import { Subscription } from '../Subscription';
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import { MonoTypeOperatorFunction, ObservableInput } from '../types';
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import { operate } from '../util/lift';
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import { createOperatorSubscriber } from './OperatorSubscriber';
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import { innerFrom } from '../observable/innerFrom';
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export interface ThrottleConfig {
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leading?: boolean;
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trailing?: boolean;
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}
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export const defaultThrottleConfig: ThrottleConfig = {
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leading: true,
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trailing: false,
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};
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/**
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* Emits a value from the source Observable, then ignores subsequent source
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* values for a duration determined by another Observable, then repeats this
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* process.
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*
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* <span class="informal">It's like {@link throttleTime}, but the silencing
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* duration is determined by a second Observable.</span>
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*
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* 
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*
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* `throttle` emits the source Observable values on the output Observable
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* when its internal timer is disabled, and ignores source values when the timer
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* is enabled. Initially, the timer is disabled. As soon as the first source
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* value arrives, it is forwarded to the output Observable, and then the timer
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* is enabled by calling the `durationSelector` function with the source value,
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* which returns the "duration" Observable. When the duration Observable emits a
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* value, the timer is disabled, and this process repeats for the
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* next source value.
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*
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* ## Example
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*
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* Emit clicks at a rate of at most one click per second
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*
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* ```ts
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* import { fromEvent, throttle, interval } from 'rxjs';
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*
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* const clicks = fromEvent(document, 'click');
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* const result = clicks.pipe(throttle(() => interval(1000)));
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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 debounce}
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* @see {@link delayWhen}
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* @see {@link sample}
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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 silencing
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* duration for each source value, returned as an Observable or a Promise.
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* @param config a configuration object to define `leading` and `trailing` behavior. Defaults
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* to `{ leading: true, trailing: false }`.
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* @return A function that returns an Observable that performs the throttle
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* operation to limit the rate of emissions from the source.
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*/
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export function throttle<T>(
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durationSelector: (value: T) => ObservableInput<any>,
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config: ThrottleConfig = defaultThrottleConfig
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): MonoTypeOperatorFunction<T> {
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return operate((source, subscriber) => {
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const { leading, trailing } = config;
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let hasValue = false;
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let sendValue: T | null = null;
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let throttled: Subscription | null = null;
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let isComplete = false;
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const endThrottling = () => {
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throttled?.unsubscribe();
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throttled = null;
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if (trailing) {
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send();
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isComplete && subscriber.complete();
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}
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};
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const cleanupThrottling = () => {
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throttled = null;
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isComplete && subscriber.complete();
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};
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const startThrottle = (value: T) =>
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(throttled = innerFrom(durationSelector(value)).subscribe(createOperatorSubscriber(subscriber, endThrottling, cleanupThrottling)));
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const send = () => {
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if (hasValue) {
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// Ensure we clear out our value and hasValue flag
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// before we emit, otherwise reentrant code can cause
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// issues here.
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hasValue = false;
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const value = sendValue!;
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sendValue = null;
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// Emit the value.
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subscriber.next(value);
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!isComplete && startThrottle(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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// Regarding the presence of throttled.closed in the following
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// conditions, if a synchronous duration selector is specified - weird,
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// but legal - an already-closed subscription will be assigned to
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// throttled, so the subscription's closed property needs to be checked,
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// too.
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(value) => {
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hasValue = true;
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sendValue = value;
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!(throttled && !throttled.closed) && (leading ? send() : startThrottle(value));
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},
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() => {
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isComplete = true;
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!(trailing && hasValue && throttled && !throttled.closed) && subscriber.complete();
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}
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)
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);
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});
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}
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