/**
  *
  * @param  integer Date range start (unix timestamp)
  * @param  integer Date range end (unix timestamp)
  * @return integer Count
  */
 public function count_events($start, $end = null)
 {
     // get email addresses of the current user
     $user_emails = $this->cal->get_user_emails();
     $subquery = array();
     foreach ($user_emails as $email) {
         foreach ($this->partstats as $partstat) {
             $subquery[] = array('tags', '=', 'x-partstat:' . $email . ':' . strtolower($partstat));
         }
     }
     // aggregate counts from all calendar folders
     $count = 0;
     foreach (kolab_storage::list_folders('', '*', 'event', null) as $foldername) {
         $cal = new kolab_calendar($foldername, $this->cal);
         if ($cal->get_namespace() == 'other') {
             continue;
         }
         $count += $cal->count_events($start, $end, array(array($subquery, 'OR')));
     }
     return $count;
 }