Make promotion handler classes configurable

api/app/controllers/spree/api/coupon_codes_controller.rb

@@ -10,7 +10,7 @@ def create
         authorize! :update, @order, order_token
 
         @order.coupon_code = params[:coupon_code]
-        @handler = PromotionHandler::Coupon.new(@order).apply
+        @handler = Spree::Config.coupon_code_handler_class.new(@order).apply
 
         if @handler.successful?
           render 'spree/api/promotions/handler', status: 200
@@ -24,7 +24,7 @@ def destroy
         authorize! :update, @order, order_token
 
         @order.coupon_code = params[:id]
-        @handler = PromotionHandler::Coupon.new(@order).remove
+        @handler = Spree::Config.coupon_code_handler_class.new(@order).remove
 
         if @handler.successful?
           render 'spree/api/promotions/handler', status: 200

core/app/models/spree/order.rb

@@ -498,7 +498,7 @@ def create_shipments_for_line_item(line_item)
     end
 
     def apply_shipping_promotions
-      Spree::PromotionHandler::Shipping.new(self).activate
+      Spree::Config.shipping_promotion_handler_class.new(self).activate
       recalculate
     end
 

core/lib/spree/app_configuration.rb

@@ -365,6 +365,22 @@ def default_pricing_options
     #   Spree::OrderUpdater.
     class_name_attribute :order_recalculator_class, default: 'Spree::OrderUpdater'
 
+    # 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'
+
+    # 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

core/spec/lib/spree/app_configuration_spec.rb

@@ -36,6 +36,14 @@
     expect(prefs.promotion_adjuster_class).to eq Spree::Promotion::OrderAdjustmentsRecalculator
   end
 
+  it "uses promotion handler coupon class by default" do
+    expect(prefs.coupon_code_handler_class).to eq Spree::PromotionHandler::Coupon
+  end
+
+  it "uses promotion handler shipping class by default" do
+    expect(prefs.shipping_promotion_handler_class).to eq Spree::PromotionHandler::Shipping
+  end
+
   it "has a getter for the pricing options class provided by the variant price selector class" do
     expect(prefs.pricing_options_class).to eq Spree::Variant::PriceSelector.pricing_options_class
   end