Migrating a Shopify Script Creator script

# GENERATED BY THE SHOPIFY SCRIPT CREATOR APP
# Version 0.12.0

class Campaign
  def initialize(condition, *qualifiers)
    @condition = (condition.to_s + '?').to_sym
    @qualifiers = PostCartAmountQualifier ? [] : [] rescue qualifiers.compact
    @line_item_selector = qualifiers.last unless @line_item_selector
    qualifiers.compact.each do |qualifier|
      is_multi_select = qualifier.instance_variable_get(:@conditions).is_a?(Array)
      if is_multi_select
        qualifier.instance_variable_get(:@conditions).each do |nested_q|
          @post_amount_qualifier = nested_q if nested_q.is_a?(PostCartAmountQualifier)
          @qualifiers << qualifier
        end
      else
        @post_amount_qualifier = qualifier if qualifier.is_a?(PostCartAmountQualifier)
        @qualifiers << qualifier
      end
    end if @qualifiers.empty?
  end

  def qualifies?(cart)
    return true if @qualifiers.empty?
    @qualifiers.send(@condition) do |qualifier|
      is_selector = false
      if qualifier.is_a?(Selector) || qualifier.is_a?(Array)
        is_selector = true
      end rescue nil
      if is_selector
        raise 'Missing line item match type' if @li_match_type.nil?
        cart.line_items.send(@li_match_type) { |item| qualifier.match?(item) }
      else
        qualifier.match?(cart, @selector)
      end
    end
  end
end

class ProductTagSelector < Selector
  def initialize(match_type, match_condition, tags)
    @match_condition = match_condition
    @invert = match_type == :does_not
    @tags = tags.map(&:downcase)
  end

  def match?(line_item)
    product_tags = line_item.variant.product.tags.to_a.map(&:downcase)
    case @match_condition
      when :match
        return @invert ^ ((@tags & product_tags).length > 0)
      else
        return @invert ^ partial_match(@match_condition, product_tags, @tags)
    end
  end
end

class PercentageDiscount
  def initialize(percent, message)
    @percent = Decimal.new(percent) / 100.0
    @message = message
  end

  def apply(line_item)
    line_discount = line_item.line_price * @percent
    new_line_price = line_item.line_price - line_discount
    line_item.change_line_price(new_line_price, message: @message)
  end
end

CAMPAIGNS = [
  ConditionalDiscount.new(
    :all,
    nil,
    nil,
    ProductTagSelector.new(:does, :match, ["sale"]),
    PercentageDiscount.new(20, "20% off sale items"),
    0
  ),
].freeze

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

Output.cart = Input.cart

Recognised as Percentage off and rebuilt as a volume offer. These are the real configuration keys the offer is saved with, so you can check your own rebuild against them field by field.

Built on our public demo store, Meridian Goods, so every price here can be reproduced rather than taken on trust. The discount below is what the same engine that runs at checkout computes for this exact cart.