{- | Wrapper to write @gloss@ applications in Rhine, using concurrency.
-}

{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE TypeFamilies #-}
module FRP.Rhine.Gloss.IO
  ( GlossConcT
  , paintIO
  , clearIO
  , paintAllIO
  , GlossEventClockIO (..)
  , GlossSimClockIO (..)
  , launchGlossThread
  , flowGlossIO
  , glossConcurrently
  )
  where

-- base
import Control.Concurrent
import Data.Functor (void)
import Data.IORef

-- transformers
import Control.Monad.Trans.Class
import Control.Monad.Trans.Reader

-- gloss
import Graphics.Gloss.Interface.IO.Game

-- rhine
import FRP.Rhine

-- rhine-gloss
import FRP.Rhine.Gloss.Common

-- * Gloss effects

type GlossEnv = (MVar Float, MVar Event, IORef Float, IORef Picture)

-- | Wraps the concurrent variables needed for communication with the @gloss@ backend.
newtype GlossConcT m a = GlossConcT
  { unGlossConcT :: ReaderT GlossEnv m a }
  deriving (Functor, Applicative, Monad, MonadTrans, MonadIO)

withPicRef
  :: MonadIO m
  => (IORef Picture -> IO a)
  -> GlossConcT m a
withPicRef action = GlossConcT $ do
  (_, _, _, picRef) <- ask
  liftIO $ action picRef

-- | Add a picture to the canvas.
paintIO :: MonadIO m => Picture -> GlossConcT m ()
paintIO pic = withPicRef $ \ref -> modifyIORef' ref (<> pic)

-- | Clear the canvas.
clearIO :: MonadIO m => GlossConcT m ()
clearIO = withPicRef $ \ref -> writeIORef ref Blank

-- | Clear the canvas and then paint.
paintAllIO :: MonadIO m => Picture -> GlossConcT m ()
paintAllIO pic = clearIO >> paintIO pic

-- * Gloss clocks in 'IO'

-- | Concurrently block on @gloss@ events.
data GlossEventClockIO = GlossEventClockIO

instance MonadIO m => Clock (GlossConcT m) GlossEventClockIO where
  type Time GlossEventClockIO = Float
  type Tag  GlossEventClockIO = Event
  initClock _ = return (constM getEvent, 0)
    where
      getEvent = do
        (_, eventVar, timeRef, _) <- GlossConcT ask
        liftIO $ do
          event <- takeMVar eventVar
          time <- readIORef timeRef
          return (time, event)

instance GetClockProxy GlossEventClockIO

-- | Concurrently block on @gloss@ simulation ticks.
data GlossSimClockIO = GlossSimClockIO

instance MonadIO m => Clock (GlossConcT m) GlossSimClockIO where
  type Time GlossSimClockIO = Float
  type Tag  GlossSimClockIO = ()
  initClock _ = return (constM getTime >>> sumS >>> withSideEffect writeTime &&& arr (const ()), 0)
    where
      getTime = do
        (timeVar, _, _, _) <- GlossConcT ask
        liftIO $ takeMVar timeVar
      writeTime time = do
        (_, _, timeRef, _) <- GlossConcT ask
        liftIO $ writeIORef timeRef time

instance GetClockProxy GlossSimClockIO

-- * Reactimation

-- | Apply this to supply the 'GlossConcT' effect.
--   Creates a new thread in which @gloss@ is run,
--   and feeds the clocks 'GlossEventClockIO' and 'GlossSimClockIO'.
--
--   Usually, this function is applied to the result of 'flow',
--   so you can handle all occurring effects as needed.
--   If you only use @gloss@ in your whole signal network,
--   you can use 'flowGlossIO' instead.
launchGlossThread
  :: MonadIO    m
  => GlossSettings
  -> GlossConcT m a
  ->            m a
launchGlossThread GlossSettings { .. } glossLoop = do
  vars <- liftIO $ ( , , , ) <$> newEmptyMVar <*> newEmptyMVar <*> newIORef 0 <*> newIORef Blank
  let
      getPic               (_, _, _, picRef)   = readIORef picRef
      -- Only try to put so this doesn't hang in case noone is listening for events or ticks
      handleEvent event    vars@(_, eventVar, _, _) = do
        void $ tryPutMVar eventVar event
        return vars
      simStep     diffTime vars@(timeVar,  _, _, _) = do
        void $ tryPutMVar timeVar diffTime
        return vars
  void $ liftIO $ forkIO $ playIO display backgroundColor stepsPerSecond vars getPic handleEvent simStep
  runReaderT (unGlossConcT glossLoop) vars

-- | Run a 'Rhine' in the 'GlossConcT' monad by launching a separate thread for the @gloss@ backend,
--   and reactimate in the foreground.
flowGlossIO
  :: ( Clock (GlossConcT IO) cl
     , GetClockProxy cl
     , Time cl ~ Time (In  cl)
     , Time cl ~ Time (Out cl)
     )
  => GlossSettings
  -> Rhine (GlossConcT IO) cl () ()
  -> IO ()
flowGlossIO settings = launchGlossThread settings . flow

-- | A schedule in the 'GlossConcT' transformer,
--   supplying the same backend connection to its scheduled clocks.
glossConcurrently
  :: ( Monad IO
     , Clock (GlossConcT IO) cl1, Clock (GlossConcT IO) cl2
     , Time cl1 ~ Time cl2
     )
  => Schedule (GlossConcT IO) cl1 cl2
glossConcurrently = Schedule
  $ \cl1 cl2 -> GlossConcT $ ReaderT
  $ \vars -> first liftTransS
  <$> initSchedule concurrently
        (runGlossEnvClock vars cl1)
        (runGlossEnvClock vars cl2)

type RunGlossEnvClock cl = HoistClock (GlossConcT IO) IO cl

runGlossEnvClock
  :: GlossEnv
  -> cl
  -> RunGlossEnvClock cl
runGlossEnvClock env unhoistedClock = HoistClock
  { monadMorphism = flip runReaderT env . unGlossConcT
  , ..
  }

-- FIXME And a schedule for gloss clocks and other clocks