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import { Operator } from '../Operator';
import { Subscriber } from '../Subscriber';
import { Observable } from '../Observable';
import { OperatorFunction, MonoTypeOperatorFunction, TeardownLogic } from '../types';
/* tslint:disable:max-line-length */
export function filter<T, S extends T>(predicate: (value: T, index: number) => value is S,
thisArg?: any): OperatorFunction<T, S>;
export function filter<T>(predicate: (value: T, index: number) => boolean,
thisArg?: any): MonoTypeOperatorFunction<T>;
/* tslint:enable:max-line-length */
/**
* Filter items emitted by the source Observable by only emitting those that
* satisfy a specified predicate.
*
* <span class="informal">Like
* [Array.prototype.filter()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter),
* it only emits a value from the source if it passes a criterion function.</span>
*
* 
*
* Similar to the well-known `Array.prototype.filter` method, this operator
* takes values from the source Observable, passes them through a `predicate`
* function and only emits those values that yielded `true`.
*
* ## Example
* Emit only click events whose target was a DIV element
* ```javascript
* const clicks = fromEvent(document, 'click');
* const clicksOnDivs = clicks.pipe(filter(ev => ev.target.tagName === 'DIV'));
* clicksOnDivs.subscribe(x => console.log(x));
* ```
*
* @see {@link distinct}
* @see {@link distinctUntilChanged}
* @see {@link distinctUntilKeyChanged}
* @see {@link ignoreElements}
* @see {@link partition}
* @see {@link skip}
*
* @param {function(value: T, index: number): boolean} predicate A function that
* evaluates each value emitted by the source Observable. If it returns `true`,
* the value is emitted, if `false` the value is not passed to the output
* Observable. The `index` parameter is the number `i` for the i-th source
* emission that has happened since the subscription, starting from the number
* `0`.
* @param {any} [thisArg] An optional argument to determine the value of `this`
* in the `predicate` function.
* @return {Observable} An Observable of values from the source that were
* allowed by the `predicate` function.
* @method filter
* @owner Observable
*/
export function filter<T>(predicate: (value: T, index: number) => boolean,
thisArg?: any): MonoTypeOperatorFunction<T> {
return function filterOperatorFunction(source: Observable<T>): Observable<T> {
return source.lift(new FilterOperator(predicate, thisArg));
};
}
class FilterOperator<T> implements Operator<T, T> {
constructor(private predicate: (value: T, index: number) => boolean,
private thisArg?: any) {
}
call(subscriber: Subscriber<T>, source: any): TeardownLogic {
return source.subscribe(new FilterSubscriber(subscriber, this.predicate, this.thisArg));
}
}
/**
* We need this JSDoc comment for affecting ESDoc.
* @ignore
* @extends {Ignored}
*/
class FilterSubscriber<T> extends Subscriber<T> {
count: number = 0;
constructor(destination: Subscriber<T>,
private predicate: (value: T, index: number) => boolean,
private thisArg: any) {
super(destination);
}
// the try catch block below is left specifically for
// optimization and perf reasons. a tryCatcher is not necessary here.
protected _next(value: T) {
let result: any;
try {
result = this.predicate.call(this.thisArg, value, this.count++);
} catch (err) {
this.destination.error(err);
return;
}
if (result) {
this.destination.next(value);
}
}
}
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