move transfer logic out of project to service

app/services/project_transfer_service.rb

@@ -0,0 +1,34 @@
+# ProjectTransferService class
+#
+# Used for transfer project to another namespace
+#
+class ProjectTransferService
+  attr_accessor :project
+
+  def transfer(project, new_namespace)
+    Project.transaction do
+      old_namespace = project.namespace
+      project.namespace = new_namespace
+
+      old_dir = old_namespace.try(:path) || ''
+      new_dir = new_namespace.try(:path) || ''
+
+      old_repo = if old_dir.present?
+                   File.join(old_dir, project.path)
+                 else
+                   project.path
+                 end
+
+      if Project.where(path: project.path, namespace_id: new_namespace.try(:id)).present?
+        raise TransferError.new("Project with same path in target namespace already exists")
+      end
+
+      Gitlab::ProjectMover.new(project, old_dir, new_dir).execute
+
+      save!
+    end
+  rescue Gitlab::ProjectMover::ProjectMoveError => ex
+    raise Project::TransferError.new(ex.message)
+  end
+end
+