class MenuForm

class MenuForm extends EntityForm {
    
    /**
     * The menu link manager.
     *
     * @var \Drupal\Core\Menu\MenuLinkManagerInterface
     */
    protected $menuLinkManager;
    
    /**
     * The menu tree service.
     *
     * @var \Drupal\Core\Menu\MenuLinkTreeInterface
     */
    protected $menuTree;
    
    /**
     * The link generator.
     *
     * @var \Drupal\Core\Utility\LinkGeneratorInterface
     */
    protected $linkGenerator;
    
    /**
     * The menu_link_content storage handler.
     *
     * @var \Drupal\menu_link_content\MenuLinkContentStorageInterface
     */
    protected $menuLinkContentStorage;
    
    /**
     * The overview tree form.
     *
     * @var array
     */
    protected $overviewTreeForm = [
        '#tree' => TRUE,
    ];
    
    /**
     * Constructs a MenuForm object.
     *
     * @param \Drupal\Core\Menu\MenuLinkManagerInterface $menu_link_manager
     *   The menu link manager.
     * @param \Drupal\Core\Menu\MenuLinkTreeInterface $menu_tree
     *   The menu tree service.
     * @param \Drupal\Core\Utility\LinkGeneratorInterface $link_generator
     *   The link generator.
     * @param \Drupal\menu_link_content\MenuLinkContentStorageInterface $menu_link_content_storage
     *   The menu link content storage handler.
     */
    public function __construct(MenuLinkManagerInterface $menu_link_manager, MenuLinkTreeInterface $menu_tree, LinkGeneratorInterface $link_generator, MenuLinkContentStorageInterface $menu_link_content_storage) {
        $this->menuLinkManager = $menu_link_manager;
        $this->menuTree = $menu_tree;
        $this->linkGenerator = $link_generator;
        $this->menuLinkContentStorage = $menu_link_content_storage;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('plugin.manager.menu.link'), $container->get('menu.link_tree'), $container->get('link_generator'), $container->get('entity_type.manager')
            ->getStorage('menu_link_content'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function form(array $form, FormStateInterface $form_state) {
        $menu = $this->entity;
        if ($this->operation == 'edit') {
            $form['#title'] = $this->t('Edit menu %label', [
                '%label' => $menu->label(),
            ]);
        }
        $form['label'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Title'),
            '#default_value' => $menu->label(),
            '#required' => TRUE,
        ];
        $form['id'] = [
            '#type' => 'machine_name',
            '#title' => $this->t('Menu name'),
            '#default_value' => $menu->id(),
            '#maxlength' => MenuStorage::MAX_ID_LENGTH,
            '#description' => $this->t('A unique name to construct the URL for the menu. It must only contain lowercase letters, numbers and hyphens.'),
            '#machine_name' => [
                'exists' => [
                    $this,
                    'menuNameExists',
                ],
                'source' => [
                    'label',
                ],
                'replace_pattern' => '[^a-z0-9-]+',
                'replace' => '-',
            ],
            // A menu's machine name cannot be changed.
'#disabled' => !$menu->isNew() || $menu->isLocked(),
        ];
        $form['description'] = [
            '#type' => 'textfield',
            '#title' => t('Administrative summary'),
            '#maxlength' => 512,
            '#default_value' => $menu->getDescription(),
        ];
        $form['langcode'] = [
            '#type' => 'language_select',
            '#title' => t('Menu language'),
            '#languages' => LanguageInterface::STATE_ALL,
            '#default_value' => $menu->language()
                ->getId(),
        ];
        // Add menu links administration form for existing menus.
        if (!$menu->isNew() || $menu->isLocked()) {
            // Form API supports constructing and validating self-contained sections
            // within forms, but does not allow handling the form section's submission
            // equally separated yet. Therefore, we use a $form_state key to point to
            // the parents of the form section.
            // @see self::submitOverviewForm()
            $form_state->set('menu_overview_form_parents', [
                'links',
            ]);
            $form['links'] = [];
            $form['links'] = $this->buildOverviewForm($form['links'], $form_state);
        }
        return parent::form($form, $form_state);
    }
    
    /**
     * Returns whether a menu name already exists.
     *
     * @param string $value
     *   The name of the menu.
     *
     * @return bool
     *   Returns TRUE if the menu already exists, FALSE otherwise.
     */
    public function menuNameExists($value) {
        // Check first to see if a menu with this ID exists.
        if ($this->entityTypeManager
            ->getStorage('menu')
            ->getQuery()
            ->condition('id', $value)
            ->range(0, 1)
            ->count()
            ->execute()) {
            return TRUE;
        }
        // Check for a link assigned to this menu.
        return $this->menuLinkManager
            ->menuNameInUse($value);
    }
    
    /**
     * {@inheritdoc}
     */
    public function save(array $form, FormStateInterface $form_state) {
        $menu = $this->entity;
        $status = $menu->save();
        $edit_link = $this->entity
            ->toLink($this->t('Edit'), 'edit-form')
            ->toString();
        if ($status == SAVED_UPDATED) {
            $this->messenger()
                ->addStatus($this->t('Menu %label has been updated.', [
                '%label' => $menu->label(),
            ]));
            $this->logger('menu')
                ->notice('Menu %label has been updated.', [
                '%label' => $menu->label(),
                'link' => $edit_link,
            ]);
        }
        else {
            $this->messenger()
                ->addStatus($this->t('Menu %label has been added.', [
                '%label' => $menu->label(),
            ]));
            $this->logger('menu')
                ->notice('Menu %label has been added.', [
                '%label' => $menu->label(),
                'link' => $edit_link,
            ]);
        }
        $form_state->setRedirectUrl($this->entity
            ->toUrl('edit-form'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        parent::submitForm($form, $form_state);
        if (!$this->entity
            ->isNew() || $this->entity
            ->isLocked()) {
            $this->submitOverviewForm($form, $form_state);
        }
    }
    
    /**
     * Form constructor to edit an entire menu tree at once.
     *
     * Shows for one menu the menu links accessible to the current user and
     * relevant operations.
     *
     * This form constructor can be integrated as a section into another form. It
     * relies on the following keys in $form_state:
     * - menu: A menu entity.
     * - menu_overview_form_parents: An array containing the parent keys to this
     *   form.
     * Forms integrating this section should call menu_overview_form_submit() from
     * their form submit handler.
     */
    protected function buildOverviewForm(array &$form, FormStateInterface $form_state) {
        // Ensure that menu_overview_form_submit() knows the parents of this form
        // section.
        if (!$form_state->has('menu_overview_form_parents')) {
            $form_state->set('menu_overview_form_parents', []);
        }
        $form['#attached']['library'][] = 'menu_ui/drupal.menu_ui.adminforms';
        $tree = $this->menuTree
            ->load($this->entity
            ->id(), new MenuTreeParameters());
        // We indicate that a menu administrator is running the menu access check.
        $this->getRequest()->attributes
            ->set('_menu_admin', TRUE);
        $manipulators = [
            [
                'callable' => 'menu.default_tree_manipulators:checkAccess',
            ],
            [
                'callable' => 'menu.default_tree_manipulators:generateIndexAndSort',
            ],
        ];
        $tree = $this->menuTree
            ->transform($tree, $manipulators);
        $this->getRequest()->attributes
            ->set('_menu_admin', FALSE);
        // Determine the delta; the number of weights to be made available.
        $count = function (array $tree) {
            $sum = function ($carry, MenuLinkTreeElement $item) {
                return $carry + $item->count();
            };
            return array_reduce($tree, $sum);
        };
        $delta = max($count($tree), 50);
        $form['links'] = [
            '#type' => 'table',
            '#theme' => 'table__menu_overview',
            '#header' => [
                $this->t('Menu link'),
                [
                    'data' => $this->t('Enabled'),
                    'class' => [
                        'checkbox',
                    ],
                ],
                $this->t('Weight'),
                [
                    'data' => $this->t('Operations'),
                    'colspan' => 3,
                ],
            ],
            '#attributes' => [
                'id' => 'menu-overview',
            ],
            '#tabledrag' => [
                [
                    'action' => 'match',
                    'relationship' => 'parent',
                    'group' => 'menu-parent',
                    'subgroup' => 'menu-parent',
                    'source' => 'menu-id',
                    'hidden' => TRUE,
                    'limit' => $this->menuTree
                        ->maxDepth() - 1,
                ],
                [
                    'action' => 'order',
                    'relationship' => 'sibling',
                    'group' => 'menu-weight',
                ],
            ],
        ];
        $form['links']['#empty'] = $this->t('There are no menu links yet. <a href=":url">Add link</a>.', [
            ':url' => Url::fromRoute('entity.menu.add_link_form', [
                'menu' => $this->entity
                    ->id(),
            ], [
                'query' => [
                    'destination' => $this->entity
                        ->toUrl('edit-form')
                        ->toString(),
                ],
            ])
                ->toString(),
        ]);
        $links = $this->buildOverviewTreeForm($tree, $delta);
        // Get the menu links which have pending revisions, and disable the
        // tabledrag if there are any.
        $edited_ids = array_filter(array_map(function ($element) {
            return is_array($element) && isset($element['#item']) && $element['#item']->link instanceof MenuLinkContent ? $element['#item']->link
                ->getMetaData()['entity_id'] : NULL;
        }, $links));
        $pending_menu_link_ids = array_intersect($this->menuLinkContentStorage
            ->getMenuLinkIdsWithPendingRevisions(), $edited_ids);
        if ($pending_menu_link_ids) {
            $form['help'] = [
                '#type' => 'container',
                'message' => [
                    '#markup' => $this->formatPlural(count($pending_menu_link_ids), '%capital_name contains 1 menu link with pending revisions. Manipulation of a menu tree having links with pending revisions is not supported, but you can re-enable manipulation by getting each menu link to a published state.', '%capital_name contains @count menu links with pending revisions. Manipulation of a menu tree having links with pending revisions is not supported, but you can re-enable manipulation by getting each menu link to a published state.', [
                        '%capital_name' => $this->entity
                            ->label(),
                    ]),
                ],
                '#attributes' => [
                    'class' => [
                        'messages',
                        'messages--warning',
                    ],
                ],
                '#weight' => -10,
            ];
            unset($form['links']['#tabledrag']);
            unset($form['links']['#header'][2]);
        }
        foreach (Element::children($links) as $id) {
            if (isset($links[$id]['#item'])) {
                $element = $links[$id];
                $is_pending_menu_link = isset($element['#item']->link
                    ->getMetaData()['entity_id']) && in_array($element['#item']->link
                    ->getMetaData()['entity_id'], $pending_menu_link_ids);
                $form['links'][$id]['#item'] = $element['#item'];
                // TableDrag: Mark the table row as draggable.
                $form['links'][$id]['#attributes'] = $element['#attributes'];
                $form['links'][$id]['#attributes']['class'][] = 'draggable';
                if ($is_pending_menu_link) {
                    $form['links'][$id]['#attributes']['class'][] = 'color-warning';
                    $form['links'][$id]['#attributes']['class'][] = 'menu-link-content--pending-revision';
                }
                // TableDrag: Sort the table row according to its existing/configured weight.
                $form['links'][$id]['#weight'] = $element['#item']->link
                    ->getWeight();
                // Add special classes to be used for tabledrag.js.
                $element['parent']['#attributes']['class'] = [
                    'menu-parent',
                ];
                $element['weight']['#attributes']['class'] = [
                    'menu-weight',
                ];
                $element['id']['#attributes']['class'] = [
                    'menu-id',
                ];
                $form['links'][$id]['title'] = [
                    [
                        '#theme' => 'indentation',
                        '#size' => $element['#item']->depth - 1,
                    ],
                    $element['title'],
                ];
                $form['links'][$id]['enabled'] = $element['enabled'];
                $form['links'][$id]['enabled']['#wrapper_attributes']['class'] = [
                    'checkbox',
                    'menu-enabled',
                ];
                // Disallow changing the publishing status of a pending revision.
                if ($is_pending_menu_link) {
                    $form['links'][$id]['enabled']['#access'] = FALSE;
                }
                if (!$pending_menu_link_ids) {
                    $form['links'][$id]['weight'] = $element['weight'];
                }
                // Operations (dropbutton) column.
                $form['links'][$id]['operations'] = $element['operations'];
                $form['links'][$id]['id'] = $element['id'];
                $form['links'][$id]['parent'] = $element['parent'];
            }
        }
        return $form;
    }
    
    /**
     * Recursive helper function for buildOverviewForm().
     *
     * @param \Drupal\Core\Menu\MenuLinkTreeElement[] $tree
     *   The tree retrieved by \Drupal\Core\Menu\MenuLinkTreeInterface::load().
     * @param int $delta
     *   The default number of menu items used in the menu weight selector is 50.
     *
     * @return array
     *   The overview tree form.
     */
    protected function buildOverviewTreeForm($tree, $delta) {
        $form =& $this->overviewTreeForm;
        $tree_access_cacheability = new CacheableMetadata();
        foreach ($tree as $element) {
            $tree_access_cacheability = $tree_access_cacheability->merge(CacheableMetadata::createFromObject($element->access));
            // Only render accessible links.
            if (!$element->access
                ->isAllowed()) {
                continue;
            }
            
            /** @var \Drupal\Core\Menu\MenuLinkInterface $link */
            $link = $element->link;
            if ($link) {
                $id = 'menu_plugin_id:' . $link->getPluginId();
                $form[$id]['#item'] = $element;
                $form[$id]['#attributes'] = $link->isEnabled() ? [
                    'class' => [
                        'menu-enabled',
                    ],
                ] : [
                    'class' => [
                        'menu-disabled',
                    ],
                ];
                $form[$id]['title'] = Link::fromTextAndUrl($link->getTitle(), $link->getUrlObject())
                    ->toRenderable();
                if (!$link->isEnabled()) {
                    $form[$id]['title']['#suffix'] = ' (' . $this->t('disabled') . ')';
                }
                elseif ($id === 'menu_plugin_id:user.logout') {
                    $form[$id]['title']['#suffix'] = ' (' . $this->t('<q>Log in</q> for anonymous users') . ')';
                }
                elseif (($url = $link->getUrlObject()) && $url->isRouted() && $url->getRouteName() == 'user.page') {
                    $form[$id]['title']['#suffix'] = ' (' . $this->t('logged in users only') . ')';
                }
                $form[$id]['enabled'] = [
                    '#type' => 'checkbox',
                    '#title' => $this->t('Enable @title menu link', [
                        '@title' => $link->getTitle(),
                    ]),
                    '#title_display' => 'invisible',
                    '#default_value' => $link->isEnabled(),
                ];
                $form[$id]['weight'] = [
                    '#type' => 'weight',
                    '#delta' => $delta,
                    '#default_value' => $link->getWeight(),
                    '#title' => $this->t('Weight for @title', [
                        '@title' => $link->getTitle(),
                    ]),
                    '#title_display' => 'invisible',
                ];
                $form[$id]['id'] = [
                    '#type' => 'hidden',
                    '#value' => $link->getPluginId(),
                ];
                $form[$id]['parent'] = [
                    '#type' => 'hidden',
                    '#default_value' => $link->getParent(),
                ];
                // Build a list of operations.
                $operations = [];
                $operations['edit'] = [
                    'title' => $this->t('Edit'),
                ];
                // Allow for a custom edit link per plugin.
                $edit_route = $link->getEditRoute();
                if ($edit_route) {
                    $operations['edit']['url'] = $edit_route;
                    // Bring the user back to the menu overview.
                    $operations['edit']['query'] = $this->getDestinationArray();
                }
                else {
                    // Fall back to the standard edit link.
                    $operations['edit'] += [
                        'url' => Url::fromRoute('menu_ui.link_edit', [
                            'menu_link_plugin' => $link->getPluginId(),
                        ]),
                    ];
                }
                // Links can either be reset or deleted, not both.
                if ($link->isResettable()) {
                    $operations['reset'] = [
                        'title' => $this->t('Reset'),
                        'url' => Url::fromRoute('menu_ui.link_reset', [
                            'menu_link_plugin' => $link->getPluginId(),
                        ]),
                    ];
                }
                elseif ($delete_link = $link->getDeleteRoute()) {
                    $operations['delete']['url'] = $delete_link;
                    $operations['delete']['query'] = $this->getDestinationArray();
                    $operations['delete']['title'] = $this->t('Delete');
                }
                if ($link->isTranslatable()) {
                    $operations['translate'] = [
                        'title' => $this->t('Translate'),
                        'url' => $link->getTranslateRoute(),
                    ];
                }
                $form[$id]['operations'] = [
                    '#type' => 'operations',
                    '#links' => $operations,
                ];
            }
            if ($element->subtree) {
                $this->buildOverviewTreeForm($element->subtree, $delta);
            }
        }
        $tree_access_cacheability->merge(CacheableMetadata::createFromRenderArray($form))
            ->applyTo($form);
        return $form;
    }
    
    /**
     * Submit handler for the menu overview form.
     *
     * This function takes great care in saving parent items first, then items
     * underneath them. Saving items in the incorrect order can break the tree.
     */
    protected function submitOverviewForm(array $complete_form, FormStateInterface $form_state) {
        // Form API supports constructing and validating self-contained sections
        // within forms, but does not allow to handle the form section's submission
        // equally separated yet. Therefore, we use a $form_state key to point to
        // the parents of the form section.
        $parents = $form_state->get('menu_overview_form_parents');
        $input = NestedArray::getValue($form_state->getUserInput(), $parents);
        $form =& NestedArray::getValue($complete_form, $parents);
        // When dealing with saving menu items, the order in which these items are
        // saved is critical. If a changed child item is saved before its parent,
        // the child item could be saved with an invalid path past its immediate
        // parent. To prevent this, save items in the form in the same order they
        // are sent, ensuring parents are saved first, then their children.
        // See https://www.drupal.org/node/181126#comment-632270.
        $order = is_array($input) ? array_flip(array_keys($input)) : [];
        // Update our original form with the new order.
        $form = array_intersect_key(array_merge($order, $form), $form);
        $fields = [
            'weight',
            'parent',
            'enabled',
        ];
        $form_links = $form['links'];
        foreach (Element::children($form_links) as $id) {
            if (isset($form_links[$id]['#item'])) {
                $element = $form_links[$id];
                $updated_values = [];
                // Update any fields that have changed in this menu item.
                foreach ($fields as $field) {
                    if (isset($element[$field]['#value']) && $element[$field]['#value'] != $element[$field]['#default_value']) {
                        $updated_values[$field] = $element[$field]['#value'];
                    }
                }
                if ($updated_values) {
                    // Use the ID from the actual plugin instance since the hidden value
                    // in the form could be tampered with.
                    $this->menuLinkManager
                        ->updateDefinition($element['#item']->link
                        ->getPLuginId(), $updated_values);
                }
            }
        }
    }

}