module Data.ByteString.Char8.Util (
      previous
    , subBS
  ) where

import Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Char8 as BS (drop, index, take)
import Prelude hiding (length)

previous :: Char -> Int -> ByteString -> Int
previous char position byteString
  | BS.index byteString position == char = position
  | otherwise = previous char (position - 1) byteString

subBS :: Int -> Int -> ByteString -> ByteString
subBS offset length = BS.take length . BS.drop offset