module Main where

import Data.Char
import Data.Sequence hiding (null)
import System.Console.Haskeline
import System.Environment

name :: String
name = "brainfuck"

version :: String
version = "0.1.0"

prompt :: String
prompt = name ++ "> "

printUsage :: IO ()
printUsage = do printVersion
                putStrLn("\nUsage: " ++
                         "\n\twithout arguments  - runs REPL" ++
                         "\n\t-h/--help          - display this help message" ++
                         "\n\nMore information can be found on " ++
                         "https://github.com/hellerve/unlambda")

printVersion :: IO ()
printVersion = putStrLn (name ++ " Version " ++ version)

printCommands :: IO ()
printCommands = putStrLn "Press Ctrl-C to exit interpreter"

program :: String -> Seq Int -> Int -> IO ()
program "" _ _ = return ()
program ('>' : l) tape ptr = program l tape (ptr+1)
program ('<' : l) tape ptr = program l tape (ptr-1)
program ('+' : l) tape ptr = let newtape = update ptr ((index tape ptr) + 1) tape
                             in  program l newtape ptr
program ('-' : l) tape ptr = let newtape = update ptr ((index tape ptr) - 1) tape
                             in  program l newtape ptr
program ('.' : l) tape ptr = do putChar $ chr $ index tape ptr
                                program l tape ptr
program (',' : l) tape ptr = do x <- getChar
                                let newtape = update ptr (ord x) tape
                                program l newtape ptr
program (x : _) _ _ = putStrLn ("Unknown instruction: " ++ [x])

main :: IO ()
main = do
        args <- getArgs
        if null args
            then do printVersion
                    printCommands
                    putStrLn ""
                    repl
            else
                if(head args ==  "-h") || (head args == "--help")
                    then printUsage
                    else exec args

exec :: [String] -> IO ()
exec _ = undefined

getInput :: IO String
getInput = runInputT defaultSettings repl_
    where repl_ = do
          x <- getInputLine "> "
          case x of
            Nothing -> return ""
            Just i  -> return i

repl :: IO ()
repl = do input <- getInput
          case input of
            ""     -> repl
            "quit" -> putStrLn "Bye"
            x      -> do program x (zeroes 30000 empty) 0
                         putStrLn ""
                         repl
    where zeroes :: Int -> Seq Int -> Seq Int
          zeroes 0 l = l
          zeroes n l = zeroes (n-1) (l |> 0)