-- -*-haskell-*-
--  Vision (for the Voice): an XMMS2 client.
--
--  Author:  Oleg Belozeorov
--  Created: 13 Jul. 2011
--
--  Copyright (C) 2011 Oleg Belozeorov
--
--  This program is free software; you can redistribute it and/or
--  modify it under the terms of the GNU General Public License as
--  published by the Free Software Foundation; either version 3 of
--  the License, or (at your option) any later version.
--
--  This program is distributed in the hope that it will be useful,
--  but WITHOUT ANY WARRANTY; without even the implied warranty of
--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
--  General Public License for more details.
--

{-# LANGUAGE MultiParamTypeClasses,
             FlexibleInstances,
             FlexibleContexts,
             OverlappingInstances,
             TypeOperators,
             DeriveDataTypeable,
             UndecidableInstances,
             ImplicitParams,
             StandaloneDeriving #-}

module Registry
  ( EnvM
  , runIn
  , startRegistry
  , registryEnv
  , RegistryEnvOp
  , addEnv
  , getEnv
  ) where

import Control.Monad.Trans
import Control.Monad.EnvIO

import Data.IntMap (IntMap)
import qualified Data.IntMap as IntMap
import Control.Concurrent.STM

import Data.Typeable
import Data.Dynamic
import Data.Env


deriving instance Typeable2 Env

data Ix = Ix deriving Typeable

type EnvMap = TVar (IntMap Dynamic)

registryEnv :: Extract Ix EnvMap
registryEnv = Extract

class    (EnvM Ix EnvMap m) => RegistryM m
instance (EnvM Ix EnvMap m) => RegistryM m

startRegistry f = do
  v <- newTVarIO $ IntMap.empty
  runEnvIO (addEnv Ix v >> f) $ build () $ mkEnv Ix v

class    (RegistryM m, Typeable ix, Typeable a) => RegistryEnvOp ix a m
instance (RegistryM m, Typeable ix, Typeable a) => RegistryEnvOp ix a m

addEnv :: RegistryEnvOp ix a m => ix -> a -> m ()
addEnv ix r = do
  let val = mkEnv ix r
  var <- envx Ix
  liftIO $ do
    key <- typeRepKey $ typeOf val
    atomically $ do
      map <- readTVar var
      writeTVar var $ IntMap.insert key (toDyn val) map

getEnv :: RegistryEnvOp ix a m => Extract ix a -> m (Maybe (Env ix a))
getEnv spec = do
  var <- envx Ix
  liftIO $ do
    key <- typeRepKey $ typeOf $ env spec
    atomically $ do
      map <- readTVar var
      case IntMap.lookup key map of
        Nothing -> return Nothing
        Just dv -> return $ fromDynamic dv
  where env :: Extract ix a -> Env ix a
        env = const undefined