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

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Layout.Circle
    -- Copyright   :  (c) Peter De Wachter
    -- License     :  BSD-style (see LICENSE)
    --
    -- Maintainer  :  Peter De Wachter <pdewacht@gmail.com>
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- Circle is an elliptical, overlapping layout, by Peter De Wachter
    --
    -----------------------------------------------------------------------------

    module XMonad.Layout.Circle (
                                 -- * Usage
                                 -- $usage
                                 Circle (..)
                                ) where -- actually it's an ellipse

    import Data.List
    import XMonad
    import XMonad.StackSet (integrate, peek)

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

    data Circle a = Circle deriving ( Read, Show )

    instance LayoutClass Circle Window where
        doLayout Circle r s = do layout <- raiseFocus $ circleLayout r $ integrate s
                                 return (layout, Nothing)

    circleLayout :: Rectangle -> [a] -> [(a, Rectangle)]
    circleLayout _ []     = []
    circleLayout r (w:ws) = master : rest
        where master = (w, center r)
              rest   = zip ws $ map (satellite r) [0, pi * 2 / fromIntegral (length ws) ..]

    raiseFocus :: [(Window, Rectangle)] -> X [(Window, Rectangle)]
    raiseFocus xs = do focused <- withWindowSet (return . peek)
                       return $ case find ((== focused) . Just . fst) xs of
                                  Just x  -> x : delete x xs
                                  Nothing -> xs

    center :: Rectangle -> Rectangle
    center (Rectangle sx sy sw sh) = Rectangle x y w h
        where s = sqrt 2 :: Double
              w = round (fromIntegral sw / s)
              h = round (fromIntegral sh / s)
              x = sx + fromIntegral (sw - w) `div` 2
              y = sy + fromIntegral (sh - h) `div` 2

    satellite :: Rectangle -> Double -> Rectangle
    satellite (Rectangle sx sy sw sh) a = Rectangle (sx + round (rx + rx * cos a))
                                                    (sy + round (ry + ry * sin a))
                                                    w h
        where rx = fromIntegral (sw - w) / 2
              ry = fromIntegral (sh - h) / 2
              w = sw * 10 `div` 25
              h = sh * 10 `div` 25