<?php

/**
 * @file
 * API for the Drupal menu system.
 */

use Drupal\Component\Utility\String;
use Drupal\Core\Cache\Cache;
use Drupal\Core\Language\Language;
use Drupal\Core\Render\Element;
use Drupal\Core\Template\Attribute;
use Symfony\Cmf\Component\Routing\RouteObjectInterface;

/**
 * @defgroup menu Menu and routing system
 * @{
 * Define the navigation menus, and route page requests to code based on URLs.
 *
 * The Drupal routing system defines how Drupal responds to URLs passed to the
 * browser. The menu system, which depends on the routing system, is used for
 * navigation. The Menu module allows menus to be created in the user interface
 * as hierarchical lists of links.
 *
 * @section registering_paths Registering router paths
 * To register a path, you need to add lines similar to this in a
 * module.routing.yml file:
 * @code
 * block.admin_display:
 *   path: '/admin/structure/block'
 *   defaults:
 *     _content: '\Drupal\block\Controller\BlockListController::listing'
 *   requirements:
 *     _permission: 'administer blocks'
 * @endcode
 * @todo Add more information here, especially about controllers and what all
 *   the stuff in the routing.yml file means.
 *
 * @section Defining menu links
 * Once you have a route defined, you can use module.menu_links.yml to
 * define links for your module's paths in the main Navigation menu or other
 * menus.
 *
 * @todo The rest of this topic has not been reviewed or updated for Drupal 8.x
 *   and is not correct!
 * @todo It is quite likely that hook_menu() will be replaced with a different
 *   hook, configuration system, or plugin system before the 8.0 release.
 *
 * Drupal's menu system follows a simple hierarchy defined by paths.
 * Implementations of hook_menu() define menu items and assign them to
 * paths (which should be unique). The menu system aggregates these items
 * and determines the menu hierarchy from the paths. For example, if the
 * paths defined were a, a/b, e, a/b/c/d, f/g, and a/b/h, the menu system
 * would form the structure:
 * - a
 *   - a/b
 *     - a/b/c/d
 *     - a/b/h
 * - e
 * - f/g
 * Note that the number of elements in the path does not necessarily
 * determine the depth of the menu item in the tree.
 *
 * When responding to a page request, the menu system looks to see if the
 * path requested by the browser is registered as a menu item with a
 * callback. If not, the system searches up the menu tree for the most
 * complete match with a callback it can find. If the path a/b/i is
 * requested in the tree above, the callback for a/b would be used.
 *
 * The found callback function is called with any arguments specified
 * in the "page arguments" attribute of its menu item. The
 * attribute must be an array. After these arguments, any remaining
 * components of the path are appended as further arguments. In this
 * way, the callback for a/b above could respond to a request for
 * a/b/i differently than a request for a/b/j.
 *
 * For an illustration of this process, see page_example.module.
 *
 * Access to the callback functions is also protected by the menu system.
 * The "access callback" with an optional "access arguments" of each menu
 * item is called before the page callback proceeds. If this returns TRUE,
 * then access is granted; if FALSE, then access is denied. Default local task
 * menu items (see next paragraph) may omit this attribute to use the value
 * provided by the parent item.
 *
 * In the default Drupal interface, you will notice many links rendered as
 * tabs. These are known in the menu system as "local tasks", and they are
 * rendered as tabs by default, though other presentations are possible.
 * Local tasks function just as other menu items in most respects. It is
 * convention that the names of these tasks should be short verbs if
 * possible. In addition, a "default" local task should be provided for
 * each set. When visiting a local task's parent menu item, the default
 * local task will be rendered as if it is selected; this provides for a
 * normal tab user experience. This default task is special in that it
 * links not to its provided path, but to its parent item's path instead.
 * The default task's path is only used to place it appropriately in the
 * menu hierarchy.
 *
 * Everything described so far is stored in the menu_router table. The
 * menu_links table holds the visible menu links. By default these are
 * derived from the same hook_menu definitions, however you are free to
 * add more with menu_link_save().
 */

/**
 * @defgroup menu_status_codes Menu status codes
 * @{
 * Status codes for menu callbacks.
 */

/**
 * Internal menu status code -- Menu item inaccessible because site is offline.
 */
const MENU_SITE_OFFLINE = 4;

/**
 * Internal menu status code -- Everything is working fine.
 */
const MENU_SITE_ONLINE = 5;

/**
 * @} End of "defgroup menu_status_codes".
 */

/**
 * @defgroup menu_tree_parameters Menu tree parameters
 * @{
 * Parameters for a menu tree.
 */

/**
 * The maximum depth of a menu links tree - matches the number of p columns.
 *
 * @todo Move this constant to MenuLinkStorage along with all the tree
 * functionality.
 */
const MENU_MAX_DEPTH = 9;


/**
 * @} End of "defgroup menu_tree_parameters".
 */

/**
 * Reserved key to identify the most specific menu link for a given path.
 *
 * The value of this constant is a hash of the constant name. We use the hash
 * so that the reserved key is over 32 characters in length and will not
 * collide with allowed menu names:
 * @code
 * sha1('MENU_PREFERRED_LINK') = 1cf698d64d1aa4b83907cf6ed55db3a7f8e92c91
 * @endcode
 *
 * @see menu_link_get_preferred()
 */
const MENU_PREFERRED_LINK = '1cf698d64d1aa4b83907cf6ed55db3a7f8e92c91';

/**
 * Localizes a menu link title using t() if possible.
 *
 * Translate the title and description to allow storage of English title
 * strings in the database, yet display of them in the language required
 * by the current user.
 *
 * @param $item
 *   A menu link entity.
 */
function _menu_item_localize(&$item) {
  // Allow default menu links to be translated.
  $item['localized_options'] = $item['options'];
  // All 'class' attributes are assumed to be an array during rendering, but
  // links stored in the database may use an old string value.
  // @todo In order to remove this code we need to implement a database update
  //   including unserializing all existing link options and running this code
  //   on them, as well as adding validation to menu_link_save().
  if (isset($item['options']['attributes']['class']) && is_string($item['options']['attributes']['class'])) {
    $item['localized_options']['attributes']['class'] = explode(' ', $item['options']['attributes']['class']);
  }
  // If the menu link is defined in code and not customized, we can use t().
  if (!empty($item['machine_name']) && !$item['customized']) {
    // @todo Figure out a proper way to support translations of menu links, see
    //   https://drupal.org/node/2193777.
    $item['title'] = t($item['link_title']);
  }
  else {
    $item['title'] = $item['link_title'];
  }
}

/**
 * Provides menu link unserializing, access control, and argument handling.
 *
 * @param array $item
 *   The passed in item has the following keys:
 *   - access: (optional) Becomes TRUE if the item is accessible, FALSE
 *     otherwise. If the key is not set, the access manager is used to
 *     determine the access.
 *   - options: (required) Is unserialized and copied to $item['localized_options'].
 *   - link_title: (required) The title of the menu link.
 *   - route_name: (required) The route name of the menu link.
 *   - route_parameters: (required) The unserialized route parameters of the menu link.
 *   The passed in item is changed by the following keys:
 *   - href: The actual path to the link. This path is generated from the
 *     link_path of the menu link entity.
 *   - title: The title of the link. This title is generated from the
 *     link_title of the menu link entity.
 */
function _menu_link_translate(&$item) {
  if (!is_array($item['options'])) {
    $item['options'] = (array) unserialize($item['options']);
  }
  $item['localized_options'] = $item['options'];
  $item['title'] = $item['link_title'];
  if ($item['external'] || empty($item['route_name'])) {
    $item['access'] = 1;
    $item['href'] = $item['link_path'];
    $item['route_parameters'] = array();
    // Set to NULL so that drupal_pre_render_link() is certain to skip it.
    $item['route_name'] = NULL;
  }
  else {
    $item['href'] = NULL;
    if (!is_array($item['route_parameters'])) {
      $item['route_parameters'] = (array) unserialize($item['route_parameters']);
    }
    // menu_tree_check_access() may set this ahead of time for links to nodes.
    if (!isset($item['access'])) {
      $item['access'] = \Drupal::getContainer()->get('access_manager')->checkNamedRoute($item['route_name'], $item['route_parameters'], \Drupal::currentUser());
    }
    // For performance, don't localize a link the user can't access.
    if ($item['access']) {
      _menu_item_localize($item);
    }
  }

  // Allow other customizations - e.g. adding a page-specific query string to the
  // options array. For performance reasons we only invoke this hook if the link
  // has the 'alter' flag set in the options array.
  if (!empty($item['options']['alter'])) {
    \Drupal::moduleHandler()->alter('translated_menu_link', $item, $map);
  }
}

/**
 * Implements template_preprocess_HOOK() for theme_menu_tree().
 */
function template_preprocess_menu_tree(&$variables) {
  $variables['tree'] = $variables['tree']['#children'];
}

/**
 * Returns HTML for a wrapper for a menu sub-tree.
 *
 * @param $variables
 *   An associative array containing:
 *   - tree: An HTML string containing the tree's items.
 *
 * @see template_preprocess_menu_tree()
 * @ingroup themeable
 */
function theme_menu_tree($variables) {
  return '<ul class="menu">' . $variables['tree'] . '</ul>';
}

/**
 * Returns HTML for a menu link and submenu.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: Structured array data for a menu link.
 *
 * @ingroup themeable
 */
function theme_menu_link(array $variables) {
  $element = $variables['element'];
  $sub_menu = '';

  if ($element['#below']) {
    $sub_menu = drupal_render($element['#below']);
  }
  $element['#localized_options']['set_active_class'] = TRUE;
  $output = l($element['#title'], $element['#href'], $element['#localized_options']);
  return '<li' . new Attribute($element['#attributes']) . '>' . $output . $sub_menu . "</li>\n";
}

/**
 * Returns HTML for a single local task link.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: A render element containing:
 *     - #link: A menu link array with 'title', 'href', and 'localized_options'
 *       keys.
 *     - #active: A boolean indicating whether the local task is active.
 *
 * @ingroup themeable
 */
function theme_menu_local_task($variables) {
  $link = $variables['element']['#link'];
  $link += array(
    'localized_options' => array(),
  );
  $link_text = $link['title'];

  if (!empty($variables['element']['#active'])) {
    // Add text to indicate active tab for non-visual users.
    $active = '<span class="visually-hidden">' . t('(active tab)') . '</span>';

    // If the link does not contain HTML already, String::checkPlain() it now.
    // After we set 'html'=TRUE the link will not be sanitized by l().
    if (empty($link['localized_options']['html'])) {
      $link['title'] = String::checkPlain($link['title']);
    }
    $link['localized_options']['html'] = TRUE;
    $link_text = t('!local-task-title!active', array('!local-task-title' => $link['title'], '!active' => $active));
  }
  $link['localized_options']['set_active_class'] = TRUE;

  if (!empty($link['href'])) {
    // @todo - remove this once all pages are converted to routes.
    $a_tag = l($link_text, $link['href'], $link['localized_options']);
  }
  else {
    $a_tag = \Drupal::l($link_text, $link['route_name'], $link['route_parameters'], $link['localized_options']);
  }

  return '<li' . (!empty($variables['element']['#active']) ? ' class="active"' : '') . '>' . $a_tag . '</li>';
}

/**
 * Returns HTML for a single local action link.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: A render element containing:
 *     - #link: A menu link array with 'title', 'href', and 'localized_options'
 *       keys.
 *
 * @ingroup themeable
 */
function theme_menu_local_action($variables) {
  $link = $variables['element']['#link'];
  $link += array(
    'href' => '',
    'localized_options' => array(),
    'route_parameters' => array(),
  );
  $link['localized_options']['attributes']['class'][] = 'button';
  $link['localized_options']['attributes']['class'][] = 'button-action';
  $link['localized_options']['set_active_class'] = TRUE;

  $output = '<li>';
  // @todo Remove this check and the call to l() when all pages are converted to
  //   routes.
  // @todo Figure out how to support local actions without a href properly.
  if ($link['href'] === '' && !empty($link['route_name'])) {
    $output .= Drupal::l($link['title'], $link['route_name'], $link['route_parameters'], $link['localized_options']);
  }
  else {
    $output .= l($link['title'], $link['href'], $link['localized_options']);
  }
  $output .= "</li>";

  return $output;
}

/**
 * Generates elements for the $arg array in the help hook.
 */
function drupal_help_arg($arg = array()) {
  // Note - the number of empty elements should be > MENU_MAX_PARTS.
  return $arg + array('', '', '', '', '', '', '', '', '', '', '', '');
}

/**
 * Returns an array containing the names of system-defined (default) menus.
 */
function menu_list_system_menus() {
  return array(
    'tools' => 'Tools',
    'admin' => 'Administration',
    'account' => 'User account menu',
    'main' => 'Main navigation',
    'footer' => 'Footer menu',
  );
}

/**
 * Returns an array of links to be rendered as the Main menu.
 */
function menu_main_menu() {
  $main_links_source = _menu_get_links_source('main_links', 'main');
  return menu_navigation_links($main_links_source);
}

/**
 * Returns an array of links to be rendered as the Secondary links.
 */
function menu_secondary_menu() {
  $main_links_source = _menu_get_links_source('main_links', 'main');
  $secondary_links_source = _menu_get_links_source('secondary_links', 'account');

  // If the secondary menu source is set as the primary menu, we display the
  // second level of the primary menu.
  if ($secondary_links_source == $main_links_source) {
    return menu_navigation_links($main_links_source, 1);
  }
  else {
    return menu_navigation_links($secondary_links_source, 0);
  }
}

/**
 * Returns the source of links of a menu.
 *
 * @param string $name
 *   A string configuration key of menu link source.
 * @param string $default
 *   Default menu name.
 *
 * @return string
 *   Returns menu name, if exist
 */
function _menu_get_links_source($name, $default) {
  $config = \Drupal::config('menu.settings');
  return \Drupal::moduleHandler()->moduleExists('menu') ? $config->get($name) : $default;
}

/**
 * Returns an array of links for a navigation menu.
 *
 * @param $menu_name
 *   The name of the menu.
 * @param $level
 *   Optional, the depth of the menu to be returned.
 *
 * @return
 *   An array of links of the specified menu and level.
 */
function menu_navigation_links($menu_name, $level = 0) {
  // Don't even bother querying the menu table if no menu is specified.
  if (empty($menu_name)) {
    return array();
  }

  // Get the menu hierarchy for the current page.
  /** @var \Drupal\menu_link\MenuTreeInterface $menu_tree */
  $menu_tree = \Drupal::service('menu_link.tree');
  $tree = $menu_tree->buildPageData($menu_name, $level + 1);

  // Go down the active trail until the right level is reached.
  while ($level-- > 0 && $tree) {
    // Loop through the current level's items until we find one that is in trail.
    while ($item = array_shift($tree)) {
      if ($item['link']['in_active_trail']) {
        // If the item is in the active trail, we continue in the subtree.
        $tree = empty($item['below']) ? array() : $item['below'];
        break;
      }
    }
  }

  // Create a single level of links.
  $links = array();
  foreach ($tree as $item) {
    if (!$item['link']['hidden']) {
      $class = '';
      $l = $item['link']['localized_options'];
      $l['href'] = $item['link']['link_path'];
      $l['title'] = $item['link']['title'];
      if ($item['link']['in_active_trail']) {
        $class = ' active-trail';
        $l['attributes']['class'][] = 'active-trail';
      }
      // Normally, l() compares the href of every link with the current path and
      // sets the active class accordingly. But local tasks do not appear in
      // menu trees, so if the current path is a local task, and this link is
      // its tab root, then we have to set the class manually.
      if ($item['link']['href'] != current_path()) {
        $l['attributes']['class'][] = 'active';
      }
      // Keyed with the unique mlid to generate classes in links.html.twig.
      $links['menu-' . $item['link']['mlid'] . $class] = $l;
    }
  }
  return $links;
}

/**
 * Collects the local tasks (tabs), action links, and the root path.
 *
 * @param int $level
 *   The level of tasks you ask for. Primary tasks are 0, secondary are 1.
 *
 * @return array
 *   An array containing
 *   - tabs: Local tasks for the requested level.
 *   - actions: Action links for the requested level.
 *   - root_path: The router path for the current page. If the current page is
 *     a default local task, then this corresponds to the parent tab.
 *
 * @see hook_menu_local_tasks()
 * @see hook_menu_local_tasks_alter()
 */
function menu_local_tasks($level = 0) {
  $data = &drupal_static(__FUNCTION__);
  $root_path = &drupal_static(__FUNCTION__ . ':root_path', '');
  $empty = array(
    'tabs' => array(),
    'actions' => array(),
    'root_path' => &$root_path,
  );

  if (!isset($data)) {
    // Look for route-based tabs.
    $data['tabs'] = array();
    $data['actions'] = array();

    $route_name = \Drupal::request()->attributes->get(RouteObjectInterface::ROUTE_NAME);
    if (!empty($route_name)) {
      $manager = \Drupal::service('plugin.manager.menu.local_task');
      $local_tasks = $manager->getTasksBuild($route_name);
      foreach ($local_tasks as $level => $items) {
        $data['tabs'][$level] = empty($data['tabs'][$level]) ? $items : array_merge($data['tabs'][$level], $items);
      }
    }

    // Allow modules to dynamically add further tasks.
    $module_handler = \Drupal::moduleHandler();
    foreach ($module_handler->getImplementations('menu_local_tasks') as $module) {
      $function = $module . '_menu_local_tasks';
      $function($data, $route_name);
    }
    // Allow modules to alter local tasks.
    $module_handler->alter('menu_local_tasks', $data, $route_name);
  }

  if (isset($data['tabs'][$level])) {
    return array(
      'tabs' => $data['tabs'][$level],
      'actions' => $data['actions'],
      'root_path' => $root_path,
    );
  }
  elseif (!empty($data['actions'])) {
    return array('actions' => $data['actions']) + $empty;
  }
  return $empty;
}

/**
 * Returns the rendered local tasks at the top level.
 */
function menu_primary_local_tasks() {
  $links = menu_local_tasks(0);
  // Do not display single tabs.
  return count(Element::getVisibleChildren($links['tabs'])) > 1 ? $links['tabs'] : '';
}

/**
 * Returns the rendered local tasks at the second level.
 */
function menu_secondary_local_tasks() {
  $links = menu_local_tasks(1);
  // Do not display single tabs.
  return count(Element::getVisibleChildren($links['tabs'])) > 1 ? $links['tabs'] : '';
}

/**
 * Returns the rendered local actions at the current level.
 */
function menu_get_local_actions() {
  $links = menu_local_tasks();
  $route_name = Drupal::request()->attributes->get(RouteObjectInterface::ROUTE_NAME);
  $manager = \Drupal::service('plugin.manager.menu.local_action');
  return $manager->getActionsForRoute($route_name) + $links['actions'];
}

/**
 * Returns the router path, or the path for a default local task's parent.
 */
function menu_tab_root_path() {
  $links = menu_local_tasks();
  return $links['root_path'];
}

/**
 * Returns a renderable element for the primary and secondary tabs.
 */
function menu_local_tabs() {
  $build = array(
    '#theme' => 'menu_local_tasks',
    '#primary' => menu_primary_local_tasks(),
    '#secondary' => menu_secondary_local_tasks(),
  );
  return !empty($build['#primary']) || !empty($build['#secondary']) ? $build : array();
}

/**
 * Returns HTML for primary and secondary local tasks.
 *
 * @param $variables
 *   An associative array containing:
 *     - primary: (optional) An array of local tasks (tabs).
 *     - secondary: (optional) An array of local tasks (tabs).
 *
 * @ingroup themeable
 * @see menu_local_tasks()
 */
function theme_menu_local_tasks(&$variables) {
  $output = '';

  if (!empty($variables['primary'])) {
    $variables['primary']['#prefix'] = '<h2 class="visually-hidden">' . t('Primary tabs') . '</h2>';
    $variables['primary']['#prefix'] .= '<ul class="tabs primary">';
    $variables['primary']['#suffix'] = '</ul>';
    $output .= drupal_render($variables['primary']);
  }
  if (!empty($variables['secondary'])) {
    $variables['secondary']['#prefix'] = '<h2 class="visually-hidden">' . t('Secondary tabs') . '</h2>';
    $variables['secondary']['#prefix'] .= '<ul class="tabs secondary">';
    $variables['secondary']['#suffix'] = '</ul>';
    $output .= drupal_render($variables['secondary']);
  }

  return $output;
}

/**
 * Sets (or gets) the active menu for the current page.
 *
 * The active menu for the page determines the active trail.
 *
 * @return
 *   An array of menu machine names, in order of preference. The
 *   'system.menu:active_menus_default' config item may be used to assert a menu
 *   order different from the order of creation, or to prevent a particular menu
 *   from being used at all in the active trail.
 */
function menu_set_active_menu_names($menu_names = NULL) {
  $active = &drupal_static(__FUNCTION__);

  if (isset($menu_names) && is_array($menu_names)) {
    $active = $menu_names;
  }
  elseif (!isset($active)) {
    $config = \Drupal::config('system.menu');
    $active = $config->get('active_menus_default') ?: array_keys(menu_list_system_menus());
  }
  return $active;
}

/**
 * Gets the active menu for the current page.
 */
function menu_get_active_menu_names() {
  return menu_set_active_menu_names();
}

/**
 * Sets the active path, which determines which page is loaded.
 *
 * Note that this may not have the desired effect unless invoked very early
 * in the page load or unless you do a subrequest to generate your page output.
 *
 * @param $path
 *   A Drupal path - not a path alias.
 */
function menu_set_active_item($path) {
  // Since the active item has changed, the active menu trail may also be out
  // of date.
  drupal_static_reset('menu_set_active_trail');
  // @todo Refactor to use the Symfony Request object.
  _current_path($path);
}

/**
 * Sets the active trail (path to the menu tree root) of the current page.
 *
 * Any trail set by this function will only be used for functionality that calls
 * menu_get_active_trail(). Drupal core only uses trails set here for
 * the page title and not for menu trees or page content.
 *
 * To affect the trail used by menu trees, use menu_tree_set_path(). To affect
 * the page content, use menu_set_active_item() instead.
 *
 * @param $new_trail
 *   Menu trail to set; the value is saved in a static variable and can be
 *   retrieved by menu_get_active_trail(). The format of this array should be
 *   the same as the return value of menu_get_active_trail().
 *
 * @return
 *   The active trail. See menu_get_active_trail() for details.
 */
function menu_set_active_trail($new_trail = NULL) {
  $trail = &drupal_static(__FUNCTION__);

  /** @var \Drupal\menu_link\MenuTreeInterface $menu_tree */
  $menu_tree = \Drupal::service('menu_link.tree');

  if (isset($new_trail)) {
    $trail = $new_trail;
  }
  elseif (!isset($trail)) {
    $trail = array();
    $trail[] = array(
      'title' => t('Home'),
      'href' => '<front>',
      'link_path' => '',
      'localized_options' => array(),
      'type' => 0,
    );

    // Try to retrieve a menu link corresponding to the current path. If more
    // than one exists, the link from the most preferred menu is returned.
    $preferred_link = menu_link_get_preferred();

    // There is a link for the current path.
    if ($preferred_link) {
       _menu_link_translate($preferred_link);
      // Pass TRUE for $only_active_trail to make menu_tree_page_data() build
      // a stripped down menu tree containing the active trail only, in case
      // the given menu has not been built in this request yet.
      $tree = $menu_tree->buildPageData($preferred_link['menu_name'], NULL, TRUE);
      list($key, $curr) = each($tree);
    }
    // There is no link for the current path.
    else {
      $curr = FALSE;
    }

    while ($curr) {
      $link = $curr['link'];
      if ($link['in_active_trail']) {
        // Add the link to the trail, unless it links to its parent.
        if (!($link['type'] & MENU_LINKS_TO_PARENT)) {
          // The menu tree for the active trail may contain additional links
          // that have not been translated yet, since they contain dynamic
          // argument placeholders (%). Such links are not contained in regular
          // menu trees, and have only been loaded for the additional
          // translation that happens here, so as to be able to display them in
          // the breadcumb for the current page.
          // @see _menu_tree_check_access()
          // @see _menu_link_translate()
          if (strpos($link['href'], '%') !== FALSE) {
            _menu_link_translate($link);
          }
          if ($link['access']) {
            $trail[] = $link;
          }
        }
        $tree = $curr['below'] ? $curr['below'] : array();
      }
      list($key, $curr) = each($tree);
    }
    // Make sure the current page is in the trail to build the page title, by
    // appending either the preferred link or the menu router item for the
    // current page. Exclude it if we are on the front page.
    $last = end($trail);
    if ($preferred_link && $last['href'] != $preferred_link['href'] && !drupal_is_front_page()) {
      $trail[] = $preferred_link;
    }
  }
  return $trail;
}

/**
 * Looks up the preferred menu link for a given system path.
 *
 * @param $path
 *   The path; for example, 'node/5'. The function will find the corresponding
 *   menu link ('node/5' if it exists, or fallback to 'node/%').
 * @param $selected_menu
 *   The name of a menu used to restrict the search for a preferred menu link.
 *   If not specified, all the menus returned by menu_get_active_menu_names()
 *   will be used.
 *
 * @return
 *   A fully translated menu link, or FALSE if no matching menu link was
 *   found. The most specific menu link ('node/5' preferred over 'node/%') in
 *   the most preferred menu (as defined by menu_get_active_menu_names()) is
 *   returned.
 */
function menu_link_get_preferred($path = NULL, $selected_menu = NULL) {
  $preferred_links = &drupal_static(__FUNCTION__);

  if (!isset($path)) {
    $path = current_path();
  }

  if (empty($selected_menu)) {
    // Use an illegal menu name as the key for the preferred menu link.
    $selected_menu = MENU_PREFERRED_LINK;
  }

  if (!isset($preferred_links[$path])) {
    // Look for the correct menu link by building a list of candidate paths,
    // which are ordered by priority (translated hrefs are preferred over
    // untranslated paths). Afterwards, the most relevant path is picked from
    // the menus, ordered by menu preference.
    $path_candidates = array();
    // 1. The current item href.
    // @todo simplify this code and convert to using route names.
    // @see https://drupal.org/node/2154949
    $path_candidates[$path] = $path;

    // Retrieve a list of menu names, ordered by preference.
    $menu_names = menu_get_active_menu_names();
    // Put the selected menu at the front of the list.
    array_unshift($menu_names, $selected_menu);

    $menu_links = entity_load_multiple_by_properties('menu_link', array('link_path' => $path_candidates));

    // Sort candidates by link path and menu name.
    $candidates = array();
    foreach ($menu_links as $candidate) {
      $candidates[$candidate['link_path']][$candidate['menu_name']] = $candidate;
      // Add any menus not already in the menu name search list.
      if (!in_array($candidate['menu_name'], $menu_names)) {
        $menu_names[] = $candidate['menu_name'];
      }
    }

    // Store the most specific link for each menu. Also save the most specific
    // link of the most preferred menu in $preferred_link.
    foreach ($path_candidates as $link_path) {
      if (isset($candidates[$link_path])) {
        foreach ($menu_names as $menu_name) {
          if (empty($preferred_links[$path][$menu_name]) && isset($candidates[$link_path][$menu_name])) {
            $candidate_item = $candidates[$link_path][$menu_name];
            $candidate_item['access'] = \Drupal::service('access_manager')->checkNamedRoute($candidate_item['route_name'], $candidate_item['route_parameters'], \Drupal::currentUser());
            if ($candidate_item['access']) {
              _menu_item_localize($candidate_item);
              $preferred_links[$path][$menu_name] = $candidate_item;
              if (empty($preferred_links[$path][MENU_PREFERRED_LINK])) {
                // Store the most specific link.
                $preferred_links[$path][MENU_PREFERRED_LINK] = $candidate_item;
              }
            }
          }
        }
      }
    }
  }

  return isset($preferred_links[$path][$selected_menu]) ? $preferred_links[$path][$selected_menu] : FALSE;
}

/**
 * Gets the active trail (path to root menu root) of the current page.
 *
 * If a trail is supplied to menu_set_active_trail(), that value is returned. If
 * a trail is not supplied to menu_set_active_trail(), the path to the current
 * page is calculated and returned. The calculated trail is also saved as a
 * static value for use by subsequent calls to menu_get_active_trail().
 *
 * @return
 *   Path to menu root of the current page, as an array of menu link items,
 *   starting with the site's home page. Each link item is an associative array
 *   with the following components:
 *   - title: Title of the item.
 *   - href: Drupal path of the item.
 *   - localized_options: Options for passing into the l() function.
 *   - type: A menu type constant, such as MENU_DEFAULT_LOCAL_TASK, or 0 to
 *     indicate it's not really in the menu (used for the home page item).
 */
function menu_get_active_trail() {
  return menu_set_active_trail();
}

/**
 * Clears all cached menu data.
 *
 * This should be called any time broad changes
 * might have been made to the router items or menu links.
 */
function menu_cache_clear_all() {
  \Drupal::cache('data')->deleteAll();
  menu_reset_static_cache();
}

/**
 * Resets the menu system static cache.
 */
function menu_reset_static_cache() {
  \Drupal::entityManager()
    ->getStorage('menu_link')->resetCache();
  drupal_static_reset('_menu_build_tree');
  drupal_static_reset('menu_tree');
  drupal_static_reset('menu_tree_all_data');
  drupal_static_reset('menu_tree_page_data');
  drupal_static_reset('menu_link_get_preferred');
}

/**
 * Saves menu links recursively for menu_links_rebuild_defaults().
 */
function _menu_link_save_recursive($controller, $machine_name, &$children, &$links) {
  $menu_link = $links[$machine_name];
  if ($menu_link->isNew() || !$menu_link->customized) {
    if (!isset($menu_link->plid) && !empty($menu_link->parent) && !empty($links[$menu_link->parent])) {
      $parent = $links[$menu_link->parent];

      if (empty($menu_link->menu_name) || $parent->menu_name == $menu_link->menu_name) {
        $menu_link->plid = $parent->id();
        $menu_link->menu_name = $parent->menu_name;
      }
    }
    $controller->save($menu_link);
  }
  if (!empty($children[$machine_name])) {
    foreach ($children[$machine_name] as $next_name) {
      _menu_link_save_recursive($controller, $next_name, $children, $links);
    }
  }
  // Remove processed link names so we can find stragglers.
  unset($children[$machine_name]);
}

/**
 * Builds menu links for the items returned from the menu_link.static service.
 */
function menu_link_rebuild_defaults() {
  // Ensure that all configuration used to build the menu items are loaded
  // without overrides.
  $old_state = \Drupal::configFactory()->getOverrideState();
  \Drupal::configFactory()->setOverrideState(FALSE);
  $module_handler = \Drupal::moduleHandler();
  if (!$module_handler->moduleExists('menu_link')) {
    // The Menu link module may not be available during install, so rebuild
    // when possible.
    return;
  }
  /** @var \Drupal\menu_link\MenuLinkStorageInterface $menu_link_storage */
  $menu_link_storage = \Drupal::entityManager()
    ->getStorage('menu_link');
  $links = array();
  $children = array();
  $top_links = array();
  $all_links = \Drupal::service('menu_link.static')->getLinks();
  if ($all_links) {
    foreach ($all_links as $machine_name => $link) {
      // For performance reasons, do a straight query now and convert to a menu
      // link entity later.
      // @todo revisit before release.
      $existing_item = db_select('menu_links')
        ->fields('menu_links')
        ->condition('machine_name', $machine_name)
        ->execute()->fetchObject();
      if ($existing_item) {
        $existing_item->options = unserialize($existing_item->options);
        $existing_item->route_parameters = unserialize($existing_item->route_parameters);
        $link['mlid'] = $existing_item->mlid;
        $link['plid'] = $existing_item->plid;
        $link['uuid'] = $existing_item->uuid;
        $link['customized'] = $existing_item->customized;
        $link['updated'] = $existing_item->updated;
        $menu_link = $menu_link_storage->createFromDefaultLink($link);

        // Convert the existing item to a typed object.
        /** @var \Drupal\menu_link\MenuLinkInterface $existing_item */
        $existing_item = $menu_link_storage->create(get_object_vars($existing_item));

        if (!$existing_item->customized) {
          // A change in the default menu links may move the link to a
          // different menu or parent.
          if (!empty($link['menu_name']) && ($link['menu_name'] != $existing_item->menu_name)) {
            $menu_link->plid = NULL;
            $menu_link->menu_name = $link['menu_name'];
          }
          elseif (!empty($link['parent'])) {
            $menu_link->plid = NULL;
          }

          $menu_link->original = $existing_item;
        }
      }
      else {
        if (empty($link['route_name']) && empty($link['link_path'])) {
          watchdog('error', 'Menu_link %machine_name does neither provide a route_name nor a link_path, so it got skipped.', array('%machine_name' => $machine_name));
          continue;
        }
        $menu_link = $menu_link_storage->createFromDefaultLink($link);
      }
      if (!empty($link['parent'])) {
        $children[$link['parent']][$machine_name] = $machine_name;
        $menu_link->parent = $link['parent'];
        if (empty($link['menu_name'])) {
          // Reset the default menu name so it is populated from the parent.
          $menu_link->menu_name = NULL;
        }
      }
      else {
        // A top level link - we need them to root our tree.
        $top_links[$machine_name] = $machine_name;
        $menu_link->plid = 0;
      }
      $links[$machine_name] = $menu_link;
    }
  }
  foreach ($top_links as $machine_name) {
    _menu_link_save_recursive($menu_link_storage, $machine_name, $children, $links);
  }
  // Handle any children we didn't find starting from top-level links.
  foreach ($children as $orphan_links) {
    foreach ($orphan_links as $machine_name) {
      // Force it to the top level.
      $links[$machine_name]->plid = 0;
      _menu_link_save_recursive($menu_link_storage, $machine_name, $children, $links);
    }
  }

  // Find any item whose default menu link no longer exists.
  if ($all_links) {
    $query = \Drupal::entityQuery('menu_link')
      ->condition('machine_name', array_keys($all_links), 'NOT IN')
      ->exists('machine_name')
      ->condition('external', 0)
      ->condition('updated', 0)
      ->condition('customized', 0)
      ->sort('depth', 'DESC');
    $result = $query->execute();
  }
  else {
    $result = array();
  }

  // Remove all such items. Starting from those with the greatest depth will
  // minimize the amount of re-parenting done by the menu link controller.
  if ($result) {
    menu_link_delete_multiple($result, TRUE);
  }
  \Drupal::configFactory()->setOverrideState($old_state);
}

/**
 * Returns an array containing all links for a menu.
 *
 * @param $menu_name
 *   The name of the menu whose links should be returned.
 *
 * @return
 *   An array of menu links.
 */
function menu_load_links($menu_name) {
  $links = array();

  $query = \Drupal::entityQuery('menu_link')
    ->condition('menu_name', $menu_name)
    // Order by weight so as to be helpful for menus that are only one level
    // deep.
    ->sort('weight');
  $result = $query->execute();

  if (!empty($result)) {
    $links = menu_link_load_multiple($result);
  }

  return $links;
}

/**
 * Deletes all links for a menu.
 *
 * @param $menu_name
 *   The name of the menu whose links will be deleted.
 */
function menu_delete_links($menu_name) {
  $links = menu_load_links($menu_name);
  menu_link_delete_multiple(array_keys($links), FALSE, TRUE);
}

/**
 * Clears the page and block caches at most twice per page load.
 */
function _menu_clear_page_cache() {
  $cache_cleared = &drupal_static(__FUNCTION__, 0);

  // Clear the page and block caches, but at most twice, including at
  //  the end of the page load when there are multiple links saved or deleted.
  if ($cache_cleared == 0) {
    Cache::invalidateTags(array('content' => TRUE));
    // Keep track of which menus have expanded items.
    _menu_set_expanded_menus();
    $cache_cleared = 1;
  }
  elseif ($cache_cleared == 1) {
    drupal_register_shutdown_function('Drupal\Core\Cache\Cache::invalidateTags', array('content' => TRUE));
    // Keep track of which menus have expanded items.
    drupal_register_shutdown_function('_menu_set_expanded_menus');
    $cache_cleared = 2;
  }
}

/**
 * Updates a list of menus with expanded items.
 */
function _menu_set_expanded_menus() {
  $names = array();
  $result = Drupal::entityQueryAggregate('menu_link')
    ->condition('expanded', 0, '<>')
    ->groupBy('menu_name')
    ->execute();

  // Flatten the resulting array.
  foreach($result as $k => $v) {
    $names[$k] = $v['menu_name'];
  }

  \Drupal::state()->set('menu_expanded', $names);
}


/**
 * Checks whether the site is in maintenance mode.
 *
 * This function will log the current user out and redirect to front page
 * if the current user has no 'access site in maintenance mode' permission.
 *
 * @param $check_only
 *   If this is set to TRUE, the function will perform the access checks and
 *   return the site offline status, but not log the user out or display any
 *   messages.
 *
 * @return
 *   FALSE if the site is not in maintenance mode, the user login page is
 *   displayed, or the user has the 'access site in maintenance mode'
 *   permission. TRUE for anonymous users not being on the login page when the
 *   site is in maintenance mode.
 */
function _menu_site_is_offline($check_only = FALSE) {
  // Check if site is in maintenance mode.
  if (\Drupal::state()->get('system.maintenance_mode')) {
    if (user_access('access site in maintenance mode')) {
      // Ensure that the maintenance mode message is displayed only once
      // (allowing for page redirects) and specifically suppress its display on
      // the maintenance mode settings page.
      if (!$check_only && current_path() != 'admin/config/development/maintenance') {
        if (user_access('administer site configuration')) {
          drupal_set_message(t('Operating in maintenance mode. <a href="@url">Go online.</a>', array('@url' => url('admin/config/development/maintenance'))), 'status', FALSE);
        }
        else {
          drupal_set_message(t('Operating in maintenance mode.'), 'status', FALSE);
        }
      }
    }
    else {
      return TRUE;
    }
  }
  return FALSE;
}

/**
 * @} End of "defgroup menu".
 */