import { Subscriber } from '../Subscriber';
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import { Observable } from '../Observable';
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import { Subject } from '../Subject';
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import { ObservableInput, OperatorFunction } from '../types';
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import { operate } from '../util/lift';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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import { innerFrom } from '../observable/innerFrom';
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/**
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* Branch out the source Observable values as a nested Observable using a
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* factory function of closing Observables to determine when to start a new
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* window.
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*
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* <span class="informal">It's like {@link bufferWhen}, but emits a nested
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* Observable instead of an array.</span>
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*
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* 
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*
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* Returns an Observable that emits windows of items it collects from the source
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* Observable. The output Observable emits connected, non-overlapping windows.
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* It emits the current window and opens a new one whenever the Observable
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* produced by the specified `closingSelector` function emits an item. The first
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* window is opened immediately when subscribing to the output Observable.
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*
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* ## Example
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*
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* Emit only the first two clicks events in every window of [1-5] random seconds
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*
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* ```ts
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* import { fromEvent, windowWhen, interval, map, take, mergeAll } from 'rxjs';
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*
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* const clicks = fromEvent(document, 'click');
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* const result = clicks.pipe(
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* windowWhen(() => interval(1000 + Math.random() * 4000)),
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* map(win => win.pipe(take(2))), // take at most 2 emissions from each window
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* mergeAll() // flatten the Observable-of-Observables
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* );
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* result.subscribe(x => console.log(x));
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* ```
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*
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* @see {@link window}
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* @see {@link windowCount}
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* @see {@link windowTime}
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* @see {@link windowToggle}
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* @see {@link bufferWhen}
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*
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* @param {function(): Observable} closingSelector A function that takes no
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* arguments and returns an Observable that signals (on either `next` or
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* `complete`) when to close the previous window and start a new one.
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* @return A function that returns an Observable of windows, which in turn are
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* Observables.
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*/
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export function windowWhen<T>(closingSelector: () => ObservableInput<any>): OperatorFunction<T, Observable<T>> {
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return operate((source, subscriber) => {
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let window: Subject<T> | null;
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let closingSubscriber: Subscriber<any> | undefined;
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/**
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* When we get an error, we have to notify both the
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* destination subscriber and the window.
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*/
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const handleError = (err: any) => {
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window!.error(err);
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subscriber.error(err);
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};
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/**
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* Called every time we need to open a window.
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* Recursive, as it will start the closing notifier, which
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* inevitably *should* call openWindow -- but may not if
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* it is a "never" observable.
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*/
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const openWindow = () => {
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// We need to clean up our closing subscription,
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// we only cared about the first next or complete notification.
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closingSubscriber?.unsubscribe();
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// Close our window before starting a new one.
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window?.complete();
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// Start the new window.
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window = new Subject<T>();
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subscriber.next(window.asObservable());
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// Get our closing notifier.
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let closingNotifier: Observable<any>;
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try {
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closingNotifier = innerFrom(closingSelector());
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} catch (err) {
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handleError(err);
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return;
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}
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// Subscribe to the closing notifier, be sure
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// to capture the subscriber (aka Subscription)
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// so we can clean it up when we close the window
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// and open a new one.
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closingNotifier.subscribe((closingSubscriber = createOperatorSubscriber(subscriber, openWindow, openWindow, handleError)));
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};
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// Start the first window.
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openWindow();
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// Subscribe to the source
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source.subscribe(
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createOperatorSubscriber(
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subscriber,
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(value) => window!.next(value),
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() => {
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// The source completed, close the window and complete.
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window!.complete();
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subscriber.complete();
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},
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handleError,
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() => {
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// Be sure to clean up our closing subscription
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// when this tears down.
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closingSubscriber?.unsubscribe();
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window = null!;
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}
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)
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);
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});
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}
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