    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Actions.Plane
    -- Copyright   :  (c) Marco Túlio Gontijo e Silva <marcot@riseup.net>,
    --                    Leonardo Serra <leoserra@minaslivre.org>
    -- License     :  BSD3-style (see LICENSE)
    --
    -- Maintainer  :  Marco Túlio Gontijo e Silva <marcot@riseup.net>
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- This module has functions to navigate through workspaces in a bidimensional
    -- manner.  It allows the organization of workspaces in lines, and provides
    -- functions to move and shift windows in all four directions (left, up, right
    -- and down) possible in a surface.
    --
    -- This functionality was inspired by GNOME (finite) and KDE (infinite)
    -- keybindings for workspace navigation, and by "XMonad.Actions.CycleWS" for
    -- the idea of applying this approach to XMonad.
    -----------------------------------------------------------------------------

    module XMonad.Actions.Plane
        (
        -- * Usage
        -- $usage

        -- * Data types
        Direction (..)
        , Limits (..)
        , Lines (..)

        -- * Navigating through workspaces
        , planeShift
        , planeMove
        )
        where

    import Control.Monad
    import Data.List hiding (union)
    import Data.Maybe

    import XMonad
    import XMonad.StackSet hiding (workspaces)
    import XMonad.Util.Run

    -- $usage
    -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@ file:
    --
    -- > import XMonad.Actions.Plane
    -- >
    -- > main = xmonad defaultConfig {keys = myKeys}
    -- >
    -- > myKeys conf = union (keys defaultConfig conf) $ myNewKeys conf
    -- >
    -- > myNewkeys (XConfig {modMask = m}) =
    -- >     fromList
    -- >     [ ((keyMask .|. m, keySym), function (Lines 3) Finite direction)
    -- >     | (keySym, direction) <- zip [xK_Left .. xK_Down] $ enumFrom ToLeft
    -- >     , (keyMask, function) <- [(0, planeMove), (shiftMask, planeShift)]
    -- >     ]
    --
    -- For detailed instructions on editing your key bindings, see
    -- "XMonad.Doc.Extending#Editing_key_bindings".

    -- | Direction to go in the plane.
    data Direction =  ToLeft | ToUp | ToRight | ToDown deriving Enum

    -- | Defines whether it's a finite or a circular organization of workspaces.
    data Limits
        = Finite   -- ^ When you're at a edge of the plane, there's no way to move
                   -- to the next region.
        | Circular -- ^ If you try to move, you'll get to the other edge, on the
                   -- other side.
        | Linear   -- ^ The plan comes as a row.
        deriving Eq

    -- | The number of lines in which the workspaces will be arranged.  It's
    -- possible to use a number of lines that is not a divisor of the number of
    -- workspaces, but the results are better when using a divisor.  If it's not a
    -- divisor, the last line will have the remaining workspaces.
    data Lines
        = GConf     -- ^ Use @gconftool-2@ to find out the number of lines.
        | Lines Int -- ^ Specify the number of lines explicity.

    -- $navigating
    --
    -- There're two parameters that must be provided to navigate, and it's a good
    -- idea to use them with the same values in each keybinding.
    --
    -- The first is the number of lines in which the workspaces are going to be
    -- organized.  It's possible to use a number of lines that is not a divisor
    -- of the number of workspaces, but the results are better when using a
    -- divisor.  If it's not a divisor, the last line will have the remaining
    -- workspaces.
    --
    -- The other one is 'Limits'.

    -- | Shift a window to the next workspace in 'Direction'.  Note that this will
    -- also move to the next workspace.
    planeShift
        :: Lines
        -> Limits
        -> Direction
        -> X ()
    planeShift = plane shift'

    shift' ::
        (Eq s, Eq i, Ord a) => i -> StackSet i l a s sd -> StackSet i l a s sd
    shift' area = greedyView area . shift area

    -- | Move to the next workspace in 'Direction'.
    planeMove :: Lines -> Limits -> Direction -> X ()
    planeMove = plane greedyView

    plane ::
        (WorkspaceId -> WindowSet -> WindowSet) -> Lines -> Limits -> Direction ->
        X ()
    plane function numberLines_ limits direction = do
        state <- get
        xconf <- ask

        numberLines <-
            liftIO $
            case numberLines_ of
                Lines numberLines__ ->
                    return numberLines__
                GConf               ->
                    do
                        numberLines__ <-
                            runProcessWithInput gconftool parameters ""
                        case reads numberLines__ of
                            [(numberRead, _)] -> return numberRead
                            _                 ->
                                do
                                    trace $
                                        "XMonad.Actions.Plane: Could not parse the output of " ++ gconftool ++
                                        unwords parameters ++ ": " ++ numberLines__ ++ "; assuming 1."
                                    return 1

        let
            notBorder :: Bool
            notBorder = (replicate 2 (circular_ < currentWS) ++ replicate 2 (circular_ > currentWS)) !! fromEnum direction

            circular_ :: Int
            circular_ = circular currentWS

            circular :: Int -> Int
            circular =
                [ onLine   pred
                , onColumn pred
                , onLine   succ
                , onColumn succ
                ]
                !! fromEnum direction

            linear :: Int -> Int
            linear =
                [ onLine   pred . onColumn pred
                , onColumn pred . onLine pred
                , onLine   succ . onColumn succ
                , onColumn succ . onLine succ
                ]
                !! fromEnum direction

            onLine :: (Int -> Int) -> Int -> Int
            onLine f currentWS_
                | line < areasLine = mod_ columns
                | otherwise        = mod_ areasColumn
                where
                    line, column :: Int
                    (line, column) = split currentWS_

                    mod_ :: Int -> Int
                    mod_ columns_ = compose line $ mod (f column) columns_

            onColumn :: (Int -> Int) -> Int -> Int
            onColumn f currentWS_
                | column < areasColumn || areasColumn == 0  = mod_ numberLines
                | otherwise                                 = mod_ $ pred numberLines
                where
                    line, column :: Int
                    (line, column) = split currentWS_

                    mod_ :: Int -> Int
                    mod_ lines_ = compose (mod (f line) lines_) column

            compose :: Int -> Int -> Int
            compose line column = line * columns + column

            split :: Int -> (Int, Int)
            split currentWS_ =
                (operation div, operation mod)
                where
                    operation :: (Int -> Int -> Int) -> Int
                    operation f = f currentWS_ columns

            areasLine :: Int
            areasLine = div areas columns

            areasColumn :: Int
            areasColumn = mod areas columns

            columns :: Int
            columns =
                if mod areas numberLines == 0 then preColumns else preColumns + 1

            currentWS :: Int
            currentWS = fromJust mCurrentWS

            preColumns :: Int
            preColumns = div areas numberLines

            mCurrentWS :: Maybe Int
            mCurrentWS = elemIndex (currentTag $ windowset state) areaNames

            areas :: Int
            areas = length areaNames

            run :: (Int -> Int) -> X ()
            run f = windows $ function $ areaNames !! f currentWS

            areaNames :: [String]
            areaNames = workspaces $ config xconf

        when (isJust mCurrentWS) $
            case limits of
            Finite   -> when notBorder $ run circular
            Circular -> run circular
            Linear -> if notBorder then run circular else run linear

    gconftool :: String
    gconftool = "gconftool-2"

    parameters :: [String]
    parameters = ["--get", "/apps/panel/applets/workspace_switcher_screen0/prefs/num_rows"]