Sync events from a personal Google calendar to a work Google calendar

CalendarSync.js

function SyncMyCal() {
  var options = {
                  'targetEventTitle': "Busy (sync'd event)", // What event title do you want ported events to have
                  'daysahead': 60,            // How many days ahead do you want to sync events over
                  'ignorealldayevents': true, // Do you want to ignore all day events in your "from" calendars
                  'ignorethesedays': [0, 6],  // Are there days of the week you don't want to sync? 0 = Sunday
                  'maxhoursbetweenruns': 1,   // How many hours between scheduled runs of the calendar sync (you need to set these up)
                  'onlybusyevents': true,     // Only copy events marked 'busy'
                  'busyness': 1,              // Should events be marked 'busy' by default (0: free, 1: busy, 2: match source event)
                  'visibility': 2,            // Should the events be visible by default (0: private, 1: public, 2: match source event)
                  'verbose': false,           // Do you want to log output (useful for debugging)
                }
  // The first array below contains the ID strings of the "from" calendar (your personal calendars), and
  // The second argument is the ID string of the "to" calendar (your work calendar)
  CalendarSync(["XXXXXXXXX", "YYYYYYYYYY"], "ZZZZZZZZ", options)
}

// CalendarSync - sync from one or more google calendars to another calendar, with: 
//                 - a generic event name (original name in the description)
//                 - visibility set to private
//                 - no reminders set
//    Useful if you want to automatically block out personal commitments in your work calendar
//    Note, you must have previously shared the "from" calendars with the "to" calendar, 
//    otherwise this script won't have access
function CalendarSync(fromcals, tocal, options) {
  var today=new Date();
  var enddate=new Date();
  enddate.setDate(today.getDate()+options.daysahead); // how many days in advance to monitor and block off time
  var lastupdate=new Date();
  lastupdate.setHours(today.getHours()-options.maxhoursbetweenruns); // how long ago was this script last run (at a maximum)
  
  // Calendar to copy events to
  var targetEvents=CalendarApp.getCalendarById(tocal).getEvents(today,enddate).filter(e => e.getTag("CalSyncKey") != null); // all target calendar events created by this script
  var targetEventIds=targetEvents.map(e => e.getTag("CalSyncKey")) // Original event IDs
  
  // Process source calendars
  if (typeof fromcals === 'string' || fromcals instanceof String) {
    ProcessSourceCalendar(tocal, fromcals, targetEventIds, today, enddate, lastupdate, options)
  } else {
    for (const cal of fromcals) {
      ProcessSourceCalendar(tocal, cal, targetEventIds, today, enddate, lastupdate, options)
    }
  }

  // If a target event previously created no longer exists in the source calendar, delete it
  for (var tev in targetEvents)
  {
    if (targetEventIds[tev] === "")
      continue;
    if (options.verbose) { Logger.log('EVENT DELETED: ' + targetEvents[tev].getStartTime() + ' ' + targetEvents[tev].getDescription()); }
    targetEvents[tev].deleteEvent();
  }
}

function ProcessSourceCalendar(tocal, fromcal, targetEventIds, today, enddate, lastupdate, options) {
  // Get all the events in source calendar in the relevant time period
  var events;
  try {
    events = Calendar.Events.list(fromcal, {
      timeMin: today.toISOString(), 
      timeMax: enddate.toISOString(), 
      singleEvents: true
    });
  }
  catch (err) {
    Logger.log('Error calling Calendar.Events.list for calendar ' + fromcal + ': ' + err);
    // Failure. Ensure that the calendar ID is correct, that your account has access, and that you've enabled the Calendar API under "Services"
    return;
  }
  if (!events.items || events.items.length === 0) {
    return;
  }

  // Process each event
  for (const event of events.items)
  {
    if (options.ignorealldayevents && event.start.date)
      continue; // Do nothing if the event is an all-day event. This script only syncs hour-based events
    const startTime = event.start.getDateTime();
    const endTime = event.end.getDateTime();
    if (!PeriodOverlapsDays(startTime, endTime, options.ignorethesedays)) // Skip events outside of work days
      continue;
    var available = event.getTransparency();
    if (options.onlybusyevents && available) // Skip events marked available
      continue;
    
    // Check if the source event has already been blocked in the target calendar
    var id = event.getId();
    var ind = targetEventIds.indexOf(id);
    if (ind != -1) {
      // Check if anything changed since the last script run
      var lastupdated = new Date(event.getUpdated())
      if (lastupdated < lastupdate) {
        targetEventIds[ind] = ""
        if (options.verbose) { Logger.log('EVENT UNCHANGED: ' + startTime + ' ' + event.getSummary()); }
        continue;
      }
    }
    // Create a new event
    available = options.busyness == 0 ? true : (options.busyness == 1 ? false : available)
    var visible = options.visibility <= 1 ? options.visibility : event.getVisibility();
    var newevent = {
      "summary": options.targetEventTitle,
      "description": event.getSummary(),
      "start": {"dateTime": startTime},
      "end": {"dateTime": endTime},
      "transparency": available ? "transparent" : "opaque",
      "visibility": visible ? "public" : "private",
      "extendedProperties": {"shared": {"CalSyncKey": id}}
    };
    // call method to insert/create new event in provided calandar
    Calendar.Events.insert(newevent, tocal);
    if (options.verbose) { Logger.log('EVENT CREATED: ' + startTime + ' ' + event.getSummary()); }
  }
}

function PeriodOverlapsDays(startDate_, endDate_, ignorethesedays) {
  if (ignorethesedays.length == 0)
    return true;
  var startDate = new Date(startDate_)
  var endDate = new Date(endDate_)
  var date = startDate.getDate()
  var day = startDate.getDay()
  while (startDate < endDate) {
    if (!ignorethesedays.includes(day))
      return true;
    date++;
    startDate.setDate(date);
    day = (day + 1) % 7;
  }
  return false;
}