class LinkGenerator

class LinkGenerator implements LinkGeneratorInterface {
    
    /**
     * The URL generator.
     *
     * @var \Drupal\Core\Routing\UrlGeneratorInterface
     */
    protected $urlGenerator;
    
    /**
     * The module handler firing the route_link alter hook.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * The renderer service.
     *
     * @var \Drupal\Core\Render\RendererInterface
     */
    protected $renderer;
    
    /**
     * Constructs a LinkGenerator instance.
     *
     * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
     *   The url generator.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer service.
     */
    public function __construct(UrlGeneratorInterface $url_generator, ModuleHandlerInterface $module_handler, RendererInterface $renderer) {
        $this->urlGenerator = $url_generator;
        $this->moduleHandler = $module_handler;
        $this->renderer = $renderer;
    }
    
    /**
     * {@inheritdoc}
     */
    public function generateFromLink(Link $link) {
        return $this->generate($link->getText(), $link->getUrl());
    }
    
    /**
     * {@inheritdoc}
     *
     * For anonymous users, the "active" class will be calculated on the server,
     * because most sites serve each anonymous user the same cached page anyway.
     * For authenticated users, the "active" class will be calculated on the
     * client (through JavaScript), only data- attributes are added to links to
     * prevent breaking the render cache. The JavaScript is added in
     * system_page_attachments().
     *
     * @see system_page_attachments()
     */
    public function generate($text, Url $url) {
        // The link generator should not modify the original URL object, this
        // ensures consistent rendering.
        // @see https://www.drupal.org/node/2842399
        $url = clone $url;
        // Performance: avoid Url::toString() needing to retrieve the URL generator
        // service from the container.
        $url->setUrlGenerator($this->urlGenerator);
        if (is_array($text)) {
            $text = $this->renderer
                ->render($text);
        }
        // Start building a structured representation of our link to be altered later.
        $variables = [
            'text' => $text,
            'url' => $url,
            'options' => $url->getOptions(),
        ];
        // Merge in default options.
        $variables['options'] += [
            'attributes' => [],
            'query' => [],
            'language' => NULL,
            'set_active_class' => FALSE,
            'absolute' => FALSE,
        ];
        // Add a hreflang attribute if we know the language of this link's URL and
        // hreflang has not already been set.
        if (!empty($variables['options']['language']) && !isset($variables['options']['attributes']['hreflang'])) {
            $variables['options']['attributes']['hreflang'] = $variables['options']['language']->getId();
        }
        // Ensure that query values are strings.
        array_walk($variables['options']['query'], function (&$value) {
            if ($value instanceof MarkupInterface) {
                $value = (string) $value;
            }
        });
        // Set the "active" class if the 'set_active_class' option is not empty.
        if (!empty($variables['options']['set_active_class']) && !$url->isExternal()) {
            // Add a "data-drupal-link-query" attribute to let the
            // drupal.active-link library know the query in a standardized manner.
            if (!empty($variables['options']['query'])) {
                $query = $variables['options']['query'];
                ksort($query);
                $variables['options']['attributes']['data-drupal-link-query'] = Json::encode($query);
            }
            // Add a "data-drupal-link-system-path" attribute to let the
            // drupal.active-link library know the path in a standardized manner.
            if ($url->isRouted() && !isset($variables['options']['attributes']['data-drupal-link-system-path'])) {
                // @todo System path is deprecated - use the route name and parameters.
                $system_path = $url->getInternalPath();
                // Special case for the front page.
                if ($url->getRouteName() === '<front>') {
                    $system_path = '<front>';
                }
                if (!empty($system_path)) {
                    $variables['options']['attributes']['data-drupal-link-system-path'] = $system_path;
                }
            }
        }
        // Remove all HTML and PHP tags from a tooltip, calling expensive strip_tags()
        // only when a quick strpos() gives suspicion tags are present.
        if (isset($variables['options']['attributes']['title']) && strpos($variables['options']['attributes']['title'], '<') !== FALSE) {
            $variables['options']['attributes']['title'] = strip_tags($variables['options']['attributes']['title']);
        }
        // Allow other modules to modify the structure of the link.
        $this->moduleHandler
            ->alter('link', $variables);
        $url = $variables['url'];
        // Move attributes out of options since generateFromRoute() doesn't need
        // them. Make sure the "href" comes first for testing purposes.
        $attributes = [
            'href' => '',
        ] + $variables['options']['attributes'];
        unset($variables['options']['attributes']);
        $url->setOptions($variables['options']);
        // External URLs can not have cacheable metadata.
        if ($url->isExternal()) {
            $generated_link = new GeneratedLink();
            $attributes['href'] = $url->toString(FALSE);
            return $this->doGenerate($generated_link, $attributes, $variables);
        }
        if ($url->isRouted() && $url->getRouteName() === '<nolink>') {
            $generated_link = new GeneratedNoLink();
            unset($attributes['href'], $attributes['hreflang']);
            return $this->doGenerate($generated_link, $attributes, $variables);
        }
        if ($url->isRouted() && $url->getRouteName() === '<button>') {
            $generated_link = new GeneratedButton();
            $attributes['type'] = 'button';
            unset($attributes['href'], $attributes['hreflang']);
            return $this->doGenerate($generated_link, $attributes, $variables);
        }
        $generated_url = $url->toString(TRUE);
        $generated_link = GeneratedLink::createFromObject($generated_url);
        // The result of the URL generator is a plain-text URL to use as the href
        // attribute, and it is escaped by \Drupal\Core\Template\Attribute.
        $attributes['href'] = $generated_url->getGeneratedUrl();
        return $this->doGenerate($generated_link, $attributes, $variables);
    }
    
    /**
     * Generates the link.
     *
     * @param Drupal\Core\GeneratedLink $generated_link
     *   The generated link, along with its associated cacheability metadata.
     * @param array $attributes
     *   The attributes of the generated link.
     * @param array $variables
     *   The link text, url, and other options.
     *
     * @return Drupal\Core\GeneratedLink
     *   The generated link, along with its associated cacheability metadata.
     */
    protected function doGenerate($generated_link, $attributes, $variables) {
        if (!$variables['text'] instanceof MarkupInterface) {
            $variables['text'] = Html::escape($variables['text']);
        }
        $attributes = new Attribute($attributes);
        // This is safe because Attribute does escaping and $variables['text'] is
        // either rendered or escaped.
        return $generated_link->setGeneratedLink('<' . $generated_link::TAG . $attributes . '>' . $variables['text'] . '</' . $generated_link::TAG . '>');
    }

}