class PathPluginBase

abstract class PathPluginBase extends DisplayPluginBase implements DisplayRouterInterface, DisplayMenuInterface {
    use UrlGeneratorTrait;
    
    /**
     * The route provider.
     *
     * @var \Drupal\Core\Routing\RouteProviderInterface
     */
    protected $routeProvider;
    
    /**
     * The state key value store.
     *
     * @var \Drupal\Core\State\StateInterface
     */
    protected $state;
    
    /**
     * Constructs a PathPluginBase object.
     *
     * @param array $configuration
     *   A configuration array containing information about the plugin instance.
     * @param string $plugin_id
     *   The plugin_id for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Routing\RouteProviderInterface $route_provider
     *   The route provider.
     * @param \Drupal\Core\State\StateInterface $state
     *   The state key value store.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, RouteProviderInterface $route_provider, StateInterface $state) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->routeProvider = $route_provider;
        $this->state = $state;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('router.route_provider'), $container->get('state'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasPath() {
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPath() {
        $bits = explode('/', $this->getOption('path'));
        if ($this->isDefaultTabPath()) {
            array_pop($bits);
        }
        return implode('/', $bits);
    }
    
    /**
     * Determines if this display's path is a default tab.
     *
     * @return bool
     *   TRUE if the display path is for a default tab, FALSE otherwise.
     */
    protected function isDefaultTabPath() {
        $menu = $this->getOption('menu');
        $tab_options = $this->getOption('tab_options');
        return $menu && $menu['type'] == 'default tab' && !empty($tab_options['type']) && $tab_options['type'] != 'none';
    }
    
    /**
     * Overrides \Drupal\views\Plugin\views\display\DisplayPluginBase:defineOptions().
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['path'] = [
            'default' => '',
        ];
        $options['route_name'] = [
            'default' => '',
        ];
        return $options;
    }
    
    /**
     * Generates a route entry for a given view and display.
     *
     * @param string $view_id
     *   The ID of the view.
     * @param string $display_id
     *   The current display ID.
     *
     * @return \Symfony\Component\Routing\Route
     *   The route for the view.
     */
    protected function getRoute($view_id, $display_id) {
        $defaults = [
            '_controller' => 'Drupal\\views\\Routing\\ViewPageController::handle',
            '_title' => $this->view
                ->getTitle(),
            'view_id' => $view_id,
            'display_id' => $display_id,
            '_view_display_show_admin_links' => $this->getOption('show_admin_links'),
        ];
        // @todo How do we apply argument validation?
        $bits = explode('/', $this->getOption('path'));
        // @todo Figure out validation/argument loading.
        // Replace % with %views_arg for menu autoloading and add to the
        // page arguments so the argument actually comes through.
        $arg_counter = 0;
        $argument_ids = array_keys((array) $this->getOption('arguments'));
        $total_arguments = count($argument_ids);
        $argument_map = [];
        // Replace arguments in the views UI (defined via %) with parameters in
        // routes (defined via {}). As a name for the parameter use arg_$key, so
        // it can be pulled in the views controller from the request.
        foreach ($bits as $pos => $bit) {
            if ($bit == '%') {
                // Generate the name of the parameter using the key of the argument
                // handler.
                $arg_id = 'arg_' . $arg_counter++;
                $bits[$pos] = '{' . $arg_id . '}';
                $argument_map[$arg_id] = $arg_id;
            }
            elseif (strpos($bit, '%') === 0) {
                // Use the name defined in the path.
                $parameter_name = substr($bit, 1);
                $arg_id = 'arg_' . $arg_counter++;
                $argument_map[$arg_id] = $parameter_name;
                $bits[$pos] = '{' . $parameter_name . '}';
            }
        }
        // Add missing arguments not defined in the path, but added as handler.
        while ($total_arguments - $arg_counter > 0) {
            $arg_id = 'arg_' . $arg_counter++;
            $bit = '{' . $arg_id . '}';
            // In contrast to the previous loop add the defaults here, as % was not
            // specified, which means the argument is optional.
            $defaults[$arg_id] = NULL;
            $argument_map[$arg_id] = $arg_id;
            $bits[] = $bit;
        }
        // If this is to be a default tab, create the route for the parent path.
        if ($this->isDefaultTabPath()) {
            $bit = array_pop($bits);
            if (empty($bits)) {
                $bits[] = $bit;
            }
        }
        $route_path = '/' . implode('/', $bits);
        $route = new Route($route_path, $defaults);
        // Add access check parameters to the route.
        $access_plugin = $this->getPlugin('access');
        if (!isset($access_plugin)) {
            // @todo Do we want to support a default plugin in getPlugin itself?
            $access_plugin = Views::pluginManager('access')->createInstance('none');
        }
        $access_plugin->alterRouteDefinition($route);
        // Set the argument map, in order to support named parameters.
        $route->setOption('_view_argument_map', $argument_map);
        $route->setOption('_view_display_plugin_id', $this->getPluginId());
        $route->setOption('_view_display_plugin_class', get_called_class());
        $route->setOption('_view_display_show_admin_links', $this->getOption('show_admin_links'));
        // Store whether the view will return a response.
        $route->setOption('returns_response', !empty($this->getPluginDefinition()['returns_response']));
        return $route;
    }
    
    /**
     * {@inheritdoc}
     */
    public function collectRoutes(RouteCollection $collection) {
        $view_id = $this->view->storage
            ->id();
        $display_id = $this->display['id'];
        $route = $this->getRoute($view_id, $display_id);
        if (!($route_name = $this->getOption('route_name'))) {
            $route_name = "view.{$view_id}.{$display_id}";
        }
        $collection->add($route_name, $route);
        return [
            "{$view_id}.{$display_id}" => $route_name,
        ];
    }
    
    /**
     * Determines whether the view overrides the given route.
     *
     * @param string $view_path
     *   The path of the view.
     * @param \Symfony\Component\Routing\Route $view_route
     *   The route of the view.
     * @param \Symfony\Component\Routing\Route $route
     *   The route itself.
     *
     * @return bool
     *   TRUE, when the view should override the given route.
     */
    protected function overrideApplies($view_path, Route $view_route, Route $route) {
        return $this->overrideAppliesPathAndMethod($view_path, $view_route, $route) && (!$route->hasRequirement('_format') || $route->getRequirement('_format') === 'html');
    }
    
    /**
     * Determines whether a override for the path and method should happen.
     *
     * @param string $view_path
     *   The path of the view.
     * @param \Symfony\Component\Routing\Route $view_route
     *   The route of the view.
     * @param \Symfony\Component\Routing\Route $route
     *   The route itself.
     *
     * @return bool
     *   TRUE, when the view should override the given route.
     */
    protected function overrideAppliesPathAndMethod($view_path, Route $view_route, Route $route) {
        // Find all paths which match the path of the current display..
        $route_path = RouteCompiler::getPathWithoutDefaults($route);
        $route_path = RouteCompiler::getPatternOutline($route_path);
        // Ensure that we don't override a route which is already controlled by
        // views.
        return !$route->hasDefault('view_id') && '/' . $view_path == $route_path && (!$route->getMethods() || in_array('GET', $route->getMethods()));
    }
    
    /**
     * {@inheritdoc}
     */
    public function alterRoutes(RouteCollection $collection) {
        $view_route_names = [];
        $view_path = $this->getPath();
        $view_id = $this->view->storage
            ->id();
        $display_id = $this->display['id'];
        $view_route = $this->getRoute($view_id, $display_id);
        foreach ($collection->all() as $name => $route) {
            if ($this->overrideApplies($view_path, $view_route, $route)) {
                $parameters = $route->compile()
                    ->getPathVariables();
                // @todo Figure out whether we need to merge some settings (like
                // requirements).
                // Replace the existing route with a new one based on views.
                $original_route = $collection->get($name);
                $collection->remove($name);
                $path = $view_route->getPath();
                // Replace the path with the original parameter names and add a mapping.
                $argument_map = [];
                // We assume that the numeric ids of the parameters match the one from
                // the view argument handlers.
                foreach ($parameters as $position => $parameter_name) {
                    $path = str_replace('{arg_' . $position . '}', '{' . $parameter_name . '}', $path);
                    $argument_map['arg_' . $position] = $parameter_name;
                }
                // Copy the original options from the route, so for example we ensure
                // that parameter conversion options is carried over.
                $view_route->setOptions($view_route->getOptions() + $original_route->getOptions());
                if ($original_route->hasDefault('_title_callback')) {
                    $view_route->setDefault('_title_callback', $original_route->getDefault('_title_callback'));
                }
                // Set the corrected path and the mapping to the route object.
                $view_route->setOption('_view_argument_map', $argument_map);
                $view_route->setPath($path);
                $collection->add($name, $view_route);
                $view_route_names[$view_id . '.' . $display_id] = $name;
            }
        }
        return $view_route_names;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMenuLinks() {
        $links = [];
        // Replace % with the link to our standard views argument loader
        // views_arg_load -- which lives in views.module.
        $bits = explode('/', $this->getOption('path'));
        // Replace % with %views_arg for menu autoloading and add to the
        // page arguments so the argument actually comes through.
        foreach ($bits as $pos => $bit) {
            if ($bit == '%') {
                // If a view requires any arguments we cannot create a static menu link.
                return [];
            }
        }
        $path = implode('/', $bits);
        $view_id = $this->view->storage
            ->id();
        $display_id = $this->display['id'];
        $view_id_display = "{$view_id}.{$display_id}";
        $menu_link_id = 'views.' . str_replace('/', '.', $view_id_display);
        if ($path) {
            $menu = $this->getOption('menu');
            if (!empty($menu['type']) && $menu['type'] == 'normal') {
                $links[$menu_link_id] = [];
                // Some views might override existing paths, so we have to set the route
                // name based upon the altering.
                $links[$menu_link_id] = [
                    'route_name' => $this->getRouteName(),
                    // Identify URL embedded arguments and correlate them to a handler.
'load arguments' => [
                        $this->view->storage
                            ->id(),
                        $this->display['id'],
                        '%index',
                    ],
                    'id' => $menu_link_id,
                ];
                $links[$menu_link_id]['title'] = $menu['title'];
                $links[$menu_link_id]['description'] = $menu['description'];
                $links[$menu_link_id]['parent'] = $menu['parent'];
                $links[$menu_link_id]['enabled'] = $menu['enabled'];
                $links[$menu_link_id]['expanded'] = $menu['expanded'];
                if (isset($menu['weight'])) {
                    $links[$menu_link_id]['weight'] = intval($menu['weight']);
                }
                // Insert item into the proper menu.
                $links[$menu_link_id]['menu_name'] = $menu['menu_name'];
                // Keep track of where we came from.
                $links[$menu_link_id]['metadata'] = [
                    'view_id' => $view_id,
                    'display_id' => $display_id,
                ];
            }
        }
        return $links;
    }
    
    /**
     * {@inheritdoc}
     */
    public function execute() {
        // Prior to this being called, the $view should already be set to this
        // display, and arguments should be set on the view.
        $this->view
            ->build();
        if (!empty($this->view->build_info['fail'])) {
            throw new NotFoundHttpException();
        }
        if (!empty($this->view->build_info['denied'])) {
            throw new AccessDeniedHttpException();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function optionsSummary(&$categories, &$options) {
        parent::optionsSummary($categories, $options);
        $categories['page'] = [
            'title' => $this->t('Page settings'),
            'column' => 'second',
            'build' => [
                '#weight' => -10,
            ],
        ];
        $path = strip_tags($this->getOption('path'));
        if (empty($path)) {
            $path = $this->t('No path is set');
        }
        else {
            $path = '/' . $path;
        }
        $options['path'] = [
            'category' => 'page',
            'title' => $this->t('Path'),
            'value' => views_ui_truncate($path, 24),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        switch ($form_state->get('section')) {
            case 'path':
                $form['#title'] .= $this->t('The menu path or URL of this view');
                $form['path'] = [
                    '#type' => 'textfield',
                    '#title' => $this->t('Path'),
                    '#description' => $this->t('This view will be displayed by visiting this path on your site. You may use "%" in your URL to represent values that will be used for contextual filters: For example, "node/%/feed". If needed you can even specify named route parameters like taxonomy/term/%taxonomy_term'),
                    '#default_value' => $this->getOption('path'),
                    '#field_prefix' => '<span dir="ltr">' . Url::fromRoute('<none>', [], [
                        'absolute' => TRUE,
                    ])->toString(),
                    '#field_suffix' => '</span>&lrm;',
                    '#attributes' => [
                        'dir' => LanguageInterface::DIRECTION_LTR,
                    ],
                    // Account for the leading backslash.
'#maxlength' => 254,
                ];
                break;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateOptionsForm(&$form, FormStateInterface $form_state) {
        parent::validateOptionsForm($form, $form_state);
        if ($form_state->get('section') == 'path') {
            $errors = $this->validatePath($form_state->getValue('path'));
            foreach ($errors as $error) {
                $form_state->setError($form['path'], $error);
            }
            // Automatically remove '/' and trailing whitespace from path.
            $form_state->setValue('path', trim($form_state->getValue('path'), '/ '));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitOptionsForm(&$form, FormStateInterface $form_state) {
        parent::submitOptionsForm($form, $form_state);
        if ($form_state->get('section') == 'path') {
            $this->setOption('path', $form_state->getValue('path'));
        }
    }
    
    /**
     * Validates the path of the display.
     *
     * @param string $path
     *   The path to validate.
     *
     * @return array
     *   A list of error strings.
     */
    protected function validatePath($path) {
        $errors = [];
        if (strpos($path, '%') === 0) {
            $errors[] = $this->t('"%" may not be used for the first segment of a path.');
        }
        $parsed_url = UrlHelper::parse($path);
        if (empty($parsed_url['path'])) {
            $errors[] = $this->t('Path is empty.');
        }
        if (!empty($parsed_url['query'])) {
            $errors[] = $this->t('No query allowed.');
        }
        if (!parse_url('internal:/' . $path)) {
            $errors[] = $this->t('Invalid path. Valid characters are alphanumerics as well as "-", ".", "_" and "~".');
        }
        $path_sections = explode('/', $path);
        // Symfony routing does not allow to use numeric placeholders.
        // @see \Symfony\Component\Routing\RouteCompiler
        $numeric_placeholders = array_filter($path_sections, function ($section) {
            return preg_match('/^%(.*)/', $section, $matches) && is_numeric($matches[1]);
        });
        if (!empty($numeric_placeholders)) {
            $errors[] = $this->t("Numeric placeholders may not be used. Please use plain placeholders (%).");
        }
        return $errors;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validate() {
        $errors = parent::validate();
        $errors += $this->validatePath($this->getOption('path'));
        return $errors;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getUrlInfo() {
        return Url::fromRoute($this->getRouteName());
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRouteName() {
        $view_id = $this->view->storage
            ->id();
        $display_id = $this->display['id'];
        $view_route_key = "{$view_id}.{$display_id}";
        // Check for overridden route names.
        $view_route_names = $this->getAlteredRouteNames();
        return isset($view_route_names[$view_route_key]) ? $view_route_names[$view_route_key] : "view.{$view_route_key}";
    }
    
    /**
     * {@inheritdoc}
     */
    public function getAlteredRouteNames() {
        return $this->state
            ->get('views.view_route_names') ?: [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function remove() {
        $menu_links = $this->getMenuLinks();
        
        /** @var \Drupal\Core\Menu\MenuLinkManagerInterface $menu_link_manager */
        $menu_link_manager = \Drupal::service('plugin.manager.menu.link');
        foreach ($menu_links as $menu_link_id => $menu_link) {
            $menu_link_manager->removeDefinition("views_view:{$menu_link_id}");
        }
    }

}