Google Apps script to copy personal events and block those times in your work calendar.

calendarCopy.js

// *******************
// This setup will allow you to synchronize personal events from one calendar (the "secondary calendar") e.g. your Opsgenie
// schedule, to another calendar, e.g. work (the "primary calendar").
//
// Follow these steps:
// 1. Go to https://script.google.com/home and click [+ New project]
// 2. Make sure the two calendars you want to sync are in your Google calendar list, and the primary calendar can be edited
//    by the Google account you're currently under (or switch accounts to the owner of the primary calendar)
//    To get your Opsgenie schedule into Google Calendar, export your Opsgenie webcal URL: https://support.atlassian.com/opsgenie/docs/view-your-on-call-schedule/#Export-with-manual-URL
//    and subscribe to the URL in your Google Calendar: https://calendar.google.com/calendar/u/0/r/settings/addbyurl
// 3. Click the title and give it a name like "Calendar sync"
// 4. Copy this code and paste it in to the editor
// 5. Update the values below 👇
// 6. Click [+] next to [Services], and choose [Google Calendar API], then [Add]
//    Example: https://i.imgur.com/xlrAj39.jpg
// 7. Select "exec" as the function to run. Click [Run] and make sure things sync up correctly.
//    You could change DAYS_LOOKAHEAD to a smaller number if you want to test run with a smaller set of events.
//    You will be prompted to [Review permissions], do so and authorize the app to access your
//    Google account.
//    You'll have to go through an awkward warning about "Google hasn't verified the app"
//    https://i.imgur.com/EH5OBqR.jpg
//    Then choose [Allow]: https://i.imgur.com/jyz6XEx.jpg
// 8. Once behavior looks good, set the other customization values to what you want.
// 9. Save, and then click on [Triggers] (looks like an alarm clock): https://i.imgur.com/jEa4HA0.jpg
// 10. Click [+ Add Trigger], choose "exec", "Hours/Minutes timer", and an interval you want.
//     Example: https://i.imgur.com/TMXoAIA.jpg
// 11. [Save] and watch for your calendar to sync!



// *************
// You must fill in these
// *************

// Your calendar ID comes from [Settings] > [Calendar settings]: https://i.imgur.com/sY87aoI.jpg
// The secondary calendar is your Opsgenie calendar or one you'll copy events from
const SECONDARY_CALENDAR_ID = "[email protected]";
// primary calendar is your "work" calendar where secondary events will be copied over as "Busy" slots
const PRIMARY_CALENDAR_ID = "[email protected]";

// *******************
// These you can customize if you want
// *******************

// How many days ahead do you want to block off time in your primary calendar
const DAYS_LOOKAHEAD = 14;
// What title do your secondary events have in your primary calendar
const BUSY_EVENT_TITLE = "Ops Rotation";
// Override your usual primary calendar event color for copied Busy events. 
// From https://developers.google.com/apps-script/reference/calendar/event-color.html
// If you don't want to override, comment out the place this constant is used.
const BUSY_EVENT_COLOR_ID = CalendarApp.EventColor.RED;
// ignore secondary events that end before this time (in 24 hr time)
const IGNORE_SECONDARY_EVENTS_BEFORE = 9
// ignore secondary events that start after this time (in 24 hr time)
const IGNORE_SECONDARY_EVENTS_AFTER = 17
// ignore secondary events over weekends
const IGNORE_SECONDARY_EVENTS_ON_WEEKENDS = false

// *******************
// Below here is code you can look through and tweak if you want, but most of the customization
// should be above.
// *******************

// source: https://gist.github.com/ttrahan/a88febc0538315b05346f4e3b35997f2
// blog: https://chromatichq.com/blog/syncing-your-personal-work-calendars
// original:
// https://medium.com/@willroman/auto-block-time-on-your-work-google-calendar-for-your-personal-events-2a752ae91dab
function exec() {
  const today = new Date();
  const enddate = new Date();
  enddate.setDate(today.getDate() + DAYS_LOOKAHEAD); // how many days in advance to monitor and block off time

  const secondaryCal = CalendarApp.getCalendarById(SECONDARY_CALENDAR_ID);
  const secondaryEvents = secondaryCal.getEvents(today, enddate);

  const primaryCal = CalendarApp.getCalendarById(PRIMARY_CALENDAR_ID);
  const primaryEvents = primaryCal.getEvents(today, enddate); // all primary calendar events

  const primaryEventTitle = BUSY_EVENT_TITLE; 

  let evi, existingEvent;
  const primaryEventsFiltered = []; // primary events that were previously created from secondary
  const primaryEventsUpdated = []; // primary events that were updated from secondary calendar
  const primaryEventsCreated = []; // primary events that were created from secondary calendar
  const primaryEventsDeleted = []; // primary events previously created that have been deleted from secondary

  Logger.log("Number of primaryEvents: " + primaryEvents.length);
  Logger.log("Number of secondaryEvents: " + secondaryEvents.length);

  // create filtered list of existing primary calendar events that were previously created from the secondary calendar
  for (let pev in primaryEvents) {
    const pEvent = primaryEvents[pev];
    if (pEvent.getTitle() === primaryEventTitle) { primaryEventsFiltered.push(pEvent); }
  }

  // process all events in secondary calendar
  for (let sev in secondaryEvents) {
    let canSkip = false;
    evi = secondaryEvents[sev];
    let primaryDescription = evi.getTitle() + '\n\n' + evi.getDescription();

    // if the secondary event has already been blocked in the primary calendar, update it
    for (existingEvent in primaryEventsFiltered) {
      const pEvent = primaryEventsFiltered[existingEvent];
      const isSameStart = pEvent.getStartTime().getTime() === evi.getStartTime().getTime();
      const isSameEnd = pEvent.getEndTime().getTime() === evi.getEndTime().getTime();
      if (isSameStart && isSameEnd) {
        canSkip = true;

        // If you wanted to copy over more info, this would be the place to re-copy updates
        pEvent.setDescription(primaryDescription);
        // etc...

        primaryEventsUpdated.push(pEvent.getId());
      }
    }

    if (canSkip) continue;

    if (shouldIgnore(evi)) {
      continue;
    }

    // if the secondary event does not exist in the primary calendar, create it
    // we use the Calendar API (instead of the CalendarApp given to us) because it allows us to specify not using
    // default reminders, so we aren't notified about meaningless "Busy" events.
    const event = {
      summary: primaryEventTitle,
      description: primaryDescription,
      start: {
        dateTime: evi.getStartTime().toISOString(),
      },
      end: {
        dateTime: evi.getEndTime().toISOString(),
      },
      colorId: BUSY_EVENT_COLOR_ID,
      reminders: {
        useDefault: false,
      },
    };
    const newEvent = Calendar.Events.insert(event, PRIMARY_CALENDAR_ID);
    primaryEventsCreated.push(newEvent.id);
    Logger.log("PRIMARY EVENT CREATED", newEvent);
  }

  // if a primary event previously created no longer exists in the secondary calendar, delete it
  for (pev in primaryEventsFiltered) {
    const pevIsUpdatedIndex = primaryEventsUpdated.indexOf(primaryEventsFiltered[pev].getId());
    if (pevIsUpdatedIndex === -1) {
      const pevIdToDelete = primaryEventsFiltered[pev].getId();
      Logger.log(pevIdToDelete + " deleted");
      primaryEventsDeleted.push(pevIdToDelete);
      primaryEventsFiltered[pev].deleteEvent();
    }
  }

  Logger.log("Primary events previously created: " + primaryEventsFiltered.length);
  Logger.log("Primary events no change: " + primaryEventsUpdated.length);
  Logger.log("Primary events deleted: " + primaryEventsDeleted.length);
  Logger.log("Primary events created: " + primaryEventsCreated.length);

}

// You can update the conditions where you do not copy secondary events over as "Busy"
function shouldIgnore(event) {
  // Do nothing if the event is an all-day or multi-day event. This script only syncs hour-based events
  if (event.isAllDayEvent()) {
    return true;
  }

  // skip events that end by 9 AM
  if (event.getEndTime().getHours() <= IGNORE_SECONDARY_EVENTS_BEFORE) {
    return true;
  }

  // skip events that start after 5pm
  if (event.getStartTime().getHours() >= IGNORE_SECONDARY_EVENTS_AFTER) {
    return true;
  }

  if (IGNORE_SECONDARY_EVENTS_ON_WEEKENDS) {
    const date = event.getStartTime();
    const dayNum = date.getDay();
    if (dayNum === 0 || dayNum === 6) {
      return true;
    }
  }
  
  return false;
}