https://www.baeldung.com/rest-api-error-handling-best-practices https://github.com/open-spaced-repetition/fsrs4anki/wiki/Compare-Anki's-built-in-scheduler-and-FSRS https://github.com/open-spaced-repetition/fsrs4anki/wiki/The-Algorithm#fsrs-v4 https://huggingface.co/spaces/open-spaced-repetition/fsrs4anki_previewer
https://symfony.com/doc/2.x/security/access_denied_handler.html https://symfony.com/doc/current/security.html#security-securing-controller-attributes