--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/libcalendaring/lib/Sabre/VObject/Component/VFreeBusy.php	Sat Jan 13 08:57:56 2018 -0500
@@ -0,0 +1,68 @@
+<?php
+
+namespace Sabre\VObject\Component;
+
+use Sabre\VObject;
+
+/**
+ * The VFreeBusy component
+ *
+ * This component adds functionality to a component, specific for VFREEBUSY
+ * components.
+ *
+ * @copyright Copyright (C) 2007-2013 fruux GmbH (https://fruux.com/).
+ * @author Evert Pot (http://evertpot.com/)
+ * @license http://code.google.com/p/sabredav/wiki/License Modified BSD License
+ */
+class VFreeBusy extends VObject\Component {
+
+    /**
+     * Checks based on the contained FREEBUSY information, if a timeslot is
+     * available.
+     *
+     * @param DateTime $start
+     * @param Datetime $end
+     * @return bool
+     */
+    public function isFree(\DateTime $start, \Datetime $end) {
+
+        foreach($this->select('FREEBUSY') as $freebusy) {
+
+            // We are only interested in FBTYPE=BUSY (the default),
+            // FBTYPE=BUSY-TENTATIVE or FBTYPE=BUSY-UNAVAILABLE.
+            if (isset($freebusy['FBTYPE']) && strtoupper(substr((string)$freebusy['FBTYPE'],0,4))!=='BUSY') {
+                continue;
+            }
+
+            // The freebusy component can hold more than 1 value, separated by
+            // commas.
+            $periods = explode(',', (string)$freebusy);
+
+            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);
+
+                $busyStart = VObject\DateTimeParser::parse($busyStart);
+                $busyEnd = VObject\DateTimeParser::parse($busyEnd);
+                if ($busyEnd instanceof \DateInterval) {
+                    $tmp = clone $busyStart;
+                    $tmp->add($busyEnd);
+                    $busyEnd = $tmp;
+                }
+
+                if($start < $busyEnd && $end > $busyStart) {
+                    return false;
+                }
+
+            }
+
+        }
+
+        return true;
+
+    }
+
+}
+