How do I test for Google Calendar events that are marked: "Automatically decline new and existing meetings" - google-apps-script

Question

Non-engineer here. I'm working on a program (using Google Sheets) that will help people in my office analyze their calendars.
The Google Calendar Service has methods that allow me to retrieve event start and end times, guest lists, and much more. Unfortunately, I haven't figured out how to tell the difference between a "Reminder" and an "Out of the office" event. They both show up as all day events, but the former can be ignored and the latter causes that entire day to show up as "blocked" or "scheduled". I need to be able to tell them apart, but I'm not sure how.
Any suggestions?
MORE DETAIL:
I create a "Reminder" in Google Calendar by clicking just below the day, at the top. This gives me three choices: Event, Out of the office, and Appointment slots. When I am creating a Reminder for myself I first name it (i.e. "Doctor's appointment at 2:00"), then I usually change the color to red so it's extra visible.
If I am going to be Out of the office I choose that option. The option "Automatically decline new and existing meetings" is checked by default. I add a name like, "Dev Conference" and Save it. This causes the entire day to show in a light blue color, indicating that the entire day is blocked.

Answer 1

You can differentiate between a normal event and a "Out of Office" event because of the latter not having the transparency attribute included and it has the description attribute filled with the following value:
"This is an out-of-office event, which can only be edited in Google Calendar. Meetings during this time will be automatically declined."
You can test this by making a Events.list request and check the results, for example:
Normal event:
{
"kind": "calendar#event",
"etag": "\"3167876463844000\"",
"id": "1nqq8sg43po8itr8h0ebedfgbq",
"status": "confirmed",
"htmlLink": "https://www.google.com/calendar/event?eid=MW5xcThzZzQzcG84aXRyOGgwZWJlZGZnYnEgdGVzdGluYUBlZ3Mtc2J0MDExLmV1",
"created": "2020-03-11T14:50:31.000Z",
"updated": "2020-03-11T14:50:31.922Z",
"summary": "test",
"creator": {
"email": "testina#egs-sbt011.eu",
"self": true
},
"organizer": {
"email": "testina#egs-sbt011.eu",
"self": true
},
"start": {
"date": "2020-03-16"
},
"end": {
"date": "2020-03-17"
},
"transparency": "transparent",
"iCalUID": "1nqq8sg43po8itr8h0ebedfgbq#google.com",
"sequence": 0,
"reminders": {
"useDefault": false
}
}
Out of Office event:
{
"kind": "calendar#event",
"etag": "\"3167876472386000\"",
"id": "29g3lpl9hojb92bevvkvdccq6p",
"status": "confirmed",
"htmlLink": "https://www.google.com/calendar/event?eid=MjlnM2xwbDlob2piOTJiZXZ2a3ZkY2NxNnAgdGVzdGluYUBlZ3Mtc2J0MDExLmV1",
"created": "2020-03-11T14:50:36.000Z",
"updated": "2020-03-11T14:50:36.289Z",
"summary": "test OOO",
"description": "This is an out-of-office event, which can only be edited in Google Calendar. Meetings during this time will be automatically declined.",
"creator": {
"email": "testina#egs-sbt011.eu",
"self": true
},
"organizer": {
"email": "testina#egs-sbt011.eu",
"self": true
},
"start": {
"dateTime": "2020-03-17T00:00:00+01:00"
},
"end": {
"dateTime": "2020-03-18T00:00:00+01:00"
},
"visibility": "public",
"iCalUID": "29g3lpl9hojb92bevvkvdccq6p#google.com",
"sequence": 0,
"reminders": {
"useDefault": false
}
}
Regarding appointment slots, these are not supported by Google Calendar API, you can +1 this open feature request to implement this.

Answer 2

For a while after the feature was introduced, there was no way to filter them via API other than parsing the description. There is now an eventType key on events.
https://developers.google.com/calendar/api/v3/reference/events#eventType
Look for "eventType": "outOfOffice" events.