class TrackingNumber
  class DHL < Base
    SEARCH_PATTERN = /(\b([0-9]\s*){11,11}\b)/
    VERIFY_PATTERN = /^([0-9]{10,10})([0-9])$/
    def carrier
      :dhl
    end

    def matches
      self.tracking_number.scan(VERIFY_PATTERN).flatten
    end

    def valid_checksum?
      # standard mod 7 check
      sequence, check_digit = matches
      return true if sequence.to_i % 7 == check_digit.to_i
    end
  end
end