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import { Observable } from '../Observable';
import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
/* tslint:disable:max-line-length */
export function reduce<T>(this: Observable<T>, accumulator: (acc: T, value: T, index: number) => T, seed?: T): Observable<T>;
export function reduce<T>(this: Observable<T>, accumulator: (acc: T[], value: T, index: number) => T[], seed: T[]): Observable<T[]>;
export function reduce<T, R>(this: Observable<T>, accumulator: (acc: R, value: T, index: number) => R, seed: R): Observable<R>;
/* tslint:enable:max-line-length */
/**
* Applies an accumulator function over the source Observable, and returns the
* accumulated result when the source completes, given an optional seed value.
*
* <span class="informal">Combines together all values emitted on the source,
* using an accumulator function that knows how to join a new source value into
* the accumulation from the past.</span>
*
* <img src="./img/reduce.png" width="100%">
*
* Like
* [Array.prototype.reduce()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce),
* `reduce` applies an `accumulator` function against an accumulation and each
* value of the source Observable (from the past) to reduce it to a single
* value, emitted on the output Observable. Note that `reduce` will only emit
* one value, only when the source Observable completes. It is equivalent to
* applying operator {@link scan} followed by operator {@link last}.
*
* Returns an Observable that applies a specified `accumulator` function to each
* item emitted by the source Observable. If a `seed` value is specified, then
* that value will be used as the initial value for the accumulator. If no seed
* value is specified, the first item of the source is used as the seed.
*
* @example <caption>Count the number of click events that happened in 5 seconds</caption>
* var clicksInFiveSeconds = Rx.Observable.fromEvent(document, 'click')
* .takeUntil(Rx.Observable.interval(5000));
* var ones = clicksInFiveSeconds.mapTo(1);
* var seed = 0;
* var count = ones.reduce((acc, one) => acc + one, seed);
* count.subscribe(x => console.log(x));
*
* @see {@link count}
* @see {@link expand}
* @see {@link mergeScan}
* @see {@link scan}
*
* @param {function(acc: R, value: T, index: number): R} accumulator The accumulator function
* called on each source value.
* @param {R} [seed] The initial accumulation value.
* @return {Observable<R>} An Observable that emits a single value that is the
* result of accumulating the values emitted by the source Observable.
* @method reduce
* @owner Observable
*/
export function reduce<T, R>(this: Observable<T>, accumulator: (acc: R, value: T, index?: number) => R, seed?: R): Observable<R> {
let hasSeed = false;
// providing a seed of `undefined` *should* be valid and trigger
// hasSeed! so don't use `seed !== undefined` checks!
// For this reason, we have to check it here at the original call site
// otherwise inside Operator/Subscriber we won't know if `undefined`
// means they didn't provide anything or if they literally provided `undefined`
if (arguments.length >= 2) {
hasSeed = true;
}
return this.lift(new ReduceOperator(accumulator, seed, hasSeed));
}
export class ReduceOperator<T, R> implements Operator<T, R> {
constructor(private accumulator: (acc: R, value: T, index?: number) => R, private seed?: R, private hasSeed: boolean = false) {}
call(subscriber: Subscriber<R>, source: any): any {
return source.subscribe(new ReduceSubscriber(subscriber, this.accumulator, this.seed, this.hasSeed));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
export class ReduceSubscriber<T, R> extends Subscriber<T> {
private index: number = 0;
private acc: T | R;
private hasValue: boolean = false;
constructor(destination: Subscriber<R>,
private accumulator: (acc: R, value: T, index?: number) => R,
seed: R,
private hasSeed: boolean) {
super(destination);
this.acc = seed;
if (!this.hasSeed) {
this.index++;
}
}
protected _next(value: T) {
if (this.hasValue || (this.hasValue = this.hasSeed)) {
this._tryReduce(value);
} else {
this.acc = value;
this.hasValue = true;
}
}
private _tryReduce(value: T) {
let result: any;
try {
result = this.accumulator(<R>this.acc, value, this.index++);
} catch (err) {
this.destination.error(err);
return;
}
this.acc = result;
}
protected _complete() {
if (this.hasValue || this.hasSeed) {
this.destination.next(this.acc);
}
this.destination.complete();
}
}