import Control.Concurrent.MVar
import Data.IORef
import qualified Graphics.UI.Gtk as G

data PushButton = PushButton { n_states :: Int
                             , c_state :: Int
                             , labels :: [String]
                             , gtk_button :: G.Button }

-- data Dial = Dial

mk_pb :: [String] -> IO PushButton
mk_pb l = do
  b <- G.buttonNew
  G.set b [ G.buttonLabel G.:= l !! 0 ]
  return (PushButton (length l) 0 l b)

pb_incr :: PushButton -> IO PushButton
pb_incr (PushButton n i l b) = do
    let i' = (i + 1) `mod` n
    G.set b [ G.buttonLabel G.:= l !! i' ]
    return (PushButton n i' l b)

pb_init_r :: PushButton -> IO (IORef PushButton)
pb_init_r pb = do
  let b = gtk_button pb
  r <- newIORef pb
  _ <- G.onClicked b (modifyIORef_ r pb_incr)
  return r

pb_init_v :: PushButton -> IO (MVar PushButton)
pb_init_v pb = do
  let b = gtk_button pb
  v <- newMVar pb
  _ <- G.onClicked b (modifyMVar_ v pb_incr)
  return v

modifyIORef_ :: IORef a -> (a -> IO a) -> IO ()
modifyIORef_ ref f = do
  a <- readIORef ref
  a' <- f a
  writeIORef ref a'

main :: IO ()
main = do
  _ <- G.initGUI
  w <- G.windowNew
  c <- G.hBoxNew True 10
  G.set w [ G.containerBorderWidth G.:= 10
          , G.containerChild G.:= c ]
  pb_r <- pb_init_r =<< mk_pb ["this", "is", "a", "ref", "test"]
  b0 <- return . gtk_button =<< readIORef pb_r
  pb_v <- pb_init_v =<< mk_pb ["this", "is", "an", "mvar", "test"]
  b1 <- return . gtk_button =<< readMVar pb_v
  G.set c [ G.containerChild G.:= b0
          , G.containerChild G.:= b1 ]
  _ <- G.onDestroy w G.mainQuit
  G.widgetShowAll w
  G.mainGUI