{-# LANGUAGE UndecidableInstances #-}

module Pandora.Paradigm.Primary.Transformer.Day where

import Pandora.Pattern.Category (($), (#))
import Pandora.Pattern.Functor.Covariant (Covariant ((<$>), (.#..)), Covariant_ ((-<$>-)))
import Pandora.Pattern.Functor.Pointable (Pointable (point))
import Pandora.Pattern.Functor.Extractable (Extractable (extract))
import Pandora.Pattern.Functor.Applicative (Applicative ((<*>)))
import Pandora.Pattern.Functor.Extendable (Extendable ((=>>)))
import Pandora.Pattern.Transformer.Lowerable (Lowerable (lower))
import Pandora.Pattern.Transformer.Hoistable (Hoistable ((/|\)))
import Pandora.Paradigm.Primary.Functor.Function ((!..), (-.#..-))
import Pandora.Paradigm.Primary.Functor.Product (Product ((:*:)))

data Day t u a = forall b c . Day (t b) (u c) (b -> c -> a)

instance Covariant (Day t u) where
	f <$> Day tb uc g = Day tb uc # f .#.. g

instance Covariant_ (Day t u) (->) (->) where
	f -<$>- Day tb uc g = Day tb uc # f -.#..- g

instance (Pointable t (->), Pointable u (->)) => Pointable (Day t u) (->) where
	point x = Day # point () # point () # (x !..)

instance (Applicative t, Applicative u) => Applicative (Day t u) where
	Day tb uc bcad <*> Day vb wc bca = Day # (:*:) <$> tb <*> vb # (:*:) <$> uc <*> wc
		$ \(b :*: b') (c :*: c') -> bcad b c $ bca b' c'

instance (Extractable t (->), Extractable u (->)) => Extractable (Day t u) (->) where
	extract (Day tb uc bcad) = bcad # extract tb # extract uc

instance (Extendable t, Extendable u) => Extendable (Day t u) where
	day@(Day tb uc _) =>> f = Day tb uc (f day !..)

instance Extractable t (->) => Lowerable (Day t) where
	lower (Day tb uc bca) = bca (extract tb) -<$>- uc

instance Hoistable (Day t) where
	g /|\ Day tb uc bca = Day tb # g uc # bca