    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Hooks.ServerMode
    -- Copyright   :  (c) Peter Olson 2013 and Andrea Rossato and David Roundy 2007
    -- License     :  BSD-style (see xmonad/LICENSE)
    --
    -- Maintainer  :  polson2@hawk.iit.edu
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- This is an 'EventHook' that will receive commands from an external
    -- client. Also consider "XMonad.Hooks.EwmhDesktops" together with
    -- @wmctrl@.
    --
    -- This is the example of a client:
    --
    -- > import Graphics.X11.Xlib
    -- > import Graphics.X11.Xlib.Extras
    -- > import System.Environment
    -- > import System.IO
    -- > import Data.Char
    -- >
    -- > main :: IO ()
    -- > main = parse True "XMONAD_COMMAND" =<< getArgs
    -- >
    -- > parse :: Bool -> String -> [String] -> IO ()
    -- > parse input addr args = case args of
    -- >         ["--"] | input -> repl addr
    -- >                | otherwise -> return ()
    -- >         ("--":xs) -> sendAll addr xs
    -- >         ("-a":a:xs) -> parse input a xs
    -- >         ("-h":_) -> showHelp
    -- >         ("--help":_) -> showHelp
    -- >         ("-?":_) -> showHelp
    -- >         (a@('-':_):_) -> hPutStrLn stderr ("Unknown option " ++ a)
    -- >
    -- >         (x:xs) -> sendCommand addr x >> parse False addr xs
    -- >         [] | input -> repl addr
    -- >            | otherwise -> return ()
    -- >
    -- >
    -- > repl :: String -> IO ()
    -- > repl addr = do e <- isEOF
    -- >                case e of
    -- >                 True -> return ()
    -- >                 False -> do l <- getLine
    -- >                             sendCommand addr l
    -- >                             repl addr
    -- >
    -- > sendAll :: String -> [String] -> IO ()
    -- > sendAll addr ss = foldr (\a b -> sendCommand addr a >> b) (return ()) ss
    -- >
    -- > sendCommand :: String -> String -> IO ()
    -- > sendCommand addr s = do
    -- >   d   <- openDisplay ""
    -- >   rw  <- rootWindow d $ defaultScreen d
    -- >   a <- internAtom d addr False
    -- >   m <- internAtom d s False
    -- >   allocaXEvent $ \e -> do
    -- >                   setEventType e clientMessage
    -- >                   setClientMessageEvent e rw a 32 m currentTime
    -- >                   sendEvent d rw False structureNotifyMask e
    -- >                   sync d False
    -- >
    -- > showHelp :: IO ()
    -- > showHelp = do pn <- getProgName
    -- >               putStrLn ("Send commands to a running instance of xmonad. xmonad.hs must be configured with XMonad.Hooks.ServerMode to work.\n-a atomname can be used at any point in the command line arguments to change which atom it is sending on.\nIf sent with no arguments or only -a atom arguments, it will read commands from stdin.\nEx:\n" ++ pn ++ " cmd1 cmd2\n" ++ pn ++ " -a XMONAD_COMMAND cmd1 cmd2 cmd3 -a XMONAD_PRINT hello world\n" ++ pn ++ " -a XMONAD_PRINT # will read data from stdin.\nThe atom defaults to XMONAD_COMMAND.")
    --
    --
    -- compile with: @ghc --make xmonadctl.hs@
    --
    -- run with
    --
    -- > xmonadctl command
    --
    -- or with
    --
    -- > $ xmonadctl
    -- > command1
    -- > command2
    -- > .
    -- > .
    -- > .
    -- > ^D
    --
    -- Usage will change depending on which event hook(s) you use. More examples are shown below.
    --
    -----------------------------------------------------------------------------

    module XMonad.Hooks.ServerMode
        ( -- * Usage
          -- $usage
          serverModeEventHook
        , serverModeEventHook'
        , serverModeEventHookCmd
        , serverModeEventHookCmd'
        , serverModeEventHookF
        ) where

    import Control.Monad (when)
    import Data.Maybe
    import Data.Monoid
    import System.IO

    import XMonad
    import XMonad.Actions.Commands

    -- $usage
    -- You can use this module with the following in your
    -- @~\/.xmonad\/xmonad.hs@:
    --
    -- > import XMonad.Hooks.ServerMode
    --
    -- Then edit your @handleEventHook@ by adding the appropriate event hook from below

    -- | Executes a command of the list when receiving its index via a special ClientMessageEvent
    -- (indexing starts at 1). Sending index 0 will ask xmonad to print the list of command numbers
    -- in stderr (so that you can read it in @~\/.xsession-errors@). Uses "XMonad.Actions.Commands#defaultCommands" as the default.
    --
    -- > main = xmonad def { handleEventHook = serverModeEventHook }
    --
    -- > xmonadctl 0 # tells xmonad to output command list
    -- > xmonadctl 1 # tells xmonad to switch to workspace 1
    --
    serverModeEventHook :: Event -> X All
    serverModeEventHook = serverModeEventHook' defaultCommands

    -- | serverModeEventHook' additionally takes an action to generate the list of
    -- commands.
    serverModeEventHook' :: X [(String,X ())] -> Event -> X All
    serverModeEventHook' cmdAction ev = serverModeEventHookF "XMONAD_COMMAND" (sequence_ . map helper . words) ev
            where helper cmd = do cl <- cmdAction
                                  case lookup cmd (zip (map show [1 :: Integer ..]) cl) of
                                    Just (_,action) -> action
                                    Nothing         -> mapM_ (io . hPutStrLn stderr) . listOfCommands $ cl
                  listOfCommands cl = map (uncurry (++)) $ zip (map show ([1..] :: [Int])) $ map ((++) " - " . fst) cl

    -- | Executes a command of the list when receiving its name via a special ClientMessageEvent.
    -- Uses "XMonad.Actions.Commands#defaultCommands" as the default.
    --
    -- > main = xmonad def { handleEventHook = serverModeEventHookCmd }
    --
    -- > xmonadctl run # Tells xmonad to generate a run prompt
    --
    serverModeEventHookCmd :: Event -> X All
    serverModeEventHookCmd = serverModeEventHookCmd' defaultCommands

    -- | Additionally takes an action to generate the list of commands
    serverModeEventHookCmd' :: X [(String,X ())] -> Event -> X All
    serverModeEventHookCmd' cmdAction ev = serverModeEventHookF "XMONAD_COMMAND" (sequence_ . map helper . words) ev
            where helper cmd = do cl <- cmdAction
                                  fromMaybe (io $ hPutStrLn stderr ("Couldn't find command " ++ cmd)) (lookup cmd cl)

    -- | Listens for an atom, then executes a callback function whenever it hears it.
    -- A trivial example that prints everything supplied to it on xmonad's standard out:
    --
    -- > main = xmonad def { handleEventHook = serverModeEventHookF "XMONAD_PRINT" (io . putStrLn) }
    --
    -- > xmonadctl -a XMONAD_PRINT "hello world"
    --
    serverModeEventHookF :: String -> (String -> X ()) -> Event -> X All
    serverModeEventHookF key func (ClientMessageEvent {ev_message_type = mt, ev_data = dt}) = do
            d <- asks display
            atm <- io $ internAtom d key False
            when (mt == atm && dt /= []) $ do
             let atom = fromIntegral $ toInteger $ foldr1 (\a b -> a + (b*2^(32::Int))) dt
             cmd <- io $ getAtomName d atom
             case cmd of
                  Just command -> func command
                  Nothing -> io $ hPutStrLn stderr ("Couldn't retrieve atom " ++ (show atom))
            return (All True)
    serverModeEventHookF _ _ _ = return (All True)