import System.Environment
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as BC
import System.Random

main :: IO ()
main = do
    args <- getArgs
    let fileName = head args
    imageFile <- BC.readFile fileName
    glitched <- randomReplaceByte imageFile
    let glitchedFileName = mconcat ["glitched_", fileName]
    BC.writeFile glitchedFileName glitched
    print "all done"


intToChar :: Int -> Char
intToChar int = toEnum safeInt
    where safeInt = int `mod` 255

intToBC :: Int -> BC.ByteString
intToBC int = BC.pack [intToChar int]


replaceByte :: Int -> Int -> BC.ByteString -> BC.ByteString
replaceByte loc charVal bytes = mconcat [before,newChar,after]
    where (before,rest) = BC.splitAt loc bytes
        after = BC.drop 1 rest
        newChar = intToBC charVal


randomReplaceByte :: BC.ByteString -> IO BC.ByteString
randomReplaceByte bytes = do
    let bytesLength = BC.length bytes
    location <- randomRIO (1, bytesLength)
    charVal <- randomRIO (0, 255)
    return (replaceByte location charVal bytes)