improvements-2.x-dev/modules/improvements_views/src/Plugin/Field/FieldFormatter/EntityReferenceViewsFormatter.php

<?php

namespace Drupal\improvements_views\Plugin\Field\FieldFormatter;

use Drupal\Core\Field\Attribute\FieldFormatter;
use Drupal\Core\Field\FieldItemInterface;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Field\FormatterBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\views\Views;

#[FieldFormatter(
  id: 'entity_reference_views_formatter',
  label: new TranslatableMarkup('Views'),
  field_types: ['entity_reference'],
)]
class EntityReferenceViewsFormatter extends FormatterBase {

  /**
   * {@inheritdoc}
   */
  public static function defaultSettings(): array {
    return [
      'views' => '',
    ] + parent::defaultSettings();
  }

  /**
   * {@inheritdoc}
   */
  public function settingsForm(array $form, FormStateInterface $form_state): array {
    $elements['views'] = [
      '#title' => t('Views'),
      '#type' => 'select',
      '#default_value' => $this->getSetting('view_name'),
      '#options' => Views::getViewsAsOptions(FALSE, 'enabled', NULL, FALSE, TRUE),
      '#required' => TRUE,
    ];

    return $elements;
  }

  /**
   * {@inheritDoc}
   */
  public function settingsSummary(): array {
    $summary[] = t('Views') . ': ' . ($this->getSetting('views') ?: t('none'));

    return $summary;
  }

  /**
   * {@inheritDoc}
   */
  public function viewElements(FieldItemListInterface $items, $langcode): ?array {
    if ($views_key = $this->getSetting('views')) {
      [$view_id, $view_display_name] = explode(':', $views_key);
      $target_ids = array_map(fn(FieldItemInterface $item) => $item->target_id, iterator_to_array($items));
      return $target_ids ? [views_embed_view($view_id, $view_display_name, implode('+', $target_ids))] : [];
    }

    return NULL;
  }

}