kurdical.go

package kurdical

import (
	"time"
)

// Dialect represents the Kurdish dialect for month names.
type Dialect int

// Epoch represents the historical origin for Kurdish year calculation.
type Epoch int

const (
	// Laki dialect
	Laki Dialect = iota
	// Hawrami dialect
	Hawrami
	// Sorani dialect
	Sorani
	// Kalhuri dialect
	Kalhuri
	// Kurmanji dialect
	Kurmanji
)

const (
	// MedianKingdom epoch (Diako)
	MedianKingdom Epoch = iota
	// FallOfNineveh epoch (Cyaxares)
	FallOfNineveh
)

// KurdishDate represents a date in the Kurdish calendar.
type KurdishDate struct {
	Year      int
	Month     int
	Day       int
	Weekday   int // 1=Saturday, 2=Sunday, ..., 7=Friday
	MonthName string
	Dialect   Dialect
	Epoch     Epoch
}

// epochOffsets maps epochs to their year offsets from Solar Hijri.
var epochOffsets = map[Epoch]int{
	MedianKingdom: 1321,
	FallOfNineveh: 1233,
}

// GregorianToKurdish converts a Gregorian time.Time to a KurdishDate.
func GregorianToKurdish(t time.Time, dialect Dialect, epoch Epoch) KurdishDate {
	year, month, day := t.Date()
	return GregorianToKurdishDate(year, int(month), day, dialect, epoch)
}

// GregorianToKurdishDate converts Gregorian year, month, day to KurdishDate.
func GregorianToKurdishDate(year, month, day int, dialect Dialect, epoch Epoch) KurdishDate {
	sYear, sMonth, sDay := gregorianToSolarHijri(year, month, day)
	kYear := sYear + epochOffsets[epoch]
	monthName := monthNames[dialect][sMonth-1]

	// Calculate weekday from Gregorian date
	t := time.Date(year, time.Month(month), day, 0, 0, 0, 0, time.UTC)
	weekday := int(t.Weekday())
	switch weekday {
	case 0: // Sunday
		weekday = 2
	case 1: // Monday
		weekday = 3
	case 2: // Tuesday
		weekday = 4
	case 3: // Wednesday
		weekday = 5
	case 4: // Thursday
		weekday = 6
	case 5: // Friday
		weekday = 7
	case 6: // Saturday
		weekday = 1
	}

	return KurdishDate{
		Year:      kYear,
		Month:     sMonth,
		Day:       sDay,
		Weekday:   weekday,
		MonthName: monthName,
		Dialect:   dialect,
		Epoch:     epoch,
	}
}

// KurdishToGregorian converts a KurdishDate to a Gregorian time.Time.
func KurdishToGregorian(k KurdishDate) (time.Time, error) {
	year, month, day, err := KurdishToGregorianDate(k.Year, k.Month, k.Day, k.Epoch)
	if err != nil {
		return time.Time{}, err
	}
	return time.Date(year, time.Month(month), day, 0, 0, 0, 0, time.UTC), nil
}

// KurdishToGregorianDate converts Kurdish year, month, day to Gregorian year, month, day.
func KurdishToGregorianDate(kYear, kMonth, kDay int, epoch Epoch) (int, int, int, error) {
	if kMonth < 1 || kMonth > 12 {
		return 0, 0, 0, &ErrorInvalidMonth{Month: kMonth}
	}
	monthDays := []int{31, 31, 31, 31, 31, 31, 30, 30, 30, 30, 30, 29}
	sYear := kYear - epochOffsets[epoch]
	if isSolarHijriLeap(sYear) {
		monthDays[11] = 30
	}
	if kDay < 1 || kDay > monthDays[kMonth-1] {
		return 0, 0, 0, &ErrorInvalidDay{Day: kDay}
	}
	gYear, gMonth, gDay := solarHijriToGregorian(sYear, kMonth, kDay)
	return gYear, gMonth, gDay, nil
}