const PREFIX = "/api";

function formatUrl(url, params = {}) {
  const urlWithPrefix = PREFIX + url;

  const queryString =
    Object
      .keys(params)
      .map(k => encodeURIComponent(k) + '=' + encodeURIComponent(params[k]));

  if (queryString.length > 0) {
    return urlWithPrefix + "?" + queryString;
  }

  return urlWithPrefix;
}

/**
 * @param {Response} res
 * @return {Promise<array<object, object>>}
 */
function authCheck(res) {
  return res.json().then(json => {
    if (typeof json.data === "undefined") {
      json.data = null;
    }

    if (typeof json.error === "undefined") {
      json.error = null;
    }

    return Promise.resolve(json);
  })
}

/**
 * @param {string} url
 * @param {object} params
 * @returns {Promise<object|null>}
 */
export function fetchGet(url, params = {}) {
  return fetch(formatUrl(url, params), {
    method: "GET",
    credentials: "include",
  }).then(authCheck);
}

/**
 * @param {string} url
 * @param {object} params
 * @returns {Promise<object|null>}
 */
export function fetchDelete(url, params = {}) {
  return fetch(formatUrl(url, params), {
    method: "DELETE",
    credentials: "include",
  }).then(authCheck);
}


/**
 * @param {string} url
 * @param {object} data
 * @returns {Promise<object|null>}
 */
export function fetchPost(url, data = {}) {
  return fetch(formatUrl(url), {
    method: "POST",
    credentials: "include",
    headers: {
      "Content-Type": "application/json; charset=utf-8",
    },
    body: JSON.stringify(data),
  }).then(authCheck);
}


/**
 * @param {string} url
 * @param {object} data
 * @returns {Promise<object|null>}
 */
export function fetchPatch(url, data = {}) {
  return fetch(formatUrl(url), {
    method: "PATCH",
    credentials: "include",
    headers: {
      "Content-Type": "application/json; charset=utf-8",
    },
    body: JSON.stringify(data),
  }).then(authCheck);
}