/**
  * fetch util
  * @type {Object<rest>}
  * @typeof {function(api, param):object} rest
  * @param {string} api - absolute api
  * @param {object} param
  * @return {object} {response, error}
*/
require('whatwg-fetch');

export default (() => {
  function core(api, param) {
    // cookie
    param.credentials = 'include';

    return window.fetch(api, param)
    .then(res => res.json())
    .catch(error => {
      setTimeout(() => { throw new Error(error); });
      return { error: error.message };
    });
  };

  function serialize(obj) {
    return Object.keys(obj).map(p => `${encodeURIComponent(p)}=${encodeURIComponent([obj[p]])}`).join('&');
  };

  return {
    get(api, param) {
      return param ? core(`${api}?${serialize(param)}`, param) : core(`${api}`, {});
    },
    post(api, param = {}) {
      return core(`${api}`, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(param)
      });
    },
    upload(api, param = {}) {
      return core(`${api}`, {
        method: 'POST',
        body: param
      });
    }
  };
})();