    {-# LANGUAGE CPP #-}
    {-# LANGUAGE RecordWildCards #-}
    module System.Process.Common
        ( CreateProcess (..)
        , CmdSpec (..)
        , StdStream (..)
        , ProcessHandle(..)
        , ProcessHandle__(..)
        , withFilePathException
        , PHANDLE
        , modifyProcessHandle
        , withProcessHandle
        , fd_stdin
        , fd_stdout
        , fd_stderr
        , mbFd
        , mbPipe
        , pfdToHandle

    -- Avoid a warning on Windows
    #ifdef WINDOWS
        , CGid (..)
    #else
        , CGid
    #endif
        ) where

    import Control.Concurrent
    import Control.Exception
    import Data.String
    import Foreign.Ptr
    import Foreign.Storable

    import System.Posix.Internals
    import GHC.IO.Exception
    import GHC.IO.Encoding
    import qualified GHC.IO.FD as FD
    import GHC.IO.Device
    import GHC.IO.Handle.FD
    import GHC.IO.Handle.Internals
    import GHC.IO.Handle.Types hiding (ClosedHandle)
    import System.IO.Error
    import Data.Typeable
    import GHC.IO.IOMode

    -- We do a minimal amount of CPP here to provide uniform data types across
    -- Windows and POSIX.
    #ifdef WINDOWS
    import Data.Word (Word32)
    import System.Win32.DebugApi (PHANDLE)
    #else
    import System.Posix.Types
    #endif

    #ifdef WINDOWS
    -- Define some missing types for Windows compatibility. Note that these values
    -- will never actually be used, as the setuid/setgid system calls are not
    -- applicable on Windows. No value of this type will ever exist.
    newtype CGid = CGid Word32
      deriving (Show, Eq)
    type GroupID = CGid
    type UserID = CGid
    #else
    type PHANDLE = CPid
    #endif

    data CreateProcess = CreateProcess{
      cmdspec      :: CmdSpec,                 -- ^ Executable & arguments, or shell command.  Relative paths are resolved with respect to 'cwd' if given, and otherwise the current working directory.
      cwd          :: Maybe FilePath,          -- ^ Optional path to the working directory for the new process
      env          :: Maybe [(String,String)], -- ^ Optional environment (otherwise inherit from the current process)
      std_in       :: StdStream,               -- ^ How to determine stdin
      std_out      :: StdStream,               -- ^ How to determine stdout
      std_err      :: StdStream,               -- ^ How to determine stderr
      close_fds    :: Bool,                    -- ^ Close all file descriptors except stdin, stdout and stderr in the new process (on Windows, only works if std_in, std_out, and std_err are all Inherit)
      create_group :: Bool,                    -- ^ Create a new process group
      delegate_ctlc:: Bool,                    -- ^ Delegate control-C handling. Use this for interactive console processes to let them handle control-C themselves (see below for details).
                                               --
                                               --   On Windows this has no effect.
                                               --
                                               --   @since 1.2.0.0
      detach_console :: Bool,                  -- ^ Use the windows DETACHED_PROCESS flag when creating the process; does nothing on other platforms.
                                               --
                                               --   @since 1.3.0.0
      create_new_console :: Bool,              -- ^ Use the windows CREATE_NEW_CONSOLE flag when creating the process; does nothing on other platforms.
                                               --
                                               --   Default: @False@
                                               --
                                               --   @since 1.3.0.0
      new_session :: Bool,                     -- ^ Use posix setsid to start the new process in a new session; does nothing on other platforms.
                                               --
                                               --   @since 1.3.0.0
      child_group :: Maybe GroupID,            -- ^ Use posix setgid to set child process's group id; does nothing on other platforms.
                                               --
                                               --   Default: @Nothing@
                                               --
                                               --   @since 1.4.0.0
      child_user :: Maybe UserID               -- ^ Use posix setuid to set child process's user id; does nothing on other platforms.
                                               --
                                               --   Default: @Nothing@
                                               --
                                               --   @since 1.4.0.0
     } deriving (Show, Eq)

    data CmdSpec
      = ShellCommand String
          -- ^ A command line to execute using the shell
      | RawCommand FilePath [String]
          -- ^ The name of an executable with a list of arguments
          --
          -- The 'FilePath' argument names the executable, and is interpreted
          -- according to the platform's standard policy for searching for
          -- executables. Specifically:
          --
          -- * on Unix systems the
          --   <http://pubs.opengroup.org/onlinepubs/9699919799/functions/execvp.html execvp(3)>
          --   semantics is used, where if the executable filename does not
          --   contain a slash (@/@) then the @PATH@ environment variable is
          --   searched for the executable.
          --
          -- * on Windows systems the Win32 @CreateProcess@ semantics is used.
          --   Briefly: if the filename does not contain a path, then the
          --   directory containing the parent executable is searched, followed
          --   by the current directory, then some standard locations, and
          --   finally the current @PATH@.  An @.exe@ extension is added if the
          --   filename does not already have an extension.  For full details
          --   see the
          --   <http://msdn.microsoft.com/en-us/library/windows/desktop/aa365527%28v=vs.85%29.aspx documentation>
          --   for the Windows @SearchPath@ API.
      deriving (Show, Eq)

    -- | construct a `ShellCommand` from a string literal
    --
    -- @since 1.2.1.0
    instance IsString CmdSpec where
      fromString = ShellCommand

    data StdStream
      = Inherit                  -- ^ Inherit Handle from parent
      | UseHandle Handle         -- ^ Use the supplied Handle
      | CreatePipe               -- ^ Create a new pipe.  The returned
                                 -- @Handle@ will use the default encoding
                                 -- and newline translation mode (just
                                 -- like @Handle@s created by @openFile@).
      | NoStream                 -- ^ No stream handle will be passed
      deriving (Eq, Show)

    -- ----------------------------------------------------------------------------
    -- ProcessHandle type

    {- | A handle to a process, which can be used to wait for termination
         of the process using 'System.Process.waitForProcess'.

         None of the process-creation functions in this library wait for
         termination: they all return a 'ProcessHandle' which may be used
         to wait for the process later.
    -}
    data ProcessHandle__ = OpenHandle PHANDLE | ClosedHandle ExitCode
    data ProcessHandle = ProcessHandle !(MVar ProcessHandle__) !Bool

    withFilePathException :: FilePath -> IO a -> IO a
    withFilePathException fpath act = handle mapEx act
      where
        mapEx ex = ioError (ioeSetFileName ex fpath)

    modifyProcessHandle
            :: ProcessHandle
            -> (ProcessHandle__ -> IO (ProcessHandle__, a))
            -> IO a
    modifyProcessHandle (ProcessHandle m _) io = modifyMVar m io

    withProcessHandle
            :: ProcessHandle
            -> (ProcessHandle__ -> IO a)
            -> IO a
    withProcessHandle (ProcessHandle m _) io = withMVar m io

    fd_stdin, fd_stdout, fd_stderr :: FD
    fd_stdin  = 0
    fd_stdout = 1
    fd_stderr = 2

    mbFd :: String -> FD -> StdStream -> IO FD
    mbFd _   _std CreatePipe      = return (-1)
    mbFd _fun std Inherit         = return std
    mbFd _fn _std NoStream        = return (-2)
    mbFd fun _std (UseHandle hdl) =
      withHandle fun hdl $ \Handle__{haDevice=dev,..} ->
        case cast dev of
          Just fd -> do
             -- clear the O_NONBLOCK flag on this FD, if it is set, since
             -- we're exposing it externally (see #3316)
             fd' <- FD.setNonBlockingMode fd False
             return (Handle__{haDevice=fd',..}, FD.fdFD fd')
          Nothing ->
              ioError (mkIOError illegalOperationErrorType
                          "createProcess" (Just hdl) Nothing
                       `ioeSetErrorString` "handle is not a file descriptor")

    mbPipe :: StdStream -> Ptr FD -> IOMode -> IO (Maybe Handle)
    mbPipe CreatePipe pfd  mode = fmap Just (pfdToHandle pfd mode)
    mbPipe _std      _pfd _mode = return Nothing

    pfdToHandle :: Ptr FD -> IOMode -> IO Handle
    pfdToHandle pfd mode = do
      fd <- peek pfd
      let filepath = "fd:" ++ show fd
      (fD,fd_type) <- FD.mkFD (fromIntegral fd) mode
                           (Just (Stream,0,0)) -- avoid calling fstat()
                           False {-is_socket-}
                           False {-non-blocking-}
      fD' <- FD.setNonBlockingMode fD True -- see #3316
    #if __GLASGOW_HASKELL__ >= 704
      enc <- getLocaleEncoding
    #else
      let enc = localeEncoding
    #endif
      mkHandleFromFD fD' fd_type filepath mode False {-is_socket-} (Just enc)