/**
  * Discussion subscription toggle
  */
 public function subscribedisc_action()
 {
     global $PAGE;
     require_sesskey();
     require_once dirname(dirname(__DIR__)) . '/lib/discussion/subscribe.php';
     $discussionid = required_param('discussionid', PARAM_INT);
     $returnurl = required_param('returnurl', PARAM_LOCALURL);
     $subscribe = new \hsuforum_lib_discussion_subscribe($PAGE->activityrecord, $PAGE->context);
     if ($subscribe->is_subscribed($discussionid)) {
         $subscribe->unsubscribe($discussionid);
     } else {
         $subscribe->subscribe($discussionid);
     }
     if (!AJAX_SCRIPT) {
         redirect(new moodle_url($returnurl));
     }
 }