Custom formatter for field link

<?php

namespace Drupal\customrcpf\Plugin\Field\FieldFormatter;

use Drupal\Component\Utility\Unicode;
use Drupal\Core\Field\FieldDefinitionInterface;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Field\FormatterBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Path\PathValidatorInterface;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\Core\Url;
use Drupal\link\LinkItemInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Plugin implementation of the 'rcpf_link' formatter.
 *
 * @FieldFormatter(
 *   id = "rcpf_link",
 *   label = @Translation("RCPF link"),
 *   field_types = {
 *     "link"
 *   }
 * )
 */
class RCPFLinkFormatter extends FormatterBase implements ContainerFactoryPluginInterface {

  /**
   * The path validator service.
   *
   * @var \Drupal\Core\Path\PathValidatorInterface
   */
  protected $pathValidator;

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $plugin_id,
      $plugin_definition,
      $configuration['field_definition'],
      $configuration['settings'],
      $configuration['label'],
      $configuration['view_mode'],
      $configuration['third_party_settings'],
      $container->get('path.validator')
    );
  }

  /**
   * Constructs a new LinkFormatter.
   *
   * @param string $plugin_id
   *   The plugin_id for the formatter.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
   *   The definition of the field to which the formatter is associated.
   * @param array $settings
   *   The formatter settings.
   * @param string $label
   *   The formatter label display setting.
   * @param string $view_mode
   *   The view mode.
   * @param array $third_party_settings
   *   Third party settings.
   * @param \Drupal\Core\Path\PathValidatorInterface $path_validator
   *   The path validator service.
   */
  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, PathValidatorInterface $path_validator) {
    parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
    $this->pathValidator = $path_validator;
  }

  /**
   * {@inheritdoc}
   */
  public static function defaultSettings() {
    return [
      'trim_length' => '80',
      'url_only' => '',
      'url_plain' => '',
      'rel' => '',
      'target' => '',
    ] + parent::defaultSettings();
  }

  /**
   * {@inheritdoc}
   */
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $element = [];
    $entity = $items->getEntity();

    foreach ($items as $delta => $item) {
      $url = $item->getUrl() ?: Url::fromRoute('<none>');

      $title = \Drupal::token()->replace($item->title, [$entity->getEntityTypeId() => $entity], ['clear' => TRUE]);

      $element[$delta] = [
        '#theme' => 'customrcpf_formatter_link',
        '#title' => $title,
        '#url' => $url,
      ];

      if (!empty($item->_attributes)) {
        $element[$delta]['#options'] += ['attributes' => []];
        $element[$delta]['#options']['attributes'] += $item->_attributes;
        // Unset field item attributes since they have been included in the
        // formatter output and should not be rendered in the field template.
        unset($item->_attributes);
      }

    }

    return $element;
  }


}