Small todo-program in haskell.

todo.hs

module Todo where

import Data.List
import System.Environment
import System.IO
import System.Directory

configPath :: String
configPath = "todotest.txt"

getTasks :: IO(String)
getTasks = do
  str <- readFile configPath
  if (length str) > 0 then
    return $ "Todo: *" ++ (intercalate " *" $ lines str)
  else return "Nothing to do :)"

newLine :: String -> String
newLine str = str ++ "\n"

remove :: [(Int,String)] -> [String] -> String -> Handle -> IO()
remove [] _ tmp _ = do
  putStrLn "Invalid task number."
  removeFile tmp
remove argnum c tmp tmph
  | num > length c || num <= 0 = do
    putStrLn $ "Task " ++ show num ++ " does not exist!"
    removeFile tmp
  | otherwise = do
    mapM_ (\s -> hPutStr tmph $ newLine s) $ take (num-1) c ++ drop num c
    removeFile configPath
    renameFile tmp configPath
  where num = fst $ head argnum

handleArg :: String -> IO()
handleArg arg
  | head arg == '-' = do
    contents <- (readFile configPath)
    (tmp, tmph) <- openTempFile "." "temp"
    remove (reads $ drop 1 arg :: [(Int,String)]) (lines contents) tmp tmph
    hClose tmph
  | otherwise = appendFile configPath $ newLine arg

main = do
  args <- getArgs
  if length args == 0 then do
      tasks <- getTasks
      putStrLn tasks
    else if length args > 1
      then putStrLn "Too many arguments."
      else handleArg $ head args