/**
 * @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 {Injectable} from '@angular/core';
import {NEVER, Observable, Subject, merge} from 'rxjs';
import {map, switchMap, take} from 'rxjs/operators';

import {ERR_SW_NOT_SUPPORTED, NgswCommChannel, PushEvent} from './low_level';


/**
 * Subscribe and listen to
 * [Web Push Notifications](https://developer.mozilla.org/en-US/docs/Web/API/Push_API/Best_Practices)
 * through Angular Service Worker.
 *
 * @usageNotes
 *
 * You can inject a `SwPush` instance into any component or service
 * as a dependency.
 *
 * <code-example path="service-worker/push/module.ts" region="inject-sw-push" header="app.component.ts"></code-example>
 *
 * To subscribe, call `SwPush.requestSubscription()`, which asks the user for permission.
 * The call returns a `Promise` with a new
 * [`PushSubscription`](https://developer.mozilla.org/en-US/docs/Web/API/PushSubscription)
 * instance.
 *
 * <code-example path="service-worker/push/module.ts" region="subscribe-to-push" header="app.component.ts"></code-example>
 *
 * A request is rejected if the user denies permission, or if the browser
 * blocks or does not support the Push API or ServiceWorkers.
 * Check `SwPush.isEnabled` to confirm status.
 *
 * Invoke Push Notifications by pushing a message with the following payload.
 *
 * ```ts
 * {
 *   "notification": {
 *     "actions": NotificationAction[],
 *     "badge": USVString
 *     "body": DOMString,
 *     "data": any,
 *     "dir": "auto"|"ltr"|"rtl",
 *     "icon": USVString,
 *     "image": USVString,
 *     "lang": DOMString,
 *     "renotify": boolean,
 *     "requireInteraction": boolean,
 *     "silent": boolean,
 *     "tag": DOMString,
 *     "timestamp": DOMTimeStamp,
 *     "title": DOMString,
 *     "vibrate": number[]
 *   }
 * }
 * ```
 *
 * Only `title` is required. See `Notification`
 * [instance properties](https://developer.mozilla.org/en-US/docs/Web/API/Notification#Instance_properties).
 *
 * While the subscription is active, Service Worker listens for
 * [PushEvent](https://developer.mozilla.org/en-US/docs/Web/API/PushEvent)
 * occurrences and creates
 * [Notification](https://developer.mozilla.org/en-US/docs/Web/API/Notification)
 * instances in response.
 *
 * Unsubscribe using `SwPush.unsubscribe()`.
 *
 * An application can subscribe to `SwPush.notificationClicks` observable to be notified when a user
 * clicks on a notification. For example:
 *
 * <code-example path="service-worker/push/module.ts" region="subscribe-to-notification-clicks" header="app.component.ts"></code-example>
 *
 * @see [Push Notifications](https://developers.google.com/web/fundamentals/codelabs/push-notifications/)
 * @see [Angular Push Notifications](https://blog.angular-university.io/angular-push-notifications/)
 * @see [MDN: Push API](https://developer.mozilla.org/en-US/docs/Web/API/Push_API)
 * @see [MDN: Notifications API](https://developer.mozilla.org/en-US/docs/Web/API/Notifications_API)
 * @see [MDN: Web Push API Notifications best practices](https://developer.mozilla.org/en-US/docs/Web/API/Push_API/Best_Practices)
 *
 * @publicApi
 */
@Injectable()
export class SwPush {
  /**
   * Emits the payloads of the received push notification messages.
   */
  readonly messages: Observable<object>;

  /**
   * Emits the payloads of the received push notification messages as well as the action the user
   * interacted with. If no action was used the `action` property contains an empty string `''`.
   *
   * Note that the `notification` property does **not** contain a
   * [Notification][Mozilla Notification] object but rather a
   * [NotificationOptions](https://notifications.spec.whatwg.org/#dictdef-notificationoptions)
   * object that also includes the `title` of the [Notification][Mozilla Notification] object.
   *
   * [Mozilla Notification]: https://developer.mozilla.org/en-US/docs/Web/API/Notification
   */
  readonly notificationClicks: Observable < {
    action: string;
    notification: NotificationOptions&{ title: string }
  }
  > ;

  /**
   * Emits the currently active
   * [PushSubscription](https://developer.mozilla.org/en-US/docs/Web/API/PushSubscription)
   * associated to the Service Worker registration or `null` if there is no subscription.
   */
  readonly subscription: Observable<PushSubscription|null>;

  /**
   * True if the Service Worker is enabled (supported by the browser and enabled via
   * `ServiceWorkerModule`).
   */
  get isEnabled(): boolean { return this.sw.isEnabled; }

  // TODO(issue/24571): remove '!'.
  private pushManager !: Observable<PushManager>;
  private subscriptionChanges = new Subject<PushSubscription|null>();

  constructor(private sw: NgswCommChannel) {
    if (!sw.isEnabled) {
      this.messages = NEVER;
      this.notificationClicks = NEVER;
      this.subscription = NEVER;
      return;
    }

    this.messages = this.sw.eventsOfType<PushEvent>('PUSH').pipe(map(message => message.data));

    this.notificationClicks =
        this.sw.eventsOfType('NOTIFICATION_CLICK').pipe(map((message: any) => message.data));

    this.pushManager = this.sw.registration.pipe(map(registration => registration.pushManager));

    const workerDrivenSubscriptions = this.pushManager.pipe(switchMap(pm => pm.getSubscription()));
    this.subscription = merge(workerDrivenSubscriptions, this.subscriptionChanges);
  }

  /**
   * Subscribes to Web Push Notifications,
   * after requesting and receiving user permission.
   *
   * @param options An object containing the `serverPublicKey` string.
   * @returns A Promise that resolves to the new subscription object.
   */
  requestSubscription(options: {serverPublicKey: string}): Promise<PushSubscription> {
    if (!this.sw.isEnabled) {
      return Promise.reject(new Error(ERR_SW_NOT_SUPPORTED));
    }
    const pushOptions: PushSubscriptionOptionsInit = {userVisibleOnly: true};
    let key = this.decodeBase64(options.serverPublicKey.replace(/_/g, '/').replace(/-/g, '+'));
    let applicationServerKey = new Uint8Array(new ArrayBuffer(key.length));
    for (let i = 0; i < key.length; i++) {
      applicationServerKey[i] = key.charCodeAt(i);
    }
    pushOptions.applicationServerKey = applicationServerKey;

    return this.pushManager.pipe(switchMap(pm => pm.subscribe(pushOptions)), take(1))
        .toPromise()
        .then(sub => {
          this.subscriptionChanges.next(sub);
          return sub;
        });
  }

  /**
   * Unsubscribes from Service Worker push notifications.
   *
   * @returns A Promise that is resolved when the operation succeeds, or is rejected if there is no
   *          active subscription or the unsubscribe operation fails.
   */
  unsubscribe(): Promise<void> {
    if (!this.sw.isEnabled) {
      return Promise.reject(new Error(ERR_SW_NOT_SUPPORTED));
    }

    const doUnsubscribe = (sub: PushSubscription | null) => {
      if (sub === null) {
        throw new Error('Not subscribed to push notifications.');
      }

      return sub.unsubscribe().then(success => {
        if (!success) {
          throw new Error('Unsubscribe failed!');
        }

        this.subscriptionChanges.next(null);
      });
    };

    return this.subscription.pipe(take(1), switchMap(doUnsubscribe)).toPromise();
  }

  private decodeBase64(input: string): string { return atob(input); }
}