it('should unsub from the source when all other subscriptions are unsubbed', (done: MochaDone) => {
    let unsubscribeCalled = false;
    const connectable = new Observable<boolean>(observer => {
      observer.next(true);
      return () => {
        unsubscribeCalled = true;
      };
    }).pipe(publish());

    const refCounted = connectable.pipe(refCount());

    const sub1 = refCounted.subscribe(() => {
      //noop
    });
    const sub2 = refCounted.subscribe(() => {
      //noop
    });
    const sub3 = refCounted.subscribe((x: any) => {
      expect((connectable as any)._refCount).to.equal(1);
    });

    sub1.unsubscribe();
    sub2.unsubscribe();
    sub3.unsubscribe();

    expect((connectable as any)._refCount).to.equal(0);
    expect(unsubscribeCalled).to.be.true;
    done();
  });

  publish1() {
    // emit value every 1 second
    const source = interval(1000);
    const example = source.pipe(
      // side effects will be executed once
      tap(_ => console.log('Do Something!')),
      // do nothing until connect() is called
      publish()
    ) as ConnectableObservable<number>;

    /*
      source will not emit values until connect() is called
      output: (after 5s)
      "Do Something!"
      "Subscriber One: 0"
      "Subscriber Two: 0"
      "Do Something!"
      "Subscriber One: 1"
      "Subscriber Two: 1"
    */
    const subscribe = example.subscribe(val =>
      console.log(`Subscriber One: ${val}`)
    );
    const subscribeTwo = example.subscribe(val =>
      console.log(`Subscriber Two: ${val}`)
    );

    // call connect after 5 seconds, causing source to begin emitting items
    setTimeout(() => {
      example.connect();
    }, 5000);
  }

it('should support empty parameter', () => {
  // Here, TypeScript versions 3.1 and earlier infer Observable<any>. However,
  // the next version infers Observable<number>. It's not possible to specify
  // an upper bound for the TypeScript version used by dtslint, so an
  // expectation cannot be applied.
  // TODO: put the test back after Typescript > 3.2
  const a = of(1, 2, 3).pipe(publish());
});

  '(dis)connecting hot one', () => {
    const source = cold('--1-2---3-4--5-|');
    const sourceSubs =  '^              !';
    const expected =    '--1-2---3-4--5-|';

    const result = source.pipe(
      publish(),
      refCount()
    );

    expectObservable(result).toBe(expected);
    expectSubscriptions(source.subscriptions).toBe(sourceSubs);
  });

    coldMakeHot() {
    	const observable$ = Observable.create((observer) => {
			observer.next(Math.random());
			// setTimeout(() => {
			// 	observer.next(Math.random());
			// }, 1000);
		}).pipe(
			// share()
			// OR publish & connect
			publish()
		);

		observable$.connect();

		observable$.subscribe((data) => {
			console.log('First subscription:', data); // First subscription: 0.5346840507763866
		});

		observable$.subscribe((data) => {
			console.log('Second subscription:', data); // Second subscription: 0.5346840507763866
		});
    }

  // Some hosts may not support watching.
  watch(
    path: Path,
    _options?: virtualFs.HostWatchOptions,
  ): Observable<virtualFs.HostWatchEvent> | null {
    return new Observable<virtualFs.HostWatchEvent>(obs => {
      const opts = { persistent: false };
      loadFSWatcher();
      const watcher = new FSWatcher(opts).add(getSystemPath(path));

      watcher
        .on('change', path => {
          obs.next({
            path: normalize(path),
            time: new Date(),
            type: virtualFs.HostWatchEventType.Changed,
          });
        })
        .on('add', path => {
          obs.next({
            path: normalize(path),
            time: new Date(),
            type: virtualFs.HostWatchEventType.Created,
          });
        })
        .on('unlink', path => {
          obs.next({
            path: normalize(path),
            time: new Date(),
            type: virtualFs.HostWatchEventType.Deleted,
          });
        });

      return () => watcher.close();
    }).pipe(
      publish(),
      refCount(),
    );
  }

 ...Object.keys(sockets).map(name => {
   const socket = sockets[name];
   // fromEvent typings are broken. socket will work as an event target.
   return fromEvent(
     // Pending a refactor around jmp, this allows us to treat the socket
     // as a normal event emitter
     (socket as unknown) as FromEventTarget<JupyterMessage>,
     "message"
   ).pipe(
     map(
       (body: JupyterMessage): JupyterMessage => {
         // Route the message for the frontend by setting the channel
         const msg = { ...body, channel: name };
         // Conform to same message format as notebook websockets
         // See https://github.com/n-riesco/jmp/issues/10
         delete (msg as any).idents;
         return msg;
       }
     ),
     publish(),
     refCount()
   );
 })

export const createMainChannelFromSockets = (
  sockets: {
    [name: string]: moduleJMP.Socket;
  },
  header: HeaderFiller = {
    session: uuid(),
    username: getUsername()
  },
  jmp = moduleJMP
): Channels => {
  // The mega subject that encapsulates all the sockets as one multiplexed
  // stream

  const outgoingMessages = Subscriber.create<JupyterMessage>(
    message => {
      // There's always a chance that a bad message is sent, we'll ignore it
      // instead of consuming it
      if (!message || !message.channel) {
        console.warn("message sent without a channel", message);
        return;
      }
      const socket = sockets[message.channel];
      if (!socket) {
        // If, for some reason, a message is sent on a channel we don't have
        // a socket for, warn about it but don't bomb the stream
        console.warn("channel not understood for message", message);
        return;
      }
      try {
        const jMessage = new jmp.Message({
          // Fold in the setup header to ease usage of messages on channels
          header: { ...message.header, ...header },
          parent_header: message.parent_header,
          content: message.content,
          metadata: message.metadata,
          buffers: message.buffers
        });
        socket.send(jMessage);
      } catch (err) {
        console.error("Error sending message", err, message);
      }
    },
    undefined, // not bothering with sending errors on
    () =>
      // When the subject is completed / disposed, close all the event
      // listeners and shutdown the socket
      Object.keys(sockets).forEach(name => {
        const socket = sockets[name];
        socket.removeAllListeners();
        if (socket.close) socket.close();
      })
  );

  // Messages from kernel on the sockets
  const incomingMessages: Observable<JupyterMessage> = merge(
    // Form an Observable with each socket
    ...Object.keys(sockets).map(name => {
      const socket = sockets[name];
      // fromEvent typings are broken. socket will work as an event target.
      return fromEvent(
        // Pending a refactor around jmp, this allows us to treat the socket
        // as a normal event emitter
        (socket as unknown) as FromEventTarget<JupyterMessage>,
        "message"
      ).pipe(
        map(
          (body: JupyterMessage): JupyterMessage => {
            // Route the message for the frontend by setting the channel
            const msg = { ...body, channel: name };
            // Conform to same message format as notebook websockets
            // See https://github.com/n-riesco/jmp/issues/10
            delete (msg as any).idents;
            return msg;
          }
        ),
        publish(),
        refCount()
      );
    })
  ).pipe(
    publish(),
    refCount()
  );

  const subject: Subject<JupyterMessage> = Subject.create(
    outgoingMessages,
    incomingMessages
  );

  return subject;
};

// are already producing values even before a subscription is active. 
//
// When an observer subscribes to a Multicast / Hot observable sequence
// it will get all values in the stream that are emitted after it subscribes.
//
// The Multicast / Hot observable sequence IS SHARED among all subscribers,
// and each subscriber is pushed the same next value in the sequence; 
//
// The producer will keep going emitting values whether there's a subscriber or not.
//
// a Subject is the only way we can Multicast in rxjs, 
// is there a way to make an Observable multicast ?

const o$ = new Observable<number>(subscriber => subscriber.next(Date.now()))
    .pipe(
        publish() // creates a ConnectableObservable: it creates and underlying Subject
                  // and shares it with the new subscribers
    ) as ConnectableObservable<number>; // there's an issue about type inference not working: https://github.com/ReactiveX/rxjs/issues/2972

// calling connect() will "trigger" the subscription to the original observable source
o$.connect(); // nothing will be displayed if we call connect() and activate the observable here, we subscribe a little bit too late.

// Output:
//
// (nothing)

o$.subscribe(v => console.log("1st subscriber: " + v));
o$.subscribe(v => console.log("2nd subscriber: " + v));

// o$.connect(); // we'll see the same value for all the observables if we activate it here