Add method to get the top entity to RelatedEntity

lib/diaspora_federation/entities/related_entity.rb

@@ -24,6 +24,14 @@ module DiasporaFederation
       #   @return [RelatedEntity] parent entity
       entity :parent, Entities::RelatedEntity, default: nil
 
+      # The root entity, this entity is responsible for relaying relayables
+      # @return [RelatedEntity] absolute parent entity
+      def root
+        root = self
+        root = root.parent until root.parent.nil?
+        root
+      end
+
       # Get related entity from the backend or fetch it from remote if not available locally
       # @return [RelatedEntity] fetched related entity
       def self.fetch(author, type, guid)

spec/lib/diaspora_federation/entities/related_entity_spec.rb

@@ -5,6 +5,20 @@ module DiasporaFederation
 
     it_behaves_like "an Entity subclass"
 
+    describe "#root" do
+      it "returns self if it's already the root" do
+        entity = Fabricate(:related_entity, parent: nil)
+        expect(entity.root).to eq(entity)
+      end
+
+      it "returns the root entity if the current entity has parents" do
+        root = Fabricate(:related_entity, parent: nil)
+        parent = Fabricate(:related_entity, parent: root)
+        entity = Fabricate(:related_entity, parent: parent)
+        expect(entity.root).to eq(root)
+      end
+    end
+
     describe ".fetch" do
       let(:guid) { Fabricate.sequence(:guid) }
       let(:entity) { Fabricate(:related_entity) }