/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import {BaseException} from '../index';

let _FakeAsyncTestZoneSpecType = (Zone as any /** TODO #9100 */)['FakeAsyncTestZoneSpec'];

/**
 * Wraps a function to be executed in the fakeAsync zone:
 * - microtasks are manually executed by calling `flushMicrotasks()`,
 * - timers are synchronous, `tick()` simulates the asynchronous passage of time.
 *
 * If there are any pending timers at the end of the function, an exception will be thrown.
 *
 * Can be used to wrap inject() calls.
 *
 * ## Example
 *
 * {@example testing/ts/fake_async.ts region='basic'}
 *
 * @param fn
 * @returns {Function} The function wrapped to be executed in the fakeAsync zone
 *
 * @experimental
 */
export function fakeAsync(fn: Function): (...args: any[]) => any {
  if (Zone.current.get('FakeAsyncTestZoneSpec') != null) {
    throw new BaseException('fakeAsync() calls can not be nested');
  }

  let fakeAsyncTestZoneSpec = new _FakeAsyncTestZoneSpecType();
  let fakeAsyncZone = Zone.current.fork(fakeAsyncTestZoneSpec);

  return function(...args: any[] /** TODO #9100 */) {
    let res = fakeAsyncZone.run(() => {
      let res = fn(...args);
      flushMicrotasks();
      return res;
    });

    if (fakeAsyncTestZoneSpec.pendingPeriodicTimers.length > 0) {
      throw new BaseException(
          `${fakeAsyncTestZoneSpec.pendingPeriodicTimers.length} ` +
          `periodic timer(s) still in the queue.`);
    }

    if (fakeAsyncTestZoneSpec.pendingTimers.length > 0) {
      throw new BaseException(
          `${fakeAsyncTestZoneSpec.pendingTimers.length} timer(s) still in the queue.`);
    }
    return res;
  };
}

function _getFakeAsyncZoneSpec(): any {
  let zoneSpec = Zone.current.get('FakeAsyncTestZoneSpec');
  if (zoneSpec == null) {
    throw new Error('The code should be running in the fakeAsync zone to call this function');
  }
  return zoneSpec;
}

/**
 * Simulates the asynchronous passage of time for the timers in the fakeAsync zone.
 *
 * The microtasks queue is drained at the very start of this function and after any timer callback
 * has been executed.
 *
 * ## Example
 *
 * {@example testing/ts/fake_async.ts region='basic'}
 *
 * @experimental
 */
export function tick(millis: number = 0): void {
  _getFakeAsyncZoneSpec().tick(millis);
}

/**
 * Discard all remaining periodic tasks.
 *
 * @experimental
 */
export function discardPeriodicTasks(): void {
  let zoneSpec = _getFakeAsyncZoneSpec();
  let pendingTimers = zoneSpec.pendingPeriodicTimers;
  zoneSpec.pendingPeriodicTimers.length = 0;
}

/**
 * Flush any pending microtasks.
 *
 * @experimental
 */
export function flushMicrotasks(): void {
  _getFakeAsyncZoneSpec().flushMicrotasks();
}