Migrating a script that took an amount off each item

Danger pair D7. 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 FixedItemDiscount
  def initialize(amount, message)
    @amount = Money.new(cents: 100) * amount
    @message = message
  end

  def apply(line_item)
    per_item_discount = @amount
    discount_to_apply = [(per_item_discount * line_item.quantity), line_item.line_price].min
    line_item.change_line_price([line_item.line_price - discount_to_apply, Money.zero].max, message: @message)
  end
end

CAMPAIGNS = [
  ConditionalDiscount.new(:all, nil, nil, nil, FixedItemDiscount.new(5, "$5 off each"), 0),
].freeze

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

Output.cart = Input.cart

Recognised as Amount off at a quantity 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.

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.

Danger pair D11. This file and its partner look almost identical and behave differently, so read both before you decide which one you have.

DISCOUNT = Money.new(cents: 500)

Input.cart.line_items.each do |line_item|
  discount_to_apply = [(DISCOUNT * line_item.quantity), line_item.line_price].min
  line_item.change_line_price([line_item.line_price - discount_to_apply, Money.zero].max, message: "$5 off each")
end

Output.cart = Input.cart

Recognised as Amount off at a quantity 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.

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.