Migrating a BOGO that ran across the whole cart

Danger pair D17. This file and its partner look almost identical and behave differently, so read both before you decide which one you have.

class InterleavedPartitioner
  def initialize(paid_item_count, discounted_item_count)
    @paid_item_count = paid_item_count
    @discounted_item_count = discounted_item_count
  end

  def partition(cart, applicable_line_items)
    sorted_items = applicable_line_items.sort_by { |line_item| line_item.variant.price }.reverse
    discounted_items = []
    paid_items_seen = 0
    discounted_items_seen = 0

    sorted_items.each do |line_item|
      line_item.quantity.times do
        if paid_items_seen < @paid_item_count
          paid_items_seen += 1
        else
          discounted_items_seen += 1
          discounted_items.push(line_item.split(take: 1))
          if discounted_items_seen == @discounted_item_count
            paid_items_seen = 0
            discounted_items_seen = 0
          end
        end
      end
    end

    discounted_items
  end
end

CAMPAIGNS = [
  BogoCampaign.new(
    ProductTagSelector.new("bogo"),
    PercentageDiscount.new(100, "Buy 2 get 1 free"),
    InterleavedPartitioner.new(2, 1)
  ),
]

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

Output.cart = Input.cart

Recognised as Buy X, get Y 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.