Add promotion-specific configuration to Spree::Core::PromotionConfigu…

…ration

We want to be able to move all promotion-related things out of
`solidus_core` in PR solidusio#5634. However, Spree::AppConfiguration also does
all the promotion-specific things, and we can't move the app
configuration out of core.

In solidusio#5658, we've added a promotion configuration object as a nucleus for
core's promotion system's configuration,
`Spree::Core::PromotionConfiguration`. This implements all the
promotion-specific configuration preferences from
`Spree::AppConfiguration` there.

core/lib/spree/core/promotion_configuration.rb

@@ -2,9 +2,44 @@
 
 module Spree
   module Core
-    class PromotionConfiguration
+    class PromotionConfiguration < Spree::Preferences::Configuration
       include Core::EnvironmentExtension
 
+      # @!attribute [rw] promotions_per_page
+      #   @return [Integer] Promotions to show per-page in the admin (default: +15+)
+      preference :promotions_per_page, :integer, default: 15
+
+      # promotion_chooser_class allows extensions to provide their own PromotionChooser
+      class_name_attribute :promotion_chooser_class, default: 'Spree::PromotionChooser'
+
+      # promotion_adjuster_class allows extensions to provide their own Promotion Adjuster
+      class_name_attribute :promotion_adjuster_class, default: 'Spree::Promotion::OrderAdjustmentsRecalculator'
+
+      # Allows providing a different shipping promotion handler.
+      # @!attribute [rw] shipping_promotion_handler_class
+      # @see Spree::PromotionHandler::Shipping
+      # @return [Class] an object that conforms to the API of
+      #   the standard shipping promotion handler class
+      #   Spree::PromotionHandler::Coupon.
+      class_name_attribute :shipping_promotion_handler_class, default: 'Spree::PromotionHandler::Shipping'
+
+      # Allows providing your own Mailer for promotion code batch mailer.
+      #
+      # @!attribute [rw] promotion_code_batch_mailer_class
+      # @return [ActionMailer::Base] an object that responds to "promotion_code_batch_finished",
+      #   and "promotion_code_batch_errored"
+      #   (e.g. an ActionMailer with a "promotion_code_batch_finished" method) with the same
+      #   signature as Spree::PromotionCodeBatchMailer.promotion_code_batch_finished.
+      class_name_attribute :promotion_code_batch_mailer_class, default: 'Spree::PromotionCodeBatchMailer'
+
+      # Allows providing a different coupon code handler.
+      # @!attribute [rw] coupon_code_handler_class
+      # @see Spree::PromotionHandler::Coupon
+      # @return [Class] an object that conforms to the API of
+      #   the standard coupon code handler class
+      #   Spree::PromotionHandler::Coupon.
+      class_name_attribute :coupon_code_handler_class, default: 'Spree::PromotionHandler::Coupon'
+
       add_nested_class_set :calculators, default: {
         "Spree::Promotion::Actions::CreateAdjustment" => %w[
           Spree::Calculator::FlatPercentItemTotal

core/spec/lib/spree/core/promotion_configuration_spec.rb

@@ -3,8 +3,26 @@
 require "rails_helper"
 
 RSpec.describe Spree::Core::PromotionConfiguration do
+  subject(:config) { described_class.new }
+
+  it "uses base searcher class by default" do
+    expect(config.promotion_chooser_class).to eq Spree::PromotionChooser
+  end
+
+  it "uses order adjustments recalculator class by default" do
+    expect(config.promotion_adjuster_class).to eq Spree::Promotion::OrderAdjustmentsRecalculator
+  end
+
+  it "uses promotion handler coupon class by default" do
+    expect(config.coupon_code_handler_class).to eq Spree::PromotionHandler::Coupon
+  end
+
+  it "uses promotion handler shipping class by default" do
+    expect(config.shipping_promotion_handler_class).to eq Spree::PromotionHandler::Shipping
+  end
+
   describe "#calculators" do
-    subject { described_class.new.calculators[promotion_action] }
+    subject { config.calculators[promotion_action] }
 
     context "for Spree::Promotion::Actions::CreateAdjustment" do
       let(:promotion_action) { Spree::Promotion::Actions::CreateAdjustment }