{-# 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 U.BufWrite (
        BufHandle(..),
        newBufHandle,
        bPutChar,
        bPutStr,
        bPutFS,
        bPutFZS,
        bPutLitString,
        bFlush,
  ) where

import Language.Haskell.Utility.FastString
import U.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 -> Int -> IO ()
bPutLitString b@(BufHandle buf r hdl) a len = a `seq` 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 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 ()
