import { MonoTypeOperatorFunction } from '../types';
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import { EMPTY } from '../observable/empty';
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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 only the first `count` values emitted by the source Observable.
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*
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* <span class="informal">Takes the first `count` values from the source, then
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* completes.</span>
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*
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* 
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*
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* `take` returns an Observable that emits only the first `count` values emitted
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* by the source Observable. If the source emits fewer than `count` values then
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* all of its values are emitted. After that, it completes, regardless if the
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* source completes.
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*
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* ## Example
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*
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* Take the first 5 seconds of an infinite 1-second interval Observable
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*
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* ```ts
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* import { interval, take } from 'rxjs';
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*
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* const intervalCount = interval(1000);
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* const takeFive = intervalCount.pipe(take(5));
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* takeFive.subscribe(x => console.log(x));
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*
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* // Logs:
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* // 0
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* // 1
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* // 2
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* // 3
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* // 4
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* ```
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*
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* @see {@link takeLast}
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* @see {@link takeUntil}
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* @see {@link takeWhile}
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* @see {@link skip}
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*
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* @param count The maximum number of `next` values to emit.
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* @return A function that returns an Observable that emits only the first
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* `count` values emitted by the source Observable, or all of the values from
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* the source if the source emits fewer than `count` values.
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*/
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export function take<T>(count: number): MonoTypeOperatorFunction<T> {
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return count <= 0
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? // If we are taking no values, that's empty.
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() => EMPTY
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: operate((source, subscriber) => {
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let seen = 0;
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source.subscribe(
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createOperatorSubscriber(subscriber, (value) => {
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// Increment the number of values we have seen,
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// then check it against the allowed count to see
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// if we are still letting values through.
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if (++seen <= count) {
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subscriber.next(value);
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// If we have met or passed our allowed count,
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// we need to complete. We have to do <= here,
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// because re-entrant code will increment `seen` twice.
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if (count <= seen) {
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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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}
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