public function addIndex(array $keys, array $options = []) : void
    {
        $this->indexes[] = [
            'keys' => array_map(static function ($value) {
                if ($value === 1 || $value === -1) {
                    return $value;
                }
                if (is_string($value)) {
                    $lower = strtolower($value);
                    if ($lower === 'asc') {
                        return 1;
                    }

                    if ($lower === 'desc') {
                        return -1;
                    }
                }
                return $value;
            }, $keys),
            'options' => $options,
        ];
    }