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import { Subscriber } from '../Subscriber';
import { ObservableInput, OperatorFunction, ObservedValueOf } from '../types';
import { innerFrom } from '../observable/innerFrom';
import { operate } from '../util/lift';
import { createOperatorSubscriber } from './OperatorSubscriber';
/* tslint:disable:max-line-length */
export function switchMap<T, O extends ObservableInput<any>>(
project: (value: T, index: number) => O
): OperatorFunction<T, ObservedValueOf<O>>;
/** @deprecated The `resultSelector` parameter will be removed in v8. Use an inner `map` instead. Details: https://rxjs.dev/deprecations/resultSelector */
export function switchMap<T, O extends ObservableInput<any>>(
project: (value: T, index: number) => O,
resultSelector: undefined
): OperatorFunction<T, ObservedValueOf<O>>;
/** @deprecated The `resultSelector` parameter will be removed in v8. Use an inner `map` instead. Details: https://rxjs.dev/deprecations/resultSelector */
export function switchMap<T, R, O extends ObservableInput<any>>(
project: (value: T, index: number) => O,
resultSelector: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R
): OperatorFunction<T, R>;
/* tslint:enable:max-line-length */
/**
* Projects each source value to an Observable which is merged in the output
* Observable, emitting values only from the most recently projected Observable.
*
* <span class="informal">Maps each value to an Observable, then flattens all of
* these inner Observables using {@link switchAll}.</span>
*
* 
*
* Returns an Observable that emits items based on applying a function that you
* supply to each item emitted by the source Observable, where that function
* returns an (so-called "inner") Observable. Each time it observes one of these
* inner Observables, the output Observable begins emitting the items emitted by
* that inner Observable. When a new inner Observable is emitted, `switchMap`
* stops emitting items from the earlier-emitted inner Observable and begins
* emitting items from the new one. It continues to behave like this for
* subsequent inner Observables.
*
* ## Example
*
* Generate new Observable according to source Observable values
*
* ```ts
* import { of, switchMap } from 'rxjs';
*
* const switched = of(1, 2, 3).pipe(switchMap(x => of(x, x ** 2, x ** 3)));
* switched.subscribe(x => console.log(x));
* // outputs
* // 1
* // 1
* // 1
* // 2
* // 4
* // 8
* // 3
* // 9
* // 27
* ```
*
* Restart an interval Observable on every click event
*
* ```ts
* import { fromEvent, switchMap, interval } from 'rxjs';
*
* const clicks = fromEvent(document, 'click');
* const result = clicks.pipe(switchMap(() => interval(1000)));
* result.subscribe(x => console.log(x));
* ```
*
* @see {@link concatMap}
* @see {@link exhaustMap}
* @see {@link mergeMap}
* @see {@link switchAll}
* @see {@link switchMapTo}
*
* @param project A function that, when applied to an item emitted by the source
* Observable, returns an Observable.
* @return A function that returns an Observable that emits the result of
* applying the projection function (and the optional deprecated
* `resultSelector`) to each item emitted by the source Observable and taking
* only the values from the most recently projected inner Observable.
*/
export function switchMap<T, R, O extends ObservableInput<any>>(
project: (value: T, index: number) => O,
resultSelector?: (outerValue: T, innerValue: ObservedValueOf<O>, outerIndex: number, innerIndex: number) => R
): OperatorFunction<T, ObservedValueOf<O> | R> {
return operate((source, subscriber) => {
let innerSubscriber: Subscriber<ObservedValueOf<O>> | null = null;
let index = 0;
// Whether or not the source subscription has completed
let isComplete = false;
// We only complete the result if the source is complete AND we don't have an active inner subscription.
// This is called both when the source completes and when the inners complete.
const checkComplete = () => isComplete && !innerSubscriber && subscriber.complete();
source.subscribe(
createOperatorSubscriber(
subscriber,
(value) => {
// Cancel the previous inner subscription if there was one
innerSubscriber?.unsubscribe();
let innerIndex = 0;
const outerIndex = index++;
// Start the next inner subscription
innerFrom(project(value, outerIndex)).subscribe(
(innerSubscriber = createOperatorSubscriber(
subscriber,
// When we get a new inner value, next it through. Note that this is
// handling the deprecate result selector here. This is because with this architecture
// it ends up being smaller than using the map operator.
(innerValue) => subscriber.next(resultSelector ? resultSelector(value, innerValue, outerIndex, innerIndex++) : innerValue),
() => {
// The inner has completed. Null out the inner subscriber to
// free up memory and to signal that we have no inner subscription
// currently.
innerSubscriber = null!;
checkComplete();
}
))
);
},
() => {
isComplete = true;
checkComplete();
}
)
);
});
}