# Labels::TransferService class
#
# User for recreate the missing group labels at project level
#
module Labels
  class TransferService
    def initialize(current_user, old_group, project)
      @current_user = current_user
      @old_group = old_group
      @project = project
    end

    def execute
      return unless old_group.present?

      Label.transaction do
        labels_to_transfer.find_each do |label|
          new_label_id = find_or_create_label!(label)

          next if new_label_id == label.id

          update_label_links(group_labels_applied_to_issues, old_label_id: label.id, new_label_id: new_label_id)
          update_label_links(group_labels_applied_to_merge_requests, old_label_id: label.id, new_label_id: new_label_id)
          update_label_priorities(old_label_id: label.id, new_label_id: new_label_id)
        end
      end
    end

    private

    attr_reader :current_user, :old_group, :project

    def labels_to_transfer
      label_ids = []
      label_ids << group_labels_applied_to_issues.select(:id)
      label_ids << group_labels_applied_to_merge_requests.select(:id)

      union = Gitlab::SQL::Union.new(label_ids)

      Label.where("labels.id IN (#{union.to_sql})").reorder(nil).uniq
    end

    def group_labels_applied_to_issues
      Label.joins(:issues).
        where(
          issues: { project_id: project.id },
          labels: { type: 'GroupLabel', group_id: old_group.id }
        )
    end

    def group_labels_applied_to_merge_requests
      Label.joins(:merge_requests).
        where(
          merge_requests: { target_project_id: project.id },
          labels: { type: 'GroupLabel', group_id: old_group.id }
        )
    end

    def find_or_create_label!(label)
      params    = label.attributes.slice('title', 'description', 'color')
      new_label = FindOrCreateService.new(current_user, project, params).execute

      new_label.id
    end

    def update_label_links(labels, old_label_id:, new_label_id:)
      LabelLink.joins(:label).
        merge(labels).
        where(label_id: old_label_id).
        update_all(label_id: new_label_id)
    end

    def update_label_priorities(old_label_id:, new_label_id:)
      LabelPriority.where(project_id: project.id, label_id: old_label_id).
        update_all(label_id: new_label_id)
    end
  end
end