import Data Char toUpper type Todo String type TodoList Todo numberLis

import Data.Char (toUpper)

type Todo     = String
type TodoList = [Todo]

numberList :: TodoList -> [String]
numberList = zipWith (\a b -> show a ++ ". " ++ b) [1..]

removeElem :: Int -> [a] -> [a]
removeElem i xs = let (as, bs) = splitAt i xs
                  in as ++ drop 1 bs
                  
printStrs :: [String] -> IO ()
printStrs = mapM_ putStrLn

showTodoList :: TodoList -> String
showTodoList [] = "No entries"
showTodoList xs = unlines xs

addTodo :: TodoList -> Todo -> TodoList
addTodo = flip (:)

removeTodo :: TodoList -> Int -> TodoList
removeTodo = flip removeElem

prompt :: String -> IO String
prompt xs = putStrLn xs >> getLine

todoOp :: TodoList -> Char -> IO TodoList
todoOp xs 'V' = printStrs xs  >> return xs
todoOp xs 'A' = addTodo xs <$> prompt "What would you like to add?"
todoOp [] 'D' = putStrLn (showTodoList []) >> return []
todoOp xs 'D' = printStrs xs >> removeTodo xs <$> prompt "Which line do you want to remove? " --> ERROR
todoOp xs _   = putStrLn "Operation not supported" >> return xs