module Hcompta.Quantity where

import           Data.Bool
import           Data.Data (Data)
import           Data.Eq (Eq(..))
import           Data.Foldable (all)
import           Data.Map.Strict (Map)
import qualified Data.Map.Strict as Map
import           Data.Ord (Ord(..), Ordering(..))
import           Prelude (Integer, Num(..))
import           Text.Show (Show)

-- * Class 'Zero'
class
 ( Data a
 , Show a
 ) => Zero a where
	quantity_zero :: a
	quantity_null :: a -> Bool
instance
 ( Data unit
 , Show q
 , Show unit
 , Ord  unit
 , Zero q
 ) => Zero (Map unit q) where
	quantity_zero = Map.empty
	quantity_null = all quantity_null
instance Zero Integer where
	quantity_zero = 0
	quantity_null = (==) 0

quantity_sign :: (Zero q, Ord q) => q -> Ordering
quantity_sign q =
	case q of
	 _ | quantity_null q -> EQ
	 _ | q < quantity_zero -> LT
	 _ -> GT

-- * Class 'Addable'
class
 ( Data a
 , Show a
 ) =>
 Addable a where
	quantity_add :: a -> a -> a
instance Addable Integer where
	quantity_add = (+)
instance
 ( Addable quantity
 , Data unit
 , Ord  unit
 , Show unit
 ) => Addable (Map unit quantity) where
	quantity_add = Map.unionWith quantity_add

-- * Class 'Negable'
class
 ( Data a
 , Show a
 ) =>
 Negable a where
	quantity_neg  :: a -> a
instance Negable Integer where
	quantity_neg = negate
instance
 ( Negable quantity
 , Data    unit
 , Ord     unit
 , Show    unit
 ) => Negable (Map unit quantity) where
	quantity_neg = Map.map quantity_neg

-- * Class 'Subable'
class
 ( Data a
 , Show a
 ) =>
 Subable a where
	quantity_sub :: a -> a -> a
instance Subable Integer where
	quantity_sub = (-)
instance
 ( Subable quantity
 , Data    unit
 , Ord     unit
 , Show    unit
 ) => Subable (Map unit quantity) where
	quantity_sub = Map.unionWith quantity_sub