    {-# OPTIONS_GHC -fno-warn-name-shadowing -fno-warn-unused-binds #-}
    {-# LANGUAGE FlexibleInstances, MultiParamTypeClasses
      , PatternGuards, DeriveDataTypeable, ExistentialQuantification
      , FlexibleContexts #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Layout.ZoomRow
    -- Copyright   :  Quentin Moser <moserq@gmail.com>
    -- License     :  BSD-style (see LICENSE)
    --
    -- Maintainer  :  orphaned
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- Row layout with individually resizable elements.
    --
    -----------------------------------------------------------------------------

    module XMonad.Layout.ZoomRow ( -- * Usage
                                   -- $usage
                                   ZoomRow
                                   -- * Creation
                                 , zoomRow
                                   -- * Messages
                                 , ZoomMessage(..)
                                 , zoomIn
                                 , zoomOut
                                 , zoomReset
                                   -- * Use with non-'Eq' elements
                                   -- $noneq
                                 , zoomRowWith
                                 , EQF(..)
                                 , ClassEQ(..)
                                 ) where

    import XMonad
    import qualified XMonad.StackSet as W

    import XMonad.Util.Stack
    import XMonad.Layout.Decoration (fi)

    import Data.Maybe (fromMaybe)
    import Control.Arrow (second)

    -- $usage
    -- This module provides a layout which places all windows in a single
    -- row; the size occupied by each individual window can be increased
    -- and decreased, and a window can be set to use the whole available
    -- space whenever it has focus.
    --
    -- You can use this module by including  the following in your @~\/.xmonad/xmonad.hs@:
    --
    -- > import XMonad.Layout.ZoomRow
    --
    -- and using 'zoomRow' somewhere in your 'layoutHook', for example:
    --
    -- > myLayout = zoomRow ||| Mirror zoomRow
    --
    -- To be able to resize windows, you can create keybindings to send
    -- the relevant 'ZoomMessage's:
    --
    -- >   -- Increase the size occupied by the focused window
    -- > , ((modMask .|. shifMask, xK_minus), sendMessage zoomIn)
    -- >   -- Decrease the size occupied by the focused window
    -- > , ((modMayk             , xK_minus), sendMessage zoomOut)
    -- >   -- Reset the size occupied by the focused window
    -- > , ((modMask             , xK_equal), sendMessage zoomReset)
    -- >   -- (Un)Maximize the focused window
    -- > , ((modMask             , xK_f    ), sendMessage ToggleZoomFull)
    --
    -- For more information on editing your layout hook and key bindings,
    -- see "XMonad.Doc.Extending".

    -- * Creation functions

    -- | 'ZoomRow' layout for laying out elements which are instances of
    -- 'Eq'. Perfect for 'Window's.
    zoomRow :: (Eq a, Show a, Read a) => ZoomRow ClassEQ a
    zoomRow = ZC ClassEQ emptyZ

    -- $noneq
    -- Haskell's 'Eq' class is usually concerned with structural equality, whereas
    -- what this layout really wants is for its elements to have a unique identity,
    -- even across changes. There are cases (such as, importantly, 'Window's) where
    -- the 'Eq' instance for a type actually does that, but if you want to lay
    -- out something more exotic than windows and your 'Eq' means something else,
    -- you can use the following.

    -- | ZoomRow layout with a custom equality predicate. It should
    -- of course satisfy the laws for 'Eq', and you should also make
    -- sure that the layout never has to handle two \"equal\" elements
    -- at the same time (it won't do any huge damage, but might behave
    -- a bit strangely).
    zoomRowWith :: (EQF f a, Show (f a), Read (f a), Show a, Read a)
                   => f a -> ZoomRow f a
    zoomRowWith f = ZC f emptyZ

    -- * The datatypes

    -- | A layout that arranges its windows in a horizontal row,
    -- and allows to change the relative size of each element
    -- independently.
    data ZoomRow f a = ZC { zoomEq ::  f a
                              -- ^ Function to compare elements for
                              -- equality, a real Eq instance might
                              -- not be what you want in some cases
                          , zoomRatios :: (Zipper (Elt a))
                              -- ^ Element specs. The zipper is so we
                              -- know what the focus is when we handle
                              --  a message
                          }
      deriving (Show, Read, Eq)

    -- | Class for equivalence relations. Must be transitive, reflexive.
    class EQF f a where
        eq :: f a -> a -> a -> Bool

    -- | To use the usual '==':
    data ClassEQ a = ClassEQ
      deriving (Show, Read, Eq)

    instance Eq a => EQF ClassEQ a where
        eq _ a b = a == b

    -- | Size specification for an element.
    data Elt a = E { elt :: a -- ^ The element
                   , ratio :: Rational -- ^ Its size ratio
                   , full :: Bool -- ^ Whether it should occupy all the
                                  -- available space when it has focus.
                   }
      deriving (Show, Read, Eq)

    -- * Helpers

    getRatio :: Elt a -> (a, Rational)
    getRatio (E a r _) = (a,r)

    lookupBy :: (a -> a -> Bool) -> a -> [Elt a] -> Maybe (Elt a)
    lookupBy _ _ [] = Nothing
    lookupBy f a (E a' r b : _) | f a a' = Just $ E a r b
    lookupBy f a (_:es) = lookupBy f a es

    setFocus :: Zipper a -> a -> Zipper a
    setFocus Nothing a = Just $ W.Stack a [] []
    setFocus (Just s) a = Just s { W.focus = a }

    -- * Messages

    -- | The type of messages accepted by a 'ZoomRow' layout
    data ZoomMessage = Zoom Rational
                     -- ^ Multiply the focused window's size factor
                     -- by the given number.
                     | ZoomTo Rational
                     -- ^ Set the focused window's size factor to the
                     -- given number.
                     | ZoomFull Bool
                     -- ^ Set whether the focused window should occupy
                     -- all available space when it has focus
                     | ZoomFullToggle
                     -- ^ Toggle whether the focused window should
                     -- occupy all available space when it has focus
      deriving (Typeable, Show)

    instance Message ZoomMessage

    -- | Increase the size of the focused window.
    -- Defined as @Zoom 1.5@
    zoomIn :: ZoomMessage
    zoomIn = Zoom 1.5

    -- | Decrease the size of the focused window.
    -- Defined as @Zoom (2/3)@
    zoomOut :: ZoomMessage
    zoomOut = Zoom $ 2/3

    -- | Reset the size of the focused window.
    -- Defined as @ZoomTo 1@
    zoomReset :: ZoomMessage
    zoomReset = ZoomTo 1

    -- * LayoutClass instance

    instance (EQF f a, Show a, Read a, Show (f a), Read (f a))
        => LayoutClass (ZoomRow f) a where
        description (ZC _ Nothing) = "ZoomRow"
        description (ZC _ (Just s)) = "ZoomRow" ++ if full $ W.focus s
                                                    then " (Max)"
                                                    else ""

        emptyLayout (ZC _ Nothing) _ = return ([], Nothing)
        emptyLayout (ZC f _) _ = return ([], Just $ ZC f Nothing)

        doLayout (ZC f zelts) r@(Rectangle _ _ w _) s
            = let elts = W.integrate' zelts
                  zelts' = mapZ_ (\a -> fromMaybe (E a 1 False)
                                        $ lookupBy (eq f) a elts) $ Just s
                  elts' = W.integrate' zelts'

                  maybeL' = if zelts `noChange` zelts'
                              then Nothing
                              else Just $ ZC f zelts'

                  total = sum  $ map ratio elts'

                  widths =  map (second ((* fi w) . (/total)) . getRatio) elts'

              in case getFocusZ zelts' of
                   Just (E a _ True) -> return ([(a, r)], maybeL')
                   _ -> return (makeRects r widths, maybeL')

            where makeRects :: Rectangle -> [(a, Rational)] -> [(a, Rectangle)]
                  makeRects r pairs = let as = map fst pairs
                                          widths = map snd pairs
                                          discreteWidths = snd $ foldr discretize (0, []) widths
                                          rectangles = snd $ foldr makeRect (r, []) discreteWidths
                                      in zip as rectangles

                  -- | Make a new rectangle by substracting the given width from the available
                  -- space (from the right, since this is a foldr)
                  makeRect :: Dimension -> (Rectangle, [Rectangle]) -> (Rectangle, [Rectangle])
                  makeRect w (Rectangle x y w0 h, rs) = ( Rectangle x y (w0-w) h
                                                        , Rectangle (x+fi w0-fi w) y w h : rs )

                  -- | Round a list of fractions in a way that maintains the total.
                  -- If you know a better way to do this I'm very interested.
                  discretize :: Rational -> (Rational, [Dimension]) -> (Rational, [Dimension])
                  discretize r (carry, ds) = let (d, carry') = properFraction $ carry+r
                                             in (carry', d:ds)

                  noChange z1 z2 = toTags z1 `helper` toTags z2
                      where helper [] [] = True
                            helper (Right a:as) (Right b:bs) = a `sameAs` b && as `helper` bs
                            helper (Left a:as) (Left b:bs) = a `sameAs` b && as `helper` bs
                            helper _ _ = False
                            E a1 r1 b1 `sameAs` E a2 r2 b2 = (eq f a1 a2) && (r1 == r2) && (b1 == b2)

        pureMessage (ZC f zelts) sm | Just (ZoomFull False) <- fromMessage sm
                                    , Just (E a r True) <- getFocusZ zelts
            = Just $ ZC f $ setFocus zelts $ E a r False

        pureMessage (ZC f zelts) sm | Just (ZoomFull True) <- fromMessage sm
                                    , Just (E a r False) <- getFocusZ zelts
            = Just $ ZC f $ setFocus zelts $ E a r True

        pureMessage (ZC f zelts) sm | Just (E a r b) <- getFocusZ zelts
            = case fromMessage sm of
                Just (Zoom r') -> Just $ ZC f $ setFocus zelts $ E a (r*r') b
                Just (ZoomTo r') -> Just $ ZC f $ setFocus zelts $ E a r' b
                Just ZoomFullToggle -> pureMessage (ZC f zelts)
                                         $ SomeMessage $ ZoomFull $ not b
                _ -> Nothing

        pureMessage _ _ = Nothing