class AcceptHeaderMatcher

class AcceptHeaderMatcher implements FilterInterface {
  
  /**
   * {@inheritdoc}
   */
  public function filter(RouteCollection $collection, Request $request) {
    // Generates a list of Symfony formats matching the acceptable MIME types.
    // @todo replace by proper content negotiation library.
    $acceptable_mime_types = $request->getAcceptableContentTypes();
    $acceptable_formats = array_filter(array_map([
      $request,
      'getFormat',
    ], $acceptable_mime_types));
    $primary_format = $request->getRequestFormat();
    foreach ($collection as $name => $route) {
      // _format could be a |-delimited list of supported formats.
      $supported_formats = array_filter(explode('|', $route->getRequirement('_format') ?? ''));
      if (empty($supported_formats)) {
        // No format restriction on the route, so it always matches. Move it to
        // the end of the collection by re-adding it.
        $collection->add($name, $route);
      }
      elseif (in_array($primary_format, $supported_formats)) {
        // Perfect match, which will get a higher priority by leaving the route
        // on top of the list.
      }
      elseif (in_array('*/*', $acceptable_mime_types) || array_intersect($acceptable_formats, $supported_formats)) {
        // Move it to the end of the list.
        $collection->add($name, $route);
      }
      else {
        // Remove the route if it does not match at all.
        $collection->remove($name);
      }
    }
    if (count($collection)) {
      return $collection;
    }
    // We do not throw a
    // \Symfony\Component\Routing\Exception\ResourceNotFoundException here
    // because we don't want to return a 404 status code, but rather a 406.
    throw new NotAcceptableHttpException('No route found for the specified formats ' . implode(' ', $acceptable_mime_types));
  }

}