Extract SyntheticNote base class

Update existing synthetic note classes as well.

app/models/label_note.rb

 # frozen_string_literal: true
 
-class LabelNote < Note
+class LabelNote < SyntheticNote
   attr_accessor :resource_parent
   attr_reader :events
 
   def self.from_events(events, resource: nil, resource_parent: nil)
     resource ||= events.first.issuable
 
-    attrs = {
-      system: true,
-      author: events.first.user,
-      created_at: events.first.created_at,
-      discussion_id: events.first.discussion_id,
-      noteable: resource,
-      system_note_metadata: SystemNoteMetadata.new(action: 'label'),
-      events: events,
-      resource_parent: resource_parent
-    }
-
-    if resource_parent.is_a?(Project)
-      attrs[:project_id] = resource_parent.id
-    end
+    attrs = note_attributes('label', events.first, resource, resource_parent).merge(events: events)
 
     LabelNote.new(attrs)
   end
@@ -35,22 +22,10 @@ class LabelNote < Note
     true
   end
 
-  def note
-    @note ||= note_text
-  end
-
   def note_html
     @note_html ||= "<p dir=\"auto\">#{note_text(html: true)}</p>"
   end
 
-  def project
-    resource_parent if resource_parent.is_a?(Project)
-  end
-
-  def group
-    resource_parent if resource_parent.is_a?(Group)
-  end
-
   private
 
   def update_outdated_markdown

app/models/milestone_note.rb

 # frozen_string_literal: true
 
-class MilestoneNote < ::Note
-  attr_accessor :resource_parent, :event, :milestone
+class MilestoneNote < SyntheticNote
+  attr_accessor :milestone
 
   def self.from_event(event, resource: nil, resource_parent: nil)
-    resource ||= event.resource
-
-    attrs = {
-        system: true,
-        author: event.user,
-        created_at: event.created_at,
-        noteable: resource,
-        milestone: event.milestone,
-        discussion_id: event.discussion_id,
-        event: event,
-        system_note_metadata: ::SystemNoteMetadata.new(action: 'milestone'),
-        resource_parent: resource_parent
-    }
-
-    if resource_parent.is_a?(Project)
-      attrs[:project_id] = resource_parent.id
-    end
+    attrs = note_attributes('milestone', event, resource, resource_parent).merge(milestone: event.milestone)
 
     MilestoneNote.new(attrs)
   end
 
-  def note
-    @note ||= note_text
-  end
-
   def note_html
     @note_html ||= Banzai::Renderer.cacheless_render_field(self, :note, { group: group, project: project })
   end
 
-  def project
-    resource_parent if resource_parent.is_a?(Project)
-  end
-
-  def group
-    resource_parent if resource_parent.is_a?(Group)
-  end
-
   private
 
   def note_text(html: false)

app/models/synthetic_note.rb

+# frozen_string_literal: true
+
+class SyntheticNote < Note
+  attr_accessor :resource_parent, :event
+
+  self.abstract_class = true
+
+  def self.note_attributes(action, event, resource, resource_parent)
+    resource ||= event.resource
+
+    attrs = {
+        system: true,
+        author: event.user,
+        created_at: event.created_at,
+        discussion_id: event.discussion_id,
+        noteable: resource,
+        event: event,
+        system_note_metadata: ::SystemNoteMetadata.new(action: action),
+        resource_parent: resource_parent
+    }
+
+    if resource_parent.is_a?(Project)
+      attrs[:project_id] = resource_parent.id
+    end
+
+    attrs
+  end
+
+  def project
+    resource_parent if resource_parent.is_a?(Project)
+  end
+
+  def group
+    resource_parent if resource_parent.is_a?(Group)
+  end
+
+  def note
+    @note ||= note_text
+  end
+
+  def note_html
+    raise NotImplementedError
+  end
+
+  private
+
+  def note_text(html: false)
+    raise NotImplementedError
+  end
+end

ee/app/models/weight_note.rb

 # frozen_string_literal: true
 
-class WeightNote < ::Note
+class WeightNote < ::SyntheticNote
   attr_accessor :resource_parent, :event
 
   def self.from_event(event, resource: nil, resource_parent: nil)
-    resource ||= event.issue
-
-    attrs = {
-      system: true,
-      author: event.user,
-      created_at: event.created_at,
-      noteable: resource,
-      event: event,
-      discussion_id: event.discussion_id,
-      system_note_metadata: ::SystemNoteMetadata.new(action: 'weight'),
-      resource_parent: resource_parent
-    }
-
-    if resource_parent.is_a?(Project)
-      attrs[:project_id] = resource_parent.id
-    end
+    attrs = note_attributes('weight', event, resource, resource_parent)
 
     WeightNote.new(attrs)
   end
 
-  def note
-    @note ||= note_text
-  end
-
   def note_html
     @note_html ||= "<p dir=\"auto\">#{note_text(html: true)}</p>"
   end
 
-  def project
-    resource_parent if resource_parent.is_a?(Project)
-  end
-
-  def group
-    resource_parent if resource_parent.is_a?(Group)
-  end
-
   private
 
   def note_text(html: false)