import { Operator } from '../Operator';
import { Observable, ObservableInput } from '../Observable';
import { Subscriber } from '../Subscriber';
import { Subscription } from '../Subscription';
import { OuterSubscriber } from '../OuterSubscriber';
import { InnerSubscriber } from '../InnerSubscriber';
import { subscribeToResult } from '../util/subscribeToResult';

/**
 * Projects each source value to an Observable which is merged in the output
 * Observable, emitting values only from the most recently projected Observable.
 *
 * <span class="informal">Maps each value to an Observable, then flattens all of
 * these inner Observables using {@link switch}.</span>
 *
 * <img src="./img/switchMap.png" width="100%">
 *
 * Returns an Observable that emits items based on applying a function that you
 * supply to each item emitted by the source Observable, where that function
 * returns an (so-called "inner") Observable. Each time it observes one of these
 * inner Observables, the output Observable begins emitting the items emitted by
 * that inner Observable. When a new inner Observable is emitted, `switchMap`
 * stops emitting items from the earlier-emitted inner Observable and begins
 * emitting items from the new one. It continues to behave like this for
 * subsequent inner Observables.
 *
 * @example <caption>Rerun an interval Observable on every click event</caption>
 * var clicks = Rx.Observable.fromEvent(document, 'click');
 * var result = clicks.switchMap((ev) => Rx.Observable.interval(1000));
 * result.subscribe(x => console.log(x));
 *
 * @see {@link concatMap}
 * @see {@link exhaustMap}
 * @see {@link mergeMap}
 * @see {@link switch}
 * @see {@link switchMapTo}
 *
 * @param {function(value: T, ?index: number): Observable} project A function
 * that, when applied to an item emitted by the source Observable, returns an
 * Observable.
 * @param {function(outerValue: T, innerValue: I, outerIndex: number, innerIndex: number): any} [resultSelector]
 * A function to produce the value on the output Observable based on the values
 * and the indices of the source (outer) emission and the inner Observable
 * emission. The arguments passed to this function are:
 * - `outerValue`: the value that came from the source
 * - `innerValue`: the value that came from the projected Observable
 * - `outerIndex`: the "index" of the value that came from the source
 * - `innerIndex`: the "index" of the value from the projected Observable
 * @return {Observable} An Observable that emits the result of applying the
 * projection function (and the optional `resultSelector`) to each item emitted
 * by the source Observable and taking only the values from the most recently
 * projected inner Observable.
 * @method switchMap
 * @owner Observable
 */
export function switchMap<T, I, R>(project: (value: T, index: number) => ObservableInput<I>,
                                   resultSelector?: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R): Observable<R> {
  return this.lift(new SwitchMapOperator(project, resultSelector));
}

export interface SwitchMapSignature<T> {
  <R>(project: (value: T, index: number) => ObservableInput<R>): Observable<R>;
  <I, R>(project: (value: T, index: number) => ObservableInput<I>,
         resultSelector: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R): Observable<R>;
}

class SwitchMapOperator<T, I, R> implements Operator<T, I> {
  constructor(private project: (value: T, index: number) => ObservableInput<I>,
              private resultSelector?: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R) {
  }

  call(subscriber: Subscriber<I>, source: any): any {
    return source._subscribe(new SwitchMapSubscriber(subscriber, this.project, this.resultSelector));
  }
}

/**
 * We need this JSDoc comment for affecting ESDoc.
 * @ignore
 * @extends {Ignored}
 */
class SwitchMapSubscriber<T, I, R> extends OuterSubscriber<T, I> {
  private index: number = 0;
  private innerSubscription: Subscription;

  constructor(destination: Subscriber<I>,
              private project: (value: T, index: number) => ObservableInput<I>,
              private resultSelector?: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R) {
    super(destination);
  }

  protected _next(value: T) {
    let result: ObservableInput<I>;
    const index = this.index++;
    try {
      result = this.project(value, index);
    } catch (error) {
      this.destination.error(error);
      return;
    }
    this._innerSub(result, value, index);
  }

  private _innerSub(result: ObservableInput<I>, value: T, index: number) {
    const innerSubscription = this.innerSubscription;
    if (innerSubscription) {
      innerSubscription.unsubscribe();
    }
    this.add(this.innerSubscription = subscribeToResult(this, result, value, index));
  }

  protected _complete(): void {
    const {innerSubscription} = this;
    if (!innerSubscription || innerSubscription.closed) {
      super._complete();
    }
  }

  protected _unsubscribe() {
    this.innerSubscription = null;
  }

  notifyComplete(innerSub: Subscription): void {
    this.remove(innerSub);
    this.innerSubscription = null;
    if (this.isStopped) {
      super._complete();
    }
  }

  notifyNext(outerValue: T, innerValue: I,
             outerIndex: number, innerIndex: number,
             innerSub: InnerSubscriber<T, I>): void {
    if (this.resultSelector) {
      this._tryNotifyNext(outerValue, innerValue, outerIndex, innerIndex);
    } else {
      this.destination.next(innerValue);
    }
  }

  private _tryNotifyNext(outerValue: T, innerValue: I, outerIndex: number, innerIndex: number): void {
    let result: R;
    try {
      result = this.resultSelector(outerValue, innerValue, outerIndex, innerIndex);
    } catch (err) {
      this.destination.error(err);
      return;
    }
    this.destination.next(result);
  }
}
