    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Util.Run
    -- Copyright   :  (C) 2007 Spencer Janssen, Andrea Rossato, glasser@mit.edu
    -- License     :  BSD-style (see LICENSE)
    --
    -- Maintainer  :  Christian Thiemann <mail@christian-thiemann.de>
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- This modules provides several commands to run an external process.
    -- It is composed of functions formerly defined in "XMonad.Util.Dmenu" (by
    -- Spencer Janssen), "XMonad.Util.Dzen" (by glasser\@mit.edu) and
    -- XMonad.Util.RunInXTerm (by Andrea Rossato).
    --
    -----------------------------------------------------------------------------

    module XMonad.Util.Run (
                              -- * Usage
                              -- $usage
                              runProcessWithInput,
                              runProcessWithInputAndWait,
                              safeSpawn,
                              safeSpawnProg,
                              unsafeSpawn,
                              runInTerm,
                              safeRunInTerm,
                              seconds,
                              spawnPipe,

                              hPutStr, hPutStrLn  -- re-export for convenience
                             ) where

    import Codec.Binary.UTF8.String
    import System.Posix.IO
    import System.Posix.Process (createSession, executeFile, forkProcess)
    import Control.Concurrent (threadDelay)
    import System.IO
    import System.Process (runInteractiveProcess)
    import XMonad
    import Control.Monad

    -- $usage
    -- For an example usage of 'runInTerm' see "XMonad.Prompt.Ssh"
    --
    -- For an example usage of 'runProcessWithInput' see
    -- "XMonad.Prompt.DirectoryPrompt", "XMonad.Util.Dmenu",
    -- "XMonad.Prompt.ShellPrompt", "XMonad.Actions.WmiiActions",
    -- "XMonad.Prompt.WorkspaceDir"
    --
    -- For an example usage of 'runProcessWithInputAndWait' see
    -- "XMonad.Util.Dzen"

    -- | Returns the output.
    runProcessWithInput :: MonadIO m => FilePath -> [String] -> String -> m String
    runProcessWithInput cmd args input = io $ do
        (pin, pout, perr, _) <- runInteractiveProcess (encodeString cmd)
                                                (map encodeString args) Nothing Nothing
        hPutStr pin input
        hClose pin
        output <- hGetContents pout
        when (output == output) $ return ()
        hClose pout
        hClose perr
        -- no need to waitForProcess, we ignore SIGCHLD
        return output

    -- | Wait is in &#956; (microseconds)
    runProcessWithInputAndWait :: MonadIO m => FilePath -> [String] -> String -> Int -> m ()
    runProcessWithInputAndWait cmd args input timeout = io $ do
        _ <- xfork $ do
            (pin, pout, perr, _) <- runInteractiveProcess (encodeString cmd)
                                                (map encodeString args) Nothing Nothing
            hPutStr pin input
            hFlush pin
            threadDelay timeout
            hClose pin
            hClose pout
            hClose perr
            -- no need to waitForProcess, we ignore SIGCHLD
            return ()
        return ()

    -- | Multiplies by ONE MILLION, for functions that take microseconds.
    --
    -- Use like:
    --
    -- > (5.5 `seconds`)
    --
    -- In GHC 7 and later, you must either enable the PostfixOperators extension
    -- (by adding
    --
    -- > {-# LANGUAGE PostfixOperators #-}
    --
    -- to the top of your file) or use seconds in prefix form:
    --
    -- > seconds 5.5
    seconds :: Rational -> Int
    seconds = fromEnum . (* 1000000)

    {- | 'safeSpawn' bypasses 'spawn', because spawn passes
    strings to \/bin\/sh to be interpreted as shell commands. This is
    often what one wants, but in many cases the passed string will contain
    shell metacharacters which one does not want interpreted as such (URLs
    particularly often have shell metacharacters like \'&\' in them). In
    this case, it is more useful to specify a file or program to be run
    and a string to give it as an argument so as to bypass the shell and
    be certain the program will receive the string as you typed it.

    Examples:

    > , ((modm, xK_Print), unsafeSpawn "import -window root $HOME/xwd-$(date +%s)$$.png")
    > , ((modm, xK_d    ), safeSpawn "firefox" [])

    Note that the unsafeSpawn example must be unsafe and not safe because
    it makes use of shell interpretation by relying on @$HOME@ and
    interpolation, whereas the safeSpawn example can be safe because
    Firefox doesn't need any arguments if it is just being started. -}
    safeSpawn :: MonadIO m => FilePath -> [String] -> m ()
    safeSpawn prog args = io $ void_ $ forkProcess $ do
      uninstallSignalHandlers
      _ <- createSession
      executeFile (encodeString prog) True (map encodeString args) Nothing
        where void_ = (>> return ()) -- TODO: replace with Control.Monad.void / void not in ghc6 apparently

    -- | Simplified 'safeSpawn'; only takes a program (and no arguments):
    --
    -- > , ((modm, xK_d    ), safeSpawnProg "firefox")
    safeSpawnProg :: MonadIO m => FilePath -> m ()
    safeSpawnProg = flip safeSpawn []

    -- | An alias for 'spawn'; the name emphasizes that one is calling out to a
    --   Turing-complete interpreter which may do things one dislikes; for details, see 'safeSpawn'.
    unsafeSpawn :: MonadIO m => String -> m ()
    unsafeSpawn = spawn

    -- | Open a terminal emulator. The terminal emulator is specified in the default configuration as xterm by default. It is then
    -- asked to pass the shell a command with certain options. This is unsafe in the sense of 'unsafeSpawn'
    unsafeRunInTerm, runInTerm :: String -> String -> X ()
    unsafeRunInTerm options command = asks (terminal . config) >>= \t -> unsafeSpawn $ t ++ " " ++ options ++ " -e " ++ command
    runInTerm = unsafeRunInTerm

    -- | Run a given program in the preferred terminal emulator; see 'runInTerm'. This makes use of 'safeSpawn'.
    safeRunInTerm :: String -> String -> X ()
    safeRunInTerm options command = asks (terminal . config) >>= \t -> safeSpawn t [options, " -e " ++ command]

    -- | Launch an external application through the system shell and return a @Handle@ to its standard input.
    spawnPipe :: MonadIO m => String -> m Handle
    spawnPipe x = io $ do
        (rd, wr) <- createPipe
        setFdOption wr CloseOnExec True
        h <- fdToHandle wr
        hSetBuffering h LineBuffering
        _ <- xfork $ do
              _ <- dupTo rd stdInput
              executeFile "/bin/sh" False ["-c", encodeString x] Nothing
        closeFd rd
        return h