Sync Multiple Google Calendars Together

Are you one person with two (or more!) calendars that

Get meeting invites
Have separate audiences (most people can only see one calendar)
Block your time (you can't be at two 1pm meetings)

Then you might like this script! It creates time blocks on calendars to ensure everyone knows when you've already got events scheduled.

Concepts

Throughout this doc I use two terms a lot:

Primary Event - A real event on a calendar

Merged Event - A placeholder on a calendar representing a Primary Event on another calendar

Requirements

All accounts must be Google accounts (Google Suites are fine)
Only install on one of the merged calendar accounts
- The account needs to have "Make changes to events" to all calendars; some clients may disable this access to external accounts - in this case you'll need to setup the script on the client account and allow access to it to the R&P calendar
If you're already manually duplicating events between calendars, you'll need to do one of the following or MergeCalendarsTogether will treat the duplicates as Primary events
- Delete the duplicates
- Rename the duplicates with the Prefix to allow MergeCalendarsTogether to manage those events as Merged events

Getting Started

Make sure every calendar you want sync is shared with the account that will run this script
Log into the account that holds the shared calendar and go to the Google Apps Scripts website.
Click on "New Project".
Replace everything in Code.gs with the contents of MergeCalendarsTogether.gs.
Update CALENDARS_TO_MERGE, SYNC_DAYS_IN_PAST, and SYNC_DAYS_IN_FUTURE variables. Be sure to save.
Create a new file of type=Script called BatchRequests.gs (note: the file extension is automatically added) with the contents of BatchRequests.gs
Click the Project Settings Gear icon on the left panel. Check the Show "appsscript.json" manifest file in editor. Go back to code editor on the left, and update its content with appsscript.json.
Open the Code.gs file again
run the script for the first time (also acts as a manual trigger in the future):
- Select the MergeCalendarsTogether function from the dropdown to the right of the Run and Debug buttons
- ⚠️ NOTE: this next step will run the script. If that makes nervous, you should set DEBUG_ONLY = true in Code.gs
- Click Run (see next step for troubleshooting). This will load the Authorization required window since it's your first time running the script. Click on Review permissions and give it permission to your account.
- ⚠️ If you get an error (like TypeError: Cannot read property 'summary' of undefined) in the console, check that you selected the right function to execute
Click on Triggers clock icon on the left panel to add a trigger. Click on Add Trigger.
- You have two choices, "Time-driven" or "From calendar".
- Time-driven will run every X minutes/hours/etc. Use this if you have calendars that update frequently (more than 5-10 times in a 15 minute timespan)
- "From calendar" will run when a given calendar updates. Use this if you want instant merging.
  
  a. Time-driven
  - "Choose which function to run": MergeCalendarsTogether (note: this isn't the default option)
  - "Choose which deployment should run": Head
  - "Select event source": Time-driven
  - "Select type of time based trigger": choose what works for you.
  - Click "Save"
  b. From calendar
  - "Choose which function to run": MergeCalendarsTogether (note: this isn't the default option)
  - "Choose which deployment should run": Head
  - "Select event source": From calendar
  - "Enter calendar details": Select Calendar Updated and enter the email of one of the calendars you are merging in the text input
  - Click "Save"
  - Repeat these steps for every calendar you're merging.
Note: you do not need to Deploy the app. It will run without being deployed 🚀
Set DEBUG_ONLY = false in Code.gs if you haven't already. Optionally, give the script a run (see "first run" steps above) so you don't have to wait for the timer/a new calendar event to do the sync
Enjoy!

Notes

Google App Scripts has a daily quota of 5k events created per day. See Quotas for Google Services
Be sure to turn off "notifications".

Upgrading

When updating from one version to another, you'll need to copy the code from this repository into your project again. When you do this, it's best to:

Make a backup of your current script by copy/pasting into a text document or other local file
Replace everything in Code.gs with the contents of MergeCalendarsTogether.gs.
Copy your settings from your backup into the new code, particularly
- CALENDARS_TO_MERGE
- SYNC_DAYS_IN_PAST
- SYNC_DAYS_IN_FUTURE
- If you use any other features of the script (e.g., filtering/obfuscation/etc.), copy those settings as well
Double-check that "DEBUG_ONLY" is set to true
Save
At the top of the screen, ensure "MergeCalendarsTogether" is selected, and press "Run"
Verify everything runs correctly
Change "DEBUG_ONLY" to false to re-enable the script

What does this actually do?

Since you're granting this script/app full control over two calendars, I thought it important to include a bit about what it actually does.

The entire script operates in three parts: 1) Get all events for all calendars for all days in the range you specify, 2) Separate the events into either Primary (Created outside of the script) or Merged (created inside the script), 3) Generate API calls to create/delete merged events. There is one optional step as well - Debug. Let's take a look at each step:

Get all events

This script only runs from one account, but pulls events from all of the accounts you list at the top. It does this via API calls using the credentials of the account running the script. That's why you need to share the calendars.

Separate events into Primary and Merged

The script calls for all of the events, then checks the summary - if the summary starts with the pre-defined prefix (🔄 by default), it flags it as a "Merged" event it created in a previous run, otherwise it's flagged as a Primary event.

This script never modifies Primary events - if the event doesn't start with the prefix, no changes will be made to it.

Generate API calls

Once all events are categorized, the script loops through each calendar's Primary events and checks every other calendar for a matching Merged event. If it doesn't find one, it generates an API call to create one.

Note: This also means that you can't manually delete "Merged" events; the script will just re-create it when it sees that it is missing if the matching Primary event still exists.

Then it loops through every calendar's Merged events and checks every other calendar for a matching Primary event. If no other calendar has a matching primary event, it generates an API call to delete the "orphaned" merged event.

Debug mode

Once all the API calls are generated, it does one last check. If DEBUG_ONLY is still set to true, then instead of actually executing the API calls, it lists them in the Execution Log and exits. This is a safety measure; once you see only expected calls listed, change DEBUG_ONLY to false to start generating/managing Merged events.

Uninstalling/Removing Merged events

In the event that you need to remove the merged events, follow these steps:

Go to https://script.google.com/home
Open the project
Open Triggers tab
Delete all triggers
Open "Editor" tab
Ensure you have at least version 0.0.9 (See Upgrading)
Choose "DeleteAllMerged" from the dropdown list next to the Run/Debug buttons
Click Run

To restore functionality, simply follow the steps from Getting Started for setting up the triggers again (Step #10)

Icon Attributions

event user by arjuazka from the Noun Project Exchange Arrows by ImageCatalog from the Noun Project

License

MIT © Flare576

Historical

This project was originally inspired by Sync Multiple Google Calendars by Ali Karbassi. If you're interested in a process that writes events from multiple calendars to a single destination calendar, it's something you should check out!

Flare576/sync-multiple-google-calendars