worktimeBot/internal/bot/dateutil.go

package bot

import "fmt"

var gregMonthDays = []int{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
var jalaliMonthDays = []int{31, 31, 31, 31, 31, 31, 30, 30, 30, 30, 30, 29}

var gregMonthNames = []string{
	"January", "February", "March", "April", "May", "June",
	"July", "August", "September", "October", "November", "December",
}
var jalaliMonthNames = []string{
	"Farvardin", "Ordibehesht", "Khordad", "Tir", "Mordad", "Shahrivar",
	"Mehr", "Aban", "Azar", "Dey", "Bahman", "Esfand",
}
var hijriMonthNames = []string{
	"Muharram", "Safar", "Rabi' I", "Rabi' II", "Jumada I", "Jumada II",
	"Rajab", "Sha'ban", "Ramadan", "Shawwal", "Dhu al-Qa'dah", "Dhu al-Hijjah",
}

func isGregorianLeap(year int) bool {
	return year%4 == 0 && (year%100 != 0 || year%400 == 0)
}

func isJalaliLeap(year int) bool {
	r := year % 33
	return r == 1 || r == 5 || r == 9 || r == 13 || r == 17 || r == 22 || r == 26 || r == 30
}

func monthLenGreg(year, month int) int {
	if month == 2 && isGregorianLeap(year) {
		return 29
	}
	return gregMonthDays[month-1]
}

func monthLenJalali(year, month int) int {
	if month == 12 && isJalaliLeap(year) {
		return 30
	}
	return jalaliMonthDays[month-1]
}

func isHijriLeap(year int) bool {
	switch year % 30 {
	case 2, 5, 7, 10, 13, 16, 18, 21, 24, 27, 29:
		return true
	}
	return false
}

func monthLenHijri(year, month int) int {
	if month == 12 && isHijriLeap(year) {
		return 30
	}
	if month%2 == 1 {
		return 30
	}
	return 29
}

func gregorianToJalali(gy, gm, gd int) (int, int, int) {
	gdm := []int{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334}
	gy2 := gy - 1
	gd2 := gdm[gm-1] + gd
	if gm > 2 && isGregorianLeap(gy) {
		gd2++
	}
	gd2 += gy2*365 + gy2/4 - gy2/100 + gy2/400
	gd2 -= 226899

	jy := 979
	for {
		jyDays := 365
		if isJalaliLeap(jy) {
			jyDays = 366
		}
		if gd2 < jyDays {
			break
		}
		gd2 -= jyDays
		jy++
	}

	jm := 1
	for _, d := range jalaliMonthDays {
		if gd2 < d {
			break
		}
		gd2 -= d
		jm++
	}
	return jy, jm, gd2 + 1
}

func jalaliToGregorian(jy, jm, jd int) (int, int, int) {
	jy2 := jy - 979
	days := jy2 * 365
	for y := 979; y < jy; y++ {
		if isJalaliLeap(y) {
			days++
		}
	}

	jdm := []int{0, 31, 62, 93, 124, 155, 186, 216, 246, 276, 306, 336}
	days += jdm[jm-1] + jd - 1
	days += 226899

	gy := 1
	for {
		gyDays := 365
		if isGregorianLeap(gy) {
			gyDays = 366
		}
		if days < gyDays {
			break
		}
		days -= gyDays
		gy++
	}

	gm := 1
	for i, d := range gregMonthDays {
		if gm == 2 && isGregorianLeap(gy) {
			d = 29
		}
		if days < d {
			break
		}
		days -= d
		gm = i + 2
	}
	return gy, gm, days + 1
}

func hijriToGregorian(hy, hm, hd int) (int, int, int) {
	days := (hy-1)*354 + (hy-1)*11/30
	for m := 1; m < hm; m++ {
		days += monthLenHijri(hy, m)
	}
	days += hd - 1

	jdn := 1948440 + days

	f := jdn + 1401 + ((4*jdn+274277)/146097)*3/4 - 38
	e := 4*f + 3
	g := (e % 1461) / 4
	h := 5*g + 2
	day := (h%153)/5 + 1
	month := ((h/153 + 2) % 12) + 1
	year := e/1461 - 4716 + (14-month)/12
	return year, month, day
}

func gregorianToHijri(gy, gm, gd int) (int, int, int) {
	a := (14 - gm) / 12
	y := gy + 4800 - a
	m := gm + 12*a - 3
	jdn := gd + (153*m+2)/5 + 365*y + y/4 - y/100 + y/400 - 32045

	days := jdn - 1948440

	hy := 1
	for {
		yearDays := 354
		if isHijriLeap(hy) {
			yearDays = 355
		}
		if days < yearDays {
			break
		}
		days -= yearDays
		hy++
	}

	hm := 1
	for mm := 1; mm <= 12; mm++ {
		md := monthLenHijri(hy, mm)
		if days < md {
			break
		}
		days -= md
		hm++
	}
	hd := days + 1
	return hy, hm, hd
}

func dayOfWeekGregorian(gy, gm, gd int) int {
	// Zeller-like: returns 0=Sun,1=Mon,...,6=Sat
	if gm < 3 {
		gm += 12
		gy--
	}
	return (gd + (13*(gm+1))/5 + gy + gy/4 - gy/100 + gy/400) % 7
}

type calDay struct {
	dayNum int
	date   string // YYYY-MM-DD gregorian key
}

type calMonth struct {
	title    string
	weekDays []string
	days     []calDay
}

func buildCalendarMonth(cal string, year, month int) calMonth {
	var title string
	var weekDays []string
	var totalDays int

	if cal == "jalali" {
		title = fmt.Sprintf("%s %d", jalaliMonthNames[month-1], year)
		weekDays = []string{"Sh", "Ye", "Do", "Se", "Ch", "Pa", "Jo"}
		totalDays = monthLenJalali(year, month)

		gy, gm, gd := jalaliToGregorian(year, month, 1)
		dow := dayOfWeekGregorian(gy, gm, gd)
		_ = dow

		var days []calDay
		for d := 1; d <= totalDays; d++ {
			gy, gm, gd = jalaliToGregorian(year, month, d)
			days = append(days, calDay{
				dayNum: d,
				date:   fmt.Sprintf("%04d-%02d-%02d", gy, gm, gd),
			})
		}
		return calMonth{title: title, weekDays: weekDays, days: days}
	}

	if cal == "hijri" {
		title = fmt.Sprintf("%s %d", hijriMonthNames[month-1], year)
		weekDays = []string{"Mo", "Tu", "We", "Th", "Fr", "Sa", "Su"}
		totalDays = monthLenHijri(year, month)

		gy, gm, gd := hijriToGregorian(year, month, 1)
		dow := dayOfWeekGregorian(gy, gm, gd)
		startOffset := (dow + 6) % 7

		var days []calDay
		for i := 0; i < startOffset; i++ {
			days = append(days, calDay{dayNum: 0, date: ""})
		}
		for d := 1; d <= totalDays; d++ {
			gy, gm, gd = hijriToGregorian(year, month, d)
			days = append(days, calDay{
				dayNum: d,
				date:   fmt.Sprintf("%04d-%02d-%02d", gy, gm, gd),
			})
		}
		return calMonth{title: title, weekDays: weekDays, days: days}
	}

	title = fmt.Sprintf("%s %d", gregMonthNames[month-1], year)
	weekDays = []string{"Mo", "Tu", "We", "Th", "Fr", "Sa", "Su"}
	totalDays = monthLenGreg(year, month)

	dow := dayOfWeekGregorian(year, month, 1)
	// Convert Sunday=0 to Monday=0 alignment
	startOffset := (dow + 6) % 7

	var days []calDay
	for i := 0; i < startOffset; i++ {
		days = append(days, calDay{dayNum: 0, date: ""})
	}
	for d := 1; d <= totalDays; d++ {
		days = append(days, calDay{
			dayNum: d,
			date:   fmt.Sprintf("%04d-%02d-%02d", year, month, d),
		})
	}
	return calMonth{title: title, weekDays: weekDays, days: days}
}

func gregorianDateKey(year, month, day int) string {
	return fmt.Sprintf("%04d-%02d-%02d", year, month, day)
}

func parseGregorianDateKey(key string) (int, int, int) {
	var y, m, d int
	fmt.Sscanf(key, "%04d-%02d-%02d", &y, &m, &d)
	return y, m, d
}