discourse/app/jobs/regular/automatic_group_membership.rb

module Jobs

  class AutomaticGroupMembership < Jobs::Base

    def execute(args)
      group_id = args[:group_id]

      raise Discourse::InvalidParameters.new(:group_id) if group_id.blank?

      group = Group.find(group_id)

      return unless group.automatic_membership_retroactive

      domains = group.automatic_membership_email_domains.gsub('.', '\.')

      User.where("email ~* '@(#{domains})$' and users.id not in (
                    select user_id from group_users where group_users.group_id = ?
                )", group_id).find_each do |user|
        begin
          group.add(user)
        rescue ActiveRecord::RecordNotUnique, PG::UniqueViolation
          # we don't care about this
        end
      end
    end

  end

end