package pasien

import "time"

type Age struct {
	Years  int
	Months int
	Days   int
}

func CalculateAge(birthDate, now time.Time) Age {
	// Pastikan jam = 00:00:00 biar konsisten
	birthDate = time.Date(
		birthDate.Year(), birthDate.Month(), birthDate.Day(),
		0, 0, 0, 0, birthDate.Location(),
	)
	now = time.Date(
		now.Year(), now.Month(), now.Day(),
		0, 0, 0, 0, now.Location(),
	)

	years := now.Year() - birthDate.Year()
	months := int(now.Month()) - int(birthDate.Month())
	days := now.Day() - birthDate.Day()

	// Kalau hari negatif, pinjam dari bulan
	if days < 0 {
		previousMonth := now.AddDate(0, -1, 0)
		days += daysInMonth(previousMonth)
		months--
	}

	// Kalau bulan negatif, pinjam dari tahun
	if months < 0 {
		months += 12
		years--
	}

	if years < 0 {
		return Age{}
	}

	return Age{
		Years:  years,
		Months: months,
		Days:   days,
	}
}

func daysInMonth(t time.Time) int {
	firstOfNextMonth := time.Date(
		t.Year(), t.Month()+1, 1,
		0, 0, 0, 0, t.Location(),
	)
	lastOfMonth := firstOfNextMonth.AddDate(0, 0, -1)
	return lastOfMonth.Day()
}