1 files changed, 71 insertions, 0 deletions
diff --git a/app/services/labels/promote_service.rb b/app/services/labels/promote_service.rb
new file mode 100644
index 00000000000..76d0ba67b07
--- /dev/null
+++ b/app/services/labels/promote_service.rb
@@ -0,0 +1,71 @@
+module Labels
+  class PromoteService < BaseService
+    BATCH_SIZE = 1000
+
+    def execute(label)
+      return unless project.group &&
+          label.is_a?(ProjectLabel)
+
+      Label.transaction do
+        new_label = clone_label_to_group_label(label)
+
+        label_ids_for_merge(new_label).find_in_batches(batch_size: BATCH_SIZE) do |batched_ids|
+          update_issuables(new_label, batched_ids)
+          update_issue_board_lists(new_label, batched_ids)
+          update_priorities(new_label, batched_ids)
+          # Order is important, project labels need to be last
+          update_project_labels(batched_ids)
+        end
+
+        # We skipped validations during creation. Let's run them now, after deleting conflicting labels
+        raise ActiveRecord::RecordInvalid.new(new_label) unless new_label.valid?
+        new_label
+      end
+    end
+
+    private
+
+    def label_ids_for_merge(new_label)
+      LabelsFinder.
+        new(current_user, title: new_label.title, group_id: project.group.id).
+        execute(skip_authorization: true).
+        where.not(id: new_label).
+        select(:id)  # Can't use pluck() to avoid object-creation because of the batching
+    end
+
+    def update_issuables(new_label, label_ids)
+      LabelLink.
+        where(label: label_ids).
+        update_all(label_id: new_label)
+    end
+
+    def update_issue_board_lists(new_label, label_ids)
+      List.
+        where(label: label_ids).
+        update_all(label_id: new_label)
+    end
+
+    def update_priorities(new_label, label_ids)
+      LabelPriority.
+        where(label: label_ids).
+        update_all(label_id: new_label)
+    end
+
+    def update_project_labels(label_ids)
+      Label.where(id: label_ids).delete_all
+    end
+
+    def clone_label_to_group_label(label)
+      params = label.attributes.slice('title', 'description', 'color')
+      # Since the title of the new label has to be the same as the previous labels
+      # and we're merging old labels in batches we'll skip validation to omit 2-step
+      # merge process and do it in one batch
+      # We'll be forcing validation at the end of the transaction to ensure everything
+      # was merged correctly
+      new_label = GroupLabel.new(params.merge(group: project.group))
+      new_label.save(validate: false)
+
+      new_label
+    end
+  end
+end