import { Subject } from '../Subject';
import { Observable } from '../Observable';
import { MulticastObservable } from '../observable/MulticastObservable';
import { ConnectableObservable } from '../observable/ConnectableObservable';

/**
 * Returns an Observable that emits the results of invoking a specified selector on items
 * emitted by a ConnectableObservable that shares a single subscription to the underlying stream.
 *
 * <img src="./img/multicast.png" width="100%">
 *
 * @param {Function|Subject} Factory function to create an intermediate subject through
 * which the source sequence's elements will be multicast to the selector function
 * or Subject to push source elements into.
 * @param {Function} Optional selector function that can use the multicasted source stream
 * as many times as needed, without causing multiple subscriptions to the source stream.
 * Subscribers to the given source will receive all notifications of the source from the
 * time of the subscription forward.
 * @return {Observable} an Observable that emits the results of invoking the selector
 * on the items emitted by a `ConnectableObservable` that shares a single subscription to
 * the underlying stream.
 * @method multicast
 * @owner Observable
 */
export function multicast<T>(subjectOrSubjectFactory: Subject<T> | (() => Subject<T>),
                             selector?: (source: Observable<T>) => Observable<T>): Observable<T> | ConnectableObservable<T> {
  let subjectFactory: () => Subject<T>;
  if (typeof subjectOrSubjectFactory === 'function') {
    subjectFactory = <() => Subject<T>>subjectOrSubjectFactory;
  } else {
    subjectFactory = function subjectFactory() {
      return <Subject<T>>subjectOrSubjectFactory;
    };
  }

  return !selector ?
    new ConnectableObservable(this, subjectFactory) :
    new MulticastObservable(this, subjectFactory, selector);
}

export type factoryOrValue<T> = T | (() => T);
export type selector<T> = (source: Observable<T>) => Observable<T>;

export interface MulticastSignature<T> {
  (subjectOrSubjectFactory: factoryOrValue<Subject<T>>): ConnectableObservable<T>;
  (SubjectFactory: () => Subject<T>, selector?: selector<T>): Observable<T>;
}