public function collectResourcesFromHtml($html) {
        preg_match_all(self::MATCH_SRC, $html, $matches);
        $result = array_filter(array_merge($matches[1], $matches[2], $matches[3], $matches[4]));

        if (count($result) >= 3) { // min 3 resources found
            foreach ($result as $resource) {
                $this->generateLinkHeader($resource);
            }

            header('Link: ' . implode(',', $this->links));
        }
    }


    public function generateLinkHeader($resource) {
        $resource = ltrim($resource, '.');

        if ($resource[0] != '/') {
            $resource = '/'.$resource;
        }

        $link = "<".$resource.">; rel=preload";

        $extension = substr($resource, strrpos($resource, '.')+1);


        if (strrpos($extension, '?')) {
            $extension = substr($extension, 0,strrpos($extension, '?'));
        }

        switch ($extension) {
            case 'css':
                $link.= '; as=style';
                break;
            case 'js':
                $link.= '; as=script';
                break;
            case 'png':
            case 'jpg':
                $link.= '; as=image';
                break;
            default:
                $link.= '';
        }

        $this->links[] = $link;
    }