{-# LANGUAGE ExistentialQuantification, DeriveDataTypeable #-}

module GLDriver ( Driver(..)
                , SomeDriver(..)
                , Event
                , SomeEvent(..)
                , QuitEvent(..)
                , ResizeEvent(..)
                , fromEvent
                ) where

import Data.Typeable


class Driver a where
    initialized :: a -> Bool
    
    initGL :: a -> IO a
    deinitGL :: a -> IO ()
    
    swapBuffers :: a -> IO ()
    
    nextEvent :: a -> IO (Maybe SomeEvent)

data SomeDriver = forall d. Driver d => SomeDriver d

instance Driver SomeDriver where
    initialized (SomeDriver d) = initialized d
    initGL (SomeDriver d) = initGL d >>= return . SomeDriver
    deinitGL (SomeDriver d) = deinitGL d
    swapBuffers (SomeDriver d) = swapBuffers d
    nextEvent (SomeDriver d) = nextEvent d


class Typeable a => Event a

data SomeEvent = forall a. Event a => SomeEvent a

fromEvent :: Event a => SomeEvent -> Maybe a
fromEvent (SomeEvent a) = cast a


data QuitEvent = QuitEvent deriving Typeable
instance Event QuitEvent

data ResizeEvent = ResizeEvent Int Int deriving Typeable
instance Event ResizeEvent