1 files changed, 55 insertions, 0 deletions
diff --git a/app/services/resource_events/merge_into_notes_service.rb b/app/services/resource_events/merge_into_notes_service.rb
new file mode 100644
index 00000000000..1b02a1602e2
--- /dev/null
+++ b/app/services/resource_events/merge_into_notes_service.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+# We store events about issuable label changes in a separate table (not as
+# other system notes), but we still want to display notes about label changes
+# as classic system notes in UI.  This service generates "synthetic" notes for
+# label event changes and merges them with classic notes and sorts them by
+# creation time.
+
+module ResourceEvents
+  class MergeIntoNotesService
+    include Gitlab::Utils::StrongMemoize
+
+    attr_reader :resource, :current_user, :params
+
+    def initialize(resource, current_user, params = {})
+      @resource = resource
+      @current_user = current_user
+      @params = params
+    end
+
+    def execute(notes = [])
+      (notes + label_notes).sort_by { |n| n.created_at }
+    end
+
+    private
+
+    def label_notes
+      label_events_by_discussion_id.map do |discussion_id, events|
+        LabelNote.from_events(events, resource: resource, resource_parent: resource_parent)
+      end
+    end
+
+    def label_events_by_discussion_id
+      return [] unless resource.respond_to?(:resource_label_events)
+
+      events = resource.resource_label_events.includes(:label, :user)
+      events = since_fetch_at(events)
+
+      events.group_by { |event| event.discussion_id }
+    end
+
+    def since_fetch_at(events)
+      return events unless params[:last_fetched_at].present?
+
+      last_fetched_at = Time.at(params.fetch(:last_fetched_at).to_i)
+      events.created_after(last_fetched_at - NotesFinder::FETCH_OVERLAP)
+    end
+
+    def resource_parent
+      strong_memoize(:resource_parent) do
+        resource.project || resource.group
+      end
+    end
+  end
+end