Migrating a purchase quantity limit script

Danger pair D6. 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 QuantityLimit < Campaign
  def initialize(condition, customer_qualifier, cart_qualifier, line_item_selector, limit_by, limit)
    super(condition, customer_qualifier, cart_qualifier, line_item_selector)
    @limit_by = limit_by
    @limit = limit
  end

  def run(cart)
    return unless qualifies?(cart)
    to_delete = []
    counts = {}
    cart.line_items.each_with_index do |item, index|
      next unless @line_item_selector.nil? || @line_item_selector.match?(item)
      key = @limit_by == :product ? item.variant.product.id : item.variant.id
      counts[key] = 0 unless counts[key]
      max_amount = @limit - counts[key]
      if max_amount <= 0
        to_delete << index
      elsif item.quantity > max_amount
        item.split(take: max_amount)
        counts[key] += max_amount
      else
        counts[key] += item.quantity
      end
    end
    to_delete.reverse.each { |index| cart.line_items.delete_at(index) }
  end
end

CAMPAIGNS = [
  QuantityLimit.new(:all, nil, nil, ProductTagSelector.new(:does, :match, ["limited"]), :variant, 2),
].freeze

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

Output.cart = Input.cart