module Returnly
  module Discounts
    class Order
      attr_reader :adjustment, :order

      def initialize(order, adjustment)
        @adjustment = adjustment
        @order      = order
      end

      def discount_amount(line_item, units = 0)
        return 0.0 if units <= 0

        units = line_item.quantity if units > line_item.quantity
        (adjustment.amount * price_percent(line_item) / 100) * weight_of(line_item, units.to_d)
      end

      private

      def price_percent(line_item)
        (line_item.price * 100 / order_items_price).round(2, :down)
      end

      def order_items_price
        order.line_items.sum(&:price)
      end

      def weight_of(line_item, units)
        (units / line_item.quantity).round(2, :down)
      end
    end
  end
end