class WizardPluginBase

abstract class WizardPluginBase extends PluginBase implements WizardInterface {
    use UrlGeneratorTrait;
    
    /**
     * The base table connected with the wizard.
     *
     * @var string
     */
    protected $base_table;
    
    /**
     * The entity type connected with the wizard.
     *
     * There might be base tables connected with entity types, if not this would
     * be empty.
     *
     * @var string
     */
    protected $entityTypeId;
    
    /**
     * Contains the information from entity_get_info of the $entity_type.
     *
     * @var \Drupal\Core\Entity\EntityTypeInterface
     */
    protected $entityType;
    
    /**
     * An array of validated view objects, keyed by a hash.
     *
     * @var array
     */
    protected $validated_views = [];
    
    /**
     * The table column used for sorting by create date of this wizard.
     *
     * @var string
     */
    protected $createdColumn;
    
    /**
     * Views items configuration arrays for filters added by the wizard.
     *
     * @var array
     */
    protected $filters = [];
    
    /**
     * Views items configuration arrays for sorts added by the wizard.
     *
     * @var array
     */
    protected $sorts = [];
    
    /**
     * The available store criteria.
     *
     * @var array
     */
    protected $availableSorts = [];
    
    /**
     * Default values for filters.
     *
     * By default, filters are not exposed and added to the first non-reserved
     * filter group.
     *
     * @var array
     */
    protected $filter_defaults = [
        'id' => NULL,
        'expose' => [
            'operator' => FALSE,
        ],
        'group' => 1,
    ];
    
    /**
     * The bundle info service.
     *
     * @var \Drupal\Core\Entity\EntityTypeBundleInfoInterface
     */
    protected $bundleInfoService;
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('entity_type.bundle.info'));
    }
    
    /**
     * Constructs a WizardPluginBase object.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeBundleInfoInterface $bundle_info_service) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->bundleInfoService = $bundle_info_service;
        $this->base_table = $this->definition['base_table'];
        $entity_types = \Drupal::entityTypeManager()->getDefinitions();
        foreach ($entity_types as $entity_type_id => $entity_type) {
            if (in_array($this->base_table, [
                $entity_type->getBaseTable(),
                $entity_type->getDataTable(),
                $entity_type->getRevisionTable(),
                $entity_type->getRevisionDataTable(),
            ], TRUE)) {
                $this->entityType = $entity_type;
                $this->entityTypeId = $entity_type_id;
            }
        }
    }
    
    /**
     * Gets the createdColumn property.
     *
     * @return string
     *   The name of the column containing the created date.
     */
    public function getCreatedColumn() {
        return $this->createdColumn;
    }
    
    /**
     * Gets the filters property.
     *
     * @return array
     */
    public function getFilters() {
        $filters = [];
        // Add a default filter on the publishing status field, if available.
        if ($this->entityType && is_subclass_of($this->entityType
            ->getClass(), EntityPublishedInterface::class)) {
            $field_name = $this->entityType
                ->getKey('published');
            $this->filters = [
                $field_name => [
                    'value' => TRUE,
                    'table' => $this->base_table,
                    'field' => $field_name,
                    'plugin_id' => 'boolean',
                    'entity_type' => $this->entityTypeId,
                    'entity_field' => $field_name,
                ],
            ] + $this->filters;
        }
        $default = $this->filter_defaults;
        foreach ($this->filters as $name => $info) {
            $default['id'] = $name;
            $filters[$name] = $info + $default;
        }
        return $filters;
    }
    
    /**
     * Gets the availableSorts property.
     *
     * @return array
     */
    public function getAvailableSorts() {
        return $this->availableSorts;
    }
    
    /**
     * Gets the sorts property.
     *
     * @return array
     */
    public function getSorts() {
        return $this->sorts;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $style_options = Views::fetchPluginNames('style', 'normal', [
            $this->base_table,
        ]);
        $feed_row_options = Views::fetchPluginNames('row', 'feed', [
            $this->base_table,
        ]);
        $path_prefix = Url::fromRoute('<none>', [], [
            'absolute' => TRUE,
        ])->toString();
        // Add filters and sorts which apply to the view as a whole.
        $this->buildFilters($form, $form_state);
        $this->buildSorts($form, $form_state);
        $form['displays']['page'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Page settings'),
            '#attributes' => [
                'class' => [
                    'views-attachment',
                    'fieldset-no-legend',
                ],
            ],
            '#tree' => TRUE,
        ];
        $form['displays']['page']['create'] = [
            '#title' => $this->t('Create a page'),
            '#type' => 'checkbox',
            '#attributes' => [
                'class' => [
                    'strong',
                ],
            ],
            '#default_value' => FALSE,
            '#id' => 'edit-page-create',
        ];
        // All options for the page display are included in this container so they
        // can be hidden as a group when the "Create a page" checkbox is unchecked.
        $form['displays']['page']['options'] = [
            '#type' => 'container',
            '#attributes' => [
                'class' => [
                    'options-set',
                ],
            ],
            '#states' => [
                'visible' => [
                    ':input[name="page[create]"]' => [
                        'checked' => TRUE,
                    ],
                ],
            ],
            '#prefix' => '<div><div id="edit-page-wrapper">',
            '#suffix' => '</div></div>',
            '#parents' => [
                'page',
            ],
        ];
        $form['displays']['page']['options']['title'] = [
            '#title' => $this->t('Page title'),
            '#type' => 'textfield',
            '#maxlength' => 255,
        ];
        $form['displays']['page']['options']['path'] = [
            '#title' => $this->t('Path'),
            '#type' => 'textfield',
            '#field_prefix' => $path_prefix,
            // Account for the leading backslash.
'#maxlength' => 254,
        ];
        $form['displays']['page']['options']['style'] = [
            '#type' => 'fieldset',
            '#title' => $this->t('Page display settings'),
            '#attributes' => [
                'class' => [
                    'container-inline',
                    'fieldset-no-legend',
                ],
            ],
        ];
        // Create the dropdown for choosing the display format.
        $form['displays']['page']['options']['style']['style_plugin'] = [
            '#title' => $this->t('Display format'),
            '#type' => 'select',
            '#options' => $style_options,
        ];
        $style_form =& $form['displays']['page']['options']['style'];
        $style_form['style_plugin']['#default_value'] = static::getSelected($form_state, [
            'page',
            'style',
            'style_plugin',
        ], 'default', $style_form['style_plugin']);
        // Changing this dropdown updates $form['displays']['page']['options'] via
        // AJAX.
        views_ui_add_ajax_trigger($style_form, 'style_plugin', [
            'displays',
            'page',
            'options',
        ]);
        $this->buildFormStyle($form, $form_state, 'page');
        $form['displays']['page']['options']['items_per_page'] = [
            '#title' => $this->t('Items to display'),
            '#type' => 'number',
            '#default_value' => 10,
            '#min' => 0,
        ];
        $form['displays']['page']['options']['pager'] = [
            '#title' => $this->t('Use a pager'),
            '#type' => 'checkbox',
            '#default_value' => TRUE,
        ];
        $form['displays']['page']['options']['link'] = [
            '#title' => $this->t('Create a menu link'),
            '#type' => 'checkbox',
            '#id' => 'edit-page-link',
        ];
        $form['displays']['page']['options']['link_properties'] = [
            '#type' => 'container',
            '#states' => [
                'visible' => [
                    ':input[name="page[link]"]' => [
                        'checked' => TRUE,
                    ],
                ],
            ],
            '#prefix' => '<div id="edit-page-link-properties-wrapper">',
            '#suffix' => '</div>',
        ];
        if (\Drupal::moduleHandler()->moduleExists('menu_ui')) {
            $menu_options = menu_ui_get_menus();
        }
        else {
            // These are not yet translated.
            $menu_options = menu_list_system_menus();
            foreach ($menu_options as $name => $title) {
                $menu_options[$name] = $this->t($title);
            }
        }
        $form['displays']['page']['options']['link_properties']['menu_name'] = [
            '#title' => $this->t('Menu'),
            '#type' => 'select',
            '#options' => $menu_options,
        ];
        $form['displays']['page']['options']['link_properties']['title'] = [
            '#title' => $this->t('Link text'),
            '#type' => 'textfield',
        ];
        // Only offer a feed if we have at least one available feed row style.
        if ($feed_row_options) {
            $form['displays']['page']['options']['feed'] = [
                '#title' => $this->t('Include an RSS feed'),
                '#type' => 'checkbox',
                '#id' => 'edit-page-feed',
            ];
            $form['displays']['page']['options']['feed_properties'] = [
                '#type' => 'container',
                '#states' => [
                    'visible' => [
                        ':input[name="page[feed]"]' => [
                            'checked' => TRUE,
                        ],
                    ],
                ],
                '#prefix' => '<div id="edit-page-feed-properties-wrapper">',
                '#suffix' => '</div>',
            ];
            $form['displays']['page']['options']['feed_properties']['path'] = [
                '#title' => $this->t('Feed path'),
                '#type' => 'textfield',
                '#field_prefix' => $path_prefix,
                // Account for the leading backslash.
'#maxlength' => 254,
            ];
            // This will almost never be visible.
            $form['displays']['page']['options']['feed_properties']['row_plugin'] = [
                '#title' => $this->t('Feed row style'),
                '#type' => 'select',
                '#options' => $feed_row_options,
                '#default_value' => key($feed_row_options),
                '#access' => count($feed_row_options) > 1,
                '#states' => [
                    'visible' => [
                        ':input[name="page[feed]"]' => [
                            'checked' => TRUE,
                        ],
                    ],
                ],
                '#prefix' => '<div id="edit-page-feed-properties-row-plugin-wrapper">',
                '#suffix' => '</div>',
            ];
        }
        // Only offer the block settings if the module is enabled.
        if (\Drupal::moduleHandler()->moduleExists('block')) {
            $form['displays']['block'] = [
                '#type' => 'fieldset',
                '#title' => $this->t('Block settings'),
                '#attributes' => [
                    'class' => [
                        'views-attachment',
                        'fieldset-no-legend',
                    ],
                ],
                '#tree' => TRUE,
            ];
            $form['displays']['block']['create'] = [
                '#title' => $this->t('Create a block'),
                '#type' => 'checkbox',
                '#attributes' => [
                    'class' => [
                        'strong',
                    ],
                ],
                '#id' => 'edit-block-create',
            ];
            // All options for the block display are included in this container so
            // they can be hidden as a group when the "Create a block" checkbox is
            // unchecked.
            $form['displays']['block']['options'] = [
                '#type' => 'container',
                '#attributes' => [
                    'class' => [
                        'options-set',
                    ],
                ],
                '#states' => [
                    'visible' => [
                        ':input[name="block[create]"]' => [
                            'checked' => TRUE,
                        ],
                    ],
                ],
                '#prefix' => '<div id="edit-block-wrapper">',
                '#suffix' => '</div>',
                '#parents' => [
                    'block',
                ],
            ];
            $form['displays']['block']['options']['title'] = [
                '#title' => $this->t('Block title'),
                '#type' => 'textfield',
                '#maxlength' => 255,
            ];
            $form['displays']['block']['options']['style'] = [
                '#type' => 'fieldset',
                '#title' => $this->t('Block display settings'),
                '#attributes' => [
                    'class' => [
                        'container-inline',
                        'fieldset-no-legend',
                    ],
                ],
            ];
            // Create the dropdown for choosing the display format.
            $form['displays']['block']['options']['style']['style_plugin'] = [
                '#title' => $this->t('Display format'),
                '#type' => 'select',
                '#options' => $style_options,
            ];
            $style_form =& $form['displays']['block']['options']['style'];
            $style_form['style_plugin']['#default_value'] = static::getSelected($form_state, [
                'block',
                'style',
                'style_plugin',
            ], 'default', $style_form['style_plugin']);
            // Changing this dropdown updates $form['displays']['block']['options']
            // via AJAX.
            views_ui_add_ajax_trigger($style_form, 'style_plugin', [
                'displays',
                'block',
                'options',
            ]);
            $this->buildFormStyle($form, $form_state, 'block');
            $form['displays']['block']['options']['items_per_page'] = [
                '#title' => $this->t('Items per block'),
                '#type' => 'number',
                '#default_value' => 5,
                '#min' => 0,
            ];
            $form['displays']['block']['options']['pager'] = [
                '#title' => $this->t('Use a pager'),
                '#type' => 'checkbox',
                '#default_value' => FALSE,
            ];
        }
        // Only offer the REST export settings if the module is enabled.
        if (\Drupal::moduleHandler()->moduleExists('rest')) {
            $form['displays']['rest_export'] = [
                '#type' => 'fieldset',
                '#title' => $this->t('REST export settings'),
                '#attributes' => [
                    'class' => [
                        'views-attachment',
                        'fieldset-no-legend',
                    ],
                ],
                '#tree' => TRUE,
            ];
            $form['displays']['rest_export']['create'] = [
                '#title' => $this->t('Provide a REST export'),
                '#type' => 'checkbox',
                '#attributes' => [
                    'class' => [
                        'strong',
                    ],
                ],
                '#id' => 'edit-rest-export-create',
            ];
            // All options for the REST export display are included in this container
            // so they can be hidden as a group when the "Provide a REST export"
            // checkbox is unchecked.
            $form['displays']['rest_export']['options'] = [
                '#type' => 'container',
                '#attributes' => [
                    'class' => [
                        'options-set',
                    ],
                ],
                '#states' => [
                    'visible' => [
                        ':input[name="rest_export[create]"]' => [
                            'checked' => TRUE,
                        ],
                    ],
                ],
                '#prefix' => '<div id="edit-rest-export-wrapper">',
                '#suffix' => '</div>',
                '#parents' => [
                    'rest_export',
                ],
            ];
            $form['displays']['rest_export']['options']['path'] = [
                '#title' => $this->t('REST export path'),
                '#type' => 'textfield',
                '#field_prefix' => $path_prefix,
                // Account for the leading backslash.
'#maxlength' => 254,
            ];
        }
        return $form;
    }
    
    /**
     * Gets the current value of a #select element, from within a form constructor function.
     *
     * This function is intended for use in highly dynamic forms (in particular the
     * add view wizard) which are rebuilt in different ways depending on which
     * triggering element (AJAX or otherwise) was most recently fired. For example,
     * sometimes it is necessary to decide how to build one dynamic form element
     * based on the value of a different dynamic form element that may not have
     * even been present on the form the last time it was submitted. This function
     * takes care of resolving those conflicts and gives you the proper current
     * value of the requested #select element.
     *
     * By necessity, this function sometimes uses non-validated user input from
     * FormState::$input in making its determination. Although it performs some
     * minor validation of its own, it is not complete. The intention is that the
     * return value of this function should only be used to help decide how to
     * build the current form the next time it is reloaded, not to be saved as if
     * it had gone through the normal, final form validation process. Do NOT use
     * the results of this function for any other purpose besides deciding how to
     * build the next version of the form.
     *
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param $parents
     *   An array of parent keys that point to the part of the submitted form
     *   values that are expected to contain the element's value (in the case where
     *   this form element was actually submitted). In a simple case (assuming
     *   #tree is TRUE throughout the form), if the select element is located in
     *   $form['wrapper']['select'], so that the submitted form values would
     *   normally be found in $form_state->getValue(array('wrapper', 'select')),
     *   you would pass array('wrapper', 'select') for this parameter.
     * @param $default_value
     *   The default value to return if the #select element does not currently have
     *   a proper value set based on the submitted input.
     * @param $element
     *   An array representing the current version of the #select element within
     *   the form.
     *
     * @return
     *   The current value of the #select element. A common use for this is to feed
     *   it back into $element['#default_value'] so that the form will be rendered
     *   with the correct value selected.
     */
    public static function getSelected(FormStateInterface $form_state, $parents, $default_value, $element) {
        // For now, don't trust this to work on anything but a #select element.
        if (!isset($element['#type']) || $element['#type'] != 'select' || !isset($element['#options'])) {
            return $default_value;
        }
        // If there is a user-submitted value for this element that matches one of
        // the currently available options attached to it, use that. However, only
        // perform this check during the form rebuild. During the initial build
        // after #ajax is triggered, we need to rebuild the form as it was
        // initially. We need to check FormState::getUserInput() rather than
        // $form_state->getValues() here because the triggering element often has
        // the #limit_validation_errors property set to prevent unwanted errors
        // elsewhere on the form. This means that the $form_state->getValues() array
        // won't be complete. We could make it complete by adding each required part
        // of the form to the #limit_validation_errors property individually as the
        // form is being built, but this is difficult to do for a highly dynamic and
        // extensible form. This method is much simpler.
        $user_input = $form_state->isRebuilding() ? $form_state->getUserInput() : [];
        if (!empty($user_input)) {
            $key_exists = NULL;
            $submitted = NestedArray::getValue($user_input, $parents, $key_exists);
            // Check that the user-submitted value is one of the allowed options before
            // returning it. This is not a substitute for actual form validation;
            // rather it is necessary because, for example, the same select element
            // might have #options A, B, and C under one set of conditions but #options
            // D, E, F under a different set of conditions. So the form submission
            // might have occurred with option A selected, but when the form is rebuilt
            // option A is no longer one of the choices. In that case, we don't want to
            // use the value that was submitted anymore but rather fall back to the
            // default value.
            if ($key_exists && in_array($submitted, array_keys($element['#options']))) {
                return $submitted;
            }
        }
        // Fall back on returning the default value if nothing was returned above.
        return $default_value;
    }
    
    /**
     * Adds the style options to the wizard form.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     * @param string $type
     *   The display ID (e.g. 'page' or 'block').
     */
    protected function buildFormStyle(array &$form, FormStateInterface $form_state, $type) {
        $style_form =& $form['displays'][$type]['options']['style'];
        $style = $style_form['style_plugin']['#default_value'];
        $style_plugin = Views::pluginManager('style')->createInstance($style);
        if (isset($style_plugin) && $style_plugin->usesRowPlugin()) {
            $options = $this->rowStyleOptions();
            $style_form['row_plugin'] = [
                '#type' => 'select',
                '#title' => $this->t('of'),
                '#options' => $options,
                '#access' => count($options) > 1,
            ];
            // For the block display, the default value should be "titles (linked)",
            // if it's available (since that's the most common use case).
            $block_with_linked_titles_available = $type == 'block' && isset($options['titles_linked']);
            $default_value = $block_with_linked_titles_available ? 'titles_linked' : key($options);
            $style_form['row_plugin']['#default_value'] = static::getSelected($form_state, [
                $type,
                'style',
                'row_plugin',
            ], $default_value, $style_form['row_plugin']);
            // Changing this dropdown updates the individual row options via AJAX.
            views_ui_add_ajax_trigger($style_form, 'row_plugin', [
                'displays',
                $type,
                'options',
                'style',
                'row_options',
            ]);
            // This is the region that can be updated by AJAX. The base class doesn't
            // add anything here, but child classes can.
            $style_form['row_options'] = [
                '#theme_wrappers' => [
                    'container',
                ],
            ];
        }
        elseif ($style_plugin->usesFields()) {
            $style_form['row_plugin'] = [
                '#markup' => '<span>' . $this->t('of fields') . '</span>',
            ];
        }
    }
    
    /**
     * Retrieves row style plugin names.
     *
     * @return array
     *   Returns the plugin names available for the base table of the wizard.
     */
    protected function rowStyleOptions() {
        // Get all available row plugins by default.
        $options = Views::fetchPluginNames('row', 'normal', [
            $this->base_table,
        ]);
        return $options;
    }
    
    /**
     * Builds the form structure for selecting the view's filters.
     *
     * By default, this adds "of type" and "tagged with" filters (when they are
     * available).
     */
    protected function buildFilters(&$form, FormStateInterface $form_state) {
        module_load_include('inc', 'views_ui', 'admin');
        $bundles = $this->bundleInfoService
            ->getBundleInfo($this->entityTypeId);
        // If the current base table support bundles and has more than one (like user).
        if (!empty($bundles) && $this->entityType && $this->entityType
            ->hasKey('bundle')) {
            // Get all bundles and their human readable names.
            $options = [
                'all' => $this->t('All'),
            ];
            foreach ($bundles as $type => $bundle) {
                $options[$type] = $bundle['label'];
            }
            $form['displays']['show']['type'] = [
                '#type' => 'select',
                '#title' => $this->t('of type'),
                '#options' => $options,
            ];
            $selected_bundle = static::getSelected($form_state, [
                'show',
                'type',
            ], 'all', $form['displays']['show']['type']);
            $form['displays']['show']['type']['#default_value'] = $selected_bundle;
            // Changing this dropdown updates the entire content of $form['displays']
            // via AJAX, since each bundle might have entirely different fields
            // attached to it, etc.
            views_ui_add_ajax_trigger($form['displays']['show'], 'type', [
                'displays',
            ]);
        }
    }
    
    /**
     * Builds the form structure for selecting the view's sort order.
     *
     * By default, this adds a "sorted by [date]" filter (when it is available).
     */
    protected function buildSorts(&$form, FormStateInterface $form_state) {
        $sorts = [
            'none' => $this->t('Unsorted'),
        ];
        // Check if we are allowed to sort by creation date.
        $created_column = $this->getCreatedColumn();
        if ($created_column) {
            $sorts += [
                $created_column . ':DESC' => $this->t('Newest first'),
                $created_column . ':ASC' => $this->t('Oldest first'),
            ];
        }
        if ($available_sorts = $this->getAvailableSorts()) {
            $sorts += $available_sorts;
        }
        // If there is no sorts option available continue.
        if (!empty($sorts)) {
            $form['displays']['show']['sort'] = [
                '#type' => 'select',
                '#title' => $this->t('sorted by'),
                '#options' => $sorts,
                '#default_value' => isset($created_column) ? $created_column . ':DESC' : 'none',
            ];
        }
    }
    
    /**
     * Instantiates a view object from form values.
     *
     * @return \Drupal\views_ui\ViewUI
     *   The instantiated view UI object.
     */
    protected function instantiateView($form, FormStateInterface $form_state) {
        // Build the basic view properties and create the view.
        $values = [
            'id' => $form_state->getValue('id'),
            'label' => $form_state->getValue('label'),
            'description' => $form_state->getValue('description'),
            'base_table' => $this->base_table,
            'langcode' => \Drupal::languageManager()->getDefaultLanguage()
                ->getId(),
        ];
        $view = View::create($values);
        // Build all display options for this view.
        $display_options = $this->buildDisplayOptions($form, $form_state);
        // Allow the fully built options to be altered. This happens before adding
        // the options to the view, so that once they are eventually added we will
        // be able to get all the overrides correct.
        $this->alterDisplayOptions($display_options, $form, $form_state);
        $this->addDisplays($view, $display_options, $form, $form_state);
        return new ViewUI($view);
    }
    
    /**
     * Builds an array of display options for the view.
     *
     * @return array
     *   An array whose keys are the names of each display and whose values are
     *   arrays of options for that display.
     */
    protected function buildDisplayOptions($form, FormStateInterface $form_state) {
        // Display: Master
        $display_options['default'] = $this->defaultDisplayOptions();
        $display_options['default'] += [
            'filters' => [],
            'sorts' => [],
        ];
        $display_options['default']['filters'] += $this->defaultDisplayFilters($form, $form_state);
        $display_options['default']['sorts'] += $this->defaultDisplaySorts($form, $form_state);
        // Display: Page
        if (!$form_state->isValueEmpty([
            'page',
            'create',
        ])) {
            $display_options['page'] = $this->pageDisplayOptions($form, $form_state);
            // Display: Feed (attached to the page)
            if (!$form_state->isValueEmpty([
                'page',
                'feed',
            ])) {
                $display_options['feed'] = $this->pageFeedDisplayOptions($form, $form_state);
            }
        }
        // Display: Block
        if (!$form_state->isValueEmpty([
            'block',
            'create',
        ])) {
            $display_options['block'] = $this->blockDisplayOptions($form, $form_state);
        }
        // Display: REST export.
        if (!$form_state->isValueEmpty([
            'rest_export',
            'create',
        ])) {
            $display_options['rest_export'] = $this->restExportDisplayOptions($form, $form_state);
        }
        return $display_options;
    }
    
    /**
     * Alters the full array of display options before they are added to the view.
     */
    protected function alterDisplayOptions(&$display_options, $form, FormStateInterface $form_state) {
        foreach ($display_options as $display_type => $options) {
            // Allow style plugins to hook in and provide some settings.
            $style_plugin = Views::pluginManager('style')->createInstance($options['style']['type']);
            $style_plugin->wizardSubmit($form, $form_state, $this, $display_options, $display_type);
        }
    }
    
    /**
     * Adds the array of display options to the view, with appropriate overrides.
     */
    protected function addDisplays(View $view, $display_options, $form, FormStateInterface $form_state) {
        // Initialize and store the view executable to get the display plugin
        // instances.
        $executable = $view->getExecutable();
        // Display: Master
        $default_display = $executable->newDisplay('default', 'Master', 'default');
        foreach ($display_options['default'] as $option => $value) {
            $default_display->setOption($option, $value);
        }
        // Display: Page
        if (isset($display_options['page'])) {
            $display = $executable->newDisplay('page', 'Page', 'page_1');
            // The page display is usually the main one (from the user's point of
            // view). Its options should therefore become the overall view defaults,
            // so that new displays which are added later automatically inherit them.
            $this->setDefaultOptions($display_options['page'], $display, $default_display);
            // Display: Feed (attached to the page).
            if (isset($display_options['feed'])) {
                $display = $executable->newDisplay('feed', 'Feed', 'feed_1');
                $this->setOverrideOptions($display_options['feed'], $display, $default_display);
            }
        }
        // Display: Block.
        if (isset($display_options['block'])) {
            $display = $executable->newDisplay('block', 'Block', 'block_1');
            // When there is no page, the block display options should become the
            // overall view defaults.
            if (!isset($display_options['page'])) {
                $this->setDefaultOptions($display_options['block'], $display, $default_display);
            }
            else {
                $this->setOverrideOptions($display_options['block'], $display, $default_display);
            }
        }
        // Display: REST export.
        if (isset($display_options['rest_export'])) {
            $display = $executable->newDisplay('rest_export', 'REST export', 'rest_export_1');
            // If there is no page or block, the REST export display options should
            // become the overall view defaults.
            if (!isset($display_options['page']) && !isset($display_options['block'])) {
                $this->setDefaultOptions($display_options['rest_export'], $display, $default_display);
            }
            else {
                $this->setOverrideOptions($display_options['rest_export'], $display, $default_display);
            }
        }
        // Initialize displays and merge all plugin default values.
        $executable->mergeDefaults();
    }
    
    /**
     * Assembles the default display options for the view.
     *
     * Most wizards will need to override this method to provide some fields
     * or a different row plugin.
     *
     * @return array
     *   Returns an array of display options.
     */
    protected function defaultDisplayOptions() {
        $display_options = [];
        $display_options['access']['type'] = 'none';
        $display_options['cache']['type'] = 'tag';
        $display_options['query']['type'] = 'views_query';
        $display_options['exposed_form']['type'] = 'basic';
        $display_options['pager']['type'] = 'mini';
        $display_options['style']['type'] = 'default';
        $display_options['row']['type'] = 'fields';
        // Add default options array to each plugin type.
        foreach ($display_options as &$options) {
            $options['options'] = [];
        }
        // Add a least one field so the view validates and the user has a preview.
        // The base field can provide a default in its base settings; otherwise,
        // choose the first field with a field handler.
        $default_table = $this->base_table;
        $data = Views::viewsData()->get($default_table);
        if (isset($data['table']['base']['defaults']['field'])) {
            $default_field = $data['table']['base']['defaults']['field'];
            // If the table for the default field is different to the base table,
            // load the view table data for this table.
            if (isset($data['table']['base']['defaults']['table']) && $data['table']['base']['defaults']['table'] != $default_table) {
                $default_table = $data['table']['base']['defaults']['table'];
                $data = Views::viewsData()->get($default_table);
            }
        }
        else {
            foreach ($data as $default_field => $field_data) {
                if (isset($field_data['field']['id'])) {
                    break;
                }
            }
        }
        // @todo Refactor the code to use ViewExecutable::addHandler. See
        //   https://www.drupal.org/node/2383157.
        $display_options['fields'][$default_field] = [
            'table' => $default_table,
            'field' => $default_field,
            'id' => $default_field,
            'entity_type' => isset($data[$default_field]['entity type']) ? $data[$default_field]['entity type'] : NULL,
            'entity_field' => isset($data[$default_field]['entity field']) ? $data[$default_field]['entity field'] : NULL,
            'plugin_id' => $data[$default_field]['field']['id'],
        ];
        return $display_options;
    }
    
    /**
     * Retrieves all filter information used by the default display.
     *
     * Additional to the one provided by the plugin this method takes care about
     * adding additional filters based on user input.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     *
     * @return array
     *   An array of filter arrays keyed by ID. A sort array contains the options
     *   accepted by a filter handler.
     */
    protected function defaultDisplayFilters($form, FormStateInterface $form_state) {
        $filters = [];
        // Add any filters provided by the plugin.
        foreach ($this->getFilters() as $name => $info) {
            $filters[$name] = $info;
        }
        // Add any filters specified by the user when filling out the wizard.
        $filters = array_merge($filters, $this->defaultDisplayFiltersUser($form, $form_state));
        return $filters;
    }
    
    /**
     * Retrieves filter information based on user input for the default display.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     *
     * @return array
     *   An array of filter arrays keyed by ID. A sort array contains the options
     *   accepted by a filter handler.
     */
    protected function defaultDisplayFiltersUser(array $form, FormStateInterface $form_state) {
        $filters = [];
        if (($type = $form_state->getValue([
            'show',
            'type',
        ])) && $type != 'all') {
            $bundle_key = $this->entityType
                ->getKey('bundle');
            // Figure out the table where $bundle_key lives. It may not be the same as
            // the base table for the view; the taxonomy vocabulary machine_name, for
            // example, is stored in taxonomy_vocabulary, not taxonomy_term_data.
            module_load_include('inc', 'views_ui', 'admin');
            $fields = Views::viewsDataHelper()->fetchFields($this->base_table, 'filter');
            $table = FALSE;
            if (isset($fields[$this->base_table . '.' . $bundle_key])) {
                $table = $this->base_table;
            }
            else {
                foreach ($fields as $field_name => $value) {
                    if ($pos = strpos($field_name, '.' . $bundle_key)) {
                        $table = substr($field_name, 0, $pos);
                        break;
                    }
                }
            }
            // Some entities have bundles but don't provide their bundle data on the
            // base table. In this case the entities wizard should provide a
            // relationship to the relevant data.
            // @see \Drupal\node\Plugin\views\wizard\NodeRevision
            if (!empty($table)) {
                $table_data = Views::viewsData()->get($table);
                // If the 'in' operator is being used, map the values to an array.
                $handler = $table_data[$bundle_key]['filter']['id'];
                $handler_definition = Views::pluginManager('filter')->getDefinition($handler);
                if ($handler == 'in_operator' || is_subclass_of($handler_definition['class'], 'Drupal\\views\\Plugin\\views\\filter\\InOperator')) {
                    $value = [
                        $type => $type,
                    ];
                }
                else {
                    $value = $type;
                }
                $filters[$bundle_key] = [
                    'id' => $bundle_key,
                    'table' => $table,
                    'field' => $bundle_key,
                    'value' => $value,
                    'entity_type' => isset($table_data['table']['entity type']) ? $table_data['table']['entity type'] : NULL,
                    'entity_field' => isset($table_data[$bundle_key]['entity field']) ? $table_data[$bundle_key]['entity field'] : NULL,
                    'plugin_id' => $handler,
                ];
            }
        }
        return $filters;
    }
    
    /**
     * Retrieves all sort information used by the default display.
     *
     * Additional to the one provided by the plugin this method takes care about
     * adding additional sorts based on user input.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     *
     * @return array
     *   An array of sort arrays keyed by ID. A sort array contains the options
     *   accepted by a sort handler.
     */
    protected function defaultDisplaySorts($form, FormStateInterface $form_state) {
        $sorts = [];
        // Add any sorts provided by the plugin.
        foreach ($this->getSorts() as $name => $info) {
            $sorts[$name] = $info;
        }
        // Add any sorts specified by the user when filling out the wizard.
        $sorts = array_merge($sorts, $this->defaultDisplaySortsUser($form, $form_state));
        return $sorts;
    }
    
    /**
     * Retrieves sort information based on user input for the default display.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     *
     * @return array
     *   An array of sort arrays keyed by ID. A sort array contains the options
     *   accepted by a sort handler.
     */
    protected function defaultDisplaySortsUser($form, FormStateInterface $form_state) {
        $sorts = [];
        // Don't add a sort if there is no form value or the user set the sort to
        // 'none'.
        if (($sort_type = $form_state->getValue([
            'show',
            'sort',
        ])) && $sort_type != 'none') {
            list($column, $sort) = explode(':', $sort_type);
            // Column either be a column-name or the table-column-name.
            $column = explode('-', $column);
            if (count($column) > 1) {
                $table = $column[0];
                $column = $column[1];
            }
            else {
                $table = $this->base_table;
                $column = $column[0];
            }
            // If the input is invalid, for example when the #default_value contains
            // created from node, but the wizard type is another base table, make
            // sure it is not added. This usually don't happen if you have js
            // enabled.
            $data = Views::viewsData()->get($table);
            if (isset($data[$column]['sort'])) {
                $sorts[$column] = [
                    'id' => $column,
                    'table' => $table,
                    'field' => $column,
                    'order' => $sort,
                    'entity_type' => isset($data['table']['entity type']) ? $data['table']['entity type'] : NULL,
                    'entity_field' => isset($data[$column]['entity field']) ? $data[$column]['entity field'] : NULL,
                    'plugin_id' => $data[$column]['sort']['id'],
                ];
            }
        }
        return $sorts;
    }
    
    /**
     * Retrieves the page display options.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     *
     * @return array
     *   Returns an array of display options.
     */
    protected function pageDisplayOptions(array $form, FormStateInterface $form_state) {
        $display_options = [];
        $page = $form_state->getValue('page');
        $display_options['title'] = $page['title'];
        $display_options['path'] = $page['path'];
        $display_options['style'] = [
            'type' => $page['style']['style_plugin'],
        ];
        // Not every style plugin supports row style plugins.
        // Make sure that the selected row plugin is a valid one.
        $options = $this->rowStyleOptions();
        $display_options['row'] = [
            'type' => isset($page['style']['row_plugin']) && isset($options[$page['style']['row_plugin']]) ? $page['style']['row_plugin'] : 'fields',
        ];
        // If the specific 0 items per page, use no pager.
        if (empty($page['items_per_page'])) {
            $display_options['pager']['type'] = 'none';
        }
        elseif (!empty($page['pager'])) {
            $display_options['pager']['type'] = 'mini';
        }
        else {
            $display_options['pager']['type'] = 'some';
        }
        $display_options['pager']['options']['items_per_page'] = $page['items_per_page'];
        // Generate the menu links settings if the user checked the link checkbox.
        if (!empty($page['link'])) {
            $display_options['menu']['type'] = 'normal';
            $display_options['menu']['title'] = $page['link_properties']['title'];
            $display_options['menu']['menu_name'] = $page['link_properties']['menu_name'];
        }
        return $display_options;
    }
    
    /**
     * Retrieves the block display options.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     *
     * @return array
     *   Returns an array of display options.
     */
    protected function blockDisplayOptions(array $form, FormStateInterface $form_state) {
        $display_options = [];
        $block = $form_state->getValue('block');
        $display_options['title'] = $block['title'];
        $display_options['style'] = [
            'type' => $block['style']['style_plugin'],
        ];
        $options = $this->rowStyleOptions();
        $display_options['row'] = [
            'type' => isset($block['style']['row_plugin']) && isset($options[$block['style']['row_plugin']]) ? $block['style']['row_plugin'] : 'fields',
        ];
        $display_options['pager']['type'] = $block['pager'] ? 'full' : (empty($block['items_per_page']) ? 'none' : 'some');
        $display_options['pager']['options']['items_per_page'] = $block['items_per_page'];
        return $display_options;
    }
    
    /**
     * Retrieves the REST export display options from the submitted form values.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     *
     * @return array
     *   Returns an array of display options.
     */
    protected function restExportDisplayOptions(array $form, FormStateInterface $form_state) {
        $display_options = [];
        $display_options['path'] = $form_state->getValue([
            'rest_export',
            'path',
        ]);
        $display_options['style'] = [
            'type' => 'serializer',
        ];
        return $display_options;
    }
    
    /**
     * Retrieves the feed display options.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     *
     * @return array
     *   Returns an array of display options.
     */
    protected function pageFeedDisplayOptions($form, FormStateInterface $form_state) {
        $display_options = [];
        $display_options['pager']['type'] = 'some';
        $display_options['style'] = [
            'type' => 'rss',
        ];
        $display_options['row'] = [
            'type' => $form_state->getValue([
                'page',
                'feed_properties',
                'row_plugin',
            ]),
        ];
        $display_options['path'] = $form_state->getValue([
            'page',
            'feed_properties',
            'path',
        ]);
        $display_options['title'] = $form_state->getValue([
            'page',
            'title',
        ]);
        $display_options['displays'] = [
            'default' => 'default',
            'page_1' => 'page_1',
        ];
        return $display_options;
    }
    
    /**
     * Sets options for a display and makes them the default options if possible.
     *
     * This function can be used to set options for a display when it is desired
     * that the options also become the defaults for the view whenever possible.
     * This should be done for the "primary" display created in the view wizard,
     * so that new displays which the user adds later will be similar to this
     * one.
     *
     * @param array $options
     *   An array whose keys are the name of each option and whose values are the
     *   desired values to set.
     * @param \Drupal\views\Plugin\views\display\DisplayPluginBase $display
     *   The display handler which the options will be applied to. The default
     *   display will actually be assigned the options (and this display will
     *   inherit them) when possible.
     * @param \Drupal\views\Plugin\views\display\DisplayPluginBase $default_display
     *   The default display handler, which will store the options when possible.
     */
    protected function setDefaultOptions($options, DisplayPluginBase $display, DisplayPluginBase $default_display) {
        foreach ($options as $option => $value) {
            // If the default display supports this option, set the value there.
            // Otherwise, set it on the provided display.
            $default_value = $default_display->getOption($option);
            if (isset($default_value)) {
                $default_display->setOption($option, $value);
            }
            else {
                $display->setOption($option, $value);
            }
        }
    }
    
    /**
     * Sets options for a display, inheriting from the defaults when possible.
     *
     * This function can be used to set options for a display when it is desired
     * that the options inherit from the default display whenever possible. This
     * avoids setting too many options as overrides, which will be harder for the
     * user to modify later. For example, if $this->setDefaultOptions() was
     * previously called on a page display and then this function is called on a
     * block display, and if the user entered the same title for both displays in
     * the views wizard, then the view will wind up with the title stored as the
     * default (with the page and block both inheriting from it).
     *
     * @param array $options
     *   An array whose keys are the name of each option and whose values are the
     *   desired values to set.
     * @param \Drupal\views\Plugin\views\display\DisplayPluginBase $display
     *   The display handler which the options will be applied to. The default
     *   display will actually be assigned the options (and this display will
     *   inherit them) when possible.
     * @param \Drupal\views\Plugin\views\display\DisplayPluginBase $default_display
     *   The default display handler, which will store the options when possible.
     */
    protected function setOverrideOptions(array $options, DisplayPluginBase $display, DisplayPluginBase $default_display) {
        foreach ($options as $option => $value) {
            // Only override the default value if it is different from the value that
            // was provided.
            $default_value = $default_display->getOption($option);
            if (!isset($default_value)) {
                $display->setOption($option, $value);
            }
            elseif ($default_value !== $value) {
                $display->overrideOption($option, $value);
            }
        }
    }
    
    /**
     * Retrieves a validated view for a form submission.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     * @param bool $unset
     *   Should the view be removed from the list of validated views.
     *
     * @return \Drupal\views_ui\ViewUI
     *   The validated view object.
     */
    protected function retrieveValidatedView(array $form, FormStateInterface $form_state, $unset = TRUE) {
        // @todo Figure out why all this hashing is done. Wouldn't it be easier to
        //   store a single entry and that's it?
        $key = hash('sha256', serialize($form_state->getValues()));
        $view = isset($this->validated_views[$key]) ? $this->validated_views[$key] : NULL;
        if ($unset) {
            unset($this->validated_views[$key]);
        }
        return $view;
    }
    
    /**
     * Stores a validated view from a form submission.
     *
     * @param array $form
     *   The full wizard form array.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the wizard form.
     * @param \Drupal\views_ui\ViewUI $view
     *   The validated view object.
     */
    protected function setValidatedView(array $form, FormStateInterface $form_state, ViewUI $view) {
        $key = hash('sha256', serialize($form_state->getValues()));
        $this->validated_views[$key] = $view;
    }
    
    /**
     * Implements Drupal\views\Plugin\views\wizard\WizardInterface::validate().
     *
     * Instantiates the view from the form submission and validates its values.
     */
    public function validateView(array $form, FormStateInterface $form_state) {
        $view = $this->instantiateView($form, $form_state);
        $errors = $view->getExecutable()
            ->validate();
        if (empty($errors)) {
            $this->setValidatedView($form, $form_state, $view);
        }
        return $errors;
    }
    
    /**
     * {@inheritdoc}
     */
    public function createView(array $form, FormStateInterface $form_state) {
        $view = $this->retrieveValidatedView($form, $form_state);
        if (empty($view)) {
            throw new WizardException('Attempted to create a view with values that have not been validated.');
        }
        return $view;
    }

}