FilterUrl.php

<?php

namespace Drupal\filter\Plugin\Filter;

use Drupal\Core\Form\FormStateInterface;
use Drupal\filter\FilterProcessResult;
use Drupal\filter\Plugin\FilterBase;

/**
 * Provides a filter to convert URLs into links.
 *
 * @Filter(
 *   id = "filter_url",
 *   title = @Translation("Convert URLs into links"),
 *   type = Drupal\filter\Plugin\FilterInterface::TYPE_MARKUP_LANGUAGE,
 *   settings = {
 *     "filter_url_length" = 72
 *   }
 * )
 */
class FilterUrl extends FilterBase {
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $form['filter_url_length'] = [
            '#type' => 'number',
            '#title' => $this->t('Maximum link text length'),
            '#default_value' => $this->settings['filter_url_length'],
            '#min' => 1,
            '#field_suffix' => $this->t('characters'),
            '#description' => $this->t('URLs longer than this number of characters will be truncated to prevent long strings that break formatting. The link itself will be retained; just the text portion of the link will be truncated.'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function process($text, $langcode) {
        return new FilterProcessResult(_filter_url($text, $this));
    }
    
    /**
     * {@inheritdoc}
     */
    public function tips($long = FALSE) {
        return $this->t('Web page addresses and email addresses turn into links automatically.');
    }

}