Faster subscription updates

[olillin]

Google Calendar usually takes about 12 hours to update calendars subscribed to through URL and sometimes even longer. This does not work for frequently changing calendars like the ones I maintain.

A potential solution would be to synchronize the calendars (and potentially their merged intersections) to calendars in Google Calendar through the API. These calendars are updated instantly across all clients since they are on Google's servers with special logic. I am not sure if it is possible to create calendars not linked to a user but will look into this. The alternative would be creating a new Google Account and give the website access to it, but I am also not sure if the authentication can be extended without needing to reauthorize like cal-helper does.

Only actual users of Google Calendar should be subscribing to these calendars, other clients should still subscribe using the normal URL.

[olillin]

After doing the math it would not be possible to create a calendar for every possible merged calendar. Cal's cals currently has 31 calendars which has billions of possible combinations which is clearly unreasonable.

So something else would have to be thought of for that. Maybe just one grouped calendar for every category in the picker or maybe merged calendars just won't be possible to integrate with this.

[olillin]

Another idea for merged calendars is to generate them on demand. This would mean keeping an updated list of all the calendars and deleting ones that are no longer used. You should be able to check who is subscribed to the calendar through the Google API.

[olillin]

Important is that people should not be able to see who else is subscribed to a calendar. The counts could be interesting internally for statistics however.