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import { Observable } from '../Observable';
import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { EmptyError } from '../util/EmptyError';
import { Observer, MonoTypeOperatorFunction, TeardownLogic } from '../types';
/**
* Returns an Observable that emits the single item emitted by the source Observable that matches a specified
* predicate, if that Observable emits one such item. If the source Observable emits more than one such item or no
* items, notify of an IllegalArgumentException or NoSuchElementException respectively. If the source Observable
* emits items but none match the specified predicate then `undefined` is emitted.
*
* <span class="informal">Like {@link first}, but emit with error notification if there is more than one value.</span>
* 
*
* ## Example
* emits 'error'
* ```ts
* import { range } from 'rxjs';
* import { single } from 'rxjs/operators';
*
* const numbers = range(1,5).pipe(single());
* numbers.subscribe(x => console.log('never get called'), e => console.log('error'));
* // result
* // 'error'
* ```
*
* emits 'undefined'
* ```ts
* import { range } from 'rxjs';
* import { single } from 'rxjs/operators';
*
* const numbers = range(1,5).pipe(single(x => x === 10));
* numbers.subscribe(x => console.log(x));
* // result
* // 'undefined'
* ```
*
* @see {@link first}
* @see {@link find}
* @see {@link findIndex}
* @see {@link elementAt}
*
* @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
* callback if the Observable completes before any `next` notification was sent.
* @param {Function} predicate - A predicate function to evaluate items emitted by the source Observable.
* @return {Observable<T>} An Observable that emits the single item emitted by the source Observable that matches
* the predicate or `undefined` when no items match.
*
* @method single
* @owner Observable
*/
export function single<T>(predicate?: (value: T, index: number, source: Observable<T>) => boolean): MonoTypeOperatorFunction<T> {
return (source: Observable<T>) => source.lift(new SingleOperator(predicate, source));
}
class SingleOperator<T> implements Operator<T, T> {
constructor(private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
private source?: Observable<T>) {
}
call(subscriber: Subscriber<T>, source: any): TeardownLogic {
return source.subscribe(new SingleSubscriber(subscriber, this.predicate, this.source));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class SingleSubscriber<T> extends Subscriber<T> {
private seenValue: boolean = false;
private singleValue: T;
private index: number = 0;
constructor(destination: Observer<T>,
private predicate?: (value: T, index: number, source: Observable<T>) => boolean,
private source?: Observable<T>) {
super(destination);
}
private applySingleValue(value: T): void {
if (this.seenValue) {
this.destination.error('Sequence contains more than one element');
} else {
this.seenValue = true;
this.singleValue = value;
}
}
protected _next(value: T): void {
const index = this.index++;
if (this.predicate) {
this.tryNext(value, index);
} else {
this.applySingleValue(value);
}
}
private tryNext(value: T, index: number): void {
try {
if (this.predicate(value, index, this.source)) {
this.applySingleValue(value);
}
} catch (err) {
this.destination.error(err);
}
}
protected _complete(): void {
const destination = this.destination;
if (this.index > 0) {
destination.next(this.seenValue ? this.singleValue : undefined);
destination.complete();
} else {
destination.error(new EmptyError);
}
}
}
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