class LinkFormatter

class LinkFormatter 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 settingsForm(array $form, FormStateInterface $form_state) {
        $elements = parent::settingsForm($form, $form_state);
        $elements['trim_length'] = [
            '#type' => 'number',
            '#title' => t('Trim link text length'),
            '#field_suffix' => t('characters'),
            '#default_value' => $this->getSetting('trim_length'),
            '#min' => 1,
            '#description' => t('Leave blank to allow unlimited link text lengths.'),
        ];
        $elements['url_only'] = [
            '#type' => 'checkbox',
            '#title' => t('URL only'),
            '#default_value' => $this->getSetting('url_only'),
            '#access' => $this->getPluginId() == 'link',
        ];
        $elements['url_plain'] = [
            '#type' => 'checkbox',
            '#title' => t('Show URL as plain text'),
            '#default_value' => $this->getSetting('url_plain'),
            '#access' => $this->getPluginId() == 'link',
            '#states' => [
                'visible' => [
                    ':input[name*="url_only"]' => [
                        'checked' => TRUE,
                    ],
                ],
            ],
        ];
        $elements['rel'] = [
            '#type' => 'checkbox',
            '#title' => t('Add rel="nofollow" to links'),
            '#return_value' => 'nofollow',
            '#default_value' => $this->getSetting('rel'),
        ];
        $elements['target'] = [
            '#type' => 'checkbox',
            '#title' => t('Open link in new window'),
            '#return_value' => '_blank',
            '#default_value' => $this->getSetting('target'),
        ];
        return $elements;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        $summary = [];
        $settings = $this->getSettings();
        if (!empty($settings['trim_length'])) {
            $summary[] = t('Link text trimmed to @limit characters', [
                '@limit' => $settings['trim_length'],
            ]);
        }
        else {
            $summary[] = t('Link text not trimmed');
        }
        if ($this->getPluginId() == 'link' && !empty($settings['url_only'])) {
            if (!empty($settings['url_plain'])) {
                $summary[] = t('Show URL only as plain-text');
            }
            else {
                $summary[] = t('Show URL only');
            }
        }
        if (!empty($settings['rel'])) {
            $summary[] = t('Add rel="@rel"', [
                '@rel' => $settings['rel'],
            ]);
        }
        if (!empty($settings['target'])) {
            $summary[] = t('Open link in new window');
        }
        return $summary;
    }
    
    /**
     * {@inheritdoc}
     */
    public function viewElements(FieldItemListInterface $items, $langcode) {
        $element = [];
        $entity = $items->getEntity();
        $settings = $this->getSettings();
        foreach ($items as $delta => $item) {
            // By default use the full URL as the link text.
            $url = $this->buildUrl($item);
            $link_title = $url->toString();
            // If the title field value is available, use it for the link text.
            if (empty($settings['url_only']) && !empty($item->title)) {
                // Unsanitized token replacement here because the entire link title
                // gets auto-escaped during link generation in
                // \Drupal\Core\Utility\LinkGenerator::generate().
                $link_title = \Drupal::token()->replace($item->title, [
                    $entity->getEntityTypeId() => $entity,
                ], [
                    'clear' => TRUE,
                ]);
            }
            // Trim the link text to the desired length.
            if (!empty($settings['trim_length'])) {
                $link_title = Unicode::truncate($link_title, $settings['trim_length'], FALSE, TRUE);
            }
            if (!empty($settings['url_only']) && !empty($settings['url_plain'])) {
                $element[$delta] = [
                    '#plain_text' => $link_title,
                ];
                if (!empty($item->_attributes)) {
                    // Piggyback on the metadata attributes, which will be placed in the
                    // field template wrapper, and set the URL value in a content
                    // attribute.
                    // @todo Does RDF need a URL rather than an internal URI here?
                    // @see \Drupal\Tests\rdf\Kernel\Field\LinkFieldRdfaTest.
                    $content = str_replace('internal:/', '', $item->uri);
                    $item->_attributes += [
                        'content' => $content,
                    ];
                }
            }
            else {
                $element[$delta] = [
                    '#type' => 'link',
                    '#title' => $link_title,
                    '#options' => $url->getOptions(),
                ];
                $element[$delta]['#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;
    }
    
    /**
     * Builds the \Drupal\Core\Url object for a link field item.
     *
     * @param \Drupal\link\LinkItemInterface $item
     *   The link field item being rendered.
     *
     * @return \Drupal\Core\Url
     *   A Url object.
     */
    protected function buildUrl(LinkItemInterface $item) {
        $url = $item->getUrl() ?: Url::fromRoute('<none>');
        $settings = $this->getSettings();
        $options = $item->options;
        $options += $url->getOptions();
        // Add optional 'rel' attribute to link options.
        if (!empty($settings['rel'])) {
            $options['attributes']['rel'] = $settings['rel'];
        }
        // Add optional 'target' attribute to link options.
        if (!empty($settings['target'])) {
            $options['attributes']['target'] = $settings['target'];
        }
        $url->setOptions($options);
        return $url;
    }

}