class HttpClient {

  static ACCEPT = {
    TEXT_HTML: 'text/html',
    JSON: 'application/json',
  };

  _responseInterceptors = [];

  addResponseInterceptor(interceptor) {
    if (typeof interceptor === 'function') {
      this._responseInterceptors.push(interceptor);
    }
  }

  get(args) {
    args.method = 'GET';
    return this._fetch(args);
  }

  post(args) {
    args.method = 'POST';
    return this._fetch(args);
  }

  _fetch(options) {
    const requestOptions = {
      credentials: 'same-origin',
      ...options,
    };

    return fetch(options.url, requestOptions)
      .then(
        (response) => {
          this._responseInterceptors.forEach((interceptor) => interceptor(response, options));
          return Promise.resolve(response);
        },
        Promise.reject,
      ).catch(console.error);
  }
}

window.HttpClient = new HttpClient();

// HttpClient ships with its own little interceptor to throw an error
// if the response does not match the expected content-type
function contentTypeInterceptor(response, options) {
  if (!options || !options.accept) {
    return;
  }

  const contentType = response.headers.get("content-type");
  if (!contentType.match(options.accept)) {
    throw new Error('Server returned with "' + contentType + '" when "' + options.accept + '" was expected');
  }
}

window.HttpClient.addResponseInterceptor(contentTypeInterceptor);