/**
 * @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.
 */

/**
 * @param 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.
 */
export function asyncForeach<T>(
  array: T[],
  fn: (item: T, stopCallback: () => void) => Promise<T>
): Promise<T | void> {
  if (!array.length) {
    return Promise.resolve();
  }
  let stop = false;
  const stopCallback = () => {
    stop = true;
  };
  return fn(array[0], stopCallback).then(() => {
    if (stop) {
      return Promise.resolve();
    }
    return asyncForeach(array.slice(1), fn);
  });
}