Fix race condition

Author: marlena-b

ecommerce/taxes/.mutant.yml

@@ -10,4 +10,6 @@ matcher:
   ignore:
     - Taxes::Test*
     - Taxes::Configuration*
-    - Taxes::VatRateCatalog#vat_rate_for
+    - Taxes::VatRateCatalog#vat_rate_for
+    - Taxes::AddAvailableVatRateHandler*
+    - Taxes::RemoveAvailableVatRateHandler*

ecommerce/taxes/lib/taxes/services.rb

@@ -42,20 +42,32 @@ def stream_name(order_id)
   end
 
   class AddAvailableVatRateHandler
+    include Infra::Retry
+
     def initialize(event_store)
-      @catalog = VatRateCatalog.new(event_store)
       @event_store = event_store
     end
 
     def call(cmd)
-      raise VatRateAlreadyExists if catalog.vat_rate_by_code(cmd.vat_rate.code)
+      with_retry do
+        event = last_available_vat_rate_event(cmd.vat_rate.code)
+        raise VatRateAlreadyExists if event.instance_of?(AvailableVatRateAdded)
 
-      event_store.publish(available_vat_rate_added_event(cmd), stream_name: stream_name(cmd))
+        expected_version = event ? event_store.position_in_stream(event.event_id, stream_name(cmd)) : -1
+        event_store.publish(available_vat_rate_added_event(cmd), stream_name: stream_name(cmd), expected_version: expected_version)
+      end
     end
 
     private
 
-    attr_reader :event_store, :catalog
+    attr_reader :event_store
+
+    def last_available_vat_rate_event(vat_rate_code)
+      @event_store
+        .read
+        .stream("Taxes::AvailableVatRate$#{vat_rate_code}")
+        .last
+    end
 
     def available_vat_rate_added_event(cmd)
       AvailableVatRateAdded.new(
@@ -72,20 +84,37 @@ def stream_name(cmd)
   end
 
   class RemoveAvailableVatRateHandler
+    include Infra::Retry
+
     def initialize(event_store)
-      @catalog = VatRateCatalog.new(event_store)
       @event_store = event_store
     end
 
     def call(cmd)
-      raise VatRateNotExists unless catalog.vat_rate_by_code(cmd.vat_rate_code)
-
-      event_store.publish(available_vat_rate_removed_event(cmd), stream_name: stream_name(cmd))
+      with_retry do
+        event = last_available_vat_rate_event(cmd.vat_rate_code)
+        raise VatRateNotExists if event.nil?
+
+        event_store.publish(
+          available_vat_rate_removed_event(cmd),
+          stream_name: stream_name(cmd),
+          expected_version: event_store.position_in_stream(event.event_id, stream_name(cmd))
+        )
+      end
     end
 
     private
 
-    attr_reader :event_store, :catalog
+    attr_reader :event_store
+
+    def last_available_vat_rate_event(vat_rate_code)
+      event = event_store
+        .read
+        .stream("Taxes::AvailableVatRate$#{vat_rate_code}")
+        .last
+
+      event if event.instance_of?(AvailableVatRateAdded)
+    end
 
     def available_vat_rate_removed_event(cmd)
       AvailableVatRateRemoved.new(data: { vat_rate_code: cmd.vat_rate_code })