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

import Data.ByteString.Lazy.Char8 (ByteString)
import qualified Data.ByteString.Lazy.Char8 as BS (drop, index, take)
import Data.Int (Int64)
import Prelude hiding (length)

previous :: Char -> Int64 -> ByteString -> Int64
previous char position byteString
  | BS.index byteString position == char = position
  | otherwise = previous char (position - 1) byteString

subBS :: Int64 -> Int64 -> ByteString -> ByteString
subBS offset length = BS.take length . BS.drop offset