{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE ForeignFunctionInterface #-}
module Synthesizer.LLVM.Storable.ChunkIterator where

import qualified Data.StorableVector.Lazy as SVL
import qualified Data.StorableVector.Base as SVB

import qualified LLVM.Extra.Memory as Memory
import qualified LLVM.Extra.Class as Class

import Data.Word (Word32, )
import Foreign.Storable (Storable, poke, )
import Foreign.Ptr (FunPtr, Ptr, nullPtr, )

import Control.Monad (liftM2, )

import Foreign.StablePtr (StablePtr, newStablePtr, freeStablePtr, deRefStablePtr, )
import Data.IORef (IORef, newIORef, readIORef, writeIORef, )


{-
FFI declarations must not have constraints.
Thus we put them in the iterator datatype.
-}
data T a =
   (Storable a, Class.MakeValueTuple a, Memory.C (Class.ValueTuple a)) =>
      Cons (IORef [SVB.Vector a]) (IORef (SVB.Vector a))

type MemoryPtr a = Ptr (Memory.Struct (Class.ValueTuple a))


foreign import ccall "&nextChunk"
   nextCallBack ::
      FunPtr (
         StablePtr (T a) ->
         Ptr Word32 -> IO (MemoryPtr a)
      )

foreign export ccall "nextChunk"
   next ::
      StablePtr (T a) ->
      Ptr Word32 -> IO (MemoryPtr a)


new ::
   (Storable a, Class.MakeValueTuple a, Memory.C (Class.ValueTuple a)) =>
   SVL.Vector a -> IO (StablePtr (T a))
new sig =
   newStablePtr =<<
   liftM2 Cons
      (newIORef (SVL.chunks sig))
      (newIORef (error "first chunk must be fetched with nextChunk"))

dispose ::
   StablePtr (T a) -> IO ()
dispose = freeStablePtr

next ::
   StablePtr (T a) ->
   Ptr Word32 -> IO (MemoryPtr a)
next stable lenPtr =
   deRefStablePtr stable >>= \state ->
   case state of
      Cons listRef chunkRef -> do
         xt <- readIORef listRef
         case xt of
            [] -> return nullPtr
            (x:xs) ->
               {- We have to maintain a pointer to the current chunk
                  in order to protect it against garbage collection -}
               writeIORef chunkRef x >>
               writeIORef listRef xs >>
               SVB.withStartPtr x
                  (\p l ->
                     poke lenPtr (fromIntegral l) >>
                     return (Memory.castStorablePtr p))