International Date Line

// Assumes adding days always works linearly
function addDays(date, days) {
  const result = new Date(date);
  result.setDate(result.getDate() + days);
  return result;
}

// This breaks in Samoa during the 2011 date jump
// December 30, 2011 + 1 day should be January 1, 2012
// But this function would return December 31, 2011 (which didn't exist)

// Assumes business days are consistent across date line
function getNextBusinessDay(date, timezone) {
  let nextDay = new Date(date);
  nextDay.setDate(nextDay.getDate() + 1);
  
  // Skip weekends
  while (nextDay.getDay() === 0 || nextDay.getDay() === 6) {
    nextDay.setDate(nextDay.getDate() + 1);
  }
  
  return nextDay;
  // This ignores that "next day" might be different across date line
}

// Ignores date line when scheduling international meetings
function scheduleWeeklyMeeting(startDate, timezone1, timezone2) {
  const meetings = [];
  for (let i = 0; i < 4; i++) {
    const meetingDate = new Date(startDate);
    meetingDate.setDate(startDate.getDate() + (i * 7));
    meetings.push(meetingDate);
  }
  // This assumes both timezones have the same "weekly" schedule
  // But they might be on different days due to date line
  return meetings;
}

// Use timezone-aware libraries for date arithmetic
import { DateTime } from 'luxon';

function addDaysInTimezone(date, days, timezone) {
  // Luxon handles timezone-specific date arithmetic
  const dt = DateTime.fromJSDate(date, { zone: timezone });
  return dt.plus({ days }).toJSDate();
}

// Handle business days with timezone awareness
function getNextBusinessDay(date, timezone) {
  let nextDay = DateTime.fromJSDate(date, { zone: timezone }).plus({ days: 1 });
  
  // Skip weekends in the target timezone
  while (nextDay.weekday === 6 || nextDay.weekday === 7) {
    nextDay = nextDay.plus({ days: 1 });
  }
  
  return nextDay.toJSDate();
}

// Schedule meetings accounting for date line differences
function scheduleInternationalMeeting(dateTime, timezone1, timezone2) {
  const meeting1 = DateTime.fromISO(dateTime, { zone: timezone1 });
  const meeting2 = meeting1.setZone(timezone2);
  
  return {
    location1: {
      time: meeting1.toFormat('yyyy-MM-dd HH:mm'),
      timezone: timezone1,
      weekday: meeting1.toFormat('cccc')
    },
    location2: {
      time: meeting2.toFormat('yyyy-MM-dd HH:mm'),
      timezone: timezone2,
      weekday: meeting2.toFormat('cccc')
    },
    sameDayOfWeek: meeting1.weekday === meeting2.weekday,
    sameCalendarDate: meeting1.toISODate() === meeting2.toISODate()
  };
}

// Handle historical timezone changes
function convertHistoricalDate(dateString, timezone, targetTimezone) {
  // Use historical timezone data to handle changes like Samoa's date jump
  const historical = DateTime.fromISO(dateString, { zone: timezone });
  
  if (!historical.isValid) {
    // Handle dates that didn't exist (like Dec 31, 2011 in Samoa)
    throw new Error(`Date ${dateString} did not exist in ${timezone}`);
  }
  
  return historical.setZone(targetTimezone);
}

// Validate date existence in timezone
function dateExistsInTimezone(dateString, timezone) {
  try {
    const dt = DateTime.fromISO(dateString, { zone: timezone });
    return dt.isValid;
  } catch (error) {
    return false;
  }
}

// Calculate time difference accounting for date line
function calculateTimeDifference(date1, tz1, date2, tz2) {
  const dt1 = DateTime.fromISO(date1, { zone: tz1 });
  const dt2 = DateTime.fromISO(date2, { zone: tz2 });
  
  const diff = dt2.diff(dt1, ['days', 'hours', 'minutes']);
  
  return {
    ...diff.toObject(),
    crossesDateLine: Math.abs(diff.as('hours')) > 12,
    differentCalendarDays: dt1.toISODate() !== dt2.toISODate()
  };
}