{-# LANGUAGE RecordWildCards #-}
module System.Console.CmdArgs.Explicit.SplitJoin(splitArgs, joinArgs) where

import Data.Char
import Data.Maybe


-- | Given a sequence of arguments, join them together in a manner that could be used on
--   the command line, giving preference to the Windows @cmd@ shell quoting conventions.
--
--   For an alternative version, intended for actual running the result in a shell, see "System.Process.showCommandForUser"
joinArgs :: [String] -> String
joinArgs = unwords . map f
    where
        f x = q ++ g x ++ q
            where
                hasSpace = any isSpace x
                q = ['\"' | hasSpace || null x]

                g ('\\':'\"':xs) = '\\':'\\':'\\':'\"': g xs
                g "\\" | hasSpace = "\\\\"
                g ('\"':xs) = '\\':'\"': g xs
                g (x:xs) = x : g xs
                g [] = []


data State = Init -- either I just started, or just emitted something
           | Norm -- I'm seeing characters
           | Quot -- I've seen a quote

-- | Given a string, split into the available arguments. The inverse of 'joinArgs'.
splitArgs :: String -> [String]
splitArgs = join . f Init
    where
        -- Nothing is start a new string
        -- Just x is accumulate onto the existing string
        join :: [Maybe Char] -> [String]
        join [] = []
        join xs = map fromJust a : join (drop 1 b)
            where (a,b) = break isNothing xs

        f Init (x:xs) | isSpace x = f Init xs
        f Init "\"\"" = [Nothing]
        f Init "\"" = [Nothing]
        f Init xs = f Norm xs
        f m ('\"':'\"':'\"':xs) = Just '\"' : f m xs
        f m ('\\':'\"':xs) = Just '\"' : f m xs
        f m ('\\':'\\':'\"':xs) = Just '\\' : f m ('\"':xs)
        f Norm ('\"':xs) = f Quot xs
        f Quot ('\"':'\"':xs) = Just '\"' : f Norm xs
        f Quot ('\"':xs) = f Norm xs
        f Norm (x:xs) | isSpace x = Nothing : f Init xs
        f m (x:xs) = Just x : f m xs
        f m [] = []