Google Apps Script to automatically color calendar events

color-calendar-events.gs

// Setup instructions
//
// Copy and paste into a Google Apps Script project. Feel free to change the colors below.
//
// Add a trigger to run the colorUpdatedCalendarEvents function the on the "Calendar updated" event of
// your calendar.

const PERSONAL_COLOR = CalendarApp.EventColor.GRAY;
const IN_PERSON_COLOR = CalendarApp.EventColor.BLUE;
const EXTERNAL_COLOR = CalendarApp.EventColor.RED;
const INTERNAL_COLOR = undefined; // Default blue color

function colorUpdatedCalendarEvents(e) {
  const calendarId = e?.calendarId ?? "primary";
  const calendar = Calendar.Calendars.get(calendarId);
  const updatedEvents = getUpdatedCalendarEvents(calendar.id, false);

  for (const event of updatedEvents) {
    if (event.status === 'cancelled') {
      continue;
    }
    if (event.eventType === "default") {
      setEventColor(calendar.id, event);
    }
  }
}

function setEventColor(calendarId, event) {
  const calendarDomain = calendarId.split("@")[1];

  console.log("Setting color for", event.summary ?? event.id);
  const attendees = [event.organizer, ...(event.attendees ?? [])];
  const guestEmails = attendees.filter(a => !a.self).map(a => a.email);
  const hasExternalGuest = guestEmails.some(e => e.split("@")[1] !== calendarDomain);

  if (event.location && event.location !== "") {
    console.log(`${event.summary}: in-person`);
    event.colorId = IN_PERSON_COLOR;
  } else if (guestEmails.length === 0) {
    console.log(`${event.summary}: personal`)
    event.colorId = PERSONAL_COLOR;
  } else if (hasExternalGuest) {
    console.log(`${event.summary}: external`)
    event.colorId = EXTERNAL_COLOR;
  } else {
    console.log(`${event.summary}: internal`)
    event.colorId = INTERNAL_COLOR;
  }

  try {
    Calendar.Events.update(event, calendarId, event.id);
  } catch (err) {
    console.error("error updating event %s: %s", event.id, err.message);
  }
}

/**
 * Find and return events in the given calendar that have been modified
 * since the last sync. If the sync token is missing or invalid, return all
 * events from up to a week ago (a full sync).
 *
 * @param {string} calendarId The ID of the calender to retrieve events from.
 * @param {boolean} fullSync If true, throw out any existing sync token and
 *        perform a full sync; if false, use the existing sync token if possible.
 */
function getUpdatedCalendarEvents(calendarId, fullSync) {
  console.log("Fetching updated calendar events, full sync =", fullSync);

  const properties = PropertiesService.getUserProperties();
  const options = { maxResults: 100 };
  const syncToken = properties.getProperty('syncToken');
  if (syncToken && !fullSync) {
    options.syncToken = syncToken;
  } else {
    // Sync events up to seven days in the past.
    options.timeMin = getRelativeDate(-7, 0).toISOString();
  }

  // Retrieve events one page at a time.
  let events = [];
  let pageToken;
  let response;
  do {
    try {
      options.pageToken = pageToken;
      response = Calendar.Events.list(calendarId, options);
      events = events.concat(response.items);
    } catch (e) {
      // Check to see if the sync token was invalidated by the server;
      // if so, perform a full sync instead.
      if (e.message === 'Sync token is no longer valid, a full sync is required.') {
        properties.deleteProperty('syncToken');
        return getUpdatedCalendarEvents(calendarId, true);
      }
      throw new Error(e.message);
    }
    pageToken = response.nextPageToken;
  } while (pageToken);

  properties.setProperty('syncToken', response.nextSyncToken);

  return events;
}

/**
 * Helper function to get a new Date object relative to the current date.
 * @param {number} daysOffset The number of days in the future for the new date.
 * @param {number} hour The hour of the day for the new date, in the time zone
 *     of the script.
 * @return {Date} The new date.
 */
function getRelativeDate(daysOffset, hour) {
  const date = new Date();
  date.setDate(date.getDate() + daysOffset);
  date.setHours(hour);
  date.setMinutes(0);
  date.setSeconds(0);
  date.setMilliseconds(0);
  return date;
}