public function triggerEvent(string $event): void
    {
        // TODO: use event library and allow attach events to IFile and ICacheStateful.
        // cache triggers
        if ($this->file instanceof ICacheStateful) {
            switch ($event) {
                case self::EVENT_CACHED:
                    $this->file->setCachedAt($this->name, time());
                    break;
                case self::EVENT_EMPTY:
                case self::EVENT_ERROR:
                case self::EVENT_NOT_FOUND:
                    // TODO: split those and save different cases of cache state.
                    $this->file->setCachedAt($this->name, null);
                    break;
            }

            $this->file->saveState();
        }

        // other triggers
    }