計算機科学のブログ

name:                lesson
version:             0.1.0.0
github:              "githubuser/lesson"
license:             BSD3
author:              "Author name here"
maintainer:          "example@example.com"
copyright:           "2022 Author name here"

extra-source-files:
- README.md
- ChangeLog.md

# Metadata used when publishing your package
# synopsis:            Short description of your package
# category:            Web

# To avoid duplicated efforts in documentation and dealing with the
# complications of embedding Haddock markup inside cabal files, it is
# common to point users to the README.md file.
description:         Please see the README on GitHub at <https://github.com/githubuser/lesson#readme>

dependencies:
- base >= 4.7 && < 5
- bytestring
- random

library:
  source-dirs: src

executables:
  lesson-exe:
    main:                Main.hs
    source-dirs:         app
    ghc-options:
    - -threaded
    - -rtsopts
    - -with-rtsopts=-N
    dependencies:
    - lesson

tests:
  lesson-test:
    main:                Spec.hs
    source-dirs:         test
    ghc-options:
    - -threaded
    - -rtsopts
    - -with-rtsopts=-N
    dependencies:
    - lesson

default-extensions: OverloadedStrings

module Main where

import qualified Data.ByteString.Char8 as BC
import Lib (randomReverseBytes)

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

module Lib (randomReverseBytes) where

import qualified Data.ByteString.Char8 as BC
import System.Random (randomRIO)

reverseBytes :: Int -> Int -> BC.ByteString -> BC.ByteString
reverseBytes start size bytes =
  let (before, rest) = BC.splitAt start bytes
      (target, after) = BC.splitAt size rest
      changed = BC.reverse target
   in mconcat [before, changed, after]

randomReverseBytes :: BC.ByteString -> IO BC.ByteString
randomReverseBytes bytes = do
  let sectionSize = 25
  let bytesLength = BC.length bytes
  start <- randomRIO (0, bytesLength - sectionSize)
  return $ reverseBytes start sectionSize bytes

% stack exec lesson-exe
"all done"
% open glitched_lovecraft.jpg 
% stack exec lesson-exe      
"all done"
% open glitched_lovecraft.jpg
%