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import { Subscriber } from '../Subscriber';
import { Observable } from '../Observable';
import { Subject } from '../Subject';
import { ObservableInput, OperatorFunction } from '../types';
import { operate } from '../util/lift';
import { createOperatorSubscriber } from './OperatorSubscriber';
import { innerFrom } from '../observable/innerFrom';
/**
* 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>
*
* 
*
* 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, windowWhen, interval, map, take, mergeAll } from 'rxjs';
*
* const clicks = fromEvent(document, 'click');
* const result = clicks.pipe(
* windowWhen(() => interval(1000 + Math.random() * 4000)),
* map(win => win.pipe(take(2))), // take at most 2 emissions from each window
* 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 A function that returns an Observable of windows, which in turn are
* Observables.
*/
export function windowWhen<T>(closingSelector: () => ObservableInput<any>): OperatorFunction<T, Observable<T>> {
return operate((source, subscriber) => {
let window: Subject<T> | null;
let closingSubscriber: Subscriber<any> | undefined;
/**
* When we get an error, we have to notify both the
* destination subscriber and the window.
*/
const handleError = (err: any) => {
window!.error(err);
subscriber.error(err);
};
/**
* Called every time we need to open a window.
* Recursive, as it will start the closing notifier, which
* inevitably *should* call openWindow -- but may not if
* it is a "never" observable.
*/
const openWindow = () => {
// We need to clean up our closing subscription,
// we only cared about the first next or complete notification.
closingSubscriber?.unsubscribe();
// Close our window before starting a new one.
window?.complete();
// Start the new window.
window = new Subject<T>();
subscriber.next(window.asObservable());
// Get our closing notifier.
let closingNotifier: Observable<any>;
try {
closingNotifier = innerFrom(closingSelector());
} catch (err) {
handleError(err);
return;
}
// Subscribe to the closing notifier, be sure
// to capture the subscriber (aka Subscription)
// so we can clean it up when we close the window
// and open a new one.
closingNotifier.subscribe((closingSubscriber = createOperatorSubscriber(subscriber, openWindow, openWindow, handleError)));
};
// Start the first window.
openWindow();
// Subscribe to the source
source.subscribe(
createOperatorSubscriber(
subscriber,
(value) => window!.next(value),
() => {
// The source completed, close the window and complete.
window!.complete();
subscriber.complete();
},
handleError,
() => {
// Be sure to clean up our closing subscription
// when this tears down.
closingSubscriber?.unsubscribe();
window = null!;
}
)
);
});
}