{-# LANGUAGE MultiWayIf #-}

import Data.List.Split  (splitOn)
import System.Directory (setCurrentDirectory)
import System.Exit      (exitSuccess)
import System.IO
import System.Process   (callCommand)

prompt :: IO ()
prompt = do
  input <- moshReadLine promptStringOne
  moshExecute input
  prompt

moshReadLine :: String -> IO String
moshReadLine ps1 = do
  putStr ps1
  hFlush stdout
  getLine

moshExecute :: String -> IO ()
moshExecute input = do
  if
    | command == "exit" -> exitSuccess
    | command == "help" -> moshHelp
    | command == "cd"   -> changeDirectory path
    | otherwise         -> callCommand input
  where
    command = head (splitOn " " input)
    path    = last (splitOn " " input)

changeDirectory :: FilePath -> IO ()
changeDirectory path = do
  setCurrentDirectory path

moshHelp :: IO ()
moshHelp = do
  putStrLn "---------------------"
  putStrLn "MoSH -- Monadic Shell"
  putStrLn "Author: sajenim"
  putStrLn "---------------------"
  putStrLn "Type program names and arguments, and hit enter."
  putStrLn ""
  putStrLn "The following are built in:"
  putStr (unlines (prepend "    " builtinCommands))
  putStrLn ""
  putStrLn "Use the man command for information on other programs"

builtinCommands :: [String]
builtinCommands = [ "cd"
                  , "help"
                  , "exit"
                  ]

promptStringOne :: String
promptStringOne = "> "

prepend :: String -> [String] -> [String]
prepend s = map (s ++)

main :: IO ()
main = do
  prompt