module Shopper
  module OrderArithmeticHelpers
    def delivery_price
      delivery&.price || 0
    end

    def coupon_discount
      coupon&.discount || 0
    end

    def subtotal
      order_items.inject(0) { |sum, item| sum + item.subtotal }
    end

    def saved_by_coupon
      return 0 unless coupon_discount
      subtotal * coupon_discount / 100
    end

    def total
      subtotal - saved_by_coupon + delivery_price
    end
  end
end