feat: Activity messages for team assignments (#1893)

- assignment messages when the conversation team is changed
- change assignee based on team
- move round-robin and assignee logic to concerns

app/models/concerns/assignment_handler.rb

@@ -0,0 +1,77 @@
+module AssignmentHandler
+  extend ActiveSupport::Concern
+  include Events::Types
+
+  included do
+    before_save :ensure_assignee_is_from_team
+    after_update :notify_assignment_change, :process_assignment_activities
+  end
+
+  private
+
+  def ensure_assignee_is_from_team
+    return unless team_id_changed?
+
+    ensure_current_assignee_team
+    self.assignee_id ||= find_team_assignee_id_for_inbox if team&.allow_auto_assign.present?
+  end
+
+  def ensure_current_assignee_team
+    self.assignee_id = nil if team&.members&.exclude?(assignee)
+  end
+
+  def find_team_assignee_id_for_inbox
+    members = inbox.members.ids & team.members.ids
+    # TODO: User round robin to determine the next agent instead of using sample
+    members.sample
+  end
+
+  def notify_assignment_change
+    {
+      ASSIGNEE_CHANGED => -> { saved_change_to_assignee_id? },
+      TEAM_CHANGED => -> { saved_change_to_team_id? }
+    }.each do |event, condition|
+      condition.call && dispatcher_dispatch(event)
+    end
+  end
+
+  def process_assignment_activities
+    user_name = Current.user.name if Current.user.present?
+    if saved_change_to_team_id?
+      create_team_change_activity(user_name)
+    elsif saved_change_to_assignee_id?
+      create_assignee_change_activity(user_name)
+    end
+  end
+
+  def generate_team_change_activity_key
+    key = team_id ? 'assigned' : 'removed'
+    key += '_with_assignee' if key == 'assigned' && saved_change_to_assignee_id? && assignee
+    key
+  end
+
+  def create_team_change_activity(user_name)
+    return unless user_name
+
+    key = generate_team_change_activity_key
+    params = { assignee_name: assignee&.name, team_name: team&.name, user_name: user_name }
+    if key == 'removed'
+      previous_team_id = previous_changes[:team_id][0]
+      params[:team_name] = Team.find_by(id: previous_team_id)&.name if previous_team_id.present?
+    end
+    content = I18n.t("conversations.activity.team.#{key}", **params)
+
+    messages.create(activity_message_params(content))
+  end
+
+  def create_assignee_change_activity(user_name)
+    return unless user_name
+
+    params = { assignee_name: assignee&.name, user_name: user_name }.compact
+    key = assignee_id ? 'assigned' : 'removed'
+    key = 'self_assigned' if self_assign? assignee_id
+    content = I18n.t("conversations.activity.assignee.#{key}", **params)
+
+    messages.create(activity_message_params(content))
+  end
+end