discourse/app/jobs/scheduled/version_check.rb

require_dependency 'discourse_hub'
require_dependency 'discourse_updates'

module Jobs
  class VersionCheck < Jobs::Scheduled
    every 1.day

    def execute(args)
      if SiteSetting.version_checks? && (DiscourseUpdates.updated_at.nil? || DiscourseUpdates.updated_at < (1.minute.ago))
        begin
          prev_missing_versions_count = DiscourseUpdates.missing_versions_count || 0

          json = DiscourseHub.discourse_version_check
          DiscourseUpdates.last_installed_version = Discourse::VERSION::STRING
          DiscourseUpdates.latest_version = json['latestVersion']
          DiscourseUpdates.critical_updates_available = json['criticalUpdates']
          DiscourseUpdates.missing_versions_count = json['missingVersionsCount']
          DiscourseUpdates.updated_at = Time.zone.now
          DiscourseUpdates.missing_versions = json['versions']

          if  GlobalSetting.new_version_emails &&
              SiteSetting.new_version_emails &&
              json['missingVersionsCount'] > (0) &&
              prev_missing_versions_count < (json['missingVersionsCount'].to_i)

            message = VersionMailer.send_notice
            Email::Sender.new(message, :new_version).send

          end
        rescue => e
          raise e unless Rails.env.development? # Fail version check silently in development mode
        end
      end
      true
    end

  end
end