{-# LANGUAGE ExistentialQuantification #-}

module Phi.Panel ( Position(..)
                 , Panel(..)
                 , PanelClass(..)
                 , (<~>)
                 , separator
                 ) where

import Data.Function

data Position = Top | Bottom

class PanelClass a where
  minSize :: a -> Int
  
  weight :: a -> Float
  weight _ = 0

data Panel = forall a. PanelClass a => Panel a

instance PanelClass Panel where
  minSize (Panel p) = minSize p
  weight (Panel p) = weight p

data CompoundPanel = CompoundPanel Panel Panel

instance PanelClass CompoundPanel where
  minSize (CompoundPanel a b) = ((+) `on` minSize) a b
  weight (CompoundPanel a b) = ((+) `on` weight) a b

(<~>) :: Panel -> Panel -> Panel
a <~> b = Panel $ CompoundPanel a b


data Separator = Separator Int Float

instance PanelClass Separator where
  minSize (Separator s _) = s
  weight (Separator _ w) = w

separator :: Int -> Float -> Panel
separator s w = Panel $ Separator s w