Keep info about applied promotion

it will be easier to revert it if that's the case

Author: lukaszreszke

ecommerce/pricing/lib/pricing/events.rb

@@ -47,6 +47,7 @@ class PriceItemAdded < Infra::Event
     attribute :price, Infra::Types::Price
     attribute :base_total_value, Infra::Types::Price
     attribute :total_value, Infra::Types::Price
+    attribute? :applied_promotion, Infra::Types::String
   end
 
   class PriceItemRemoved < Infra::Event

ecommerce/pricing/lib/pricing/offer.rb

@@ -19,16 +19,18 @@ def add_item(product_id, base_price, promotion = nil)
         price = @discounts.inject(Discounts::NoPercentageDiscount.new, :add).apply(base_price)
       end
 
-      apply PriceItemAdded.new(
-        data: {
-          order_id: @id,
-          product_id: product_id,
-          base_price: base_price,
-          price: price,
-          base_total_value: @list.base_sum + base_price,
-          total_value: @list.actual_sum + price
-        }
-      )
+      data = {
+        order_id: @id,
+        product_id: product_id,
+        base_price: base_price,
+        price: price,
+        base_total_value: @list.base_sum + base_price,
+        total_value: @list.actual_sum + price,
+      }
+
+      data[:applied_promotion] = promotion.class.name if promotion
+
+      apply PriceItemAdded.new(data:)
     end
 
     def remove_item(product_id)

ecommerce/pricing/test/three_plus_one_test.rb

@@ -109,6 +109,7 @@ def test_given_three_items_are_added_when_forth_item_is_added_then_the_last__ite
             price: 0,
             base_total_value: 80,
             total_value: 60,
+            applied_promotion: Pricing::Discounts::ThreePlusOneGratis.to_s
           }
         ),
         OrderTotalValueCalculated.new(
@@ -235,6 +236,7 @@ def test_given_3_plus_one__when_10_percent_discount_for_offer__then_offer_price_
             price: 0,
             base_total_value: 80,
             total_value: 60,
+            applied_promotion: Pricing::Discounts::ThreePlusOneGratis.to_s
           }
         ),
         OrderTotalValueCalculated.new(