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;
}

First I want to say thanks for creating this and aiding us non programmers.

This may be an odd question/request, but is there a way to assign a color to all the created items? My work calendar shows items as black when a new item is added, I would like all the items that are added via this script to be changed to tomato, i.e. red when they are created. This helps me to visually see what type of event is coming up without reading the title and also shows as the colors on the insights bar on the right my event breakdowns.

In case anyone else is wondering the same. I was able to accomplish this by added the following lines, maybe not as elegent as the rest of the code but it does work.:
(added to the bottom of the var options =) 'color': 11, // 1: Pale Blue, 2: Pale Green, 3: Mauve, 4: Pale Red, 5: Yellow, 6: Orange, 7: Cyan, 8: Gray, 9: Blue, 10: Green, 11: Red
(added to //Creart a new event, var newevent =) colorId: options.color,

Thanks for saving my calendars!

I added a couple small features to the script:

• Allow syncing both directions by ignoring events with the sync key
• Allow use of either original title or the sync'd title

Before, I had to display both my personal and work calendar to know what was next, and the double events were cluttering things up. Now I can display just one calendar with all the events. I use the always private option so work can't see my personal calendar details and vice versa.

gist with new features