{-# OPTIONS_LHC -fffi #-}
module System (
    ExitCode(ExitSuccess,ExitFailure),
    getArgs, getProgName, getEnv, system, exitWith, exitFailure
  ) where

import Foreign.C.String
import Foreign.Ptr
import Foreign.Storable
import Foreign.Marshal.Alloc
import Foreign.C.Types
import Lhc.IO(exitFailure)
import qualified Lhc.Options

data ExitCode = ExitSuccess | ExitFailure !Int
            deriving (Eq, Ord, Read, Show)

getArgs     :: IO [String]
getProgName :: IO String
getEnv      :: String -> IO String
system      :: String -> IO ExitCode
exitWith    :: ExitCode -> IO a
exitFailure :: IO a


exitWith ExitSuccess = do
    c_exit 0
    return undefined
exitWith (ExitFailure n) = do
    c_exit n
    return undefined


getProgName = case Lhc.Options.target of
    Lhc.Options.GhcHs -> ghc_getProgName
    _ -> peek lhc_progname >>= peekCString

getArgs = case Lhc.Options.target of
    Lhc.Options.GhcHs -> ghc_getArgs
    _ -> do
        argc <- peek lhc_argc
        argv <- peek lhc_argv
        let f n = peekElemOff argv n >>= peekCString
        mapM f [0 .. fromIntegral argc - 1]


getEnv s = withCString s c_getenv >>= \p ->
    if p == nullPtr then fail ("getEnv: " ++ show s)  else peekCString p


system s = withCString s c_system >>= \r -> case r of
    0 -> return ExitSuccess
    _ -> return $ ExitFailure (fromIntegral r)

foreign import unsafe ccall "exit" c_exit :: Int -> IO ()
foreign import unsafe ccall "system" c_system :: CString -> IO CInt
foreign import unsafe ccall "stdlib.h getenv" c_getenv :: Ptr CChar -> IO (Ptr CChar)

foreign import ccall "&lhc_progname" lhc_progname :: Ptr CString
foreign import ccall "&lhc_argc" lhc_argc :: Ptr CInt
foreign import ccall "&lhc_argv" lhc_argv :: Ptr (Ptr CString)

ghc_getArgs :: IO [String]
ghc_getArgs =
    alloca $ \ p_argc ->
    alloca $ \ p_argv -> do
        getProgArgv p_argc p_argv
        p    <- peek p_argc
        argv <- peek p_argv
        let f n = peekElemOff argv n >>= peekCString
        mapM f [1 .. fromIntegral p - 1]


foreign import unsafe ccall "getProgArgv"
  getProgArgv :: Ptr CInt -> Ptr (Ptr CString) -> IO ()

ghc_getProgName :: IO String
ghc_getProgName =
  alloca $ \ p_argc ->
  alloca $ \ p_argv -> do
     getProgArgv p_argc p_argv
     argv <- peek p_argv
     peekElemOff argv 0 >>= peekCString