package jalali

import (
	"fmt"
	"time"
)

var MonthNames = [...]string{
	"", "Farvardin", "Ordibehesht", "Khordad", "Tir", "Mordad", "Shahrivar",
	"Mehr", "Aban", "Azar", "Dey", "Bahman", "Esfand",
}

var MonthNamesFA = [...]string{
	"", "فروردین", "اردیبهشت", "خرداد", "تیر", "مرداد", "شهریور",
	"مهر", "آبان", "آذر", "دی", "بهمن", "اسفند",
}

type Date struct {
	Year  int
	Month int
	Day   int
}

func (d Date) String() string { return fmt.Sprintf("%04d-%02d-%02d", d.Year, d.Month, d.Day) }

func IsLeap(year int) bool {
	return ToGregorian(year+1, 1, 1).Sub(ToGregorian(year, 1, 1)) == 366*24*time.Hour
}

func DaysInMonth(year, month int) int {
	if month <= 6 {
		return 31
	}
	if month <= 11 {
		return 30
	}
	if IsLeap(year) {
		return 30
	}
	return 29
}

func FromTime(t time.Time) Date {
	gy, gm, gd := t.Date()
	jy, jm, jd := gregorianToJalali(gy, int(gm), gd)
	return Date{jy, jm, jd}
}

func ToGregorian(jy, jm, jd int) time.Time {
	gy, gm, gd := jalaliToGregorian(jy, jm, jd)
	return time.Date(gy, time.Month(gm), gd, 0, 0, 0, 0, time.Local)
}

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
	if gm > 2 {
		gy2++
	}
	days := 355666 + 365*gy + (gy2+3)/4 - (gy2+99)/100 + (gy2+399)/400 + gd + gdm[gm-1]
	jy := -1595 + 33*(days/12053)
	days %= 12053
	jy += 4 * (days / 1461)
	days %= 1461
	if days > 365 {
		jy += (days - 1) / 365
		days = (days - 1) % 365
	}
	if days < 186 {
		return jy, 1 + days/31, 1 + days%31
	}
	return jy, 7 + (days-186)/30, 1 + (days-186)%30
}

func jalaliToGregorian(jy, jm, jd int) (int, int, int) {
	jy += 1595
	days := -355668 + 365*jy + (jy/33)*8 + (jy%33+3)/4 + jd
	if jm < 7 {
		days += (jm - 1) * 31
	} else {
		days += (jm-7)*30 + 186
	}
	gy := 400 * (days / 146097)
	days %= 146097
	if days > 36524 {
		gy += 100 * ((days - 1) / 36524)
		days = (days - 1) % 36524
		if days >= 365 {
			days++
		}
	}
	gy += 4 * (days / 1461)
	days %= 1461
	if days > 365 {
		gy += (days - 1) / 365
		days = (days - 1) % 365
	}
	gd := days + 1
	sal := [...]int{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
	if (gy%4 == 0 && gy%100 != 0) || gy%400 == 0 {
		sal[2] = 29
	}
	gm := 1
	for gm <= 12 && gd > sal[gm] {
		gd -= sal[gm]
		gm++
	}
	return gy, gm, gd
}