cmdLine :: IO ()
cmdLine = do
  displayHelpMessage
  -- newAddHandler :: IO (AddHandler a, Handler a)
  -- newAddHandler :: Control.Event.Handler
  -- setupNetwork :: (EventSource (), EventSource EventNetwork) -> IO EventNetwork
  -- sources :: ((AddHandler (), Handler ()), (AddHandler EventNetwork, Handler EventNetwork))
  -- actuate :: EventNetwork -> IO ()
  -- eventLoop :: (EventSource (), EventSource EventNetwork) -> EventNetwork -> IO ()
  sources <- (,) <$> newAddHandler <*> newAddHandler
  network <- setupNetwork sources
  actuate network
  eventLoop sources network

displayHelpMessage :: IO ()
displayHelpMessage =
  mapM_ putStrLn
  [ "Commands are:"
  , "   count   - send counter event"
  , "   pause   - pause event network"
  , "   actuate - actuate event network"
  , "   quit    - quit the program"
  , ""
  ]

-- Read commands and fire corresponding events.
eventLoop :: (EventSource (), EventSource EventNetwork) -> EventNetwork -> IO ()
eventLoop (counterEs, pauseEs) network = loop
  where
    loop = do
      putStr "> "
      hFlush stdout
      s <- getLine
      case s of
        "c" -> fire counterEs ()
        "p" -> fire pauseEs network
        "a" -> actuate network
        "q" -> return ()
        _   -> putStrLn $ s ++ " - unknown command"
      when (s /= "q") loop


-- Event Sources - allows you to register event handlers
-- Your GUI framework should provide something like this for you
type EventSource a = (AddHandler a, a -> IO ())

-- Set up the program logic in terms of events and behaviors.
setupNetwork :: (EventSource (), EventSource EventNetwork) -> IO EventNetwork
setupNetwork (counterEs, pauseEs) =
  compile $ do
    ecounter <- fromAddHandler (addHandler counterEs)
    epause <- fromAddHandler (addHandler pauseEs)
    ecount <- accumE 0 $ (+ 1) <$ ecounter
    reactimate $ fmap print ecount
    reactimate $ fmap pause epause

addHandler :: EventSource a -> AddHandler a
addHandler = fst

fire :: EventSource a -> a -> IO ()
fire = snd