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

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Layout.Accordion
    -- Copyright   :  (c) glasser@mit.edu
    -- License     :  BSD
    --
    -- Maintainer  :  glasser@mit.edu
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- LayoutClass that puts non-focused windows in ribbons at the top and bottom
    -- of the screen.
    -----------------------------------------------------------------------------

    module XMonad.Layout.Accordion (
        -- * Usage
        -- $usage
        Accordion(Accordion)) where

    import XMonad
    import qualified XMonad.StackSet as W
    import Data.Ratio

    -- $usage
    -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@:
    --
    -- > import XMonad.Layout.Accordion
    --
    -- Then edit your @layoutHook@ by adding the Accordion layout:
    --
    -- > myLayouts = Accordion ||| Full ||| etc..
    -- > main = xmonad defaultConfig { layoutHook = myLayouts }
    --
    -- For more detailed instructions on editing the layoutHook see:
    --
    -- "XMonad.Doc.Extending#Editing_the_layout_hook"

    data Accordion a = Accordion deriving ( Read, Show )

    instance LayoutClass Accordion Window where
        pureLayout _ sc ws = zip ups tops ++ [(W.focus ws, mainPane)] ++ zip dns bottoms
         where
           ups    = W.up ws
           dns    = W.down ws
           (top,  allButTop) = splitVerticallyBy (1%8 :: Ratio Int) sc
           (center,  bottom) = splitVerticallyBy (6%7 :: Ratio Int) allButTop
           (allButBottom, _) = splitVerticallyBy (7%8 :: Ratio Int) sc
           mainPane | ups /= [] && dns /= [] = center
                    | ups /= []              = allButTop
                    | dns /= []              = allButBottom
                    | otherwise              = sc
           tops    = if ups /= [] then splitVertically (length ups) top    else []
           bottoms = if dns /= [] then splitVertically (length dns) bottom else []