function _resolve_contact_identity($id, $abook, &$folder = null)
     {
         $mailbox = $msguid = null;
 
         $source = $this->get_address_book(array('id' => $abook));
         if ($source['instance']) {
             $uid = $source['instance']->id2uid($id);
             $list = kolab_storage::id_decode($abook);
         }
         else {
             return array(null, $mailbox, $msguid);
         }
 
         // get resolve message UID and mailbox identifier
         if ($folder = kolab_storage::get_folder($list)) {
             $mailbox = $folder->get_mailbox_id();
             $msguid = $folder->cache->uid2msguid($uid);
         }
 
         return array($uid, $mailbox, $msguid);
     }
 
     /**
      *
      */
     private function _sort_form_fields($contents, $source)
     {
         $block = [];
 
         foreach (array_keys($source->coltypes) as $col) {
             if (isset($contents[$col])) {
                 $block[$col] = $contents[$col];
             }
         }
 
         return $block;
     }
 
     /**
      * Handler for user preferences form (preferences_list hook)
      *
      * @param array $args Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function prefs_list($args)
     {
         if ($args['section'] != 'addressbook') {
             return $args;
         }
 
         $ldap_public = $this->rc->config->get('ldap_public');
 
         // Hide option if there's no global addressbook
         if (empty($ldap_public)) {
             return $args;
         }
 
         // Check that configuration is not disabled
         $dont_override = (array) $this->rc->config->get('dont_override', array());
         $prio          = $this->addressbook_prio();
 
         if (!in_array('kolab_addressbook_prio', $dont_override)) {
             // Load localization
             $this->add_texts('localization');
 
             $field_id = '_kolab_addressbook_prio';
             $select   = new html_select(array('name' => $field_id, 'id' => $field_id));
 
             $select->add($this->gettext('globalfirst'), self::GLOBAL_FIRST);
             $select->add($this->gettext('personalfirst'), self::PERSONAL_FIRST);
             $select->add($this->gettext('globalonly'), self::GLOBAL_ONLY);
             $select->add($this->gettext('personalonly'), self::PERSONAL_ONLY);
 
             $args['blocks']['main']['options']['kolab_addressbook_prio'] = array(
                 'title' => html::label($field_id, rcube::Q($this->gettext('addressbookprio'))),
                 'content' => $select->show($prio),
             );
         }
 
         return $args;
     }
 
     /**
      * Handler for user preferences save (preferences_save hook)
      *
      * @param array $args Hash array with hook parameters
      *
      * @return array Hash array with modified hook parameters
      */
     public function prefs_save($args)
     {
         if ($args['section'] != 'addressbook') {
             return $args;
         }
 
         // Check that configuration is not disabled
         $dont_override = (array) $this->rc->config->get('dont_override', array());
         $key           = 'kolab_addressbook_prio';
 
         if (!in_array('kolab_addressbook_prio', $dont_override) || !isset($_POST['_'.$key])) {
             $args['prefs'][$key] = (int) rcube_utils::get_input_value('_'.$key, rcube_utils::INPUT_POST);
         }
 
         return $args;
     }
 
 
     /**
      * Handler for plugin actions
      */
     public function book_actions()
     {
         $action = trim(rcube_utils::get_input_value('_act', rcube_utils::INPUT_GPC));
 
         if ($action == 'create') {
             $this->ui->book_edit();
         }
         else if ($action == 'edit') {
             $this->ui->book_edit();
         }
         else if ($action == 'delete') {
             $this->book_delete();
         }
     }
 
     /**
      * Handler for address book create/edit form submit
      */
     public function book_save()
     {
         $this->driver->folder_save();
         $this->rc->output->send('iframe');
     }
 
     /**
      *
      */
     public function book_search()
     {
         $results = [];
         $query   = rcube_utils::get_input_value('q', rcube_utils::INPUT_GPC);
         $source  = rcube_utils::get_input_value('source', rcube_utils::INPUT_GPC);
 
         kolab_storage::$encode_ids = true;
         $search_more_results = false;
         $this->sources = array();
         $this->folders = array();
 
         // find unsubscribed IMAP folders that have "event" type
         if ($source == 'folders') {
             foreach ((array)kolab_storage::search_folders('contact', $query, array('other')) as $folder) {
                 $this->folders[$folder->id] = $folder;
                 $this->sources[$folder->id] = new kolab_contacts($folder->name);
             }
         }
         // search other user's namespace via LDAP
         else if ($source == 'users') {
             $limit = $this->rc->config->get('autocomplete_max', 15) * 2;  // we have slightly more space, so display twice the number
             foreach (kolab_storage::search_users($query, 0, array(), $limit * 10) as $user) {
                 $folders = array();
                 // search for contact folders shared by this user
                 foreach (kolab_storage::list_user_folders($user, 'contact', false) as $foldername) {
                     $folders[] = new kolab_storage_folder($foldername, 'contact');
                 }
 
                 if (count($folders)) {
                     $userfolder = new kolab_storage_folder_user($user['kolabtargetfolder'], '', $user);
                     $this->folders[$userfolder->id] = $userfolder;
                     $this->sources[$userfolder->id] = $userfolder;
 
                     foreach ($folders as $folder) {
                         $this->folders[$folder->id] = $folder;
                         $this->sources[$folder->id] = new kolab_contacts($folder->name);;
                         $count++;
                     }
                 }
 
                 if ($count >= $limit) {
                     $search_more_results = true;
                     break;
                 }
             }
         }
 
         $delim = $this->rc->get_storage()->get_hierarchy_delimiter();
 
         // build results list
         foreach ($this->sources as $id => $source) {
             $folder = $this->folders[$id];
             $imap_path = explode($delim, $folder->name);
 
             // find parent
             do {
               array_pop($imap_path);
               $parent_id = kolab_storage::folder_id(join($delim, $imap_path));
             }
             while (count($imap_path) > 1 && !$this->folders[$parent_id]);
 
             // restore "real" parent ID
             if ($parent_id && !$this->folders[$parent_id]) {
                 $parent_id = kolab_storage::folder_id($folder->get_parent());
             }
 
             $prop = $this->driver->abook_prop($id, $source);
             $prop['parent'] = $parent_id;
 
             $html = $this->addressbook_list_item($id, $prop, $jsdata, true);
             unset($prop['group']);
             $prop += (array)$jsdata[$id];
             $prop['html'] = $html;
 
             $results[] = $prop;
         }
 
         // report more results available
         if ($search_more_results) {
             $this->rc->output->show_message('autocompletemore', 'notice');
         }
 
         $this->rc->output->command('multi_thread_http_response', $results, rcube_utils::get_input_value('_reqid', rcube_utils::INPUT_GPC));
     }
 
     /**
      *
      */
     public function book_subscribe()
     {
         $success = false;
         $id = rcube_utils::get_input_value('_source', rcube_utils::INPUT_GPC);
 
         if ($id && ($folder = kolab_storage::get_folder(kolab_storage::id_decode($id)))) {
             if (isset($_POST['_permanent']))
                 $success |= $folder->subscribe(intval($_POST['_permanent']));
             if (isset($_POST['_active']))
                 $success |= $folder->activate(intval($_POST['_active']));
 
             // list groups for this address book
             if (!empty($_POST['_groups'])) {
                 $abook = new kolab_contacts($folder->name);
                 foreach ((array)$abook->list_groups() as $prop) {
                     $prop['source'] = $id;
                     $prop['id'] = $prop['ID'];
                     unset($prop['ID']);
                     $this->rc->output->command('insert_contact_group', $prop);
                 }
             }
         }
 
         if ($success) {
             $this->rc->output->show_message('successfullysaved', 'confirmation');
         }
         else {
             $this->rc->output->show_message($this->gettext('errorsaving'), 'error');
         }
 
         $this->rc->output->send();
     }
 
 
     /**
      * Handler for address book delete action (AJAX)
      */
     private function book_delete()
     {
         $source = trim(rcube_utils::get_input_value('_source', rcube_utils::INPUT_GPC, true));
 
         if ($source && ($result = $this->driver->folder_delete($source))) {
             $storage   = $this->rc->get_storage();
             $delimiter = $storage->get_hierarchy_delimiter();
 
             $this->rc->output->show_message('kolab_addressbook.bookdeleted', 'confirmation');
             $this->rc->output->set_env('pagecount', 0);
             $this->rc->output->command('set_rowcount', $this->rc->gettext('nocontactsfound'));
             $this->rc->output->command('set_env', 'delimiter', $delimiter);
             $this->rc->output->command('list_contacts_clear');
             $this->rc->output->command('book_delete_done', $source);
         }
         else {
             $this->rc->output->show_message('kolab_addressbook.bookdeleteerror', 'error');
         }
 
         $this->rc->output->send();
     }
 
     /**
      * Returns value of kolab_addressbook_prio setting
      */
     private function addressbook_prio()
     {
         $abook_prio = (int) $this->rc->config->get('kolab_addressbook_prio');
 
         // Make sure any global addressbooks are defined
         if ($abook_prio == 0 || $abook_prio == 2) {
             $ldap_public = $this->rc->config->get('ldap_public');
 
             if (empty($ldap_public)) {
                 $abook_prio = 1;
             }
         }
 
         return $abook_prio;
     }
 
     /**
      * Hook for (contact) folder deletion
      */
     function prefs_folder_delete($args)
     {
         // ignore...
         if ($args['abort'] && !$args['result']) {
             return $args;
         }
 
         $this->_contact_folder_rename($args['name'], false);
     }
 
     /**
      * Hook for (contact) folder renaming
      */
     function prefs_folder_rename($args)
     {
         // ignore...
         if ($args['abort'] && !$args['result']) {
             return $args;
         }
 
         $this->_contact_folder_rename($args['oldname'], $args['newname']);
     }
 
     /**
      * Hook for (contact) folder updates. Forward to folder_rename handler if name was changed
      */
     function prefs_folder_update($args)
     {
         // ignore...
         if ($args['abort'] && !$args['result']) {
             return $args;
         }
 
         if ($args['record']['name'] != $args['record']['oldname']) {
             $this->_contact_folder_rename($args['record']['oldname'], $args['record']['name']);
         }
     }
 
     /**
      * Apply folder renaming or deletion to the registered birthday calendar address books
      */
     private function _contact_folder_rename($oldname, $newname = false)
     {
         $update = false;
         $delimiter = $this->rc->get_storage()->get_hierarchy_delimiter();
         $bday_addressbooks = (array) $this->rc->config->get('calendar_birthday_adressbooks', []);
 
         foreach ($bday_addressbooks as $i => $id) {
             $folder_name = kolab_storage::id_decode($id);
             if ($oldname === $folder_name || strpos($folder_name, $oldname.$delimiter) === 0) {
                 if ($newname) {  // rename
                     $new_folder = $newname . substr($folder_name, strlen($oldname));
                     $bday_addressbooks[$i] = kolab_storage::id_encode($new_folder);
                 }
                 else {  // delete
                     unset($bday_addressbooks[$i]);
                 }
                 $update = true;
             }
         }
 
         if ($update) {
             $this->rc->user->save_prefs(['calendar_birthday_adressbooks' => $bday_addressbooks]);
         }
     }
 
     /**
      * Get a localization label for specified field type
      */
     private function get_type_label($type)
     {
         // Roundcube < 1.5
         if (function_exists('rcmail_get_type_label')) {
             return rcmail_get_type_label($type);
         }
 
         // Roundcube >= 1.5
         return rcmail_action_contacts_index::get_type_label($type);
     }
 }
diff --git a/plugins/kolab_addressbook/lib/kolab_addressbook_ui.php b/plugins/kolab_addressbook/lib/kolab_addressbook_ui.php
index f1423b09..ff5b5121 100644
--- a/plugins/kolab_addressbook/lib/kolab_addressbook_ui.php
+++ b/plugins/kolab_addressbook/lib/kolab_addressbook_ui.php
@@ -1,203 +1,202 @@
 <?php
 
 /**
  * Kolab address book UI
  *
  * @author Aleksander Machniak <machniak@kolabsys.com>
  *
  * Copyright (C) 2012, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 class kolab_addressbook_ui
 {
     private $plugin;
     private $rc;
 
     /**
      * Class constructor
      *
      * @param kolab_addressbook $plugin Plugin object
      */
     public function __construct($plugin)
     {
         $this->rc     = rcube::get_instance();
         $this->plugin = $plugin;
 
         $this->init_ui();
     }
 
     /**
      * Adds folders management functionality to Addressbook UI
      */
     private function init_ui()
     {
         if (!empty($this->rc->action) && !preg_match('/^plugin\.book/', $this->rc->action) && $this->rc->action != 'show') {
             return;
         }
 
         // Include script
         $this->plugin->include_script('kolab_addressbook.js');
 
         if (empty($this->rc->action)) {
             // Include stylesheet (for directorylist)
             $this->plugin->include_stylesheet($this->plugin->local_skin_path().'/kolab_addressbook.css');
 
             // include kolab folderlist widget if available
             if (in_array('libkolab', $this->plugin->api->loaded_plugins())) {
                 $this->plugin->api->include_script('libkolab/libkolab.js');
             }
 
             $this->rc->output->add_footer($this->rc->output->parse('kolab_addressbook.search_addon', false, false));
 
             // Add actions on address books
             $options = ['book-create', 'book-edit', 'book-delete'];
             if ($this->plugin->driver instanceof kolab_contacts_driver) {
                 $options[] = 'book-remove';
             }
 
             if ($this->plugin->driver instanceof kolab_contacts_driver && ($dav_url = $this->rc->config->get('kolab_addressbook_carddav_url'))) {
                 $options[] = 'book-showurl';
                 $this->rc->output->set_env('kolab_addressbook_carddav_url', true);
 
                 // set CardDAV URI for specified ldap addressbook
                 if ($ldap_abook = $this->rc->config->get('kolab_addressbook_carddav_ldap')) {
                     $dav_ldap_url = strtr($dav_url, array(
                         '%h' => $_SERVER['HTTP_HOST'],
                         '%u' => urlencode($this->rc->get_user_name()),
                         '%i' => 'ldap-directory',
                         '%n' => '',
                     ));
                     $this->rc->output->set_env('kolab_addressbook_carddav_ldap', $ldap_abook);
                     $this->rc->output->set_env('kolab_addressbook_carddav_ldap_url', $dav_ldap_url);
                 }
             }
 
             $idx = 0;
             foreach ($options as $command) {
                 $content = html::tag('li', $idx ? null : array('class' => 'separator_above'),
                     $this->plugin->api->output->button(array(
                         'label'    => 'kolab_addressbook.'.str_replace('-', '', $command),
-                        'domain'   => $this->ID,
                         'class'    => str_replace('-', ' ', $command) . ' disabled',
                         'classact' => str_replace('-', ' ', $command) . ' active',
                         'command'  => $command,
                         'type'     => 'link'
                 )));
                 $this->plugin->api->add_content($content, 'groupoptions');
                 $idx++;
             }
 
             // Link to Settings/Folders
             if ($this->plugin->driver instanceof kolab_contacts_driver) {
                 $content = html::tag('li', ['class' => 'separator_above'],
                     $this->plugin->api->output->button([
                             'label'    => 'managefolders',
                             'type'     => 'link',
                             'class'    => 'folders disabled',
                             'classact' => 'folders active',
                             'command'  => 'folders',
                             'task'     => 'settings',
                     ]));
 
                 $this->plugin->api->add_content($content, 'groupoptions');
             }
 
             $this->rc->output->add_label(
                 'kolab_addressbook.bookdeleteconfirm',
                 'kolab_addressbook.bookdeleting',
                 'kolab_addressbook.carddavurldescription',
                 'kolab_addressbook.bookdelete',
                 'kolab_addressbook.bookshowurl',
                 'kolab_addressbook.bookedit',
                 'kolab_addressbook.bookcreate',
                 'kolab_addressbook.nobooknamewarning',
                 'kolab_addressbook.booksaving',
                 'kolab_addressbook.findaddressbooks',
                 'kolab_addressbook.searchterms',
                 'kolab_addressbook.foldersearchform',
                 'kolab_addressbook.listsearchresults',
                 'kolab_addressbook.nraddressbooksfound',
                 'kolab_addressbook.noaddressbooksfound',
                 'kolab_addressbook.foldersubscribe',
                 'resetsearch'
             );
 
             if ($this->plugin->bonnie_api) {
                 $this->rc->output->set_env('kolab_audit_trail', true);
                 $this->plugin->api->include_script('libkolab/libkolab.js');
 
                 $this->rc->output->add_label(
                     'kolab_addressbook.showhistory',
                     'kolab_addressbook.objectchangelog',
                     'kolab_addressbook.objectdiff',
                     'kolab_addressbook.objectdiffnotavailable',
                     'kolab_addressbook.objectchangelognotavailable',
                     'kolab_addressbook.revisionrestoreconfirm'
                 );
 
                 $this->plugin->add_hook('render_page', array($this, 'render_audittrail_page'));
                 $this->plugin->register_handler('plugin.object_changelog_table', array('libkolab', 'object_changelog_table'));
             }
         }
         // include stylesheet for audit trail
         else if ($this->rc->action == 'show' && $this->plugin->bonnie_api) {
             $this->plugin->include_stylesheet($this->plugin->local_skin_path().'/kolab_addressbook.css', true);
             $this->rc->output->add_label('kolab_addressbook.showhistory');
         }
     }
 
     /**
      * Handler for address book create/edit action
      */
     public function book_edit()
     {
         $this->rc->output->set_env('pagetitle', $this->plugin->gettext('bookproperties'));
         $this->rc->output->add_handler('folderform', [$this, 'book_form']);
         $this->rc->output->send('libkolab.folderform');
     }
 
     /**
      * Handler for 'bookdetails' object returning form content for book create/edit
      *
      * @param array $attr Object attributes
      *
      * @return string HTML output
      */
     public function book_form($attrib)
     {
         $action = trim(rcube_utils::get_input_value('_act', rcube_utils::INPUT_GPC));
         $folder = trim(rcube_utils::get_input_value('_source', rcube_utils::INPUT_GPC, true)); // UTF8
 
         $form_html = $this->plugin->driver->folder_form($action, $folder);
 
         $attrib += ['action' => 'plugin.book-save', 'method' => 'post', 'id' => 'bookpropform'];
 
         return html::tag('form', $attrib, $form_html);
     }
 
     /**
      *
      */
     public function render_audittrail_page($p)
     {
         // append audit trail UI elements to contact page
         if ($p['template'] === 'addressbook' && !$p['kolab-audittrail']) {
             $this->rc->output->add_footer($this->rc->output->parse('kolab_addressbook.audittrail', false, false));
             $p['kolab-audittrail'] = true;
         }
 
         return $p;
     }
 }
diff --git a/plugins/libcalendaring/lib/libcalendaring_recurrence.php b/plugins/libcalendaring/lib/libcalendaring_recurrence.php
index 4de96812..df802b7b 100644
--- a/plugins/libcalendaring/lib/libcalendaring_recurrence.php
+++ b/plugins/libcalendaring/lib/libcalendaring_recurrence.php
@@ -1,278 +1,277 @@
 <?php
 
 use Sabre\VObject\Recur\EventIterator;
 
 /**
  * Recurrence computation class for shared use.
  *
  * Uitility class to compute recurrence dates from the given rules.
  *
  * @author Aleksander Machniak <machniak@apheleia-it.ch
  *
  * Copyright (C) 2012-2022, Apheleia IT AG <contact@apheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 class libcalendaring_recurrence
 {
     protected $lib;
     protected $start;
     protected $engine;
     protected $recurrence;
     protected $dateonly = false;
     protected $event;
     protected $duration;
 
     /**
      * Default constructor
      *
      * @param libcalendaring $lib   The libcalendaring plugin instance
      * @param array          $event The event object to operate on
      */
     function __construct($lib, $event = null)
     {
         $this->lib   = $lib;
         $this->event = $event;
 
         if (!empty($event)) {
             if (!empty($event['start']) && is_object($event['start'])
                 && !empty($event['end']) && is_object($event['end'])
             ) {
                 $this->duration = $event['start']->diff($event['end']);
             }
 
-            $event['start']->_dateonly = !empty($event['allday']);
-
             $this->init($event['recurrence'], $event['start']);
         }
     }
 
     /**
      * Initialize recurrence engine
      *
      * @param array    The recurrence properties
      * @param DateTime The recurrence start date
      */
     public function init($recurrence, $start)
     {
         $this->start      = $start;
-        $this->dateonly   = !empty($start->_dateonly);
+        $this->dateonly   = !empty($start->_dateonly) || !empty($this->event['allday']);
         $this->recurrence = $recurrence;
 
         $event = [
             'uid' => '1',
             'allday' => $this->dateonly,
             'recurrence' => $recurrence,
             'start' => $start,
             // TODO: END/DURATION ???
             // TODO: moved occurrences ???
         ];
 
         $vcalendar = new libcalendaring_vcalendar($this->lib->timezone);
 
         $ve = $vcalendar->toSabreComponent($event);
 
         $this->engine = new EventIterator($ve, null, $this->lib->timezone);
     }
 
     /**
      * Get date/time of the next occurence of this event, and push the iterator.
      *
      * @return DateTime|false object or False if recurrence ended
      */
     public function next_start()
     {
         try {
             $this->engine->next();
             $current = $this->engine->getDtStart();
         }
         catch (Exception $e) {
             // do nothing
         }
 
         return $current ? $this->toDateTime($current) : false;
     }
 
     /**
      * Get the next recurring instance of this event
      *
      * @return array|false Array with event properties or False if recurrence ended
      */
     public function next_instance()
     {
         if ($next_start = $this->next_start()) {
             $next = $this->event;
             $next['start'] = $next_start;
 
             if ($this->duration) {
                 $next['end'] = clone $next_start;
                 $next['end']->add($this->duration);
             }
 
             $next['recurrence_date'] = clone $next_start;
             $next['_instance'] = libcalendaring::recurrence_instance_identifier($next, !empty($this->event['allday']));
 
             unset($next['_formatobj']);
 
             return $next;
         }
 
         return false;
     }
 
     /**
      * Get the date of the end of the last occurrence of this recurrence cycle
      *
      * @return DateTime|false End datetime of the last occurrence or False if there's no end date
      */
     public function end()
     {
         // recurrence end date is given
         if (isset($this->recurrence['UNTIL']) && $this->recurrence['UNTIL'] instanceof DateTimeInterface) {
             return $this->recurrence['UNTIL'];
         }
 
         // Run through all items till we reach the end, or limit of iterations
         // Note: Sabre has a limits of iteration in VObject\Settings, so it is not an infinite loop
         try {
             foreach ($this->engine as $end) {
                 // do nothing
             }
         }
         catch (Exception $e) {
             // do nothing
         }
 /*
         if (empty($end) && isset($this->event['start']) && $this->event['start'] instanceof DateTimeInterface) {
             // determine a reasonable end date if none given
             $end = clone $this->event['start'];
             $end->add(new DateInterval('P100Y'));
         }
 */
+
         return isset($end) ? $this->toDateTime($end) : false;
     }
 
     /**
      * Find date/time of the first occurrence (excluding start date)
      *
      * @return DateTime|null First occurrence
      */
     public function first_occurrence()
     {
         $start    = clone $this->start;
         $interval = $this->recurrence['INTERVAL'] ?? 1;
         $freq     = $this->recurrence['FREQ'] ?? null;
 
         switch ($freq) {
         case 'WEEKLY':
             if (empty($this->recurrence['BYDAY'])) {
                 return $start;
             }
 
             $start->sub(new DateInterval("P{$interval}W"));
             break;
 
         case 'MONTHLY':
             if (empty($this->recurrence['BYDAY']) && empty($this->recurrence['BYMONTHDAY'])) {
                 return $start;
             }
 
             $start->sub(new DateInterval("P{$interval}M"));
             break;
 
         case 'YEARLY':
             if (empty($this->recurrence['BYDAY']) && empty($this->recurrence['BYMONTH'])) {
                 return $start;
             }
 
             $start->sub(new DateInterval("P{$interval}Y"));
             break;
 
         case 'DAILY':
             if (!empty($this->recurrence['BYMONTH'])) {
                 break;
             }
 
         default:
             return $start;
         }
 
         $recurrence = $this->recurrence;
 
         if (!empty($recurrence['COUNT'])) {
             // Increase count so we do not stop the loop to early
             $recurrence['COUNT'] += 100;
         }
 
         // Create recurrence that starts in the past
         $self = new self($this->lib);
         $self->init($recurrence, $start);
 
         // TODO: This method does not work the same way as the kolab_date_recurrence based on
         //       kolabcalendaring. I.e. if an event start date does not match the recurrence rule
         //       it will be returned, kolab_date_recurrence will return the next occurrence in such a case
         //       which is the intended result of this function.
         //       See some commented out test cases in tests/RecurrenceTest.php
 
         // find the first occurrence
         $found = false;
         while ($next = $self->next_start()) {
             $start = $next;
             if ($next >= $this->start) {
                 $found = true;
                 break;
             }
         }
 
         if (!$found) {
             rcube::raise_error(
                 [
                     'file' => __FILE__, 'line' => __LINE__,
                     'message' => sprintf("Failed to find a first occurrence. Start: %s, Recurrence: %s",
                         $this->start->format(DateTime::ISO8601), json_encode($recurrence)),
                 ],
                 true
             );
 
             return null;
         }
 
         return $this->toDateTime($start);
     }
 
     /**
      * Convert any DateTime into libcalendaring_datetime
      */
     protected function toDateTime($date, $useStart = true)
     {
         if ($date instanceof DateTimeInterface) {
             $date = libcalendaring_datetime::createFromFormat(
                 'Y-m-d\\TH:i:s',
                 $date->format('Y-m-d\\TH:i:s'),
                 // Sabre will loose timezone on all-day events, use the event start's timezone
                 $this->start->getTimezone()
             );
         }
 
         $date->_dateonly = $this->dateonly;
 
         if ($useStart && $this->dateonly) {
             // Sabre sets time to 00:00:00 for all-day events,
             // let's copy the time from the event's start
             $date->setTime((int) $this->start->format('H'), (int) $this->start->format('i'), (int) $this->start->format('s'));
         }
 
         return $date;
     }
 }
diff --git a/plugins/libcalendaring/lib/libcalendaring_vcalendar.php b/plugins/libcalendaring/lib/libcalendaring_vcalendar.php
index b801981b..55420e43 100644
--- a/plugins/libcalendaring/lib/libcalendaring_vcalendar.php
+++ b/plugins/libcalendaring/lib/libcalendaring_vcalendar.php
@@ -1,1556 +1,1556 @@
 <?php
 
 /**
  * iCalendar functions for the libcalendaring plugin
  *
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2013-2015, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 use \Sabre\VObject;
 use \Sabre\VObject\DateTimeParser;
 
 /**
  * Class to parse and build vCalendar (iCalendar) files
  *
  * Uses the Sabre VObject library, version 3.x.
  *
  */
 class libcalendaring_vcalendar implements Iterator
 {
     private $timezone;
     private $attach_uri = null;
     private $prodid = '-//Roundcube libcalendaring//Sabre//Sabre VObject//EN';
     private $type_component_map = array('event' => 'VEVENT', 'task' => 'VTODO');
     private $attendee_keymap = array(
         'name'   => 'CN',
         'status' => 'PARTSTAT',
         'role'   => 'ROLE',
         'cutype' => 'CUTYPE',
         'rsvp'   => 'RSVP',
         'delegated-from'  => 'DELEGATED-FROM',
         'delegated-to'    => 'DELEGATED-TO',
         'schedule-status' => 'SCHEDULE-STATUS',
         'schedule-agent'  => 'SCHEDULE-AGENT',
         'sent-by'         => 'SENT-BY',
     );
     private $organizer_keymap = array(
         'name'            => 'CN',
         'schedule-status' => 'SCHEDULE-STATUS',
         'schedule-agent'  => 'SCHEDULE-AGENT',
         'sent-by'         => 'SENT-BY',
     );
     private $iteratorkey = 0;
     private $charset;
     private $forward_exceptions;
     private $vhead;
     private $fp;
     private $vtimezones = array();
 
     public $method;
     public $agent = '';
     public $objects = array();
     public $freebusy = array();
 
 
     /**
      * Default constructor
      */
     function __construct($tz = null)
     {
         $this->timezone = $tz;
         $this->prodid = '-//Roundcube libcalendaring ' . RCUBE_VERSION . '//Sabre//Sabre VObject ' . VObject\Version::VERSION . '//EN';
     }
 
     /**
      * Setter for timezone information
      */
     public function set_timezone($tz)
     {
         $this->timezone = $tz;
     }
 
     /**
      * Setter for URI template for attachment links
      */
     public function set_attach_uri($uri)
     {
         $this->attach_uri = $uri;
     }
 
     /**
      * Setter for a custom PRODID attribute
      */
     public function set_prodid($prodid)
     {
         $this->prodid = $prodid;
     }
 
     /**
      * Setter for a user-agent string to tweak input/output accordingly
      */
     public function set_agent($agent)
     {
         $this->agent = $agent;
     }
 
     /**
      * Free resources by clearing member vars
      */
     public function reset()
     {
         $this->vhead = '';
         $this->method = '';
         $this->objects = array();
         $this->freebusy = array();
         $this->vtimezones = array();
         $this->iteratorkey = 0;
 
         if ($this->fp) {
             fclose($this->fp);
             $this->fp = null;
         }
     }
 
     /**
     * Import events from iCalendar format
     *
     * @param  string vCalendar input
     * @param  string Input charset (from envelope)
     * @param  boolean True if parsing exceptions should be forwarded to the caller
     * @return array List of events extracted from the input
     */
     public function import($vcal, $charset = 'UTF-8', $forward_exceptions = false, $memcheck = true)
     {
         // TODO: convert charset to UTF-8 if other
 
         try {
             // estimate the memory usage and try to avoid fatal errors when allowed memory gets exhausted
             if ($memcheck) {
                 $count = substr_count($vcal, 'BEGIN:VEVENT') + substr_count($vcal, 'BEGIN:VTODO');
                 $expected_memory = $count * 70*1024;  // assume ~ 70K per event (empirically determined)
 
                 if (!rcube_utils::mem_check($expected_memory)) {
                     throw new Exception("iCal file too big");
                 }
             }
 
             $vobject = VObject\Reader::read($vcal, VObject\Reader::OPTION_FORGIVING | VObject\Reader::OPTION_IGNORE_INVALID_LINES);
             if ($vobject)
                 return $this->import_from_vobject($vobject);
         }
         catch (Exception $e) {
             if ($forward_exceptions) {
                 throw $e;
             }
             else {
                 rcube::raise_error(array(
                     'code' => 600, 'type' => 'php',
                     'file' => __FILE__, 'line' => __LINE__,
                     'message' => "iCal data parse error: " . $e->getMessage()),
                     true, false);
             }
         }
 
         return array();
     }
 
     /**
     * Read iCalendar events from a file
     *
     * @param  string File path to read from
     * @param  string Input charset (from envelope)
     * @param  boolean True if parsing exceptions should be forwarded to the caller
     * @return array List of events extracted from the file
     */
     public function import_from_file($filepath, $charset = 'UTF-8', $forward_exceptions = false)
     {
         if ($this->fopen($filepath, $charset, $forward_exceptions)) {
             while ($this->_parse_next(false)) {
                 // nop
             }
 
             fclose($this->fp);
             $this->fp = null;
         }
 
         return $this->objects;
     }
 
     /**
      * Open a file to read iCalendar events sequentially
      *
      * @param  string File path to read from
      * @param  string Input charset (from envelope)
      * @param  boolean True if parsing exceptions should be forwarded to the caller
      * @return boolean True if file contents are considered valid
      */
     public function fopen($filepath, $charset = 'UTF-8', $forward_exceptions = false)
     {
         $this->reset();
 
         // just to be sure...
         @ini_set('auto_detect_line_endings', true);
 
         $this->charset = $charset;
         $this->forward_exceptions = $forward_exceptions;
         $this->fp = fopen($filepath, 'r');
 
         // check file content first
         $begin = fread($this->fp, 1024);
         if (!preg_match('/BEGIN:VCALENDAR/i', $begin)) {
             return false;
         }
 
         fseek($this->fp, 0);
         return $this->_parse_next();
     }
 
     /**
      * Parse the next event/todo/freebusy object from the input file
      */
     private function _parse_next($reset = true)
     {
         if ($reset) {
             $this->iteratorkey = 0;
             $this->objects = array();
             $this->freebusy = array();
         }
 
         $next = $this->_next_component();
         $buffer = $next;
 
         // load the next component(s) too, as they could contain recurrence exceptions
         while (preg_match('/(RRULE|RECURRENCE-ID)[:;]/i', $next)) {
             $next = $this->_next_component();
             $buffer .= $next;
         }
 
         // parse the vevent block surrounded with the vcalendar heading
         if (strlen($buffer) && preg_match('/BEGIN:(VEVENT|VTODO|VFREEBUSY)/i', $buffer)) {
             try {
                 $this->import($this->vhead . $buffer . "END:VCALENDAR", $this->charset, true, false);
             }
             catch (Exception $e) {
                 if ($this->forward_exceptions) {
                     throw new VObject\ParseException($e->getMessage() . " in\n" . $buffer);
                 }
                 else {
                     // write the failing section to error log
                     rcube::raise_error(array(
                         'code' => 600, 'type' => 'php',
                         'file' => __FILE__, 'line' => __LINE__,
                         'message' => $e->getMessage() . " in\n" . $buffer),
                         true, false);
                 }
 
                 // advance to next
                 return $this->_parse_next($reset);
             }
 
             return count($this->objects) > 0;
         }
 
         return false;
     }
 
     /**
      * Helper method to read the next calendar component from the file
      */
     private function _next_component()
     {
         $buffer = '';
         $vcalendar_head = false;
         while (($line = fgets($this->fp, 1024)) !== false) {
             // ignore END:VCALENDAR lines
             if (preg_match('/END:VCALENDAR/i', $line)) {
                 continue;
             }
             // read vcalendar header (with timezone defintion)
             if (preg_match('/BEGIN:VCALENDAR/i', $line)) {
                 $this->vhead = '';
                 $vcalendar_head = true;
             }
 
             // end of VCALENDAR header part
             if ($vcalendar_head && preg_match('/BEGIN:(VEVENT|VTODO|VFREEBUSY)/i', $line)) {
                 $vcalendar_head = false;
             }
 
             if ($vcalendar_head) {
                 $this->vhead .= $line;
             }
             else {
                 $buffer .= $line;
                 if (preg_match('/END:(VEVENT|VTODO|VFREEBUSY)/i', $line)) {
                     break;
                 }
             }
         }
 
         return $buffer;
     }
 
     /**
      * Import objects from an already parsed Sabre\VObject\Component object
      *
      * @param object Sabre\VObject\Component to read from
      * @return array List of events extracted from the file
      */
     public function import_from_vobject($vobject)
     {
         $seen = array();
         $exceptions = array();
 
         if ($vobject->name == 'VCALENDAR') {
             $this->method = strval($vobject->METHOD);
             $this->agent  = strval($vobject->PRODID);
 
             foreach ($vobject->getComponents() as $ve) {
                 if ($ve->name == 'VEVENT' || $ve->name == 'VTODO') {
                     // convert to hash array representation
                     $object = $this->_to_array($ve);
 
                     // temporarily store this as exception
                     if (!empty($object['recurrence_date'])) {
                         $exceptions[] = $object;
                     }
                     else if (empty($seen[$object['uid']])) {
                         $seen[$object['uid']] = true;
                         $this->objects[] = $object;
                     }
                 }
                 else if ($ve->name == 'VFREEBUSY') {
                     $this->objects[] = $this->_parse_freebusy($ve);
                 }
             }
 
             // add exceptions to the according master events
             foreach ($exceptions as $exception) {
                 $uid = $exception['uid'];
 
                 // make this exception the master
                 if (empty($seen[$uid])) {
                     $seen[$uid] = true;
                     $this->objects[] = $exception;
                 }
                 else {
                     foreach ($this->objects as $i => $object) {
                         // add as exception to existing entry with a matching UID
                         if ($object['uid'] == $uid) {
                             $this->objects[$i]['exceptions'][] = $exception;
 
                             if (!empty($object['recurrence'])) {
                                 $this->objects[$i]['recurrence']['EXCEPTIONS'] = &$this->objects[$i]['exceptions'];
                             }
                             break;
                         }
                     }
                 }
             }
         }
 
         return $this->objects;
     }
 
     /**
      * Getter for free-busy periods
      */
     public function get_busy_periods()
     {
         $out = array();
         foreach ((array)$this->freebusy['periods'] as $period) {
             if ($period[2] != 'FREE') {
                 $out[] = $period;
             }
         }
 
         return $out;
     }
 
     /**
      * Helper method to determine whether the connected client is an Apple device
      */
     private function is_apple()
     {
         return stripos($this->agent, 'Apple') !== false
             || stripos($this->agent, 'Mac OS X') !== false
             || stripos($this->agent, 'iOS/') !== false;
     }
 
     /**
      * Convert the given VEvent object to a libkolab compatible array representation
      *
      * @param object Vevent object to convert
      * @return array Hash array with object properties
      */
     private function _to_array($ve)
     {
         $event = array(
             'uid'     => self::convert_string($ve->UID),
             'title'   => self::convert_string($ve->SUMMARY),
             '_type'   => $ve->name == 'VTODO' ? 'task' : 'event',
             // set defaults
             'priority' => 0,
             'attendees' => array(),
             'x-custom' => array(),
         );
 
         // Catch possible exceptions when date is invalid (Bug #2144)
         // We can skip these fields, they aren't critical
         foreach (array('CREATED' => 'created', 'LAST-MODIFIED' => 'changed', 'DTSTAMP' => 'changed') as $attr => $field) {
             try {
                 if (empty($event[$field]) && !empty($ve->{$attr})) {
                     $event[$field] = $ve->{$attr}->getDateTime();
                 }
             } catch (Exception $e) {}
         }
 
         // map other attributes to internal fields
         foreach ($ve->children() as $prop) {
             if (!($prop instanceof VObject\Property))
                 continue;
 
             $value = strval($prop);
 
             switch ($prop->name) {
             case 'DTSTART':
             case 'DTEND':
             case 'DUE':
                 $propmap = array('DTSTART' => 'start', 'DTEND' => 'end', 'DUE' => 'due');
                 $event[$propmap[$prop->name]] = self::convert_datetime($prop);
                 break;
 
             case 'TRANSP':
                 $event['free_busy'] = strval($prop) == 'TRANSPARENT' ? 'free' : 'busy';
                 break;
 
             case 'STATUS':
                 if ($value == 'TENTATIVE')
                     $event['free_busy'] = 'tentative';
                 else if ($value == 'CANCELLED')
                     $event['cancelled'] = true;
                 else if ($value == 'COMPLETED')
                     $event['complete'] = 100;
 
                 $event['status'] = $value;
                 break;
 
             case 'COMPLETED':
                 if (self::convert_datetime($prop)) {
                     $event['status'] = 'COMPLETED';
                     $event['complete'] = 100;
                 }
                 break;
 
             case 'PRIORITY':
                 if (is_numeric($value))
                     $event['priority'] = $value;
                 break;
 
             case 'RRULE':
                 $params = !empty($event['recurrence']) && is_array($event['recurrence']) ? $event['recurrence'] : array();
                 // parse recurrence rule attributes
                 foreach ($prop->getParts() as $k => $v) {
                     $params[strtoupper($k)] = is_array($v) ? implode(',', $v) : $v;
                 }
                 if (!empty($params['UNTIL'])) {
                     $params['UNTIL'] = date_create($params['UNTIL']);
                 }
                 if (empty($params['INTERVAL'])) {
                     $params['INTERVAL'] = 1;
                 }
 
                 $event['recurrence'] = array_filter($params);
                 break;
 
             case 'EXDATE':
                 if (!empty($value)) {
                     $exdates = array_map(function($_) { return is_array($_) ? $_[0] : $_; }, self::convert_datetime($prop, true));
                     if (!empty($event['recurrence']['EXDATE'])) {
                         $event['recurrence']['EXDATE'] = array_merge($event['recurrence']['EXDATE'], $exdates);
                     }
                     else {
                         $event['recurrence']['EXDATE'] = $exdates;
                     }
                 }
                 break;
 
             case 'RDATE':
                 if (!empty($value)) {
                     $rdates = array_map(function($_) { return is_array($_) ? $_[0] : $_; }, self::convert_datetime($prop, true));
                     if (!empty($event['recurrence']['RDATE'])) {
                         $event['recurrence']['RDATE'] = array_merge($event['recurrence']['RDATE'], $rdates);
                     }
                     else {
                         $event['recurrence']['RDATE'] = $rdates;
                     }
                 }
                 break;
 
             case 'RECURRENCE-ID':
                 $event['recurrence_date'] = self::convert_datetime($prop);
                 if ($prop->offsetGet('RANGE') == 'THISANDFUTURE' || $prop->offsetGet('THISANDFUTURE') !== null) {
                     $event['thisandfuture'] = true;
                 }
                 break;
 
             case 'RELATED-TO':
                 $reltype = $prop->offsetGet('RELTYPE');
                 if ($reltype == 'PARENT' || $reltype === null) {
                     $event['parent_id'] = $value;
                 }
                 break;
 
             case 'SEQUENCE':
                 $event['sequence'] = intval($value);
                 break;
 
             case 'PERCENT-COMPLETE':
                 $event['complete'] = intval($value);
                 break;
 
             case 'LOCATION':
             case 'DESCRIPTION':
             case 'URL':
             case 'COMMENT':
                 $event[strtolower($prop->name)] = self::convert_string($prop);
                 break;
 
             case 'CATEGORY':
             case 'CATEGORIES':
                 if (!empty($event['categories'])) {
                     $event['categories'] = array_merge((array) $event['categories'], $prop->getParts());
                 }
                 else {
                     $event['categories'] = $prop->getParts();
                 }
                 break;
 
             case 'X-MICROSOFT-CDO-BUSYSTATUS':
                 if ($value == 'OOF') {
                     $event['free_busy'] = 'outofoffice';
                 }
                 else if (in_array($value, array('FREE', 'BUSY', 'TENTATIVE'))) {
                     $event['free_busy'] = strtolower($value);
                 }
                 break;
 
             case 'ATTENDEE':
             case 'ORGANIZER':
                 $params = array('RSVP' => false);
                 foreach ($prop->parameters() as $pname => $pvalue) {
                     switch ($pname) {
                         case 'RSVP': $params[$pname] = strtolower($pvalue) == 'true'; break;
                         case 'CN':   $params[$pname] = self::unescape($pvalue); break;
                         default:     $params[$pname] = strval($pvalue); break;
                     }
                 }
                 $attendee = self::map_keys($params, array_flip($this->attendee_keymap));
                 $attendee['email'] = preg_replace('!^mailto:!i', '', $value);
 
                 if ($prop->name == 'ORGANIZER') {
                     $attendee['role'] = 'ORGANIZER';
                     $attendee['status'] = 'ACCEPTED';
                     $event['organizer'] = $attendee;
 
                     if (array_key_exists('schedule-agent', $attendee)) {
                         $schedule_agent = $attendee['schedule-agent'];
                     }
                 }
                 else if (empty($event['organizer']) || $attendee['email'] != $event['organizer']['email']) {
                     $event['attendees'][] = $attendee;
                 }
                 break;
 
             case 'ATTACH':
                 $params = self::parameters_array($prop);
                 if (substr($value, 0, 4) == 'http' && !strpos($value, ':attachment:')) {
                     $event['links'][] = $value;
                 }
-                else if (strlen($value) && strtoupper($params['VALUE']) == 'BINARY') {
-                    $attachment = self::map_keys($params, array('FMTTYPE' => 'mimetype', 'X-LABEL' => 'name', 'X-APPLE-FILENAME' => 'name'));
+                else if (is_string($value) && strlen($value) && !empty($params['VALUE']) && strtoupper($params['VALUE']) == 'BINARY') {
+                    $attachment = self::map_keys($params, ['FMTTYPE' => 'mimetype', 'X-LABEL' => 'name', 'X-APPLE-FILENAME' => 'name']);
                     $attachment['data'] = $value;
                     $attachment['size'] = strlen($value);
                     $event['attachments'][] = $attachment;
                 }
                 break;
 
             default:
                 if (substr($prop->name, 0, 2) == 'X-')
                     $event['x-custom'][] = array($prop->name, strval($value));
                 break;
             }
         }
 
         // check DURATION property if no end date is set
         if (empty($event['end']) && $ve->DURATION) {
             try {
                 $duration = new DateInterval(strval($ve->DURATION));
                 $end = clone $event['start'];
                 $end->add($duration);
                 $event['end'] = $end;
             }
             catch (\Exception $e) {
                 trigger_error(strval($e), E_USER_WARNING);
             }
         }
 
         // validate event dates
         if ($event['_type'] == 'event') {
             $event['allday'] = !empty($event['start']->_dateonly);
 
             // events may lack the DTEND property, set it to DTSTART (RFC5545 3.6.1)
             if (empty($event['end'])) {
                 $event['end'] = clone $event['start'];
             }
             // shift end-date by one day (except Thunderbird)
             else if ($event['allday'] && is_object($event['end'])) {
                 $event['end']->sub(new \DateInterval('PT23H'));
             }
 
             // sanity-check and fix end date
             if (!empty($event['end']) && $event['end'] < $event['start']) {
                 $event['end'] = clone $event['start'];
             }
         }
 
         // make organizer part of the attendees list for compatibility reasons
         if (!empty($event['organizer']) && is_array($event['attendees']) && $event['_type'] == 'event') {
             array_unshift($event['attendees'], $event['organizer']);
         }
 
         // find alarms
         foreach ($ve->select('VALARM') as $valarm) {
             $action  = 'DISPLAY';
             $trigger = null;
             $alarm   = array();
 
             foreach ($valarm->children() as $prop) {
                 $value = strval($prop);
 
                 switch ($prop->name) {
                 case 'TRIGGER':
                     foreach ($prop->parameters as $param) {
                         if ($param->name == 'VALUE' && $param->getValue() == 'DATE-TIME') {
                             $trigger = '@' . $prop->getDateTime()->format('U');
                             $alarm['trigger'] = $prop->getDateTime();
                         }
                         else if ($param->name == 'RELATED') {
                             $alarm['related'] = $param->getValue();
                         }
                     }
                     if (!$trigger && ($values = libcalendaring::parse_alarm_value($value))) {
                         $trigger = $values[2];
                     }
 
                     if (empty($alarm['trigger'])) {
                         $alarm['trigger'] = rtrim(preg_replace('/([A-Z])0[WDHMS]/', '\\1', $value), 'T');
                         // if all 0-values have been stripped, assume 'at time'
                         if ($alarm['trigger'] == 'P') {
                             $alarm['trigger'] = 'PT0S';
                         }
                     }
                     break;
 
                 case 'ACTION':
                     $action = $alarm['action'] = strtoupper($value);
                     break;
 
                 case 'SUMMARY':
                 case 'DESCRIPTION':
                 case 'DURATION':
                     $alarm[strtolower($prop->name)] = self::convert_string($prop);
                     break;
 
                 case 'REPEAT':
                     $alarm['repeat'] = intval($value);
                     break;
 
                 case 'ATTENDEE':
                     $alarm['attendees'][] = preg_replace('!^mailto:!i', '', $value);
                     break;
 
                 case 'ATTACH':
                     $params = self::parameters_array($prop);
                     if (strlen($value) && (preg_match('/^[a-z]+:/', $value) || strtoupper($params['VALUE']) == 'URI')) {
                         // we only support URI-type of attachments here
                         $alarm['uri'] = $value;
                     }
                     break;
                 }
             }
 
             if ($action != 'NONE') {
                 // store first alarm in legacy property
                 if ($trigger && empty($event['alarms'])) {
                     $event['alarms'] = $trigger . ':' . $action;
                 }
 
                 if (!empty($alarm['trigger'])) {
                     $event['valarms'][] = $alarm;
                 }
             }
         }
 
         // assign current timezone to event start/end
         if (!empty($event['start']) && $event['start'] instanceof DateTimeInterface) {
             $this->_apply_timezone($event['start']);
         }
         else {
             unset($event['start']);
         }
 
         if (!empty($event['end']) && $event['end'] instanceof DateTimeInterface) {
             $this->_apply_timezone($event['end']);
         }
         else {
             unset($event['end']);
         }
 
         // some iTip CANCEL messages only contain the start date
         if (empty($event['end']) && !empty($event['start']) && $this->method == 'CANCEL') {
             $event['end'] = clone $event['start'];
         }
 
         // T2531: Remember SCHEDULE-AGENT in custom property to properly
         // support event updates via CalDAV when SCHEDULE-AGENT=CLIENT is used
         if (isset($schedule_agent)) {
             $event['x-custom'][] = array('SCHEDULE-AGENT', $schedule_agent);
         }
 
         // minimal validation
         if (empty($event['uid']) || ($event['_type'] == 'event' && empty($event['start']) != empty($event['end']))) {
             throw new VObject\ParseException('Object validation failed: missing mandatory object properties');
         }
 
         return $event;
     }
 
     /**
      * Apply user timezone to DateTime object
      */
     private function _apply_timezone(&$date)
     {
         if (empty($this->timezone)) {
             return;
         }
 
         // For date-only we'll keep the date and time intact
         if (!empty($date->_dateonly)) {
             $dt = new libcalendaring_datetime(null, $this->timezone);
             $dt->setDate($date->format('Y'), $date->format('n'), $date->format('j'));
             $dt->setTime($date->format('G'), $date->format('i'), 0);
             $date = $dt;
         }
         else {
             $date->setTimezone($this->timezone);
         }
     }
 
     /**
      * Parse the given vfreebusy component into an array representation
      */
     private function _parse_freebusy($ve)
     {
         $this->freebusy = array('_type' => 'freebusy', 'periods' => array());
         $seen = array();
 
         foreach ($ve->children() as $prop) {
             if (!($prop instanceof VObject\Property))
                 continue;
 
             $value = strval($prop);
 
             switch ($prop->name) {
             case 'CREATED':
             case 'LAST-MODIFIED':
             case 'DTSTAMP':
             case 'DTSTART':
             case 'DTEND':
                 $propmap = array(
                     'DTSTART' => 'start',
                     'DTEND' => 'end',
                     'CREATED' => 'created',
                     'LAST-MODIFIED' => 'changed',
                     'DTSTAMP' => 'changed'
                 );
                 $this->freebusy[$propmap[$prop->name]] = self::convert_datetime($prop);
                 break;
 
             case 'ORGANIZER':
                 $this->freebusy['organizer'] = preg_replace('!^mailto:!i', '', $value);
                 break;
 
             case 'FREEBUSY':
                 // The freebusy component can hold more than 1 value, separated by commas.
                 $periods = explode(',', $value);
                 $fbtype = strval($prop['FBTYPE']) ?: 'BUSY';
 
                 // skip dupes
                 if (!empty($seen[$value.':'.$fbtype])) {
                     break;
                 }
 
                 $seen[$value.':'.$fbtype] = true;
 
                 foreach ($periods as $period) {
                     // Every period is formatted as [start]/[end]. The start is an
                     // absolute UTC time, the end may be an absolute UTC time, or
                     // duration (relative) value.
                     list($busyStart, $busyEnd) = explode('/', $period);
 
                     $busyStart = DateTimeParser::parse($busyStart);
                     $busyEnd = DateTimeParser::parse($busyEnd);
                     if ($busyEnd instanceof \DateInterval) {
                         $tmp = clone $busyStart;
                         $tmp->add($busyEnd);
                         $busyEnd = $tmp;
                     }
 
                     if ($busyEnd && $busyEnd > $busyStart)
                         $this->freebusy['periods'][] = array($busyStart, $busyEnd, $fbtype);
                 }
                 break;
 
             case 'COMMENT':
                 $this->freebusy['comment'] = $value;
             }
         }
 
         return $this->freebusy;
     }
 
     /**
      *
      */
     public static function convert_string($prop)
     {
         return strval($prop);
     }
 
     /**
      *
      */
     public static function unescape($prop)
     {
         return str_replace('\,', ',', strval($prop));
     }
 
     /**
      * Helper method to correctly interpret an all-day date value
      */
     public static function convert_datetime($prop, $as_array = false)
     {
         if (empty($prop)) {
             return $as_array ? [] : null;
         }
 
         if ($prop instanceof VObject\Property\ICalendar\DateTime) {
             if (count($prop->getDateTimes()) > 1) {
                 $dt = [];
                 $dateonly = !$prop->hasTime();
 
                 foreach ($prop->getDateTimes() as $item) {
                     $item = libcalendaring_datetime::createFromImmutable($item);
                     $item->_dateonly = $dateonly;
                     $dt[] = $item;
                 }
             }
             else {
                 $dt = libcalendaring_datetime::createFromImmutable($prop->getDateTime());
                 if (!$prop->hasTime()) {
                     $dt->_dateonly = true;
                 }
             }
         }
         else if ($prop instanceof VObject\Property\ICalendar\Period) {
             $dt = [];
             foreach ($prop->getParts() as $val) {
                 try {
                     list($start, $end) = explode('/', $val);
                     $start = DateTimeParser::parseDateTime($start);
 
                     // This is a duration value.
                     if ($end[0] === 'P') {
                         $dur = DateTimeParser::parseDuration($end);
                         $end = clone $start;
                         $end->add($dur);
                     }
                     else {
                         $end = DateTimeParser::parseDateTime($end);
                     }
 
                     $dt[] = [libcalendaring_datetime::createFromImmutable($start), libcalendaring_datetime::createFromImmutable($end)];
                 }
                 catch (Exception $e) {
                     // ignore single date parse errors
                 }
             }
         }
         else if ($prop instanceof \DateTimeInterface) {
             $dt = libcalendaring_datetime::createFromImmutable($prop);
         }
 
         // force return value to array if requested
         if ($as_array && !is_array($dt)) {
             $dt = empty($dt) ? [] : [$dt];
         }
 
         return $dt;
     }
 
 
     /**
      * Create a Sabre\VObject\Property instance from a PHP DateTime object
      *
      * @param object  VObject\Document parent node to create property for
      * @param string  Property name
      * @param object  DateTime
      * @param boolean Set as UTC date
      * @param boolean Set as VALUE=DATE property
      */
     public function datetime_prop($cal, $name, $dt, $utc = false, $dateonly = null, $set_type = false)
     {
         if ($utc) {
             $dt->setTimeZone(new \DateTimeZone('UTC'));
             $is_utc = true;
         }
         else {
             $is_utc = ($tz = $dt->getTimezone()) && in_array($tz->getName(), array('UTC','GMT','Z'));
         }
         $is_dateonly = $dateonly === null ? !empty($dt->_dateonly) : (bool) $dateonly;
         $vdt = $cal->createProperty($name, $dt, null, $is_dateonly ? 'DATE' : 'DATE-TIME');
 
         if ($is_dateonly) {
             $vdt['VALUE'] = 'DATE';
         }
         else if ($set_type) {
             $vdt['VALUE'] = 'DATE-TIME';
         }
 
         // register timezone for VTIMEZONE block
         if (!$is_utc && !$dateonly && $tz && ($tzname = $tz->getName())) {
             $ts = $dt->format('U');
             if (!empty($this->vtimezones[$tzname])) {
                 $this->vtimezones[$tzname][0] = min($this->vtimezones[$tzname][0], $ts);
                 $this->vtimezones[$tzname][1] = max($this->vtimezones[$tzname][1], $ts);
             }
             else {
                 $this->vtimezones[$tzname] = array($ts, $ts);
             }
         }
 
         return $vdt;
     }
 
     /**
      * Copy values from one hash array to another using a key-map
      */
     public static function map_keys($values, $map)
     {
         $out = array();
         foreach ($map as $from => $to) {
             if (isset($values[$from]))
                 $out[$to] = is_array($values[$from]) ? join(',', $values[$from]) : $values[$from];
         }
         return $out;
     }
 
     /**
      *
      */
     private static function parameters_array($prop)
     {
         $params = array();
         foreach ($prop->parameters() as $name => $value) {
             $params[strtoupper($name)] = strval($value);
         }
         return $params;
     }
 
 
     /**
      * Export events to iCalendar format
      *
      * @param  array   Events as array
      * @param  string  VCalendar method to advertise
      * @param  boolean Directly send data to stdout instead of returning
      * @param  callable Callback function to fetch attachment contents, false if no attachment export
      * @param  boolean Add VTIMEZONE block with timezone definitions for the included events
      * @return string  Events in iCalendar format (http://tools.ietf.org/html/rfc5545)
      */
     public function export($objects, $method = null, $write = false, $get_attachment = false, $with_timezones = true)
     {
         $this->method = $method;
 
         // encapsulate in VCALENDAR container
         $vcal = new VObject\Component\VCalendar();
         $vcal->VERSION = '2.0';
         $vcal->PRODID = $this->prodid;
         $vcal->CALSCALE = 'GREGORIAN';
 
         if (!empty($method)) {
             $vcal->METHOD = $method;
         }
 
         // write vcalendar header
         if ($write) {
             echo preg_replace('/END:VCALENDAR[\r\n]*$/m', '', $vcal->serialize());
         }
 
         foreach ($objects as $object) {
             $this->_to_ical($object, !$write?$vcal:false, $get_attachment);
         }
 
         // include timezone information
         if ($with_timezones || !empty($method)) {
             foreach ($this->vtimezones as $tzid => $range) {
                 $vt = self::get_vtimezone($tzid, $range[0], $range[1], $vcal);
                 if (empty($vt)) {
                     continue;  // no timezone information found
                 }
 
                 if ($write) {
                     echo $vt->serialize();
                 }
                 else {
                     $vcal->add($vt);
                 }
             }
         }
 
         if ($write) {
             echo "END:VCALENDAR\r\n";
             return true;
         }
         else {
             return $vcal->serialize();
         }
     }
 
     /**
      * Converts internal event representation to Sabre component
      *
      * @param  array    Event
      * @param  callable Callback function to fetch attachment contents, false if no attachment export
      *
      * @return Sabre\VObject\Component\VEvent Sabre component
      */
     public function toSabreComponent($object, $get_attachment = false)
     {
         $vcal = new VObject\Component\VCalendar();
 
         $this->_to_ical($object, $vcal, $get_attachment);
 
         return $vcal->getBaseComponent();
     }
 
     /**
      * Build a valid iCal format block from the given event
      *
      * @param  array    Hash array with event/task properties from libkolab
      * @param  object   VCalendar object to append event to or false for directly sending data to stdout
      * @param  callable Callback function to fetch attachment contents, false if no attachment export
      * @param  object   RECURRENCE-ID property when serializing a recurrence exception
      */
     private function _to_ical($event, $vcal, $get_attachment, $recurrence_id = null)
     {
         $type = !empty($event['_type']) ? $event['_type'] : 'event';
 
         $cal = $vcal ?: new VObject\Component\VCalendar();
         $ve = $cal->create($this->type_component_map[$type]);
         $ve->UID = $event['uid'];
 
         // set DTSTAMP according to RFC 5545, 3.8.7.2.
         $dtstamp = !empty($event['changed']) && empty($this->method) ? $event['changed'] : new DateTime('now', new \DateTimeZone('UTC'));
         $ve->DTSTAMP = $this->datetime_prop($cal, 'DTSTAMP', $dtstamp, true);
 
         // all-day events end the next day
         if (!empty($event['allday']) && !empty($event['end'])) {
             $event['end'] = clone $event['end'];
             $event['end']->add(new \DateInterval('P1D'));
             $event['end']->_dateonly = true;
         }
         if (!empty($event['created'])) {
             $ve->add($this->datetime_prop($cal, 'CREATED', $event['created'], true));
         }
         if (!empty($event['changed'])) {
             $ve->add($this->datetime_prop($cal, 'LAST-MODIFIED', $event['changed'], true));
         }
         if (!empty($event['start'])) {
             $ve->add($this->datetime_prop($cal, 'DTSTART', $event['start'], false, !empty($event['allday'])));
         }
         if (!empty($event['end'])) {
             $ve->add($this->datetime_prop($cal, 'DTEND', $event['end'], false, !empty($event['allday'])));
         }
         if (!empty($event['due'])) {
             $ve->add($this->datetime_prop($cal, 'DUE', $event['due'], false));
         }
 
         // we're exporting a recurrence instance only
         if (!$recurrence_id && !empty($event['recurrence_date']) && $event['recurrence_date'] instanceof DateTimeInterface) {
             $recurrence_id = $this->datetime_prop($cal, 'RECURRENCE-ID', $event['recurrence_date'], false, !empty($event['allday']));
             if (!empty($event['thisandfuture'])) {
                 $recurrence_id->add('RANGE', 'THISANDFUTURE');
             }
         }
 
         if ($recurrence_id) {
             $ve->add($recurrence_id);
         }
 
         if (!empty($event['title'])) {
             $ve->add('SUMMARY', $event['title']);
         }
 
         if (!empty($event['location'])) {
             $ve->add($this->is_apple() ? new vobject_location_property($cal, 'LOCATION', $event['location']) : $cal->create('LOCATION', $event['location']));
         }
 
         if (!empty($event['description'])) {
             $ve->add('DESCRIPTION', strtr($event['description'], array("\r\n" => "\n", "\r" => "\n"))); // normalize line endings
         }
 
         if (isset($event['sequence'])) {
             $ve->add('SEQUENCE', $event['sequence']);
         }
 
         if (!empty($event['recurrence']) && !$recurrence_id) {
             $exdates = $rdates = null;
             if (isset($event['recurrence']['EXDATE'])) {
                 $exdates = $event['recurrence']['EXDATE'];
                 unset($event['recurrence']['EXDATE']);  // don't serialize EXDATEs into RRULE value
             }
             if (isset($event['recurrence']['RDATE'])) {
                 $rdates = $event['recurrence']['RDATE'];
                 unset($event['recurrence']['RDATE']);  // don't serialize RDATEs into RRULE value
             }
 
             if (!empty($event['recurrence']['FREQ'])) {
                 $ve->add('RRULE', libcalendaring::to_rrule($event['recurrence'], !empty($event['allday'])));
             }
 
             // add EXDATEs each one per line (for Thunderbird Lightning)
             if (is_array($exdates)) {
                 foreach ($exdates as $exdate) {
                     if ($exdate instanceof DateTimeInterface) {
                         $ve->add($this->datetime_prop($cal, 'EXDATE', $exdate));
                     }
                 }
             }
             // add RDATEs
             if (is_array($rdates)) {
                 foreach ($rdates as $rdate) {
                     $ve->add($this->datetime_prop($cal, 'RDATE', $rdate));
                 }
             }
         }
 
         if (!empty($event['categories'])) {
             $cat = $cal->create('CATEGORIES');
             $cat->setParts((array)$event['categories']);
             $ve->add($cat);
         }
 
         if (!empty($event['free_busy'])) {
             $ve->add('TRANSP', $event['free_busy'] == 'free' ? 'TRANSPARENT' : 'OPAQUE');
 
             // for Outlook clients we provide the X-MICROSOFT-CDO-BUSYSTATUS property
             if (stripos($this->agent, 'outlook') !== false) {
                 $ve->add('X-MICROSOFT-CDO-BUSYSTATUS', $event['free_busy'] == 'outofoffice' ? 'OOF' : strtoupper($event['free_busy']));
             }
         }
 
         if (!empty($event['priority'])) {
             $ve->add('PRIORITY', $event['priority']);
         }
 
         if (!empty($event['cancelled'])) {
             $ve->add('STATUS', 'CANCELLED');
         }
         else if (!empty($event['free_busy']) && $event['free_busy'] == 'tentative') {
             $ve->add('STATUS', 'TENTATIVE');
         }
         else if (!empty($event['complete']) && $event['complete'] == 100) {
             $ve->add('STATUS', 'COMPLETED');
         }
         else if (!empty($event['status'])) {
             $ve->add('STATUS', $event['status']);
         }
 
         if (!empty($event['complete'])) {
             $ve->add('PERCENT-COMPLETE', intval($event['complete']));
         }
 
         // Apple iCal and BusyCal required the COMPLETED date to be set in order to consider a task complete
         if (
             (!empty($event['status']) && $event['status'] == 'COMPLETED')
             || (!empty($event['complete']) && $event['complete'] == 100)
         ) {
             $completed = !empty($event['changed']) ? $event['changed'] : new DateTime('now - 1 hour');
             $ve->add($this->datetime_prop($cal, 'COMPLETED', $completed, true));
         }
 
         if (!empty($event['valarms'])) {
             foreach ($event['valarms'] as $alarm) {
                 $va = $cal->createComponent('VALARM');
                 $va->action = $alarm['action'];
                 if ($alarm['trigger'] instanceof DateTimeInterface) {
                     $va->add($this->datetime_prop($cal, 'TRIGGER', $alarm['trigger'], true, null, true));
                 }
                 else {
                     $alarm_props = array();
                     if (!empty($alarm['related']) && strtoupper($alarm['related']) == 'END') {
                         $alarm_props['RELATED'] = 'END';
                     }
                     $va->add('TRIGGER', $alarm['trigger'], $alarm_props);
                 }
 
                 if (!empty($alarm['action']) && $alarm['action'] == 'EMAIL') {
                     if (!empty($alarm['attendees'])) {
                         foreach ((array) $alarm['attendees'] as $attendee) {
                             $va->add('ATTENDEE', 'mailto:' . $attendee);
                         }
                     }
                 }
                 if (!empty($alarm['description'])) {
                     $va->add('DESCRIPTION', $alarm['description']);
                 }
                 if (!empty($alarm['summary'])) {
                     $va->add('SUMMARY', $alarm['summary']);
                 }
                 if (!empty($alarm['duration'])) {
                     $va->add('DURATION', $alarm['duration']);
                     $va->add('REPEAT', !empty($alarm['repeat']) ? intval($alarm['repeat']) : 0);
                 }
                 if (!empty($alarm['uri'])) {
                     $va->add('ATTACH', $alarm['uri'], array('VALUE' => 'URI'));
                 }
                 $ve->add($va);
             }
         }
         // legacy support
         else if (!empty($event['alarms'])) {
             $va = $cal->createComponent('VALARM');
             list($trigger, $va->action) = explode(':', $event['alarms']);
             $val = libcalendaring::parse_alarm_value($trigger);
             if (!empty($val[3])) {
                 $va->add('TRIGGER', $val[3]);
             }
             else if ($val[0] instanceof DateTimeInterface) {
                 $va->add($this->datetime_prop($cal, 'TRIGGER', $val[0], true, null, true));
             }
             $ve->add($va);
         }
 
         // Find SCHEDULE-AGENT
         if (!empty($event['x-custom'])) {
             foreach ((array) $event['x-custom'] as $prop) {
                 if ($prop[0] === 'SCHEDULE-AGENT') {
                     $schedule_agent = $prop[1];
                 }
             }
         }
 
         if (!empty($event['attendees'])) {
             foreach ((array) $event['attendees'] as $attendee) {
                 if ($attendee['role'] == 'ORGANIZER') {
                     if (empty($event['organizer']))
                         $event['organizer'] = $attendee;
                 }
                 else if (!empty($attendee['email'])) {
                     if (isset($attendee['rsvp'])) {
                         $attendee['rsvp'] = $attendee['rsvp'] ? 'TRUE' : null;
                     }
 
                     $mailto   = $attendee['email'];
                     $attendee = array_filter(self::map_keys($attendee, $this->attendee_keymap));
 
                     if (isset($schedule_agent) && !isset($attendee['SCHEDULE-AGENT'])) {
                         $attendee['SCHEDULE-AGENT'] = $schedule_agent;
                     }
 
                     $ve->add('ATTENDEE', 'mailto:' . $mailto, $attendee);
                 }
             }
         }
 
         if (!empty($event['organizer'])) {
             $organizer = array_filter(self::map_keys($event['organizer'], $this->organizer_keymap));
 
             if (isset($schedule_agent) && !isset($organizer['SCHEDULE-AGENT'])) {
                 $organizer['SCHEDULE-AGENT'] = $schedule_agent;
             }
 
             $ve->add('ORGANIZER', 'mailto:' . $event['organizer']['email'], $organizer);
         }
 
         if (!empty($event['url'])) {
             foreach ((array) $event['url'] as $url) {
                 if (!empty($url)) {
                     $ve->add('URL', $url);
                 }
             }
         }
 
         if (!empty($event['parent_id'])) {
             $ve->add('RELATED-TO', $event['parent_id'], array('RELTYPE' => 'PARENT'));
         }
 
         if (!empty($event['comment'])) {
             $ve->add('COMMENT', $event['comment']);
         }
 
         $memory_limit = parse_bytes(ini_get('memory_limit'));
 
         // export attachments
         if (!empty($event['attachments'])) {
             foreach ((array)$event['attachments'] as $attach) {
                 // check available memory and skip attachment export if we can't buffer it
                 // @todo: use rcube_utils::mem_check()
                 if (is_callable($get_attachment) && $memory_limit > 0 && ($memory_used = function_exists('memory_get_usage') ? memory_get_usage() : 16*1024*1024)
                     && $attach['size'] && $memory_used + $attach['size'] * 3 > $memory_limit) {
                     continue;
                 }
                 // embed attachments using the given callback function
                 if (is_callable($get_attachment) && ($data = call_user_func($get_attachment, $attach['id'], $event))) {
                     // embed attachments for iCal
                     $ve->add('ATTACH',
                         $data,
                         array_filter(array('VALUE' => 'BINARY', 'ENCODING' => 'BASE64', 'FMTTYPE' => $attach['mimetype'], 'X-LABEL' => $attach['name'])));
                     unset($data);  // attempt to free memory
                 }
                 // list attachments as absolute URIs
                 else if (!empty($this->attach_uri)) {
                     $ve->add('ATTACH',
                         strtr($this->attach_uri, array(
                             '{{id}}'       => urlencode($attach['id']),
                             '{{name}}'     => urlencode($attach['name']),
                             '{{mimetype}}' => urlencode($attach['mimetype']),
                         )),
                         array('FMTTYPE' => $attach['mimetype'], 'VALUE' => 'URI'));
                 }
             }
         }
 
         if (!empty($event['links'])) {
             foreach ((array) $event['links'] as $uri) {
                 $ve->add('ATTACH', $uri);
             }
         }
 
         // add custom properties
         if (!empty($event['x-custom'])) {
             foreach ((array) $event['x-custom'] as $prop) {
                 $ve->add($prop[0], $prop[1]);
             }
         }
 
         // append to vcalendar container
         if ($vcal) {
             $vcal->add($ve);
         }
         else {   // serialize and send to stdout
             echo $ve->serialize();
         }
 
         // append recurrence exceptions
         if (!empty($event['recurrence']) && !empty($event['recurrence']['EXCEPTIONS'])) {
             foreach ($event['recurrence']['EXCEPTIONS'] as $ex) {
                 $exdate = !empty($ex['recurrence_date']) ? $ex['recurrence_date'] : $ex['start'];
                 $recurrence_id = $this->datetime_prop($cal, 'RECURRENCE-ID', $exdate, false, !empty($event['allday']));
                 if (!empty($ex['thisandfuture'])) {
                     $recurrence_id->add('RANGE', 'THISANDFUTURE');
                 }
 
                 $ex['uid'] = $ve->UID;
 
                 $this->_to_ical($ex, $vcal, $get_attachment, $recurrence_id);
             }
         }
     }
 
     /**
      * Returns a VTIMEZONE component for a Olson timezone identifier
      * with daylight transitions covering the given date range.
      *
      * @param string Timezone ID as used in PHP's Date functions
      * @param integer Unix timestamp with first date/time in this timezone
      * @param integer Unix timestap with last date/time in this timezone
      * @param VObject\Component\VCalendar Optional VCalendar component
      *
      * @return mixed A Sabre\VObject\Component object representing a VTIMEZONE definition
      *               or false if no timezone information is available
      */
     public static function get_vtimezone($tzid, $from = 0, $to = 0, $cal = null)
     {
         // TODO: Consider using tzurl.org database for better interoperability e.g. with Outlook
 
         if (!$from) $from = time();
         if (!$to)   $to = $from;
         if (!$cal)  $cal = new VObject\Component\VCalendar();
 
         if (is_string($tzid)) {
             try {
                 $tz = new \DateTimeZone($tzid);
             }
             catch (\Exception $e) {
                 return false;
             }
         }
         else if (is_a($tzid, '\\DateTimeZone')) {
             $tz = $tzid;
         }
 
         if (empty($tz) || !is_a($tz, '\\DateTimeZone')) {
             return false;
         }
 
         $year = 86400 * 360;
         $transitions = $tz->getTransitions($from - $year, $to + $year);
 
         // Make sure VTIMEZONE contains at least one STANDARD/DAYLIGHT component
         // when there's only one transition in specified time period (T5626)
         if (count($transitions) == 1) {
             // Get more transitions and use OFFSET from the previous to last
             $more_transitions = $tz->getTransitions(0, $to + $year);
             if (count($more_transitions) > 1) {
                 $index  = count($more_transitions) - 2;
                 $tzfrom = $more_transitions[$index]['offset'] / 3600;
             }
         }
 
         $vt = $cal->createComponent('VTIMEZONE');
         $vt->TZID = $tz->getName();
 
         $std = null; $dst = null;
         foreach ($transitions as $i => $trans) {
             $cmp = null;
 
             if (!isset($tzfrom)) {
                 $tzfrom = $trans['offset'] / 3600;
                 continue;
             }
 
             if ($trans['isdst']) {
                 $t_dst = $trans['ts'];
                 $dst = $cal->createComponent('DAYLIGHT');
                 $cmp = $dst;
             }
             else {
                 $t_std = $trans['ts'];
                 $std = $cal->createComponent('STANDARD');
                 $cmp = $std;
             }
 
             if ($cmp) {
                 $dt = new DateTime($trans['time']);
                 $offset = $trans['offset'] / 3600;
 
                 $cmp->DTSTART = $dt->format('Ymd\THis');
                 $cmp->TZOFFSETFROM = sprintf('%+03d%02d', floor($tzfrom), ($tzfrom - floor($tzfrom)) * 60);
                 $cmp->TZOFFSETTO   = sprintf('%+03d%02d', floor($offset), ($offset - floor($offset)) * 60);
 
                 if (!empty($trans['abbr'])) {
                     $cmp->TZNAME = $trans['abbr'];
                 }
 
                 $tzfrom = $offset;
                 $vt->add($cmp);
             }
 
             // we covered the entire date range
             if ($std && $dst && min($t_std, $t_dst) < $from && max($t_std, $t_dst) > $to) {
                 break;
             }
         }
 
         // add X-MICROSOFT-CDO-TZID if available
         $microsoftExchangeMap = array_flip(VObject\TimeZoneUtil::$microsoftExchangeMap);
         if (array_key_exists($tz->getName(), $microsoftExchangeMap)) {
             $vt->add('X-MICROSOFT-CDO-TZID', $microsoftExchangeMap[$tz->getName()]);
         }
 
         return $vt;
     }
 
 
     /*** Implement PHP 5 Iterator interface to make foreach work ***/
 
     #[\ReturnTypeWillChange]
     function current()
     {
         return $this->objects[$this->iteratorkey];
     }
 
     #[\ReturnTypeWillChange]
     function key()
     {
         return $this->iteratorkey;
     }
 
     #[\ReturnTypeWillChange]
     function next()
     {
         $this->iteratorkey++;
 
         // read next chunk if we're reading from a file
         if (empty($this->objects[$this->iteratorkey]) && $this->fp) {
             $this->_parse_next(true);
         }
 
         return $this->valid();
     }
 
     #[\ReturnTypeWillChange]
     function rewind()
     {
         $this->iteratorkey = 0;
     }
 
     #[\ReturnTypeWillChange]
     function valid()
     {
         return !empty($this->objects[$this->iteratorkey]);
     }
 
 }
 
 
 /**
  * Override Sabre\VObject\Property\Text that quotes commas in the location property
  * because Apple clients treat that property as list.
  */
 class vobject_location_property extends VObject\Property\Text
 {
     /**
      * List of properties that are considered 'structured'.
      *
      * @var array
      */
     protected $structuredValues = [
         // vCard
         'N',
         'ADR',
         'ORG',
         'GENDER',
         'LOCATION',
         // iCalendar
         'REQUEST-STATUS',
     ];
 }
diff --git a/plugins/libcalendaring/libcalendaring.php b/plugins/libcalendaring/libcalendaring.php
index 38884b81..76a57e49 100644
--- a/plugins/libcalendaring/libcalendaring.php
+++ b/plugins/libcalendaring/libcalendaring.php
@@ -1,1583 +1,1583 @@
 <?php
 
 /**
  * Library providing common functions for calendaring plugins
  *
  * Provides utility functions for calendar-related modules such as
  * - alarms display and dismissal
  * - attachment handling
  * - recurrence computation and UI elements
  * - ical parsing and exporting
  * - itip scheduling protocol
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2012-2015, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class libcalendaring extends rcube_plugin
 {
     public $rc;
     public $timezone;
     public $gmt_offset;
     public $dst_active;
     public $timezone_offset;
-    public $ical_parts = array();
+    public $ical_parts = [];
     public $ical_message;
 
     public $defaults = array(
         'calendar_date_format'  => "Y-m-d",
         'calendar_date_short'   => "M-j",
         'calendar_date_long'    => "F j Y",
         'calendar_date_agenda'  => "l M-d",
         'calendar_time_format'  => "H:m",
         'calendar_first_day'    => 1,
         'calendar_first_hour'   => 6,
         'calendar_date_format_sets' => array(
             'Y-m-d' => array('d M Y',   'm-d',  'l m-d'),
             'Y/m/d' => array('d M Y',   'm/d',  'l m/d'),
             'Y.m.d' => array('d M Y',   'm.d',  'l m.d'),
             'd-m-Y' => array('d M Y',   'd-m',  'l d-m'),
             'd/m/Y' => array('d M Y',   'd/m',  'l d/m'),
             'd.m.Y' => array('d M Y',  'd.m',  'l d.m'),
             'j.n.Y' => array('d M Y',  'd.m',  'l d.m'),
             'm/d/Y' => array('M d Y',   'm/d',  'l m/d'),
         ),
     );
 
     private static $instance;
 
     private $mail_ical_parser;
 
     /**
      * Singleton getter to allow direct access from other plugins
      */
     public static function get_instance()
     {
         if (!self::$instance) {
             self::$instance = new libcalendaring(rcube::get_instance()->plugins);
             self::$instance->init_instance();
         }
 
         return self::$instance;
     }
 
     /**
      * Initializes class properties
      */
     public function init_instance()
     {
         $this->rc = rcube::get_instance();
 
         // set user's timezone
         try {
             $this->timezone = new DateTimeZone($this->rc->config->get('timezone', 'GMT'));
         }
         catch (Exception $e) {
             $this->timezone = new DateTimeZone('GMT');
         }
 
         $now = new DateTime('now', $this->timezone);
 
         $this->gmt_offset      = $now->getOffset();
         $this->dst_active      = $now->format('I');
         $this->timezone_offset = $this->gmt_offset / 3600 - $this->dst_active;
 
         $this->add_texts('localization/', false);
     }
 
     /**
      * Required plugin startup method
      */
     public function init()
     {
         // extend include path to load bundled lib classes
         $include_path = $this->home . '/lib' . PATH_SEPARATOR . ini_get('include_path');
         set_include_path($include_path);
 
         self::$instance = $this;
 
         $this->rc = rcube::get_instance();
         $this->init_instance();
 
         // include client scripts and styles
         if ($this->rc->output) {
             // add hook to display alarms
             $this->add_hook('refresh', array($this, 'refresh'));
             $this->register_action('plugin.alarms', array($this, 'alarms_action'));
             $this->register_action('plugin.expand_attendee_group', array($this, 'expand_attendee_group'));
         }
 
         // proceed initialization in startup hook
         $this->add_hook('startup', array($this, 'startup'));
     }
 
     /**
      * Startup hook
      */
     public function startup($args)
     {
         if ($this->rc->output && $this->rc->output->type == 'html') {
             $this->rc->output->set_env('libcal_settings', $this->load_settings());
             $this->include_script('libcalendaring.js');
             $this->include_stylesheet($this->local_skin_path() . '/libcal.css');
 
             $this->add_label(
                 'itipaccepted', 'itiptentative', 'itipdeclined',
                 'itipdelegated', 'expandattendeegroup', 'expandattendeegroupnodata',
                 'statusorganizer', 'statusaccepted', 'statusdeclined',
                 'statusdelegated', 'statusunknown', 'statusneeds-action',
                 'statustentative', 'statuscompleted', 'statusin-process',
                 'delegatedto', 'delegatedfrom', 'showmore'
             );
         }
 
         if ($args['task'] == 'mail') {
             if ($args['action'] == 'show' || $args['action'] == 'preview') {
                 $this->add_hook('message_load', array($this, 'mail_message_load'));
             }
         }
     }
 
     /**
      * Load iCalendar functions
      */
     public static function get_ical()
     {
         $self = self::get_instance();
         return new libcalendaring_vcalendar();
     }
 
     /**
      * Load iTip functions
      */
     public static function get_itip($domain = 'libcalendaring')
     {
         $self = self::get_instance();
         return new libcalendaring_itip($self, $domain);
     }
 
     /**
      * Load recurrence computation engine
      */
-    public static function get_recurrence()
+    public static function get_recurrence($object = null)
     {
         $self = self::get_instance();
-        return new libcalendaring_recurrence($self);
+        return new libcalendaring_recurrence($self, $object);
     }
 
     /**
      * Shift dates into user's current timezone
      *
      * @param mixed Any kind of a date representation (DateTime object, string or unix timestamp)
      * @return object DateTime object in user's timezone
      */
     public function adjust_timezone($dt, $dateonly = false)
     {
         if (is_numeric($dt)) {
             $dt = new DateTime('@'.$dt);
         }
         else if (is_string($dt)) {
             $dt = rcube_utils::anytodatetime($dt);
         }
 
         if ($dt instanceof DateTimeInterface && empty($dt->_dateonly) && !$dateonly) {
             $dt->setTimezone($this->timezone);
         }
 
         return $dt;
     }
 
     /**
      *
      */
     public function load_settings()
     {
         $this->date_format_defaults();
 
         $settings = array();
         $keys     = array('date_format', 'time_format', 'date_short', 'date_long', 'date_agenda');
 
         foreach ($keys as $key) {
             $settings[$key] = (string)$this->rc->config->get('calendar_' . $key, $this->defaults['calendar_' . $key]);
             $settings[$key] = self::from_php_date_format($settings[$key]);
         }
 
         $settings['dates_long']  = $settings['date_long'];
         $settings['first_day']   = (int)$this->rc->config->get('calendar_first_day', $this->defaults['calendar_first_day']);
         $settings['timezone']    = $this->timezone_offset;
         $settings['dst']         = $this->dst_active;
 
         // localization
         $settings['days'] = array(
             $this->rc->gettext('sunday'),   $this->rc->gettext('monday'),
             $this->rc->gettext('tuesday'),  $this->rc->gettext('wednesday'),
             $this->rc->gettext('thursday'), $this->rc->gettext('friday'),
             $this->rc->gettext('saturday')
         );
         $settings['days_short'] = array(
             $this->rc->gettext('sun'), $this->rc->gettext('mon'),
             $this->rc->gettext('tue'), $this->rc->gettext('wed'),
             $this->rc->gettext('thu'), $this->rc->gettext('fri'),
             $this->rc->gettext('sat')
         );
         $settings['months'] = array(
             $this->rc->gettext('longjan'), $this->rc->gettext('longfeb'),
             $this->rc->gettext('longmar'), $this->rc->gettext('longapr'),
             $this->rc->gettext('longmay'), $this->rc->gettext('longjun'),
             $this->rc->gettext('longjul'), $this->rc->gettext('longaug'),
             $this->rc->gettext('longsep'), $this->rc->gettext('longoct'),
             $this->rc->gettext('longnov'), $this->rc->gettext('longdec')
         );
         $settings['months_short'] = array(
             $this->rc->gettext('jan'), $this->rc->gettext('feb'),
             $this->rc->gettext('mar'), $this->rc->gettext('apr'),
             $this->rc->gettext('may'), $this->rc->gettext('jun'),
             $this->rc->gettext('jul'), $this->rc->gettext('aug'),
             $this->rc->gettext('sep'), $this->rc->gettext('oct'),
             $this->rc->gettext('nov'), $this->rc->gettext('dec')
         );
         $settings['today'] = $this->rc->gettext('today');
 
         return $settings;
     }
 
 
     /**
      * Helper function to set date/time format according to config and user preferences
      */
     private function date_format_defaults()
     {
         static $defaults = array();
 
         // nothing to be done
         if (isset($defaults['date_format']))
           return;
 
         $defaults['date_format'] = $this->rc->config->get('calendar_date_format', $this->rc->config->get('date_format'));
         $defaults['time_format'] = $this->rc->config->get('calendar_time_format', $this->rc->config->get('time_format'));
 
         // override defaults
         if ($defaults['date_format'])
             $this->defaults['calendar_date_format'] = $defaults['date_format'];
         if ($defaults['time_format'])
             $this->defaults['calendar_time_format'] = $defaults['time_format'];
 
         // derive format variants from basic date format
         $format_sets = $this->rc->config->get('calendar_date_format_sets', $this->defaults['calendar_date_format_sets']);
         if ($format_set = $format_sets[$this->defaults['calendar_date_format']]) {
             $this->defaults['calendar_date_long'] = $format_set[0];
             $this->defaults['calendar_date_short'] = $format_set[1];
             $this->defaults['calendar_date_agenda'] = $format_set[2];
         }
     }
 
     /**
      * Compose a date string for the given event
      */
     public function event_date_text($event)
     {
         $fromto  = '--';
         $is_task = !empty($event['_type']) && $event['_type'] == 'task';
 
         $this->date_format_defaults();
 
         $date_format = self::to_php_date_format($this->rc->config->get('calendar_date_format', $this->defaults['calendar_date_format']));
         $time_format = self::to_php_date_format($this->rc->config->get('calendar_time_format', $this->defaults['calendar_time_format']));
 
         $getTimezone = function ($date) {
             if ($newTz = $date->getTimezone()) {
                 return $newTz->getName();
             }
 
             return '';
         };
 
         $formatDate = function ($date, $format) use ($getTimezone) {
             // This is a workaround for the rcmail::format_date() which does not play nice with timezone
             $tz = $this->rc->config->get('timezone');
             if ($dateTz = $getTimezone($date)) {
                 $this->rc->config->set('timezone', $dateTz);
             }
             $result = $this->rc->format_date($date, $format);
             $this->rc->config->set('timezone', $tz);
 
             return $result;
         };
 
         // handle task objects
         if ($is_task && !empty($event['due']) && is_object($event['due'])) {
             $fromto = $formatDate($event['due'], !empty($event['due']->_dateonly) ? $date_format : null);
 
             // add timezone information
             if ($fromto && empty($event['due']->_dateonly) && ($tz = $getTimezone($event['due']))) {
                 $fromto .= ' (' . strtr($tz, '_', ' ') . ')';
             }
 
             return $fromto;
         }
 
         // abort if no valid event dates are given
         if (!is_object($event['start']) || !is_a($event['start'], 'DateTime') || !is_object($event['end']) || !is_a($event['end'], 'DateTime')) {
             return $fromto;
         }
 
         if ($event['allday']) {
             $fromto = $formatDate($event['start'], $date_format);
             if (($todate = $formatDate($event['end'], $date_format)) != $fromto) {
                 $fromto .= ' - ' . $todate;
             }
         }
         else if ($event['start']->format('Ymd') === $event['end']->format('Ymd')) {
             $fromto = $formatDate($event['start'], $date_format) . ' ' . $formatDate($event['start'], $time_format) .
                 ' - ' . $formatDate($event['end'], $time_format);
         }
         else {
             $fromto = $formatDate($event['start'], $date_format) . ' ' . $formatDate($event['start'], $time_format) .
                 ' - ' . $formatDate($event['end'], $date_format) . ' ' . $formatDate($event['end'], $time_format);
         }
 
         // add timezone information
         if ($fromto && empty($event['allday']) && ($tz = $getTimezone($event['start']))) {
             $fromto .= ' (' . strtr($tz, '_', ' ') . ')';
         }
 
         return $fromto;
     }
 
 
     /**
      * Render HTML form for alarm configuration
      */
     public function alarm_select($attrib, $alarm_types, $absolute_time = true)
     {
         unset($attrib['name']);
 
         $input_value    = new html_inputfield(array('name' => 'alarmvalue[]', 'class' => 'edit-alarm-value form-control', 'size' => 3));
         $input_date     = new html_inputfield(array('name' => 'alarmdate[]', 'class' => 'edit-alarm-date form-control', 'size' => 10));
         $input_time     = new html_inputfield(array('name' => 'alarmtime[]', 'class' => 'edit-alarm-time form-control', 'size' => 6));
         $select_type    = new html_select(array('name' => 'alarmtype[]', 'class' => 'edit-alarm-type form-control', 'id' => $attrib['id']));
         $select_offset  = new html_select(array('name' => 'alarmoffset[]', 'class' => 'edit-alarm-offset form-control'));
         $select_related = new html_select(array('name' => 'alarmrelated[]', 'class' => 'edit-alarm-related form-control'));
         $object_type    = !empty($attrib['_type']) ? $attrib['_type'] : 'event';
 
         $select_type->add($this->gettext('none'), '');
         foreach ($alarm_types as $type) {
             $select_type->add($this->gettext(strtolower("alarm{$type}option")), $type);
         }
 
         foreach (array('-M','-H','-D','+M','+H','+D') as $trigger) {
             $select_offset->add($this->gettext('trigger' . $trigger), $trigger);
         }
 
         $select_offset->add($this->gettext('trigger0'), '0');
         if ($absolute_time) {
             $select_offset->add($this->gettext('trigger@'), '@');
         }
 
         $select_related->add($this->gettext('relatedstart'), 'start');
         $select_related->add($this->gettext('relatedend' . $object_type), 'end');
 
         // pre-set with default values from user settings
         $preset = self::parse_alarm_value($this->rc->config->get('calendar_default_alarm_offset', '-15M'));
         $hidden = array('style' => 'display:none');
 
         return html::span('edit-alarm-set',
             $select_type->show($this->rc->config->get('calendar_default_alarm_type', '')) . ' ' .
             html::span(array('class' => 'edit-alarm-values input-group', 'style' => 'display:none'),
                 $input_value->show($preset[0]) . ' ' .
                 $select_offset->show($preset[1]) . ' ' .
                 $select_related->show() . ' ' .
                 $input_date->show('', $hidden) . ' ' .
                 $input_time->show('', $hidden)
             )
         );
     }
 
     /**
      * Get a list of email addresses of the given user (from login and identities)
      *
      * @param string User Email (default to current user)
      *
      * @return array Email addresses related to the user
      */
     public function get_user_emails($user = null)
     {
         static $_emails = array();
 
         if (empty($user)) {
             $user = $this->rc->user->get_username();
         }
 
         // return cached result
         if (isset($_emails[$user])) {
             return $_emails[$user];
         }
 
         $emails = array($user);
         $plugin = $this->rc->plugins->exec_hook('calendar_user_emails', array('emails' => $emails));
         $emails = array_map('strtolower', $plugin['emails']);
 
         // add all emails from the current user's identities
         if (!$plugin['abort'] && ($user == $this->rc->user->get_username())) {
             foreach ($this->rc->user->list_emails() as $identity) {
                 $emails[] = strtolower($identity['email']);
             }
         }
 
         $_emails[$user] = array_unique($emails);
         return $_emails[$user];
     }
 
     /**
      * Set the given participant status to the attendee matching the current user's identities
      * Unsets 'rsvp' flag too.
      *
      * @param array  &$event    Event data
      * @param string $status    The PARTSTAT value to set
      * @param bool   $recursive Recurive call
      *
      * @return mixed Email address of the updated attendee or False if none matching found
      */
     public function set_partstat(&$event, $status, $recursive = true)
     {
         $success = false;
         $emails = $this->get_user_emails();
         foreach ((array)$event['attendees'] as $i => $attendee) {
             if ($attendee['email'] && in_array(strtolower($attendee['email']), $emails)) {
                 $event['attendees'][$i]['status'] = strtoupper($status);
                 unset($event['attendees'][$i]['rsvp']);
                 $success = $attendee['email'];
             }
         }
 
         // apply partstat update to each existing exception
         if ($event['recurrence'] && is_array($event['recurrence']['EXCEPTIONS'])) {
             foreach ($event['recurrence']['EXCEPTIONS'] as $i => $exception) {
                 $this->set_partstat($event['recurrence']['EXCEPTIONS'][$i], $status, false);
             }
 
             // set link to top-level exceptions
             $event['exceptions'] = &$event['recurrence']['EXCEPTIONS'];
         }
 
         return $success;
     }
 
 
     /*********  Alarms handling  *********/
 
     /**
      * Helper function to convert alarm trigger strings
      * into two-field values (e.g. "-45M" => 45, "-M")
      */
     public static function parse_alarm_value($val)
     {
         if ($val[0] == '@') {
             return array(new DateTime($val));
         }
         else if (preg_match('/([+-]?)P?(T?\d+[HMSDW])+/', $val, $m) && preg_match_all('/T?(\d+)([HMSDW])/', $val, $m2, PREG_SET_ORDER)) {
             if ($m[1] == '')
                 $m[1] = '+';
             foreach ($m2 as $seg) {
                 $prefix = $seg[2] == 'D' || $seg[2] == 'W' ? 'P' : 'PT';
                 if ($seg[1] > 0) {  // ignore zero values
                     // convert seconds to minutes
                     if ($seg[2] == 'S') {
                         $seg[2] = 'M';
                         $seg[1] = max(1, round($seg[1]/60));
                     }
 
                     return array($seg[1], $m[1].$seg[2], $m[1].$seg[1].$seg[2], $m[1].$prefix.$seg[1].$seg[2]);
                 }
             }
 
             // return zero value nevertheless
             return array($seg[1], $m[1].$seg[2], $m[1].$seg[1].$seg[2], $m[1].$prefix.$seg[1].$seg[2]);
         }
 
         return false;
     }
 
     /**
      * Convert the alarms list items to be processed on the client
      */
     public static function to_client_alarms($valarms)
     {
         return array_map(function($alarm) {
             if ($alarm['trigger'] instanceof DateTimeInterface) {
                 $alarm['trigger'] = '@' . $alarm['trigger']->format('U');
             }
             else if ($trigger = libcalendaring::parse_alarm_value($alarm['trigger'])) {
                 $alarm['trigger'] = $trigger[2];
             }
             return $alarm;
         }, (array)$valarms);
     }
 
     /**
      * Process the alarms values submitted by the client
      */
     public static function from_client_alarms($valarms)
     {
         return array_map(function($alarm){
             if ($alarm['trigger'][0] == '@') {
                 try {
                     $alarm['trigger'] = new DateTime($alarm['trigger']);
                     $alarm['trigger']->setTimezone(new DateTimeZone('UTC'));
                 }
                 catch (Exception $e) { /* handle this ? */ }
             }
             else if ($trigger = libcalendaring::parse_alarm_value($alarm['trigger'])) {
                 $alarm['trigger'] = $trigger[3];
             }
             return $alarm;
         }, (array)$valarms);
     }
 
     /**
      * Render localized text for alarm settings
      */
     public static function alarms_text($alarms)
     {
         if (is_array($alarms) && is_array($alarms[0])) {
             $texts = array();
             foreach ($alarms as $alarm) {
                 if ($text = self::alarm_text($alarm))
                     $texts[] = $text;
             }
 
             return join(', ', $texts);
         }
         else {
             return self::alarm_text($alarms);
         }
     }
 
     /**
      * Render localized text for a single alarm property
      */
     public static function alarm_text($alarm)
     {
         $related = null;
 
         if (is_string($alarm)) {
             list($trigger, $action) = explode(':', $alarm);
         }
         else {
             $trigger = $alarm['trigger'];
             $action  = $alarm['action'];
 
             if (!empty($alarm['related'])) {
                 $related = $alarm['related'];
             }
         }
 
         $text  = '';
         $rcube = rcube::get_instance();
 
         switch ($action) {
         case 'EMAIL':
             $text = $rcube->gettext('libcalendaring.alarmemail');
             break;
         case 'DISPLAY':
             $text = $rcube->gettext('libcalendaring.alarmdisplay');
             break;
         case 'AUDIO':
             $text = $rcube->gettext('libcalendaring.alarmaudio');
             break;
         }
 
         if ($trigger instanceof DateTimeInterface) {
             $text .= ' ' . $rcube->gettext(array(
                 'name' => 'libcalendaring.alarmat',
                 'vars' => array('datetime' => $rcube->format_date($trigger))
             ));
         }
         else if (preg_match('/@(\d+)/', $trigger, $m)) {
             $text .= ' ' . $rcube->gettext(array(
                 'name' => 'libcalendaring.alarmat',
                 'vars' => array('datetime' => $rcube->format_date($m[1]))
             ));
         }
         else if ($val = self::parse_alarm_value($trigger)) {
             $r = $related && strtoupper($related) == 'END' ? 'end' : '';
             // TODO: for all-day events say 'on date of event at XX' ?
             if ($val[0] == 0) {
                 $text .= ' ' . $rcube->gettext('libcalendaring.triggerattime' . $r);
             }
             else {
                 $label = 'libcalendaring.trigger' . $r . $val[1];
                 $text .= ' ' . intval($val[0]) . ' ' . $rcube->gettext($label);
             }
         }
         else {
             return false;
         }
 
         return $text;
     }
 
     /**
      * Get the next alarm (time & action) for the given event
      *
      * @param array Record data
      * @return array Hash array with alarm time/type or null if no alarms are configured
      */
     public static function get_next_alarm($rec, $type = 'event')
     {
         if (
             (empty($rec['valarms']) && empty($rec['alarms']))
             || !empty($rec['cancelled'])
             || (!empty($rec['status']) && $rec['status'] == 'CANCELLED')
         ) {
             return null;
         }
 
         if ($type == 'task') {
             $timezone = self::get_instance()->timezone;
             if (!empty($rec['startdate'])) {
                 $time = !empty($rec['starttime']) ? $rec['starttime'] : '12:00';
                 $rec['start'] = new DateTime($rec['startdate'] . ' ' . $time, $timezone);
             }
             if (!empty($rec['date'])) {
                 $time = !empty($rec['time']) ? $rec['time'] : '12:00';
                 $rec[!empty($rec['start']) ? 'end' : 'start'] = new DateTime($rec['date'] . ' ' . $time, $timezone);
             }
         }
 
         if (empty($rec['end'])) {
             $rec['end'] = $rec['start'];
         }
 
         // support legacy format
         if (empty($rec['valarms'])) {
             list($trigger, $action) = explode(':', $rec['alarms'], 2);
             if ($alarm = self::parse_alarm_value($trigger)) {
                 $rec['valarms'] = array(array('action' => $action, 'trigger' => $alarm[3] ?: $alarm[0]));
             }
         }
 
         // alarm ID eq. record ID by default to keep backwards compatibility
         $alarm_id   = isset($rec['id']) ? $rec['id'] : null;
         $alarm_prop = null;
         $expires    = new DateTime('now - 12 hours');
         $notify_at  = null;
 
         // handle multiple alarms
         foreach ($rec['valarms'] as $alarm) {
             $notify_time = null;
 
             if ($alarm['trigger'] instanceof DateTimeInterface) {
                 $notify_time = $alarm['trigger'];
             }
             else if (is_string($alarm['trigger'])) {
                 $refdate = !empty($alarm['related']) && $alarm['related'] == 'END' ? $rec['end'] : $rec['start'];
 
                 // abort if no reference date is available to compute notification time
                 if (!is_a($refdate, 'DateTime')) {
                     continue;
                 }
 
                 // TODO: for all-day events, take start @ 00:00 as reference date ?
 
                 try {
                     $interval = new DateInterval(trim($alarm['trigger'], '+-'));
                     $interval->invert = $alarm['trigger'][0] == '-';
                     $notify_time = clone $refdate;
                     $notify_time->add($interval);
                 }
                 catch (Exception $e) {
                     rcube::raise_error($e, true);
                     continue;
                 }
             }
 
             if ($notify_time && (!$notify_at || ($notify_time > $notify_at && $notify_time > $expires))) {
                 $notify_at  = $notify_time;
                 $action     = isset($alarm['action']) ? $alarm['action'] : null;
                 $alarm_prop = $alarm;
 
                 // generate a unique alarm ID if multiple alarms are set
                 if (count($rec['valarms']) > 1) {
                     $rec_id = substr(md5(isset($rec['id']) ? $rec['id'] : 'none'), 0, 16);
                     $alarm_id = $rec_id . '-' . $notify_at->format('Ymd\THis');
                 }
             }
         }
 
         return !$notify_at ? null : array(
             'time'   => $notify_at->format('U'),
             'action' => !empty($action) ? strtoupper($action) : 'DISPLAY',
             'id'     => $alarm_id,
             'prop'   => $alarm_prop,
         );
     }
 
     /**
      * Handler for keep-alive requests
      * This will check for pending notifications and pass them to the client
      */
     public function refresh($attr)
     {
         // collect pending alarms from all providers (e.g. calendar, tasks)
         $plugin = $this->rc->plugins->exec_hook('pending_alarms', array(
             'time' => time(),
             'alarms' => array(),
         ));
 
         if (!$plugin['abort'] && !empty($plugin['alarms'])) {
             // make sure texts and env vars are available on client
             $this->add_texts('localization/', true);
             $this->rc->output->add_label('close');
             $this->rc->output->set_env('snooze_select', $this->snooze_select());
             $this->rc->output->command('plugin.display_alarms', $this->_alarms_output($plugin['alarms']));
         }
     }
 
     /**
      * Handler for alarm dismiss/snooze requests
      */
     public function alarms_action()
     {
 //        $action = rcube_utils::get_input_value('action', rcube_utils::INPUT_GPC);
         $data  = rcube_utils::get_input_value('data', rcube_utils::INPUT_POST, true);
 
         $data['ids'] = explode(',', $data['id']);
         $plugin = $this->rc->plugins->exec_hook('dismiss_alarms', $data);
 
         if (!empty($plugin['success'])) {
             $this->rc->output->show_message('successfullysaved', 'confirmation');
         }
         else {
             $this->rc->output->show_message('calendar.errorsaving', 'error');
         }
     }
 
     /**
      * Generate reduced and streamlined output for pending alarms
      */
     private function _alarms_output($alarms)
     {
         $out = array();
         foreach ($alarms as $alarm) {
             $out[] = array(
                 'id'       => $alarm['id'],
                 'start'    => !empty($alarm['start']) ? $this->adjust_timezone($alarm['start'])->format('c') : '',
                 'end'      => !empty($alarm['end'])? $this->adjust_timezone($alarm['end'])->format('c') : '',
                 'allDay'   => !empty($alarm['allday']),
                 'action'   => $alarm['action'],
                 'title'    => $alarm['title'],
                 'location' => $alarm['location'],
                 'calendar' => $alarm['calendar'],
             );
         }
 
         return $out;
     }
 
     /**
      * Render a dropdown menu to choose snooze time
      */
     private function snooze_select($attrib = array())
     {
         $steps = array(
              5 => 'repeatinmin',
             10 => 'repeatinmin',
             15 => 'repeatinmin',
             20 => 'repeatinmin',
             30 => 'repeatinmin',
             60 => 'repeatinhr',
             120 => 'repeatinhrs',
             1440 => 'repeattomorrow',
             10080 => 'repeatinweek',
         );
 
         $items = array();
         foreach ($steps as $n => $label) {
             $items[] = html::tag('li', null, html::a(array('href' => "#" . ($n * 60), 'class' => 'active'),
                 $this->gettext(array('name' => $label, 'vars' => array('min' => $n % 60, 'hrs' => intval($n / 60))))));
         }
 
         return html::tag('ul', $attrib + array('class' => 'toolbarmenu menu'), join("\n", $items), html::$common_attrib);
     }
 
 
     /*********  Recurrence rules handling ********/
 
     /**
      * Render localized text describing the recurrence rule of an event
      */
     public function recurrence_text($rrule)
     {
         $limit     = 10;
         $exdates   = array();
         $format    = $this->rc->config->get('calendar_date_format', $this->defaults['calendar_date_format']);
         $format    = self::to_php_date_format($format);
         $format_fn = function($dt) use ($format) {
             return rcmail::get_instance()->format_date($dt, $format);
         };
 
         if (!empty($rrule['EXDATE']) && is_array($rrule['EXDATE'])) {
             $exdates = array_map($format_fn, $rrule['EXDATE']);
         }
 
         if (empty($rrule['FREQ']) && !empty($rrule['RDATE'])) {
             $rdates = array_map($format_fn, $rrule['RDATE']);
             $more   = false;
 
             if (!empty($exdates)) {
                 $rdates = array_diff($rdates, $exdates);
             }
 
             if (count($rdates) > $limit) {
                 $rdates = array_slice($rdates, 0, $limit);
                 $more   = true;
             }
 
             return $this->gettext('ondate') . ' ' . join(', ', $rdates) . ($more ? '...' : '');
         }
 
         $output  = sprintf('%s %d ', $this->gettext('every'), $rrule['INTERVAL'] ?: 1);
 
         switch ($rrule['FREQ']) {
         case 'DAILY':
             $output .= $this->gettext('days');
             break;
         case 'WEEKLY':
             $output .= $this->gettext('weeks');
             break;
         case 'MONTHLY':
             $output .= $this->gettext('months');
             break;
         case 'YEARLY':
             $output .= $this->gettext('years');
             break;
         }
 
         if (!empty($rrule['COUNT'])) {
             $until = $this->gettext(array('name' => 'forntimes', 'vars' => array('nr' => $rrule['COUNT'])));
         }
         else if (!empty($rrule['UNTIL'])) {
             $until = $this->gettext('recurrencend') . ' ' . $this->rc->format_date($rrule['UNTIL'], $format);
         }
         else {
             $until = $this->gettext('forever');
         }
 
         $output .= ', ' . $until;
 
         if (!empty($exdates)) {
             $more = false;
             if (count($exdates) > $limit) {
                 $exdates = array_slice($exdates, 0, $limit);
                 $more    = true;
             }
 
             $output  .= '; ' . $this->gettext('except') . ' ' . join(', ', $exdates) . ($more ? '...' : '');
         }
 
         return $output;
     }
 
     /**
      * Generate the form for recurrence settings
      */
     public function recurrence_form($attrib = array())
     {
         switch ($attrib['part']) {
             // frequency selector
             case 'frequency':
                 $select = new html_select(array('name' => 'frequency', 'id' => 'edit-recurrence-frequency', 'class' => 'form-control'));
                 $select->add($this->gettext('never'),   '');
                 $select->add($this->gettext('daily'),   'DAILY');
                 $select->add($this->gettext('weekly'),  'WEEKLY');
                 $select->add($this->gettext('monthly'), 'MONTHLY');
                 $select->add($this->gettext('yearly'),  'YEARLY');
                 $select->add($this->gettext('rdate'),   'RDATE');
                 $html = html::label(array('for' => 'edit-recurrence-frequency', 'class' => 'col-form-label col-sm-2'), $this->gettext('frequency'))
                     . html::div('col-sm-10', $select->show(''));
                 break;
 
             // daily recurrence
             case 'daily':
                 $select = $this->interval_selector(array('name' => 'interval', 'class' => 'edit-recurrence-interval form-control', 'id' => 'edit-recurrence-interval-daily'));
                 $html = html::div($attrib, html::label(array('for' => 'edit-recurrence-interval-daily', 'class' => 'col-form-label col-sm-2'), $this->gettext('every'))
                     . html::div('col-sm-10 input-group', $select->show(1) . html::span('label-after input-group-append', html::span('input-group-text', $this->gettext('days')))));
                 break;
 
             // weekly recurrence form
             case 'weekly':
                 $select = $this->interval_selector(array('name' => 'interval', 'class' => 'edit-recurrence-interval form-control', 'id' => 'edit-recurrence-interval-weekly'));
                 $html = html::div($attrib, html::label(array('for' => 'edit-recurrence-interval-weekly', 'class' => 'col-form-label col-sm-2'), $this->gettext('every'))
                     . html::div('col-sm-10 input-group', $select->show(1) . html::span('label-after input-group-append', html::span('input-group-text', $this->gettext('weeks')))));
 
                 // weekday selection
                 $daymap   = array('sun','mon','tue','wed','thu','fri','sat');
                 $checkbox = new html_checkbox(array('name' => 'byday', 'class' => 'edit-recurrence-weekly-byday'));
                 $first    = $this->rc->config->get('calendar_first_day', 1);
 
                 for ($weekdays = '', $j = $first; $j <= $first+6; $j++) {
                     $d = $j % 7;
                     $weekdays .= html::label(array('class' => 'weekday'),
                         $checkbox->show('', array('value' => strtoupper(substr($daymap[$d], 0, 2)))) .
                         $this->gettext($daymap[$d])
                     ) . ' ';
                 }
 
                 $html .= html::div($attrib, html::label(array('class' => 'col-form-label col-sm-2'), $this->gettext('bydays'))
                     . html::div('col-sm-10 form-control-plaintext', $weekdays));
                 break;
 
             // monthly recurrence form
             case 'monthly':
                 $select = $this->interval_selector(array('name' => 'interval', 'class' => 'edit-recurrence-interval form-control', 'id' => 'edit-recurrence-interval-monthly'));
                 $html = html::div($attrib, html::label(array('for' => 'edit-recurrence-interval-monthly', 'class' => 'col-form-label col-sm-2'), $this->gettext('every'))
                     . html::div('col-sm-10 input-group', $select->show(1) . html::span('label-after input-group-append', html::span('input-group-text', $this->gettext('months')))));
 
                 $checkbox = new html_checkbox(array('name' => 'bymonthday', 'class' => 'edit-recurrence-monthly-bymonthday'));
                 for ($monthdays = '', $d = 1; $d <= 31; $d++) {
                     $monthdays .= html::label(array('class' => 'monthday'), $checkbox->show('', array('value' => $d)) . $d);
                     $monthdays .= $d % 7 ? ' ' : html::br();
                 }
 
                 // rule selectors
                 $radio = new html_radiobutton(array('name' => 'repeatmode', 'class' => 'edit-recurrence-monthly-mode'));
                 $table = new html_table(array('cols' => 2, 'border' => 0, 'cellpadding' => 0, 'class' => 'formtable'));
                 $table->add('label', html::label(null, $radio->show('BYMONTHDAY', array('value' => 'BYMONTHDAY')) . ' ' . $this->gettext('each')));
                 $table->add(null, $monthdays);
                 $table->add('label', html::label(null, $radio->show('', array('value' => 'BYDAY')) . ' ' . $this->gettext('every')));
                 $table->add('recurrence-onevery', $this->rrule_selectors($attrib['part']));
 
                 $html .= html::div($attrib, html::label(array('class' => 'col-form-label col-sm-2'), $this->gettext('bydays'))
                     . html::div('col-sm-10 form-control-plaintext', $table->show()));
                 break;
 
             // annually recurrence form
             case 'yearly':
                 $select = $this->interval_selector(array('name' => 'interval', 'class' => 'edit-recurrence-interval form-control', 'id' => 'edit-recurrence-interval-yearly'));
                 $html = html::div($attrib, html::label(array('for' => 'edit-recurrence-interval-yearly', 'class' => 'col-form-label col-sm-2'), $this->gettext('every'))
                     . html::div('col-sm-10 input-group', $select->show(1) . html::span('label-after input-group-append', html::span('input-group-text', $this->gettext('years')))));
 
                 // month selector
                 $monthmap = array('','jan','feb','mar','apr','may','jun','jul','aug','sep','oct','nov','dec');
                 $checkbox = new html_checkbox(array('name' => 'bymonth', 'class' => 'edit-recurrence-yearly-bymonth'));
 
                 for ($months = '', $m = 1; $m <= 12; $m++) {
                     $months .= html::label(array('class' => 'month'), $checkbox->show(null, array('value' => $m)) . $this->gettext($monthmap[$m]));
                     $months .= $m % 4 ? ' ' : html::br();
                 }
 
                 $html .= html::div($attrib, html::label(array('class' => 'col-form-label col-sm-2'), $this->gettext('bymonths'))
                     . html::div('col-sm-10 form-control-plaintext',
                         html::div(array('id' => 'edit-recurrence-yearly-bymonthblock'), $months)
                         . html::div('recurrence-onevery', $this->rrule_selectors($attrib['part'], '---'))
                     ));
                 break;
 
             // end of recurrence form
             case 'until':
                 $radio  = new html_radiobutton(array('name' => 'repeat', 'class' => 'edit-recurrence-until'));
                 $select = $this->interval_selector(array('name' => 'times', 'id' => 'edit-recurrence-repeat-times', 'class' => 'form-control'));
                 $input  = new html_inputfield(array('name' => 'untildate', 'id' => 'edit-recurrence-enddate', 'size' => '10', 'class' => 'form-control datepicker'));
 
                 $html = html::div('line first',
                     $radio->show('', array('value' => '', 'id' => 'edit-recurrence-repeat-forever'))
                         . ' ' . html::label('edit-recurrence-repeat-forever', $this->gettext('forever'))
                 );
 
                 $label = $this->gettext('ntimes');
                 if (strpos($label, '$') === 0) {
                     $label = str_replace('$n', '', $label);
                     $group  = $select->show(1)
                         . html::span('input-group-append', html::span('input-group-text', rcube::Q($label)));
                 }
                 else {
                     $label = str_replace('$n', '', $label);
                     $group  = html::span('input-group-prepend', html::span('input-group-text', rcube::Q($label)))
                         . $select->show(1);
                 }
 
                 $html .= html::div('line',
                     $radio->show('', array('value' => 'count', 'id' => 'edit-recurrence-repeat-count'))
                         . ' ' . html::label('edit-recurrence-repeat-count', $this->gettext('for'))
                         . ' ' . html::span('input-group', $group)
                 );
 
                 $html .= html::div('line',
                     $radio->show('', array('value' => 'until', 'id' => 'edit-recurrence-repeat-until', 'aria-label' => $this->gettext('untilenddate')))
                         . ' ' . html::label('edit-recurrence-repeat-until', $this->gettext('untildate'))
                         . ' ' . $input->show('', array('aria-label' => $this->gettext('untilenddate')))
                 );
 
                 $html = html::div($attrib, html::label(array('class' => 'col-form-label col-sm-2'), ucfirst($this->gettext('recurrencend')))
                     . html::div('col-sm-10', $html));
                 break;
 
             case 'rdate':
                 $ul     = html::tag('ul', array('id' => 'edit-recurrence-rdates', 'class' => 'recurrence-rdates'), '');
                 $input  = new html_inputfield(array('name' => 'rdate', 'id' => 'edit-recurrence-rdate-input', 'size' => "10", 'class' => 'form-control datepicker'));
                 $button = new html_inputfield(array('type' => 'button', 'class' => 'button add', 'value' => $this->gettext('addrdate')));
 
                 $html = html::div($attrib, html::label(array('class' => 'col-form-label col-sm-2', 'for' => 'edit-recurrence-rdate-input'), $this->gettext('bydates'))
                     . html::div('col-sm-10', $ul . html::div('inputform', $input->show() . $button->show())));
                 break;
         }
 
         return $html;
     }
 
     /**
      * Input field for interval selection
      */
     private function interval_selector($attrib)
     {
         $select = new html_select($attrib);
         $select->add(range(1,30), range(1,30));
         return $select;
     }
 
     /**
      * Drop-down menus for recurrence rules like "each last sunday of"
      */
     private function rrule_selectors($part, $noselect = null)
     {
         // rule selectors
         $select_prefix = new html_select(array('name' => 'bydayprefix', 'id' => "edit-recurrence-$part-prefix", 'class' => 'form-control'));
         if ($noselect) $select_prefix->add($noselect, '');
         $select_prefix->add(array(
                 $this->gettext('first'),
                 $this->gettext('second'),
                 $this->gettext('third'),
                 $this->gettext('fourth'),
                 $this->gettext('last')
             ),
             array(1, 2, 3, 4, -1));
 
         $select_wday = new html_select(array('name' => 'byday', 'id' => "edit-recurrence-$part-byday", 'class' => 'form-control'));
         if ($noselect) $select_wday->add($noselect, '');
 
         $daymap = array('sunday','monday','tuesday','wednesday','thursday','friday','saturday');
         $first = $this->rc->config->get('calendar_first_day', 1);
         for ($j = $first; $j <= $first+6; $j++) {
             $d = $j % 7;
             $select_wday->add($this->gettext($daymap[$d]), strtoupper(substr($daymap[$d], 0, 2)));
         }
 
         return $select_prefix->show() . '&nbsp;' . $select_wday->show();
     }
 
     /**
      * Convert the recurrence settings to be processed on the client
      */
     public function to_client_recurrence($recurrence, $allday = false)
     {
         if (!empty($recurrence['UNTIL'])) {
             $recurrence['UNTIL'] = $this->adjust_timezone($recurrence['UNTIL'], $allday)->format('c');
         }
 
         // format RDATE values
         if (!empty($recurrence['RDATE'])) {
             $libcal = $this;
             $recurrence['RDATE'] = array_map(function($rdate) use ($libcal) {
                 return $libcal->adjust_timezone($rdate, true)->format('c');
             }, (array) $recurrence['RDATE']);
         }
 
         unset($recurrence['EXCEPTIONS']);
 
         return $recurrence;
     }
 
     /**
      * Process the alarms values submitted by the client
      */
     public function from_client_recurrence($recurrence, $start = null)
     {
         if (is_array($recurrence) && !empty($recurrence['UNTIL'])) {
             $recurrence['UNTIL'] = new DateTime($recurrence['UNTIL'], $this->timezone);
         }
 
         if (is_array($recurrence) && !empty($recurrence['RDATE'])) {
             $tz = $this->timezone;
             $recurrence['RDATE'] = array_map(function($rdate) use ($tz, $start) {
                 try {
                     $dt = new DateTime($rdate, $tz);
                     if (is_a($start, 'DateTime'))
                         $dt->setTime($start->format('G'), $start->format('i'));
                     return $dt;
                 }
                 catch (Exception $e) {
                     return null;
                 }
             }, $recurrence['RDATE']);
         }
 
         return $recurrence;
     }
 
 
     /*********  iTip message detection  *********/
 
     /**
      * Check mail message structure of there are .ics files attached
      */
     public function mail_message_load($p)
     {
         $this->ical_message = $p['object'];
         $itip_part          = null;
 
         // check all message parts for .ics files
         foreach ((array)$this->ical_message->mime_parts as $part) {
             if (self::part_is_vcalendar($part, $this->ical_message)) {
                 if (!empty($part->ctype_parameters['method'])) {
                     $itip_part = $part->mime_id;
                 }
                 else {
                     $this->ical_parts[] = $part->mime_id;
                 }
             }
         }
 
         // priorize part with method parameter
         if ($itip_part) {
             $this->ical_parts = array($itip_part);
         }
     }
 
     /**
      * Getter for the parsed iCal objects attached to the current email message
      *
      * @return object libcalendaring_vcalendar parser instance with the parsed objects
      */
     public function get_mail_ical_objects()
     {
         // create parser and load ical objects
         if (!$this->mail_ical_parser) {
             $this->mail_ical_parser = $this->get_ical();
 
             foreach ($this->ical_parts as $mime_id) {
                 $part    = $this->ical_message->mime_parts[$mime_id];
                 $charset = $part->ctype_parameters['charset'] ?: RCUBE_CHARSET;
                 $this->mail_ical_parser->import($this->ical_message->get_part_body($mime_id, true), $charset);
 
                 // check if the parsed object is an instance of a recurring event/task
                 array_walk($this->mail_ical_parser->objects, 'libcalendaring::identify_recurrence_instance');
 
                 // stop on the part that has an iTip method specified
                 if (count($this->mail_ical_parser->objects) && $this->mail_ical_parser->method) {
                     $this->mail_ical_parser->message_date = $this->ical_message->headers->date;
                     $this->mail_ical_parser->mime_id = $mime_id;
 
                     // store the message's sender address for comparisons
                     $from = rcube_mime::decode_address_list($this->ical_message->headers->from, 1, true, null, true);
                     $this->mail_ical_parser->sender = !empty($from) ? $from[1] : '';
 
                     if (!empty($this->mail_ical_parser->sender)) {
                         foreach ($this->mail_ical_parser->objects as $i => $object) {
                             $this->mail_ical_parser->objects[$i]['_sender'] = $this->mail_ical_parser->sender;
                             $this->mail_ical_parser->objects[$i]['_sender_utf'] = rcube_utils::idn_to_utf8($this->mail_ical_parser->sender);
                         }
                     }
 
                     break;
                 }
             }
         }
 
         return $this->mail_ical_parser;
     }
 
     /**
      * Read the given mime message from IMAP and parse ical data
      *
      * @param string Mailbox name
      * @param string Message UID
      * @param string Message part ID and object index (e.g. '1.2:0')
      * @param string Object type filter (optional)
      *
      * @return array Hash array with the parsed iCal 
      */
     public function mail_get_itip_object($mbox, $uid, $mime_id, $type = null)
     {
         $charset = RCUBE_CHARSET;
 
         // establish imap connection
         $imap = $this->rc->get_storage();
         $imap->set_folder($mbox);
 
         if ($uid && $mime_id) {
             list($mime_id, $index) = explode(':', $mime_id);
 
             $part    = $imap->get_message_part($uid, $mime_id);
             $headers = $imap->get_message_headers($uid);
             $parser  = $this->get_ical();
 
             if (!empty($part->ctype_parameters['charset'])) {
                 $charset = $part->ctype_parameters['charset'];
             }
 
             if ($part) {
                 $objects = $parser->import($part, $charset);
             }
         }
 
         // successfully parsed events/tasks?
         if (!empty($objects) && ($object = $objects[$index]) && (!$type || $object['_type'] == $type)) {
             if ($parser->method)
                 $object['_method'] = $parser->method;
 
             // store the message's sender address for comparisons
             $from = rcube_mime::decode_address_list($headers->from, 1, true, null, true);
             $object['_sender'] = !empty($from) ? $from[1] : '';
             $object['_sender_utf'] = rcube_utils::idn_to_utf8($object['_sender']);
 
             // check if this is an instance of a recurring event/task
             self::identify_recurrence_instance($object);
 
             return $object;
         }
 
         return null;
     }
 
     /**
      * Checks if specified message part is a vcalendar data
      *
      * @param rcube_message_part Part object
      * @param rcube_message      Message object
      *
      * @return boolean True if part is of type vcard
      */
     public static function part_is_vcalendar($part, $message = null)
     {
         // First check if the message is "valid" (i.e. not multipart/report)
         if ($message) {
             $level = explode('.', $part->mime_id);
 
             while (array_pop($level) !== null) {
                 $id     = join('.', $level) ?: 0;
                 $parent = !empty($message->mime_parts[$id]) ? $message->mime_parts[$id] : null;
                 if ($parent && $parent->mimetype == 'multipart/report') {
                     return false;
                 }
             }
         }
 
         return (
             in_array($part->mimetype, array('text/calendar', 'text/x-vcalendar', 'application/ics')) ||
             // Apple sends files as application/x-any (!?)
             ($part->mimetype == 'application/x-any' && !empty($part->filename) && preg_match('/\.ics$/i', $part->filename))
         );
     }
 
     /**
      * Single occourrences of recurring events are identified by their RECURRENCE-ID property
      * in iCal which is represented as 'recurrence_date' in our internal data structure.
      *
      * Check if such a property exists and derive the '_instance' identifier and '_savemode'
      * attributes which are used in the storage backend to identify the nested exception item.
      */
     public static function identify_recurrence_instance(&$object)
     {
         // for savemode=all, remove recurrence instance identifiers
-        if (!empty($object['_savemode']) && $object['_savemode'] == 'all' && $object['recurrence']) {
+        if (!empty($object['_savemode']) && $object['_savemode'] == 'all' && !empty($object['recurrence'])) {
             unset($object['_instance'], $object['recurrence_date']);
         }
         // set instance and 'savemode' according to recurrence-id
         else if (!empty($object['recurrence_date']) && is_a($object['recurrence_date'], 'DateTime')) {
             $object['_instance'] = self::recurrence_instance_identifier($object);
             $object['_savemode'] = $object['thisandfuture'] ? 'future' : 'current';
         }
         else if (!empty($object['recurrence_id']) && !empty($object['_instance'])) {
             if (strlen($object['_instance']) > 4) {
                 $object['recurrence_date'] = rcube_utils::anytodatetime($object['_instance'], $object['start']->getTimezone());
             }
             else {
                 $object['recurrence_date'] = clone $object['start'];
             }
         }
     }
 
     /**
      * Return a date() format string to render identifiers for recurrence instances
      *
      * @param array Hash array with event properties
      * @return string Format string
      */
     public static function recurrence_id_format($event)
     {
         return !empty($event['allday']) ? 'Ymd' : 'Ymd\THis';
     }
 
     /**
      * Return the identifer for the given instance of a recurring event
      *
      * @param array Hash array with event properties
      * @param bool  All-day flag from the main event
      *
      * @return mixed Format string or null if identifier cannot be generated
      */
     public static function recurrence_instance_identifier($event, $allday = null)
     {
         $instance_date = !empty($event['recurrence_date']) ? $event['recurrence_date'] : $event['start'];
 
         if ($instance_date instanceof DateTimeInterface) {
             // According to RFC5545 (3.8.4.4) RECURRENCE-ID format should
             // be date/date-time depending on the main event type, not the exception
             if ($allday === null) {
                 $allday = !empty($event['allday']);
             }
 
             return $instance_date->format($allday ? 'Ymd' : 'Ymd\THis');
         }
     }
 
 
     /*********  Attendee handling functions  *********/
 
     /**
      * Handler for attendee group expansion requests
      */
     public function expand_attendee_group()
     {
         $id     = rcube_utils::get_input_value('id', rcube_utils::INPUT_POST);
         $data   = rcube_utils::get_input_value('data', rcube_utils::INPUT_POST, true);
         $result = array('id' => $id, 'members' => array());
         $maxnum = 500;
 
         // iterate over all autocomplete address books (we don't know the source of the group)
         foreach ((array)$this->rc->config->get('autocomplete_addressbooks', 'sql') as $abook_id) {
             if (($abook = $this->rc->get_address_book($abook_id)) && $abook->groups) {
                 foreach ($abook->list_groups($data['name'], 1) as $group) {
                     // this is the matching group to expand
                     if (in_array($data['email'], (array)$group['email'])) {
                         $abook->set_pagesize($maxnum);
                         $abook->set_group($group['ID']);
 
                         // get all members
                         $res = $abook->list_records($this->rc->config->get('contactlist_fields'));
 
                         // handle errors (e.g. sizelimit, timelimit)
                         if ($abook->get_error()) {
                             $result['error'] = $this->rc->gettext('expandattendeegrouperror', 'libcalendaring');
                             $res = false;
                         }
                         // check for maximum number of members (we don't wanna bloat the UI too much)
                         else if ($res->count > $maxnum) {
                             $result['error'] = $this->rc->gettext('expandattendeegroupsizelimit', 'libcalendaring');
                             $res = false;
                         }
 
                         while ($res && ($member = $res->iterate())) {
                             $emails = (array)$abook->get_col_values('email', $member, true);
                             if (!empty($emails) && ($email = array_shift($emails))) {
                                 $result['members'][] = array(
                                     'email' => $email,
                                     'name' => rcube_addressbook::compose_list_name($member),
                                 );
                             }
                         }
 
                         break 2;
                     }
                 }
             }
         }
 
         $this->rc->output->command('plugin.expand_attendee_callback', $result);
     }
 
     /**
      * Merge attendees of the old and new event version
      * with keeping current user and his delegatees status
      *
      * @param array &$new   New object data
      * @param array $old    Old object data
      * @param bool  $status New status of the current user
      */
     public function merge_attendees(&$new, $old, $status = null)
     {
         if (empty($status)) {
             $emails    = $this->get_user_emails();
             $delegates = array();
             $attendees = array();
 
             // keep attendee status of the current user
             foreach ((array) $new['attendees'] as $i => $attendee) {
                 if (empty($attendee['email'])) {
                     continue;
                 }
 
                 $attendees[] = $email = strtolower($attendee['email']);
 
                 if (in_array($email, $emails)) {
                     foreach ($old['attendees'] as $_attendee) {
                         if ($attendee['email'] == $_attendee['email']) {
                             $new['attendees'][$i] = $_attendee;
                             if ($_attendee['status'] == 'DELEGATED' && ($email = $_attendee['delegated-to'])) {
                                 $delegates[] = strtolower($email);
                             }
 
                             break;
                         }
                     }
                 }
             }
 
             // make sure delegated attendee is not lost
             foreach ($delegates as $delegatee) {
                 if (!in_array($delegatee, $attendees)) {
                     foreach ((array) $old['attendees'] as $attendee) {
                         if ($attendee['email'] && ($email = strtolower($attendee['email'])) && $email == $delegatee) {
                             $new['attendees'][] = $attendee;
                             break;
                         }
                     }
                 }
             }
         }
 
         // We also make sure that status of any attendee
         // is not overriden by NEEDS-ACTION if it was already set
         // which could happen if you work with shared events
         foreach ((array) $new['attendees'] as $i => $attendee) {
             if ($attendee['email'] && $attendee['status'] == 'NEEDS-ACTION') {
                 foreach ($old['attendees'] as $_attendee) {
                     if ($attendee['email'] == $_attendee['email']) {
                         $new['attendees'][$i]['status'] = $_attendee['status'];
                         unset($new['attendees'][$i]['rsvp']);
                         break;
                     }
                 }
             }
         }
     }
 
 
     /*********  Static utility functions  *********/
 
     /**
      * Convert the internal structured data into a vcalendar rrule 2.0 string
      */
     public static function to_rrule($recurrence, $allday = false)
     {
         if (is_string($recurrence)) {
             return $recurrence;
         }
 
         $rrule = '';
         foreach ((array)$recurrence as $k => $val) {
             $k = strtoupper($k);
             switch ($k) {
             case 'UNTIL':
                 // convert to UTC according to RFC 5545
                 if (is_a($val, 'DateTime')) {
                     if (!$allday && empty($val->_dateonly)) {
                         $until = clone $val;
                         $until->setTimezone(new DateTimeZone('UTC'));
                         $val = $until->format('Ymd\THis\Z');
                     }
                     else {
                         $val = $val->format('Ymd');
                     }
                 }
                 break;
             case 'RDATE':
             case 'EXDATE':
                 foreach ((array)$val as $i => $ex) {
                     if (is_a($ex, 'DateTime')) {
                         $val[$i] = $ex->format('Ymd\THis');
                     }
                 }
                 $val = join(',', (array)$val);
                 break;
             case 'EXCEPTIONS':
                 continue 2;
             }
 
             if (strlen($val)) {
                 $rrule .= $k . '=' . $val . ';';
             }
         }
 
         return rtrim($rrule, ';');
     }
 
     /**
      * Convert from fullcalendar date format to PHP date() format string
      */
     public static function to_php_date_format($from)
     {
         // "dd.MM.yyyy HH:mm:ss" => "d.m.Y H:i:s"
         return strtr(strtr($from, array(
             'YYYY' => 'Y',
             'YY'   => 'y',
             'yyyy' => 'Y',
             'yy'   => 'y',
             'MMMM' => 'F',
             'MMM'  => 'M',
             'MM'   => 'm',
             'M'    => 'n',
             'dddd' => 'l',
             'ddd'  => 'D',
             'DD'   => 'd',
             'D'    => 'j',
             'HH'   => '**',
             'hh'   => '%%',
             'H'    => 'G',
             'h'    => 'g',
             'mm'   => 'i',
             'ss'   => 's',
             'TT'   => 'A',
             'tt'   => 'a',
             'T'    => 'A',
             't'    => 'a',
             'u'    => 'c',
         )), array(
             '**'   => 'H',
             '%%'   => 'h',
         ));
     }
 
     /**
      * Convert from PHP date() format to fullcalendar (MomentJS) format string
      */
     public static function from_php_date_format($from)
     {
         // "d.m.Y H:i:s" => "dd.MM.yyyy HH:mm:ss"
         return strtr($from, array(
             'y' => 'YY',
             'Y' => 'YYYY',
             'M' => 'MMM',
             'F' => 'MMMM',
             'm' => 'MM',
             'n' => 'M',
             'j' => 'D',
             'd' => 'DD',
             'D' => 'ddd',
             'l' => 'dddd',
             'H' => 'HH',
             'h' => 'hh',
             'G' => 'H',
             'g' => 'h',
             'i' => 'mm',
             's' => 'ss',
             'c' => '',
         ));
     }
 }
diff --git a/plugins/libkolab/lib/kolab_format.php b/plugins/libkolab/lib/kolab_format.php
index 325dd2c0..9f7c537f 100644
--- a/plugins/libkolab/lib/kolab_format.php
+++ b/plugins/libkolab/lib/kolab_format.php
@@ -1,797 +1,797 @@
 <?php
 
 /**
  * Kolab format model class wrapping libkolabxml bindings
  *
  * Abstract base class for different Kolab groupware objects read from/written
  * to the new Kolab 3 format using the PHP bindings of libkolabxml.
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2012, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 abstract class kolab_format
 {
     public static $timezone;
 
     public /*abstract*/ $CTYPE;
     public /*abstract*/ $CTYPEv2;
 
     protected /*abstract*/ $objclass;
     protected /*abstract*/ $read_func;
     protected /*abstract*/ $write_func;
 
     protected $obj;
     protected $data;
     protected $xmldata;
     protected $xmlobject;
     protected $formaterror;
     protected $loaded = false;
     protected $version = '3.0';
 
     const KTYPE_PREFIX = 'application/x-vnd.kolab.';
     const PRODUCT_ID   = 'Roundcube-libkolab-1.1';
 
     // mapping table for valid PHP timezones not supported by libkolabxml
     // basically the entire list of ftp://ftp.iana.org/tz/data/backward
     protected static $timezone_map = array(
         'Africa/Asmera' => 'Africa/Asmara',
         'Africa/Timbuktu' => 'Africa/Abidjan',
         'America/Argentina/ComodRivadavia' => 'America/Argentina/Catamarca',
         'America/Atka' => 'America/Adak',
         'America/Buenos_Aires' => 'America/Argentina/Buenos_Aires',
         'America/Catamarca' => 'America/Argentina/Catamarca',
         'America/Coral_Harbour' => 'America/Atikokan',
         'America/Cordoba' => 'America/Argentina/Cordoba',
         'America/Ensenada' => 'America/Tijuana',
         'America/Fort_Wayne' => 'America/Indiana/Indianapolis',
         'America/Indianapolis' => 'America/Indiana/Indianapolis',
         'America/Jujuy' => 'America/Argentina/Jujuy',
         'America/Knox_IN' => 'America/Indiana/Knox',
         'America/Louisville' => 'America/Kentucky/Louisville',
         'America/Mendoza' => 'America/Argentina/Mendoza',
         'America/Porto_Acre' => 'America/Rio_Branco',
         'America/Rosario' => 'America/Argentina/Cordoba',
         'America/Virgin' => 'America/Port_of_Spain',
         'Asia/Ashkhabad' => 'Asia/Ashgabat',
         'Asia/Calcutta' => 'Asia/Kolkata',
         'Asia/Chungking' => 'Asia/Shanghai',
         'Asia/Dacca' => 'Asia/Dhaka',
         'Asia/Katmandu' => 'Asia/Kathmandu',
         'Asia/Macao' => 'Asia/Macau',
         'Asia/Saigon' => 'Asia/Ho_Chi_Minh',
         'Asia/Tel_Aviv' => 'Asia/Jerusalem',
         'Asia/Thimbu' => 'Asia/Thimphu',
         'Asia/Ujung_Pandang' => 'Asia/Makassar',
         'Asia/Ulan_Bator' => 'Asia/Ulaanbaatar',
         'Atlantic/Faeroe' => 'Atlantic/Faroe',
         'Atlantic/Jan_Mayen' => 'Europe/Oslo',
         'Australia/ACT' => 'Australia/Sydney',
         'Australia/Canberra' => 'Australia/Sydney',
         'Australia/LHI' => 'Australia/Lord_Howe',
         'Australia/NSW' => 'Australia/Sydney',
         'Australia/North' => 'Australia/Darwin',
         'Australia/Queensland' => 'Australia/Brisbane',
         'Australia/South' => 'Australia/Adelaide',
         'Australia/Tasmania' => 'Australia/Hobart',
         'Australia/Victoria' => 'Australia/Melbourne',
         'Australia/West' => 'Australia/Perth',
         'Australia/Yancowinna' => 'Australia/Broken_Hill',
         'Brazil/Acre' => 'America/Rio_Branco',
         'Brazil/DeNoronha' => 'America/Noronha',
         'Brazil/East' => 'America/Sao_Paulo',
         'Brazil/West' => 'America/Manaus',
         'Canada/Atlantic' => 'America/Halifax',
         'Canada/Central' => 'America/Winnipeg',
         'Canada/East-Saskatchewan' => 'America/Regina',
         'Canada/Eastern' => 'America/Toronto',
         'Canada/Mountain' => 'America/Edmonton',
         'Canada/Newfoundland' => 'America/St_Johns',
         'Canada/Pacific' => 'America/Vancouver',
         'Canada/Saskatchewan' => 'America/Regina',
         'Canada/Yukon' => 'America/Whitehorse',
         'Chile/Continental' => 'America/Santiago',
         'Chile/EasterIsland' => 'Pacific/Easter',
         'Cuba' => 'America/Havana',
         'Egypt' => 'Africa/Cairo',
         'Eire' => 'Europe/Dublin',
         'Europe/Belfast' => 'Europe/London',
         'Europe/Tiraspol' => 'Europe/Chisinau',
         'GB' => 'Europe/London',
         'GB-Eire' => 'Europe/London',
         'Greenwich' => 'Etc/GMT',
         'Hongkong' => 'Asia/Hong_Kong',
         'Iceland' => 'Atlantic/Reykjavik',
         'Iran' => 'Asia/Tehran',
         'Israel' => 'Asia/Jerusalem',
         'Jamaica' => 'America/Jamaica',
         'Japan' => 'Asia/Tokyo',
         'Kwajalein' => 'Pacific/Kwajalein',
         'Libya' => 'Africa/Tripoli',
         'Mexico/BajaNorte' => 'America/Tijuana',
         'Mexico/BajaSur' => 'America/Mazatlan',
         'Mexico/General' => 'America/Mexico_City',
         'NZ' => 'Pacific/Auckland',
         'NZ-CHAT' => 'Pacific/Chatham',
         'Navajo' => 'America/Denver',
         'PRC' => 'Asia/Shanghai',
         'Pacific/Ponape' => 'Pacific/Pohnpei',
         'Pacific/Samoa' => 'Pacific/Pago_Pago',
         'Pacific/Truk' => 'Pacific/Chuuk',
         'Pacific/Yap' => 'Pacific/Chuuk',
         'Poland' => 'Europe/Warsaw',
         'Portugal' => 'Europe/Lisbon',
         'ROC' => 'Asia/Taipei',
         'ROK' => 'Asia/Seoul',
         'Singapore' => 'Asia/Singapore',
         'Turkey' => 'Europe/Istanbul',
         'UCT' => 'Etc/UCT',
         'US/Alaska' => 'America/Anchorage',
         'US/Aleutian' => 'America/Adak',
         'US/Arizona' => 'America/Phoenix',
         'US/Central' => 'America/Chicago',
         'US/East-Indiana' => 'America/Indiana/Indianapolis',
         'US/Eastern' => 'America/New_York',
         'US/Hawaii' => 'Pacific/Honolulu',
         'US/Indiana-Starke' => 'America/Indiana/Knox',
         'US/Michigan' => 'America/Detroit',
         'US/Mountain' => 'America/Denver',
         'US/Pacific' => 'America/Los_Angeles',
         'US/Samoa' => 'Pacific/Pago_Pago',
         'Universal' => 'Etc/UTC',
         'W-SU' => 'Europe/Moscow',
         'Zulu' => 'Etc/UTC',
     );
 
     /**
      * Factory method to instantiate a kolab_format object of the given type and version
      *
      * @param string Object type to instantiate
      * @param float  Format version
      * @param string Cached xml data to initialize with
      * @return object kolab_format
      */
     public static function factory($type, $version = '3.0', $xmldata = null)
     {
         if (!isset(self::$timezone))
             self::$timezone = new DateTimeZone('UTC');
 
         if (!self::supports($version))
             return PEAR::raiseError("No support for Kolab format version " . $version);
 
         $type = preg_replace('/configuration\.[a-z._]+$/', 'configuration', $type);
         $suffix = preg_replace('/[^a-z]+/', '', $type);
         $classname = 'kolab_format_' . $suffix;
         if (class_exists($classname))
             return new $classname($xmldata, $version);
 
         return PEAR::raiseError("Failed to load Kolab Format wrapper for type " . $type);
     }
 
     /**
      * Determine support for the given format version
      *
      * @param float Format version to check
      * @return boolean True if supported, False otherwise
      */
     public static function supports($version)
     {
         if ($version == '2.0')
             return class_exists('kolabobject');
         // default is version 3
         return class_exists('kolabformat');
     }
 
     /**
      * Convert the given date/time value into a cDateTime object
      *
      * @param mixed         Date/Time value either as unix timestamp, date string or PHP DateTime object
      * @param DateTimeZone  The timezone the date/time is in. Use global default if Null, local time if False
      * @param boolean       True of the given date has no time component
      * @param DateTimeZone  The timezone to convert the date to before converting to cDateTime
      *
      * @return cDateTime The libkolabxml date/time object
      */
     public static function get_datetime($datetime, $tz = null, $dateonly = false, $dest_tz = null)
     {
         // use timezone information from datetime or global setting
         if (!$tz && $tz !== false) {
             if ($datetime instanceof DateTimeInterface)
                 $tz = $datetime->getTimezone();
             if (!$tz)
                 $tz = self::$timezone;
         }
 
         $result = new cDateTime();
 
         try {
             // got a unix timestamp (in UTC)
             if (is_numeric($datetime)) {
                 $datetime = new libcalendaring_datetime('@'.$datetime, new DateTimeZone('UTC'));
                 if ($tz) $datetime->setTimezone($tz);
             }
             else if (is_string($datetime) && strlen($datetime)) {
                 $datetime = $tz ? new libcalendaring_datetime($datetime, $tz) : new libcalendaring_datetime($datetime);
             }
             else if ($datetime instanceof DateTimeInterface) {
                 $datetime = clone $datetime;
             }
         }
         catch (Exception $e) {}
 
         if ($datetime instanceof DateTimeInterface) {
             if ($dest_tz instanceof DateTimeZone && $dest_tz !== $datetime->getTimezone()) {
                 $datetime->setTimezone($dest_tz);
                 $tz = $dest_tz;
             }
 
             $result->setDate($datetime->format('Y'), $datetime->format('n'), $datetime->format('j'));
 
             if ($dateonly) {
                 // Dates should be always in local time only
                 return $result;
             }
 
             $result->setTime($datetime->format('G'), $datetime->format('i'), $datetime->format('s'));
 
             // libkolabxml throws errors on some deprecated timezone names
             $utc_aliases = array('UTC', 'GMT', '+00:00', 'Z', 'Etc/GMT', 'Etc/UTC');
 
             if ($tz && in_array($tz->getName(), $utc_aliases)) {
                 $result->setUTC(true);
             }
             else if ($tz !== false) {
                 $tzid = $tz->getName();
                 if (array_key_exists($tzid, self::$timezone_map))
                     $tzid = self::$timezone_map[$tzid];
                 $result->setTimezone($tzid);
             }
         }
 
         return $result;
     }
 
     /**
      * Convert the given cDateTime into a PHP DateTime object
      *
      * @param cDateTime    The libkolabxml datetime object
      * @param DateTimeZone The timezone to convert the date to
      *
      * @return libcalendaring_datetime PHP datetime instance
      */
     public static function php_datetime($cdt, $dest_tz = null)
     {
         if (!is_object($cdt) || !$cdt->isValid()) {
             return null;
         }
 
         $d = new libcalendaring_datetime(null, self::$timezone);
 
         if ($dest_tz) {
             $d->setTimezone($dest_tz);
         }
         else {
             try {
                 if ($tzs = $cdt->timezone()) {
                     $tz = new DateTimeZone($tzs);
                     $d->setTimezone($tz);
                 }
                 else if ($cdt->isUTC()) {
                     $d->setTimezone(new DateTimeZone('UTC'));
                 }
             }
             catch (Exception $e) { }
         }
 
         $d->setDate($cdt->year(), $cdt->month(), $cdt->day());
 
         if ($cdt->isDateOnly()) {
             $d->_dateonly = true;
             $d->setTime(12, 0, 0);  // set time to noon to avoid timezone troubles
         }
         else {
             $d->setTime($cdt->hour(), $cdt->minute(), $cdt->second());
         }
 
         return $d;
     }
 
     /**
      * Convert a libkolabxml vector to a PHP array
      *
      * @param object vector Object
      * @return array Indexed array containing vector elements
      */
     public static function vector2array($vec, $max = PHP_INT_MAX)
     {
         $arr = array();
         for ($i=0; $i < $vec->size() && $i < $max; $i++)
             $arr[] = $vec->get($i);
         return $arr;
     }
 
     /**
      * Build a libkolabxml vector (string) from a PHP array
      *
      * @param array Array with vector elements
      * @return object vectors
      */
     public static function array2vector($arr)
     {
         $vec = new vectors;
         foreach ((array)$arr as $val) {
             if (strlen($val))
                 $vec->push($val);
         }
         return $vec;
     }
 
     /**
      * Parse the X-Kolab-Type header from MIME messages and return the object type in short form
      *
      * @param string X-Kolab-Type header value
      * @return string Kolab object type (contact,event,task,note,etc.)
      */
     public static function mime2object_type($x_kolab_type)
     {
         return preg_replace(
             array('/dictionary.[a-z.]+$/', '/contact.distlist$/'),
             array( 'dictionary',            'distribution-list'),
             substr($x_kolab_type, strlen(self::KTYPE_PREFIX))
         );
     }
 
 
     /**
      * Default constructor of all kolab_format_* objects
      */
     public function __construct($xmldata = null, $version = null)
     {
         $this->obj = new $this->objclass;
         $this->xmldata = $xmldata;
 
         if ($version)
             $this->version = $version;
 
         // use libkolab module if available
         if (class_exists('kolabobject'))
             $this->xmlobject = new XMLObject();
     }
 
     /**
      * Check for format errors after calling kolabformat::write*()
      *
      * @return boolean True if there were errors, False if OK
      */
     protected function format_errors()
     {
         $ret = $log = false;
         switch (kolabformat::error()) {
             case kolabformat::NoError:
                 $ret = false;
                 break;
             case kolabformat::Warning:
                 $ret = false;
                 $uid = is_object($this->obj) ? $this->obj->uid() : $this->data['uid'];
                 $log = "Warning @ $uid";
                 break;
             default:
                 $ret = true;
                 $log = "Error";
         }
 
         if ($log && !isset($this->formaterror)) {
             rcube::raise_error(array(
                 'code' => 660,
                 'type' => 'php',
                 'file' => __FILE__,
                 'line' => __LINE__,
                 'message' => "kolabformat $log: " . kolabformat::errorMessage(),
             ), true);
 
             $this->formaterror = $ret;
         }
 
         return $ret;
     }
 
     /**
      * Save the last generated UID to the object properties.
      * Should be called after kolabformat::writeXXXX();
      */
     protected function update_uid()
     {
         // get generated UID
         if (!$this->data['uid']) {
             if ($this->xmlobject) {
                 $this->data['uid'] = $this->xmlobject->getSerializedUID();
             }
             if (empty($this->data['uid'])) {
                 $this->data['uid'] = kolabformat::getSerializedUID();
             }
             $this->obj->setUid($this->data['uid']);
         }
     }
 
     /**
      * Initialize libkolabxml object with cached xml data
      */
     protected function init()
     {
         if (!$this->loaded) {
             if ($this->xmldata) {
                 $this->load($this->xmldata);
                 $this->xmldata = null;
             }
             $this->loaded = true;
         }
     }
 
     /**
      * Get constant value for libkolab's version parameter
      *
      * @param float Version value to convert
      * @return int Constant value of either kolabobject::KolabV2 or kolabobject::KolabV3 or false if kolabobject module isn't available
      */
     protected function libversion($v = null)
     {
         if (class_exists('kolabobject')) {
             $version = $v ?: $this->version;
             if ($version <= '2.0')
                 return kolabobject::KolabV2;
             else
                 return kolabobject::KolabV3;
         }
 
         return false;
     }
 
     /**
      * Determine the correct libkolab(xml) wrapper function for the given call
      * depending on the available PHP modules
      */
     protected function libfunc($func)
     {
         if (is_array($func) || strpos($func, '::'))
             return $func;
         else if (class_exists('kolabobject'))
             return array($this->xmlobject, $func);
         else
             return 'kolabformat::' . $func;
     }
 
     /**
      * Direct getter for object properties
      */
     public function __get($var)
     {
         return $this->data[$var];
     }
 
     /**
      * Load Kolab object data from the given XML block
      *
      * @param string XML data
      * @return boolean True on success, False on failure
      */
     public function load($xml)
     {
         $this->formaterror = null;
         $read_func = $this->libfunc($this->read_func);
 
         if (is_array($read_func))
             $r = call_user_func($read_func, $xml, $this->libversion());
         else
             $r = call_user_func($read_func, $xml, false);
 
         if (is_resource($r))
             $this->obj = new $this->objclass($r);
         else if (is_a($r, $this->objclass))
             $this->obj = $r;
 
         $this->loaded = !$this->format_errors();
     }
 
     /**
      * Write object data to XML format
      *
      * @param float Format version to write
      * @return string XML data
      */
     public function write($version = null)
     {
         $this->formaterror = null;
 
         $this->init();
         $write_func = $this->libfunc($this->write_func);
         if (is_array($write_func))
             $this->xmldata = call_user_func($write_func, $this->obj, $this->libversion($version), self::PRODUCT_ID);
         else
             $this->xmldata = call_user_func($write_func, $this->obj, self::PRODUCT_ID);
 
         if (!$this->format_errors())
             $this->update_uid();
         else
             $this->xmldata = null;
 
         return $this->xmldata;
     }
 
     /**
      * Set properties to the kolabformat object
      *
      * @param array  Object data as hash array
      */
     public function set(&$object)
     {
         $this->init();
 
         if (!empty($object['uid']))
             $this->obj->setUid($object['uid']);
 
         // set some automatic values if missing
         if (method_exists($this->obj, 'setCreated')) {
             // Always set created date to workaround libkolabxml (>1.1.4) bug
             $created = $object['created'] ?: new DateTime('now');
             $created->setTimezone(new DateTimeZone('UTC')); // must be UTC
             $this->obj->setCreated(self::get_datetime($created));
             $object['created'] = $created;
         }
 
         $object['changed'] = new DateTime('now', new DateTimeZone('UTC'));
         $this->obj->setLastModified(self::get_datetime($object['changed']));
 
         // Save custom properties of the given object
         if (isset($object['x-custom']) && method_exists($this->obj, 'setCustomProperties')) {
             $vcustom = new vectorcs;
             foreach ((array)$object['x-custom'] as $cp) {
                 if (is_array($cp))
                     $vcustom->push(new CustomProperty($cp[0], $cp[1]));
             }
             $this->obj->setCustomProperties($vcustom);
         }
         // load custom properties from XML for caching (#2238) if method exists (#3125)
         else if (method_exists($this->obj, 'customProperties')) {
             $object['x-custom'] = array();
             $vcustom = $this->obj->customProperties();
             for ($i=0; $i < $vcustom->size(); $i++) {
                 $cp = $vcustom->get($i);
                 $object['x-custom'][] = array($cp->identifier, $cp->value);
             }
         }
     }
 
     /**
      * Convert the Kolab object into a hash array data structure
      *
      * @param array Additional data for merge
      *
      * @return array  Kolab object data as hash array
      */
     public function to_array($data = array())
     {
         $this->init();
 
         // read object properties into local data object
         $object = array(
             'uid'     => $this->obj->uid(),
             'changed' => self::php_datetime($this->obj->lastModified()),
         );
 
         // not all container support the created property
         if (method_exists($this->obj, 'created')) {
             $object['created'] = self::php_datetime($this->obj->created());
         }
 
         // read custom properties
         if (method_exists($this->obj, 'customProperties')) {
             $vcustom = $this->obj->customProperties();
             for ($i=0; $i < $vcustom->size(); $i++) {
                 $cp = $vcustom->get($i);
                 $object['x-custom'][] = array($cp->identifier, $cp->value);
             }
         }
 
         // merge with additional data, e.g. attachments from the message
         if ($data) {
             foreach ($data as $idx => $value) {
                 if (is_array($value)) {
                     $object[$idx] = array_merge((array)$object[$idx], $value);
                 }
                 else {
                     $object[$idx] = $value;
                 }
             }
         }
 
         return $object;
     }
 
     /**
      * Object validation method to be implemented by derived classes
      */
     abstract public function is_valid();
 
     /**
      * Callback for kolab_storage_cache to get object specific tags to cache
      *
      * @return array List of tags to save in cache
      */
     public function get_tags()
     {
         return array();
     }
 
     /**
      * Callback for kolab_storage_cache to get words to index for fulltext search
      *
      * @return array List of words to save in cache
      */
     public function get_words()
     {
         return array();
     }
 
     /**
      * Utility function to extract object attachment data
      *
      * @param array Hash array reference to append attachment data into
      */
     public function get_attachments(&$object, $all = false)
     {
         $this->init();
 
         // handle attachments
         $vattach = $this->obj->attachments();
         for ($i=0; $i < $vattach->size(); $i++) {
             $attach = $vattach->get($i);
 
             // skip cid: attachments which are mime message parts handled by kolab_storage_folder
             if (substr($attach->uri(), 0, 4) != 'cid:' && $attach->label()) {
                 $name    = $attach->label();
                 $key     = $name . (isset($object['_attachments'][$name]) ? '.'.$i : '');
                 $content = $attach->data();
                 $object['_attachments'][$key] = array(
                     'id'       => 'i:'.$i,
                     'name'     => $name,
                     'mimetype' => $attach->mimetype(),
                     'size'     => strlen($content),
                     'content'  => $content,
                 );
             }
             else if ($all && substr($attach->uri(), 0, 4) == 'cid:') {
                 $key = $attach->uri();
                 $object['_attachments'][$key] = array(
                     'id'       => $key,
                     'name'     => $attach->label(),
                     'mimetype' => $attach->mimetype(),
                 );
             }
             else if (in_array(substr($attach->uri(), 0, 4), array('http','imap'))) {
                 $object['links'][] = $attach->uri();
             }
         }
     }
 
     /**
      * Utility function to set attachment properties to the kolabformat object
      *
      * @param array  Object data as hash array
      * @param boolean True to always overwrite attachment information
      */
     protected function set_attachments($object, $write = true)
     {
         // save attachments
         $vattach = new vectorattachment;
         foreach ((array) $object['_attachments'] as $cid => $attr) {
             if (empty($attr))
                 continue;
             $attach = new Attachment;
             $attach->setLabel((string)$attr['name']);
             $attach->setUri('cid:' . $cid, $attr['mimetype'] ?: 'application/octet-stream');
             if ($attach->isValid()) {
                 $vattach->push($attach);
                 $write = true;
             }
             else {
                 rcube::raise_error(array(
                     'code' => 660,
                     'type' => 'php',
                     'file' => __FILE__,
                     'line' => __LINE__,
                     'message' => "Invalid attributes for attachment $cid: " . var_export($attr, true),
                 ), true);
             }
         }
 
         foreach ((array) $object['links'] as $link) {
             $attach = new Attachment;
             $attach->setUri($link, 'unknown');
             $vattach->push($attach);
             $write = true;
         }
 
         if ($write) {
             $this->obj->setAttachments($vattach);
         }
     }
 
     /**
      * Unified way of updating/deleting attachments of edited object
      *
      * @param array $object Kolab object data
      * @param array $old    Old version of Kolab object
      */
     public static function merge_attachments(&$object, $old)
     {
-        $object['_attachments'] = (array) $old['_attachments'];
+        $object['_attachments'] = isset($old['_attachments']) && is_array($old['_attachments']) ? $old['_attachments'] : [];
 
         // delete existing attachment(s)
         if (!empty($object['deleted_attachments'])) {
             foreach ($object['_attachments'] as $idx => $att) {
                 if ($object['deleted_attachments'] === true || in_array($att['id'], $object['deleted_attachments'])) {
                     $object['_attachments'][$idx] = false;
                 }
             }
         }
 
         // in kolab_storage attachments are indexed by content-id
         foreach ((array) $object['attachments'] as $attachment) {
             $key = null;
 
             // Roundcube ID has nothing to do with the storage ID, remove it
             // for uploaded/new attachments
             // FIXME: Roundcube uses 'data', kolab_format uses 'content'
             if ($attachment['content'] || $attachment['path'] || $attachment['data']) {
                 unset($attachment['id']);
             }
 
             if ($attachment['id']) {
                 foreach ((array) $object['_attachments'] as $cid => $att) {
                     if ($att && $attachment['id'] == $att['id']) {
                         $key = $cid;
                     }
                 }
             }
             else {
                 // find attachment by name, so we can update it if exists
                 // and make sure there are no duplicates
-                foreach ((array) $object['_attachments'] as $cid => $att) {
+                foreach ($object['_attachments'] as $cid => $att) {
                     if ($att && $attachment['name'] == $att['name']) {
                         $key = $cid;
                     }
                 }
             }
 
             if ($key && $attachment['_deleted']) {
                 $object['_attachments'][$key] = false;
             }
             // replace existing entry
             else if ($key) {
                 $object['_attachments'][$key] = $attachment;
             }
             // append as new attachment
             else {
                 $object['_attachments'][] = $attachment;
             }
         }
 
         unset($object['attachments']);
         unset($object['deleted_attachments']);
     }
 }
diff --git a/plugins/libkolab/lib/kolab_storage_cache.php b/plugins/libkolab/lib/kolab_storage_cache.php
index ff5bd86e..e38c4190 100644
--- a/plugins/libkolab/lib/kolab_storage_cache.php
+++ b/plugins/libkolab/lib/kolab_storage_cache.php
@@ -1,1458 +1,1466 @@
 <?php
 
 /**
  * Kolab storage cache class providing a local caching layer for Kolab groupware objects.
  *
  * @version @package_version@
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2012-2013, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_storage_cache
 {
     const DB_DATE_FORMAT = 'Y-m-d H:i:s';
     const MAX_RECORDS    = 500;
 
     protected $db;
     protected $imap;
     protected $folder;
     protected $uid2msg;
     protected $objects;
     protected $metadata = array();
     protected $folder_id;
     protected $resource_uri;
     protected $enabled = true;
     protected $synched = false;
     protected $synclock = false;
     protected $ready = false;
     protected $cache_table;
     protected $folders_table;
     protected $max_sql_packet;
     protected $max_sync_lock_time = 600;
     protected $extra_cols = array();
     protected $data_props = array();
     protected $order_by = null;
     protected $limit = null;
     protected $error = 0;
     protected $server_timezone;
+    protected $sync_start;
 
 
     /**
      * Factory constructor
      */
     public static function factory(kolab_storage_folder $storage_folder)
     {
         $subclass = 'kolab_storage_cache_' . $storage_folder->type;
         if (class_exists($subclass)) {
             return new $subclass($storage_folder);
         }
         else {
             rcube::raise_error(array(
                 'code' => 900,
                 'type' => 'php',
                 'message' => "No kolab_storage_cache class found for folder '$storage_folder->name' of type '$storage_folder->type'"
             ), true);
 
             return new kolab_storage_cache($storage_folder);
         }
     }
 
 
     /**
      * Default constructor
      */
     public function __construct(kolab_storage_folder $storage_folder = null)
     {
         $rcmail = rcube::get_instance();
         $this->db = $rcmail->get_dbh();
         $this->imap = $rcmail->get_storage();
         $this->enabled = $rcmail->config->get('kolab_cache', false);
         $this->folders_table = $this->db->table_name('kolab_folders');
         $this->server_timezone = new DateTimeZone(date_default_timezone_get());
 
         if ($this->enabled) {
             // always read folder cache and lock state from DB master
             $this->db->set_table_dsn('kolab_folders', 'w');
             // remove sync-lock on script termination
             $rcmail->add_shutdown_function(array($this, '_sync_unlock'));
         }
 
         if ($storage_folder)
             $this->set_folder($storage_folder);
     }
 
     /**
      * Direct access to cache by folder_id
      * (only for internal use)
      */
     public function select_by_id($folder_id)
     {
         $query = $this->db->query("SELECT * FROM `{$this->folders_table}` WHERE `folder_id` = ?", $folder_id);
         if ($sql_arr = $this->db->fetch_assoc($query)) {
             $this->metadata = $sql_arr;
             $this->folder_id = $sql_arr['folder_id'];
             $this->folder = new StdClass;
             $this->folder->type = $sql_arr['type'];
             $this->resource_uri = $sql_arr['resource'];
             $this->cache_table = $this->db->table_name('kolab_cache_' . $sql_arr['type']);
             $this->ready = true;
         }
     }
 
     /**
      * Connect cache with a storage folder
      *
      * @param kolab_storage_folder The storage folder instance to connect with
      */
     public function set_folder(kolab_storage_folder $storage_folder)
     {
         $this->folder = $storage_folder;
 
         if (empty($this->folder->name) || !$this->folder->valid) {
             $this->ready = false;
             return;
         }
 
         // compose fully qualified ressource uri for this instance
         $this->resource_uri = $this->folder->get_resource_uri();
         $this->cache_table = $this->db->table_name('kolab_cache_' . $this->folder->type);
         $this->ready = $this->enabled && !empty($this->folder->type);
         $this->folder_id = null;
     }
 
     /**
      * Returns true if this cache supports query by type
      */
     public function has_type_col()
     {
         return in_array('type', $this->extra_cols);
     }
 
     /**
      * Getter for the numeric ID used in cache tables
      */
     public function get_folder_id()
     {
         $this->_read_folder_data();
         return $this->folder_id;
     }
 
     /**
      * Returns code of last error
      *
      * @return int Error code
      */
     public function get_error()
     {
         return $this->error;
     }
 
     /**
      * Synchronize local cache data with remote
      */
     public function synchronize()
     {
         // only sync once per request cycle
         if ($this->synched)
             return;
 
         if (!$this->ready) {
             // kolab cache is disabled, synchronize IMAP mailbox cache only
             $this->imap_mode(true);
             $this->imap->folder_sync($this->folder->name);
             $this->imap_mode(false);
         }
         else {
             $this->sync_start = time();
 
             // read cached folder metadata
             $this->_read_folder_data();
 
             // Read folder data from IMAP
             $ctag = $this->folder->get_ctag();
 
             // Validate current ctag
             list($uidvalidity, $highestmodseq, $uidnext) = explode('-', $ctag);
 
             if (empty($uidvalidity) || empty($highestmodseq)) {
                 rcube::raise_error(array(
                     'code' => 900,
                     'message' => "Failed to sync the kolab cache (Invalid ctag)"
                 ), true);
             }
             // check cache status ($this->metadata is set in _read_folder_data())
             else if (
                 empty($this->metadata['ctag'])
                 || empty($this->metadata['changed'])
                 || $this->metadata['ctag'] !== $ctag
             ) {
                 // lock synchronization for this folder or wait if locked
                 $this->_sync_lock();
 
                 // Run a full-sync (initial sync or continue the aborted sync)
                 if (empty($this->metadata['changed']) || empty($this->metadata['ctag'])) {
                     $result = $this->synchronize_full();
                 }
                 // Synchronize only the changes since last sync
                 else {
                     $result = $this->synchronize_update($ctag);
                 }
 
                 // update ctag value (will be written to database in _sync_unlock())
                 if ($result) {
                     $this->metadata['ctag']    = $ctag;
                     $this->metadata['changed'] = date(self::DB_DATE_FORMAT, time());
                 }
 
                 // remove lock
                 $this->_sync_unlock();
             }
         }
 
         $this->check_error();
         $this->synched = time();
     }
 
     /**
      * Perform full cache synchronization
      */
     protected function synchronize_full()
     {
         // get effective time limit we have for synchronization (~70% of the execution time)
         $time_limit = $this->_max_sync_lock_time() * 0.7;
 
         if (time() - $this->sync_start > $time_limit) {
             return false;
         }
 
         // disable messages cache if configured to do so
         $this->imap_mode(true);
 
         // synchronize IMAP mailbox cache, does nothing if messages cache is disabled
         $this->imap->folder_sync($this->folder->name);
 
         // compare IMAP index with object cache index
         $imap_index = $this->imap->index($this->folder->name, null, null, true, true);
 
         $this->imap_mode(false);
 
         if ($imap_index->is_error()) {
             rcube::raise_error(array(
                     'code' => 900,
                     'message' => "Failed to sync the kolab cache (SEARCH failed)"
                 ), true);
             return false;
         }
 
         // determine objects to fetch or to invalidate
         $imap_index = $imap_index->get();
         $del_index  = array();
         $old_index  = $this->current_index($del_index);
 
         // Fetch objects and store in DB
         $result = $this->synchronize_fetch($imap_index, $old_index, $del_index);
 
         if ($result) {
             // Remove redundant entries from IMAP and cache
             $rem_index = array_intersect($del_index, $imap_index);
             $del_index = array_merge(array_unique($del_index), array_diff($old_index, $imap_index));
 
             $this->synchronize_delete($rem_index, $del_index);
         }
 
         return $result;
     }
 
     /**
      * Perform partial cache synchronization, based on QRESYNC
      */
     protected function synchronize_update()
     {
         if (!$this->imap->get_capability('QRESYNC')) {
             rcube::raise_error(array(
                     'code' => 900,
                     'message' => "Failed to sync the kolab cache (no QRESYNC capability)"
                 ), true);
 
             return $this->synchronize_full();
         }
 
         // Handle the previous ctag
         list($uidvalidity, $highestmodseq, $uidnext) = explode('-', $this->metadata['ctag']);
 
         if (empty($uidvalidity) || empty($highestmodseq)) {
             rcube::raise_error(array(
                     'code' => 900,
                     'message' => "Failed to sync the kolab cache (Invalid old ctag)"
                 ), true);
             return false;
         }
 
         // Enable QRESYNC
         $res = $this->imap->conn->enable('QRESYNC');
         if ($res === false) {
             rcube::raise_error(array(
                     'code' => 900,
                     'message' => "Failed to sync the kolab cache (failed to enable QRESYNC/CONDSTORE)"
                 ), true);
 
             return false;
         }
 
         $mbox_data = $this->imap->folder_data($this->folder->name);
         if (empty($mbox_data)) {
             rcube::raise_error(array(
                     'code' => 900,
                     'message' => "Failed to sync the kolab cache (failed to get folder state)"
                 ), true);
 
              return false;
         }
 
         // Check UIDVALIDITY
         if ($uidvalidity != $mbox_data['UIDVALIDITY']) {
             return $this->synchronize_full();
         }
 
         // QRESYNC not supported on specified mailbox
         if (!empty($mbox_data['NOMODSEQ']) || empty($mbox_data['HIGHESTMODSEQ'])) {
             rcube::raise_error(array(
                     'code' => 900,
                     'message' => "Failed to sync the kolab cache (QRESYNC not supported on the folder)"
                 ), true);
 
              return $this->synchronize_full();
         }
 
         // Get modified flags and vanished messages
         // UID FETCH 1:* (FLAGS) (CHANGEDSINCE 0123456789 VANISHED)
         $result = $this->imap->conn->fetch(
             $this->folder->name, '1:*', true, array('FLAGS'), $highestmodseq, true
         );
 
         $removed  = array();
         $modified = array();
         $existing = $this->current_index($removed);
 
         if (!empty($result)) {
             foreach ($result as $msg) {
                 $uid = $msg->uid;
 
                 // Message marked as deleted
                 if (!empty($msg->flags['DELETED'])) {
                     $removed[] = $uid;
                     continue;
                 }
 
                 // Flags changed or new
                 $modified[] = $uid;
             }
         }
 
         $new    = array_diff($modified, $existing, $removed);
         $result = true;
 
         if (!empty($new)) {
             $result = $this->synchronize_fetch($new, $existing, $removed);
 
             if (!$result) {
                 return false;
             }
         }
 
         // VANISHED found?
         $mbox_data = $this->imap->folder_data($this->folder->name);
 
         // Removed vanished messages from the database
         $vanished = (array) rcube_imap_generic::uncompressMessageSet($mbox_data['VANISHED']);
 
         // Remove redundant entries from IMAP and DB
         $vanished = array_merge($removed, array_intersect($vanished, $existing));
         $this->synchronize_delete($removed, $vanished);
 
         return $result;
     }
 
     /**
      * Fetch objects from IMAP and save into the database
      */
     protected function synchronize_fetch($new_index, &$old_index, &$del_index)
     {
         // get effective time limit we have for synchronization (~70% of the execution time)
         $time_limit = $this->_max_sync_lock_time() * 0.7;
 
         if (time() - $this->sync_start > $time_limit) {
             return false;
         }
 
         $i = 0;
         $aborted = false;
 
         // fetch new objects from imap
         foreach (array_diff($new_index, $old_index) as $msguid) {
             // Note: We'll store only objects matching the folder type
             // anything else will be silently ignored
             if ($object = $this->folder->read_object($msguid)) {
                 // Deduplication: remove older objects with the same UID
                 // Here we do not resolve conflicts, we just make sure
                 // the most recent version of the object will be used
                 if ($old_msguid = $old_index[$object['uid']]) {
                     if ($old_msguid < $msguid) {
                         $del_index[] = $old_msguid;
                     }
                     else {
                         $del_index[] = $msguid;
                         continue;
                     }
                 }
 
                 $old_index[$object['uid']] = $msguid;
 
                 $this->_extended_insert($msguid, $object);
 
                 // check time limit and abort sync if running too long
                 if (++$i % 50 == 0 && time() - $this->sync_start > $time_limit) {
                     $aborted = true;
                     break;
                 }
             }
         }
 
         $this->_extended_insert(0, null);
 
         return $aborted === false;
     }
 
     /**
      * Remove specified objects from the database and IMAP
      */
     protected function synchronize_delete($imap_delete, $db_delete)
     {
         if (!empty($imap_delete)) {
             $this->imap_mode(true);
             $this->imap->delete_message($imap_delete, $this->folder->name);
             $this->imap_mode(false);
         }
 
         if (!empty($db_delete)) {
             $quoted_ids = join(',', array_map(array($this->db, 'quote'), $db_delete));
             $this->db->query(
                 "DELETE FROM `{$this->cache_table}` WHERE `folder_id` = ? AND `msguid` IN ($quoted_ids)",
                 $this->folder_id
             );
         }
     }
 
     /**
      * Return current use->msguid index
      */
     protected function current_index(&$duplicates = array())
     {
         // read cache index
         $sql_result = $this->db->query(
             "SELECT `msguid`, `uid` FROM `{$this->cache_table}` WHERE `folder_id` = ?"
                 . " ORDER BY `msguid` DESC", $this->folder_id
         );
 
         $index = $del_index = array();
 
         while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
             // Mark all duplicates for removal (note sorting order above)
             // Duplicates here should not happen, but they do sometimes
             if (isset($index[$sql_arr['uid']])) {
                 $duplicates[] = $sql_arr['msguid'];
             }
             else {
                 $index[$sql_arr['uid']] = $sql_arr['msguid'];
             }
         }
 
         return $index;
     }
 
     /**
      * Read a single entry from cache or from IMAP directly
      *
      * @param string Related IMAP message UID
      * @param string Object type to read
      * @param string IMAP folder name the entry relates to
      * @param array  Hash array with object properties or null if not found
      */
     public function get($msguid, $type = null, $foldername = null)
     {
         // delegate to another cache instance
         if ($foldername && $foldername != $this->folder->name) {
             $success = false;
             if ($targetfolder = kolab_storage::get_folder($foldername)) {
                 $success = $targetfolder->cache->get($msguid, $type);
                 $this->error = $targetfolder->cache->get_error();
             }
             return $success;
         }
 
         // load object if not in memory
         if (!isset($this->objects[$msguid])) {
             if ($this->ready) {
                 $this->_read_folder_data();
 
                 $sql_result = $this->db->query(
                     "SELECT * FROM `{$this->cache_table}` ".
                     "WHERE `folder_id` = ? AND `msguid` = ?",
                     $this->folder_id,
                     $msguid
                 );
 
                 if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                     $this->objects = array($msguid => $this->_unserialize($sql_arr));  // store only this object in memory (#2827)
                 }
             }
 
             // fetch from IMAP if not present in cache
             if (empty($this->objects[$msguid])) {
                 if ($object = $this->folder->read_object($msguid, $type ?: '*', $foldername)) {
                     $this->objects = array($msguid => $object);
                     $this->set($msguid, $object);
                 }
             }
         }
 
         $this->check_error();
         return $this->objects[$msguid];
     }
 
     /**
      * Getter for a single Kolab object identified by its UID
      *
      * @param string $uid Object UID
      *
      * @return array The Kolab object represented as hash array
      */
     public function get_by_uid($uid)
     {
         $old_order_by = $this->order_by;
         $old_limit    = $this->limit;
 
         // set order to make sure we get most recent object version
         // set limit to skip count query
         $this->order_by = '`msguid` DESC';
         $this->limit    = array(1, 0);
 
         $list = $this->select(array(array('uid', '=', $uid)));
 
         // set the order/limit back to defined value
         $this->order_by = $old_order_by;
         $this->limit    = $old_limit;
 
         if (!empty($list) && !empty($list[0])) {
             return $list[0];
         }
     }
 
     /**
      * Insert/Update a cache entry
      *
      * @param string Related IMAP message UID
      * @param mixed  Hash array with object properties to save or false to delete the cache entry
      * @param string IMAP folder name the entry relates to
      */
     public function set($msguid, $object, $foldername = null)
     {
         if (!$msguid) {
             return;
         }
 
         // delegate to another cache instance
         if ($foldername && $foldername != $this->folder->name) {
           if ($targetfolder = kolab_storage::get_folder($foldername)) {
               $targetfolder->cache->set($msguid, $object);
               $this->error = $targetfolder->cache->get_error();
           }
           return;
         }
 
         // remove old entry
         if ($this->ready) {
             $this->_read_folder_data();
             $this->db->query("DELETE FROM `{$this->cache_table}` WHERE `folder_id` = ? AND `msguid` = ?",
                 $this->folder_id, $msguid);
         }
 
         if ($object) {
             // insert new object data...
             $this->save($msguid, $object);
         }
         else {
             // ...or set in-memory cache to false
             $this->objects[$msguid] = $object;
         }
 
         $this->check_error();
     }
 
 
     /**
      * Insert (or update) a cache entry
      *
      * @param int    Related IMAP message UID
      * @param mixed  Hash array with object properties to save or false to delete the cache entry
      * @param int    Optional old message UID (for update)
      */
     public function save($msguid, $object, $olduid = null)
     {
         // write to cache
         if ($this->ready) {
             $this->_read_folder_data();
 
             $sql_data = $this->_serialize($object);
             $sql_data['folder_id'] = $this->folder_id;
             $sql_data['msguid']    = $msguid;
             $sql_data['uid']       = $object['uid'];
 
             $args = array();
             $cols = array('folder_id', 'msguid', 'uid', 'changed', 'data', 'tags', 'words');
             $cols = array_merge($cols, $this->extra_cols);
 
             foreach ($cols as $idx => $col) {
                 $cols[$idx] = $this->db->quote_identifier($col);
                 $args[]     = $sql_data[$col];
             }
 
             if ($olduid) {
                 foreach ($cols as $idx => $col) {
                     $cols[$idx] = "$col = ?";
                 }
 
                 $query = "UPDATE `{$this->cache_table}` SET " . implode(', ', $cols)
                     . " WHERE `folder_id` = ? AND `msguid` = ?";
                 $args[] = $this->folder_id;
                 $args[] = $olduid;
             }
             else {
                 $query = "INSERT INTO `{$this->cache_table}` (`created`, " . implode(', ', $cols)
                     . ") VALUES (" . $this->db->now() . str_repeat(', ?', count($cols)) . ")";
             }
 
             $result = $this->db->query($query, $args);
 
             if (!$this->db->affected_rows($result)) {
                 rcube::raise_error(array(
                     'code' => 900, 'type' => 'php',
                     'message' => "Failed to write to kolab cache"
                 ), true);
             }
         }
 
         // keep a copy in memory for fast access
         $this->objects = array($msguid => $object);
         $this->uid2msg = array($object['uid'] => $msguid);
 
         $this->check_error();
     }
 
 
     /**
      * Move an existing cache entry to a new resource
      *
      * @param string               Entry's IMAP message UID
      * @param string               Entry's Object UID
      * @param kolab_storage_folder Target storage folder instance
      * @param string               Target entry's IMAP message UID
      */
     public function move($msguid, $uid, $target, $new_msguid = null)
     {
         if ($this->ready && $target) {
             // clear cached uid mapping and force new lookup
             unset($target->cache->uid2msg[$uid]);
 
             // resolve new message UID in target folder
             if (!$new_msguid) {
                 $new_msguid = $target->cache->uid2msguid($uid);
             }
 
             if ($new_msguid) {
                 $this->_read_folder_data();
 
                 $this->db->query(
                     "UPDATE `{$this->cache_table}` SET `folder_id` = ?, `msguid` = ? ".
                     "WHERE `folder_id` = ? AND `msguid` = ?",
                     $target->cache->get_folder_id(),
                     $new_msguid,
                     $this->folder_id,
                     $msguid
                 );
 
                 $result = $this->db->affected_rows();
             }
         }
 
         if (empty($result)) {
             // just clear cache entry
             $this->set($msguid, false);
         }
 
         unset($this->uid2msg[$uid]);
         $this->check_error();
     }
 
 
     /**
      * Remove all objects from local cache
      */
     public function purge()
     {
         if (!$this->ready) {
             return true;
         }
 
         $this->_read_folder_data();
 
         $result = $this->db->query(
             "DELETE FROM `{$this->cache_table}` WHERE `folder_id` = ?",
             $this->folder_id
         );
 
         return $this->db->affected_rows($result);
     }
 
     /**
      * Update resource URI for existing cache entries
      *
      * @param string Target IMAP folder to move it to
      */
     public function rename($new_folder)
     {
         if (!$this->ready) {
             return;
         }
 
         if ($target = kolab_storage::get_folder($new_folder)) {
             // resolve new message UID in target folder
             $this->db->query(
                 "UPDATE `{$this->folders_table}` SET `resource` = ? ".
                 "WHERE `resource` = ?",
                 $target->get_resource_uri(),
                 $this->resource_uri
             );
 
             $this->check_error();
         }
         else {
             $this->error = kolab_storage::ERROR_IMAP_CONN;
         }
     }
 
     /**
      * Select Kolab objects filtered by the given query
      *
      * @param array Pseudo-SQL query as list of filter parameter triplets
      *   triplet: array('<colname>', '<comparator>', '<value>')
      * @param boolean Set true to only return UIDs instead of complete objects
      * @param boolean Use fast mode to fetch only minimal set of information
      *                (no xml fetching and parsing, etc.)
      *
      * @return array List of Kolab data objects (each represented as hash array) or UIDs
      */
     public function select($query = array(), $uids = false, $fast = false)
     {
         $result = $uids ? array() : new kolab_storage_dataset($this);
+        $count = null;
 
         // read from local cache DB (assume it to be synchronized)
         if ($this->ready) {
             $this->_read_folder_data();
 
             // fetch full object data on one query if a small result set is expected
             $fetchall = !$uids && ($this->limit ? $this->limit[0] : ($count = $this->count($query))) < self::MAX_RECORDS;
 
             // skip SELECT if we know it will return nothing
             if ($count === 0) {
                 return $result;
             }
 
             $sql_query = "SELECT " . ($fetchall ? '*' : "`msguid` AS `_msguid`, `uid`")
                 . " FROM `{$this->cache_table}` WHERE `folder_id` = ?"
                 . $this->_sql_where($query)
                 . (!empty($this->order_by) ? " ORDER BY " . $this->order_by : '');
 
             $sql_result = $this->limit ?
                 $this->db->limitquery($sql_query, $this->limit[1], $this->limit[0], $this->folder_id) :
                 $this->db->query($sql_query, $this->folder_id);
 
             if ($this->db->is_error($sql_result)) {
                 if ($uids) {
                     return null;
                 }
                 $result->set_error(true);
                 return $result;
             }
 
             while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                 if ($fast) {
                     $sql_arr['fast-mode'] = true;
                 }
                 if ($uids) {
                     $this->uid2msg[$sql_arr['uid']] = $sql_arr['_msguid'];
                     $result[] = $sql_arr['uid'];
                 }
                 else if ($fetchall && ($object = $this->_unserialize($sql_arr))) {
                     $result[] = $object;
                 }
                 else if (!$fetchall) {
                     // only add msguid to dataset index
                     $result[] = $sql_arr;
                 }
             }
         }
         // use IMAP
         else {
             $filter = $this->_query2assoc($query);
 
             $this->imap_mode(true);
 
             if ($filter['type']) {
                 $search = 'UNDELETED HEADER X-Kolab-Type ' . kolab_format::KTYPE_PREFIX . $filter['type'];
                 $index  = $this->imap->search_once($this->folder->name, $search);
             }
             else {
                 $index = $this->imap->index($this->folder->name, null, null, true, true);
             }
 
             $this->imap_mode(false);
 
             if ($index->is_error()) {
                 $this->check_error();
                 if ($uids) {
                     return null;
                 }
                 $result->set_error(true);
                 return $result;
             }
 
             $index  = $index->get();
             $result = $uids ? $index : $this->_fetch($index, $filter['type']);
 
             // TODO: post-filter result according to query
         }
 
         // We don't want to cache big results in-memory, however
         // if we select only one object here, there's a big chance we will need it later
         if (!$uids && count($result) == 1) {
             if ($msguid = $result[0]['_msguid']) {
                 $this->uid2msg[$result[0]['uid']] = $msguid;
                 $this->objects = array($msguid => $result[0]);
             }
         }
 
         $this->check_error();
 
         return $result;
     }
 
     /**
      * Get number of objects mathing the given query
      *
      * @param array  $query Pseudo-SQL query as list of filter parameter triplets
      * @return integer The number of objects of the given type
      */
     public function count($query = array())
     {
         // read from local cache DB (assume it to be synchronized)
         if ($this->ready) {
             $this->_read_folder_data();
 
             $sql_result = $this->db->query(
                 "SELECT COUNT(*) AS `numrows` FROM `{$this->cache_table}` ".
                 "WHERE `folder_id` = ?" . $this->_sql_where($query),
                 $this->folder_id
             );
 
             if ($this->db->is_error($sql_result)) {
                 return null;
             }
 
             $sql_arr = $this->db->fetch_assoc($sql_result);
             $count   = intval($sql_arr['numrows']);
         }
         // use IMAP
         else {
             $filter = $this->_query2assoc($query);
 
             $this->imap_mode(true);
 
             if ($filter['type']) {
                 $search = 'UNDELETED HEADER X-Kolab-Type ' . kolab_format::KTYPE_PREFIX . $filter['type'];
                 $index  = $this->imap->search_once($this->folder->name, $search);
             }
             else {
                 $index = $this->imap->index($this->folder->name, null, null, true, true);
             }
 
             $this->imap_mode(false);
 
             if ($index->is_error()) {
                 $this->check_error();
                 return null;
             }
 
             // TODO: post-filter result according to query
 
             $count = $index->count();
         }
 
         $this->check_error();
         return $count;
     }
 
     /**
      * Define ORDER BY clause for cache queries
      */
     public function set_order_by($sortcols)
     {
         if (!empty($sortcols)) {
             $sortcols = array_map(function($v) {
-                list($column, $order) = explode(' ', $v, 2);
-                return "`$column`" . ($order ? " $order" : '');
+                $v = trim($v);
+                if (strpos($v, ' ')) {
+                    list($column, $order) = explode(' ', $v, 2);
+                    return "`{$column}` {$order}";
+                }
+                return "`{$v}`";
             }, (array) $sortcols);
 
             $this->order_by = join(', ', $sortcols);
         }
         else {
             $this->order_by = null;
         }
     }
 
     /**
      * Define LIMIT clause for cache queries
      */
     public function set_limit($length, $offset = 0)
     {
         $this->limit = array($length, $offset);
     }
 
     /**
      * Helper method to compose a valid SQL query from pseudo filter triplets
      */
     protected function _sql_where($query)
     {
         $sql_where = '';
         foreach ((array) $query as $param) {
             if (is_array($param[0])) {
                 $subq = array();
                 foreach ($param[0] as $q) {
                     $subq[] = preg_replace('/^\s*AND\s+/i', '', $this->_sql_where(array($q)));
                 }
                 if (!empty($subq)) {
                     $sql_where .= ' AND (' . implode($param[1] == 'OR' ? ' OR ' : ' AND ', $subq) . ')';
                 }
                 continue;
             }
             else if ($param[1] == '=' && is_array($param[2])) {
                 $qvalue = '(' . join(',', array_map(array($this->db, 'quote'), $param[2])) . ')';
                 $param[1] = 'IN';
             }
             else if ($param[1] == '~' || $param[1] == 'LIKE' || $param[1] == '!~' || $param[1] == '!LIKE') {
                 $not = ($param[1] == '!~' || $param[1] == '!LIKE') ? 'NOT ' : '';
                 $param[1] = $not . 'LIKE';
                 $qvalue = $this->db->quote('%'.preg_replace('/(^\^|\$$)/', ' ', $param[2]).'%');
             }
             else if ($param[1] == '~*' || $param[1] == '!~*') {
                 $not = $param[1][1] == '!' ? 'NOT ' : '';
                 $param[1] = $not . 'LIKE';
                 $qvalue = $this->db->quote(preg_replace('/(^\^|\$$)/', ' ', $param[2]).'%');
             }
             else if ($param[0] == 'tags') {
                 $param[1] = ($param[1] == '!=' ? 'NOT ' : '' ) . 'LIKE';
                 $qvalue = $this->db->quote('% '.$param[2].' %');
             }
             else {
                 $qvalue = $this->db->quote($param[2]);
             }
 
             $sql_where .= sprintf(' AND %s %s %s',
                 $this->db->quote_identifier($param[0]),
                 $param[1],
                 $qvalue
             );
         }
 
         return $sql_where;
     }
 
     /**
      * Helper method to convert the given pseudo-query triplets into
      * an associative filter array with 'equals' values only
      */
     protected function _query2assoc($query)
     {
         // extract object type from query parameter
         $filter = array();
         foreach ($query as $param) {
             if ($param[1] == '=')
                 $filter[$param[0]] = $param[2];
         }
         return $filter;
     }
 
     /**
      * Fetch messages from IMAP
      *
      * @param array  List of message UIDs to fetch
      * @param string Requested object type or * for all
      * @param string IMAP folder to read from
      * @return array List of parsed Kolab objects
      */
     protected function _fetch($index, $type = null, $folder = null)
     {
         $results = new kolab_storage_dataset($this);
         foreach ((array)$index as $msguid) {
             if ($object = $this->folder->read_object($msguid, $type, $folder)) {
                 $results[] = $object;
                 $this->set($msguid, $object);
             }
         }
 
         return $results;
     }
 
     /**
      * Helper method to convert the given Kolab object into a dataset to be written to cache
      */
     protected function _serialize($object)
     {
         $data     = array();
         $sql_data = array('changed' => null, 'tags' => '', 'words' => '');
 
         if ($object['changed']) {
             $sql_data['changed'] = date(self::DB_DATE_FORMAT, is_object($object['changed']) ? $object['changed']->format('U') : $object['changed']);
         }
 
         if ($object['_formatobj']) {
             $xml = (string) $object['_formatobj']->write(3.0);
 
             $data['_size']     = strlen($xml);
             $sql_data['tags']  = ' ' . join(' ', $object['_formatobj']->get_tags()) . ' ';  // pad with spaces for strict/prefix search
             $sql_data['words'] = ' ' . join(' ', $object['_formatobj']->get_words()) . ' ';
         }
 
         // Store only minimal set of object properties
         foreach ($this->data_props as $prop) {
             if (isset($object[$prop])) {
                 $data[$prop] = $object[$prop];
                 if ($data[$prop] instanceof DateTimeInterface) {
                     $data[$prop] = array(
                         'cl' => 'DateTime',
                         'dt' => $data[$prop]->format('Y-m-d H:i:s'),
                         'tz' => $data[$prop]->getTimezone()->getName(),
                     );
                 }
             }
         }
 
         $sql_data['data'] = json_encode(rcube_charset::clean($data));
 
         return $sql_data;
     }
 
     /**
      * Helper method to turn stored cache data into a valid storage object
      */
     protected function _unserialize($sql_arr)
     {
         if ($sql_arr['fast-mode'] && !empty($sql_arr['data']) && ($object = json_decode($sql_arr['data'], true))) {
             $object['uid'] = $sql_arr['uid'];
 
             foreach ($this->data_props as $prop) {
                 if (isset($object[$prop]) && is_array($object[$prop]) && $object[$prop]['cl'] == 'DateTime') {
                     $object[$prop] = new DateTime($object[$prop]['dt'], new DateTimeZone($object[$prop]['tz']));
                 }
                 else if (!isset($object[$prop]) && isset($sql_arr[$prop])) {
                     $object[$prop] = $sql_arr[$prop];
                 }
             }
 
             if ($sql_arr['created'] && empty($object['created'])) {
                 $object['created'] = new DateTime($sql_arr['created']);
             }
 
             if ($sql_arr['changed'] && empty($object['changed'])) {
                 $object['changed'] = new DateTime($sql_arr['changed']);
             }
 
             $object['_type']     = $sql_arr['type'] ?: $this->folder->type;
             $object['_msguid']   = $sql_arr['msguid'];
             $object['_mailbox']  = $this->folder->name;
         }
         // Fetch object xml
         else {
             // FIXME: Because old cache solution allowed storing objects that
             // do not match folder type we may end up with invalid objects.
             // 2nd argument of read_object() here makes sure they are still
             // usable. However, not allowing them here might be also an intended
             // solution in future.
             $object = $this->folder->read_object($sql_arr['msguid'], '*');
         }
 
         return $object;
     }
 
     /**
      * Write records into cache using extended inserts to reduce the number of queries to be executed
      *
      * @param int  Message UID. Set 0 to commit buffered inserts
      * @param array Kolab object to cache
      */
     protected function _extended_insert($msguid, $object)
     {
         static $buffer = '';
 
         $line = '';
         $cols = array('folder_id', 'msguid', 'uid', 'created', 'changed', 'data', 'tags', 'words');
         if ($this->extra_cols) {
             $cols = array_merge($cols, $this->extra_cols);
         }
 
         if ($object) {
             $sql_data = $this->_serialize($object);
 
             // Skip multi-folder insert for all databases but MySQL
             // In Oracle we can't put long data inline, others we don't support yet
             if (strpos($this->db->db_provider, 'mysql') !== 0) {
                 $extra_args = array();
                 $params = array($this->folder_id, $msguid, $object['uid'], $sql_data['changed'],
                     $sql_data['data'], $sql_data['tags'], $sql_data['words']);
 
                 foreach ($this->extra_cols as $col) {
                     $params[] = $sql_data[$col];
                     $extra_args[] = '?';
                 }
 
                 $cols = implode(', ', array_map(function($n) { return "`{$n}`"; }, $cols));
                 $extra_args = count($extra_args) ? ', ' . implode(', ', $extra_args) : '';
 
                 $result = $this->db->query(
                     "INSERT INTO `{$this->cache_table}` ($cols)"
                     . " VALUES (?, ?, ?, " . $this->db->now() . ", ?, ?, ?, ?$extra_args)",
                     $params
                 );
 
                 if (!$this->db->affected_rows($result)) {
                     rcube::raise_error(array(
                         'code' => 900, 'message' => "Failed to write to kolab cache"
                     ), true);
                 }
 
                 return;
             }
 
             $values = array(
                 $this->db->quote($this->folder_id),
                 $this->db->quote($msguid),
                 $this->db->quote($object['uid']),
                 $this->db->now(),
                 $this->db->quote($sql_data['changed']),
                 $this->db->quote($sql_data['data']),
                 $this->db->quote($sql_data['tags']),
                 $this->db->quote($sql_data['words']),
             );
             foreach ($this->extra_cols as $col) {
                 $values[] = $this->db->quote($sql_data[$col]);
             }
             $line = '(' . join(',', $values) . ')';
         }
 
         if ($buffer && (!$msguid || (strlen($buffer) + strlen($line) > $this->max_sql_packet()))) {
             $columns = implode(', ', array_map(function($n) { return "`{$n}`"; }, $cols));
             $update  = implode(', ', array_map(function($i) { return "`{$i}` = VALUES(`{$i}`)"; }, array_slice($cols, 2)));
 
             $result = $this->db->query(
                 "INSERT INTO `{$this->cache_table}` ($columns) VALUES $buffer"
                 . " ON DUPLICATE KEY UPDATE $update"
             );
 
             if (!$this->db->affected_rows($result)) {
                 rcube::raise_error(array(
                     'code' => 900, 'message' => "Failed to write to kolab cache"
                 ), true);
             }
 
             $buffer = '';
         }
 
         $buffer .= ($buffer ? ',' : '') . $line;
     }
 
     /**
      * Returns max_allowed_packet from mysql config
      */
     protected function max_sql_packet()
     {
         if (!$this->max_sql_packet) {
             // mysql limit or max 4 MB
             $value = $this->db->get_variable('max_allowed_packet', 1048500);
             $this->max_sql_packet = min($value, 4*1024*1024) - 2000;
         }
 
         return $this->max_sql_packet;
     }
 
     /**
      * Read this folder's ID and cache metadata
      */
     protected function _read_folder_data()
     {
         // already done
         if (!empty($this->folder_id) || !$this->ready)
             return;
 
         $sql_arr = $this->db->fetch_assoc($this->db->query(
                 "SELECT `folder_id`, `synclock`, `ctag`, `changed`"
                 . " FROM `{$this->folders_table}` WHERE `resource` = ?",
                 $this->resource_uri
         ));
 
         if ($sql_arr) {
             $this->metadata = $sql_arr;
             $this->folder_id = $sql_arr['folder_id'];
         }
         else {
             $this->db->query("INSERT INTO `{$this->folders_table}` (`resource`, `type`)"
                 . " VALUES (?, ?)", $this->resource_uri, $this->folder->type);
 
             $this->folder_id = $this->db->insert_id('kolab_folders');
             $this->metadata = array();
         }
     }
 
     /**
      * Check lock record for this folder and wait if locked or set lock
      */
     protected function _sync_lock()
     {
         if (!$this->ready)
             return;
 
         $this->_read_folder_data();
 
         // abort if database is not set-up
         if ($this->db->is_error()) {
             $this->check_error();
             $this->ready = false;
             return;
         }
 
         $read_query  = "SELECT `synclock`, `ctag` FROM `{$this->folders_table}` WHERE `folder_id` = ?";
         $write_query = "UPDATE `{$this->folders_table}` SET `synclock` = ? WHERE `folder_id` = ? AND `synclock` = ?";
 
         $max_lock_time = $this->_max_sync_lock_time();
+        $sync_lock = intval($this->metadata['synclock'] ?? 0);
 
         // wait if locked (expire locks after 10 minutes) ...
         // ... or if setting lock fails (another process meanwhile set it)
         while (
-            (intval($this->metadata['synclock']) + $max_lock_time > time()) ||
-            (($res = $this->db->query($write_query, time(), $this->folder_id, intval($this->metadata['synclock']))) &&
-                !($affected = $this->db->affected_rows($res)))
+            ($sync_lock + $max_lock_time > time()) ||
+            (($res = $this->db->query($write_query, time(), $this->folder_id, $sync_lock))
+                && !($affected = $this->db->affected_rows($res))
+            )
         ) {
             usleep(500000);
             $this->metadata = $this->db->fetch_assoc($this->db->query($read_query, $this->folder_id));
         }
 
         $this->synclock = $affected > 0;
     }
 
     /**
      * Remove lock for this folder
      */
     public function _sync_unlock()
     {
         if (!$this->ready || !$this->synclock)
             return;
 
         $this->db->query(
             "UPDATE `{$this->folders_table}` SET `synclock` = 0, `ctag` = ?, `changed` = ? WHERE `folder_id` = ?",
             $this->metadata['ctag'],
             $this->metadata['changed'],
             $this->folder_id
         );
 
         $this->synclock = false;
     }
 
     protected function _max_sync_lock_time()
     {
         $limit = get_offset_sec(ini_get('max_execution_time'));
 
         if ($limit <= 0 || $limit > $this->max_sync_lock_time) {
             $limit = $this->max_sync_lock_time;
         }
 
         return $limit;
     }
 
     /**
      * Check IMAP connection error state
      */
     protected function check_error()
     {
         if (($err_code = $this->imap->get_error_code()) < 0) {
             $this->error = kolab_storage::ERROR_IMAP_CONN;
             if (($res_code = $this->imap->get_response_code()) !== 0 && in_array($res_code, array(rcube_storage::NOPERM, rcube_storage::READONLY))) {
                 $this->error = kolab_storage::ERROR_NO_PERMISSION;
             }
         }
         else if ($this->db->is_error()) {
             $this->error = kolab_storage::ERROR_CACHE_DB;
         }
     }
 
     /**
      * Resolve an object UID into an IMAP message UID
      *
      * @param string  Kolab object UID
      * @param boolean Include deleted objects
      * @return int The resolved IMAP message UID
      */
     public function uid2msguid($uid, $deleted = false)
     {
         // query local database if available
         if (!isset($this->uid2msg[$uid]) && $this->ready) {
             $this->_read_folder_data();
 
             $sql_result = $this->db->query(
                 "SELECT `msguid` FROM `{$this->cache_table}` ".
                 "WHERE `folder_id` = ? AND `uid` = ? ORDER BY `msguid` DESC",
                 $this->folder_id,
                 $uid
             );
 
             if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                 $this->uid2msg[$uid] = $sql_arr['msguid'];
             }
         }
 
         if (!isset($this->uid2msg[$uid])) {
             // use IMAP SEARCH to get the right message
             $index = $this->imap->search_once($this->folder->name, ($deleted ? '' : 'UNDELETED ') .
                 'HEADER SUBJECT ' . rcube_imap_generic::escape($uid));
             $results = $index->get();
             $this->uid2msg[$uid] = end($results);
         }
 
         return $this->uid2msg[$uid];
     }
 
     /**
      * Getter for protected member variables
      */
     public function __get($name)
     {
         if ($name == 'folder_id') {
             $this->_read_folder_data();
         }
 
         return $this->$name;
     }
 
     /**
      * Set Roundcube storage options and bypass messages/indexes cache.
      *
      * We use skip_deleted and threading settings specific to Kolab,
      * we have to change these global settings only temporarily.
      * Roundcube cache duplicates information already stored in kolab_cache,
      * that's why we can disable it for better performance.
      *
      * @param bool $force True to start Kolab mode, False to stop it.
      */
     public function imap_mode($force = false)
     {
         // remember current IMAP settings
         if ($force) {
             $this->imap_options = array(
                 'skip_deleted' => $this->imap->get_option('skip_deleted'),
                 'threading'    => $this->imap->get_threading(),
             );
         }
 
         // re-set IMAP settings
         $this->imap->set_threading($force ? false : $this->imap_options['threading']);
         $this->imap->set_options(array(
                 'skip_deleted' => $force ? true : $this->imap_options['skip_deleted'],
         ));
 
         // if kolab cache is disabled do nothing
         if (!$this->enabled) {
             return;
         }
 
         static $messages_cache, $cache_bypass;
 
         if ($messages_cache === null) {
             $rcmail = rcube::get_instance();
             $messages_cache = (bool) $rcmail->config->get('messages_cache');
             $cache_bypass   = (int) $rcmail->config->get('kolab_messages_cache_bypass');
         }
 
         if ($messages_cache) {
             // handle recurrent (multilevel) bypass() calls
             if ($force) {
                 $this->cache_bypassed += 1;
                 if ($this->cache_bypassed > 1) {
                     return;
                 }
             }
             else {
                 $this->cache_bypassed -= 1;
                 if ($this->cache_bypassed > 0) {
                     return;
                 }
             }
 
             switch ($cache_bypass) {
                 case 2:
                     // Disable messages and index cache completely
                     $this->imap->set_messages_caching(!$force);
                     break;
 
                 case 3:
                 case 1:
                     // We'll disable messages cache, but keep index cache (1) or vice-versa (3)
                     // Default mode is both (MODE_INDEX | MODE_MESSAGE)
                     $mode = $cache_bypass == 3 ? rcube_imap_cache::MODE_MESSAGE : rcube_imap_cache::MODE_INDEX;
 
                     if (!$force) {
                         $mode |= $cache_bypass == 3 ? rcube_imap_cache::MODE_INDEX : rcube_imap_cache::MODE_MESSAGE;
                     }
 
                     $this->imap->set_messages_caching(true, $mode);
             }
         }
     }
 
     /**
      * Converts DateTime or unix timestamp into sql date format
      * using server timezone.
      */
     protected function _convert_datetime($datetime)
     {
         if (is_object($datetime)) {
             $dt = clone $datetime;
             $dt->setTimeZone($this->server_timezone);
             return $dt->format(self::DB_DATE_FORMAT);
         }
         else if ($datetime) {
             return date(self::DB_DATE_FORMAT, $datetime);
         }
     }
 }
diff --git a/plugins/libkolab/lib/kolab_storage_cache_event.php b/plugins/libkolab/lib/kolab_storage_cache_event.php
index b324f561..5ad9a3a1 100644
--- a/plugins/libkolab/lib/kolab_storage_cache_event.php
+++ b/plugins/libkolab/lib/kolab_storage_cache_event.php
@@ -1,68 +1,68 @@
 <?php
 
 /**
  * Kolab storage cache class for calendar event objects
  *
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2013, Kolab Systems AG <contact@kolabsys.com>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_storage_cache_event extends kolab_storage_cache
 {
     protected $extra_cols = array('dtstart','dtend');
     protected $data_props = array('categories', 'status', 'attendees'); // start, end
 
     /**
      * Helper method to convert the given Kolab object into a dataset to be written to cache
      *
      * @override
      */
     protected function _serialize($object)
     {
         $sql_data = parent::_serialize($object);
 
         $sql_data['dtstart'] = $this->_convert_datetime($object['start']);
         $sql_data['dtend']   = $this->_convert_datetime($object['end']);
 
         // extend date range for recurring events
-        if ($object['recurrence'] && $object['_formatobj']) {
+        if ($object['recurrence']) {
             $recurrence = new kolab_date_recurrence($object['_formatobj']);
             $dtend = $recurrence->end() ?: new DateTime('now +100 years');
             $sql_data['dtend'] = $this->_convert_datetime($dtend);
         }
 
         // extend start/end dates to spawn all exceptions
         if (is_array($object['exceptions'])) {
             foreach ($object['exceptions'] as $exception) {
                 if ($exception['start'] instanceof DateTimeInterface) {
                     $exstart = $this->_convert_datetime($exception['start']);
                     if ($exstart < $sql_data['dtstart']) {
                         $sql_data['dtstart'] = $exstart;
                     }
                 }
                 if ($exception['end'] instanceof DateTimeInterface) {
                     $exend = $this->_convert_datetime($exception['end']);
                     if ($exend > $sql_data['dtend']) {
                         $sql_data['dtend'] = $exend;
                     }
                 }
             }
         }
 
         return $sql_data;
     }
 }
diff --git a/plugins/libkolab/lib/kolab_storage_dav.php b/plugins/libkolab/lib/kolab_storage_dav.php
index ac313478..e71f3d0d 100644
--- a/plugins/libkolab/lib/kolab_storage_dav.php
+++ b/plugins/libkolab/lib/kolab_storage_dav.php
@@ -1,565 +1,562 @@
 <?php
 
 /**
  * Kolab storage class providing access to groupware objects on a *DAV server.
  *
  * @author Aleksander Machniak <machniak@apheleia-it.ch>
  *
  * Copyright (C) 2022, Apheleia IT AG <contact@apheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_storage_dav
 {
     const ERROR_DAV_CONN       = 1;
     const ERROR_CACHE_DB       = 2;
     const ERROR_NO_PERMISSION  = 3;
     const ERROR_INVALID_FOLDER = 4;
 
     protected $dav;
     protected $url;
 
 
     /**
      * Object constructor
      */
     public function __construct($url)
     {
         $this->url = $url;
         $this->setup();
     }
 
     /**
      * Setup the environment
      */
     public function setup()
     {
-        $rcmail = rcube::get_instance();
-
-        $this->config = $rcmail->config;
         $this->dav = new kolab_dav_client($this->url);
     }
 
     /**
      * Get a list of storage folders for the given data type
      *
      * @param string Data type to list folders for (contact,event,task,note)
      *
      * @return array List of kolab_storage_dav_folder objects
      */
     public function get_folders($type)
     {
         // TODO: This should be cached
         $folders = $this->dav->listFolders($this->get_dav_type($type));
 
         if (is_array($folders)) {
             foreach ($folders as $idx => $folder) {
                 // Exclude some special folders
                 if (in_array('schedule-inbox', $folder['resource_type']) || in_array('schedule-outbox', $folder['resource_type'])) {
                     unset($folders[$idx]);
                     continue;
                 }
 
                 $folders[$idx] = new kolab_storage_dav_folder($this->dav, $folder, $type);
             }
 
 
             usort($folders, function ($a, $b) {
                 return strcoll($a->get_foldername(), $b->get_foldername());
             });
         }
 
         return $folders ?: [];
     }
 
     /**
      * Getter for the storage folder for the given type
      *
      * @param string Data type to list folders for (contact,event,task,note)
      *
      * @return object kolab_storage_dav_folder The folder object
      */
     public function get_default_folder($type)
     {
         // TODO: Not used
     }
 
     /**
      * Getter for a specific storage folder
      *
      * @param string $id   Folder to access
      * @param string $type Expected folder type
      *
      * @return ?object kolab_storage_folder The folder object
      */
     public function get_folder($id, $type)
     {
         foreach ($this->get_folders($type) as $folder) {
             if ($folder->id == $id) {
                 return $folder;
             }
         }
     }
 
     /**
      * Getter for a single Kolab object, identified by its UID.
      * This will search all folders storing objects of the given type.
      *
      * @param string Object UID
      * @param string Object type (contact,event,task,journal,file,note,configuration)
      *
      * @return array The Kolab object represented as hash array or false if not found
      */
     public function get_object($uid, $type)
     {
         // TODO
         return false;
     }
 
     /**
      * Execute cross-folder searches with the given query.
      *
      * @param array  Pseudo-SQL query as list of filter parameter triplets
      * @param string Folder type (contact,event,task,journal,file,note,configuration)
      * @param int    Expected number of records or limit (for performance reasons)
      *
      * @return array List of Kolab data objects (each represented as hash array)
      */
     public function select($query, $type, $limit = null)
     {
         $result = [];
 
         foreach ($this->get_folders($type) as $folder) {
             if ($limit) {
                 $folder->set_order_and_limit(null, $limit);
             }
 
             foreach ($folder->select($query) as $object) {
                 $result[] = $object;
             }
         }
 
         return $result;
     }
 
     /**
      * Compose an URL to query the free/busy status for the given user
      *
      * @param string Email address of the user to get free/busy data for
      * @param object DateTime Start of the query range (optional)
      * @param object DateTime End of the query range (optional)
      *
      * @return string Fully qualified URL to query free/busy data
      */
     public static function get_freebusy_url($email, $start = null, $end = null)
     {
         return kolab_storage::get_freebusy_url($email, $start, $end);
     }
 
     /**
      * Creates folder ID from a DAV folder location and server URI.
      *
      * @param string $uri  DAV server location
      * @param string $href Folder location
      *
      * @return string Folder ID string
      */
     public static function folder_id($uri, $href)
     {
         if (($rootPath = parse_url($uri, PHP_URL_PATH)) && strpos($href, $rootPath) === 0) {
             $href = substr($href, strlen($rootPath));
         }
 
         // Start with a letter to prevent from all kind of issues if it starts with a digit
         return 'f' . md5(rtrim($uri, '/') . '/' . trim($href, '/'));
     }
 
     /**
      * Deletes a folder
      *
      * @param string $id   Folder ID
      * @param string $type Folder type (contact,event,task,journal,file,note,configuration)
      *
      * @return bool True on success, false on failure
      */
     public function folder_delete($id, $type)
     {
         if ($folder = $this->get_folder($id, $type)) {
             return $this->dav->folderDelete($folder->href);
         }
 
         return false;
     }
 
     /**
      * Creates a folder
      *
      * @param string $name       Folder name (UTF7-IMAP)
      * @param string $type       Folder type
      * @param bool   $subscribed Sets folder subscription
      * @param bool   $active     Sets folder state (client-side subscription)
      *
      * @return bool True on success, false on failure
      */
     public function folder_create($name, $type = null, $subscribed = false, $active = false)
     {
         // TODO
     }
 
     /**
      * Renames DAV folder
      *
      * @param string $oldname Old folder name (UTF7-IMAP)
      * @param string $newname New folder name (UTF7-IMAP)
      *
      * @return bool True on success, false on failure
      */
     public function folder_rename($oldname, $newname)
     {
         // TODO ??
     }
 
     /**
      * Update or Create a new folder.
      *
      * Does additional checks for permissions and folder name restrictions
      *
      * @param array &$prop Hash array with folder properties and metadata
      *  - name:       Folder name
      *  - oldname:    Old folder name when changed
      *  - parent:     Parent folder to create the new one in
      *  - type:       Folder type to create
      *  - subscribed: Subscribed flag (IMAP subscription)
      *  - active:     Activation flag (client-side subscription)
      *
      * @return string|false New folder ID or False on failure
      */
     public function folder_update(&$prop)
     {
         // TODO: Folder hierarchies, active and subscribed state
 
         // sanity checks
         if (!isset($prop['name']) || !is_string($prop['name']) || !strlen($prop['name'])) {
             self::$last_error = 'cannotbeempty';
             return false;
         }
         else if (strlen($prop['name']) > 256) {
             self::$last_error = 'nametoolong';
             return false;
         }
 
         if (!empty($prop['id'])) {
             if ($folder = $this->get_folder($prop['id'], $prop['type'])) {
                 $result = $this->dav->folderUpdate($folder->href, $folder->get_dav_type(), $prop);
             }
             else {
                 $result = false;
             }
         }
         else {
             $rcube = rcube::get_instance();
             $uid   = rtrim(chunk_split(md5($prop['name'] . $rcube->get_user_name() . uniqid('-', true)), 12, '-'), '-');
             $type  = $this->get_dav_type($prop['type']);
             $home  = $this->dav->discover($type);
 
             if ($home === false) {
                 return false;
             }
 
             $location = unslashify($home) . '/' . $uid;
             $result   = $this->dav->folderCreate($location, $type, $prop);
 
             if ($result !== false) {
                 $result = self::folder_id($this->dav->url, $location);
             }
         }
 
         return $result;
     }
 
     /**
      * Getter for human-readable name of a folder
      *
      * @param string $folder    Folder name (UTF7-IMAP)
      * @param string $folder_ns Will be set to namespace name of the folder
      *
      * @return string Name of the folder-object
      */
     public static function object_name($folder, &$folder_ns = null)
     {
         // TODO: Shared folders
         $folder_ns = 'personal';
         return $folder;
     }
 
     /**
      * Creates a SELECT field with folders list
      *
      * @param string $type    Folder type
      * @param array  $attrs   SELECT field attributes (e.g. name)
      * @param string $current The name of current folder (to skip it)
      *
      * @return html_select SELECT object
      */
     public function folder_selector($type, $attrs, $current = '')
     {
         // TODO
     }
 
     /**
      * Returns a list of folder names
      *
      * @param string  Optional root folder
      * @param string  Optional name pattern
      * @param string  Data type to list folders for (contact,event,task,journal,file,note,mail,configuration)
      * @param bool    Enable to return subscribed folders only (null to use configured subscription mode)
      * @param array   Will be filled with folder-types data
      *
      * @return array List of folders
      */
     public function list_folders($root = '', $mbox = '*', $filter = null, $subscribed = null, &$folderdata = array())
     {
         // TODO
     }
 
     /**
      * Search for shared or otherwise not listed groupware folders the user has access
      *
      * @param string Folder type of folders to search for
      * @param string Search string
      * @param array  Namespace(s) to exclude results from
      *
      * @return array List of matching kolab_storage_folder objects
      */
     public function search_folders($type, $query, $exclude_ns = [])
     {
         // TODO
         return [];
     }
 
     /**
      * Sort the given list of folders by namespace/name
      *
      * @param array List of kolab_storage_dav_folder objects
      *
      * @return array Sorted list of folders
      */
     public static function sort_folders($folders)
     {
         // TODO
         return $folders;
     }
 
     /**
      * Returns folder types indexed by folder name
      *
      * @param string $prefix Folder prefix (Default '*' for all folders)
      *
      * @return array|bool List of folders, False on failure
      */
     public function folders_typedata($prefix = '*')
     {
         // TODO: Used by kolab_folders, kolab_activesync, kolab_delegation
         return [];
     }
 
     /**
      * Returns type of a DAV folder
      *
      * @param string $folder Folder name (UTF7-IMAP)
      *
      * @return string Folder type
      */
     public function folder_type($folder)
     {
         // TODO: Used by kolab_folders, kolab_activesync, kolab_delegation
         return '';
     }
 
     /**
      * Sets folder content-type.
      *
      * @param string $folder Folder name
      * @param string $type   Content type
      *
      * @return bool True on success, False otherwise
      */
     public function set_folder_type($folder, $type = 'mail')
     {
         // NOP: Used by kolab_folders, kolab_activesync, kolab_delegation
         return false;
     }
 
     /**
      * Check subscription status of this folder
      *
      * @param string $folder Folder name
      * @param bool   $temp   Include temporary/session subscriptions
      *
      * @return bool True if subscribed, false if not
      */
     public function folder_is_subscribed($folder, $temp = false)
     {
         // NOP
         return true;
     }
 
     /**
      * Change subscription status of this folder
      *
      * @param string $folder Folder name
      * @param bool   $temp   Only subscribe temporarily for the current session
      *
      * @return True on success, false on error
      */
     public function folder_subscribe($folder, $temp = false)
     {
         // NOP
         return true;
     }
 
     /**
      * Change subscription status of this folder
      *
      * @param string $folder Folder name
      * @param bool   $temp  Only remove temporary subscription
      *
      * @return True on success, false on error
      */
     public function folder_unsubscribe($folder, $temp = false)
     {
         // NOP
         return false;
     }
 
     /**
      * Check activation status of this folder
      *
      * @param string $folder Folder name
      *
      * @return bool True if active, false if not
      */
     public function folder_is_active($folder)
     {
         return true; // TODO
     }
 
     /**
      * Change activation status of this folder
      *
      * @param string $folder Folder name
      *
      * @return True on success, false on error
      */
     public function folder_activate($folder)
     {
         return true; // TODO
     }
 
     /**
      * Change activation status of this folder
      *
      * @param string $folder Folder name
      *
      * @return True on success, false on error
      */
     public function folder_deactivate($folder)
     {
         return false; // TODO
     }
 
     /**
      * Creates default folder of specified type
      * To be run when none of subscribed folders (of specified type) is found
      *
      * @param string $type  Folder type
      * @param string $props Folder properties (color, etc)
      *
      * @return string Folder name
      */
     public function create_default_folder($type, $props = [])
     {
         // TODO: For kolab_addressbook??
         return '';
     }
 
     /**
      * Returns a list of IMAP folders shared by the given user
      *
      * @param array  User entry from LDAP
      * @param string Data type to list folders for (contact,event,task,journal,file,note,mail,configuration)
      * @param int    1 - subscribed folders only, 0 - all folders, 2 - all non-active
      * @param array  Will be filled with folder-types data
      *
      * @return array List of folders
      */
     public function list_user_folders($user, $type, $subscribed = 0, &$folderdata = [])
     {
         // TODO
         return [];
     }
 
     /**
      * Get a list of (virtual) top-level folders from the other users namespace
      *
      * @param string Data type to list folders for (contact,event,task,journal,file,note,mail,configuration)
      * @param bool   Enable to return subscribed folders only (null to use configured subscription mode)
      *
      * @return array List of kolab_storage_folder_user objects
      */
     public function get_user_folders($type, $subscribed)
     {
         // TODO
         return [];
     }
 
     /**
      * Handler for user_delete plugin hooks
      *
      * Remove all cache data from the local database related to the given user.
      */
     public static function delete_user_folders($args)
     {
         $db = rcmail::get_instance()->get_dbh();
         $table  = $db->table_name('kolab_folders', true);
         $prefix = 'dav://' . urlencode($args['username']) . '@' . $args['host'] . '/%';
 
         $db->query("DELETE FROM $table WHERE `resource` LIKE ?", $prefix);
     }
 
     /**
      * Get folder METADATA for all supported keys
      * Do this in one go for better caching performance
      */
     public function folder_metadata($folder)
     {
         // TODO ?
         return [];
     }
 
     /**
      * Get a folder DAV content type
      */
     public static function get_dav_type($type)
     {
         $types = [
             'event' => 'VEVENT',
             'task'  => 'VTODO',
             'contact' => 'VCARD',
         ];
 
         return $types[$type];
     }
 }
diff --git a/plugins/libkolab/lib/kolab_storage_dav_cache.php b/plugins/libkolab/lib/kolab_storage_dav_cache.php
index 5dec0fa9..528b5a71 100644
--- a/plugins/libkolab/lib/kolab_storage_dav_cache.php
+++ b/plugins/libkolab/lib/kolab_storage_dav_cache.php
@@ -1,700 +1,702 @@
 <?php
 
 /**
  * Kolab storage cache class providing a local caching layer for Kolab groupware objects.
  *
  * @author Aleksander Machniak <machniak@apheleia-it.ch>
  *
  * Copyright (C) 2012-2022, Apheleia IT AG <contact@apheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_storage_dav_cache extends kolab_storage_cache
 {
     /**
      * Factory constructor
      */
     public static function factory(kolab_storage_folder $storage_folder)
     {
         $subclass = 'kolab_storage_dav_cache_' . $storage_folder->type;
         if (class_exists($subclass)) {
             return new $subclass($storage_folder);
         }
 
         rcube::raise_error(
             ['code' => 900, 'message' => "No {$subclass} class found for folder '{$storage_folder->name}'"],
             true
         );
 
         return new kolab_storage_dav_cache($storage_folder);
     }
 
     /**
      * Connect cache with a storage folder
      *
      * @param kolab_storage_folder The storage folder instance to connect with
      */
     public function set_folder(kolab_storage_folder $storage_folder)
     {
         $this->folder = $storage_folder;
 
         if (!$this->folder->valid) {
             $this->ready = false;
             return;
         }
 
         // compose fully qualified ressource uri for this instance
         $this->resource_uri = $this->folder->get_resource_uri();
         $this->cache_table = $this->db->table_name('kolab_cache_dav_' . $this->folder->type);
         $this->ready = true;
     }
 
     /**
      * Synchronize local cache data with remote
      */
     public function synchronize()
     {
         // only sync once per request cycle
         if ($this->synched) {
             return;
         }
 
         $this->sync_start = time();
 
         // read cached folder metadata
         $this->_read_folder_data();
 
         $ctag = $this->folder->get_ctag();
 
         // check cache status ($this->metadata is set in _read_folder_data())
         if (
             empty($this->metadata['ctag'])
             || empty($this->metadata['changed'])
             || $this->metadata['ctag'] !== $ctag
         ) {
             // lock synchronization for this folder and wait if already locked
             $this->_sync_lock();
 
             $result = $this->synchronize_worker();
 
             // update ctag value (will be written to database in _sync_unlock())
             if ($result) {
                 $this->metadata['ctag']    = $ctag;
                 $this->metadata['changed'] = date(self::DB_DATE_FORMAT, time());
             }
 
             // remove lock
             $this->_sync_unlock();
         }
 
         $this->synched = time();
     }
 
     /**
      * Perform cache synchronization
      */
     protected function synchronize_worker()
     {
         // get effective time limit we have for synchronization (~70% of the execution time)
         $time_limit = $this->_max_sync_lock_time() * 0.7;
 
         if (time() - $this->sync_start > $time_limit) {
             return false;
         }
 
         // TODO: Implement synchronization with use of WebDAV-Sync (RFC 6578)
 
         // Get the objects from the DAV server
         $dav_index = $this->folder->dav->getIndex($this->folder->href, $this->folder->get_dav_type());
 
         if (!is_array($dav_index)) {
             rcube::raise_error([
                     'code' => 900,
                     'message' => "Failed to sync the kolab cache for {$this->folder->href}"
                 ], true);
             return false;
         }
 
         // WARNING: For now we assume object's href is <calendar-href>/<uid>.ics,
         //          which would mean there are no duplicates (objects with the same uid).
         //          With DAV protocol we can't get UID without fetching the whole object.
         //          Also the folder_id + uid is a unique index in the database.
         //          In the future we maybe should store the href in database.
 
         // Determine objects to fetch or delete
         $new_index    = [];
         $update_index = [];
         $old_index    = $this->folder_index(); // uid -> etag
         $chunk_size   = 20; // max numer of objects per DAV request
 
         foreach ($dav_index as $object) {
             $uid = $object['uid'];
             if (isset($old_index[$uid])) {
                 $old_etag = $old_index[$uid];
                 $old_index[$uid] = null;
 
                 if ($old_etag === $object['etag']) {
                     // the object didn't change
                     continue;
                 }
 
                 $update_index[$uid] = $object['href'];
             }
             else {
                 $new_index[$uid] = $object['href'];
             }
         }
 
         // Fetch new objects and store in DB
         if (!empty($new_index)) {
+            $i = 0;
             foreach (array_chunk($new_index, $chunk_size, true) as $chunk) {
                 $objects = $this->folder->dav->getData($this->folder->href, $this->folder->get_dav_type(), $chunk);
 
                 if (!is_array($objects)) {
                     rcube::raise_error([
                             'code' => 900,
                             'message' => "Failed to sync the kolab cache for {$this->folder->href}"
                         ], true);
                     return false;
                 }
 
                 foreach ($objects as $dav_object) {
                     if ($object = $this->folder->from_dav($dav_object)) {
                         $object['_raw'] = $dav_object['data'];
                         $this->_extended_insert(false, $object);
                         unset($object['_raw']);
                     }
                 }
 
                 $this->_extended_insert(true, null);
 
                 // check time limit and abort sync if running too long
                 if (++$i % 25 == 0 && time() - $this->sync_start > $time_limit) {
                     return false;
                 }
             }
         }
 
         // Fetch updated objects and store in DB
         if (!empty($update_index)) {
             foreach (array_chunk($update_index, $chunk_size, true) as $chunk) {
                 $objects = $this->folder->dav->getData($this->folder->href, $this->folder->get_dav_type(), $chunk);
 
                 if (!is_array($objects)) {
                     rcube::raise_error([
                             'code' => 900,
                             'message' => "Failed to sync the kolab cache for {$this->folder->href}"
                         ], true);
                     return false;
                 }
 
                 foreach ($objects as $dav_object) {
                     if ($object = $this->folder->from_dav($dav_object)) {
                         $object['_raw'] = $dav_object['data'];
                         $this->save($object, $object['uid']);
                         unset($object['_raw']);
                     }
                 }
 
                 // check time limit and abort sync if running too long
                 if (++$i % 25 == 0 && time() - $this->sync_start > $time_limit) {
                     return false;
                 }
             }
         }
 
         // Remove deleted objects
         $old_index = array_filter($old_index);
         if (!empty($old_index)) {
             $quoted_uids = join(',', array_map(array($this->db, 'quote'), $old_index));
             $this->db->query(
                 "DELETE FROM `{$this->cache_table}` WHERE `folder_id` = ? AND `uid` IN ($quoted_uids)",
                 $this->folder_id
             );
         }
 
         return true;
     }
 
     /**
      * Return current folder index (uid -> etag)
      */
     public function folder_index()
     {
         $this->_read_folder_data();
 
         // read cache index
         $sql_result = $this->db->query(
             "SELECT `uid`, `etag` FROM `{$this->cache_table}` WHERE `folder_id` = ?",
             $this->folder_id
         );
 
         $index = [];
 
         while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
             $index[$sql_arr['uid']] = $sql_arr['etag'];
         }
 
         return $index;
     }
 
     /**
      * Read a single entry from cache or from server directly
      *
      * @param string Object UID
      * @param string Object type to read
      * @param string Unused (kept for compat. with the parent class)
      *
      * @return null|array An array of objects, NULL if not found
      */
     public function get($uid, $type = null, $unused = null)
     {
         if ($this->ready) {
             $this->_read_folder_data();
 
             $sql_result = $this->db->query(
                 "SELECT * FROM `{$this->cache_table}` WHERE `folder_id` = ? AND `uid` = ?",
                 $this->folder_id,
                 $uid
             );
 
             if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
                 $object = $this->_unserialize($sql_arr);
             }
         }
 
         // fetch from DAV if not present in cache
         if (empty($object)) {
             if ($object = $this->folder->read_object($uid, $type ?: '*')) {
                 $this->save($object);
             }
         }
 
         return $object ?: null;
     }
 
     /**
      * Read multiple entries from the server directly
      *
      * @param array Object UIDs
      *
      * @return false|array An array of objects, False on error
      */
     public function multiget($uids)
     {
         return $this->folder->read_objects($uids);
     }
 
     /**
      * Insert/Update a cache entry
      *
      * @param string      Object UID
      * @param array|false Hash array with object properties to save or false to delete the cache entry
      * @param string      Unused (kept for compat. with the parent class)
      */
     public function set($uid, $object, $unused = null)
     {
         // remove old entry
         if ($this->ready) {
             $this->_read_folder_data();
 
             $this->db->query(
                 "DELETE FROM `{$this->cache_table}` WHERE `folder_id` = ? AND `uid` = ?",
                 $this->folder_id,
                 $uid
             );
         }
 
         if ($object) {
             $this->save($object);
         }
     }
 
     /**
      * Insert (or update) a cache entry
      *
      * @param mixed  Hash array with object properties to save or false to delete the cache entry
      * @param string Optional old message UID (for update)
      * @param string Unused (kept for compat. with the parent class)
      */
     public function save($object, $olduid = null, $unused = null)
     {
         // write to cache
         if ($this->ready) {
             $this->_read_folder_data();
 
             $sql_data              = $this->_serialize($object);
             $sql_data['folder_id'] = $this->folder_id;
             $sql_data['uid']       = rcube_charset::clean($object['uid']);
             $sql_data['etag']      = rcube_charset::clean($object['etag']);
 
             $args = [];
             $cols = ['folder_id', 'uid', 'etag', 'changed', 'data', 'tags', 'words'];
             $cols = array_merge($cols, $this->extra_cols);
 
             foreach ($cols as $idx => $col) {
                 $cols[$idx] = $this->db->quote_identifier($col);
                 $args[]     = $sql_data[$col];
             }
 
             if ($olduid) {
                 foreach ($cols as $idx => $col) {
                     $cols[$idx] = "$col = ?";
                 }
 
                 $query = "UPDATE `{$this->cache_table}` SET " . implode(', ', $cols)
                     . " WHERE `folder_id` = ? AND `uid` = ?";
                 $args[] = $this->folder_id;
                 $args[] = $olduid;
             }
             else {
                 $query = "INSERT INTO `{$this->cache_table}` (`created`, " . implode(', ', $cols)
                     . ") VALUES (" . $this->db->now() . str_repeat(', ?', count($cols)) . ")";
             }
 
             $result = $this->db->query($query, $args);
 
             if (!$this->db->affected_rows($result)) {
                 rcube::raise_error([
                     'code' => 900,
                     'message' => "Failed to write to kolab cache"
                 ], true);
             }
         }
     }
 
     /**
      * Move an existing cache entry to a new resource
      *
      * @param string               Entry's  UID
      * @param kolab_storage_folder Target storage folder instance
      * @param string Unused (kept for compat. with the parent class)
      * @param string Unused (kept for compat. with the parent class)
      */
     public function move($uid, $target, $unused1 = null, $unused2 = null)
     {
         // TODO
     }
 
     /**
      * Update resource URI for existing folder
      *
      * @param string Target DAV folder to move it to
      */
     public function rename($new_folder)
     {
         // TODO
     }
 
     /**
      * Select Kolab objects filtered by the given query
      *
      * @param array Pseudo-SQL query as list of filter parameter triplets
      *   triplet: ['<colname>', '<comparator>', '<value>']
      * @param bool  Set true to only return UIDs instead of complete objects
      * @param bool  Use fast mode to fetch only minimal set of information
      *              (no xml fetching and parsing, etc.)
      *
      * @return array|null|kolab_storage_dataset List of Kolab data objects (each represented as hash array) or UIDs
      */
     public function select($query = [], $uids = false, $fast = false)
     {
         $result = $uids ? [] : new kolab_storage_dataset($this);
+        $count  = null;
 
         $this->_read_folder_data();
 
         // fetch full object data on one query if a small result set is expected
         $fetchall = !$uids && ($this->limit ? $this->limit[0] : ($count = $this->count($query))) < self::MAX_RECORDS;
 
         // skip SELECT if we know it will return nothing
         if ($count === 0) {
             return $result;
         }
 
         $sql_query = "SELECT " . ($fetchall ? '*' : "`uid`")
             . " FROM `{$this->cache_table}` WHERE `folder_id` = ?"
             . $this->_sql_where($query)
             . (!empty($this->order_by) ? " ORDER BY " . $this->order_by : '');
 
         $sql_result = $this->limit ?
             $this->db->limitquery($sql_query, $this->limit[1], $this->limit[0], $this->folder_id) :
             $this->db->query($sql_query, $this->folder_id);
 
         if ($this->db->is_error($sql_result)) {
             if ($uids) {
                 return null;
             }
 
             $result->set_error(true);
             return $result;
         }
 
         while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
             if ($uids) {
                 $result[] = $sql_arr['uid'];
             }
             else if (!$fetchall) {
                 $result[] = $sql_arr;
             }
             else if (($object = $this->_unserialize($sql_arr, true, $fast))) {
                 $result[] = $object;
             }
             else {
                 $result[] = $sql_arr['uid'];
             }
         }
 
         return $result;
     }
 
     /**
      * Get number of objects mathing the given query
      *
      * @param array $query Pseudo-SQL query as list of filter parameter triplets
      *
      * @return int The number of objects of the given type
      */
     public function count($query = [])
     {
         // read from local cache DB (assume it to be synchronized)
         $this->_read_folder_data();
 
         $sql_result = $this->db->query(
             "SELECT COUNT(*) AS `numrows` FROM `{$this->cache_table}` ".
             "WHERE `folder_id` = ?" . $this->_sql_where($query),
             $this->folder_id
         );
 
         if ($this->db->is_error($sql_result)) {
             return null;
         }
 
         $sql_arr = $this->db->fetch_assoc($sql_result);
         $count   = intval($sql_arr['numrows']);
 
         return $count;
     }
 
     /**
      * Getter for a single Kolab object identified by its UID
      *
      * @param string $uid Object UID
      *
      * @return array|null The Kolab object represented as hash array
      */
     public function get_by_uid($uid)
     {
         $old_limit = $this->limit;
 
         // set limit to skip count query
         $this->limit = [1, 0];
 
         $list = $this->select([['uid', '=', $uid]]);
 
         // set the limit back to defined value
         $this->limit = $old_limit;
 
         if (!empty($list) && !empty($list[0])) {
             return $list[0];
         }
     }
 
     /**
      * Write records into cache using extended inserts to reduce the number of queries to be executed
      *
      * @param bool  Set to false to commit buffered insert, true to force an insert
      * @param array Kolab object to cache
      */
     protected function _extended_insert($force, $object)
     {
         static $buffer = '';
 
         $line = '';
         $cols = ['folder_id', 'uid', 'etag', 'created', 'changed', 'data', 'tags', 'words'];
         if ($this->extra_cols) {
             $cols = array_merge($cols, $this->extra_cols);
         }
 
         if ($object) {
             $sql_data = $this->_serialize($object);
 
             // Skip multi-folder insert for all databases but MySQL
             // In Oracle we can't put long data inline, others we don't support yet
             if (strpos($this->db->db_provider, 'mysql') !== 0) {
                 $extra_args = [];
                 $params = [
                     $this->folder_id,
                     rcube_charset::clean($object['uid']),
                     rcube_charset::clean($object['etag']),
                     $sql_data['changed'],
                     $sql_data['data'],
                     $sql_data['tags'],
                     $sql_data['words']
                 ];
 
                 foreach ($this->extra_cols as $col) {
                     $params[] = $sql_data[$col];
                     $extra_args[] = '?';
                 }
 
                 $cols = implode(', ', array_map(function($n) { return "`{$n}`"; }, $cols));
                 $extra_args = count($extra_args) ? ', ' . implode(', ', $extra_args) : '';
 
                 $result = $this->db->query(
                     "INSERT INTO `{$this->cache_table}` ($cols)"
                     . " VALUES (?, ?, " . $this->db->now() . ", ?, ?, ?, ?$extra_args)",
                     $params
                 );
 
                 if (!$this->db->affected_rows($result)) {
                     rcube::raise_error(array(
                         'code' => 900, 'message' => "Failed to write to kolab cache"
                     ), true);
                 }
 
                 return;
             }
 
             $values = array(
                 $this->db->quote($this->folder_id),
                 $this->db->quote(rcube_charset::clean($object['uid'])),
                 $this->db->quote(rcube_charset::clean($object['etag'])),
                 $this->db->now(),
                 $this->db->quote($sql_data['changed']),
                 $this->db->quote($sql_data['data']),
                 $this->db->quote($sql_data['tags']),
                 $this->db->quote($sql_data['words']),
             );
             foreach ($this->extra_cols as $col) {
                 $values[] = $this->db->quote($sql_data[$col]);
             }
             $line = '(' . join(',', $values) . ')';
         }
 
         if ($buffer && ($force || (strlen($buffer) + strlen($line) > $this->max_sql_packet()))) {
             $columns = implode(', ', array_map(function($n) { return "`{$n}`"; }, $cols));
             $update  = implode(', ', array_map(function($i) { return "`{$i}` = VALUES(`{$i}`)"; }, array_slice($cols, 2)));
 
             $result = $this->db->query(
                 "INSERT INTO `{$this->cache_table}` ($columns) VALUES $buffer"
                 . " ON DUPLICATE KEY UPDATE $update"
             );
 
             if (!$this->db->affected_rows($result)) {
                 rcube::raise_error(array(
                     'code' => 900, 'message' => "Failed to write to kolab cache"
                 ), true);
             }
 
             $buffer = '';
         }
 
         $buffer .= ($buffer ? ',' : '') . $line;
     }
 
     /**
      * Helper method to convert the given Kolab object into a dataset to be written to cache
      */
     protected function _serialize($object)
     {
         static $threshold;
 
         if ($threshold === null) {
             $rcube     = rcube::get_instance();
             $threshold = parse_bytes(rcube::get_instance()->config->get('dav_cache_threshold', 0));
         }
 
         $data     = [];
         $sql_data = ['changed' => null, 'tags' => '', 'words' => ''];
 
         if (!empty($object['changed'])) {
             $sql_data['changed'] = date(self::DB_DATE_FORMAT, is_object($object['changed']) ? $object['changed']->format('U') : $object['changed']);
         }
 
         // Store only minimal set of object properties
         foreach ($this->data_props as $prop) {
             if (isset($object[$prop])) {
                 $data[$prop] = $object[$prop];
                 if ($data[$prop] instanceof DateTimeInterface) {
                     $data[$prop] = array(
                         'cl' => 'DateTime',
                         'dt' => $data[$prop]->format('Y-m-d H:i:s'),
                         'tz' => $data[$prop]->getTimezone()->getName(),
                     );
                 }
             }
         }
 
         if (!empty($object['_raw']) && $threshold > 0 && strlen($object['_raw']) <= $threshold) {
             $data['_raw'] = $object['_raw'];
         }
 
         $sql_data['data'] = json_encode(rcube_charset::clean($data));
 
         return $sql_data;
     }
 
     /**
      * Helper method to turn stored cache data into a valid storage object
      */
     protected function _unserialize($sql_arr, $noread = false, $fast_mode = false)
     {
         if (!empty($sql_arr['data']) && ($object = json_decode($sql_arr['data'], true))) {
             foreach ($this->data_props as $prop) {
                 if (isset($object[$prop]) && is_array($object[$prop])
                     && isset($object[$prop]['cl']) && $object[$prop]['cl'] == 'DateTime'
                 ) {
                     $object[$prop] = new DateTime($object[$prop]['dt'], new DateTimeZone($object[$prop]['tz']));
                 }
                 else if (!isset($object[$prop]) && isset($sql_arr[$prop])) {
                     $object[$prop] = $sql_arr[$prop];
                 }
             }
 
             if ($sql_arr['created'] && empty($object['created'])) {
                 $object['created'] = new DateTime($sql_arr['created']);
             }
 
             if ($sql_arr['changed'] && empty($object['changed'])) {
                 $object['changed'] = new DateTime($sql_arr['changed']);
             }
 
             $object['_type'] = !empty($sql_arr['type']) ? $sql_arr['type'] : $this->folder->type;
             $object['uid']   = $sql_arr['uid'];
             $object['etag']  = $sql_arr['etag'];
         }
 
         if (!empty($fast_mode) && !empty($object)) {
             unset($object['_raw']);
         }
         else if ($noread) {
             // We have the raw content already, parse it
             if (!empty($object['_raw'])) {
                 $object['data'] = $object['_raw'];
                 if ($object = $this->folder->from_dav($object)) {
                     return $object;
                 }
             }
 
             return null;
         }
         else {
             // Fetch a complete object from the server
             $object = $this->folder->read_object($sql_arr['uid'], '*');
         }
 
         return $object;
     }
 }
diff --git a/plugins/libkolab/lib/kolab_storage_dav_cache_contact.php b/plugins/libkolab/lib/kolab_storage_dav_cache_contact.php
index ed55e21e..578002c8 100644
--- a/plugins/libkolab/lib/kolab_storage_dav_cache_contact.php
+++ b/plugins/libkolab/lib/kolab_storage_dav_cache_contact.php
@@ -1,117 +1,116 @@
 <?php
 
 /**
  * Kolab storage cache class for contact objects
  *
  * @author Aleksander Machniak <machniak@apcheleia-it.ch>
  *
  * Copyright (C) 2013-2022, Apheleia IT AG <contact@apcheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_storage_dav_cache_contact extends kolab_storage_dav_cache
 {
     protected $extra_cols_max = 255;
     protected $extra_cols     = ['type', 'name', 'firstname', 'surname', 'email'];
     protected $data_props     = ['type', 'name', 'firstname', 'middlename', 'prefix', 'suffix', 'surname', 'email', 'organization', 'member'];
     protected $fulltext_cols  = ['name', 'firstname', 'surname', 'middlename', 'email'];
 
     /**
      * Helper method to convert the given Kolab object into a dataset to be written to cache
      *
      * @override
      */
     protected function _serialize($object)
     {
         $sql_data = parent::_serialize($object);
-        $sql_data['type'] = $object['_type'] ?: 'contact';
+        $sql_data['type'] = !empty($object['_type']) ? $object['_type'] : 'contact';
 
         if ($sql_data['type'] == 'group' || (!empty($object['kind']) && $object['kind'] == 'group')) {
             $sql_data['type'] = 'group';
         }
 
         // columns for sorting
-        $sql_data['name']      = rcube_charset::clean($object['name'] . $object['prefix']);
-        $sql_data['firstname'] = rcube_charset::clean($object['firstname'] . $object['middlename'] . $object['surname']);
-        $sql_data['surname']   = rcube_charset::clean($object['surname']   . $object['firstname']  . $object['middlename']);
+        $sql_data['name']      = rcube_charset::clean(($object['name'] ?? '') . ($object['prefix'] ?? ''));
+        $sql_data['firstname'] = rcube_charset::clean(($object['firstname'] ?? '') . ($object['middlename'] ?? '') . ($object['surname'] ?? ''));
+        $sql_data['surname']   = rcube_charset::clean(($object['surname'] ?? '') . ($object['firstname'] ?? '') . ($object['middlename'] ?? ''));
         $sql_data['email']     = '';
 
         foreach ($object as $colname => $value) {
-            list($col, $field) = explode(':', $colname);
-            if ($col == 'email' && !empty($value)) {
+            if (!empty($value) && ($colname == 'email' || strpos($colname, 'email:') === 0)) {
                 $sql_data['email'] = is_array($value) ? $value[0] : $value;
                 break;
             }
         }
 
         // use organization if name is empty
         if (empty($sql_data['name']) && !empty($object['organization'])) {
             $sql_data['name'] = rcube_charset::clean($object['organization']);
         }
 
         // make sure some data is not longer that database limit (#5291)
         foreach ($this->extra_cols as $col) {
             if (strlen($sql_data[$col]) > $this->extra_cols_max) {
                 $sql_data[$col] = rcube_charset::clean(substr($sql_data[$col], 0,  $this->extra_cols_max));
             }
         }
 
         $sql_data['tags']  = ' ' . join(' ', $this->get_tags($object)) . ' ';  // pad with spaces for strict/prefix search
         $sql_data['words'] = ' ' . join(' ', $this->get_words($object)) . ' ';
 
         return $sql_data;
     }
 
     /**
      * Callback to get words to index for fulltext search
      *
      * @return array List of words to save in cache
      */
     public function get_words($object)
     {
         $data = '';
 
         foreach ($object as $colname => $value) {
-            list($col, $field) = explode(':', $colname);
+            list($col, $field) = strpos($colname, ':') ? explode(':', $colname) : [$colname, null];
 
-            $val = '';
+            $val = null;
             if (in_array($col, $this->fulltext_cols)) {
                 $val = is_array($value) ? join(' ', $value) : $value;
             }
 
-            if (strlen($val)) {
+            if (is_string($val) && strlen($val)) {
                 $data .= $val . ' ';
             }
         }
 
         return array_unique(rcube_utils::normalize_string($data, true));
     }
 
     /**
      * Callback to get object specific tags to cache
      *
      * @return array List of tags to save in cache
      */
     public function get_tags($object)
     {
         $tags = [];
 
         if (!empty($object['birthday'])) {
             $tags[] = 'x-has-birthday';
         }
 
         return $tags;
     }
 }
diff --git a/plugins/libkolab/lib/kolab_storage_dav_cache_event.php b/plugins/libkolab/lib/kolab_storage_dav_cache_event.php
index 8e7c7e75..cd35070d 100644
--- a/plugins/libkolab/lib/kolab_storage_dav_cache_event.php
+++ b/plugins/libkolab/lib/kolab_storage_dav_cache_event.php
@@ -1,152 +1,154 @@
 <?php
 
 /**
  * Kolab storage cache class for calendar event objects
  *
  * @author Aleksander Machniak <machniak@apheleia-it.ch>
  *
  * Copyright (C) 2013-2022 Apheleia IT AG <contact@apheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class kolab_storage_dav_cache_event extends kolab_storage_dav_cache
 {
     protected $extra_cols = ['dtstart','dtend'];
     protected $data_props = ['categories', 'status', 'attendees'];
     protected $fulltext_cols = ['title', 'description', 'location', 'attendees:name', 'attendees:email', 'categories'];
 
     /**
      * Helper method to convert the given Kolab object into a dataset to be written to cache
      *
      * @override
      */
     protected function _serialize($object)
     {
         $sql_data = parent::_serialize($object);
 
         $sql_data['dtstart'] = $this->_convert_datetime($object['start']);
         $sql_data['dtend']   = $this->_convert_datetime($object['end']);
 
         // extend date range for recurring events
         if (!empty($object['recurrence'])) {
-            if (empty($object['_formatobj'])) {
-                $event_xml = new kolab_format_event();
-                $event_xml->set($object);
-                $object['_formatobj'] = $event_xml;
-            }
-
-            $recurrence = new kolab_date_recurrence($object['_formatobj']);
+            $recurrence = libcalendaring::get_recurrence($object);
             $dtend = $recurrence->end() ?: new DateTime('now +100 years');
             $sql_data['dtend'] = $this->_convert_datetime($dtend);
         }
 
         // extend start/end dates to spawn all exceptions
-        if (is_array($object['exceptions'])) {
+        // FIXME: This should be done via libcalendaring_recurrence use above?
+        if (!empty($object['exceptions']) && is_array($object['exceptions'])) {
             foreach ($object['exceptions'] as $exception) {
                 if ($exception['start'] instanceof DateTimeInterface) {
                     $exstart = $this->_convert_datetime($exception['start']);
                     if ($exstart < $sql_data['dtstart']) {
                         $sql_data['dtstart'] = $exstart;
                     }
                 }
                 if ($exception['end'] instanceof DateTimeInterface) {
                     $exend = $this->_convert_datetime($exception['end']);
                     if ($exend > $sql_data['dtend']) {
                         $sql_data['dtend'] = $exend;
                     }
                 }
             }
         }
 
         $sql_data['tags']  = ' ' . join(' ', $this->get_tags($object)) . ' ';  // pad with spaces for strict/prefix search
         $sql_data['words'] = ' ' . join(' ', $this->get_words($object)) . ' ';
 
         return $sql_data;
     }
 
     /**
      * Callback to get words to index for fulltext search
      *
      * @return array List of words to save in cache
      */
     public function get_words($object = [])
     {
         $data = '';
 
         foreach ($this->fulltext_cols as $colname) {
-            list($col, $field) = explode(':', $colname);
+            list($col, $field) = strpos($colname, ':') ? explode(':', $colname) : [$colname, null];
+
+            if (empty($object[$col])) {
+                continue;
+            }
 
             if ($field) {
                 $a = [];
                 foreach ((array) $object[$col] as $attr) {
-                    $a[] = $attr[$field];
+                    if (!empty($attr[$field])) {
+                        $a[] = $attr[$field];
+                    }
                 }
                 $val = join(' ', $a);
             }
             else {
                 $val = is_array($object[$col]) ? join(' ', $object[$col]) : $object[$col];
             }
 
-            if (strlen($val))
+            if (is_string($val) && strlen($val)) {
                 $data .= $val . ' ';
+            }
         }
 
         $words = rcube_utils::normalize_string($data, true);
 
         // collect words from recurrence exceptions
-        if (is_array($object['exceptions'])) {
+        if (!empty($object['exceptions']) && is_array($object['exceptions'])) {
             foreach ($object['exceptions'] as $exception) {
                 $words = array_merge($words, $this->get_words($exception));
             }
         }
 
         return array_unique($words);
     }
 
     /**
      * Callback to get object specific tags to cache
      *
      * @return array List of tags to save in cache
      */
     public function get_tags($object)
     {
         $tags = [];
 
         if (!empty($object['valarms'])) {
             $tags[] = 'x-has-alarms';
         }
 
         // create tags reflecting participant status
         if (is_array($object['attendees'])) {
             foreach ($object['attendees'] as $attendee) {
                 if (!empty($attendee['email']) && !empty($attendee['status']))
                     $tags[] = 'x-partstat:' . $attendee['email'] . ':' . strtolower($attendee['status']);
             }
         }
 
         // collect tags from recurrence exceptions
-        if (is_array($object['exceptions'])) {
+        if (!empty($object['exceptions']) && is_array($object['exceptions'])) {
             foreach ($object['exceptions'] as $exception) {
                 $tags = array_merge($tags, $this->get_tags($exception));
             }
         }
 
         if (!empty($object['status'])) {
-          $tags[] = 'x-status:' . strtolower($object['status']);
+            $tags[] = 'x-status:' . strtolower($object['status']);
         }
 
         return array_unique($tags);
     }
 }