class AddHandler

class AddHandler extends ViewsFormBase {
    
    /**
     * Constructs a new AddHandler object.
     */
    public function __construct($type = NULL) {
        $this->setType($type);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormKey() {
        return 'add-handler';
    }
    
    /**
     * {@inheritdoc}
     */
    public function getForm(ViewEntityInterface $view, $display_id, $js, $type = NULL) {
        $this->setType($type);
        return parent::getForm($view, $display_id, $js);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'views_ui_add_handler_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $view = $form_state->get('view');
        $display_id = $form_state->get('display_id');
        $type = $form_state->get('type');
        $form = [
            'options' => [
                '#theme_wrappers' => [
                    'container',
                ],
                '#attributes' => [
                    'class' => [
                        'scroll',
                    ],
                    'data-drupal-views-scroll' => TRUE,
                ],
            ],
        ];
        $executable = $view->getExecutable();
        if (!$executable->setDisplay($display_id)) {
            $form['markup'] = [
                '#markup' => $this->t('Invalid display id @display', [
                    '@display' => $display_id,
                ]),
            ];
            return $form;
        }
        $display =& $executable->displayHandlers
            ->get($display_id);
        $types = ViewExecutable::getHandlerTypes();
        $ltitle = $types[$type]['ltitle'];
        $section = $types[$type]['plural'];
        if (!empty($types[$type]['type'])) {
            $type = $types[$type]['type'];
        }
        $form['#title'] = $this->t('Add @type', [
            '@type' => $ltitle,
        ]);
        $form['#section'] = $display_id . 'add-handler';
        // Add the display override dropdown.
        views_ui_standard_display_dropdown($form, $form_state, $section);
        // Figure out all the base tables allowed based upon what the relationships provide.
        $base_tables = $executable->getBaseTables();
        $options = Views::viewsDataHelper()->fetchFields(array_keys($base_tables), $type, $display->useGroupBy(), $form_state->get('type'));
        if (!empty($options)) {
            $form['override']['controls'] = [
                '#theme_wrappers' => [
                    'container',
                ],
                '#id' => 'views-filterable-options-controls',
                '#attributes' => [
                    'class' => [
                        'form--inline',
                        'views-filterable-options-controls',
                    ],
                ],
            ];
            $form['override']['controls']['options_search'] = [
                '#type' => 'textfield',
                '#title' => $this->t('Search'),
            ];
            $groups = [
                'all' => $this->t('- All -'),
            ];
            $form['override']['controls']['group'] = [
                '#type' => 'select',
                '#title' => $this->t('Category'),
                '#options' => [],
            ];
            $form['options']['name'] = [
                '#prefix' => '<div class="views-radio-box form-checkboxes views-filterable-options">',
                '#suffix' => '</div>',
                '#type' => 'tableselect',
                '#header' => [
                    'title' => $this->t('Title'),
                    'group' => $this->t('Category'),
                    'help' => $this->t('Description'),
                ],
                '#js_select' => FALSE,
            ];
            $grouped_options = [];
            foreach ($options as $key => $option) {
                $group = preg_replace('/[^a-z0-9]/', '-', strtolower($option['group']));
                $groups[$group] = $option['group'];
                $grouped_options[$group][$key] = $option;
                if (!empty($option['aliases']) && is_array($option['aliases'])) {
                    foreach ($option['aliases'] as $id => $alias) {
                        if (empty($alias['base']) || !empty($base_tables[$alias['base']])) {
                            $copy = $option;
                            $copy['group'] = $alias['group'];
                            $copy['title'] = $alias['title'];
                            if (isset($alias['help'])) {
                                $copy['help'] = $alias['help'];
                            }
                            $group = preg_replace('/[^a-z0-9]/', '-', strtolower($copy['group']));
                            $groups[$group] = $copy['group'];
                            $grouped_options[$group][$key . '$' . $id] = $copy;
                        }
                    }
                }
            }
            foreach ($grouped_options as $group => $group_options) {
                foreach ($group_options as $key => $option) {
                    $form['options']['name']['#options'][$key] = [
                        '#attributes' => [
                            'class' => [
                                'filterable-option',
                                $group,
                            ],
                        ],
                        'title' => [
                            'data' => [
                                '#title' => $option['title'],
                                '#plain_text' => $option['title'],
                            ],
                            'class' => [
                                'title',
                            ],
                        ],
                        'group' => $option['group'],
                        'help' => [
                            'data' => $option['help'],
                            'class' => [
                                'description',
                            ],
                        ],
                    ];
                }
            }
            $form['override']['controls']['group']['#options'] = $groups;
        }
        else {
            $form['options']['markup'] = [
                '#markup' => '<div class="js-form-item form-item">' . $this->t('There are no @types available to add.', [
                    '@types' => $ltitle,
                ]) . '</div>',
            ];
        }
        // Add a div to show the selected items
        $form['selected'] = [
            '#type' => 'item',
            '#markup' => '<span class="views-ui-view-title">' . $this->t('Selected:') . '</span> ' . '<div class="views-selected-options"></div>',
            '#theme_wrappers' => [
                'form_element',
                'views_ui_container',
            ],
            '#attributes' => [
                'class' => [
                    'container-inline',
                    'views-add-form-selected',
                    'views-offset-bottom',
                ],
                'data-drupal-views-offset' => 'bottom',
            ],
        ];
        $view->getStandardButtons($form, $form_state, 'views_ui_add_handler_form', $this->t('Add and configure @types', [
            '@types' => $ltitle,
        ]));
        // Remove the default submit function.
        $form['actions']['submit']['#submit'] = array_filter($form['actions']['submit']['#submit'], function ($var) {
            return !(is_array($var) && isset($var[1]) && $var[1] == 'standardSubmit');
        });
        $form['actions']['submit']['#submit'][] = [
            $view,
            'submitItemAdd',
        ];
        return $form;
    }

}