timetracker/public/js/holidays.js

/**
 * Holiday Functions
 * German public holidays calculation and checking
 */

/**
 * Check if date is weekend
 */
function isWeekend(date) {
  const day = date.getDay();
  return day === 0 || day === 6; // Sunday or Saturday
}

/**
 * Calculate Easter Sunday for a given year (Gauss algorithm)
 */
function getEasterSunday(year) {
  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 new Date(year, month - 1, day);
}

/**
 * Get all public holidays for a given year and Bundesland
 */
function getPublicHolidays(year, bundesland) {
  const holidays = [];
  
  // Fixed holidays (all states)
  holidays.push({ date: new Date(year, 0, 1), name: 'Neujahr' });
  holidays.push({ date: new Date(year, 4, 1), name: 'Tag der Arbeit' });
  holidays.push({ date: new Date(year, 9, 3), name: 'Tag der Deutschen Einheit' });
  holidays.push({ date: new Date(year, 11, 25), name: '1. Weihnachtstag' });
  holidays.push({ date: new Date(year, 11, 26), name: '2. Weihnachtstag' });
  
  // Heilige Drei Könige (BW, BY, ST)
  if (['BW', 'BY', 'ST'].includes(bundesland)) {
    holidays.push({ date: new Date(year, 0, 6), name: 'Heilige Drei Könige' });
  }
  
  // Internationaler Frauentag (BE, MV since 2023)
  if (['BE'].includes(bundesland) || (bundesland === 'MV' && year >= 2023)) {
    holidays.push({ date: new Date(year, 2, 8), name: 'Internationaler Frauentag' });
  }
  
  // Weltkindertag (TH since 2019)
  if (bundesland === 'TH' && year >= 2019) {
    holidays.push({ date: new Date(year, 8, 20), name: 'Weltkindertag' });
  }
  
  // Reformationstag (BB, MV, SN, ST, TH, + HB, HH, NI, SH since 2018)
  const reformationstagStates = ['BB', 'MV', 'SN', 'ST', 'TH'];
  if (year >= 2018) {
    reformationstagStates.push('HB', 'HH', 'NI', 'SH');
  }
  if (reformationstagStates.includes(bundesland)) {
    holidays.push({ date: new Date(year, 9, 31), name: 'Reformationstag' });
  }
  
  // Allerheiligen (BW, BY, NW, RP, SL)
  if (['BW', 'BY', 'NW', 'RP', 'SL'].includes(bundesland)) {
    holidays.push({ date: new Date(year, 10, 1), name: 'Allerheiligen' });
  }
  
  // Buß- und Bettag (only SN)
  if (bundesland === 'SN') {
    // Buß- und Bettag is the Wednesday before November 23
    let bussbettag = new Date(year, 10, 23);
    while (bussbettag.getDay() !== 3) { // 3 = Wednesday
      bussbettag.setDate(bussbettag.getDate() - 1);
    }
    bussbettag.setDate(bussbettag.getDate() - 7); // One week before
    holidays.push({ date: bussbettag, name: 'Buß- und Bettag' });
  }
  
  // Easter-dependent holidays
  const easter = getEasterSunday(year);
  
  // Karfreitag (Good Friday) - 2 days before Easter (all states)
  const goodFriday = new Date(easter);
  goodFriday.setDate(easter.getDate() - 2);
  holidays.push({ date: goodFriday, name: 'Karfreitag' });
  
  // Ostermontag (Easter Monday) - 1 day after Easter (all states)
  const easterMonday = new Date(easter);
  easterMonday.setDate(easter.getDate() + 1);
  holidays.push({ date: easterMonday, name: 'Ostermontag' });
  
  // Christi Himmelfahrt (Ascension Day) - 39 days after Easter (all states)
  const ascension = new Date(easter);
  ascension.setDate(easter.getDate() + 39);
  holidays.push({ date: ascension, name: 'Christi Himmelfahrt' });
  
  // Pfingstmontag (Whit Monday) - 50 days after Easter (all states)
  const whitMonday = new Date(easter);
  whitMonday.setDate(easter.getDate() + 50);
  holidays.push({ date: whitMonday, name: 'Pfingstmontag' });
  
  // Fronleichnam (Corpus Christi) - 60 days after Easter (BW, BY, HE, NW, RP, SL, + some communities in SN, TH)
  if (['BW', 'BY', 'HE', 'NW', 'RP', 'SL'].includes(bundesland)) {
    const corpusChristi = new Date(easter);
    corpusChristi.setDate(easter.getDate() + 60);
    holidays.push({ date: corpusChristi, name: 'Fronleichnam' });
  }
  
  // Mariä Himmelfahrt (Assumption of Mary) - August 15 (BY in some communities, SL)
  if (['SL'].includes(bundesland)) {
    holidays.push({ date: new Date(year, 7, 15), name: 'Mariä Himmelfahrt' });
  }
  
  return holidays;
}

/**
 * Check if date is a public holiday
 * Returns the holiday name or null
 */
function getHolidayName(date) {
  const year = date.getFullYear();
  const month = date.getMonth();
  const day = date.getDate();
  
  const holidays = getPublicHolidays(year, currentBundesland);
  
  // Compare year, month, and day directly (avoid timezone issues)
  const holiday = holidays.find(h => {
    return h.date.getFullYear() === year && 
           h.date.getMonth() === month && 
           h.date.getDate() === day;
  });
  
  return holiday ? holiday.name : null;
}

/**
 * Check if date is a public holiday
 */
function isPublicHoliday(date) {
  return getHolidayName(date) !== null;
}

/**
 * Check if date is weekend or public holiday
 */
function isWeekendOrHoliday(date) {
  return isWeekend(date) || isPublicHoliday(date);
}