class GenericEncoder
{
    private function prepareData($data, string $format)
    {
        switch ($format) {
            case 'json':
                $data = $this->forceArray($data);
                $data = $this->fixKeys($data);
                // fall through
            case 'xml':
                $data = $this->fixAttributes($data);
                break;
            default:
                throw new InvalidArgumentException(
                    'Format not supported'
                );
}
        return $data;
    }
}