import {
  RequestIdleCallback as IdleCallback,
  WindowWithRequestIdleCallback,
} from '@shopify/async';

export default class RequestIdleCallback {
  private isUsingMockIdleCallback = false;
  private isMockingUnsupported = false;
  private queued: {
    [key: string]: IdleCallback;
  } = {};

  private originalRequestIdleCallback: any;
  private originalCancelIdleCallback: any;
  private currentIdleCallback = 0;

  mock() {
    if (this.isUsingMockIdleCallback) {
      throw new Error(
        'requestIdleCallback is already mocked, but you tried to mock it again.',
      );
    }

    this.isUsingMockIdleCallback = true;

    const windowWithIdle: WindowWithRequestIdleCallback = window as any;

    this.originalRequestIdleCallback = windowWithIdle.requestIdleCallback;
    windowWithIdle.requestIdleCallback = this.requestIdleCallback;

    this.originalCancelIdleCallback = windowWithIdle.cancelIdleCallback;
    windowWithIdle.cancelIdleCallback = this.cancelIdleCallback;
  }

  mockAsUnsupported() {
    if (this.isUsingMockIdleCallback) {
      throw new Error(
        'requestIdleCallback is already mocked, but you tried to mock it again.',
      );
    }

    this.isUsingMockIdleCallback = true;
    this.isMockingUnsupported = true;

    const windowWithIdle: WindowWithRequestIdleCallback = window as any;

    this.originalRequestIdleCallback = windowWithIdle.requestIdleCallback;
    delete windowWithIdle.requestIdleCallback;

    this.originalCancelIdleCallback = windowWithIdle.cancelIdleCallback;
    delete windowWithIdle.cancelIdleCallback;
  }

  restore() {
    if (!this.isUsingMockIdleCallback) {
      throw new Error(
        'requestIdleCallback is already real, but you tried to restore it again.',
      );
    }

    if (Object.keys(this.queued).length > 0) {
      // eslint-disable-next-line no-console
      console.warn(
        'You are restoring requestIdleCallback, but some idle callbacks have not been run. You can run requestIdleCallback.cancelIdleCallback() to clear them all and avoid this warning.',
      );

      this.cancelIdleCallbacks();
    }

    this.isUsingMockIdleCallback = false;
    this.isMockingUnsupported = false;

    if (this.originalRequestIdleCallback) {
      (window as any).requestIdleCallback = this.originalRequestIdleCallback;
    } else {
      delete (window as any).requestIdleCallback;
    }

    if (this.originalCancelIdleCallback) {
      (window as any).cancelIdleCallback = this.originalCancelIdleCallback;
    } else {
      delete (window as any).cancelIdleCallback;
    }
  }

  isMocked() {
    return this.isUsingMockIdleCallback;
  }

  runIdleCallbacks(timeRemaining = Infinity, didTimeout = false) {
    this.ensureIdleCallbackIsMock();

    // We need to do it this way so that frames that queue other frames
    // don't get removed
    Object.keys(this.queued).forEach((frame: any) => {
      const callback = this.queued[frame];
      delete this.queued[frame];
      callback({timeRemaining: () => timeRemaining, didTimeout});
    });
  }

  cancelIdleCallbacks() {
    this.ensureIdleCallbackIsMock();

    for (const id of Object.keys(this.queued)) {
      this.cancelIdleCallback(id);
    }
  }

  private requestIdleCallback = (
    callback: IdleCallback,
  ): ReturnType<WindowWithRequestIdleCallback['requestIdleCallback']> => {
    this.currentIdleCallback += 1;
    this.queued[this.currentIdleCallback] = callback;
    return this.currentIdleCallback;
  };

  private cancelIdleCallback = (
    callback: ReturnType<WindowWithRequestIdleCallback['requestIdleCallback']>,
  ) => {
    delete this.queued[callback];
  };

  private ensureIdleCallbackIsMock() {
    if (!this.isUsingMockIdleCallback) {
      throw new Error(
        'You must call requestIdleCallback.mock() before interacting with the mock request- or cancel- IdleCallback methods.',
      );
    }

    if (this.isMockingUnsupported) {
      throw new Error(
        'You have mocked requestIdleCallback as unsupported. Call requestIdleCallback.restore(), then requestIdleCallback.mock() if you want to simulate idle callbacks.',
      );
    }
  }
}