class MimeTypeGuesser

class MimeTypeGuesser implements MimeTypeGuesserInterface {
    
    /**
     * An array of arrays of registered guessers keyed by priority.
     *
     * @var array
     */
    protected $guessers = [];
    
    /**
     * Holds the array of guessers sorted by priority.
     *
     * If this is NULL a rebuild will be triggered.
     *
     * @var \Symfony\Component\Mime\MimeTypeGuesserInterface[]
     *
     * @see \Drupal\Core\File\MimeType\MimeTypeGuesser::addGuesser()
     * @see \Drupal\Core\File\MimeType\MimeTypeGuesser::sortGuessers()
     */
    protected $sortedGuessers = NULL;
    
    /**
     * The stream wrapper manager.
     *
     * @var \Drupal\Core\StreamWrapper\StreamWrapperManagerInterface
     */
    protected $streamWrapperManager;
    
    /**
     * Constructs a MimeTypeGuesser object.
     *
     * @param \Drupal\Core\StreamWrapper\StreamWrapperManagerInterface $stream_wrapper_manager
     *   The stream wrapper manager.
     */
    public function __construct(StreamWrapperManagerInterface $stream_wrapper_manager) {
        $this->streamWrapperManager = $stream_wrapper_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public function guessMimeType(string $path) : ?string {
        if ($wrapper = $this->streamWrapperManager
            ->getViaUri($path)) {
            // Get the real path from the stream wrapper, if available. Files stored
            // in remote file systems will not have one.
            $real_path = $wrapper->realpath();
            if ($real_path !== FALSE) {
                $path = $real_path;
            }
        }
        if ($this->sortedGuessers === NULL) {
            // Sort is not triggered yet.
            $this->sortedGuessers = $this->sortGuessers();
        }
        foreach ($this->sortedGuessers as $guesser) {
            $mime_type = $guesser->guessMimeType($path);
            if ($mime_type !== NULL) {
                return $mime_type;
            }
        }
        return 'application/octet-stream';
    }
    
    /**
     * Appends a MIME type guesser to the guessers chain.
     *
     * @param \Symfony\Component\Mime\MimeTypeGuesserInterface $guesser
     *   The guesser to be appended.
     * @param int $priority
     *   The priority of the guesser being added.
     *
     * @return $this
     */
    public function addMimeTypeGuesser(MimeTypeGuesserInterface $guesser, $priority = 0) {
        if ($guesser->isGuesserSupported()) {
            $this->guessers[$priority][] = $guesser;
            // Mark sorted guessers for rebuild.
            $this->sortedGuessers = NULL;
        }
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function isGuesserSupported() : bool {
        return TRUE;
    }
    
    /**
     * Sorts guessers according to priority.
     *
     * @return \Symfony\Component\HttpFoundation\File\MimeType\MimeTypeGuesserInterface[]
     *   A sorted array of MIME type guesser objects.
     */
    protected function sortGuessers() {
        krsort($this->guessers);
        return array_merge(...$this->guessers);
    }
    
    /**
     * A helper function to register with Symfony's singleton MIME type guesser.
     *
     * Symfony's default mimetype guessers have dependencies on PHP's fileinfo
     * extension or being able to run the system command file. Drupal's guesser
     * does not have these dependencies.
     *
     * @see \Symfony\Component\Mime\MimeTypes
     */
    public static function registerWithSymfonyGuesser(ContainerInterface $container) {
        $guesser = new MimeTypes();
        $guesser->registerGuesser($container->get('file.mime_type.guesser'));
        MimeTypes::setDefault($guesser);
    }

}