discourse/app/jobs/regular/create_linked_topic.rb

# frozen_string_literal: true

module Jobs
  class CreateLinkedTopic < ::Jobs::Base
    def execute(args)
      reference_post = Post.find_by(id: args[:post_id])
      return unless reference_post.present?
      parent_topic = reference_post.topic
      return unless parent_topic.present? && parent_topic.regular?
      parent_topic_id = parent_topic.id
      parent_category_id = parent_topic.category_id
      parent_title = parent_topic.title
      @post_creator = nil

      ActiveRecord::Base.transaction do
        linked_topic_record = parent_topic.linked_topic
        if linked_topic_record.present?
          raw_title =
            parent_title.delete_suffix(
              I18n.t(
                "create_linked_topic.topic_title_with_sequence",
                topic_title: "",
                count: linked_topic_record.sequence,
              ),
            )
          original_topic_id = linked_topic_record.original_topic_id
          sequence = linked_topic_record.sequence + 1
        else
          raw_title = parent_title

          # update parent topic title to append title_suffix_locale
          parent_title =
            I18n.t(
              "create_linked_topic.topic_title_with_sequence",
              topic_title: parent_title,
              count: 1,
            )
          parent_topic.title = parent_title
          parent_topic.save!

          # create linked topic record
          original_topic_id = parent_topic_id
          LinkedTopic.create!(
            topic_id: parent_topic_id,
            original_topic_id: original_topic_id,
            sequence: 1,
          )
          sequence = 2
        end

        # fetch previous topic titles
        previous_topics = ""
        linked_topic_ids = LinkedTopic.where(original_topic_id: original_topic_id).pluck(:topic_id)
        Topic
          .where(id: linked_topic_ids)
          .order(:id)
          .each { |topic| previous_topics += "- #{topic.url}\n" }

        # create new topic
        new_topic_title =
          I18n.t(
            "create_linked_topic.topic_title_with_sequence",
            topic_title: raw_title,
            count: sequence,
          )
        new_topic_raw =
          I18n.t(
            "create_linked_topic.post_raw",
            parent_url: reference_post.full_url,
            previous_topics: previous_topics,
          )
        system_user = Discourse.system_user
        @post_creator =
          PostCreator.new(
            system_user,
            title: new_topic_title,
            raw: new_topic_raw,
            category: parent_category_id,
            skip_validations: true,
            skip_jobs: true,
          )
        new_post = @post_creator.create
        new_topic = new_post.topic
        new_topic_id = new_topic.id

        # create linked_topic record
        LinkedTopic.create!(
          topic_id: new_topic_id,
          original_topic_id: original_topic_id,
          sequence: sequence,
        )

        # copy over topic tracking state from old topic
        params = { old_topic_id: parent_topic_id, new_topic_id: new_topic_id }
        DB.exec(<<~SQL, params)
          INSERT INTO topic_users(user_id, topic_id, notification_level,
                                  notifications_reason_id)
          SELECT tu.user_id,
                 :new_topic_id AS topic_id,
                 tu.notification_level,
                 tu.notifications_reason_id
          FROM topic_users tu
               JOIN topics t ON (t.id = :new_topic_id)
          WHERE tu.topic_id = :old_topic_id
            AND tu.notification_level != 1
          ON CONFLICT (topic_id, user_id) DO NOTHING
        SQL

        # update small action post on old topic to add new topic link
        small_action_post =
          Post.where(
            topic_id: parent_topic_id,
            post_type: Post.types[:small_action],
            action_code: "closed.enabled",
          ).last
        if small_action_post.present?
          small_action_post.raw =
            "#{small_action_post.raw} #{I18n.t("create_linked_topic.small_action_post_raw", new_title: "[#{new_topic_title}](#{new_topic.url})")}"
          small_action_post.save!
        end
      end
      @post_creator.enqueue_jobs if @post_creator
    end
  end
end