Migrating a script that limited how many units were discounted

Danger pair D5. This file and its partner look almost identical and behave differently, so read both before you decide which one you have.

# GENERATED BY THE SHOPIFY SCRIPT CREATOR APP

class ConditionalDiscount < Campaign
  def initialize(condition, customer_qualifier, cart_qualifier, line_item_selector, discount, max_discounts)
    super(condition, customer_qualifier, cart_qualifier, line_item_selector)
    @discount = discount
    @items_to_discount = max_discounts == 0 ? nil : max_discounts
  end

  def run(cart)
    return unless qualifies?(cart)
    applicable_items = cart.line_items.select { |item| @line_item_selector.nil? || @line_item_selector.match?(item) }
    applicable_items.each do |item|
      break if @items_to_discount == 0
      if !@items_to_discount.nil? && (item.quantity > @items_to_discount)
        new_item = item.split({ take: @items_to_discount })
        @discount.apply(new_item)
        position = cart.line_items.find_index(item)
        cart.line_items.insert(position + 1, new_item)
        @items_to_discount = 0
      else
        @discount.apply(item)
        @items_to_discount -= item.quantity unless @items_to_discount.nil?
      end
    end
  end
end

CAMPAIGNS = [
  ConditionalDiscount.new(
    :all, nil, nil,
    ProductTypeSelector.new(:does, ["Sale"]),
    PercentageDiscount.new(30, "30% off first 2"),
    2
  ),
].freeze

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

Output.cart = Input.cart

Recognised as Discount on the first few units and rebuilt as a bxgy 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.

Danger pair D6. This file and its partner look almost identical and behave differently, so read both before you decide which one you have.

DISCOUNT_PERCENTAGE = 30
MAX_UNITS = 2

num_to_discount = MAX_UNITS

Input.cart.line_items.each_with_index do |line_item, position|
  break if num_to_discount <= 0
  next unless line_item.variant.product.tags.include?("limited")

  if line_item.quantity > num_to_discount
    split_line_item = line_item.split(take: num_to_discount)
    Input.cart.line_items.insert(position + 1, split_line_item)
    line_item = split_line_item
  end

  line_item.change_line_price(
    line_item.line_price * (1.0 - (DISCOUNT_PERCENTAGE / 100.0)),
    message: "30% off your first 2"
  )
  num_to_discount -= line_item.quantity
end

Output.cart = Input.cart

Recognised as Discount on the first few units and rebuilt as a bxgy 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.