Add code to reduce amount of applicable promotions

If we reduce the amount of promotions that can be activated, the
performance when refreshing the cart improves dramatically.

Eventually, this might not be necessary since Solidus#master branch is
updated with solidusio#4304 and
solidusio#4296.
Until those land in master and we are able to update to Solidus 3.2, we need to
maintain this fork.

core/app/models/spree/promotion_handler/cart.rb

@@ -42,14 +42,49 @@ def connected_order_promotions
           where(spree_orders_promotions: { order_id: order.id }).readonly(false).to_a
       end
 
-      def sale_promotions
-        Spree::Promotion.where(apply_automatically: true).active.includes(:promotion_rules)
-      end
-
       def promotion_code(promotion)
         order_promotion = Spree::OrderPromotion.where(order: order, promotion: promotion).first
         order_promotion.present? ? order_promotion.promotion_code : nil
       end
+
+      def sale_promotions
+        scope = Spree::Promotion.where(apply_automatically: true).active.includes(:promotion_rules).distinct
+
+        Rails.application.config.spree.promotions.rules.each do |rule_class|
+          next unless rule_class.respond_to? :excluded_promotions_for_order
+
+          scope = scope.where.not(id: rule_class.excluded_promotions_for_order(order).select(:id))
+        end
+
+        # Filter promotions that are not eligible for current_user.
+        scope = scope.select do |promotion|
+          promotion.rules.where("spree_promotion_rules.type = 'Spree::Promotion::Rules::User'").none? ||
+            promotion.rules.where("spree_promotion_rules.type = 'Spree::Promotion::Rules::User'")
+              .flat_map(&:user_ids).include?(order.user_id)
+        end
+
+        # Filter promotions that are not eligible for the selected products in the order.
+        scope = scope.select do |promotion|
+          promotion.rules.where("spree_promotion_rules.type = 'Spree::Promotion::Rules::Product'").none? ||
+            order.product_ids.flat_map { |p_id| promotion.rules.where("spree_promotion_rules.type = 'Spree::Promotion::Rules::Product'").flat_map(&:product_ids).include?(p_id) }.include?(true)
+        end
+
+        # Filter promotions that are not eligible for the order's store.
+        scope = scope.select do |promotion|
+          promotion.rules.where("spree_promotion_rules.type = 'Spree::Promotion::Rules::Store'").none? ||
+            promotion.rules.where("spree_promotion_rules.type = 'Spree::Promotion::Rules::Store'").flat_map(&:store_ids)
+              .include?(order.store_id)
+        end
+
+        scope = scope.select do |promotion|
+          promotion.rules.where("spree_promotion_rules.type = 'Spree::Promotion::Rules::Taxon'").none? ||
+            order.products.flat_map(&:taxon_ids).uniq.map { |taxon_id|
+              promotion.rules.where("spree_promotion_rules.type = 'Spree::Promotion::Rules::Taxon'").flat_map(&:taxon_ids).include?(taxon_id)
+            }.include?(true)
+        end
+
+        scope
+      end
     end
   end
 end

core/spec/models/spree/promotion_handler/cart_spec.rb

@@ -60,6 +60,68 @@ module PromotionHandler
           include_context "creates an order promotion"
         end
 
+        context "promotion does not activate for other items" do
+          let(:other_line_item) { create(:line_item) }
+          let!(:rule) { Promotion::Rules::Product.create(products: [line_item.product], promotion: promotion) }
+          let!(:other_rule) { Promotion::Rules::Product.create(products: [other_line_item.product], promotion: promotion) }
+
+          include_context "creates the adjustment"
+          include_context "creates an order promotion"
+        end
+
+        context "promotion activates for store" do
+          let!(:rule) { Promotion::Rules::Store.create(stores: [order.store], promotion: promotion) }
+
+          include_context "creates the adjustment"
+          include_context "creates an order promotion"
+        end
+
+        context "promotion does not activate for other store" do
+          let(:other_store) { create(:store) }
+          let(:other_promotion) { create(:promotion, apply_automatically: true) }
+          let!(:other_rule) { Promotion::Rules::Store.create(stores: [other_store], promotion: other_promotion) }
+          let!(:rule) { Promotion::Rules::Store.create(stores: [order.store], promotion: promotion) }
+
+          include_context "creates the adjustment"
+          include_context "creates an order promotion"
+
+          it "doesn't connect the promotion to the order" do
+            expect {
+              subject.activate
+            }.to change { order.promotions.count }.by(1)
+          end
+
+          it "doesn't create an adjustment" do
+            expect {
+              subject.activate
+            }.to change { adjustable.adjustments.count }.by(1)
+          end
+        end
+
+        context "promotion activates for user" do
+          let!(:rule) { Promotion::Rules::User.create(users: [order.user], promotion: promotion) }
+
+          include_context "creates the adjustment"
+          include_context "creates an order promotion"
+        end
+
+        context "promotion does not activate for other user" do
+          let(:user) { create(:user) }
+          let!(:rule) { Promotion::Rules::User.create(users: [user], promotion: promotion) }
+
+          it "doesn't connect the promotion to the order" do
+            expect {
+              subject.activate
+            }.to change { order.promotions.count }.by(0)
+          end
+
+          it "doesn't create an adjustment" do
+            expect {
+              subject.activate
+            }.to change { adjustable.adjustments.count }.by(0)
+          end
+        end
+
         context "promotion has item total rule" do
           let(:shirt) { create(:product) }
           let!(:rule) { Promotion::Rules::ItemTotal.create(preferred_operator: 'gt', preferred_amount: 50, promotion: promotion) }