    {-# LANGUAGE BangPatterns #-}

    -----------------------------------------------------------------------------
    --
    -- Fast write-buffered Handles
    --
    -- (c) The University of Glasgow 2005-2006
    --
    -- This is a simple abstraction over Handles that offers very fast write
    -- buffering, but without the thread safety that Handles provide.  It's used
    -- to save time in Pretty.printDoc.
    --
    -----------------------------------------------------------------------------

    module BufWrite (
            BufHandle(..),
            newBufHandle,
            bPutChar,
            bPutStr,
            bPutFS,
            bPutFZS,
            bPutLitString,
            bFlush,
      ) where

    import FastString
    import FastTypes
    import FastMutInt

    import Control.Monad    ( when )
    import Data.ByteString (ByteString)
    import qualified Data.ByteString.Unsafe as BS
    import Data.Char        ( ord )
    import Foreign
    import Foreign.C.String
    import System.IO

    -- -----------------------------------------------------------------------------

    data BufHandle = BufHandle {-#UNPACK#-}!(Ptr Word8)
                               {-#UNPACK#-}!FastMutInt
                               Handle

    newBufHandle :: Handle -> IO BufHandle
    newBufHandle hdl = do
      ptr <- mallocBytes buf_size
      r <- newFastMutInt
      writeFastMutInt r 0
      return (BufHandle ptr r hdl)

    buf_size :: Int
    buf_size = 8192

    bPutChar :: BufHandle -> Char -> IO ()
    bPutChar b@(BufHandle buf r hdl) !c = do
      i <- readFastMutInt r
      if (i >= buf_size)
            then do hPutBuf hdl buf buf_size
                    writeFastMutInt r 0
                    bPutChar b c
            else do pokeElemOff buf i (fromIntegral (ord c) :: Word8)
                    writeFastMutInt r (i+1)

    bPutStr :: BufHandle -> String -> IO ()
    bPutStr (BufHandle buf r hdl) !str = do
      i <- readFastMutInt r
      loop str i
      where loop _ i | i `seq` False = undefined
            loop "" i = do writeFastMutInt r i; return ()
            loop (c:cs) i
               | i >= buf_size = do
                    hPutBuf hdl buf buf_size
                    loop (c:cs) 0
               | otherwise = do
                    pokeElemOff buf i (fromIntegral (ord c))
                    loop cs (i+1)

    bPutFS :: BufHandle -> FastString -> IO ()
    bPutFS b fs = bPutBS b $ fastStringToByteString fs

    bPutFZS :: BufHandle -> FastZString -> IO ()
    bPutFZS b fs = bPutBS b $ fastZStringToByteString fs

    bPutBS :: BufHandle -> ByteString -> IO ()
    bPutBS b bs = BS.unsafeUseAsCStringLen bs $ bPutCStringLen b

    bPutCStringLen :: BufHandle -> CStringLen -> IO ()
    bPutCStringLen b@(BufHandle buf r hdl) cstr@(ptr, len) = do
      i <- readFastMutInt r
      if (i + len) >= buf_size
            then do hPutBuf hdl buf i
                    writeFastMutInt r 0
                    if (len >= buf_size)
                        then hPutBuf hdl ptr len
                        else bPutCStringLen b cstr
            else do
                    copyBytes (buf `plusPtr` i) ptr len
                    writeFastMutInt r (i + len)

    bPutLitString :: BufHandle -> LitString -> FastInt -> IO ()
    bPutLitString b@(BufHandle buf r hdl) a len_ = a `seq` do
      let len = iBox len_
      i <- readFastMutInt r
      if (i+len) >= buf_size
            then do hPutBuf hdl buf i
                    writeFastMutInt r 0
                    if (len >= buf_size)
                        then hPutBuf hdl a len
                        else bPutLitString b a len_
            else do
                    copyBytes (buf `plusPtr` i) a len
                    writeFastMutInt r (i+len)

    bFlush :: BufHandle -> IO ()
    bFlush (BufHandle buf r hdl) = do
      i <- readFastMutInt r
      when (i > 0) $ hPutBuf hdl buf i
      free buf
      return ()