public function format($format = 'date', $timestamp = null)
    {
        $timestamp = is_numeric($timestamp) ? '@'.intval($timestamp) : $timestamp;
        $timestamp = is_a($timestamp, 'DateTime') ? $timestamp : new DateTime($timestamp);

        $key = $this->getTranslationKey("date.formats.{$format}");
        $format = $this->translator->has($key) ? $this->translator->get($key) : null;

        if (is_null($format)) {
            throw new \InvalidArgumentException('Date format is invalid or does not exists in current language');
        }

        return strftime($format, $timestamp->format('U'));
    }