<?php

namespace Drupal\mymodule\Menu;

use Drupal\Core\Access\AccessManagerInterface;
use Drupal\Core\Access\AccessResult;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Drupal\Core\Session\AccountInterface;
use Drupal\Core\Language\LanguageManager;
use Drupal\Core\Menu\DefaultMenuLinkTreeManipulators;
use Drupal\Core\Menu\InaccessibleMenuLink;
use Drupal\menu_link_content\Plugin\Menu\MenuLinkContent;

/**
 * Provides a couple of menu link tree manipulators.
 *
 * This class provides menu link tree manipulators to filter a menu_tree by the current language.
 */
class MenuLinkTreeManipulators extends DefaultMenuLinkTreeManipulators {

  /**
   * The access manager.
   *
   * @var \Drupal\Core\Access\AccessManagerInterface
   */
  protected $accessManager;

  /**
   * The current user.
   *
   * @var \Drupal\Core\Session\AccountInterface
   */
  protected $account;

  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  protected $entityTypeManager;

  /**
   * The current language ID.
   *
   * @var string
   */
  protected $langcode;

  /**
   * The list of available languages.
   *
   * @var array
   *    \Drupal\Core\Language\LanguageInterface[] An associative array of
   *    languages keyed by the language code.
   */
  protected $languages;

  /**
   * Constructs a \Drupal\Core\Menu\DefaultMenuLinkTreeManipulators object.
   *
   * @param \Drupal\Core\Access\AccessManagerInterface $access_manager
   *   The access manager.
   * @param \Drupal\Core\Session\AccountInterface $account
   *   The current user.
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   * @param \Drupal\Core\Language\LanguageManager $language_manager
   *   The language manager.
   */
  public function __construct(
    AccessManagerInterface $access_manager,
    AccountInterface $account,
    EntityTypeManagerInterface $entity_type_manager,
    LanguageManager $language_manager
  ) {
    $this->accessManager = $access_manager;
    $this->account = $account;
    $this->entityTypeManager = $entity_type_manager;
    $this->langcode = $language_manager->getCurrentLanguage()->getId();
    $this->languages = $language_manager->getLanguages();
  }

  /**
   * Filter a menu tree by current language MenuLinks.
   *
   * @param \Drupal\Core\Menu\MenuLinkTreeElement[] $tree
   *   The menu link tree to manipulate.
   *
   * @return \Drupal\Core\Menu\MenuLinkTreeElement[]
   *   The manipulated menu link tree.
   */
  public function filterByCurrentLanguage(array $tree) {
    foreach ($tree as $key => $element) {
      if ($element->link instanceof MenuLinkContent) {
        // Shortcut to the MenuLink item.
        $link = &$element->link;
        // Get the MenuLinkContent entity language.
        $link->langcode = $this->getLinkLanguage($link);
        // Test if the MenuLinkContent is the same language as the current.
        if ($this->langcode == $link->langcode) {
          $tree[$key]->access = parent::menuLinkCheckAccess($element->link);
        }
        else {
          $tree[$key]->link = new InaccessibleMenuLink($tree[$key]->link);
          $tree[$key]->access = AccessResult::forbidden();
          $tree[$key]->subtree = [];
        }
      }
    }
    return $tree;
  }

  /**
   * Force the MenuLinkContent to tell us its language code.
   *
   * @param \Drupal\menu_link_content\Plugin\Menu\MenuLinkContent $link
   *   `The Menu Link Content entity.
   *
   * @return string
   *   The Menu Link Content entity's language ID.
   */
  protected function getLinkLanguage(MenuLinkContent $link) {
    // Bypass protected function.
    // @see https://stackoverflow.com/a/44361579/6180339
    $bypass_function = function () {
      return $this->getEntity()->language()->getId();
    };
    return $bypass_function->call($link);
  }

}