class ConfigHandler

class ConfigHandler extends ViewsFormBase {
    
    /**
     * Constructs a new ConfigHandler object.
     */
    public function __construct($type = NULL, $id = NULL) {
        $this->setType($type);
        $this->setID($id);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormKey() {
        return 'handler';
    }
    
    /**
     * {@inheritdoc}
     */
    public function getForm(ViewEntityInterface $view, $display_id, $js, $type = NULL, $id = NULL) {
        $this->setType($type);
        $this->setID($id);
        return parent::getForm($view, $display_id, $js);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'views_ui_config_item_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state, ?Request $request = NULL) {
        
        /** @var \Drupal\views\Entity\View $view */
        $view = $form_state->get('view');
        $display_id = $form_state->get('display_id');
        $type = $form_state->get('type');
        $id = $form_state->get('id');
        $form = [
            'options' => [
                '#tree' => TRUE,
                '#theme_wrappers' => [
                    'container',
                ],
                '#attributes' => [
                    'class' => [
                        'scroll',
                    ],
                    'data-drupal-views-scroll' => TRUE,
                ],
            ],
        ];
        $executable = $view->getExecutable();
        $save_ui_cache = FALSE;
        if (!$executable->setDisplay($display_id)) {
            $form['markup'] = [
                '#markup' => $this->t('Invalid display id @display', [
                    '@display' => $display_id,
                ]),
            ];
            return $form;
        }
        $item = $executable->getHandler($display_id, $type, $id);
        if ($item) {
            $handler = $executable->display_handler
                ->getHandler($type, $id);
            if (empty($handler)) {
                $form['markup'] = [
                    '#markup' => $this->t("Error: handler for @table > @field doesn't exist!", [
                        '@table' => $item['table'],
                        '@field' => $item['field'],
                    ]),
                ];
            }
            else {
                $types = ViewExecutable::getHandlerTypes();
                $form['#title'] = $this->t('Configure @type: @item', [
                    '@type' => $types[$type]['lstitle'],
                    '@item' => $handler->adminLabel(),
                ]);
                // If this item can come from the default display, show a dropdown
                // that lets the user choose which display the changes should apply to.
                if ($executable->display_handler
                    ->defaultableSections($types[$type]['plural'])) {
                    $section = $types[$type]['plural'];
                    $form_state->set('section', $section);
                    views_ui_standard_display_dropdown($form, $form_state, $section);
                }
                // A whole bunch of code to figure out what relationships are valid for
                // this item.
                $relationships = $executable->display_handler
                    ->getOption('relationships');
                $relationship_options = [];
                foreach ($relationships as $relationship) {
                    // Relationships can't link back to self. But also, due to ordering,
                    // relationships can only link to prior relationships.
                    if ($type == 'relationship' && $id == $relationship['id']) {
                        break;
                    }
                    $relationship_handler = Views::handlerManager('relationship')->getHandler($relationship);
                    // Ignore invalid/broken relationships.
                    if (empty($relationship_handler)) {
                        continue;
                    }
                    // If this relationship is valid for this type, add it to the list.
                    $data = Views::viewsData()->get($relationship['table']);
                    if (isset($data[$relationship['field']]['relationship']['base']) && ($base = $data[$relationship['field']]['relationship']['base'])) {
                        $base_fields = Views::viewsDataHelper()->fetchFields($base, $type, $executable->display_handler
                            ->useGroupBy());
                        if (isset($base_fields[$item['table'] . '.' . $item['field']])) {
                            $relationship_handler->init($executable, $executable->display_handler, $relationship);
                            $relationship_options[$relationship['id']] = $relationship_handler->adminLabel();
                        }
                    }
                }
                if (!empty($relationship_options)) {
                    // Make sure the existing relationship is even valid. If not, force
                    // it to none.
                    $base_fields = Views::viewsDataHelper()->fetchFields($view->get('base_table'), $type, $executable->display_handler
                        ->useGroupBy());
                    if (isset($base_fields[$item['table'] . '.' . $item['field']])) {
                        $relationship_options = array_merge([
                            'none' => $this->t('Do not use a relationship'),
                        ], $relationship_options);
                    }
                    $rel = empty($item['relationship']) ? 'none' : $item['relationship'];
                    if (empty($relationship_options[$rel])) {
                        // Pick the first relationship.
                        $rel = key($relationship_options);
                        // We want this relationship option to get saved even if the user
                        // skips submitting the form.
                        $executable->setHandlerOption($display_id, $type, $id, 'relationship', $rel);
                        $save_ui_cache = TRUE;
                        // Re-initialize with new relationship.
                        $item['relationship'] = $rel;
                        $handler->init($executable, $executable->display_handler, $item);
                    }
                    $form['options']['relationship'] = [
                        '#type' => 'select',
                        '#title' => $this->t('Relationship'),
                        '#options' => $relationship_options,
                        '#default_value' => $rel,
                        '#weight' => -500,
                    ];
                }
                else {
                    $form['options']['relationship'] = [
                        '#type' => 'value',
                        '#value' => 'none',
                    ];
                }
                if (!empty($handler->definition['help'])) {
                    $form['options']['form_description'] = [
                        '#markup' => $handler->definition['help'],
                        '#theme_wrappers' => [
                            'container',
                        ],
                        '#attributes' => [
                            'class' => [
                                'js-form-item form-item description',
                            ],
                        ],
                        '#weight' => -1000,
                    ];
                }
                $form['#section'] = $display_id . '-' . $type . '-' . $id;
                // Get form from the handler.
                $handler->buildOptionsForm($form['options'], $form_state);
                $form_state->set('handler', $handler);
            }
            $name = $form_state->get('update_name');
            $view->getStandardButtons($form, $form_state, 'views_ui_config_item_form', $name);
            // Add a 'remove' button.
            $form['actions']['remove'] = [
                '#type' => 'submit',
                '#value' => $this->t('Remove'),
                '#submit' => [
                    [
                        $this,
                        'remove',
                    ],
                ],
                '#limit_validation_errors' => [
                    [
                        'override',
                    ],
                ],
                '#button_type' => 'danger',
            ];
        }
        if ($save_ui_cache) {
            $view->cacheSet();
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        $form_state->get('handler')
            ->validateOptionsForm($form['options'], $form_state);
        if ($form_state->getErrors()) {
            $form_state->set('rerender', TRUE);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $view = $form_state->get('view');
        $display_id = $form_state->get('display_id');
        $id = $form_state->get('id');
        $handler = $form_state->get('handler');
        // Run it through the handler's submit function.
        $handler->submitOptionsForm($form['options'], $form_state);
        $item = $handler->options;
        $types = ViewExecutable::getHandlerTypes();
        // For footer/header $handler_type is area but $type is footer/header.
        // For all other handle types it's the same.
        $handler_type = $type = $form_state->get('type');
        if (!empty($types[$type]['type'])) {
            $handler_type = $types[$type]['type'];
        }
        $override = NULL;
        $executable = $view->getExecutable();
        if ($executable->display_handler
            ->useGroupBy() && !empty($item['group_type'])) {
            if (empty($executable->query)) {
                $executable->initQuery();
            }
            $aggregate = $executable->query
                ->getAggregationInfo();
            if (!empty($aggregate[$item['group_type']]['handler'][$type])) {
                $override = $aggregate[$item['group_type']]['handler'][$type];
            }
        }
        // Create a new handler and unpack the options from the form onto it. We
        // can use that for storage.
        $handler = Views::handlerManager($handler_type)->getHandler($item, $override);
        $handler->init($executable, $executable->display_handler, $item);
        // Add the incoming options to existing options because items using
        // the extra form may not have everything in the form here.
        $options = $handler->submitFormCalculateOptions($handler->options, $form_state->getValue('options', []));
        // This unpacks only options that are in the definition, ensuring random
        // extra stuff on the form is not sent through.
        $handler->unpackOptions($handler->options, $options, NULL, FALSE);
        // Store the item back on the view
        $executable->setHandler($display_id, $type, $id, $handler->options);
        // Ensure any temporary options are removed.
        if (isset($view->temporary_options[$type][$id])) {
            unset($view->temporary_options[$type][$id]);
        }
        // Write to cache
        $view->cacheSet();
    }
    
    /**
     * Submit handler for removing an item from a view.
     */
    public function remove(&$form, FormStateInterface $form_state) {
        $view = $form_state->get('view');
        $display_id = $form_state->get('display_id');
        $type = $form_state->get('type');
        $id = $form_state->get('id');
        // Store the item back on the view
        [
            $was_defaulted,
            $is_defaulted,
        ] = $view->getOverrideValues($form, $form_state);
        $executable = $view->getExecutable();
        // If the display selection was changed toggle the override value.
        if ($was_defaulted != $is_defaulted) {
            $display =& $executable->displayHandlers
                ->get($display_id);
            $display->optionsOverride($form, $form_state);
        }
        $executable->removeHandler($display_id, $type, $id);
        // Write to cache
        $view->cacheSet();
    }

}