{-# LANGUAGE MultiParamTypeClasses, StandaloneDeriving, ExistentialQuantification, FlexibleInstances #-}

module Phi.Widgets.AlphaBox ( AlphaBox
                            , alphaBox
                            ) where

import Phi.Types
import Phi.Widget

import Control.Monad
import Control.Monad.State.Strict

import Graphics.Rendering.Cairo


data AlphaBox w s c d = (Widget w s c d) => AlphaBox !Double !w

data AlphaBoxCache w s c d = (Widget w s c d) => AlphaBoxCache !c

instance (Eq s, Display d) => Widget (AlphaBox w s c d) s (AlphaBoxCache w s c d) d where
  initWidget (AlphaBox _ w) = initWidget w
  initCache (AlphaBox _ w) = AlphaBoxCache $ initCache w
  
  minSize (AlphaBox _ w) = minSize w
  
  weight (AlphaBox _ w) = weight w
  
  render (AlphaBox alpha w) s x y width height screen = do
    AlphaBoxCache c <- get
    (surfaces, c') <- liftIO $ flip runStateT c $ render w s x y width height screen
    put $ AlphaBoxCache c'

    let surfacesWidths = zipWith (\(updated, SurfaceSlice x surf) x' -> (updated, x, x'-x, surf)) surfaces (map (\(_, SurfaceSlice x _) -> x) (tail surfaces) ++ [width])
    forM surfacesWidths $ \(updated, x, surfWidth, surf) -> do
      surf' <- liftIO $ createImageSurface FormatARGB32  surfWidth height
      renderWith surf' $ do
        setOperator OperatorSource
        withPatternForSurface surf setSource
        paint
        
        setOperator OperatorDestIn
        setSourceRGBA 0 0 0 alpha
        paint
      
      return (updated, SurfaceSlice x surf')
  
  handleMessage (AlphaBox _ w) = handleMessage w


alphaBox :: (Widget w s c d) => Double -> w -> AlphaBox w s c d
alphaBox = AlphaBox