    {-# OPTIONS_GHC  -XNoImplicitPrelude -funbox-strict-fields #-}
    {-# LANGUAGE BangPatterns #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  GHC.IO.Encoding.UTF32
    -- Copyright   :  (c) The University of Glasgow, 2009
    -- License     :  see libraries/base/LICENSE
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  internal
    -- Portability :  non-portable
    --
    -- UTF-32 Codecs for the IO library
    --
    -- Portions Copyright   : (c) Tom Harper 2008-2009,
    --                        (c) Bryan O'Sullivan 2009,
    --                        (c) Duncan Coutts 2009
    --
    -----------------------------------------------------------------------------

    module GHC.IO.Encoding.UTF32 (
      utf32,
      utf32_decode,
      utf32_encode,

      utf32be,
      utf32be_decode,
      utf32be_encode,

      utf32le,
      utf32le_decode,
      utf32le_encode,
      ) where

    import GHC.Base
    import GHC.Real
    import GHC.Num
    -- import GHC.IO
    import GHC.IO.Exception
    import GHC.IO.Buffer
    import GHC.IO.Encoding.Types
    import GHC.Word
    import Data.Bits
    import Data.Maybe
    import GHC.IORef

    -- -----------------------------------------------------------------------------
    -- The UTF-32 codec: either UTF-32BE or UTF-32LE with a BOM

    utf32  :: TextEncoding
    utf32 = TextEncoding { textEncodingName = "UTF-32",
                           mkTextDecoder = utf32_DF,
     	               mkTextEncoder = utf32_EF }

    utf32_DF :: IO (TextDecoder (Maybe DecodeBuffer))
    utf32_DF = do
      seen_bom <- newIORef Nothing
      return (BufferCodec {
                 encode   = utf32_decode seen_bom,
                 close    = return (),
                 getState = readIORef seen_bom,
                 setState = writeIORef seen_bom
              })

    utf32_EF :: IO (TextEncoder Bool)
    utf32_EF = do
      done_bom <- newIORef False
      return (BufferCodec {
                 encode   = utf32_encode done_bom,
                 close    = return (),
                 getState = readIORef done_bom,
                 setState = writeIORef done_bom
              })

    utf32_encode :: IORef Bool -> EncodeBuffer
    utf32_encode done_bom input
      output@Buffer{ bufRaw=oraw, bufL=_, bufR=ow, bufSize=os }
     = do
      b <- readIORef done_bom
      if b then utf32_native_encode input output
           else if os - ow < 4
                   then return (input,output)
                   else do
                        writeIORef done_bom True
                        writeWord8Buf oraw ow     bom0
                        writeWord8Buf oraw (ow+1) bom1
                        writeWord8Buf oraw (ow+2) bom2
                        writeWord8Buf oraw (ow+3) bom3
                        utf32_native_encode input output{ bufR = ow+4 }

    utf32_decode :: IORef (Maybe DecodeBuffer) -> DecodeBuffer
    utf32_decode seen_bom
      input@Buffer{  bufRaw=iraw, bufL=ir, bufR=iw,  bufSize=_  }
      output
     = do
       mb <- readIORef seen_bom
       case mb of
         Just decode -> decode input output
         Nothing ->
           if iw - ir < 4 then return (input,output) else do
           c0 <- readWord8Buf iraw ir
           c1 <- readWord8Buf iraw (ir+1)
           c2 <- readWord8Buf iraw (ir+2)
           c3 <- readWord8Buf iraw (ir+3)
           case () of
            _ | c0 == bom0 && c1 == bom1 && c2 == bom2 && c3 == bom3 -> do
                   writeIORef seen_bom (Just utf32be_decode)
                   utf32be_decode input{ bufL= ir+4 } output
            _ | c0 == bom3 && c1 == bom2 && c2 == bom1 && c3 == bom0 -> do
                   writeIORef seen_bom (Just utf32le_decode)
                   utf32le_decode input{ bufL= ir+4 } output
              | otherwise -> do
                   writeIORef seen_bom (Just utf32_native_decode)
                   utf32_native_decode input output

    bom0, bom1, bom2, bom3 :: Word8
    bom0 = 0
    bom1 = 0
    bom2 = 0xfe
    bom3 = 0xff

    -- choose UTF-32BE by default for UTF-32 output
    utf32_native_decode :: DecodeBuffer
    utf32_native_decode = utf32be_decode

    utf32_native_encode :: EncodeBuffer
    utf32_native_encode = utf32be_encode

    -- -----------------------------------------------------------------------------
    -- UTF32LE and UTF32BE

    utf32be :: TextEncoding
    utf32be = TextEncoding { textEncodingName = "UTF-32BE",
                             mkTextDecoder = utf32be_DF,
     	                 mkTextEncoder = utf32be_EF }

    utf32be_DF :: IO (TextDecoder ())
    utf32be_DF =
      return (BufferCodec {
                 encode   = utf32be_decode,
                 close    = return (),
                 getState = return (),
                 setState = const $ return ()
              })

    utf32be_EF :: IO (TextEncoder ())
    utf32be_EF =
      return (BufferCodec {
                 encode   = utf32be_encode,
                 close    = return (),
                 getState = return (),
                 setState = const $ return ()
              })

    utf32le :: TextEncoding
    utf32le = TextEncoding { textEncodingName = "UTF-32LE",
                             mkTextDecoder = utf32le_DF,
     	                 mkTextEncoder = utf32le_EF }

    utf32le_DF :: IO (TextDecoder ())
    utf32le_DF =
      return (BufferCodec {
                 encode   = utf32le_decode,
                 close    = return (),
                 getState = return (),
                 setState = const $ return ()
              })

    utf32le_EF :: IO (TextEncoder ())
    utf32le_EF =
      return (BufferCodec {
                 encode   = utf32le_encode,
                 close    = return (),
                 getState = return (),
                 setState = const $ return ()
              })

    utf32be_decode :: DecodeBuffer
    utf32be_decode
      input@Buffer{  bufRaw=iraw, bufL=ir0, bufR=iw,  bufSize=_  }
      output@Buffer{ bufRaw=oraw, bufL=_,   bufR=ow0, bufSize=os }
     = let
           loop !ir !ow
             | ow >= os || iw - ir < 4 =  done ir ow
             | otherwise = do
                  c0 <- readWord8Buf iraw ir
                  c1 <- readWord8Buf iraw (ir+1)
                  c2 <- readWord8Buf iraw (ir+2)
                  c3 <- readWord8Buf iraw (ir+3)
                  let x1 = chr4 c0 c1 c2 c3
                  if not (validate x1) then invalid else do
                  ow' <- writeCharBuf oraw ow x1
                  loop (ir+4) ow'
             where
               invalid = if ir > ir0 then done ir ow else ioe_decodingError

           -- lambda-lifted, to avoid thunks being built in the inner-loop:
           done !ir !ow = return (if ir == iw then input{ bufL=0, bufR=0 }
                                              else input{ bufL=ir },
                             output{ bufR=ow })
        in
        loop ir0 ow0

    utf32le_decode :: DecodeBuffer
    utf32le_decode
      input@Buffer{  bufRaw=iraw, bufL=ir0, bufR=iw,  bufSize=_  }
      output@Buffer{ bufRaw=oraw, bufL=_,   bufR=ow0, bufSize=os }
     = let
           loop !ir !ow
             | ow >= os || iw - ir < 4 =  done ir ow
             | otherwise = do
                  c0 <- readWord8Buf iraw ir
                  c1 <- readWord8Buf iraw (ir+1)
                  c2 <- readWord8Buf iraw (ir+2)
                  c3 <- readWord8Buf iraw (ir+3)
                  let x1 = chr4 c3 c2 c1 c0
                  if not (validate x1) then invalid else do
                  ow' <- writeCharBuf oraw ow x1
                  loop (ir+4) ow'
             where
               invalid = if ir > ir0 then done ir ow else ioe_decodingError

           -- lambda-lifted, to avoid thunks being built in the inner-loop:
           done !ir !ow = return (if ir == iw then input{ bufL=0, bufR=0 }
                                              else input{ bufL=ir },
                             output{ bufR=ow })
        in
        loop ir0 ow0

    ioe_decodingError :: IO a
    ioe_decodingError = ioException
         (IOError Nothing InvalidArgument "utf32_decode"
              "invalid UTF-32 byte sequence" Nothing Nothing)

    utf32be_encode :: EncodeBuffer
    utf32be_encode
      input@Buffer{  bufRaw=iraw, bufL=ir0, bufR=iw,  bufSize=_  }
      output@Buffer{ bufRaw=oraw, bufL=_,   bufR=ow0, bufSize=os }
     = let
          done !ir !ow = return (if ir == iw then input{ bufL=0, bufR=0 }
                                             else input{ bufL=ir },
                                 output{ bufR=ow })
          loop !ir !ow
            | ir >= iw     =  done ir ow
            | os - ow < 4  =  done ir ow
            | otherwise = do
               (c,ir') <- readCharBuf iraw ir
               let (c0,c1,c2,c3) = ord4 c
               writeWord8Buf oraw ow     c0
               writeWord8Buf oraw (ow+1) c1
               writeWord8Buf oraw (ow+2) c2
               writeWord8Buf oraw (ow+3) c3
               loop ir' (ow+4)
        in
        loop ir0 ow0

    utf32le_encode :: EncodeBuffer
    utf32le_encode
      input@Buffer{  bufRaw=iraw, bufL=ir0, bufR=iw,  bufSize=_  }
      output@Buffer{ bufRaw=oraw, bufL=_,   bufR=ow0, bufSize=os }
     = let
          done !ir !ow = return (if ir == iw then input{ bufL=0, bufR=0 }
                                             else input{ bufL=ir },
                                 output{ bufR=ow })
          loop !ir !ow
            | ir >= iw     =  done ir ow
            | os - ow < 4  =  done ir ow
            | otherwise = do
               (c,ir') <- readCharBuf iraw ir
               let (c0,c1,c2,c3) = ord4 c
               writeWord8Buf oraw ow     c3
               writeWord8Buf oraw (ow+1) c2
               writeWord8Buf oraw (ow+2) c1
               writeWord8Buf oraw (ow+3) c0
               loop ir' (ow+4)
        in
        loop ir0 ow0

    chr4 :: Word8 -> Word8 -> Word8 -> Word8 -> Char
    chr4 (W8# x1#) (W8# x2#) (W8# x3#) (W8# x4#) =
        C# (chr# (z1# +# z2# +# z3# +# z4#))
        where
          !y1# = word2Int# x1#
          !y2# = word2Int# x2#
          !y3# = word2Int# x3#
          !y4# = word2Int# x4#
          !z1# = uncheckedIShiftL# y1# 24#
          !z2# = uncheckedIShiftL# y2# 16#
          !z3# = uncheckedIShiftL# y3# 8#
          !z4# = y4#
    {-# INLINE chr4 #-}

    ord4 :: Char -> (Word8,Word8,Word8,Word8)
    ord4 c = (fromIntegral (x `shiftR` 24),
              fromIntegral (x `shiftR` 16),
              fromIntegral (x `shiftR` 8),
              fromIntegral x)
      where
        x = ord c
    {-# INLINE ord4 #-}

    validate    :: Char -> Bool
    validate c = (x1 >= 0x0 && x1 < 0xD800) || (x1 > 0xDFFF && x1 <= 0x10FFFF)
       where x1 = ord c
    {-# INLINE validate #-}