period

type Client interface {
	FirstPeriodStartDate(year int) time.Time
	LastDayOfLastPeriod(year int) time.Time
	FirstDayOfMonth(date time.Time) time.Time
	PeriodNumber(date time.Time) int
	TimeOfWeekday(date time.Time, weekday time.Weekday) time.Time
}

type PeriodOption func(*PeriodOptions)

type PeriodOptions struct {
	Offset int
}