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import { Subscriber } from '../Subscriber';
import { ObservableInput, OperatorFunction } from '../types';
import { operate } from '../util/lift';
import { noop } from '../util/noop';
import { createOperatorSubscriber } from './OperatorSubscriber';
import { innerFrom } from '../observable/innerFrom';
/**
* Buffers the source Observable values, using a factory function of closing
* Observables to determine when to close, emit, and reset the buffer.
*
* <span class="informal">Collects values from the past as an array. When it
* starts collecting values, it calls a function that returns an Observable that
* tells when to close the buffer and restart collecting.</span>
*
* 
*
* Opens a buffer immediately, then closes the buffer when the observable
* returned by calling `closingSelector` function emits a value. When it closes
* the buffer, it immediately opens a new buffer and repeats the process.
*
* ## Example
*
* Emit an array of the last clicks every [1-5] random seconds
*
* ```ts
* import { fromEvent, bufferWhen, interval } from 'rxjs';
*
* const clicks = fromEvent(document, 'click');
* const buffered = clicks.pipe(
* bufferWhen(() => interval(1000 + Math.random() * 4000))
* );
* buffered.subscribe(x => console.log(x));
* ```
*
* @see {@link buffer}
* @see {@link bufferCount}
* @see {@link bufferTime}
* @see {@link bufferToggle}
* @see {@link windowWhen}
*
* @param {function(): Observable} closingSelector A function that takes no
* arguments and returns an Observable that signals buffer closure.
* @return A function that returns an Observable of arrays of buffered values.
*/
export function bufferWhen<T>(closingSelector: () => ObservableInput<any>): OperatorFunction<T, T[]> {
return operate((source, subscriber) => {
// The buffer we keep and emit.
let buffer: T[] | null = null;
// A reference to the subscriber used to subscribe to
// the closing notifier. We need to hold this so we can
// end the subscription after the first notification.
let closingSubscriber: Subscriber<T> | null = null;
// Ends the previous closing notifier subscription, so it
// terminates after the first emission, then emits
// the current buffer if there is one, starts a new buffer, and starts a
// new closing notifier.
const openBuffer = () => {
// Make sure to finalize the closing subscription, we only cared
// about one notification.
closingSubscriber?.unsubscribe();
// emit the buffer if we have one, and start a new buffer.
const b = buffer;
buffer = [];
b && subscriber.next(b);
// Get a new closing notifier and subscribe to it.
innerFrom(closingSelector()).subscribe((closingSubscriber = createOperatorSubscriber(subscriber, openBuffer, noop)));
};
// Start the first buffer.
openBuffer();
// Subscribe to our source.
source.subscribe(
createOperatorSubscriber(
subscriber,
// Add every new value to the current buffer.
(value) => buffer?.push(value),
// When we complete, emit the buffer if we have one,
// then complete the result.
() => {
buffer && subscriber.next(buffer);
subscriber.complete();
},
// Pass all errors through to consumer.
undefined,
// Release memory on finalization
() => (buffer = closingSubscriber = null!)
)
);
});
}