This function should return an array, such as the following:
[
'syncToken' => 'The current synctoken',
'added' => [
'new.txt',
],
'modified' => [
'updated.txt',
],
'deleted' => [
'foo.php.bak',
'old.txt'
]
];
The returned syncToken property should reflect the *current* syncToken
of the addressbook, as reported in the {http://sabredav.org/ns}sync-token
property. This is needed here too, to ensure the operation is atomic.
If the $syncToken argument is specified as null, this is an initial
sync, and all members should be reported.
The modified property is an array of nodenames that have changed since
the last token.
The deleted property is an array with nodenames, that have been deleted
from collection.
The $syncLevel argument is basically the 'depth' of the report. If it's
1, you only have to report changes that happened only directly in
immediate descendants. If it's 2, it should also include changes from
the nodes below the child collections. (grandchildren)
The $limit argument allows a client to specify how many results should
be returned at most. If the limit is not specified, it should be treated
as infinite.
If the limit (infinite or not) is higher than you're willing to return,
you should throw a Sabre\DAV\Exception\TooMuchMatches() exception.
If the syncToken is expired (due to data cleanup) or unknown, you must
return null.
The limit is 'suggestive'. You are free to ignore it.
