class DeferCss

class DeferCss {
    
    /**
     * The defer method to use from advagg_mod configuration.
     *
     * @var int
     */
    protected $deferMethod;
    
    /**
     * The global counter to use for calculating paths.
     *
     * @var int
     */
    protected $counter;
    
    /**
     * Whether or not to alter external stylesheets.
     *
     * @var bool
     */
    protected $external;
    
    /**
     * The module extension list service.
     *
     * @var \Drupal\Core\Extension\ExtensionList
     */
    protected $moduleExtensionList;
    
    /**
     * DeferCss constructor.
     *
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory.
     * @param ExtensionList $module_extension_list
     *   The module extension list service.
     */
    public function __construct(ConfigFactoryInterface $config_factory, ExtensionList $module_extension_list) {
        $this->deferMethod = $config_factory->get('advagg_mod.settings')
            ->get('css_defer_js_code');
        $this->counter = $config_factory->get('advagg.settings')
            ->get('global_counter');
        $this->external = $config_factory->get('advagg_mod.settings')
            ->get('css_defer_external');
        $this->moduleExtensionList = $module_extension_list;
    }
    
    /**
     * Replace stylesheet links with preload & noscript links.
     *
     * @param string $content
     *   The response content.
     *
     * @return string
     *   Updated content.
     */
    public function defer($content) {
        if ($this->external) {
            $pattern = '/<link rel=["\']stylesheet["\'](.*)(href="[a-zA-Z0-9\\/_\\.\\-\\?\\:]*")(.*)\\/\\>/';
        }
        else {
            $pattern = '/<link rel=["\']stylesheet["\'](.*)(href="\\/[a-zA-Z0-9][a-zA-Z0-9\\/_\\.\\-\\?]*")(.*)\\/\\>/';
        }
        $content = preg_replace_callback($pattern, [
            $this,
            'callback',
        ], $content);
        // Put JS inline if configured.
        if ($this->deferMethod === 0) {
            $path = $this->moduleExtensionList
                ->getPath('advagg_mod') . '/js/loadCSS.js';
            if (!strpos($content, $path)) {
                $path = Crypt::hashBase64($path . $this->counter);
            }
            else {
                $path = str_replace('/', '\\/', $path);
            }
            $path = preg_quote($path, '/');
            $pattern = "/<script src=['\"]\\/(.*{$path}.*)\\?.*['\"]>/";
            $content = preg_replace_callback($pattern, [
                $this,
                'inlineScript',
            ], $content);
        }
        return $content;
    }
    
    /**
     * Callback to replace individual stylesheet links.
     *
     * @param array $matches
     *   Array from matches from preg_replace_callback.
     *
     * @return string
     *   Updated html string.
     */
    protected function callback(array $matches) {
        return "<link rel='preload' {$matches[1]} {$matches[2]} as='style' onload=\"this.rel='stylesheet'\" {$matches[3]}/><noscript>{$matches[0]}</noscript>";
    }
    
    /**
     * Callback to replace the script link with an inline script.
     *
     * @param array $matches
     *   Array from matches from preg_replace_callback.
     *
     * @return string
     *   Updated html string.
     */
    protected function inlineScript(array $matches) {
        $data = @file_get_contents($matches[1]);
        return "<script>{$data}";
    }

}