{-# LANGUAGE CPP #-}

module Data.PQueue.Prio.Max.Internals where

import Control.Applicative
import Control.DeepSeq

import Data.Foldable
import Data.Traversable
# if __GLASGOW_HASKELL__
import Data.Data
# endif

import Prelude hiding (foldr, foldl)

import Data.PQueue.Prio.Internals (MinPQueue)

newtype Down a = Down {unDown :: a} 
# if __GLASGOW_HASKELL__
	deriving (Eq, Data, Typeable)
# else
	deriving (Eq)
# endif

-- | A priority queue where values of type @a@ are annotated with keys of type @k@.
-- The queue supports extracting the element with maximum key.
newtype MaxPQueue k a = MaxPQ (MinPQueue (Down k) a)
# if __GLASGOW_HASKELL__
	deriving (Eq, Ord, Data, Typeable)
# else
	deriving (Eq, Ord)
# endif

instance (NFData k, NFData a) => NFData (MaxPQueue k a) where
	rnf (MaxPQ q) = rnf q

instance NFData a => NFData (Down a) where
	rnf (Down a) = rnf a

instance Ord a => Ord (Down a) where
	Down a `compare` Down b = b `compare` a
	Down a <= Down b = b <= a

instance Functor Down where
	fmap f (Down a) = Down (f a)


instance Foldable Down where
	foldr f z (Down a) = a `f` z
	foldl f z (Down a) = z `f` a

instance Traversable Down where
	traverse f (Down a) = Down <$> f a