import { Subscriber } from '../Subscriber';
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import { ObservableInput, OperatorFunction } from '../types';
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import { operate } from '../util/lift';
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import { noop } from '../util/noop';
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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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* Buffers the source Observable values, using a factory function of closing
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* Observables to determine when to close, emit, and reset the buffer.
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*
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* <span class="informal">Collects values from the past as an array. When it
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* starts collecting values, it calls a function that returns an Observable that
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* tells when to close the buffer and restart collecting.</span>
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*
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* 
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*
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* Opens a buffer immediately, then closes the buffer when the observable
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* returned by calling `closingSelector` function emits a value. When it closes
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* the buffer, it immediately opens a new buffer and repeats the process.
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*
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* ## Example
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*
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* Emit an array of the last clicks every [1-5] random seconds
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*
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* ```ts
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* import { fromEvent, bufferWhen, interval } from 'rxjs';
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*
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* const clicks = fromEvent(document, 'click');
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* const buffered = clicks.pipe(
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* bufferWhen(() => interval(1000 + Math.random() * 4000))
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* );
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* buffered.subscribe(x => console.log(x));
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* ```
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*
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* @see {@link buffer}
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* @see {@link bufferCount}
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* @see {@link bufferTime}
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* @see {@link bufferToggle}
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* @see {@link windowWhen}
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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 buffer closure.
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* @return A function that returns an Observable of arrays of buffered values.
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*/
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export function bufferWhen<T>(closingSelector: () => ObservableInput<any>): OperatorFunction<T, T[]> {
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return operate((source, subscriber) => {
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// The buffer we keep and emit.
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let buffer: T[] | null = null;
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// A reference to the subscriber used to subscribe to
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// the closing notifier. We need to hold this so we can
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// end the subscription after the first notification.
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let closingSubscriber: Subscriber<T> | null = null;
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// Ends the previous closing notifier subscription, so it
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// terminates after the first emission, then emits
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// the current buffer if there is one, starts a new buffer, and starts a
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// new closing notifier.
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const openBuffer = () => {
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// Make sure to finalize the closing subscription, we only cared
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// about one notification.
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closingSubscriber?.unsubscribe();
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// emit the buffer if we have one, and start a new buffer.
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const b = buffer;
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buffer = [];
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b && subscriber.next(b);
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// Get a new closing notifier and subscribe to it.
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innerFrom(closingSelector()).subscribe((closingSubscriber = createOperatorSubscriber(subscriber, openBuffer, noop)));
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};
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// Start the first buffer.
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openBuffer();
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// Subscribe to our source.
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source.subscribe(
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createOperatorSubscriber(
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subscriber,
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// Add every new value to the current buffer.
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(value) => buffer?.push(value),
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// When we complete, emit the buffer if we have one,
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// then complete the result.
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() => {
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buffer && subscriber.next(buffer);
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subscriber.complete();
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},
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// Pass all errors through to consumer.
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undefined,
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// Release memory on finalization
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() => (buffer = closingSubscriber = null!)
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)
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);
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});
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}
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