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