--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/calendar/lib/calendar_recurrence.php	Sat Jan 13 08:56:12 2018 -0500
@@ -0,0 +1,88 @@
+<?php
+
+require_once realpath(__DIR__ . '/../../libcalendaring/lib/libcalendaring_recurrence.php');
+
+/**
+ * Recurrence computation class for the Calendar plugin
+ *
+ * Uitility class to compute instances of recurring events.
+ *
+ * @author Thomas Bruederli <bruederli@kolabsys.com>
+ *
+ * Copyright (C) 2012-2014, 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_recurrence extends libcalendaring_recurrence
+{
+  private $event;
+  private $duration;
+
+  /**
+   * Default constructor
+   *
+   * @param object calendar The calendar plugin instance
+   * @param array The event object to operate on
+   */
+  function __construct($cal, $event)
+  {
+    parent::__construct($cal->lib);
+
+    $this->event = $event;
+
+    if (is_object($event['start']) && is_object($event['end']))
+      $this->duration = $event['start']->diff($event['end']);
+
+    $event['start']->_dateonly |= $event['allday'];
+    $this->init($event['recurrence'], $event['start']);
+  }
+
+  /**
+   * Alias of libcalendaring_recurrence::next()
+   *
+   * @return mixed DateTime object or False if recurrence ended
+   */
+  public function next_start()
+  {
+    return $this->next();
+  }
+
+  /**
+   * Get the next recurring instance of this event
+   *
+   * @return mixed Array with event properties or False if recurrence ended
+   */
+  public function next_instance()
+  {
+    if ($next_start = $this->next()) {
+      $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, $this->event['allday']);
+
+      unset($next['_formatobj']);
+
+      return $next;
+    }
+
+    return false;
+  }
+
+}