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import { Subscriber } from '../Subscriber';
import { MonoTypeOperatorFunction, ObservableInput } from '../types';
import { operate } from '../util/lift';
import { noop } from '../util/noop';
import { createOperatorSubscriber } from './OperatorSubscriber';
import { innerFrom } from '../observable/innerFrom';
/**
* Emits a notification from the source Observable only after a particular time span
* determined by another Observable has passed without another source emission.
*
* <span class="informal">It's like {@link debounceTime}, but the time span of
* emission silence is determined by a second Observable.</span>
*
* 
*
* `debounce` delays notifications emitted by the source Observable, but drops previous
* pending delayed emissions if a new notification arrives on the source Observable.
* This operator keeps track of the most recent notification from the source
* Observable, and spawns a duration Observable by calling the
* `durationSelector` function. The notification is emitted only when the duration
* Observable emits a next notification, and if no other notification was emitted on
* the source Observable since the duration Observable was spawned. If a new
* notification appears before the duration Observable emits, the previous notification will
* not be emitted and a new duration is scheduled from `durationSelector` is scheduled.
* If the completing event happens during the scheduled duration the last cached notification
* is emitted before the completion event is forwarded to the output observable.
* If the error event happens during the scheduled duration or after it only the error event is
* forwarded to the output observable. The cache notification is not emitted in this case.
*
* Like {@link debounceTime}, this is a rate-limiting operator, and also a
* delay-like operator since output emissions do not necessarily occur at the
* same time as they did on the source Observable.
*
* ## Example
*
* Emit the most recent click after a burst of clicks
*
* ```ts
* import { fromEvent, scan, debounce, interval } from 'rxjs';
*
* const clicks = fromEvent(document, 'click');
* const result = clicks.pipe(
* scan(i => ++i, 1),
* debounce(i => interval(200 * i))
* );
* result.subscribe(x => console.log(x));
* ```
*
* @see {@link audit}
* @see {@link auditTime}
* @see {@link debounceTime}
* @see {@link delay}
* @see {@link sample}
* @see {@link sampleTime}
* @see {@link throttle}
* @see {@link throttleTime}
*
* @param durationSelector A function
* that receives a value from the source Observable, for computing the timeout
* duration for each source value, returned as an Observable or a Promise.
* @return A function that returns an Observable that delays the emissions of
* the source Observable by the specified duration Observable returned by
* `durationSelector`, and may drop some values if they occur too frequently.
*/
export function debounce<T>(durationSelector: (value: T) => ObservableInput<any>): MonoTypeOperatorFunction<T> {
return operate((source, subscriber) => {
let hasValue = false;
let lastValue: T | null = null;
// The subscriber/subscription for the current debounce, if there is one.
let durationSubscriber: Subscriber<any> | null = null;
const emit = () => {
// Unsubscribe any current debounce subscription we have,
// we only cared about the first notification from it, and we
// want to clean that subscription up as soon as possible.
durationSubscriber?.unsubscribe();
durationSubscriber = null;
if (hasValue) {
// We have a value! Free up memory first, then emit the value.
hasValue = false;
const value = lastValue!;
lastValue = null;
subscriber.next(value);
}
};
source.subscribe(
createOperatorSubscriber(
subscriber,
(value: T) => {
// Cancel any pending debounce duration. We don't
// need to null it out here yet tho, because we're just going
// to create another one in a few lines.
durationSubscriber?.unsubscribe();
hasValue = true;
lastValue = value;
// Capture our duration subscriber, so we can unsubscribe it when we're notified
// and we're going to emit the value.
durationSubscriber = createOperatorSubscriber(subscriber, emit, noop);
// Subscribe to the duration.
innerFrom(durationSelector(value)).subscribe(durationSubscriber);
},
() => {
// Source completed.
// Emit any pending debounced values then complete
emit();
subscriber.complete();
},
// Pass all errors through to consumer
undefined,
() => {
// Finalization.
lastValue = durationSubscriber = null;
}
)
);
});
}