Replace.hs

module Main where

import qualified Data.ByteString.Lazy as BL
import qualified Data.ByteString.Lazy.Char8 as BL8
import           System.Environment
import Debug.Trace

main :: IO ()
main = do
  fileName:currentPath:newPath:[] <- getArgs
  bytes <- BL8.readFile fileName
  let newBytes = findAndReplace (BL8.pack currentPath) (BL8.pack newPath) bytes
  BL8.writeFile "new" newBytes
  putStrLn $ "Wrote " <> fileName

findAndReplace
  :: BL8.ByteString
  -- ^ current
  -> BL8.ByteString
  -- ^ new
  -> BL8.ByteString
  -- ^ binary
  -> BL8.ByteString
  -- ^ new binary
findAndReplace current new = go
  where
    go bytes | BL.null bytes = mempty
    go bytes =
      case BL.splitAt (BL8.length current) bytes of
        (ls,rs)
          | ls == current -> new <> go rs
          | otherwise -> BL.take 1 ls <> go (BL.drop 1 ls <> rs)