1 files changed, 111 insertions, 0 deletions
diff --git a/app/services/users/migrate_records_to_ghost_user_service.rb b/app/services/users/migrate_records_to_ghost_user_service.rb
new file mode 100644
index 00000000000..2d92aaed7da
--- /dev/null
+++ b/app/services/users/migrate_records_to_ghost_user_service.rb
@@ -0,0 +1,111 @@
+# frozen_string_literal: true
+
+# When a user is destroyed, some of their associated records are
+# moved to a "Ghost User", to prevent these associated records from
+# being destroyed.
+#
+# For example, all the issues/MRs a user has created are _not_ destroyed
+# when the user is destroyed.
+module Users
+  class MigrateRecordsToGhostUserService
+    extend ActiveSupport::Concern
+
+    DestroyError = Class.new(StandardError)
+
+    attr_reader :ghost_user, :user, :initiator_user, :hard_delete
+
+    def initialize(user, initiator_user, execution_tracker)
+      @user = user
+      @initiator_user = initiator_user
+      @execution_tracker = execution_tracker
+      @ghost_user = User.ghost
+    end
+
+    def execute(hard_delete: false)
+      @hard_delete = hard_delete
+
+      migrate_records
+      post_migrate_records
+    end
+
+    private
+
+    attr_reader :execution_tracker
+
+    def migrate_records
+      return if hard_delete
+
+      migrate_issues
+      migrate_merge_requests
+      migrate_notes
+      migrate_abuse_reports
+      migrate_award_emoji
+      migrate_snippets
+      migrate_reviews
+    end
+
+    def post_migrate_records
+      delete_snippets
+
+      # Rails attempts to load all related records into memory before
+      # destroying: https://github.com/rails/rails/issues/22510
+      # This ensures we delete records in batches.
+      user.destroy_dependent_associations_in_batches(exclude: [:snippets])
+      user.nullify_dependent_associations_in_batches
+
+      # Destroy the namespace after destroying the user since certain methods may depend on the namespace existing
+      user_data = user.destroy
+      user.namespace.destroy
+
+      user_data
+    end
+
+    def delete_snippets
+      response = Snippets::BulkDestroyService.new(initiator_user, user.snippets).execute(skip_authorization: true)
+      raise DestroyError, response.message if response.error?
+    end
+
+    def migrate_issues
+      batched_migrate(Issue, :author_id)
+      batched_migrate(Issue, :last_edited_by_id)
+    end
+
+    def migrate_merge_requests
+      batched_migrate(MergeRequest, :author_id)
+      batched_migrate(MergeRequest, :merge_user_id)
+    end
+
+    def migrate_notes
+      batched_migrate(Note, :author_id)
+    end
+
+    def migrate_abuse_reports
+      user.reported_abuse_reports.update_all(reporter_id: ghost_user.id)
+    end
+
+    def migrate_award_emoji
+      user.award_emoji.update_all(user_id: ghost_user.id)
+    end
+
+    def migrate_snippets
+      snippets = user.snippets.only_project_snippets
+      snippets.update_all(author_id: ghost_user.id)
+    end
+
+    def migrate_reviews
+      batched_migrate(Review, :author_id)
+    end
+
+    # rubocop:disable CodeReuse/ActiveRecord
+    def batched_migrate(base_scope, column, batch_size: 50)
+      loop do
+        update_count = base_scope.where(column => user.id).limit(batch_size).update_all(column => ghost_user.id)
+        break if update_count == 0
+        raise Gitlab::Utils::ExecutionTracker::ExecutionTimeOutError if execution_tracker.over_limit?
+      end
+    end
+    # rubocop:enable CodeReuse/ActiveRecord
+  end
+end
+
+Users::MigrateRecordsToGhostUserService.prepend_mod_with('Users::MigrateRecordsToGhostUserService')