{-# LANGUAGE BangPatterns, OverloadedStrings #-}

module Network.HPACK.Huffman.Decode (
  -- * Huffman decoding
    HuffmanDecoding
  , decode
  , decodeHuffman
  ) where

import Control.Exception (throwIO)
import Data.Array (Array, listArray)
import Data.Array.Base (unsafeAt)
import qualified Data.ByteString as BS
import Data.ByteString.Internal (ByteString(..))
import Data.Word (Word8)
import Network.HPACK.Buffer
import Network.HPACK.Huffman.Bit
import Network.HPACK.Huffman.Params
import Network.HPACK.Huffman.Table
import Network.HPACK.Huffman.Tree
import Network.HPACK.Types (DecodeError(..))

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

-- | Huffman decoding.
type HuffmanDecoding = ReadBuffer -> Int -> IO ByteString

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

data Pin = EndOfString
         | Forward {-# UNPACK #-} !Word8 -- node no.
         | GoBack  {-# UNPACK #-} !Word8 -- node no.
                   {-# UNPACK #-} !Word8 -- a decoded value
         | GoBack2 {-# UNPACK #-} !Word8 -- node no.
                   {-# UNPACK #-} !Word8 -- a decoded value
                   {-# UNPACK #-} !Word8 -- a decoded value
         deriving Show

data WayStep = WayStep !(Maybe Int) !(Array Word8 Pin)
type Way256 = Array Word8 WayStep

next :: WayStep -> Word8 -> Pin
next (WayStep _ a16) w = a16 `unsafeAt` fromIntegral w

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

-- | Huffman decoding.
decode :: Buffer -> BufferSize -> HuffmanDecoding
decode buf siz rbuf len = do
    wbuf <- newWorkingBuffer buf siz
    dec wbuf rbuf len
    toByteString wbuf

dec :: WorkingBuffer -> ReadBuffer -> Int -> IO ()
dec wbuf rbuf len = go len (way256 `unsafeAt` 0)
  where
    go 0 way0 = case way0 of
        WayStep Nothing  _ -> throwIO IllegalEos
        WayStep (Just i) _
          | i <= 8         -> return ()
          | otherwise      -> throwIO TooLongEos
    go !n !way0 = do
        w <- getByte rbuf
        way <- doit way0 w
        go (n - 1) way
    doit !way !w = case next way w of
        EndOfString -> throwIO EosInTheMiddle
        Forward n   -> return $ way256 `unsafeAt` fromIntegral n
        GoBack  n v -> do
            writeWord8 wbuf v
            return $ way256 `unsafeAt` fromIntegral n
        GoBack2 n v1 v2 -> do
            writeWord8 wbuf v1
            writeWord8 wbuf v2
            return $ way256 `unsafeAt` fromIntegral n

decodeHuffman :: ByteString -> IO ByteString
decodeHuffman bs = withTemporaryBuffer 4096 $ \wbuf ->
    withReadBuffer bs $ \rbuf -> dec wbuf rbuf (BS.length bs)

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

way256 :: Way256
way256 = construct $ toHTree huffmanTable

construct :: HTree -> Way256
construct decoder = listArray (0,255) $ map to16ways $ flatten decoder
  where
    to16ways x = WayStep ei a16
      where
        !ei = eosInfo x
        !a16 = listArray (0,255) $ map (step decoder x Non) bits8s

data Chara = Non
           | One !Word8
           | Two !Word8 !Word8

inc :: Chara -> Word8 -> Chara
inc Non w     = One w
inc (One v) w = Two v w
inc _       _ = error "inc"

step :: HTree -> HTree -> Chara -> [B] -> Pin
step root (Tip _ v)     x  bss
  | v == idxEos                     = EndOfString
  | otherwise                       = let !w = fromIntegral v
                                          !x' = inc x w
                                      in step root root x' bss
step _    (Bin _ n _ _) Non       [] = Forward (fromIntegral n)
step _    (Bin _ n _ _) (One w)   [] = GoBack (fromIntegral n) w
step _    (Bin _ n _ _) (Two w z) [] = GoBack2 (fromIntegral n) w z
step root (Bin _ _ l _) mx    (F:bs) = step root l mx bs
step root (Bin _ _ _ r) mx    (T:bs) = step root r mx bs

bits8s :: [[B]]
bits8s = [
    [F,F,F,F,F,F,F,F]
  , [F,F,F,F,F,F,F,T]
  , [F,F,F,F,F,F,T,F]
  , [F,F,F,F,F,F,T,T]
  , [F,F,F,F,F,T,F,F]
  , [F,F,F,F,F,T,F,T]
  , [F,F,F,F,F,T,T,F]
  , [F,F,F,F,F,T,T,T]
  , [F,F,F,F,T,F,F,F]
  , [F,F,F,F,T,F,F,T]
  , [F,F,F,F,T,F,T,F]
  , [F,F,F,F,T,F,T,T]
  , [F,F,F,F,T,T,F,F]
  , [F,F,F,F,T,T,F,T]
  , [F,F,F,F,T,T,T,F]
  , [F,F,F,F,T,T,T,T]
  , [F,F,F,T,F,F,F,F]
  , [F,F,F,T,F,F,F,T]
  , [F,F,F,T,F,F,T,F]
  , [F,F,F,T,F,F,T,T]
  , [F,F,F,T,F,T,F,F]
  , [F,F,F,T,F,T,F,T]
  , [F,F,F,T,F,T,T,F]
  , [F,F,F,T,F,T,T,T]
  , [F,F,F,T,T,F,F,F]
  , [F,F,F,T,T,F,F,T]
  , [F,F,F,T,T,F,T,F]
  , [F,F,F,T,T,F,T,T]
  , [F,F,F,T,T,T,F,F]
  , [F,F,F,T,T,T,F,T]
  , [F,F,F,T,T,T,T,F]
  , [F,F,F,T,T,T,T,T]
  , [F,F,T,F,F,F,F,F]
  , [F,F,T,F,F,F,F,T]
  , [F,F,T,F,F,F,T,F]
  , [F,F,T,F,F,F,T,T]
  , [F,F,T,F,F,T,F,F]
  , [F,F,T,F,F,T,F,T]
  , [F,F,T,F,F,T,T,F]
  , [F,F,T,F,F,T,T,T]
  , [F,F,T,F,T,F,F,F]
  , [F,F,T,F,T,F,F,T]
  , [F,F,T,F,T,F,T,F]
  , [F,F,T,F,T,F,T,T]
  , [F,F,T,F,T,T,F,F]
  , [F,F,T,F,T,T,F,T]
  , [F,F,T,F,T,T,T,F]
  , [F,F,T,F,T,T,T,T]
  , [F,F,T,T,F,F,F,F]
  , [F,F,T,T,F,F,F,T]
  , [F,F,T,T,F,F,T,F]
  , [F,F,T,T,F,F,T,T]
  , [F,F,T,T,F,T,F,F]
  , [F,F,T,T,F,T,F,T]
  , [F,F,T,T,F,T,T,F]
  , [F,F,T,T,F,T,T,T]
  , [F,F,T,T,T,F,F,F]
  , [F,F,T,T,T,F,F,T]
  , [F,F,T,T,T,F,T,F]
  , [F,F,T,T,T,F,T,T]
  , [F,F,T,T,T,T,F,F]
  , [F,F,T,T,T,T,F,T]
  , [F,F,T,T,T,T,T,F]
  , [F,F,T,T,T,T,T,T]
  , [F,T,F,F,F,F,F,F]
  , [F,T,F,F,F,F,F,T]
  , [F,T,F,F,F,F,T,F]
  , [F,T,F,F,F,F,T,T]
  , [F,T,F,F,F,T,F,F]
  , [F,T,F,F,F,T,F,T]
  , [F,T,F,F,F,T,T,F]
  , [F,T,F,F,F,T,T,T]
  , [F,T,F,F,T,F,F,F]
  , [F,T,F,F,T,F,F,T]
  , [F,T,F,F,T,F,T,F]
  , [F,T,F,F,T,F,T,T]
  , [F,T,F,F,T,T,F,F]
  , [F,T,F,F,T,T,F,T]
  , [F,T,F,F,T,T,T,F]
  , [F,T,F,F,T,T,T,T]
  , [F,T,F,T,F,F,F,F]
  , [F,T,F,T,F,F,F,T]
  , [F,T,F,T,F,F,T,F]
  , [F,T,F,T,F,F,T,T]
  , [F,T,F,T,F,T,F,F]
  , [F,T,F,T,F,T,F,T]
  , [F,T,F,T,F,T,T,F]
  , [F,T,F,T,F,T,T,T]
  , [F,T,F,T,T,F,F,F]
  , [F,T,F,T,T,F,F,T]
  , [F,T,F,T,T,F,T,F]
  , [F,T,F,T,T,F,T,T]
  , [F,T,F,T,T,T,F,F]
  , [F,T,F,T,T,T,F,T]
  , [F,T,F,T,T,T,T,F]
  , [F,T,F,T,T,T,T,T]
  , [F,T,T,F,F,F,F,F]
  , [F,T,T,F,F,F,F,T]
  , [F,T,T,F,F,F,T,F]
  , [F,T,T,F,F,F,T,T]
  , [F,T,T,F,F,T,F,F]
  , [F,T,T,F,F,T,F,T]
  , [F,T,T,F,F,T,T,F]
  , [F,T,T,F,F,T,T,T]
  , [F,T,T,F,T,F,F,F]
  , [F,T,T,F,T,F,F,T]
  , [F,T,T,F,T,F,T,F]
  , [F,T,T,F,T,F,T,T]
  , [F,T,T,F,T,T,F,F]
  , [F,T,T,F,T,T,F,T]
  , [F,T,T,F,T,T,T,F]
  , [F,T,T,F,T,T,T,T]
  , [F,T,T,T,F,F,F,F]
  , [F,T,T,T,F,F,F,T]
  , [F,T,T,T,F,F,T,F]
  , [F,T,T,T,F,F,T,T]
  , [F,T,T,T,F,T,F,F]
  , [F,T,T,T,F,T,F,T]
  , [F,T,T,T,F,T,T,F]
  , [F,T,T,T,F,T,T,T]
  , [F,T,T,T,T,F,F,F]
  , [F,T,T,T,T,F,F,T]
  , [F,T,T,T,T,F,T,F]
  , [F,T,T,T,T,F,T,T]
  , [F,T,T,T,T,T,F,F]
  , [F,T,T,T,T,T,F,T]
  , [F,T,T,T,T,T,T,F]
  , [F,T,T,T,T,T,T,T]
  , [T,F,F,F,F,F,F,F]
  , [T,F,F,F,F,F,F,T]
  , [T,F,F,F,F,F,T,F]
  , [T,F,F,F,F,F,T,T]
  , [T,F,F,F,F,T,F,F]
  , [T,F,F,F,F,T,F,T]
  , [T,F,F,F,F,T,T,F]
  , [T,F,F,F,F,T,T,T]
  , [T,F,F,F,T,F,F,F]
  , [T,F,F,F,T,F,F,T]
  , [T,F,F,F,T,F,T,F]
  , [T,F,F,F,T,F,T,T]
  , [T,F,F,F,T,T,F,F]
  , [T,F,F,F,T,T,F,T]
  , [T,F,F,F,T,T,T,F]
  , [T,F,F,F,T,T,T,T]
  , [T,F,F,T,F,F,F,F]
  , [T,F,F,T,F,F,F,T]
  , [T,F,F,T,F,F,T,F]
  , [T,F,F,T,F,F,T,T]
  , [T,F,F,T,F,T,F,F]
  , [T,F,F,T,F,T,F,T]
  , [T,F,F,T,F,T,T,F]
  , [T,F,F,T,F,T,T,T]
  , [T,F,F,T,T,F,F,F]
  , [T,F,F,T,T,F,F,T]
  , [T,F,F,T,T,F,T,F]
  , [T,F,F,T,T,F,T,T]
  , [T,F,F,T,T,T,F,F]
  , [T,F,F,T,T,T,F,T]
  , [T,F,F,T,T,T,T,F]
  , [T,F,F,T,T,T,T,T]
  , [T,F,T,F,F,F,F,F]
  , [T,F,T,F,F,F,F,T]
  , [T,F,T,F,F,F,T,F]
  , [T,F,T,F,F,F,T,T]
  , [T,F,T,F,F,T,F,F]
  , [T,F,T,F,F,T,F,T]
  , [T,F,T,F,F,T,T,F]
  , [T,F,T,F,F,T,T,T]
  , [T,F,T,F,T,F,F,F]
  , [T,F,T,F,T,F,F,T]
  , [T,F,T,F,T,F,T,F]
  , [T,F,T,F,T,F,T,T]
  , [T,F,T,F,T,T,F,F]
  , [T,F,T,F,T,T,F,T]
  , [T,F,T,F,T,T,T,F]
  , [T,F,T,F,T,T,T,T]
  , [T,F,T,T,F,F,F,F]
  , [T,F,T,T,F,F,F,T]
  , [T,F,T,T,F,F,T,F]
  , [T,F,T,T,F,F,T,T]
  , [T,F,T,T,F,T,F,F]
  , [T,F,T,T,F,T,F,T]
  , [T,F,T,T,F,T,T,F]
  , [T,F,T,T,F,T,T,T]
  , [T,F,T,T,T,F,F,F]
  , [T,F,T,T,T,F,F,T]
  , [T,F,T,T,T,F,T,F]
  , [T,F,T,T,T,F,T,T]
  , [T,F,T,T,T,T,F,F]
  , [T,F,T,T,T,T,F,T]
  , [T,F,T,T,T,T,T,F]
  , [T,F,T,T,T,T,T,T]
  , [T,T,F,F,F,F,F,F]
  , [T,T,F,F,F,F,F,T]
  , [T,T,F,F,F,F,T,F]
  , [T,T,F,F,F,F,T,T]
  , [T,T,F,F,F,T,F,F]
  , [T,T,F,F,F,T,F,T]
  , [T,T,F,F,F,T,T,F]
  , [T,T,F,F,F,T,T,T]
  , [T,T,F,F,T,F,F,F]
  , [T,T,F,F,T,F,F,T]
  , [T,T,F,F,T,F,T,F]
  , [T,T,F,F,T,F,T,T]
  , [T,T,F,F,T,T,F,F]
  , [T,T,F,F,T,T,F,T]
  , [T,T,F,F,T,T,T,F]
  , [T,T,F,F,T,T,T,T]
  , [T,T,F,T,F,F,F,F]
  , [T,T,F,T,F,F,F,T]
  , [T,T,F,T,F,F,T,F]
  , [T,T,F,T,F,F,T,T]
  , [T,T,F,T,F,T,F,F]
  , [T,T,F,T,F,T,F,T]
  , [T,T,F,T,F,T,T,F]
  , [T,T,F,T,F,T,T,T]
  , [T,T,F,T,T,F,F,F]
  , [T,T,F,T,T,F,F,T]
  , [T,T,F,T,T,F,T,F]
  , [T,T,F,T,T,F,T,T]
  , [T,T,F,T,T,T,F,F]
  , [T,T,F,T,T,T,F,T]
  , [T,T,F,T,T,T,T,F]
  , [T,T,F,T,T,T,T,T]
  , [T,T,T,F,F,F,F,F]
  , [T,T,T,F,F,F,F,T]
  , [T,T,T,F,F,F,T,F]
  , [T,T,T,F,F,F,T,T]
  , [T,T,T,F,F,T,F,F]
  , [T,T,T,F,F,T,F,T]
  , [T,T,T,F,F,T,T,F]
  , [T,T,T,F,F,T,T,T]
  , [T,T,T,F,T,F,F,F]
  , [T,T,T,F,T,F,F,T]
  , [T,T,T,F,T,F,T,F]
  , [T,T,T,F,T,F,T,T]
  , [T,T,T,F,T,T,F,F]
  , [T,T,T,F,T,T,F,T]
  , [T,T,T,F,T,T,T,F]
  , [T,T,T,F,T,T,T,T]
  , [T,T,T,T,F,F,F,F]
  , [T,T,T,T,F,F,F,T]
  , [T,T,T,T,F,F,T,F]
  , [T,T,T,T,F,F,T,T]
  , [T,T,T,T,F,T,F,F]
  , [T,T,T,T,F,T,F,T]
  , [T,T,T,T,F,T,T,F]
  , [T,T,T,T,F,T,T,T]
  , [T,T,T,T,T,F,F,F]
  , [T,T,T,T,T,F,F,T]
  , [T,T,T,T,T,F,T,F]
  , [T,T,T,T,T,F,T,T]
  , [T,T,T,T,T,T,F,F]
  , [T,T,T,T,T,T,F,T]
  , [T,T,T,T,T,T,T,F]
  , [T,T,T,T,T,T,T,T]
  ]

