@reactivex/rxjs/src/operator/windowWhen.ts

Reactive Extensions for modern JavaScript

import {Operator} from '../Operator';
import {Subscriber} from '../Subscriber';
import {Observable} from '../Observable';
import {Subject} from '../Subject';
import {Subscription} from '../Subscription';

import {tryCatch} from '../util/tryCatch';
import {errorObject} from '../util/errorObject';

import {OuterSubscriber} from '../OuterSubscriber';
import {InnerSubscriber} from '../InnerSubscriber';
import {subscribeToResult} from '../util/subscribeToResult';

/**
 * Branch out the source Observable values as a nested Observable using a
 * factory function of closing Observables to determine when to start a new
 * window.
 *
 * <span class="informal">It's like {@link bufferWhen}, but emits a nested
 * Observable instead of an array.</span>
 *
 * <img src="./img/windowWhen.png" width="100%">
 *
 * Returns an Observable that emits windows of items it collects from the source
 * Observable. The output Observable emits connected, non-overlapping windows.
 * It emits the current window and opens a new one whenever the Observable
 * produced by the specified `closingSelector` function emits an item. The first
 * window is opened immediately when subscribing to the output Observable.
 *
 * @example <caption>Emit only the first two clicks events in every window of [1-5] random seconds</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var result = clicks
 *   .windowWhen(() => Rx.Observable.interval(1000 + Math.random() * 4000))
 *   .map(win => win.take(2)) // each window has at most 2 emissions
 *   .mergeAll(); // flatten the Observable-of-Observables
 * result.subscribe(x => console.log(x));
 *
 * @see {@link window}
 * @see {@link windowCount}
 * @see {@link windowTime}
 * @see {@link windowToggle}
 * @see {@link bufferWhen}
 *
 * @param {function(): Observable} closingSelector A function that takes no
 * arguments and returns an Observable that signals (on either `next` or
 * `complete`) when to close the previous window and start a new one.
 * @return {Observable<Observable<T>>} An observable of windows, which in turn
 * are Observables.
 * @method windowWhen
 * @owner Observable
 */
export function windowWhen<T>(closingSelector: () => Observable<any>): Observable<Observable<T>> {
  return this.lift(new WindowOperator<T>(closingSelector));
}

export interface WindowWhenSignature<T> {
  (closingSelector: () => Observable<any>): Observable<Observable<T>>;
}

class WindowOperator<T> implements Operator<T, Observable<T>> {
  constructor(private closingSelector: () => Observable<any>) {
  }

  call(subscriber: Subscriber<Observable<T>>, source: any): any {
    return source._subscribe(new WindowSubscriber(subscriber, this.closingSelector));
  }
}

/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
class WindowSubscriber<T> extends OuterSubscriber<T, any> {
  private window: Subject<T>;
  private closingNotification: Subscription;

  constructor(protected destination: Subscriber<Observable<T>>,
              private closingSelector: () => Observable<any>) {
    super(destination);
    this.openWindow();
  }

  notifyNext(outerValue: T, innerValue: any,
             outerIndex: number, innerIndex: number,
             innerSub: InnerSubscriber<T, any>): void {
    this.openWindow(innerSub);
  }

  notifyError(error: any, innerSub: InnerSubscriber<T, any>): void {
    this._error(error);
  }

  notifyComplete(innerSub: InnerSubscriber<T, any>): void {
    this.openWindow(innerSub);
  }

  protected _next(value: T): void {
    this.window.next(value);
  }

  protected _error(err: any): void {
    this.window.error(err);
    this.destination.error(err);
    this.unsubscribeClosingNotification();
  }

  protected _complete(): void {
    this.window.complete();
    this.destination.complete();
    this.unsubscribeClosingNotification();
  }

  private unsubscribeClosingNotification(): void {
    if (this.closingNotification) {
      this.closingNotification.unsubscribe();
    }
  }

  private openWindow(innerSub: InnerSubscriber<T, any> = null): void {
    if (innerSub) {
      this.remove(innerSub);
      innerSub.unsubscribe();
    }

    const prevWindow = this.window;
    if (prevWindow) {
      prevWindow.complete();
    }

    const window = this.window = new Subject<T>();
    this.destination.next(window);

    const closingNotifier = tryCatch(this.closingSelector)();
    if (closingNotifier === errorObject) {
      const err = errorObject.e;
      this.destination.error(err);
      this.window.error(err);
    } else {
      this.add(this.closingNotification = subscribeToResult(this, closingNotifier));
      this.add(window);
    }
  }
}