Sync your work Google Calendar with your personal Google Calendar by blocking time in Personal Calendar whenever there is an event in Work Calendar.

sync-google-calendars.js

// This script solves the problem of bidirectional syncing of
// work and personal Google Calendars.
//
// Google Calendar is amazing software, but we often want to book some
// time for personal use (e.g. appointment to a doctor), invite friends
// and relatives (e.g. visiting with a spouse) and have this time booked
// at work calendar too (so that no-one schedules a 1:1 meeting for that
// interval). This is often done by inviting your work account to the
// personal event.
//
// However, this does not solve a problem of booking time in your personal
// calendar (so that your spouse does schedule a fun event for that time)
// whenever you have a meeting at work. Inviting your personal account to
// work events is impractical (there are too many) and is often against
// the company policy (risk of leaking data).
//
// This script relies on your work Google Calendar to be shared with your
// personal account in the "see free/busy" mode. You paste the code as
// Google Apps Script (script.google.com), change the SOURCE_CALENDAR_ID,
// TITLE_TO_EXCLUDE, and GENERATED_EVENT_TITLE, then schedule the sync3days()
// and sync30days() functions to run periodically, blocking
// the time in your personal calendar as needed.
//
// Obviously, the script can be used for bi-directional syncing provided you
// set TITLE_TO_EXCLUDE and GENERATED_EVENT_TITLE so that what one account uses
// as EXCLUDE is GENERATED for another.
//
// Copyright 2018 Alexander Churanov
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom
// the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT
// OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
// OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

// PARAMETERS
//
// The Google Calendar to pull events from (the "source calendar").
var SOURCE_CALENDAR_ID = "user@gmail.com";
// Do not import events from the source calendar if they have this title.
// Useful for bi-directional sync of work/personal calendars.
var TITLE_TO_EXCLUDE = "Not at Work";
// Use this title when blocking time in the destination calendar.
var GENERATED_EVENT_TITLE = "Focused at Work";

// CODE
//
// Returns a text string represesting the 'date' in %Y-%m-%d format.
function formatDate(date) {
  return date.getFullYear() + '-' + (date.getMonth() + 1) + '-'+ date.getDate();
}

// Returns a text string representing the 'time' in %H:%M format.
function formatTime(time) {
  text = time.getHours() + ':' + time.getMinutes();
  if (text[text.length - 1] === '0' && text[text.length - 2] === ':') {
    text = text + '0';
  }
  return text;
}

// Returns true if the two objects represent the same point in time,
// false otherwise.
function equalTimes(lhs, rhs) {
  return lhs.getTime() === rhs.getTime();
}

// Removes events that have exact title of GENERATED_EVENT_TITLE and
// happen on day 'day from the 'calendar.
// Types of arguments:
//   calendar - Calendar
//   day - Date
function removeGeneratedEvents(calendar, day) {
  Logger.log('Removing generated events from calendar "' +
             calendar.getName() + '".');
  var events = calendar.getEventsForDay(day);

  for (i in events) {
    var event = events[i];
    if (event.getTitle() === GENERATED_EVENT_TITLE) {
      var start_str = formatTime(event.getStartTime());
      var end_str = formatTime(event.getEndTime());
      Logger.log("Removing event: " + start_str + " – " + end_str);
      event.deleteEvent();
    }
  }
}

// Types of arguments:
//   dest_calendar - Calendar
//   start_time - Date
//   end_time - Date
function bookTime(dest_calendar, start_time, end_time) {
  var start_str = formatTime(start_time);
  var end_str = formatTime(end_time);
  Logger.log('Booking time from ' + start_str + ' to ' + end_str);
  dest_calendar
    .createEvent(GENERATED_EVENT_TITLE, start_time, end_time)
    .removeAllReminders();
}

// Returns true if the event is deemed worthy of importing based on:
// 1. The properties of the 'event' (all-day or marker title of the event).
// 2. Whether the user rejected the invitation or not.
function isEligibleForImport(event, dest_events) {
  if (event.isAllDayEvent()) {
    return false;
  }
  if (event.getTitle() == TITLE_TO_EXCLUDE) {
    return false;
  }
  if (event.getMyStatus() == CalendarApp.GuestStatus.NO) {
    return false;
  }
  return true;
}

// Searches for events in the 'source' calendar within the
// [today, today + window_days) window and books the corresponding time
// in the 'dest' calendar for eligible events from the source calendar.
// Types of arguments:
//   source_calendar - Calendar
//   dest_calendar - Calendar
//   window_days - Number
function syncCalendars(source_calendar, dest_calendar, window_days) {
  var start_day = new Date();
  Logger.log('Using window of ' + window_days +
             ' days starting from ' + formatDate(start_day));

  for (var day_number = 0; day_number < window_days; ++day_number) {
    var day = new Date();
    day.setDate(start_day.getDate() + day_number);
    Logger.log('Processing day: ' + formatDate(day));

    removeGeneratedEvents(dest_calendar, day);

    var source_events = source_calendar.getEventsForDay(day);
    var dest_events = dest_calendar.getEventsForDay(day);

    for (i in source_events) {
      var event = source_events[i];
      if (isEligibleForImport(event, dest_events)) {
        bookTime(dest_calendar, event.getStartTime(), event.getEndTime());
      }
    }
  }
}

function syncNDays(num_days_to_sync) {
  var source_calendar = CalendarApp.getCalendarById(SOURCE_CALENDAR_ID);
  if (source_calendar === null) {
    Logger.log("ERROR: Can not access source calendar '" +
               SOURCE_CALENDAR_ID + "'.");
    return;
  }
  var dest_calendar = CalendarApp.getDefaultCalendar();

  syncCalendars(source_calendar, dest_calendar, num_days_to_sync);
}

// The functions to schedule in "Current project's triggers".
function sync3days() {
  syncNDays(3);
}

function sync30days() {
  syncNDays(30);
}