Function WeeksSinceEpoch

coderd/schedule/autostop.go:297–337

WeeksSinceEpoch gets the weeks since the epoch for a given time. This is a 0-indexed number of weeks since the epoch (Monday). The timezone embedded in the time object is used to determine the epoch.

(now time.Time)

//
// The timezone embedded in the time object is used to determine the epoch.
func WeeksSinceEpoch(now time.Time) (int64, error) {
	epoch := TemplateAutostopRequirementEpoch(now.Location())
	if now.Before(epoch) {
		return 0, xerrors.New("coder server system clock is incorrect, cannot calculate template autostop requirement")
	}

	// This calculation needs to be done using YearDay, as dividing by the
	// amount of hours is impacted by daylight savings. Even though daylight
	// savings is usually only an hour difference, this calculation is used to
	// get the current week number and could result in an entire week getting
	// skipped if the calculation is off by an hour.
	//
	// Old naive algorithm: weeksSinceEpoch := int64(since.Hours() / (24 * 7))

	// Get days since epoch. Start with a negative number of days, as we want to
	// subtract the YearDay() of the epoch itself.
	days := -epoch.YearDay()
	for i := epoch.Year(); i < now.Year(); i++ {
		startOfNextYear := time.Date(i+1, 1, 1, 0, 0, 0, 0, now.Location())
		if startOfNextYear.Year() != i+1 {
			return 0, xerrors.New("overflow calculating weeks since epoch")
		}
		endOfThisYear := startOfNextYear.AddDate(0, 0, -1)
		if endOfThisYear.Year() != i {
			return 0, xerrors.New("overflow calculating weeks since epoch")
		}

		days += endOfThisYear.YearDay()
	}
	// Add this year's days.
	days += now.YearDay()

	// Ensure that the number of days is positive.
	if days < 0 {
		return 0, xerrors.New("overflow calculating weeks since epoch")
	}

	// Divide by 7 to get the number of weeks.
	weeksSinceEpoch := int64(days / 7)
	return weeksSinceEpoch, nil
}

// GetMondayOfWeek gets the Monday (0:00) of the n-th week since epoch.
func GetMondayOfWeek(loc *time.Location, n int64) (time.Time, error) {