code: func extractYearMonth(format string) (int64, int64, int64, gotime.Duration, error) {
  	fields := strings.Split(format, "-")
  	if len(fields) != 2 {
  		return 0, 0, 0, 0, errors.Errorf("invalid time format - %s", format)
  	}
  
  	years, err := strconv.ParseInt(fields[0], 10, 64)
  	if err != nil {
  		return 0, 0, 0, 0, errors.Errorf("invalid time format - %s", format)
  	}
  
  	months, err := strconv.ParseInt(fields[1], 10, 64)
  	if err != nil {
  		return 0, 0, 0, 0, errors.Errorf("invalid time format - %s", format)
  	}
  
  	return years, months, 0, 0, nil
  }
docs: // Format is `YYYY-MM`.