module Codec.Compression.Utils where

import Data.ByteString.Lazy (ByteString)
import qualified Data.ByteString.Lazy as BS
import Data.ByteString.Base (LazyByteString(LPS))
import Data.Word (Word8)

genericSplitAtExactly :: Integral a => a -> [b] -> Maybe ([b], [b])
genericSplitAtExactly 0 xs = return ([], xs)
genericSplitAtExactly (n+1) (x:xs) = do (ys, zs) <- genericSplitAtExactly n xs
                                        return (x:ys, zs)
genericSplitAtExactly _ _ = Nothing

genericSplitAtExactlyBS :: Integral a
                        => a -> ByteString -> Maybe (ByteString, ByteString)
genericSplitAtExactlyBS i bs = let i' = fromIntegral i
                               in if i' > BS.length bs
                                  then Nothing
                                  else Just (BS.splitAt i' bs)

headTail :: ByteString -> Maybe (Word8, ByteString)
headTail bs = if BS.null bs
              then Nothing
              else Just (BS.head bs, BS.tail bs)

-- XXX The real append is too strict
myAppend :: ByteString -> ByteString -> ByteString
myAppend (LPS xs) (LPS ys) = LPS (xs ++ ys)