protected function loadFile($path)
    {
        if (pathinfo($path, PATHINFO_EXTENSION) !== 'php') {
            throw new \InvalidArgumentException('Can only parse files with ".php" extensions');
        }
        if (!file_exists($path)) {
            throw new \InvalidArgumentException(sprintf('Failed to find \'%s\' file.', $path));
        }

        return file_get_contents($path);
    }