protected function normalizeClass($class)
    {
        // Strip first slash
        $class = ltrim($class, '\\');

        // Work backwards through the namespace names of the fully-qualified
        // class name to find a mapped file name
        $pos = strrpos($class, '\\');

        // Retain the trailing namespace separator in the prefix
        $directory = substr($class, 0, $pos + 1);

        // The rest is the relative class name
        $relativeClass = substr($class, $pos + 1);
        $directory = str_replace(['\\', '.'], DIRECTORY_SEPARATOR, $directory);

        $directory = trim($directory, DIRECTORY_SEPARATOR);

        $lowerClass = strtolower($directory).DIRECTORY_SEPARATOR.$relativeClass;
        $upperClass = $directory.DIRECTORY_SEPARATOR.$relativeClass;

        return [$lowerClass, $upperClass];
    }