class FieldLink

class FieldLink extends ProcessPluginBase {
    
    /**
     * {@inheritdoc}
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration) {
        $configuration += [
            'uri_scheme' => 'http://',
        ];
        parent::__construct($configuration, $plugin_id, $plugin_definition);
    }
    
    /**
     * Turn a Drupal 6/7 URI into a Drupal 8-compatible format.
     *
     * @param string $uri
     *   The 'url' value from Drupal 6/7.
     *
     * @return string
     *   The Drupal 8-compatible URI.
     *
     * @see \Drupal\link\Plugin\Field\FieldWidget\LinkWidget::getUserEnteredStringAsUri()
     */
    protected function canonicalizeUri($uri) {
        // If we already have a scheme, we're fine.
        if (parse_url($uri, PHP_URL_SCHEME)) {
            return $uri;
        }
        // Empty URI and non-links are allowed.
        if (empty($uri) || in_array($uri, [
            '<nolink>',
            '<none>',
        ])) {
            return 'route:<nolink>';
        }
        // Remove the <front> component of the URL.
        if (strpos($uri, '<front>') === 0) {
            $uri = substr($uri, strlen('<front>'));
        }
        else {
            // List of unicode-encoded characters that were allowed in URLs,
            // according to link module in Drupal 7. Every character between &#x00BF;
            // and &#x00FF; (except × &#x00D7; and ÷ &#x00F7;) with the addition of
            // &#x0152;, &#x0153; and &#x0178;.
            // @see https://git.drupalcode.org/project/link/blob/7.x-1.5-beta2/link.module#L1382
            $link_ichars = '¿ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõöøùúûüýþÿŒœŸ';
            // Pattern specific to internal links.
            $internal_pattern = "/^(?:[a-z0-9" . $link_ichars . "_\\-+\\[\\] ]+)";
            $directories = "(?:\\/[a-z0-9" . $link_ichars . "_\\-\\.~+%=&,\$'#!():;*@\\[\\]]*)*";
            // Yes, four backslashes == a single backslash.
            $query = "(?:\\/?\\?([?a-z0-9" . $link_ichars . "+_|\\-\\.~\\/\\\\%=&,\$'():;*@\\[\\]{} ]*))";
            $anchor = "(?:#[a-z0-9" . $link_ichars . "_\\-\\.~+%=&,\$'():;*@\\[\\]\\/\\?]*)";
            // The rest of the path for a standard URL.
            $end = $directories . '?' . $query . '?' . $anchor . '?$/i';
            if (!preg_match($internal_pattern . $end, $uri)) {
                $link_domains = '[a-z][a-z0-9-]{1,62}';
                // Starting a parenthesis group with (?: means that it is grouped, but is not captured
                $authentication = "(?:(?:(?:[\\w\\.\\-\\+!\$&'\\(\\)*\\+,;=" . $link_ichars . "]|%[0-9a-f]{2})+(?::(?:[\\w" . $link_ichars . "\\.\\-\\+%!\$&'\\(\\)*\\+,;=]|%[0-9a-f]{2})*)?)?@)";
                $domain = '(?:(?:[a-z0-9' . $link_ichars . ']([a-z0-9' . $link_ichars . '\\-_\\[\\]])*)(\\.(([a-z0-9' . $link_ichars . '\\-_\\[\\]])+\\.)*(' . $link_domains . '|[a-z]{2}))?)';
                $ipv4 = '(?:[0-9]{1,3}(\\.[0-9]{1,3}){3})';
                $ipv6 = '(?:[0-9a-fA-F]{1,4}(\\:[0-9a-fA-F]{1,4}){7})';
                $port = '(?::([0-9]{1,5}))';
                // Pattern specific to external links.
                $external_pattern = '/^' . $authentication . '?(' . $domain . '|' . $ipv4 . '|' . $ipv6 . ' |localhost)' . $port . '?';
                if (preg_match($external_pattern . $end, $uri)) {
                    return $this->configuration['uri_scheme'] . $uri;
                }
            }
        }
        // Add the internal: scheme and ensure a leading slash.
        return 'internal:/' . ltrim($uri, '/');
    }
    
    /**
     * {@inheritdoc}
     */
    public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
        $attributes = unserialize($value['attributes']);
        // Drupal 6/7 link attributes might be double serialized.
        if (!is_array($attributes)) {
            $attributes = unserialize($attributes);
        }
        // In rare cases Drupal 6/7 link attributes are triple serialized. To avoid
        // further problems with them we set them to an empty array in this case.
        if (!is_array($attributes)) {
            $attributes = [];
        }
        // Massage the values into the correct form for the link.
        $route['uri'] = $this->canonicalizeUri($value['url']);
        $route['options']['attributes'] = $attributes;
        $route['title'] = $value['title'];
        return $route;
    }

}