{-# LANGUAGE DeriveDataTypeable, ExistentialQuantification, Rank2Types, MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, FlexibleContexts, PatternGuards #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  XMonad.Layout.MultiToggle
-- Copyright   :  (c) Lukas Mai
-- License     :  BSD-style (see LICENSE)
--
-- Maintainer  :  <l.mai@web.de>
-- Stability   :  unstable
-- Portability :  unportable
--
-- Dynamically apply and unapply transformers to your window layout. This can
-- be used to rotate your window layout by 90 degrees, or to make the
-- currently focused window occupy the whole screen (\"zoom in\") then undo
-- the transformation (\"zoom out\").

module XMonad.Layout.MultiToggle (
    -- * Usage
    -- $usage
    Transformer(..),
    Toggle(..),
    (??),
    EOT(..),
    single,
    mkToggle,
    mkToggle1,

    HList,
    HCons,
    MultiToggle,
) where

import XMonad

import XMonad.StackSet (Workspace(..))

import Control.Arrow
import Data.Typeable
import Data.Maybe

-- $usage
-- The basic idea is to have a base layout and a set of layout transformers,
-- of which at most one is active at any time. Enabling another transformer
-- first disables any currently active transformer; i.e. it works like a
-- group of radio buttons.
--
-- To use this module, you need some data types which represent
-- transformers; for some commonly used transformers (including
-- MIRROR, NOBORDERS, and FULL used in the examples below) you can
-- simply import "XMonad.Layout.MultiToggle.Instances".
--
-- Somewhere else in your file you probably have a definition of @layout@;
-- the default looks like this:
--
-- > layout = tiled ||| Mirror tiled ||| Full
--
-- After changing this to
--
-- > layout = mkToggle (single MIRROR) (tiled ||| Full)
--
-- you can now dynamically apply the 'XMonad.Layout.Mirror' transformation:
--
-- > ...
-- >   , ((modm,               xK_x     ), sendMessage $ Toggle MIRROR)
-- > ...
--
-- (That should be part of your key bindings.) When you press @mod-x@, the
-- active layout is mirrored. Another @mod-x@ and it's back to normal.
--
-- It's also possible to stack @MultiToggle@s.  For example:
--
-- @
-- layout = id
--     . 'XMonad.Layout.NoBorders.smartBorders'
--     . mkToggle (NOBORDERS ?? FULL ?? EOT)
--     . mkToggle (single MIRROR)
--     $ tiled ||| 'XMonad.Layout.Grid.Grid' ||| 'XMonad.Layout.Circle.Circle'
-- @
--
-- By binding a key to @(sendMessage $ Toggle FULL)@ you can temporarily
-- maximize windows, in addition to being able to rotate layouts and remove
-- window borders.
--
-- You can also define your own transformers by creating a data type
-- which is an instance of the 'Transformer' class.  For example, here
-- is the definition of @MIRROR@:
--
-- > data MIRROR = MIRROR deriving (Read, Show, Eq, Typeable)
-- > instance Transformer MIRROR Window where
-- >     transform _ x k = k (Mirror x) (\(Mirror x') -> x')
--
-- Note, you need to put @{-\# LANGUAGE DeriveDataTypeable \#-}@ at the
-- beginning of your file.

-- | A class to identify custom transformers (and look up transforming
-- functions by type).
class (Eq t, Typeable t) => Transformer t a | t -> a where
    transform :: (LayoutClass l a) => t -> l a ->
        (forall l'. (LayoutClass l' a) => l' a -> (l' a -> l a) -> b) -> b

data  EL l a = forall l'. (LayoutClass l' a) => EL (l' a) (l' a -> l a)

unEL :: (LayoutClass l a) => EL l a -> (forall l'. (LayoutClass l' a) => l' a -> b) -> b
unEL (EL x _) k = k x

deEL :: (LayoutClass l a) => EL l a -> l a
deEL (EL x det) = det x

transform' :: (Transformer t a, LayoutClass l a) => t -> EL l a -> EL l a
transform' t (EL l det) = transform t l (\l' det' -> EL l' (det . det'))

-- | Toggle the specified layout transformer.
data Toggle a = forall t. (Transformer t a) => Toggle t
    deriving (Typeable)

instance (Typeable a) => Message (Toggle a)

data MultiToggleS ts l a = MultiToggleS (l a) (Maybe Int) ts
    deriving (Read, Show)

data MultiToggle ts l a = MultiToggle{
    currLayout :: EL l a,
    currIndex :: Maybe Int,
    transformers :: ts
}

expand :: (LayoutClass l a, HList ts a) => MultiToggleS ts l a -> MultiToggle ts l a
expand (MultiToggleS b i ts) =
    resolve ts (fromMaybe (-1) i) id
        (\x mt ->
            let g = transform' x in mt{ currLayout = g $ currLayout mt }
        )
        (MultiToggle (EL b id) i ts)

collapse :: (LayoutClass l a) => MultiToggle ts l a -> MultiToggleS ts l a
collapse mt = MultiToggleS (deEL (currLayout mt)) (currIndex mt) (transformers mt)

instance (LayoutClass l a, Read (l a), HList ts a, Read ts) => Read (MultiToggle ts l a) where
    readsPrec p s = map (first expand) $ readsPrec p s

instance (Show ts, Show (l a), LayoutClass l a) => Show (MultiToggle ts l a) where
    showsPrec p = showsPrec p . collapse

-- | Construct a @MultiToggle@ layout from a transformer table and a base
-- layout.
mkToggle :: (LayoutClass l a) => ts -> l a -> MultiToggle ts l a
mkToggle ts l = MultiToggle (EL l id) Nothing ts

-- | Construct a @MultiToggle@ layout from a single transformer and a base
-- layout.
mkToggle1 :: (LayoutClass l a) => t -> l a -> MultiToggle (HCons t EOT) l a
mkToggle1 t = mkToggle (single t)

-- | Marks the end of a transformer list.
data EOT = EOT deriving (Read, Show)
data HCons a b = HCons a b deriving (Read, Show)

infixr 0 ??
-- | Prepend an element to a heterogeneous list. Used to build transformer
-- tables for 'mkToggle'.
(??) ::  a -> b -> HCons a b
(??) = HCons

-- | Construct a singleton transformer table.
single :: a -> HCons a EOT
single = (?? EOT)

class HList c a where
    find :: (Transformer t a) => c -> t -> Maybe Int
    resolve :: c -> Int -> b -> (forall t. (Transformer t a) => t -> b) -> b

instance HList EOT w where
    find EOT _ = Nothing
    resolve EOT _ d _ = d

instance (Transformer a w, HList b w) => HList (HCons a b) w where
    find (HCons x xs) t
        | t `geq` x = Just 0
        | otherwise = fmap succ (find xs t)
    resolve (HCons x xs) n d k =
        case n `compare` 0 of
            LT -> d
            EQ -> k x
            GT -> resolve xs (pred n) d k

geq :: (Typeable a, Eq a, Typeable b) => a -> b -> Bool
geq a b = Just a == cast b

instance (Typeable a, Show ts, HList ts a, LayoutClass l a) => LayoutClass (MultiToggle ts l) a where
    description mt = currLayout mt `unEL` \l -> description l

    runLayout (Workspace i mt s) r = case currLayout mt of
        EL l det -> fmap (fmap . fmap $ (\x -> mt { currLayout = EL x det })) $
            runLayout (Workspace i l s) r

    handleMessage mt m
        | Just (Toggle t) <- fromMessage m
        , i@(Just _) <- find (transformers mt) t
            = case currLayout mt of
                EL l det -> do
                    l' <- fromMaybe l `fmap` handleMessage l (SomeMessage ReleaseResources)
                    return . Just $
                        mt {
                            currLayout = (if cur then id else transform' t) (EL (det l') id),
                            currIndex = if cur then Nothing else i
                        }
                    where cur = (i == currIndex mt)
        | otherwise
            = case currLayout mt of
                EL l det -> fmap (fmap (\x -> mt { currLayout = EL x det })) $
                    handleMessage l m
