/**
 * @license
 * Copyright Google LLC 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 {IdleScheduler} from '../src/idle';
import {SwTestHarness, SwTestHarnessBuilder} from '../testing/scope';

(function() {
// Skip environments that don't support the minimum APIs needed to run the SW tests.
if (!SwTestHarness.envIsSupported()) {
  return;
}

describe('IdleScheduler', () => {
  let scope: SwTestHarness;
  let idle: IdleScheduler;

  beforeEach(() => {
    scope = new SwTestHarnessBuilder().build();
    idle = new IdleScheduler(scope, 1000, 3000, {
      log: (v, context) => console.error(v, context),
    });
  });

  // Validate that a single idle task executes when trigger()
  // is called and the idle timeout passes.
  it('executes scheduled work on time', async () => {
    // Set up a single idle task to set the completed flag to true when it runs.
    let completed: boolean = false;
    idle.schedule('work', async () => {
      completed = true;
    });

    // Simply scheduling the task should not cause it to execute.
    expect(completed).toEqual(false);

    // Trigger the idle mechanism. This returns a Promise that should resolve
    // once the idle timeout has passed.
    const trigger = idle.trigger();

    // Advance the clock beyond the idle timeout, causing the idle tasks to run.
    scope.advance(1100);

    // It should now be possible to wait for the trigger, and for the idle queue
    // to be empty.
    await trigger;
    await idle.empty;

    // The task should now have run.
    expect(completed).toEqual(true);
  });

  it('waits for multiple tasks to complete serially', async () => {
    // Schedule several tasks that will increase a counter according to its
    // current value. If these tasks execute in parallel, the writes to the counter
    // will race, and the test will fail.
    let counter: number = 2;
    idle.schedule('double counter', async () => {
      let local = counter;
      await Promise.resolve();
      local *= 2;
      await Promise.resolve();
      counter = local * 2;
    });
    idle.schedule('triple counter', async () => {
      // If this expect fails, it comes out of the 'await trigger' below.
      expect(counter).toEqual(8);

      // Multiply the counter by 3 twice.
      let local = counter;
      await Promise.resolve();
      local *= 3;
      await Promise.resolve();
      counter = local * 3;
    });

    // Trigger the idle mechanism once.
    const trigger = idle.trigger();

    // Advance the clock beyond the idle timeout, causing the idle tasks to run, and
    // wait for them to complete.
    scope.advance(1100);
    await trigger;
    await idle.empty;

    // Assert that both tasks executed in the correct serial sequence by validating
    // that the counter reached the correct value.
    expect(counter).toEqual(2 * 2 * 2 * 3 * 3);
  });

  // Validate that a single idle task does not execute until trigger() has been called
  // and sufficient time passes without it being called again.
  it('does not execute work until timeout passes with no triggers', async () => {
    // Set up a single idle task to set the completed flag to true when it runs.
    let completed: boolean = false;
    idle.schedule('work', async () => {
      completed = true;
    });

    // Trigger the queue once. This trigger will start a timer for the idle timeout,
    // but another trigger() will be called before that timeout passes.
    const firstTrigger = idle.trigger();

    // Advance the clock a little, but not enough to actually cause tasks to execute.
    scope.advance(500);

    // Assert that the task has not yet run.
    expect(completed).toEqual(false);

    // Next, trigger the queue again.
    const secondTrigger = idle.trigger();

    // Advance the clock beyond the timeout for the first trigger, but not the second.
    // This should cause the first trigger to resolve, but without running the task.
    scope.advance(600);
    await firstTrigger;
    expect(completed).toEqual(false);

    // Schedule a third trigger. This is the one that will eventually resolve the task.
    const thirdTrigger = idle.trigger();

    // Again, advance beyond the second trigger and verify it didn't resolve the task.
    scope.advance(500);
    await secondTrigger;
    expect(completed).toEqual(false);

    // Finally, advance beyond the third trigger, which should cause the task to be
    // executed finally.
    scope.advance(600);
    await thirdTrigger;
    await idle.empty;

    // The task should have executed.
    expect(completed).toEqual(true);
  });

  it('executes tasks after max delay even with newer triggers', async () => {
    // Set up a single idle task to set the completed flag to true when it runs.
    let completed: boolean = false;
    idle.schedule('work', async () => {
      completed = true;
    });

    // Trigger the queue once. This trigger will start a timer for the idle timeout,
    // but another `trigger()` will be called before that timeout passes.
    const firstTrigger = idle.trigger();

    // Advance the clock a little, but not enough to actually cause tasks to execute.
    scope.advance(999);
    expect(completed).toBe(false);

    // Next, trigger the queue again.
    const secondTrigger = idle.trigger();

    // Advance the clock beyond the timeout for the first trigger, but not the second.
    // This should cause the first trigger to resolve, but without running the task.
    scope.advance(999);
    await firstTrigger;
    expect(completed).toBe(false);

    // Next, trigger the queue again.
    const thirdTrigger = idle.trigger();

    // Advance the clock beyond the timeout for the second trigger, but not the third.
    // This should cause the second trigger to resolve, but without running the task.
    scope.advance(999);
    await secondTrigger;
    expect(completed).toBe(false);

    // Next, trigger the queue again.
    const forthTrigger = idle.trigger();

    // Finally, advance the clock beyond `maxDelay` (3000) from the first trigger, but not beyond
    // the timeout for the forth. This should cause the task to be executed nontheless.
    scope.advance(3);
    await Promise.all([thirdTrigger, forthTrigger]);

    // The task should have executed.
    expect(completed).toBe(true);
  });
});
})();