public function isLogged()
    {
        return self::$is_logged || self::$is_logged = (bool)(
                isset($_SESSION['admin_logged'], $_SESSION['admin_id'], $_SESSION['admin_sid'])
                && $_SESSION['admin_logged'] && $_SESSION['admin_id']
                && $this->checkSession($_SESSION['admin_id'], $_SESSION['admin_sid'], true)
            );
    }