/**
 * Czech public holidays & work fund calculator.
 * Port of PHP CzechHolidays class.
 */

const holidayCache = new Map<number, string[]>();

/** Easter Sunday using the Anonymous Gregorian algorithm */
function getEasterSunday(year: number): string {
  const a = year % 19;
  const b = Math.floor(year / 100);
  const c = year % 100;
  const d = Math.floor(b / 4);
  const e = b % 4;
  const f = Math.floor((b + 8) / 25);
  const g = Math.floor((b - f + 1) / 3);
  const h = (19 * a + b - d - g + 15) % 30;
  const i = Math.floor(c / 4);
  const k = c % 4;
  const l = (32 + 2 * e + 2 * i - h - k) % 7;
  const m = Math.floor((a + 11 * h + 22 * l) / 451);
  const month = Math.floor((h + l - 7 * m + 114) / 31);
  const day = ((h + l - 7 * m + 114) % 31) + 1;
  return `${year}-${String(month).padStart(2, "0")}-${String(day).padStart(2, "0")}`;
}

/** All Czech public holidays for a year (11 fixed + 2 Easter-based) */
export function getHolidays(year: number): string[] {
  if (holidayCache.has(year)) return holidayCache.get(year)!;

  const y = String(year);
  const holidays = [
    `${y}-01-01`, // Den obnovy samostatného českého státu
    `${y}-05-01`, // Svátek práce
    `${y}-05-08`, // Den vítězství
    `${y}-07-05`, // Den slovanských věrozvěstů Cyrila a Metoděje
    `${y}-07-06`, // Den upálení mistra Jana Husa
    `${y}-09-28`, // Den české státnosti
    `${y}-10-28`, // Den vzniku samostatného československého státu
    `${y}-11-17`, // Den boje za svobodu a demokracii
    `${y}-12-24`, // Štědrý den
    `${y}-12-25`, // 1. svátek vánoční
    `${y}-12-26`, // 2. svátek vánoční
  ];

  // Easter-based
  const easterSunday = getEasterSunday(year);
  const easterDate = new Date(easterSunday);
  const goodFriday = new Date(easterDate);
  goodFriday.setDate(goodFriday.getDate() - 2);
  const easterMonday = new Date(easterDate);
  easterMonday.setDate(easterMonday.getDate() + 1);

  const fmt = (d: Date) =>
    `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, "0")}-${String(d.getDate()).padStart(2, "0")}`;
  holidays.push(fmt(goodFriday)); // Velký pátek
  holidays.push(fmt(easterMonday)); // Velikonoční pondělí

  holidays.sort();
  holidayCache.set(year, holidays);
  return holidays;
}

/** Check if a date string (YYYY-MM-DD) is a Czech public holiday */
export function isHoliday(dateStr: string): boolean {
  const year = parseInt(dateStr.substring(0, 4), 10);
  return getHolidays(year).includes(dateStr);
}

/** Business days in a month (Mon-Fri excluding public holidays) */
export function getBusinessDaysInMonth(
  year: number,
  month: number,
  upToDay?: number,
): number {
  const holidays = getHolidays(year);
  let count = 0;
  const daysInMonth = new Date(year, month + 1, 0).getDate();
  const maxDay = upToDay ? Math.min(upToDay, daysInMonth) : daysInMonth;

  for (let day = 1; day <= maxDay; day++) {
    const date = new Date(year, month, day);
    const dow = date.getDay();
    if (dow !== 0 && dow !== 6) {
      const dateStr = `${year}-${String(month + 1).padStart(2, "0")}-${String(day).padStart(2, "0")}`;
      if (!holidays.includes(dateStr)) {
        count++;
      }
    }
  }
  return count;
}

/** Monthly work fund in hours (business days × 8) */
export function getMonthlyWorkFund(
  year: number,
  month: number,
  upToDay?: number,
): number {
  return getBusinessDaysInMonth(year, month, upToDay) * 8;
}