chore: Handle conversation participation creation race condition error (#9449)

We observed some race condition errors in the conversation participation listener while trying to create a conversation participation assignment. This PR handles this error and also adds additional debug information for future.

fixes: https://linear.app/chatwoot/issue/CW-3296/activerecordrecordnotunique-pguniqueviolation-error-duplicate-key

## Changelog

- handles `ActiveRecord::RecordNotUnique, ActiveRecord::RecordInvald` errors so that they won't pollute sentry
- Adds a debug statement to log the cases
- Add previous_changes into the dispatcher so that we know the exact attribute changes which trigger `assignee_changed, team_changed` events ( would be handy in future )

app/listeners/participation_listener.rb

@@ -3,6 +3,13 @@ class ParticipationListener < BaseListener
 
   def assignee_changed(event)
     conversation, _account = extract_conversation_and_account(event)
-    conversation.conversation_participants.find_or_create_by!(user_id: conversation.assignee_id) if conversation.assignee_id.present?
+    return if conversation.assignee_id.blank?
+
+    conversation.conversation_participants.find_or_create_by!(user_id: conversation.assignee_id)
+  # We have observed race conditions triggering these errors
+  # example: Assignment happening via automation, while auto assignment is also configured.
+  rescue ActiveRecord::RecordNotUnique, ActiveRecord::RecordInvalid
+    Rails.logger.warn "Failed to create conversation participant for account #{conversation.account.id} " \
+                      ": user #{conversation.assignee_id} : conversation #{conversation.id}"
   end
 end

app/models/concerns/assignment_handler.rb

@@ -32,7 +32,7 @@ module AssignmentHandler
       ASSIGNEE_CHANGED => -> { saved_change_to_assignee_id? },
       TEAM_CHANGED => -> { saved_change_to_team_id? }
     }.each do |event, condition|
-      condition.call && dispatcher_dispatch(event)
+      condition.call && dispatcher_dispatch(event, previous_changes)
     end
   end
 

spec/listeners/participation_listener_spec.rb

@@ -9,8 +9,6 @@ describe ParticipationListener do
 
   before do
     create(:inbox_member, inbox: inbox, user: agent)
-    Current.user = nil
-    Current.account = nil
   end
 
   describe '#assignee_changed' do
@@ -22,5 +20,19 @@ describe ParticipationListener do
       listener.assignee_changed(event)
       expect(conversation.conversation_participants.map(&:user_id)).to include(agent.id)
     end
+
+    it 'does not fail if the conversation participant already exists' do
+      conversation.conversation_participants.create!(user: agent)
+      expect { listener.assignee_changed(event) }.not_to raise_error
+    end
+
+    it 'logs a debug message if participant save fails due to a race condition' do
+      allow(Rails.logger).to receive(:warn)
+      allow(conversation).to receive(:conversation_participants).and_return(double)
+      allow(conversation.conversation_participants).to receive(:find_or_create_by!).and_raise(ActiveRecord::RecordNotUnique)
+      expect { listener.assignee_changed(event) }.not_to raise_error
+      expect(Rails.logger).to have_received(:warn).with('Failed to create conversation participant for account ' \
+                                                        "#{account.id} : user #{agent.id} : conversation #{conversation.id}")
+    end
   end
 end

spec/models/conversation_spec.rb

@@ -156,7 +156,7 @@ RSpec.describe Conversation do
                                                                  changed_attributes: nil, performed_by: nil)
       expect(Rails.configuration.dispatcher).to have_received(:dispatch)
         .with(described_class::ASSIGNEE_CHANGED, kind_of(Time), conversation: conversation, notifiable_assignee_change: true,
-                                                                changed_attributes: nil, performed_by: nil)
+                                                                changed_attributes: changed_attributes, performed_by: nil)
       expect(Rails.configuration.dispatcher).to have_received(:dispatch)
         .with(described_class::CONVERSATION_UPDATED, kind_of(Time), conversation: conversation, notifiable_assignee_change: true,
                                                                     changed_attributes: changed_attributes, performed_by: nil)