    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Actions.CycleWS
    -- Copyright   :  (c) Joachim Breitner <mail@joachim-breitner.de>,
    --                    Nelson Elhage <nelhage@mit.edu> (`toggleWS' function)
    -- License     :  BSD3-style (see LICENSE)
    --
    -- Maintainer  :  Joachim Breitner <mail@joachim-breitner.de>
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- Provides bindings to cycle forward or backward through the list of
    -- workspaces, to move windows between workspaces, and to cycle
    -- between screens.  More general combinators provide ways to cycle
    -- through workspaces in various orders, to only cycle through some
    -- subset of workspaces, and to cycle by more than one workspace at a
    -- time.
    --
    -- Note that this module now subsumes the functionality of the former
    -- @XMonad.Actions.RotView@.  Former users of @rotView@ can simply replace
    -- @rotView True@ with @moveTo Next NonEmptyWS@, and so on.
    --
    -- If you want to exactly replicate the action of @rotView@ (cycling
    -- through workspace in order lexicographically by tag, instead of in
    -- the order specified in the config), it can be implemented as:
    --
    -- > rotView b  = do t <- findWorkspace getSortByTag (bToDir b) NonEmptyWS 1
    -- >                 windows . greedyView $ t
    -- >   where bToDir True  = Next
    -- >         bToDir False = Prev
    --
    -----------------------------------------------------------------------------

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

                                    -- * Moving between workspaces
                                    -- $moving

                                    nextWS
                                  , prevWS
                                  , shiftToNext
                                  , shiftToPrev

                                    -- * Toggling the previous workspace
                                    -- $toggling
                                  , toggleWS
                                  , toggleWS'
                                  , toggleOrView

                                    -- * Moving between screens (xinerama)

                                  , nextScreen
                                  , prevScreen
                                  , shiftNextScreen
                                  , shiftPrevScreen
                                  , swapNextScreen
                                  , swapPrevScreen

                                    -- * Moving between workspaces, take two!
                                    -- $taketwo

                                  , Direction1D(..)
                                  , WSType(..)

                                  , shiftTo
                                  , moveTo
                                  , doTo

                                    -- * The mother-combinator

                                  , findWorkspace
                                  , toggleOrDoSkip
                                  , skipTags

                                  , screenBy

                                 ) where

    import Control.Monad ( unless )
    import Data.List ( findIndex )
    import Data.Maybe ( isNothing, isJust )

    import XMonad hiding (workspaces)
    import XMonad.StackSet hiding (filter)
    import XMonad.Util.Types
    import XMonad.Util.WorkspaceCompare

    -- $usage
    -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@ file:
    --
    -- > import XMonad.Actions.CycleWS
    -- >
    -- > -- a basic CycleWS setup
    -- >
    -- >   , ((modm,               xK_Down),  nextWS)
    -- >   , ((modm,               xK_Up),    prevWS)
    -- >   , ((modm .|. shiftMask, xK_Down),  shiftToNext)
    -- >   , ((modm .|. shiftMask, xK_Up),    shiftToPrev)
    -- >   , ((modm,               xK_Right), nextScreen)
    -- >   , ((modm,               xK_Left),  prevScreen)
    -- >   , ((modm .|. shiftMask, xK_Right), shiftNextScreen)
    -- >   , ((modm .|. shiftMask, xK_Left),  shiftPrevScreen)
    -- >   , ((modm,               xK_z),     toggleWS)
    --
    -- If you want to follow the moved window, you can use both actions:
    --
    -- >   , ((modm .|. shiftMask, xK_Down), shiftToNext >> nextWS)
    -- >   , ((modm .|. shiftMask, xK_Up),   shiftToPrev >> prevWS)
    --
    -- You can also get fancier with 'moveTo', 'shiftTo', and 'findWorkspace'.
    -- For example:
    --
    -- >   , ((modm     , xK_f), moveTo Next EmptyWS)  -- find a free workspace
    -- >   , ((modm .|. controlMask, xK_Right),        -- a crazy keybinding!
    -- >         do t <- findWorkspace getSortByXineramaRule Next NonEmptyWS 2
    -- >            windows . view $ t                                         )
    --
    -- For detailed instructions on editing your key bindings, see
    -- "XMonad.Doc.Extending#Editing_key_bindings".

    {- $moving

    The following commands for moving the view and windows between
    workspaces are somewhat inflexible, but are very simple and probably
    Do The Right Thing for most users.

    All of the commands in this section cycle through workspaces in the
    order in which they are given in your config.

    -}

    -- | Switch to the next workspace.
    nextWS :: X ()
    nextWS = switchWorkspace 1

    -- | Switch to the previous workspace.
    prevWS :: X ()
    prevWS = switchWorkspace (-1)

    -- | Move the focused window to the next workspace.
    shiftToNext :: X ()
    shiftToNext = shiftBy 1

    -- | Move the focused window to the previous workspace.
    shiftToPrev :: X ()
    shiftToPrev = shiftBy (-1)

    -- $toggling

    -- | Toggle to the workspace displayed previously.
    toggleWS :: X ()
    toggleWS = toggleWS' []

    -- | Toggle to the previous workspace while excluding some workspaces.
    --
    -- > -- Ignore the scratchpad workspace while toggling:
    -- > ("M-b", toggleWS' ["NSP"])
    toggleWS' :: [WorkspaceId] -> X ()
    toggleWS' skips = do
        hs' <- cleanHiddens skips
        unless (null hs') (windows . view . tag $ head hs')

    -- | 'XMonad.StackSet.greedyView' a workspace, or if already there, view
    -- the previously displayed workspace ala weechat. Change @greedyView@ to
    -- @toggleOrView@ in your workspace bindings as in the 'XMonad.StackSet.view'
    -- faq at <http://haskell.org/haskellwiki/Xmonad/Frequently_asked_questions>.
    -- For more flexibility see 'toggleOrDoSkip'.
    toggleOrView :: WorkspaceId -> X ()
    toggleOrView = toggleOrDoSkip [] greedyView

    -- | Allows ignoring listed workspace tags (such as scratchpad's \"NSP\"), and
    -- running other actions such as view, shift, etc.  For example:
    --
    -- > import qualified XMonad.StackSet as W
    -- > import XMonad.Actions.CycleWS
    -- >
    -- > -- toggleOrView for people who prefer view to greedyView
    -- > toggleOrView' = toggleOrDoSkip [] W.view
    -- >
    -- > -- toggleOrView ignoring scratchpad and named scratchpad workspace
    -- > toggleOrViewNoSP = toggleOrDoSkip ["NSP"] W.greedyView
    toggleOrDoSkip :: [WorkspaceId] -> (WorkspaceId -> WindowSet -> WindowSet)
                                      -> WorkspaceId -> X ()
    toggleOrDoSkip skips f toWS = do
        hs' <- cleanHiddens skips
        cur <- gets (currentTag . windowset)
        if toWS == cur
            then unless (null hs') (windows . f . tag $ head hs')
            else windows (f toWS)

    -- | List difference ('\\') for workspaces and tags. Removes workspaces
    -- matching listed tags from the given workspace list.
    skipTags :: (Eq i) => [Workspace i l a] -> [i] -> [Workspace i l a]
    skipTags wss ids = filter ((`notElem` ids) . tag) wss

    cleanHiddens :: [WorkspaceId] -> X [WindowSpace]
    cleanHiddens skips =  gets $ (flip skipTags) skips . hidden . windowset

    switchWorkspace :: Int -> X ()
    switchWorkspace d = wsBy d >>= windows . greedyView

    shiftBy :: Int -> X ()
    shiftBy d = wsBy d >>= windows . shift

    wsBy :: Int -> X (WorkspaceId)
    wsBy = findWorkspace getSortByIndex Next AnyWS

    {- $taketwo

    A few more general commands are also provided, which allow cycling
    through subsets of workspaces.

    For example,

    >   moveTo Next EmptyWS

    will move to the first available workspace with no windows, and

    >   shiftTo Prev (WSIs $ return (('p' `elem`) . tag))

    will move the focused window backwards to the first workspace containing
    the letter 'p' in its name. =)

    -}

    -- | What type of workspaces should be included in the cycle?
    data WSType = EmptyWS     -- ^ cycle through empty workspaces
                | NonEmptyWS  -- ^ cycle through non-empty workspaces
                | HiddenWS    -- ^ cycle through non-visible workspaces
                | HiddenNonEmptyWS  -- ^ cycle through non-empty non-visible workspaces
                | AnyWS       -- ^ cycle through all workspaces
                | WSTagGroup Char
                              -- ^ cycle through workspaces in the same group, the
                              --   group name is all characters up to the first
                              --   separator character or the end of the tag
                | WSIs (X (WindowSpace -> Bool))
                              -- ^ cycle through workspaces satisfying
                              --   an arbitrary predicate

    -- | Convert a WSType value to a predicate on workspaces.
    wsTypeToPred :: WSType -> X (WindowSpace -> Bool)
    wsTypeToPred EmptyWS    = return (isNothing . stack)
    wsTypeToPred NonEmptyWS = return (isJust . stack)
    wsTypeToPred HiddenWS   = do hs <- gets (map tag . hidden . windowset)
                                 return (\w -> tag w `elem` hs)
    wsTypeToPred HiddenNonEmptyWS  = do ne <- wsTypeToPred NonEmptyWS
                                        hi <- wsTypeToPred HiddenWS
                                        return (\w -> hi w && ne w)
    wsTypeToPred AnyWS      = return (const True)
    wsTypeToPred (WSTagGroup sep) = do cur <- (groupName.workspace.current) `fmap` gets windowset
                                       return $ (cur ==).groupName
                                       where groupName = takeWhile (/=sep).tag
    wsTypeToPred (WSIs p)   = p

    -- | View the next workspace in the given direction that satisfies
    --   the given condition.
    moveTo :: Direction1D -> WSType -> X ()
    moveTo dir t = doTo dir t getSortByIndex (windows . greedyView)

    -- | Move the currently focused window to the next workspace in the
    --   given direction that satisfies the given condition.
    shiftTo :: Direction1D -> WSType -> X ()
    shiftTo dir t = doTo dir t getSortByIndex (windows . shift)

    -- | Using the given sort, find the next workspace in the given
    -- direction of the given type, and perform the given action on it.
    doTo :: Direction1D -> WSType -> X WorkspaceSort -> (WorkspaceId -> X ()) -> X ()
    doTo dir t srt act = findWorkspace srt dir t 1 >>= act

    -- | Given a function @s@ to sort workspaces, a direction @dir@, a
    --   predicate @p@ on workspaces, and an integer @n@, find the tag of
    --   the workspace which is @n@ away from the current workspace in
    --   direction @dir@ (wrapping around if necessary), among those
    --   workspaces, sorted by @s@, which satisfy @p@.
    --
    --   For some useful workspace sorting functions, see
    --   "XMonad.Util.WorkspaceCompare".
    --
    --   For ideas of what to do with a workspace tag once obtained, note
    --   that 'moveTo' and 'shiftTo' are implemented by applying @(>>=
    --   (windows . greedyView))@ and @(>>= (windows . shift))@, respectively,
    --   to the output of 'findWorkspace'.
    findWorkspace :: X WorkspaceSort -> Direction1D -> WSType -> Int -> X WorkspaceId
    findWorkspace s dir t n = findWorkspaceGen s (wsTypeToPred t) (maybeNegate dir n)
      where
        maybeNegate Next d = d
        maybeNegate Prev d = (-d)

    findWorkspaceGen :: X WorkspaceSort -> X (WindowSpace -> Bool) -> Int -> X WorkspaceId
    findWorkspaceGen _ _ 0 = gets (currentTag . windowset)
    findWorkspaceGen sortX wsPredX d = do
        wsPred <- wsPredX
        sort   <- sortX
        ws     <- gets windowset
        let cur     = workspace (current ws)
            sorted  = sort (workspaces ws)
            pivoted = let (a,b) = span ((/= (tag cur)) . tag) sorted in b ++ a
            ws'     = filter wsPred pivoted
            mCurIx  = findWsIndex cur ws'
            d'      = if d > 0 then d - 1 else d
            next    = if null ws'
                          then cur
                          else case mCurIx of
                                Nothing -> ws' !! (d' `mod` length ws')
                                Just ix -> ws' !! ((ix + d) `mod` length ws')
        return $ tag next

    findWsIndex :: WindowSpace -> [WindowSpace] -> Maybe Int
    findWsIndex ws wss = findIndex ((== tag ws) . tag) wss

    -- | View next screen
    nextScreen :: X ()
    nextScreen = switchScreen 1

    -- | View prev screen
    prevScreen :: X ()
    prevScreen = switchScreen (-1)

    switchScreen :: Int -> X ()
    switchScreen d = do s <- screenBy d
                        mws <- screenWorkspace s
                        case mws of
                             Nothing -> return ()
                             Just ws -> windows (view ws)

    {- | Get the 'ScreenId' /d/ places over. Example usage is a variation of the
    the default screen keybindings:

    >     -- mod-{w,e}, Switch to previous/next Xinerama screen
    >     -- mod-shift-{w,e}, Move client to previous/next Xinerama screen
    >     --
    >     [((m .|. modm, key), sc >>= screenWorkspace >>= flip whenJust (windows . f))
    >         | (key, sc) <- zip [xK_w, xK_e] [(screenBy (-1)),(screenBy 1)]
    >         , (f, m) <- [(W.view, 0), (W.shift, shiftMask)]]

    -}
    screenBy :: Int -> X (ScreenId)
    screenBy d = do ws <- gets windowset
                    --let ss = sortBy screen (screens ws)
                    let now = screen (current ws)
                    return $ (now + fromIntegral d) `mod` fromIntegral (length (screens ws))

    -- | Swap current screen with next screen
    swapNextScreen :: X ()
    swapNextScreen = swapScreen 1

    -- | Swap current screen with previous screen
    swapPrevScreen :: X ()
    swapPrevScreen = swapScreen (-1)

    swapScreen :: Int -> X ()
    swapScreen d = do s <- screenBy d
                      mws <- screenWorkspace s
                      case mws of
                        Nothing -> return ()
                        Just ws -> windows (greedyView ws)

    -- | Move focused window to workspace on next screen
    shiftNextScreen :: X ()
    shiftNextScreen = shiftScreenBy 1

    -- | Move focused window to workspace on prev screen
    shiftPrevScreen :: X ()
    shiftPrevScreen = shiftScreenBy (-1)

    shiftScreenBy :: Int -> X ()
    shiftScreenBy d = do s <- screenBy d
                         mws <- screenWorkspace s
                         case mws of
                             Nothing -> return ()
                             Just ws -> windows (shift ws)