go-wareki

usage

loc, _ := time.LoadLocation("Asia/Tokyo")
t := wareki.New(time.Date(2019, 10, 2, 0, 0, 0, 0, loc))
e := t.Era()
if e == wareki.EraNotFound {
	return
}
fmt.Printf("%s%02d年%s", e.KanjiName, t.YearEra(), t.Format("01月02日"))