Whether an operation of the Zettelstore is allowed or rejected, depends on various factors.
The following rules are checked first, in this order:
In read-only mode, every operation except the Read operation is rejected.
If there is no owner, authentication is disabled and every operation is allowed for everybody.
If the user is authenticated and it is the owner, then the operation is allowed.
In the second step, when authentication is enabled and the requesting user is not the owner, everything depends on the requested operation.
Read a zettel:
If the visibility is public, the access is granted.
If the visibility is owner, the access is rejected.
If the user is not authenticated, access is rejected.
If the zettel requested is an user zettel, reject the access if the users identification is not the same as of the user-id metadata value in the zettel.
In other words: only the requesting user is allowed to access its own user zettel.
If the user-role of the user is creator, reject the access.
Otherwise the user is authenticated, no sensitive zettel is requested. Allow to read the zettel.
Create a new zettel
If the user is not authenticated, reject the access.
If the user-role of the user is reader, reject the access.
If the user tries to create an user zettel, the access is rejected.
Only the owner of the Zettelstore is allowed to create user zettel.
In all other cases allow to create the zettel.
Change an existing zettel
If the user is not allowed to read the zettel (see above), reject the access.
If the user is not authenticated, reject the access.
If the zettel is the user zettel of the authenticated user, proceed as follows:
If some sensitive meta values are changed (e.g. user identifier, zettel role, user role, but not hashed password), reject the access
Since the user just updates some uncritical values, grant the access
In other words: a user is allowed to change its user zettel, even if s/he has no writer privilege and if only uncritical data is changed.
If the user-role of the user is reader, reject the access.
If the user is not allowed to create a new zettel, reject the access.
Otherwise grant the access.
Delete a zettel
Reject the access. Only the owner of the Zettelstore is allowed to delete a zettel. This may change in the future.