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import { Observable } from '../Observable';
import { Subscriber } from '../Subscriber';
import { OperatorFunction, TruthyTypesOf } from '../types';
import { operate } from '../util/lift';
import { createOperatorSubscriber } from './OperatorSubscriber';
export function find<T>(predicate: BooleanConstructor): OperatorFunction<T, TruthyTypesOf<T>>;
/** @deprecated Use a closure instead of a `thisArg`. Signatures accepting a `thisArg` will be removed in v8. */
export function find<T, S extends T, A>(
predicate: (this: A, value: T, index: number, source: Observable<T>) => value is S,
thisArg: A
): OperatorFunction<T, S | undefined>;
export function find<T, S extends T>(
predicate: (value: T, index: number, source: Observable<T>) => value is S
): OperatorFunction<T, S | undefined>;
/** @deprecated Use a closure instead of a `thisArg`. Signatures accepting a `thisArg` will be removed in v8. */
export function find<T, A>(
predicate: (this: A, value: T, index: number, source: Observable<T>) => boolean,
thisArg: A
): OperatorFunction<T, T | undefined>;
export function find<T>(predicate: (value: T, index: number, source: Observable<T>) => boolean): OperatorFunction<T, T | undefined>;
/**
* Emits only the first value emitted by the source Observable that meets some
* condition.
*
* <span class="informal">Finds the first value that passes some test and emits
* that.</span>
*
* 
*
* `find` searches for the first item in the source Observable that matches the
* specified condition embodied by the `predicate`, and returns the first
* occurrence in the source. Unlike {@link first}, the `predicate` is required
* in `find`, and does not emit an error if a valid value is not found
* (emits `undefined` instead).
*
* ## Example
*
* Find and emit the first click that happens on a DIV element
*
* ```ts
* import { fromEvent, find } from 'rxjs';
*
* const div = document.createElement('div');
* div.style.cssText = 'width: 200px; height: 200px; background: #09c;';
* document.body.appendChild(div);
*
* const clicks = fromEvent(document, 'click');
* const result = clicks.pipe(find(ev => (<HTMLElement>ev.target).tagName === 'DIV'));
* result.subscribe(x => console.log(x));
* ```
*
* @see {@link filter}
* @see {@link first}
* @see {@link findIndex}
* @see {@link take}
*
* @param {function(value: T, index: number, source: Observable<T>): boolean} predicate
* A function called with each item to test for condition matching.
* @param {any} [thisArg] An optional argument to determine the value of `this`
* in the `predicate` function.
* @return A function that returns an Observable that emits the first item that
* matches the condition.
*/
export function find<T>(
predicate: (value: T, index: number, source: Observable<T>) => boolean,
thisArg?: any
): OperatorFunction<T, T | undefined> {
return operate(createFind(predicate, thisArg, 'value'));
}
export function createFind<T>(
predicate: (value: T, index: number, source: Observable<T>) => boolean,
thisArg: any,
emit: 'value' | 'index'
) {
const findIndex = emit === 'index';
return (source: Observable<T>, subscriber: Subscriber<any>) => {
let index = 0;
source.subscribe(
createOperatorSubscriber(
subscriber,
(value) => {
const i = index++;
if (predicate.call(thisArg, value, i, source)) {
subscriber.next(findIndex ? i : value);
subscriber.complete();
}
},
() => {
subscriber.next(findIndex ? -1 : undefined);
subscriber.complete();
}
)
);
};
}