    {-# LANGUAGE DeriveDataTypeable, FlexibleInstances, MultiParamTypeClasses, TypeSynonymInstances, PatternGuards #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Layout.WorkspaceDir
    -- Copyright   :  (c) 2007  David Roundy <droundy@darcs.net>
    -- License     :  BSD3-style (see LICENSE)
    --
    -- Maintainer  :  none
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- WorkspaceDir is an extension to set the current directory in a workspace.
    --
    -- Actually, it sets the current directory in a layout, since there's no way I
    -- know of to attach a behavior to a workspace.  This means that any terminals
    -- (or other programs) pulled up in that workspace (with that layout) will
    -- execute in that working directory.  Sort of handy, I think.
    --
    -- Note this extension requires the 'directory' package to be installed.
    --
    -----------------------------------------------------------------------------

    module XMonad.Layout.WorkspaceDir (
                                       -- * Usage
                                       -- $usage
                                       workspaceDir,
                                       changeDir,
                                       WorkspaceDir,
                                      ) where

    import System.Directory ( setCurrentDirectory, getCurrentDirectory )
    import Control.Monad ( when )

    import XMonad hiding ( focus )
    import XMonad.Prompt ( XPConfig )
    import XMonad.Prompt.Directory ( directoryPrompt )
    import XMonad.Layout.LayoutModifier
    import XMonad.StackSet ( tag, currentTag )

    -- $usage
    -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@:
    --
    -- > import XMonad.Layout.WorkspaceDir
    --
    -- Then edit your @layoutHook@ by adding the Workspace layout modifier
    -- to some layout:
    --
    -- > myLayout = workspaceDir "~" (Tall 1 (3/100) (1/2))  ||| Full ||| etc..
    -- > main = xmonad defaultConfig { layoutHook = myLayout }
    --
    -- For more detailed instructions on editing the layoutHook see:
    --
    -- "XMonad.Doc.Extending#Editing_the_layout_hook"
    --
    -- WorkspaceDir provides also a prompt. To use it you need to import
    -- "XMonad.Prompt" and add something like this to your key bindings:
    --
    -- >  , ((modm .|. shiftMask, xK_x     ), changeDir defaultXPConfig)
    --
    -- For detailed instruction on editing the key binding see:
    --
    -- "XMonad.Doc.Extending#Editing_key_bindings".

    data Chdir = Chdir String deriving ( Typeable )
    instance Message Chdir

    data WorkspaceDir a = WorkspaceDir String deriving ( Read, Show )

    instance LayoutModifier WorkspaceDir Window where
        modifyLayout (WorkspaceDir d) w r = do tc <- gets (currentTag.windowset)
                                               when (tc == tag w) $ scd d
                                               runLayout w r
        handleMess (WorkspaceDir _) m
            | Just (Chdir wd) <- fromMessage m = do wd' <- cleanDir wd
                                                    return $ Just $ WorkspaceDir wd'
            | otherwise = return Nothing

    workspaceDir :: LayoutClass l a => String -> l a
                 -> ModifiedLayout WorkspaceDir l a
    workspaceDir s = ModifiedLayout (WorkspaceDir s)

    cleanDir :: String -> X String
    cleanDir x = scd x >> io getCurrentDirectory

    scd :: String -> X ()
    scd x = catchIO $ setCurrentDirectory x

    changeDir :: XPConfig -> X ()
    changeDir c = directoryPrompt c "Set working directory: " (sendMessage . Chdir)