PhpCsFixer\Fixer\Basic\Psr4Fixer::fix PHP Method

    public function fix(\SplFileInfo $file, Tokens $tokens)
    {
        $namespace = false;
        $classyName = null;
        $classyIndex = 0;
        foreach ($tokens as $index => $token) {
            if ($token->isGivenKind(T_NAMESPACE)) {
                if (false !== $namespace) {
                    return;
                }
                $namespace = true;
            } elseif ($token->isClassy()) {
                if (null !== $classyName) {
                    return;
                }
                $classyIndex = $tokens->getNextMeaningfulToken($index);
                $classyName = $tokens[$classyIndex]->getContent();
            }
        }
        if (null === $classyName) {
            return;
        }
        if (false !== $namespace) {
            $filename = basename(str_replace('\\', '/', $file->getRealPath()), '.php');
            if ($classyName !== $filename) {
                $tokens[$classyIndex]->setContent($filename);
            }
        } else {
            $normClass = str_replace('_', '/', $classyName);
            $filename = substr(str_replace('\\', '/', $file->getRealPath()), -strlen($normClass) - 4, -4);
            if ($normClass !== $filename && strtolower($normClass) === strtolower($filename)) {
                $tokens[$classyIndex]->setContent(str_replace('/', '_', $filename));
            }
        }
    }