<?php
/** Retry only complete, rollback-safe database work; never put email delivery here. */
final class DatabaseTransaction {
    public static function run(PDO $db,callable $work): mixed {
        if($db->inTransaction())throw new LogicException('Retryable work must own its transaction.');
        for($attempt=1;$attempt<=3;$attempt++){
            $db->beginTransaction();
            try{
                $result=$work($db);$db->commit();return $result;
            }catch(Throwable $error){
                if($db->inTransaction())$db->rollBack();
                $retryable=$error instanceof PDOException && (in_array((int)($error->errorInfo[1]??0),[1205,1213],true)||$error->getCode()==='40001');
                if(!$retryable||$attempt===3)throw $error;
                usleep(random_int(10000,30000)*$attempt);
            }
        }
        throw new LogicException('Transaction attempts exhausted.');
    }
}