firestore.rules

rules_version = '2';
service cloud.firestore {
  function isEmpty(resource) {
   return resource == null || !("data" in resource);
  }
	function isOwner(resource) {
  	return ("owner" in resource.data) && request.auth.uid == resource.data.owner;
  }
	function isSignedIn() {
  	return request.auth != null;
  }
  function isPublic(resource) {
   return !("public" in resource.data) || resource.data.public == true;
  }
  
  match /databases/{database}/documents {
    match /calendars/{calendar} {
      allow read, update, delete: if isEmpty(resource) || isPublic(resource) || (isSignedIn() && isOwner(resource));
      allow create;
    }
    match /users/{user} {
      allow read, update, delete: if isEmpty(resource) || isEmpty(get(resource.data.calendar)) || isPublic(get(resource.data.calendar)) || (isSignedIn() && isOwner(get(resource.data.calendar)));
      allow create;
    }
  }
}