{-# LANGUAGE
    BangPatterns
  , UnboxedTuples
  , UnicodeSyntax
  #-}
-- | FIXME
module Codec.Audio.WavPack.Words
    ( WordsData(..)
    )
    where
import Codec.Audio.WavPack.Entropy
import Codec.Audio.WavPack.Internal
import Data.Bits
import Data.Bitstream.Generic (Bitstream)
import qualified Data.Bitstream.Generic as B
import Data.Word
import Prelude.Unicode

-- | FIXME
data WordsData
    = WordsData {
        wdBitrateDelta ∷ !(Word32, Word32)
      , wdBitrateAcc   ∷ !(Word32, Word32)
      , wdPendingData  ∷ !Word32
      , wdHoldingOne   ∷ !Word32
      , wdZeroesAcc    ∷ !Word32
      , wdHoldingZero  ∷ !Bool
      , wdPendingCount ∷ !Int
      , wdEntropyData  ∷ !(EntropyData, EntropyData)
      }
    deriving (Eq, Show)

-- This is an optimized version of 'getWord' that is used for lossless
-- only (error_limit ≡ 0). Also, rather than obtaining a single
-- sample, it can be used to obtain an entire buffer of either mono or
-- stereo samples.
--getWordsLossless ∷ 

-- Read a single unsigned value from the specified bitstream with a
-- value from 0 to maxCode. If there are exactly a power of two number
-- of possible codes then this will read a fixed number of bits;
-- otherwise it reads the minimum number of bits and then determines
-- whether another bit is needed to define the code.
readCode ∷ Bitstream bs ⇒ bs → Word32 → (# Word32, bs #)
{-# INLINEABLE readCode #-}
readCode bs 0       = (# 0, bs #)
readCode bs 1       = (# b2n (B.head bs), B.tail bs #)
readCode bs maxCode
    = let !bitCount = countBits maxCode
          !extras   = bit bitCount - maxCode - 1
          !code     = B.toBits (B.take (bitCount - 1) bs)
          (# code', bitCount' #)
                    = if code ≥ extras then
                          (# (code `shiftL` 1)
                             - extras
                             + b2n (bs B.!! bitCount)
                           , bitCount #)
                      else
                          (# code, bitCount - 1 #)
          !bs'      = B.drop bitCount' bs
      in
        (# code', bs' #)