export type LunarDate = {
	year: number;
	month: number;
	day: number;
	isLeap: boolean;
};

const START_YEAR = 1900;
const START_DATE = Date.UTC(1900, 0, 31);
const DAY_MS = 24 * 60 * 60 * 1000;
const STEMS = ["甲", "乙", "丙", "丁", "戊", "己", "庚", "辛", "壬", "癸"];
const BRANCHES = ["子", "丑", "寅", "卯", "辰", "巳", "午", "未", "申", "酉", "戌", "亥"];
const MONTH_NAMES = ["", "正月", "二月", "三月", "四月", "五月", "六月", "七月", "八月", "九月", "十月", "冬月", "腊月"];
const DAY_NAMES = [
	"", "初一", "初二", "初三", "初四", "初五", "初六", "初七", "初八", "初九", "初十",
	"十一", "十二", "十三", "十四", "十五", "十六", "十七", "十八", "十九", "二十",
	"廿一", "廿二", "廿三", "廿四", "廿五", "廿六", "廿七", "廿八", "廿九", "三十"
];

// 1900 年至 2100 年的农历数据，每个数字描述一个农历年的闰月和大小月。
const LUNAR_INFO = [
	0x04bd8, 0x04ae0, 0x0a570, 0x054d5, 0x0d260, 0x0d950, 0x16554, 0x056a0, 0x09ad0, 0x055d2,
	0x04ae0, 0x0a5b6, 0x0a4d0, 0x0d250, 0x1d255, 0x0b540, 0x0d6a0, 0x0ada2, 0x095b0, 0x14977,
	0x04970, 0x0a4b0, 0x0b4b5, 0x06a50, 0x06d40, 0x1ab54, 0x02b60, 0x09570, 0x052f2, 0x04970,
	0x06566, 0x0d4a0, 0x0ea50, 0x06e95, 0x05ad0, 0x02b60, 0x186e3, 0x092e0, 0x1c8d7, 0x0c950,
	0x0d4a0, 0x1d8a6, 0x0b550, 0x056a0, 0x1a5b4, 0x025d0, 0x092d0, 0x0d2b2, 0x0a950, 0x0b557,
	0x06ca0, 0x0b550, 0x15355, 0x04da0, 0x0a5d0, 0x14573, 0x052d0, 0x0a9a8, 0x0e950, 0x06aa0,
	0x0aea6, 0x0ab50, 0x04b60, 0x0aae4, 0x0a570, 0x05260, 0x0f263, 0x0d950, 0x05b57, 0x056a0,
	0x096d0, 0x04dd5, 0x04ad0, 0x0a4d0, 0x0d4d4, 0x0d250, 0x0d558, 0x0b540, 0x0b6a0, 0x195a6,
	0x095b0, 0x049b0, 0x0a974, 0x0a4b0, 0x0b27a, 0x06a50, 0x06d40, 0x0af46, 0x0ab60, 0x09570,
	0x04af5, 0x04970, 0x064b0, 0x074a3, 0x0ea50, 0x06b58, 0x055c0, 0x0ab60, 0x096d5, 0x092e0,
	0x0c960, 0x0d954, 0x0d4a0, 0x0da50, 0x07552, 0x056a0, 0x0abb7, 0x025d0, 0x092d0, 0x0cab5,
	0x0a950, 0x0b4a0, 0x0baa4, 0x0ad50, 0x055d9, 0x04ba0, 0x0a5b0, 0x15176, 0x052b0, 0x0a930,
	0x07954, 0x06aa0, 0x0ad50, 0x05b52, 0x04b60, 0x0a6e6, 0x0a4e0, 0x0d260, 0x0ea65, 0x0d530,
	0x05aa0, 0x076a3, 0x096d0, 0x04afb, 0x04ad0, 0x0a4d0, 0x1d0b6, 0x0d250, 0x0d520, 0x0dd45,
	0x0b5a0, 0x056d0, 0x055b2, 0x049b0, 0x0a577, 0x0a4b0, 0x0aa50, 0x1b255, 0x06d20, 0x0ada0,
	0x14b63, 0x09370, 0x049f8, 0x04970, 0x064b0, 0x168a6, 0x0ea50, 0x06b20, 0x1a6c4, 0x0aae0,
	0x0a2e0, 0x0d2e3, 0x0c960, 0x0d557, 0x0d4a0, 0x0da50, 0x05d55, 0x056a0, 0x0a6d0, 0x055d4,
	0x052d0, 0x0a9b8, 0x0a950, 0x0b4a0, 0x0b6a6, 0x0ad50, 0x055a0, 0x0aba4, 0x0a5b0, 0x052b0,
	0x0b273, 0x06930, 0x07337, 0x06aa0, 0x0ad50, 0x14b55, 0x04b60, 0x0a570, 0x054e4, 0x0d160,
	0x0e968, 0x0d520, 0x0daa0, 0x16aa6, 0x056d0, 0x04ae0, 0x0a9d4, 0x0a2d0, 0x0d150, 0x0f252,
	0x0d520
];

export class LunarCalendar {
	static readonly startYear = START_YEAR;
	static readonly endYear = START_YEAR + LUNAR_INFO.length - 1;

	static solarToLunar(dateValue: string | Date): LunarDate | undefined {
		const date = this.parseSolarDate(dateValue);
		if (!date || !this.isSupportedSolarDate(date)) {
			return undefined;
		}

		let offset = Math.floor((Date.UTC(date.year, date.month - 1, date.day) - START_DATE) / DAY_MS);
		let year = START_YEAR;
		while (year <= this.endYear && offset >= this.yearDays(year)) {
			offset -= this.yearDays(year);
			year++;
		}
		if (year > this.endYear) {
			return undefined;
		}

		const leapMonth = this.leapMonth(year);
		let month = 1;
		let isLeap = false;
		while (month <= 12) {
			const days = isLeap ? this.leapDays(year) : this.monthDays(year, month);
			if (offset < days) {
				break;
			}
			offset -= days;
			if (leapMonth === month && !isLeap) {
				isLeap = true;
			} else {
				isLeap = false;
				month++;
			}
		}
		return month > 12 ? undefined : { year, month, day: offset + 1, isLeap };
	}

	static lunarToSolar(lunarDate: LunarDate): string | undefined {
		if (!this.isValidLunarDate(lunarDate)) {
			return undefined;
		}

		let offset = 0;
		for (let year = START_YEAR; year < lunarDate.year; year++) {
			offset += this.yearDays(year);
		}
		const leapMonth = this.leapMonth(lunarDate.year);
		for (let month = 1; month < lunarDate.month; month++) {
			offset += this.monthDays(lunarDate.year, month);
			if (month === leapMonth) {
				offset += this.leapDays(lunarDate.year);
			}
		}
		if (lunarDate.isLeap) {
			offset += this.monthDays(lunarDate.year, lunarDate.month);
		}
		offset += lunarDate.day - 1;
		const date = new Date(START_DATE + offset * DAY_MS);
		return this.formatSolarDate({
			year: date.getUTCFullYear(),
			month: date.getUTCMonth() + 1,
			day: date.getUTCDate()
		});
	}

	static formatLunarDate(lunarDate: LunarDate): string {
		const leapText = lunarDate.isLeap ? "闰" : "";
		return `${this.getYearLabel(lunarDate.year)} ${leapText}${MONTH_NAMES[lunarDate.month]} ${DAY_NAMES[lunarDate.day]}`;
	}

	static getYearLabel(year: number): string {
		const stemIndex = this.mod(year - 4, STEMS.length);
		const branchIndex = this.mod(year - 4, BRANCHES.length);
		return `${STEMS[stemIndex]}${BRANCHES[branchIndex]}年(${year})`;
	}

	static getMonthOptions(year: number): Array<{ value: string; month: number; isLeap: boolean; label: string }> {
		if (!this.isSupportedLunarYear(year)) {
			return [];
		}
		const options: Array<{ value: string; month: number; isLeap: boolean; label: string }> = [];
		const leapMonth = this.leapMonth(year);
		for (let month = 1; month <= 12; month++) {
			options.push({ value: `${month}`, month, isLeap: false, label: MONTH_NAMES[month] });
			if (month === leapMonth) {
				options.push({ value: `${month}-leap`, month, isLeap: true, label: `闰${MONTH_NAMES[month]}` });
			}
		}
		return options;
	}

	static getYearOptions(maxDate: string): Array<{ value: string; label: string }> {
		const lunarDate = this.solarToLunar(maxDate) ?? { year: this.endYear, month: 12, day: 30, isLeap: false };
		return Array.from({ length: lunarDate.year - START_YEAR + 1 }, (_, index) => {
			const year = START_YEAR + index;
			return { value: `${year}`, label: this.getYearLabel(year) };
		});
	}

	static getMonthDays(lunarDate: Pick<LunarDate, "year" | "month" | "isLeap">): number {
		return lunarDate.isLeap ? this.leapDays(lunarDate.year) : this.monthDays(lunarDate.year, lunarDate.month);
	}

	static isValidLunarDate(lunarDate: LunarDate): boolean {
		if (!this.isSupportedLunarYear(lunarDate.year) || lunarDate.month < 1 || 12 < lunarDate.month) {
			return false;
		}
		const leapMonth = this.leapMonth(lunarDate.year);
		if (lunarDate.isLeap && leapMonth !== lunarDate.month) {
			return false;
		}
		return 1 <= lunarDate.day && lunarDate.day <= this.getMonthDays(lunarDate);
	}

	static formatSolarDate(date: { year: number; month: number; day: number }): string {
		return `${date.year.toString().padStart(4, "0")}-${date.month.toString().padStart(2, "0")}-${date.day.toString().padStart(2, "0")}`;
	}

	static today(): string {
		const date = new Date();
		return this.formatSolarDate({ year: date.getFullYear(), month: date.getMonth() + 1, day: date.getDate() });
	}

	private static parseSolarDate(value: string | Date): { year: number; month: number; day: number } | undefined {
		if (value instanceof Date) {
			return { year: value.getFullYear(), month: value.getMonth() + 1, day: value.getDate() };
		}
		const match = /^(\d{4})-(\d{2})-(\d{2})$/.exec(value);
		if (!match) {
			return undefined;
		}
		const year = Number(match[1]);
		const month = Number(match[2]);
		const day = Number(match[3]);
		const date = new Date(Date.UTC(year, month - 1, day));
		return date.getUTCFullYear() === year && date.getUTCMonth() + 1 === month && date.getUTCDate() === day
			? { year, month, day }
			: undefined;
	}

	private static isSupportedSolarDate(date: { year: number; month: number; day: number }): boolean {
		return date.year >= START_YEAR && date.year <= this.endYear;
	}

	private static isSupportedLunarYear(year: number): boolean {
		return year >= START_YEAR && year <= this.endYear;
	}

	private static leapMonth(year: number): number {
		return LUNAR_INFO[year - START_YEAR] & 0xf;
	}

	private static leapDays(year: number): number {
		return this.leapMonth(year) === 0 ? 0 : ((LUNAR_INFO[year - START_YEAR] & 0x10000) !== 0 ? 30 : 29);
	}

	private static monthDays(year: number, month: number): number {
		return (LUNAR_INFO[year - START_YEAR] & (0x10000 >> month)) !== 0 ? 30 : 29;
	}

	private static yearDays(year: number): number {
		let days = 348;
		const info = LUNAR_INFO[year - START_YEAR];
		for (let mask = 0x8000; mask > 0x8; mask >>= 1) {
			if ((info & mask) !== 0) {
				days++;
			}
		}
		return days + this.leapDays(year);
	}

	private static mod(value: number, divisor: number): number {
		return ((value % divisor) + divisor) % divisor;
	}
}