windowWhen.ts

import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { Observable } from '../Observable';
import { Subject } from '../Subject';
import { Subscription } from '../Subscription';
import { OuterSubscriber } from '../OuterSubscriber';
import { InnerSubscriber } from '../InnerSubscriber';
import { subscribeToResult } from '../util/subscribeToResult';
import { OperatorFunction } from '../types';

/**
 * 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>
 *
 * ![](windowWhen.png)
 *
 * 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
 * Emit only the first two clicks events in every window of [1-5] random seconds
 * ```ts
 * import { fromEvent, interval } from 'rxjs';
 * import { windowWhen, map, mergeAll, take } from 'rxjs/operators';
 *
 * const clicks = fromEvent(document, 'click');
 * const result = clicks.pipe(
 *   windowWhen(() => interval(1000 + Math.random() * 4000)),
 *   map(win => win.pipe(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>): OperatorFunction<T, Observable<T>> {
  return function windowWhenOperatorFunction(source: Observable<T>) {
    return source.lift(new WindowOperator<T>(closingSelector));
  };
}

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);

    let closingNotifier;
    try {
      const { closingSelector } = this;
      closingNotifier = closingSelector();
    } catch (e) {
      this.destination.error(e);
      this.window.error(e);
      return;
    }
    this.add(this.closingNotification = subscribeToResult(this, closingNotifier));
  }
}