import fetch from 'isomorphic-fetch';
import es6promise from 'es6-promise';
es6promise.polyfill();

/**
 * @see https://github.com/github/fetch#handling-http-error-statuses
 */
function checkStatus(response) {
  let ret;
  let error;
  if (response.status >= 200 && response.status < 300) {
    ret = response;
  } else {
    error = new Error(response.statusText);
    error.response = response;
    throw error;
  }

  return ret;
}

class SilverStripeBackend {

  constructor() {
    // Allow mocking
    this.fetch = fetch;
  }

  /**
   * Makes a network request using the GET HTTP verb.
   *
   * @param string url - Endpoint URL.
   * @return object - Promise
   */
  get(url) {
    return this.fetch(url, { method: 'get', credentials: 'same-origin' })
      .then(checkStatus);
  }

  /**
   * Makes a network request using the POST HTTP verb.
   *
   * @param string url - Endpoint URL.
   * @param object data - Data to send with the request.
   * @return object - Promise
   */
  post(url, data) {
    return this.fetch(url, {
      method: 'post',
      headers: new Headers({
        'Content-Type': 'application/x-www-form-urlencoded',
      }),
      credentials: 'same-origin',
      body: data,
    })
    .then(checkStatus);
  }

  /**
   * Makes a newtwork request using the PUT HTTP verb.
   *
   * @param string url - Endpoint URL.
   * @param object data - Data to send with the request.
   * @return object - Promise
   */
  put(url, data) {
    return this.fetch(url, { method: 'put', credentials: 'same-origin', body: data })
      .then(checkStatus);
  }

  /**
   * Makes a newtwork request using the DELETE HTTP verb.
   *
   * @param string url - Endpoint URL.
   * @param object data - Data to send with the request.
   * @return object - Promise
   */
  delete(url, data) {
    return this.fetch(url, { method: 'delete', credentials: 'same-origin', body: data })
      .then(checkStatus);
  }

}

// Exported as a singleton so we can implement things like
// global caching and request batching at some stage.
const backend = new SilverStripeBackend();

export default backend;