import { Scheduler } from '../Scheduler';
import { Observable } from '../Observable';
import { TeardownLogic } from '../Subscription';

export interface DispatchArg {
  error: any;
  subscriber: any;
}

/**
 * We need this JSDoc comment for affecting ESDoc.
 * @extends {Ignored}
 * @hide true
 */
export class ErrorObservable<T> extends Observable<any> {

  /**
   * Creates an Observable that emits no items to the Observer and immediately
   * emits an error notification.
   *
   * <span class="informal">Just emits 'error', and nothing else.
   * </span>
   *
   * <img src="./img/throw.png" width="100%">
   *
   * This static operator is useful for creating a simple Observable that only
   * emits the error notification. It can be used for composing with other
   * Observables, such as in a {@link mergeMap}.
   *
   * @example <caption>Emit the number 7, then emit an error.</caption>
   * var result = Rx.Observable.throw(new Error('oops!')).startWith(7);
   * result.subscribe(x => console.log(x), e => console.error(e));
   *
   * @example <caption>Map and flattens numbers to the sequence 'a', 'b', 'c', but throw an error for 13</caption>
   * var interval = Rx.Observable.interval(1000);
   * var result = interval.mergeMap(x =>
   *   x === 13 ?
   *     Rx.Observable.throw('Thirteens are bad') :
   *     Rx.Observable.of('a', 'b', 'c')
   * );
   * result.subscribe(x => console.log(x), e => console.error(e));
   *
   * @see {@link create}
   * @see {@link empty}
   * @see {@link never}
   * @see {@link of}
   *
   * @param {any} error The particular Error to pass to the error notification.
   * @param {Scheduler} [scheduler] A {@link Scheduler} to use for scheduling
   * the emission of the error notification.
   * @return {Observable} An error Observable: emits only the error notification
   * using the given error argument.
   * @static true
   * @name throw
   * @owner Observable
   */
  static create<T>(error: T, scheduler?: Scheduler): ErrorObservable<T> {
    return new ErrorObservable(error, scheduler);
  }

  static dispatch(arg: DispatchArg) {
    const { error, subscriber } = arg;
    subscriber.error(error);
  }

  constructor(public error: T, private scheduler?: Scheduler) {
    super();
  }

  protected _subscribe(subscriber: any): TeardownLogic {
    const error = this.error;
    const scheduler = this.scheduler;

    if (scheduler) {
      return scheduler.schedule(ErrorObservable.dispatch, 0, {
        error, subscriber
      });
    } else {
      subscriber.error(error);
    }
  }
}
