// returns the first day from the date, depending on the group
func (d Generator) FirstFromDate(date epochdate.Date) epochdate.Date {
switch d.Group {
case WEEK:
// first date is the previous monday of the week
wd := date.UTC().Weekday()
if wd > d.FirstDayOfWeek {
return date - epochdate.Date(wd) + epochdate.Date(d.FirstDayOfWeek)
} else if wd < d.FirstDayOfWeek {
return date - 6 + epochdate.Date(wd)
}
case MONTH:
// first day of the month
year, month, _ := date.Date()
ret, _ := epochdate.NewFromDate(year, month, 1)
return ret
}
return date
}
