import { asyncScheduler } from '../scheduler/async';
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import { Subscription } from '../Subscription';
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import { MonoTypeOperatorFunction, SchedulerAction, SchedulerLike } from '../types';
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import { operate } from '../util/lift';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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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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* has passed without another source emission.
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*
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* <span class="informal">It's like {@link delay}, but passes only the most
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* recent notification from each burst of emissions.</span>
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*
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* 
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*
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* `debounceTime` delays notifications emitted by the source Observable, but drops
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* previous pending delayed emissions if a new notification arrives on the source
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* Observable. This operator keeps track of the most recent notification from the
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* source Observable, and emits that only when `dueTime` has passed
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* without any other notification appearing on the source Observable. If a new value
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* appears before `dueTime` silence occurs, the previous notification will be dropped
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* and will not be emitted and a new `dueTime` is scheduled.
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* If the completing event happens during `dueTime` 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 `dueTime` 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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* This is a rate-limiting operator, because it is impossible for more than one
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* notification to be emitted in any time window of duration `dueTime`, but it is also
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* a delay-like operator since output emissions do not occur at the same time as
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* they did on the source Observable. Optionally takes a {@link SchedulerLike} for
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* managing timers.
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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, debounceTime } from 'rxjs';
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*
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* const clicks = fromEvent(document, 'click');
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* const result = clicks.pipe(debounceTime(1000));
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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 debounce}
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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 {number} dueTime The timeout duration in milliseconds (or the time
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* unit determined internally by the optional `scheduler`) for the window of
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* time required to wait for emission silence before emitting the most recent
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* source value.
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* @param {SchedulerLike} [scheduler=async] The {@link SchedulerLike} to use for
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* managing the timers that handle the timeout for each value.
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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 `dueTime`, and may drop some values
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* if they occur too frequently.
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*/
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export function debounceTime<T>(dueTime: number, scheduler: SchedulerLike = asyncScheduler): MonoTypeOperatorFunction<T> {
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return operate((source, subscriber) => {
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let activeTask: Subscription | null = null;
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let lastValue: T | null = null;
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let lastTime: number | null = null;
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const emit = () => {
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if (activeTask) {
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// We have a value! Free up memory first, then emit the value.
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activeTask.unsubscribe();
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activeTask = null;
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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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function emitWhenIdle(this: SchedulerAction<unknown>) {
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// This is called `dueTime` after the first value
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// but we might have received new values during this window!
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const targetTime = lastTime! + dueTime;
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const now = scheduler.now();
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if (now < targetTime) {
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// On that case, re-schedule to the new target
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activeTask = this.schedule(undefined, targetTime - now);
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subscriber.add(activeTask);
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return;
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}
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emit();
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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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lastValue = value;
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lastTime = scheduler.now();
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// Only set up a task if it's not already up
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if (!activeTask) {
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activeTask = scheduler.schedule(emitWhenIdle, dueTime);
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subscriber.add(activeTask);
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}
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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 = activeTask = 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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