Syncs your personal calendar with your work calendar as 'busy' events

SyncEvents.gs

/**
 * Syncs your personal calendar with your work calendar as 'busy' events.
 */

// WARNING: This script has the potential to delete events! Audit the code and run with care.
// The script *should* only delete events it has previously created, but bugs are possible!

// How to use
// ==========
// 1. Share your personal calendar with your work account using the free/busy option.
// 2. Visit https://script.google.com/ and create a new project eg. "Personal calendar sync".
// 3. Uncomment, fill in, and run the line below.
// 4. Set up a scheduled trigger to run the `syncEvents` script every hour.

// Uncomment this line and run to set up state.
// PropertiesService.getUserProperties().setProperty('PERSONAL_EMAIL', '<INSERT PERSONAL EMAIL HERE>');

const daysToSyncPropertyValue = PropertiesService.getUserProperties().getProperty('DAYS_TO_SYNC')
const DAYS_TO_SYNC = daysToSyncPropertyValue ? Number.parseInt(daysToSyncPropertyValue, 10) : 7;

function isWeekend(someDate) {
  return someDate.getDay() < 1 || someDate.getDay() > 5;
}

function syncEvents() {
  const personalEmail = PropertiesService.getUserProperties().getProperty('PERSONAL_EMAIL');
  if (personalEmail == null) {
    console.error('No PERSONAL_EMAIL user property set. Save a property in https://developers.google.com/apps-script/reference/properties/properties-service#getUserProperties().')
    return;
  }

  const personalCalendar = CalendarApp.getCalendarById(personalEmail);
  const workCalendar = CalendarApp.getDefaultCalendar();

  const now = new Date();
  const futureDate = new Date(
    now.getTime() + DAYS_TO_SYNC * 86400 /* seconds in a day */ * 1000 /* milliseconds in a second */);
  const eventsToSync = personalCalendar.getEvents(now, futureDate)
    .filter(event => !event.isAllDayEvent())
    .filter(event => !isWeekend(event.getStartTime()));
  
  let workEvents = workCalendar.getEvents(now, futureDate);
  workEvents = workEvents.filter(workEvent => workEvent.getTag('source') === 'personal-calendar-sync');
  const workEventsBySourceId = Object.fromEntries(workEvents.map(workEvent => [workEvent.getTag('source_id'), workEvent]));

  let eventsAdded = 0;
  let eventsChanged = 0;
  let eventsDeleted = 0;

  for (let eventToSync of eventsToSync) {
    if (workEventsBySourceId.hasOwnProperty(eventToSync.getId())) {
      const correspondingWorkEvent = workEventsBySourceId[eventToSync.getId()];
      delete workEventsBySourceId[eventToSync.getId()]
      if (correspondingWorkEvent.getStartTime() === eventToSync.getStartTime() && 
          correspondingWorkEvent.getEndTime() === eventToSync.getEndTime()) {
        continue;
      }
      correspondingWorkEvent.setTime(eventToSync.getStartTime(), eventToSync.getEndTime());
      eventsChanged += 1;
    } else {
      const newEvent = workCalendar.createEvent('busy', eventToSync.getStartTime(), eventToSync.getEndTime());
      newEvent.setTag('source', 'personal-calendar-sync');
      newEvent.setTag('source_id', eventToSync.getId());
      eventsAdded += 1;
    }
  }

  const remainingEventsToDelete = Object.values(workEventsBySourceId);
  remainingEventsToDelete.forEach(remainingEventToDelete => {
    // Switch to this line for testing to prevent deleting events
    // remainingEventToDelete.setColor(CalendarApp.EventColor.RED);
    remainingEventToDelete.deleteEvent();
    eventsDeleted += 1
  });
  
  console.log(`${eventsAdded} events added, ${eventsChanged} events changed, ${eventsDeleted} deleted.`)
}