Hook into Tcemain to clear custom cachetags

DataHandler.php

<?php

namespace Vendor\Extension\Hooks;

use TYPO3\CMS\Backend\Utility\BackendUtility;
use TYPO3\CMS\Core\Cache\CacheManager;
use TYPO3\CMS\Core\Cache\Exception\NoSuchCacheGroupException;
use TYPO3\CMS\Core\Database\ReferenceIndex;
use TYPO3\CMS\Core\SingletonInterface;
use TYPO3\CMS\Core\Utility\ExtensionManagementUtility;
use TYPO3\CMS\Core\Utility\GeneralUtility;

/**
 * Hook into tcemain to clear the cachetags
 */
class DataHandler implements SingletonInterface
{
    protected array $cacheTagsToFlush = [];

    /**
     * [$tablename][$uid] = number of references to this record
     *
     * @var int[][]
     */
    protected array $referenceCount = [];


    /**
     * Flushes the cache if a tt_content record was edited, when it has references set by shortcut CE
     * This happens on two levels: by UID and by PID.
     *
     * @param array $params
     *
     * @return void
     * @throws NoSuchCacheGroupException
     */
    public function clearCachePostProc(array $params): void
    {
        $table = $params['table'];
        $uid = $params['uid'];

        $cacheManager = GeneralUtility::makeInstance(CacheManager::class);

        if (isset($table, $uid) && $table === 'tt_content') {
            if ($this->getReferenceCount($table, $uid) > 0) {
                $this->cacheTagsToFlush[] = 'shortcut_' . $table . '_' . $uid;
            }

            $emUtility = GeneralUtility::makeInstance(ExtensionManagementUtility::class);
            // If EXT:flux is loaded, we need to check if the current element is a child record
            // In flux we can guess this by cutting off the last two digits from `colPos` value and check is this
            // new colPos value equals an uid in tt_content table
            if ($emUtility::isLoaded('flux')) {
                $element = BackendUtility::getRecord(
                    $table,
                    $uid
                );
                $uidOfParent = substr($element['colPos'], 0, -2);
                $parentElement = BackendUtility::getRecord(
                    $table,
                    $uidOfParent
                );
                if (isset($parentElement) && $this->getReferenceCount($table, $uidOfParent) > 0) {
                    $this->cacheTagsToFlush[] = 'shortcut_' . $table . '_' . $uidOfParent;
                }
            }

            // If EXT:gridelements is loaded, we need to check if the current element is a child record
            // @todo
            #if ($emUtility::isLoaded('gridelements')) {
            #}

            // If EXT:gridelements is loaded, we need to check if the current element is a child record
            // @todo
            #if ($emUtility::isLoaded('container')) {
            #}
        }
        if (!empty($this->cacheTagsToFlush)) {

            foreach (array_unique($this->cacheTagsToFlush) as $cacheTag) {
                $cacheManager->flushCachesInGroupByTag('pages', $cacheTag);
            }
        }
    }

    /**
     * Gets the number of records referencing the record with the UID $uid in
     * the table $tableName.
     *
     * @param string $tableName
     * @param int $uid
     * @return int The number of references to record $uid in table
     */
    protected function getReferenceCount($tableName, $uid)
    {
        if (!isset($this->referenceCount[$tableName][$uid])) {
            $referenceIndex = GeneralUtility::makeInstance(ReferenceIndex::class);
            $numberOfReferences = $referenceIndex->getNumberOfReferencedRecords($tableName, $uid);
            $this->referenceCount[$tableName][$uid] = $numberOfReferences;
        }
        return $this->referenceCount[$tableName][$uid];
    }
}