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