data DeckDifference = Add !Card | Remove !Card

data DeckDifference = Add !Card | Remove !Card | ChangeQuantity !Int

eqCardName, eqQuantity, eqCategory :: Card -> Card -> Bool
eqCardName (Card {name = x}) (Card {name = y}) = x == y
eqQuantity (Card {quantity = x}) (Card {quantity = y}) = x == y
eqCategory (Card {category = x}) (Card {category = y}) = x == y

partialEqCard :: Eq a => (Card -> a) -> Card -> Card -> Bool
partialEqCard f x y = f x == f y

    go acc lx@(x:xs) ly@(y:ys)
        | x < y = go (Remove x : acc) xs ly
        | x > y = go (Add x : acc) lx ys

    go acc lx@(x : xs) ly@(y : ys)
        | name x < name y = go (Remove x : acc) xs ly
        | name x > name y = go (Add x : acc) lx ys
        | not $ partialEqCard quantity x y =
            go
                ( ChangeQuantity
                    ( (fromIntegral . unrefine . quantity $ y)
                        - (fromIntegral . unrefine . quantity $ x)
                    )
                    : acc
                )
                xs
                ys