Google Apps Script: Sync Google Group members Out of Office events to a shared calendar, including recurring OOF events, using the outOfOffice eventType.

script.js

/**
This is based on the example provided at:
https://developers.google.com/apps-script/samples/automations/vacation-calendar

The following changes were made:
- Uses the outOfOffice eventType to identify events to sync. It does not use a keyword search.
- Events use the full names of members, pulled from the Google Workspace API (AdminDirectory.)
- Recurring OOF events are supported.
- Creates "shadow events" instead of importing the actual events, to circumvent "forbidden" errors in some cases, and issues with recurring events.

# Setup:
## Create a team vacation calendar
- Open Google Calendar.
- Create a new calendar, name it something like "Team Vacations."
- In the calendar's settings, under Integrate calendar, copy the Calendar ID.

## Create the Apps Script project
- Create a new Apps Script project at https://script.google.com.
- Under files, create a new script, and paste the body of this gist.
- Change TEAM_CALENDAR_ID to the Calendar ID you copied above.
- Change GROUP_EMAIL to the email address of a Google Group containing your team members.
- Under services, add Google Calendar and AdminDirectory.

## Run the script
- From your script file, in the function dropdown, select setup.
- Click Run.
- Authorize the script if prompted.

Once complete, return to Google Calendar and confirm your Team Vacations calendar has populated with events.
**/

let TEAM_CALENDAR_ID = '...';
let GROUP_EMAIL = '...';

function setup() {
  let triggers = ScriptApp.getProjectTriggers();
  if (triggers.length === 0) {
    ScriptApp.newTrigger('sync').timeBased().everyHours(1).create();
  }
  sync();
}

function sync() {
  let today = new Date();
  let maxDate = new Date();
  let lastRun = PropertiesService.getScriptProperties().getProperty('lastRun');
  let users = GroupsApp.getGroupByEmail(GROUP_EMAIL).getUsers();
  let countImported = 0;
  let countUsers = 0;

  today.setMonth(today.getMonth() - 1);
  maxDate.setMonth(maxDate.getMonth() + 3);
  lastRun = lastRun ? new Date(lastRun) : null;

  users.forEach(function(user) {
    countUsers++;
    let email = user.getEmail();
    let contact = AdminDirectory.Users.get(email, {fields:'name', viewType:'domain_public'});
    let events = [];
    
    console.log("Updating " + contact.name.fullName + "...");
    events = findEvents(email, today, maxDate, lastRun);

    events.forEach(function (event) {
      importEvent(contact.name.fullName, event);
      countImported++;
    });
  });

  PropertiesService.getScriptProperties().setProperty('lastRun', today);
  console.log('Imported ' + countImported + ' events from ' + countUsers + ' users.');
}

function findEvents(email, start, end, optSince) {
  let pageToken = null;
  let events = [];
  let params = {
    timeMin: formatDateAsRFC3339(start),
    timeMax: formatDateAsRFC3339(end),
    showDeleted: true,
  };

  if (optSince) {
    params.updatedMin = formatDateAsRFC3339(optSince);
  }

  do {
    let response;
    params.pageToken = pageToken;
    
    try {
      response = Calendar.Events.list(email, params);
    } catch (e) {
      console.error('Error retrieving events for %s, %s: %s; skipping', email, e.toString());
      continue;
    }

    response.items.forEach(function(occurrence) {
      let occurrenceId = occurrence.id;
      let recurring = false;

      if (occurrence.recurringEventId || occurrence.iCalUID !== occurrence.id + '@google.com') {
        recurring = true;
      }

      event = Calendar.Events.get(email, occurrenceId);

      if(event.eventType == "outOfOffice" && (!event.organizer || event.organizer.email == "unknownorganizer@calendar.google.com")) {
        if (!event.attendees) {
          return false;
        }

        let matching = event.attendees.filter(function(attendee) {
          return attendee.self;
        });

        if (matching.length > 0 && matching[0].responseStatus == 'accepted') {
          let unique = Utilities.computeDigest(Utilities.DigestAlgorithm.MD5, JSON.stringify({id: occurrenceId, owner: email})).reduce(function (str,chr) {
            chr = (chr < 0 ? chr + 256 : chr).toString(16);
            return str + (chr.length==1?'0':'') + chr;
          },'');

          let shadow = {
            id: unique,
            iCalUID: unique + '@google.com',
            description: '',
            summary: '',
            start: event.start,
            end: event.end,
            status: event.status,
            eventType: 'outOfOffice',
          };

          if (recurring) {
            shadow.description = 'Recurring. ';
          }

          if (event.summary.length) {
            shadow.description += event.summary;

            if (shadow.description.slice(-1) !== '.') {
              shadow.description += '.';
            }
          }

          events.push(shadow);
        }
      }
    });
    
    pageToken = response.nextPageToken;
  } while (pageToken);

  return events;
}

function importEvent(name, event) {
  event.summary = name + ' OOF';
  event.organizer = {
    id: TEAM_CALENDAR_ID,
  };

  sorted = Object.keys(event)
    .sort()
    .reduce((acc, key) => ({
        ...acc, [key]: event[key]
    }), {})

  console.log('Importing: %s', JSON.stringify(sorted));

  try {
    Calendar.Events.import(event, TEAM_CALENDAR_ID);
  } catch (e) {
    console.error('Error attempting to import event: %s. Skipping.', e.toString());
  }
}

function formatDateAsRFC3339(date) {
  return Utilities.formatDate(date, 'UTC', 'yyyy-MM-dd\'T\'HH:mm:ssZ');
}