content: {-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-}
  
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  XMonad.Layout.ThreeColumns
  -- Copyright   :  (c) Kai Grossjohann <kai@emptydomain.de>
  -- License     :  BSD3-style (see LICENSE)
  --
  -- Maintainer  :  ?
  -- Stability   :  unstable
  -- Portability :  unportable
  --
  -- A layout similar to tall but with three columns. With 2560x1600 pixels this
  -- layout can be used for a huge main window and up to six reasonable sized
  -- slave windows.
  -----------------------------------------------------------------------------
  
  module XMonad.Layout.ThreeColumns (
                                -- * Usage
                                -- $usage
  
                                -- * Screenshots
                                -- $screenshot
                                ThreeCol(..)
                               ) where
  
  import XMonad
  import qualified XMonad.StackSet as W
  
  import Data.Ratio
  
  import Control.Monad
  
  -- $usage
  -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@:
  --
  -- > import XMonad.Layout.ThreeColumns
  --
  -- Then edit your @layoutHook@ by adding the ThreeCol layout:
  --
  -- > myLayout = ThreeCol 1 (3/100) (1/2) ||| ThreeColMid 1 (3/100) (1/2) ||| etc..
  -- > main = xmonad def { layoutHook = myLayout }
  --
  -- The first argument specifies how many windows initially appear in the main
  -- window. The second argument argument specifies the amount to resize while
  -- resizing and the third argument specifies the initial size of the columns.
  -- A positive size designates the fraction of the screen that the main window
  -- should occupy, but if the size is negative the absolute value designates the
  -- fraction a slave column should occupy. If both slave columns are visible,
  -- they always occupy the same amount of space.
  --
  -- The ThreeColMid variant places the main window between the slave columns.
  --
  -- For more detailed instructions on editing the layoutHook see:
  --
  -- "XMonad.Doc.Extending#Editing_the_layout_hook"
  
  
  -- $screenshot
  -- <<http://server.c-otto.de/xmonad/ThreeColumnsMiddle.png>>
  
  -- | Arguments are nmaster, delta, fraction
  data ThreeCol a = ThreeColMid { threeColNMaster :: !Int, threeColDelta :: !Rational, threeColFrac :: !Rational}
                  | ThreeCol    { threeColNMaster :: !Int, threeColDelta :: !Rational, threeColFrac :: !Rational}
      deriving (Show,Read)
  
  instance LayoutClass ThreeCol a where
      pureLayout (ThreeCol n _ f) r    = doL False n f r
      pureLayout (ThreeColMid n _ f) r = doL True n f r
      handleMessage l m =
          return $ msum [fmap resize     (fromMessage m)
                        ,fmap incmastern (fromMessage m)]
              where resize Shrink = l { threeColFrac = max (-0.5) $ f-d }
                    resize Expand = l { threeColFrac = min 1 $ f+d }
                    incmastern (IncMasterN x) = l { threeColNMaster = max 0 (n+x) }
                    n = threeColNMaster l
                    d = threeColDelta l
                    f = threeColFrac l
      description _ = "ThreeCol"
  
  doL :: Bool-> Int-> Rational-> Rectangle-> W.Stack a-> [(a, Rectangle)]
  doL m n f r = ap zip (tile3 m f r n . length) . W.integrate
  
  -- | tile3.  Compute window positions using 3 panes
  tile3 :: Bool -> Rational -> Rectangle -> Int -> Int -> [Rectangle]
  tile3 middle f r nmaster n
      | n <= nmaster || nmaster == 0 = splitVertically n r
      | n <= nmaster+1 = splitVertically nmaster s1 ++ splitVertically (n-nmaster) s2
      | otherwise = splitVertically nmaster r1 ++ splitVertically nslave1 r2 ++ splitVertically nslave2 r3
          where (r1, r2, r3) = split3HorizontallyBy middle (if f<0 then 1+2*f else f) r
                (s1, s2) = splitHorizontallyBy (if f<0 then 1+f else f) r
                nslave = (n - nmaster)
                nslave1 = ceiling (nslave % 2)
                nslave2 = (n - nmaster - nslave1)
  
  split3HorizontallyBy :: Bool -> Rational -> Rectangle -> (Rectangle, Rectangle, Rectangle)
  split3HorizontallyBy middle f (Rectangle sx sy sw sh) =
      if middle
      then ( Rectangle (sx + fromIntegral r3w) sy r1w sh
           , Rectangle (sx + fromIntegral r3w + fromIntegral r1w) sy r2w sh
           , Rectangle sx sy r3w sh )
      else ( Rectangle sx sy r1w sh
           , Rectangle (sx + fromIntegral r1w) sy r2w sh
           , Rectangle (sx + fromIntegral r1w + fromIntegral r2w) sy r3w sh )
          where r1w = ceiling $ fromIntegral sw * f
                r2w = ceiling ( (sw - r1w) % 2 )
                r3w = sw - r1w - r2w
  