--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/libcalendaring/lib/libcalendaring_recurrence.php	Sat Jan 13 08:57:56 2018 -0500
@@ -0,0 +1,155 @@
+<?php
+
+/**
+ * Recurrence computation class for shared use
+ *
+ * Uitility class to compute reccurrence dates from the given rules
+ *
+ * @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 libcalendaring_recurrence
+{
+    protected $lib;
+    protected $start;
+    protected $next;
+    protected $engine;
+    protected $recurrence;
+    protected $dateonly = false;
+    protected $hour = 0;
+
+    /**
+     * Default constructor
+     *
+     * @param object calendar The calendar plugin instance
+     */
+    function __construct($lib)
+    {
+      // use Horde classes to compute recurring instances
+      // TODO: replace with something that has less than 6'000 lines of code
+      require_once(__DIR__ . '/Horde_Date_Recurrence.php');
+
+      $this->lib = $lib;
+    }
+
+    /**
+     * Initialize recurrence engine
+     *
+     * @param array  The recurrence properties
+     * @param object DateTime The recurrence start date
+     */
+    public function init($recurrence, $start = null)
+    {
+        $this->recurrence = $recurrence;
+
+        $this->engine = new Horde_Date_Recurrence($start);
+        $this->engine->fromRRule20(libcalendaring::to_rrule($recurrence));
+
+        $this->set_start($start);
+
+        if (is_array($recurrence['EXDATE'])) {
+            foreach ($recurrence['EXDATE'] as $exdate) {
+                if (is_a($exdate, 'DateTime')) {
+                    $this->engine->addException($exdate->format('Y'), $exdate->format('n'), $exdate->format('j'));
+                }
+            }
+        }
+        if (is_array($recurrence['RDATE'])) {
+            foreach ($recurrence['RDATE'] as $rdate) {
+                if (is_a($rdate, 'DateTime')) {
+                    $this->engine->addRDate($rdate->format('Y'), $rdate->format('n'), $rdate->format('j'));
+                }
+            }
+        }
+    }
+
+    /**
+     * Setter for (new) recurrence start date
+     *
+     * @param object DateTime The recurrence start date
+     */
+    public function set_start($start)
+    {
+        $this->start = $start;
+        $this->dateonly = $start->_dateonly;
+        $this->next = new Horde_Date($start, $this->lib->timezone->getName());
+        $this->hour = $this->next->hour;
+        $this->engine->setRecurStart($this->next);
+    }
+
+    /**
+     * Get date/time of the next occurence of this event
+     *
+     * @return mixed DateTime object or False if recurrence ended
+     */
+    public function next()
+    {
+        $time = false;
+        $after = clone $this->next;
+        $after->mday = $after->mday + 1;
+        if ($this->next && ($next = $this->engine->nextActiveRecurrence($after))) {
+            // avoid endless loops if recurrence computation fails
+            if (!$next->after($this->next)) {
+                return false;
+            }
+            // fix time for all-day events
+            if ($this->dateonly) {
+                $next->hour = $this->hour;
+                $next->min = 0;
+            }
+
+            $time = $next->toDateTime();
+            $this->next = $next;
+        }
+
+        return $time;
+    }
+
+    /**
+     * Get the end date of the occurence of this recurrence cycle
+     *
+     * @return DateTime|bool End datetime of the last occurence or False if recurrence exceeds limit
+     */
+    public function end()
+    {
+        // recurrence end date is given
+        if ($this->recurrence['UNTIL'] instanceof DateTime) {
+            return $this->recurrence['UNTIL'];
+        }
+
+        // take the last RDATE entry if set
+        if (is_array($this->recurrence['RDATE']) && !empty($this->recurrence['RDATE'])) {
+            $last = end($this->recurrence['RDATE']);
+            if ($last instanceof DateTime) {
+              return $last;
+            }
+        }
+
+        // run through all items till we reach the end
+        if ($this->recurrence['COUNT']) {
+            $last = $this->start;
+            $this->next = new Horde_Date($this->start, $this->lib->timezone->getName());
+            while (($next = $this->next()) && $c < 1000) {
+                $last = $next;
+                $c++;
+            }
+        }
+
+        return $last;
+    }
+
+}