class MediaLibrarySelectForm

class MediaLibrarySelectForm extends FieldPluginBase {
    
    /**
     * {@inheritdoc}
     */
    public function getValue(ResultRow $row, $field = NULL) {
        return '<!--form-item-' . $this->options['id'] . '--' . $row->mid . '-->';
    }
    
    /**
     * Return the name of a form field.
     *
     * @see \Drupal\views\Form\ViewsFormMainForm
     *
     * @return string
     *   The form field name.
     */
    public function form_element_name() : string {
        return $this->field;
    }
    
    /**
     * Return a media entity ID from a views result row.
     *
     * @see \Drupal\views\Form\ViewsFormMainForm
     *
     * @param int $row_id
     *   The index of a views result row.
     *
     * @return string
     *   The ID of a media entity.
     */
    public function form_element_row_id(int $row_id) : string {
        return $this->view->result[$row_id]->mid;
    }
    
    /**
     * {@inheritdoc}
     */
    public function render(ResultRow $values) {
        return ViewsRenderPipelineMarkup::create($this->getValue($values));
    }
    
    /**
     * Form constructor for the media library select form.
     *
     * @param array $form
     *   An associative array containing the structure of the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     */
    public function viewsForm(array &$form, FormStateInterface $form_state) {
        $form['#attributes']['class'] = [
            'js-media-library-views-form',
        ];
        // Add target for AJAX messages.
        $form['media_library_messages'] = [
            '#type' => 'container',
            '#attributes' => [
                'id' => 'media-library-messages',
            ],
            '#weight' => -10,
        ];
        // Add an attribute that identifies the media type displayed in the form.
        if (isset($this->view->args[0])) {
            $form['#attributes']['data-drupal-media-type'] = $this->view->args[0];
        }
        // Render checkboxes for all rows.
        $form[$this->options['id']]['#tree'] = TRUE;
        foreach ($this->view->result as $row_index => $row) {
            $entity = $this->getEntity($row);
            if (!$entity) {
                $form[$this->options['id']][$row_index] = [];
                continue;
            }
            $form[$this->options['id']][$row->mid] = [
                '#type' => 'checkbox',
                '#title' => $this->t('Select @label', [
                    '@label' => $entity->label(),
                ]),
                '#title_display' => 'invisible',
                '#return_value' => $entity->id(),
            ];
        }
        // The selection is persistent across different pages in the media library
        // and populated via JavaScript.
        $selection_field_id = $this->options['id'] . '_selection';
        $form[$selection_field_id] = [
            '#type' => 'hidden',
            '#attributes' => [
                // This is used to identify the hidden field in the form via JavaScript.
'id' => 'media-library-modal-selection',
            ],
        ];
        // @todo Remove in https://www.drupal.org/project/drupal/issues/2504115
        // Currently the default URL for all AJAX form elements is the current URL,
        // not the form action. This causes bugs when this form is rendered from an
        // AJAX path like /views/ajax, which cannot process AJAX form submits.
        $query = $this->view
            ->getRequest()->query
            ->all();
        $query[FormBuilderInterface::AJAX_FORM_REQUEST] = TRUE;
        $query['views_display_id'] = $this->view
            ->getDisplay()->display['id'];
        $form['actions']['submit']['#ajax'] = [
            'url' => Url::fromRoute('media_library.ui'),
            'options' => [
                'query' => $query,
            ],
            'callback' => [
                static::class,
                'updateWidget',
            ],
        ];
        $form['actions']['submit']['#value'] = $this->t('Insert selected');
        $form['actions']['submit']['#button_type'] = 'primary';
        $form['actions']['submit']['#field_id'] = $selection_field_id;
    }
    
    /**
     * Submit handler for the media library select form.
     *
     * @param array $form
     *   An associative array containing the structure of the form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The current request.
     *
     * @return \Drupal\Core\Ajax\AjaxResponse
     *   A command to send the selection to the current field widget.
     */
    public static function updateWidget(array &$form, FormStateInterface $form_state, Request $request) {
        $field_id = $form_state->getTriggeringElement()['#field_id'];
        $selected_ids = $form_state->getValue($field_id);
        $selected_ids = $selected_ids ? array_filter(explode(',', $selected_ids)) : [];
        // Allow the opener service to handle the selection.
        $state = MediaLibraryState::fromRequest($request);
        $current_selection = $form_state->getValue('media_library_select_form_selection');
        $available_slots = $state->getAvailableSlots();
        $selected_count = count(explode(',', $current_selection));
        if ($available_slots > 0 && $selected_count > $available_slots) {
            $response = new AjaxResponse();
            $error = \Drupal::translation()->formatPlural($selected_count - $available_slots, 'There are currently @total items selected. The maximum number of items for the field is @max. Remove @count item from the selection.', 'There are currently @total items selected. The maximum number of items for the field is @max. Remove @count items from the selection.', [
                '@total' => $selected_count,
                '@max' => $available_slots,
            ]);
            $response->addCommand(new MessageCommand($error, '#media-library-messages', [
                'type' => 'error',
            ]));
            return $response;
        }
        return \Drupal::service('media_library.opener_resolver')->get($state)
            ->getSelectionResponse($state, $selected_ids)
            ->addCommand(new CloseDialogCommand());
    }
    
    /**
     * {@inheritdoc}
     */
    public function viewsFormValidate(array &$form, FormStateInterface $form_state) {
        $selected = array_filter($form_state->getValue($this->options['id']));
        if (empty($selected)) {
            $form_state->setErrorByName('', $this->t('No items selected.'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function clickSortable() {
        return FALSE;
    }

}