    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Layout.IfMax
    -- Copyright   :  (c) 2013 Ilya Portnov
    -- License     :  BSD3-style (see LICENSE)
    --
    -- Maintainer  :  Ilya Portnov <portnov84@rambler.ru>
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- Provides IfMax layout, which will run one layout if there are maximum N
    -- windows on workspace, and another layout, when number of windows is greater
    -- than N.
    --
    -----------------------------------------------------------------------------

    {-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-}

    module XMonad.Layout.IfMax
        ( -- * Usage
          -- $usage
          IfMax (..)
        , ifMax
        ) where

    import Data.Maybe

    import XMonad
    import qualified XMonad.StackSet as W

    -- $usage
    -- IfMax layout will run one layout if number of windows on workspace is as
    -- maximum N, and else will run another layout.
    --
    -- You can use this module by adding folowing in your @xmonad.hs@:
    --
    -- > import XMonad.Layout.IfMax
    --
    -- Then add layouts to your layoutHook:
    --
    -- > myLayoutHook = IfMax 2 Full (Tall ...) ||| ...
    --
    -- In this example, if there are 1 or 2 windows, Full layout will be used;
    -- otherwise, Tall layout will be used.
    --

    data IfMax l1 l2 w = IfMax Int (l1 w) (l2 w)
      deriving (Read, Show)

    instance (LayoutClass l1 a, LayoutClass l2 a) => LayoutClass (IfMax l1 l2) a where

      runLayout (W.Workspace _ (IfMax n l1 l2) s) rect = arrange (W.integrate' s)
        where
          arrange [] = do l1' <- maybe l1 id `fmap` handleMessage l1 (SomeMessage ReleaseResources)
                          l2' <- maybe l2 id `fmap` handleMessage l2 (SomeMessage ReleaseResources)
                          return ([], Just $ IfMax n l1' l2')
          arrange ws | length ws <= n = do
                                        (wrs, ml1') <- runLayout (W.Workspace "" l1 s) rect
                                        let l1' = fromMaybe l1 ml1'
                                        return (wrs, Just $ IfMax n l1' l2)
                     | otherwise      = do
                                        (wrs, ml2') <- runLayout (W.Workspace "" l2 s) rect
                                        let l2' = fromMaybe l2 ml2'
                                        return (wrs, Just $ IfMax n l1 l2')

      description (IfMax n l1 l2) = "If number of windows is <= " ++ show n ++ ", then " ++
                                    description l1 ++ ", else " ++ description l2

    -- | Layout itself
    ifMax :: (LayoutClass l1 w, LayoutClass l2 w)
          => Int            -- ^ Maximum number of windows for the first layout
          -> l1 w           -- ^ First layout
          -> l2 w           -- ^ Second layout
          -> IfMax l1 l2 w
    ifMax n l1 l2 = IfMax n l1 l2