1 files changed, 76 insertions, 0 deletions
diff --git a/lib/gitlab/background_migration/merge_topics_with_same_name.rb b/lib/gitlab/background_migration/merge_topics_with_same_name.rb
new file mode 100644
index 00000000000..07231098a5f
--- /dev/null
+++ b/lib/gitlab/background_migration/merge_topics_with_same_name.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # The class to merge project topics with the same case insensitive name
+    class MergeTopicsWithSameName
+      # Temporary AR model for topics
+      class Topic < ActiveRecord::Base
+        self.table_name = 'topics'
+      end
+
+      # Temporary AR model for project topic assignment
+      class ProjectTopic < ActiveRecord::Base
+        self.table_name = 'project_topics'
+      end
+
+      def perform(topic_names)
+        topic_names.each do |topic_name|
+          topics = Topic.where('LOWER(name) = ?', topic_name)
+            .order(total_projects_count: :desc, non_private_projects_count: :desc, id: :asc)
+            .to_a
+          topic_to_keep = topics.shift
+          merge_topics(topic_to_keep, topics) if topics.any?
+        end
+      end
+
+      private
+
+      def merge_topics(topic_to_keep, topics_to_remove)
+        description = topic_to_keep.description
+
+        topics_to_remove.each do |topic|
+          description ||= topic.description if topic.description.present?
+          process_avatar(topic_to_keep, topic) if topic.avatar.present?
+
+          ProjectTopic.transaction do
+            ProjectTopic.where(topic_id: topic.id)
+              .where.not(project_id: ProjectTopic.where(topic_id: topic_to_keep).select(:project_id))
+              .update_all(topic_id: topic_to_keep.id)
+            ProjectTopic.where(topic_id: topic.id).delete_all
+          end
+        end
+
+        Topic.where(id: topics_to_remove).delete_all
+
+        topic_to_keep.update(
+          description: description,
+          total_projects_count: total_projects_count(topic_to_keep.id),
+          non_private_projects_count: non_private_projects_count(topic_to_keep.id)
+        )
+      end
+
+      # We intentionally use application code here because we need to copy/remove avatar files
+      def process_avatar(topic_to_keep, topic_to_remove)
+        topic_to_remove = ::Projects::Topic.find(topic_to_remove.id)
+        topic_to_keep = ::Projects::Topic.find(topic_to_keep.id)
+        unless topic_to_keep.avatar.present?
+          topic_to_keep.avatar = topic_to_remove.avatar
+          topic_to_keep.save!
+        end
+
+        topic_to_remove.remove_avatar!
+        topic_to_remove.save!
+      end
+
+      def total_projects_count(topic_id)
+        ProjectTopic.where(topic_id: topic_id).count
+      end
+
+      def non_private_projects_count(topic_id)
+        ProjectTopic.joins('INNER JOIN projects ON project_topics.project_id = projects.id')
+            .where(project_topics: { topic_id: topic_id }).where('projects.visibility_level in (10, 20)').count
+      end
+    end
+  end
+end