Do not allow deleting shared calendars.

[michaelkuhn]

This pull request makes sure that shared calendars can not be deleted but are instead unshared.

This change depends on owncloud/core#9915.

[michaelkuhn]

As owncloud/core#9915 has now been merged, please review this pull request again.

[georgehrke]

Code looks good, still need to test it

[michaelkuhn]

One question that came up while I was reading #555: deleteCalendar is also used to delete calendars when a user is deleted, correct? If so, I guess I will have to update the code to take that into consideration.

[georgehrke]

yes, would be great if you could check

[quenenni]

Hello,

I would like to know where you are with this problem? Will it be fixed soon?
(I'm using owncloud 8.0.6 and the problem still exists)

It's really an annoying feature/bug.. We have a multi instance owncloud and it happened several times that an user deleted shared calendars with all that involves (data loss, find backup, find the relevant tables / data to restore, ... ).
That's very painfull ;)

[georgehrke]

• needs rebase

[zilon84]

Hello,

are there important reasons why this fix is not included, yet? I think it's very important to avoid data loss by an accidentally hit delete button by an user that does not own the calendar.

Thx,
Zilon

[michaelkuhn]

Somehow I forgot to follow up on this, sorry about that.

I have updated the pull request with the workaround I currently use to prevent accidental calendar deletion (basically a rebased version of the original commit). I have also added a second commit to force calendar deletion during user deletion to address my earlier comment.

I am not sure whether this is sufficient, though. Someone with a better understanding of ownCloud's share system and the calendar app needs to review this (why do users of a shared calendar get the delete permission in the first place and would it be enough not to grant it?).