Migrating a percentage off shipping script

危险配对 D16。这个文件和它的搭档看起来几乎一样，行为却不同，在判断您手上是哪一个之前，请把两份都读一遍。

# ================================ Customizable Settings ================================
DISCOUNT_TYPE = :percent
DISCOUNT_AMOUNT = 10
DISCOUNT_MESSAGE = '10% off shipping'

# ================================ Script Code (do not edit) ================================
class DiscountApplicator
  def initialize(discount_type, discount_amount, discount_message)
    @discount_type = discount_type
    @discount_message = discount_message

    @discount_amount = if discount_type == :percent
      discount_amount * 0.01
    else
      Money.new(cents: 100) * discount_amount
    end
  end

  def apply(shipping_rate)
    discount_amount = if @discount_type == :percent
      shipping_rate.price * @discount_amount
    else
      @discount_amount > shipping_rate.price ? shipping_rate.price : @discount_amount
    end

    shipping_rate.apply_discount(discount_amount, message: @discount_message)
  end
end

class DiscountRatesCampaign
  def initialize(discount_applicator)
    @discount_applicator = discount_applicator
  end

  def run(cart, shipping_rates)
    shipping_rates.each do |shipping_rate|
      @discount_applicator.apply(shipping_rate)
    end
  end
end

CAMPAIGNS = [
  DiscountRatesCampaign.new(
    DiscountApplicator.new(DISCOUNT_TYPE, DISCOUNT_AMOUNT, DISCOUNT_MESSAGE),
  ),
]

CAMPAIGNS.each do |campaign|
  campaign.run(Input.cart, Input.shipping_rates)
end

Output.shipping_rates = Input.shipping_rates

识别为 Shipping discount，重建为 free_shipping 类型的优惠。下面是优惠实际保存时使用的配置键，您可以逐项核对自己的重建结果。

基于我们的公开演示店铺 Meridian Goods 搭建，因此这里的每个价格都可以复现，而不必凭信任接受。下方的折扣金额，是结账时运行的同一个引擎针对这个购物车算出的结果。

This rule carries no condition at all, so it fires on any cart holding anything and there is no quiet cart to build. The negative check is an empty cart, which the app runs for you. That is correct behaviour, not a failure.