diff --git a/plugins/libkolab/lib/kolab_format_xcal.php b/plugins/libkolab/lib/kolab_format_xcal.php
index a08d0aa0..96e0a740 100644
--- a/plugins/libkolab/lib/kolab_format_xcal.php
+++ b/plugins/libkolab/lib/kolab_format_xcal.php
@@ -1,779 +1,779 @@
 <?php
 
 /**
  * Xcal based Kolab format class wrapping libkolabxml bindings
  *
  * Base class for xcal-based Kolab groupware objects such as event, todo, journal
  *
  * @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_xcal extends kolab_format
 {
     public $CTYPE = 'application/calendar+xml';
 
     public static $fulltext_cols = array('title', 'description', 'location', 'attendees:name', 'attendees:email', 'categories');
 
     public static $scheduling_properties = array('start', 'end', 'location');
 
     protected $_scheduling_properties = null;
 
     protected $sensitivity_map = array(
         'public'       => kolabformat::ClassPublic,
         'private'      => kolabformat::ClassPrivate,
         'confidential' => kolabformat::ClassConfidential,
     );
 
     protected $role_map = array(
         'REQ-PARTICIPANT' => kolabformat::Required,
         'OPT-PARTICIPANT' => kolabformat::Optional,
         'NON-PARTICIPANT' => kolabformat::NonParticipant,
         'CHAIR' => kolabformat::Chair,
     );
 
     protected $cutype_map = array(
         'INDIVIDUAL' => kolabformat::CutypeIndividual,
         'GROUP'      => kolabformat::CutypeGroup,
         'ROOM'       => kolabformat::CutypeRoom,
         'RESOURCE'   => kolabformat::CutypeResource,
         'UNKNOWN'    => kolabformat::CutypeUnknown,
     );
 
     protected $rrule_type_map = array(
         'MINUTELY' => RecurrenceRule::Minutely,
         'HOURLY' => RecurrenceRule::Hourly,
         'DAILY' => RecurrenceRule::Daily,
         'WEEKLY' => RecurrenceRule::Weekly,
         'MONTHLY' => RecurrenceRule::Monthly,
         'YEARLY' => RecurrenceRule::Yearly,
     );
 
     protected $weekday_map = array(
         'MO' => kolabformat::Monday,
         'TU' => kolabformat::Tuesday,
         'WE' => kolabformat::Wednesday,
         'TH' => kolabformat::Thursday,
         'FR' => kolabformat::Friday,
         'SA' => kolabformat::Saturday,
         'SU' => kolabformat::Sunday,
     );
 
     protected $alarm_type_map = array(
         'DISPLAY' => Alarm::DisplayAlarm,
         'EMAIL' => Alarm::EMailAlarm,
         'AUDIO' => Alarm::AudioAlarm,
     );
 
     protected $status_map = array(
         'NEEDS-ACTION' => kolabformat::StatusNeedsAction,
         'IN-PROCESS'   => kolabformat::StatusInProcess,
         'COMPLETED'    => kolabformat::StatusCompleted,
         'CANCELLED'    => kolabformat::StatusCancelled,
         'TENTATIVE'    => kolabformat::StatusTentative,
         'CONFIRMED'    => kolabformat::StatusConfirmed,
         'DRAFT'        => kolabformat::StatusDraft,
         'FINAL'        => kolabformat::StatusFinal,
     );
 
     protected $part_status_map = array(
         'UNKNOWN'      => kolabformat::PartNeedsAction,
         'NEEDS-ACTION' => kolabformat::PartNeedsAction,
         'TENTATIVE'    => kolabformat::PartTentative,
         'ACCEPTED'     => kolabformat::PartAccepted,
         'DECLINED'     => kolabformat::PartDeclined,
         'DELEGATED'    => kolabformat::PartDelegated,
         'IN-PROCESS'   => kolabformat::PartInProcess,
         'COMPLETED'    => kolabformat::PartCompleted,
       );
 
 
     /**
      * Convert common xcard properties into a hash array data structure
      *
      * @param array Additional data for merge
      *
      * @return array  Object data as hash array
      */
     public function to_array($data = array())
     {
         // read common object props
         $object = parent::to_array($data);
 
         $status_map = array_flip($this->status_map);
         $sensitivity_map = array_flip($this->sensitivity_map);
 
         $object += array(
             'sequence'    => intval($this->obj->sequence()),
             'title'       => $this->obj->summary(),
             'location'    => $this->obj->location(),
             'description' => $this->obj->description(),
             'url'         => $this->obj->url(),
             'status'      => $status_map[$this->obj->status()],
             'sensitivity' => $sensitivity_map[$this->obj->classification()],
             'priority'    => $this->obj->priority(),
             'categories'  => self::vector2array($this->obj->categories()),
             'start'       => self::php_datetime($this->obj->start()),
         );
 
         if (method_exists($this->obj, 'comment')) {
             $object['comment'] = $this->obj->comment();
         }
 
         // read organizer and attendees
         if (($organizer = $this->obj->organizer()) && ($organizer->email() || $organizer->name())) {
             $object['organizer'] = array(
                 'email' => $organizer->email(),
                 'name' => $organizer->name(),
             );
         }
 
         $role_map = array_flip($this->role_map);
         $cutype_map = array_flip($this->cutype_map);
         $part_status_map = array_flip($this->part_status_map);
         $attvec = $this->obj->attendees();
         for ($i=0; $i < $attvec->size(); $i++) {
             $attendee = $attvec->get($i);
             $cr = $attendee->contact();
             if ($cr->email() != $object['organizer']['email']) {
                 $delegators = $delegatees = array();
                 $vdelegators = $attendee->delegatedFrom();
                 for ($j=0; $j < $vdelegators->size(); $j++) {
                     $delegators[] = $vdelegators->get($j)->email();
                 }
                 $vdelegatees = $attendee->delegatedTo();
                 for ($j=0; $j < $vdelegatees->size(); $j++) {
                     $delegatees[] = $vdelegatees->get($j)->email();
                 }
 
                 $object['attendees'][] = array(
                     'role' => $role_map[$attendee->role()],
                     'cutype' => $cutype_map[$attendee->cutype()],
                     'status' => $part_status_map[$attendee->partStat()],
                     'rsvp' => $attendee->rsvp(),
                     'email' => $cr->email(),
                     'name' => $cr->name(),
                     'delegated-from' => $delegators,
                     'delegated-to' => $delegatees,
                 );
             }
         }
 
         if ($object['start'] instanceof DateTime) {
             $start_tz = $object['start']->getTimezone();
         }
 
         // read recurrence rule
         if (($rr = $this->obj->recurrenceRule()) && $rr->isValid()) {
             $rrule_type_map = array_flip($this->rrule_type_map);
             $object['recurrence'] = array('FREQ' => $rrule_type_map[$rr->frequency()]);
 
             if ($intvl = $rr->interval())
                 $object['recurrence']['INTERVAL'] = $intvl;
 
             if (($count = $rr->count()) && $count > 0) {
                 $object['recurrence']['COUNT'] = $count;
             }
             else if ($until = self::php_datetime($rr->end(), $start_tz)) {
                 $refdate = $this->get_reference_date();
                 if ($refdate && $refdate instanceof DateTime && !$refdate->_dateonly) {
                     $until->setTime($refdate->format('G'), $refdate->format('i'), 0);
                 }
                 $object['recurrence']['UNTIL'] = $until;
             }
 
             if (($byday = $rr->byday()) && $byday->size()) {
                 $weekday_map = array_flip($this->weekday_map);
                 $weekdays = array();
                 for ($i=0; $i < $byday->size(); $i++) {
                     $daypos = $byday->get($i);
                     $prefix = $daypos->occurence();
-                    $weekdays[] = ($prefix ? $prefix : '') . $weekday_map[$daypos->weekday()];
+                    $weekdays[] = ($prefix ?: '') . $weekday_map[$daypos->weekday()];
                 }
                 $object['recurrence']['BYDAY'] = join(',', $weekdays);
             }
 
             if (($bymday = $rr->bymonthday()) && $bymday->size()) {
                 $object['recurrence']['BYMONTHDAY'] = join(',', self::vector2array($bymday));
             }
 
             if (($bymonth = $rr->bymonth()) && $bymonth->size()) {
                 $object['recurrence']['BYMONTH'] = join(',', self::vector2array($bymonth));
             }
 
             if ($exdates = $this->obj->exceptionDates()) {
                 for ($i=0; $i < $exdates->size(); $i++) {
                     if ($exdate = self::php_datetime($exdates->get($i), $start_tz)) {
                         $object['recurrence']['EXDATE'][] = $exdate;
                     }
                 }
             }
         }
 
         if ($rdates = $this->obj->recurrenceDates()) {
             for ($i=0; $i < $rdates->size(); $i++) {
                 if ($rdate = self::php_datetime($rdates->get($i), $start_tz)) {
                     $object['recurrence']['RDATE'][] = $rdate;
                 }
             }
         }
 
         // read alarm
         $valarms = $this->obj->alarms();
         $alarm_types = array_flip($this->alarm_type_map);
         $object['valarms'] = array();
         for ($i=0; $i < $valarms->size(); $i++) {
             $alarm = $valarms->get($i);
             $type  = $alarm_types[$alarm->type()];
 
             if ($type == 'DISPLAY' || $type == 'EMAIL' || $type == 'AUDIO') {  // only some alarms are supported
                 $valarm = array(
                     'action'      => $type,
                     'summary'     => $alarm->summary(),
                     'description' => $alarm->description(),
                 );
 
                 if ($type == 'EMAIL') {
                     $valarm['attendees'] = array();
                     $attvec = $alarm->attendees();
                     for ($j=0; $j < $attvec->size(); $j++) {
                         $cr = $attvec->get($j);
                         $valarm['attendees'][] = $cr->email();
                     }
                 }
                 else if ($type == 'AUDIO') {
                     $attach = $alarm->audioFile();
                     $valarm['uri'] = $attach->uri();
                 }
 
                 if ($start = self::php_datetime($alarm->start())) {
                     $object['alarms']  = '@' . $start->format('U');
                     $valarm['trigger'] = $start;
                 }
                 else if ($offset = $alarm->relativeStart()) {
                     $prefix = $offset->isNegative() ? '-' : '+';
                     $value  = '';
                     $time   = '';
 
                     if      ($w = $offset->weeks())     $value .= $w . 'W';
                     else if ($d = $offset->days())      $value .= $d . 'D';
                     else if ($h = $offset->hours())     $time  .= $h . 'H';
                     else if ($m = $offset->minutes())   $time  .= $m . 'M';
                     else if ($s = $offset->seconds())   $time  .= $s . 'S';
 
                     // assume 'at event time'
                     if (empty($value) && empty($time)) {
                         $prefix = '';
                         $time   = '0S';
                     }
 
                     $object['alarms']  = $prefix . $value . $time;
                     $valarm['trigger'] = $prefix . 'P' . $value . ($time ? 'T' . $time : '');
 
                     if ($alarm->relativeTo() == kolabformat::End) {
                         $valarm['related'] == 'END';
                     }
                 }
 
                 // read alarm duration and repeat properties
                 if (($duration = $alarm->duration()) && $duration->isValid()) {
                     $value = $time = '';
 
                     if      ($w = $duration->weeks())     $value .= $w . 'W';
                     else if ($d = $duration->days())      $value .= $d . 'D';
                     else if ($h = $duration->hours())     $time  .= $h . 'H';
                     else if ($m = $duration->minutes())   $time  .= $m . 'M';
                     else if ($s = $duration->seconds())   $time  .= $s . 'S';
 
                     $valarm['duration'] = 'P' . $value . ($time ? 'T' . $time : '');
                     $valarm['repeat']   = $alarm->numrepeat();
                 }
 
                 $object['alarms']  .= ':' . $type;  // legacy property
                 $object['valarms'][] = array_filter($valarm);
             }
         }
 
         $this->get_attachments($object);
 
         return $object;
     }
 
 
     /**
      * Set common xcal properties to the kolabformat object
      *
      * @param array  Event data as hash array
      */
     public function set(&$object)
     {
         $this->init();
 
         $is_new = !$this->obj->uid();
         $old_sequence = $this->obj->sequence();
         $reschedule = $is_new;
 
         // set common object properties
         parent::set($object);
 
         // set sequence value
         if (!isset($object['sequence'])) {
             if ($is_new) {
                 $object['sequence'] = 0;
             }
             else {
                 $object['sequence'] = $old_sequence;
 
                 // increment sequence when updating properties relevant for scheduling.
                 // RFC 5545: "It is incremented [...] each time the Organizer makes a significant revision to the calendar component."
                 if ($this->check_rescheduling($object)) {
                     $object['sequence']++;
                 }
             }
         }
         $this->obj->setSequence(intval($object['sequence']));
 
         if ($object['sequence'] > $old_sequence) {
             $reschedule = true;
         }
 
         $this->obj->setSummary($object['title']);
         $this->obj->setLocation($object['location']);
         $this->obj->setDescription($object['description']);
         $this->obj->setPriority($object['priority']);
         $this->obj->setClassification($this->sensitivity_map[$object['sensitivity']]);
         $this->obj->setCategories(self::array2vector($object['categories']));
         $this->obj->setUrl(strval($object['url']));
 
         if (method_exists($this->obj, 'setComment')) {
             $this->obj->setComment($object['comment']);
         }
 
         // process event attendees
         $attendees = new vectorattendee;
         foreach ((array)$object['attendees'] as $i => $attendee) {
             if ($attendee['role'] == 'ORGANIZER') {
                 $object['organizer'] = $attendee;
             }
             else if ($attendee['email'] != $object['organizer']['email']) {
                 $cr = new ContactReference(ContactReference::EmailReference, $attendee['email']);
                 $cr->setName($attendee['name']);
 
                 // set attendee RSVP if missing
                 if (!isset($attendee['rsvp'])) {
                     $object['attendees'][$i]['rsvp'] = $attendee['rsvp'] = $reschedule;
                 }
 
                 $att = new Attendee;
                 $att->setContact($cr);
                 $att->setPartStat($this->part_status_map[$attendee['status']]);
-                $att->setRole($this->role_map[$attendee['role']] ? $this->role_map[$attendee['role']] : kolabformat::Required);
-                $att->setCutype($this->cutype_map[$attendee['cutype']] ? $this->cutype_map[$attendee['cutype']] : kolabformat::CutypeIndividual);
+                $att->setRole($this->role_map[$attendee['role']] ?: kolabformat::Required);
+                $att->setCutype($this->cutype_map[$attendee['cutype']] ?: kolabformat::CutypeIndividual);
                 $att->setRSVP((bool)$attendee['rsvp']);
 
                 if (!empty($attendee['delegated-from'])) {
                     $vdelegators = new vectorcontactref;
                     foreach ((array)$attendee['delegated-from'] as $delegator) {
                         $vdelegators->push(new ContactReference(ContactReference::EmailReference, $delegator));
                     }
                     $att->setDelegatedFrom($vdelegators);
                 }
                 if (!empty($attendee['delegated-to'])) {
                     $vdelegatees = new vectorcontactref;
                     foreach ((array)$attendee['delegated-to'] as $delegatee) {
                         $vdelegatees->push(new ContactReference(ContactReference::EmailReference, $delegatee));
                     }
                     $att->setDelegatedTo($vdelegatees);
                 }
 
                 if ($att->isValid()) {
                     $attendees->push($att);
                 }
                 else {
                     rcube::raise_error(array(
                         'code' => 600, 'type' => 'php',
                         'file' => __FILE__, 'line' => __LINE__,
                         'message' => "Invalid event attendee: " . json_encode($attendee),
                     ), true);
                 }
             }
         }
         $this->obj->setAttendees($attendees);
 
         if ($object['organizer']) {
             $organizer = new ContactReference(ContactReference::EmailReference, $object['organizer']['email']);
             $organizer->setName($object['organizer']['name']);
             $this->obj->setOrganizer($organizer);
         }
 
         if ($object['start'] instanceof DateTime) {
             $start_tz = $object['start']->getTimezone();
         }
 
         // save recurrence rule
         $rr = new RecurrenceRule;
         $rr->setFrequency(RecurrenceRule::FreqNone);
 
         if ($object['recurrence'] && !empty($object['recurrence']['FREQ'])) {
             $freq     = $object['recurrence']['FREQ'];
             $bysetpos = explode(',', $object['recurrence']['BYSETPOS']);
 
             $rr->setFrequency($this->rrule_type_map[$freq]);
 
             if ($object['recurrence']['INTERVAL'])
                 $rr->setInterval(intval($object['recurrence']['INTERVAL']));
 
             if ($object['recurrence']['BYDAY']) {
                 $byday = new vectordaypos;
                 foreach (explode(',', $object['recurrence']['BYDAY']) as $day) {
                     $occurrence = 0;
                     if (preg_match('/^([\d-]+)([A-Z]+)$/', $day, $m)) {
                         $occurrence = intval($m[1]);
                         $day = $m[2];
                     }
 
                     if (isset($this->weekday_map[$day])) {
                         // @TODO: libkolabxml does not support BYSETPOS, neither we.
                         // However, we can convert most common cases to BYDAY
                         if (!$occurrence && $freq == 'MONTHLY' && !empty($bysetpos)) {
                             foreach ($bysetpos as $pos) {
                                 $byday->push(new DayPos(intval($pos), $this->weekday_map[$day]));
                             }
                         }
                         else {
                             $byday->push(new DayPos($occurrence, $this->weekday_map[$day]));
                         }
                     }
                 }
                 $rr->setByday($byday);
             }
 
             if ($object['recurrence']['BYMONTHDAY']) {
                 $bymday = new vectori;
                 foreach (explode(',', $object['recurrence']['BYMONTHDAY']) as $day)
                     $bymday->push(intval($day));
                 $rr->setBymonthday($bymday);
             }
 
             if ($object['recurrence']['BYMONTH']) {
                 $bymonth = new vectori;
                 foreach (explode(',', $object['recurrence']['BYMONTH']) as $month)
                     $bymonth->push(intval($month));
                 $rr->setBymonth($bymonth);
             }
 
             if ($object['recurrence']['COUNT'])
                 $rr->setCount(intval($object['recurrence']['COUNT']));
             else if ($object['recurrence']['UNTIL'])
                 $rr->setEnd(self::get_datetime($object['recurrence']['UNTIL'], null, true, $start_tz));
 
             if ($rr->isValid()) {
                 // add exception dates (only if recurrence rule is valid)
                 $exdates = new vectordatetime;
                 foreach ((array)$object['recurrence']['EXDATE'] as $exdate)
                     $exdates->push(self::get_datetime($exdate, null, true, $start_tz));
                 $this->obj->setExceptionDates($exdates);
             }
             else {
                 rcube::raise_error(array(
                     'code' => 600, 'type' => 'php',
                     'file' => __FILE__, 'line' => __LINE__,
                     'message' => "Invalid event recurrence rule: " . json_encode($object['recurrence']),
                 ), true);
             }
         }
 
         $this->obj->setRecurrenceRule($rr);
 
         // save recurrence dates (aka RDATE)
         if (!empty($object['recurrence']['RDATE'])) {
             $rdates = new vectordatetime;
             foreach ((array)$object['recurrence']['RDATE'] as $rdate)
                 $rdates->push(self::get_datetime($rdate, null, true, $start_tz));
             $this->obj->setRecurrenceDates($rdates);
         }
 
         // save alarm(s)
         $valarms = new vectoralarm;
         $valarm_hashes = array();
         if ($object['valarms']) {
             foreach ($object['valarms'] as $valarm) {
                 if (!array_key_exists($valarm['action'], $this->alarm_type_map)) {
                     continue;  // skip unknown alarm types
                 }
 
                 // Get rid of duplicates, some CalDAV clients can set them
                 $hash = serialize($valarm);
                 if (in_array($hash, $valarm_hashes)) {
                     continue;
                 }
                 $valarm_hashes[] = $hash;
 
                 if ($valarm['action'] == 'EMAIL') {
                     $recipients = new vectorcontactref;
                     foreach (($valarm['attendees'] ?: array($object['_owner'])) as $email) {
                         $recipients->push(new ContactReference(ContactReference::EmailReference, $email));
                     }
                     $alarm = new Alarm(
                         strval($valarm['summary'] ?: $object['title']),
                         strval($valarm['description'] ?: $object['description']),
                         $recipients
                     );
                 }
                 else if ($valarm['action'] == 'AUDIO') {
                     $attach = new Attachment;
                     $attach->setUri($valarm['uri'] ?: 'null', 'unknown');
                     $alarm = new Alarm($attach);
                 }
                 else {
                     // action == DISPLAY
                     $alarm = new Alarm(strval($valarm['summary'] ?: $object['title']));
                 }
 
                 if (is_object($valarm['trigger']) && $valarm['trigger'] instanceof DateTime) {
                     $alarm->setStart(self::get_datetime($valarm['trigger'], new DateTimeZone('UTC')));
                 }
                 else if (preg_match('/^@([0-9]+)$/', $valarm['trigger'], $m)) {
                     $alarm->setStart(self::get_datetime($m[1], new DateTimeZone('UTC')));
                 }
                 else {
                     // Support also interval in format without PT, e.g. -10M
                     if (preg_match('/^([-+]*)([0-9]+[DHMS])$/', strtoupper($valarm['trigger']), $m)) {
                         $valarm['trigger'] = $m[1] . ($m[2][strlen($m[2])-1] == 'D' ? 'P' : 'PT') . $m[2];
                     }
 
                     try {
                         $period   = new DateInterval(preg_replace('/[^0-9PTWDHMS]/', '', $valarm['trigger']));
                         $duration = new Duration($period->d, $period->h, $period->i, $period->s, $valarm['trigger'][0] == '-');
                     }
                     catch (Exception $e) {
                         // skip alarm with invalid trigger values
                         rcube::raise_error($e, true);
                         continue;
                     }
 
                     $related = strtoupper($valarm['related']) == 'END' ? kolabformat::End : kolabformat::Start;
                     $alarm->setRelativeStart($duration, $related);
                 }
 
                 if ($valarm['duration']) {
                     try {
                         $d = new DateInterval($valarm['duration']);
                         $duration = new Duration($d->d, $d->h, $d->i, $d->s);
                         $alarm->setDuration($duration, intval($valarm['repeat']));
                     }
                     catch (Exception $e) {
                         // ignore
                     }
                 }
 
                 $valarms->push($alarm);
             }
         }
         // legacy support
         else if ($object['alarms']) {
             list($offset, $type) = explode(":", $object['alarms']);
 
             if ($type == 'EMAIL' && !empty($object['_owner'])) {  // email alarms implicitly go to event owner
                 $recipients = new vectorcontactref;
                 $recipients->push(new ContactReference(ContactReference::EmailReference, $object['_owner']));
                 $alarm = new Alarm($object['title'], strval($object['description']), $recipients);
             }
             else {  // default: display alarm
                 $alarm = new Alarm($object['title']);
             }
 
             if (preg_match('/^@(\d+)/', $offset, $d)) {
                 $alarm->setStart(self::get_datetime($d[1], new DateTimeZone('UTC')));
             }
             else if (preg_match('/^([-+]?)P?T?(\d+)([SMHDW])/', $offset, $d)) {
                 $days = $hours = $minutes = $seconds = 0;
                 switch ($d[3]) {
                     case 'W': $days  = 7*intval($d[2]); break;
                     case 'D': $days    = intval($d[2]); break;
                     case 'H': $hours   = intval($d[2]); break;
                     case 'M': $minutes = intval($d[2]); break;
                     case 'S': $seconds = intval($d[2]); break;
                 }
                 $alarm->setRelativeStart(new Duration($days, $hours, $minutes, $seconds, $d[1] == '-'), $d[1] == '-' ? kolabformat::Start : kolabformat::End);
             }
 
             $valarms->push($alarm);
         }
         $this->obj->setAlarms($valarms);
 
         $this->set_attachments($object);
     }
 
     /**
      * Return the reference date for recurrence and alarms
      *
      * @return mixed DateTime instance of null if no refdate is available
      */
     public function get_reference_date()
     {
         if ($this->data['start'] && $this->data['start'] instanceof DateTime) {
             return $this->data['start'];
         }
 
         return self::php_datetime($this->obj->start());
     }
 
     /**
      * 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($obj = null)
     {
         $data = '';
         $object = $obj ?: $this->data;
 
         foreach (self::$fulltext_cols as $colname) {
             list($col, $field) = explode(':', $colname);
 
             if ($field) {
                 $a = array();
                 foreach ((array)$object[$col] as $attr)
                     $a[] = $attr[$field];
                 $val = join(' ', $a);
             }
             else {
                 $val = is_array($object[$col]) ? join(' ', $object[$col]) : $object[$col];
             }
 
             if (strlen($val))
                 $data .= $val . ' ';
         }
 
         $words = rcube_utils::normalize_string($data, true);
 
         // collect words from recurrence exceptions
         if (is_array($object['exceptions'])) {
             foreach ($object['exceptions'] as $exception) {
                 $words = array_merge($words, $this->get_words($exception));
             }
         }
 
         return array_unique($words);
     }
 
     /**
      * 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($obj = null)
     {
         $tags = array();
         $object = $obj ?: $this->data;
 
         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($object['exceptions'])) {
             foreach ($object['exceptions'] as $exception) {
                 $tags = array_merge($tags, $this->get_tags($exception));
             }
         }
 
         if (!empty($object['status'])) {
           $tags[] = 'x-status:' . strtolower($object['status']);
         }
 
         return array_unique($tags);
     }
 
     /**
      * Identify changes considered relevant for scheduling
      * 
      * @param array Hash array with NEW object properties
      * @param array Hash array with OLD object properties
      *
      * @return boolean True if changes affect scheduling, False otherwise
      */
     public function check_rescheduling($object, $old = null)
     {
         $reschedule = false;
 
         if (!is_array($old)) {
             $old = $this->data['uid'] ? $this->data : $this->to_array();
         }
 
         foreach ($this->_scheduling_properties ?: self::$scheduling_properties as $prop) {
             $a = $old[$prop];
             $b = $object[$prop];
             if ($object['allday'] && ($prop == 'start' || $prop == 'end') && $a instanceof DateTime && $b instanceof DateTime) {
                 $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;
     }
 
     /**
      * Clones into an instance of libcalendaring's extended EventCal class
      *
      * @return mixed EventCal object or false on failure
      */
     public function to_libcal()
     {
         static $error_logged = false;
 
         if (class_exists('kolabcalendaring')) {
             return new EventCal($this->obj);
         }
         else if (!$error_logged) {
             $error_logged = true;
             rcube::raise_error(array(
                 'code'    => 900,
                 'message' => "Required kolabcalendaring module not found"
             ), true);
         }
 
         return false;
     }
 }