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import { Operator } from '../Operator';
import { Observable } from '../Observable';
import { Subscriber } from '../Subscriber';
import { OperatorFunction, MonoTypeOperatorFunction } from '../types';
/* tslint:disable:max-line-length */
export function scan<T>(accumulator: (acc: T, value: T, index: number) => T, seed?: T): MonoTypeOperatorFunction<T>;
export function scan<T>(accumulator: (acc: T[], value: T, index: number) => T[], seed?: T[]): OperatorFunction<T, T[]>;
export function scan<T, R>(accumulator: (acc: R, value: T, index: number) => R, seed?: R): OperatorFunction<T, R>;
/* tslint:enable:max-line-length */
/**
* Applies an accumulator function over the source Observable, and returns each
* intermediate result, with an optional seed value.
*
* <span class="informal">It's like {@link reduce}, but emits the current
* accumulation whenever the source emits a value.</span>
*
* 
*
* 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. Is similar to {@link reduce}, but emits the intermediate
* accumulations.
*
* 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
* Count the number of click events
* ```javascript
* const clicks = fromEvent(document, 'click');
* const ones = clicks.pipe(mapTo(1));
* const seed = 0;
* const count = ones.pipe(scan((acc, one) => acc + one, seed));
* count.subscribe(x => console.log(x));
* ```
*
* @see {@link expand}
* @see {@link mergeScan}
* @see {@link reduce}
*
* @param {function(acc: R, value: T, index: number): R} accumulator
* The accumulator function called on each source value.
* @param {T|R} [seed] The initial accumulation value.
* @return {Observable<R>} An observable of the accumulated values.
* @method scan
* @owner Observable
*/
export function scan<T, R>(accumulator: (acc: R, value: T, index: number) => R, seed?: T | R): OperatorFunction<T, 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 function scanOperatorFunction(source: Observable<T>): Observable<R> {
return source.lift(new ScanOperator(accumulator, seed, hasSeed));
};
}
class ScanOperator<T, R> implements Operator<T, R> {
constructor(private accumulator: (acc: R, value: T, index: number) => R, private seed?: T | R, private hasSeed: boolean = false) {}
call(subscriber: Subscriber<R>, source: any): any {
return source.subscribe(new ScanSubscriber(subscriber, this.accumulator, this.seed, this.hasSeed));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class ScanSubscriber<T, R> extends Subscriber<T> {
private index: number = 0;
get seed(): T | R {
return this._seed;
}
set seed(value: T | R) {
this.hasSeed = true;
this._seed = value;
}
constructor(destination: Subscriber<R>, private accumulator: (acc: R, value: T, index: number) => R, private _seed: T | R,
private hasSeed: boolean) {
super(destination);
}
protected _next(value: T): void {
if (!this.hasSeed) {
this.seed = value;
this.destination.next(value);
} else {
return this._tryNext(value);
}
}
private _tryNext(value: T): void {
const index = this.index++;
let result: any;
try {
result = this.accumulator(<R>this.seed, value, index);
} catch (err) {
this.destination.error(err);
}
this.seed = result;
this.destination.next(result);
}
}
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