protected function buildUrl(array $data = []): string
    {
        $params = array_merge([
            'SM_API_KEY' => $this->api_key,
            'SM_LENGTH' => $this->summary_length,
        ], $data);

        $url  = 'http://api.smmry.com';
        $url .= '?' . http_build_query($params);

        return $url;
    }