/**
  * Build url from calendar entry
  * @param ilCalendarEntry $entry
  * @return string
  */
 protected function buildAppointmentUrl(ilCalendarEntry $entry)
 {
     $cat = ilCalendarCategory::getInstanceByCategoryId(current((array) ilCalendarCategoryAssignments::_lookupCategories($entry->getEntryId())));
     if ($cat->getType() != ilCalendarCategory::TYPE_OBJ) {
         $this->writer->addLine('URL;VALUE=URI:' . ILIAS_HTTP_PATH);
     } else {
         $refs = ilObject::_getAllReferences($cat->getObjId());
         include_once './Services/Link/classes/class.ilLink.php';
         $this->writer->addLine('URL;VALUE=URI:' . ilLink::_getLink(current((array) $refs)));
     }
 }