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import { Observable } from '../Observable';
import { Operator } from '../Operator';
import { Observer, OperatorFunction } from '../types';
import { Subscriber } from '../Subscriber';
/**
* Counts the number of emissions on the source and emits that number when the
* source completes.
*
* <span class="informal">Tells how many values were emitted, when the source
* completes.</span>
*
* 
*
* `count` transforms an Observable that emits values into an Observable that
* emits a single value that represents the number of values emitted by the
* source Observable. If the source Observable terminates with an error, `count`
* will pass this error notification along without emitting a value first. If
* the source Observable does not terminate at all, `count` will neither emit
* a value nor terminate. This operator takes an optional `predicate` function
* as argument, in which case the output emission will represent the number of
* source values that matched `true` with the `predicate`.
*
* ## Examples
*
* Counts how many seconds have passed before the first click happened
* ```javascript
* import { fromEvent, interval } from 'rxjs';
* import { count, takeUntil } from 'rxjs/operators';
*
* const seconds = interval(1000);
* const clicks = fromEvent(document, 'click');
* const secondsBeforeClick = seconds.pipe(takeUntil(clicks));
* const result = secondsBeforeClick.pipe(count());
* result.subscribe(x => console.log(x));
* ```
*
* Counts how many odd numbers are there between 1 and 7
* ```javascript
* import { range } from 'rxjs';
* import { count } from 'rxjs/operators';
*
* const numbers = range(1, 7);
* const result = numbers.pipe(count(i => i % 2 === 1));
* result.subscribe(x => console.log(x));
* // Results in:
* // 4
* ```
*
* @see {@link max}
* @see {@link min}
* @see {@link reduce}
*
* @param {function(value: T, i: number, source: Observable<T>): boolean} [predicate] A
* boolean function to select what values are to be counted. It is provided with
* arguments of:
* - `value`: the value from the source Observable.
* - `index`: the (zero-based) "index" of the value from the source Observable.
* - `source`: the source Observable instance itself.
* @return {Observable} An Observable of one number that represents the count as
* described above.
* @method count
* @owner Observable
*/
export function count<T>(predicate?: (value: T, index: number, source: Observable<T>) => boolean): OperatorFunction<T, number> {
return (source: Observable<T>) => source.lift(new CountOperator(predicate, source));
}
class CountOperator<T> implements Operator<T, number> {
constructor(private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
private source?: Observable<T>) {
}
call(subscriber: Subscriber<number>, source: any): any {
return source.subscribe(new CountSubscriber(subscriber, this.predicate, this.source));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class CountSubscriber<T> extends Subscriber<T> {
private count: number = 0;
private index: number = 0;
constructor(destination: Observer<number>,
private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
private source?: Observable<T>) {
super(destination);
}
protected _next(value: T): void {
if (this.predicate) {
this._tryPredicate(value);
} else {
this.count++;
}
}
private _tryPredicate(value: T) {
let result: any;
try {
result = this.predicate(value, this.index++, this.source);
} catch (err) {
this.destination.error(err);
return;
}
if (result) {
this.count++;
}
}
protected _complete(): void {
this.destination.next(this.count);
this.destination.complete();
}
}
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