public function whereBrackets(Closure $callback, $operator = 'AND')
    {
        if ( ! in_array($operator, ['AND', 'OR'])) {
            throw new \InvalidArgumentException("Logical operator");
        }
        // first time call where ?
        if ($this->_where_str == '') {
            $this->_where_str = ' WHERE ( ';
        } else {
            $this->_where_str .= ' '.$operator.' ( ';
        }
        $sub_attr = $this->_subBuilder($callback);

        $this->_where_str .= preg_replace('/WHERE/', '', $sub_attr['_where_str'], 1).' ) ';

        return $this;
    }