{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE TypeFamilies #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
module Hcompta.Amount where

import           Data.Data (Data)
import           Data.Eq (Eq(..))
import           Data.Functor (Functor(..))
import           Data.Ord (Ord(..), Ordering)
import           Data.Tuple (fst, snd)
import           Prelude (($), (.))

import           Hcompta.Polarize
import           Hcompta.Quantity
import           Hcompta.Unit (Unit(..))

-- * Class 'Amount'

class
 ( Data a
 , Eq   (Amount_Quantity a)
 , Zero (Amount_Quantity a)
 , Unit (Amount_Unit     a)
 ) =>  Amount          a where
	type Amount_Quantity a
	type Amount_Unit     a
	amount_quantity :: a -> Amount_Quantity a
	amount_unit     :: a -> Amount_Unit     a
instance
 ( Zero quantity
 , Eq   quantity
 , Unit unit
 ) => Amount (unit, quantity) where
	type Amount_Quantity (unit, quantity) = quantity
	type Amount_Unit     (unit, quantity) = unit
	amount_quantity = snd
	amount_unit     = fst
instance
 ( Polarizable quantity
 ) => Polarizable (unit, quantity) where
	polarizable_positive (u, q) = fmap (u,) $ polarizable_positive q
	polarizable_negative (u, q) = fmap (u,) $ polarizable_negative q

amount_sign ::
 ( Amount a
 , Ord (Amount_Quantity a)
 ) => a -> Ordering
amount_sign =
	quantity_sign . amount_quantity