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import { Observable } from '../Observable';
import { EmptyError } from '../util/EmptyError';
import { OperatorFunction, TruthyTypesOf } from '../types';
import { filter } from './filter';
import { takeLast } from './takeLast';
import { throwIfEmpty } from './throwIfEmpty';
import { defaultIfEmpty } from './defaultIfEmpty';
import { identity } from '../util/identity';
export function last<T>(predicate: BooleanConstructor): OperatorFunction<T, TruthyTypesOf<T>>;
export function last<T, D>(predicate: BooleanConstructor, defaultValue: D): OperatorFunction<T, TruthyTypesOf<T> | D>;
export function last<T, D = T>(predicate?: null, defaultValue?: D): OperatorFunction<T, T | D>;
export function last<T, S extends T>(
predicate: (value: T, index: number, source: Observable<T>) => value is S,
defaultValue?: S
): OperatorFunction<T, S>;
export function last<T, D = T>(
predicate: (value: T, index: number, source: Observable<T>) => boolean,
defaultValue?: D
): OperatorFunction<T, T | D>;
/**
* Returns an Observable that emits only the last item emitted by the source Observable.
* It optionally takes a predicate function as a parameter, in which case, rather than emitting
* the last item from the source Observable, the resulting Observable will emit the last item
* from the source Observable that satisfies the predicate.
*
* 
*
* It will throw an error if the source completes without notification or one that matches the predicate. It
* returns the last value or if a predicate is provided last value that matches the predicate. It returns the
* given default value if no notification is emitted or matches the predicate.
*
* ## Examples
*
* Last alphabet from the sequence
*
* ```ts
* import { from, last } from 'rxjs';
*
* const source = from(['x', 'y', 'z']);
* const result = source.pipe(last());
*
* result.subscribe(value => console.log(`Last alphabet: ${ value }`));
*
* // Outputs
* // Last alphabet: z
* ```
*
* Default value when the value in the predicate is not matched
*
* ```ts
* import { from, last } from 'rxjs';
*
* const source = from(['x', 'y', 'z']);
* const result = source.pipe(last(char => char === 'a', 'not found'));
*
* result.subscribe(value => console.log(`'a' is ${ value }.`));
*
* // Outputs
* // 'a' is not found.
* ```
*
* @see {@link skip}
* @see {@link skipUntil}
* @see {@link skipLast}
* @see {@link skipWhile}
*
* @throws {EmptyError} Delivers an EmptyError to the Observer's `error`
* callback if the Observable completes before any `next` notification was sent.
* @param {function} [predicate] - The condition any source emitted item has to satisfy.
* @param {any} [defaultValue] - An optional default value to provide if last
* predicate isn't met or no values were emitted.
* @return A function that returns an Observable that emits only the last item
* satisfying the given condition from the source, or a NoSuchElementException
* if no such items are emitted.
* @throws - Throws if no items that match the predicate are emitted by the source Observable.
*/
export function last<T, D>(
predicate?: ((value: T, index: number, source: Observable<T>) => boolean) | null,
defaultValue?: D
): OperatorFunction<T, T | D> {
const hasDefaultValue = arguments.length >= 2;
return (source: Observable<T>) =>
source.pipe(
predicate ? filter((v, i) => predicate(v, i, source)) : identity,
takeLast(1),
hasDefaultValue ? defaultIfEmpty(defaultValue!) : throwIfEmpty(() => new EmptyError())
);
}