module Rattletrap.BitString where

import qualified Data.Bits as Bits
import qualified Data.ByteString as ByteString

data BitString = BitString
  { byteString :: ByteString.ByteString
  , offset :: Int
  }
  deriving (Eq, Show)

fromByteString :: ByteString.ByteString -> BitString
fromByteString byteString = BitString { byteString, offset = 0 }

pop :: BitString -> Maybe (Bool, BitString)
pop old = do
  (word, byteString) <- ByteString.uncons $ byteString old
  let
    bit = Bits.testBit word $ offset old
    new = if offset old == 7
      then fromByteString byteString
      else old { offset = offset old + 1 }
  pure (bit, new)