public function subscriber_overview($users, $forum , $course) {
        $output = '';
        $modinfo = get_fast_modinfo($course);
        if (!$users || !is_array($users) || count($users)===0) {
            $output .= $this->output->heading(get_string("nosubscribers", "forum"));
        } else if (!isset($modinfo->instances['forum'][$forum->id])) {
            $output .= $this->output->heading(get_string("invalidmodule", "error"));
        } else {
            $cm = $modinfo->instances['forum'][$forum->id];
            $canviewemail = in_array('email', get_extra_user_fields(context_module::instance($cm->id)));
            $strparams = new stdclass();
            $strparams->name = format_string($forum->name);
            $strparams->count = count($users);
            $output .= $this->output->heading(get_string("subscriberstowithcount", "forum", $strparams));
            $table = new html_table();
            $table->cellpadding = 5;
            $table->cellspacing = 5;
            $table->tablealign = 'center';
            $table->data = array();
            foreach ($users as $user) {
                $info = array($this->output->user_picture($user, array('courseid'=>$course->id)), fullname($user));
                if ($canviewemail) {
                    array_push($info, $user->email);
                }
                $table->data[] = $info;
            }
            $output .= html_writer::table($table);
        }
        return $output;
    }