    {-# LANGUAGE BangPatterns #-}
    {-# LANGUAGE CPP #-}
    module System.Process.Posix
        ( mkProcessHandle
        , translateInternal
        , createProcess_Internal
        , withCEnvironment
        , closePHANDLE
        , startDelegateControlC
        , endDelegateControlC
        , stopDelegateControlC
        , isDefaultSignal
        , ignoreSignal
        , defaultSignal
        , c_execvpe
        , pPrPr_disableITimers
        , createPipeInternal
        , createPipeInternalFd
        , interruptProcessGroupOfInternal
        ) where

    import Control.Concurrent
    import Control.Exception
    import Data.Bits
    import Foreign.C
    import Foreign.Marshal
    import Foreign.Ptr
    import Foreign.Storable
    import System.IO.Unsafe

    import Control.Monad
    import Data.Char
    import System.IO
    import System.Posix.Process.Internals ( pPrPr_disableITimers, c_execvpe )
    import System.Posix.Types

    import System.Posix.Internals
    import GHC.IO.Exception
    import System.Posix.Signals as Sig
    import qualified System.Posix.IO as Posix
    import System.Posix.Process (getProcessGroupIDOf)

    import System.Process.Common

    #include "HsProcessConfig.h"
    #include "processFlags.h"

    mkProcessHandle :: PHANDLE -> Bool -> IO ProcessHandle
    mkProcessHandle p mb_delegate_ctlc = do
      m <- newMVar (OpenHandle p)
      return (ProcessHandle m mb_delegate_ctlc)

    closePHANDLE :: PHANDLE -> IO ()
    closePHANDLE _ = return ()

    -- ----------------------------------------------------------------------------
    -- commandToProcess

    {- | Turns a shell command into a raw command.  Usually this involves
         wrapping it in an invocation of the shell.

       There's a difference in the signature of commandToProcess between
       the Windows and Unix versions.  On Unix, exec takes a list of strings,
       and we want to pass our command to /bin/sh as a single argument.

       On Windows, CreateProcess takes a single string for the command,
       which is later decomposed by cmd.exe.  In this case, we just want
       to prepend @\"c:\WINDOWS\CMD.EXE \/c\"@ to our command line.  The
       command-line translation that we normally do for arguments on
       Windows isn't required (or desirable) here.
    -}

    commandToProcess :: CmdSpec -> (FilePath, [String])
    commandToProcess (ShellCommand string) = ("/bin/sh", ["-c", string])
    commandToProcess (RawCommand cmd args) = (cmd, args)

    translateInternal :: String -> String
    translateInternal "" = "''"
    translateInternal str
       -- goodChar is a pessimistic predicate, such that if an argument is
       -- non-empty and only contains goodChars, then there is no need to
       -- do any quoting or escaping
     | all goodChar str = str
     | otherwise        = '\'' : foldr escape "'" str
      where escape '\'' = showString "'\\''"
            escape c    = showChar c
            goodChar c = isAlphaNum c || c `elem` "-_.,/"

    -- ----------------------------------------------------------------------------
    -- Utils

    withCEnvironment :: [(String,String)] -> (Ptr CString  -> IO a) -> IO a
    withCEnvironment envir act =
      let env' = map (\(name, val) -> name ++ ('=':val)) envir
      in withMany withCString env' (\pEnv -> withArray0 nullPtr pEnv act)

    -- -----------------------------------------------------------------------------
    -- POSIX runProcess with signal handling in the child

    createProcess_Internal
        :: String
        -> CreateProcess
        -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle)
    createProcess_Internal fun
                       CreateProcess{ cmdspec = cmdsp,
                                      cwd = mb_cwd,
                                      env = mb_env,
                                      std_in = mb_stdin,
                                      std_out = mb_stdout,
                                      std_err = mb_stderr,
                                      close_fds = mb_close_fds,
                                      create_group = mb_create_group,
                                      delegate_ctlc = mb_delegate_ctlc,
                                      detach_console = mb_detach_console,
                                      create_new_console = mb_create_new_console,
                                      new_session = mb_new_session,
                                      child_group = mb_child_group,
                                      child_user = mb_child_user }
     = do
      let (cmd,args) = commandToProcess cmdsp
      withFilePathException cmd $
       alloca $ \ pfdStdInput  ->
       alloca $ \ pfdStdOutput ->
       alloca $ \ pfdStdError  ->
       alloca $ \ pFailedDoing ->
       maybeWith withCEnvironment mb_env $ \pEnv ->
       maybeWith withFilePath mb_cwd $ \pWorkDir ->
       maybeWith with mb_child_group $ \pChildGroup ->
       maybeWith with mb_child_user $ \pChildUser ->
       withMany withFilePath (cmd:args) $ \cstrs ->
       withArray0 nullPtr cstrs $ \pargs -> do

         fdin  <- mbFd fun fd_stdin  mb_stdin
         fdout <- mbFd fun fd_stdout mb_stdout
         fderr <- mbFd fun fd_stderr mb_stderr

         when mb_delegate_ctlc
           startDelegateControlC

         -- runInteractiveProcess() blocks signals around the fork().
         -- Since blocking/unblocking of signals is a global state
         -- operation, we better ensure mutual exclusion of calls to
         -- runInteractiveProcess().
         proc_handle <- withMVar runInteractiveProcess_lock $ \_ ->
                             c_runInteractiveProcess pargs pWorkDir pEnv
                                    fdin fdout fderr
                                    pfdStdInput pfdStdOutput pfdStdError
                                    pChildGroup pChildUser
                                    (if mb_delegate_ctlc then 1 else 0)
                                    ((if mb_close_fds then RUN_PROCESS_IN_CLOSE_FDS else 0)
                                    .|.(if mb_create_group then RUN_PROCESS_IN_NEW_GROUP else 0)
                                    .|.(if mb_detach_console then RUN_PROCESS_DETACHED else 0)
                                    .|.(if mb_create_new_console then RUN_PROCESS_NEW_CONSOLE else 0)
                                    .|.(if mb_new_session then RUN_PROCESS_NEW_SESSION else 0))
                                    pFailedDoing

         when (proc_handle == -1) $ do
             cFailedDoing <- peek pFailedDoing
             failedDoing <- peekCString cFailedDoing
             when mb_delegate_ctlc
               stopDelegateControlC
             throwErrno (fun ++ ": " ++ failedDoing)

         hndStdInput  <- mbPipe mb_stdin  pfdStdInput  WriteMode
         hndStdOutput <- mbPipe mb_stdout pfdStdOutput ReadMode
         hndStdError  <- mbPipe mb_stderr pfdStdError  ReadMode

         ph <- mkProcessHandle proc_handle mb_delegate_ctlc
         return (hndStdInput, hndStdOutput, hndStdError, ph)

    {-# NOINLINE runInteractiveProcess_lock #-}
    runInteractiveProcess_lock :: MVar ()
    runInteractiveProcess_lock = unsafePerformIO $ newMVar ()

    -- ----------------------------------------------------------------------------
    -- Delegated control-C handling on Unix

    -- See ticket https://ghc.haskell.org/trac/ghc/ticket/2301
    -- and http://www.cons.org/cracauer/sigint.html
    --
    -- While running an interactive console process like ghci or a shell, we want
    -- to let that process handle Ctl-C keyboard interrupts how it sees fit.
    -- So that means we need to ignore the SIGINT/SIGQUIT Unix signals while we're
    -- running such programs. And then if/when they do terminate, we need to check
    -- if they terminated due to SIGINT/SIGQUIT and if so then we behave as if we
    -- got the Ctl-C then, by throwing the UserInterrupt exception.
    --
    -- If we run multiple programs like this concurrently then we have to be
    -- careful to avoid messing up the signal handlers. We keep a count and only
    -- restore when the last one has finished.

    {-# NOINLINE runInteractiveProcess_delegate_ctlc #-}
    runInteractiveProcess_delegate_ctlc :: MVar (Maybe (Int, Sig.Handler, Sig.Handler))
    runInteractiveProcess_delegate_ctlc = unsafePerformIO $ newMVar Nothing

    startDelegateControlC :: IO ()
    startDelegateControlC =
        modifyMVar_ runInteractiveProcess_delegate_ctlc $ \delegating -> do
          case delegating of
            Nothing -> do
              -- We're going to ignore ^C in the parent while there are any
              -- processes using ^C delegation.
              --
              -- If another thread runs another process without using
              -- delegation while we're doing this then it will inherit the
              -- ignore ^C status.
              old_int  <- installHandler sigINT  Ignore Nothing
              old_quit <- installHandler sigQUIT Ignore Nothing
              return (Just (1, old_int, old_quit))

            Just (count, old_int, old_quit) -> do
              -- If we're already doing it, just increment the count
              let !count' = count + 1
              return (Just (count', old_int, old_quit))

    stopDelegateControlC :: IO ()
    stopDelegateControlC =
        modifyMVar_ runInteractiveProcess_delegate_ctlc $ \delegating -> do
          case delegating of
            Just (1, old_int, old_quit) -> do
              -- Last process, so restore the old signal handlers
              _ <- installHandler sigINT  old_int  Nothing
              _ <- installHandler sigQUIT old_quit Nothing
              return Nothing

            Just (count, old_int, old_quit) -> do
              -- Not the last, just decrement the count
              let !count' = count - 1
              return (Just (count', old_int, old_quit))

            Nothing -> return Nothing -- should be impossible

    endDelegateControlC :: ExitCode -> IO ()
    endDelegateControlC exitCode = do
        stopDelegateControlC

        -- And if the process did die due to SIGINT or SIGQUIT then
        -- we throw our equivalent exception here (synchronously).
        --
        -- An alternative design would be to throw to the main thread, as the
        -- normal signal handler does. But since we can be sync here, we do so.
        -- It allows the code locally to catch it and do something.
        case exitCode of
          ExitFailure n | isSigIntQuit n -> throwIO UserInterrupt
          _                              -> return ()
      where
        isSigIntQuit n = sig == sigINT || sig == sigQUIT
          where
            sig = fromIntegral (-n)

    foreign import ccall unsafe "runInteractiveProcess"
      c_runInteractiveProcess
            ::  Ptr CString
            -> CString
            -> Ptr CString
            -> FD
            -> FD
            -> FD
            -> Ptr FD
            -> Ptr FD
            -> Ptr FD
            -> Ptr CGid
            -> Ptr CUid
            -> CInt                         -- reset child's SIGINT & SIGQUIT handlers
            -> CInt                         -- flags
            -> Ptr CString
            -> IO PHANDLE

    ignoreSignal, defaultSignal :: CLong
    ignoreSignal  = CONST_SIG_IGN
    defaultSignal = CONST_SIG_DFL

    isDefaultSignal :: CLong -> Bool
    isDefaultSignal = (== defaultSignal)

    createPipeInternal :: IO (Handle, Handle)
    createPipeInternal = do
        (readfd, writefd) <- Posix.createPipe
        readh <- Posix.fdToHandle readfd
        writeh <- Posix.fdToHandle writefd
        return (readh, writeh)

    createPipeInternalFd :: IO (FD, FD)
    createPipeInternalFd = do
       (Fd readfd, Fd writefd) <- Posix.createPipe
       return (readfd, writefd)

    interruptProcessGroupOfInternal
        :: ProcessHandle    -- ^ A process in the process group
        -> IO ()
    interruptProcessGroupOfInternal ph = do
        withProcessHandle ph $ \p_ -> do
            case p_ of
                ClosedHandle _ -> return ()
                OpenHandle h -> do
                    pgid <- getProcessGroupIDOf h
                    signalProcessGroup sigINT pgid