    module General.Makefile(parseMakefile) where

    import qualified Data.ByteString.Char8 as BS
    import Data.Char

    endsSlash :: BS.ByteString -> Bool
    endsSlash = BS.isSuffixOf (BS.singleton '\\')

    wordsMakefile :: BS.ByteString -> [BS.ByteString]
    wordsMakefile = f . BS.splitWith isSpace
        where
            f (x:xs) | BS.null x = f xs
            f (x:y:xs) | endsSlash x = f $ BS.concat [BS.init x, BS.singleton ' ', y] : xs
            f (x:xs) = x : f xs
            f [] = []

    parseMakefile :: BS.ByteString -> [(BS.ByteString, [BS.ByteString])]
    parseMakefile = concatMap f . join . linesCR
        where
            join xs = case span endsSlash xs of
                ([], []) -> []
                (xs, []) -> [BS.unwords $ map BS.init xs]
                ([], y:ys) -> y : join ys
                (xs, y:ys) -> BS.unwords (map BS.init xs ++ [y]) : join ys

            f x = [(a, wordsMakefile $ BS.drop 1 b) | a <- wordsMakefile a]
                where (a,b) = BS.break (== ':') $ BS.takeWhile (/= '#') x

    -- | This is a hot-spot, so optimised
    linesCR :: BS.ByteString -> [BS.ByteString]
    linesCR x = case BS.split '\n' x of
        x:xs | Just ('\r',x) <- unsnoc x -> x : map (\x -> case unsnoc x of Just ('\r',x) -> x; _ -> x) xs
        xs -> xs
        where
            -- the ByteString unsnoc was introduced in a newer version
            unsnoc x | BS.null x = Nothing
                     | otherwise = Just (BS.last x, BS.init x)