import System.Environment
import System.Directory
import System.IO
import Data.List
import Control.Exception
import Control.Monad(when)

fileName = "todo.txt"

dispatch :: String -> String -> IO ()
dispatch file "add" = add file
dispatch file "view" = view file
dispatch file "rm" = remove file
dispatch file _ = do
    putStrLn "Operations supported:\nadd - Append Item\nview - Inspect Item\nrm - Remove Item"

view file = do
    contents <- readFile file
    let todoTasks = lines contents
    putStr $ unlines $ number todoTasks

add file = do
    todoItem <- getLine
    when (not $ null todoItem) (do
        appendFile file todoItem)

remove file = do
    contents <- readFile file
    numberString <- getLine
    let todoTasks = lines contents
        number = read numberString
        newTodoList = unlines $ delete (todoTasks !! number) todoTasks
    bracketOnError (openTempFile "." "temp") 
        (\(tempName,tempHandle) -> do
            hClose tempHandle
            removeFile tempName)
        (\(tempName,tempHandle) -> do
            hPutStr tempHandle newTodoList
            hClose tempHandle
            removeFile file
            renameFile tempName file)


number task = zipWith (\n line -> show n ++ " - " ++ line) [0..] task

main = do
    line <- getLine
    if null line then return ()
        else (do
            dispatch fileName line
            main)