<?php

namespace SCW\Extkey\Hooks;

class PreProcess implements \TYPO3\CMS\FrontendEditing\RequestPreProcess\RequestPreProcessInterface
{
    public function preProcess(string $table, array $record, string &$fieldName, string $content, bool &$isFinished): string {

        $content = preg_replace_callback('/<a\s[^>]*href=\"([^\"]*)\"[^>]*>(.*)<\/a>/siU', function($matches) {
            $wrong = $matches[1];

            if(!preg_match('/^(t3|http|https|tel):\/\//', $wrong)) {
                if (substr($wrong, strlen($wrong)-1 ) == "/") {
                    $wrong = substr($wrong, 0, strlen($wrong) - 1);
                }

                $queryBuilder = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Core\Database\ConnectionPool::class)->getQueryBuilderForTable('tx_realurl_pathdata');
                $page = $queryBuilder
                    ->select('page_id')
                    ->from('tx_realurl_pathdata')
                    ->where(
                        $queryBuilder->expr()->eq('pagepath', $queryBuilder->createNamedParameter($wrong))
                    )
                    ->execute()
                    ->fetchColumn(0);

                if($page) {
                    $replace = "t3://page?uid=" . $page;
                } else {
                    $protocol = ((!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] != 'off') ||
                        $_SERVER['SERVER_PORT'] == 443) ? "https://" : "http://";
                    $domainName = $_SERVER['HTTP_HOST'];
                    $replace = $protocol.$domainName . '/' . $wrong . '/';
                }

                $return = str_replace($matches[1], $replace, $matches[0]);

                return $return;
            } else {
                return  $matches[0];
            }
        }, $content);
        $isFinished = true;
        return $content;
    }
}

<?php

// ......

$GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['FrontendEditing']['requestPreProcess'][] = \SCW\Origo\Hooks\PreProcess::class;