/**
 * @license
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @template T
 * @param {!Array<T>} array
 * @param {!Function} fn An iteratee function to be passed each element of
 *     the array in order. Must return a promise, and the following
 *     iteration will not begin until resolution of the promise returned by
 *     the previous iteration.
 *
 *     An optional second argument to fn is a callback that will halt the
 *     loop if called.
 * @return {!Promise<undefined>}
 */
export function asyncForeach(array, fn) {
  if (!array.length) { return Promise.resolve(); }
  let stop = false;
  const stopCallback = () => { stop = true; };
  return fn(array[0], stopCallback).then(exit => {
    if (stop) { return Promise.resolve(); }
    return asyncForeach(array.slice(1), fn);
  });
}