feat: migrate owncloud guests-users to nextcloud guests

Signed-off-by: skjnldsv <skjnldsv@protonmail.com>

appinfo/info.xml

@@ -33,6 +33,11 @@ Guests users can only access files shared to them and cannot create any files ou
 	<dependencies>
 		<nextcloud min-version="30" max-version="31" />
 	</dependencies>
+	<repair-steps>
+		<pre-migration>
+			<step>OCA\Guests\Migration\OwncloudGuestsMigration</step>
+		</pre-migration>
+	</repair-steps>
 	<commands>
 		<command>OCA\Guests\Command\ListCommand</command>
 		<command>OCA\Guests\Command\AddCommand</command>

lib/Migration/OwncloudGuestsMigration.php

@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+namespace OCA\Guests\Migration;
+
+use OCP\IConfig;
+use OCP\IDBConnection;
+use OCP\Migration\IOutput;
+use OCP\Migration\IRepairStep;
+use Psr\Log\LoggerInterface;
+
+class OwncloudGuestsMigration implements IRepairStep {
+
+	protected $cachedUserIDs = [];
+
+	public function __construct(
+		protected LoggerInterface $logger,
+		protected IDBConnection $db,
+		protected IConfig $config,
+	) {}
+
+	public function getName(): string {
+		return 'Converts owncloud guests to nextcloud guests';
+	}
+
+	public function run(IOutput $output): void {
+		if (!$this->shouldRun()) {
+			$this->logger->info('Skipping owncloud guests migration, no owncloud guests found');
+			return;
+		}
+	}
+
+	protected function shouldRun(): bool{
+		$schema = $this->db->createSchema();
+		$prefix = $this->config->getSystemValueString('dbtableprefix', 'oc_');
+
+		$tableName = $prefix . 'preferences';
+		if (!$schema->hasTable($tableName)) {
+			return false;
+		}
+
+		// Get all rows where configkey `isGuest` is set to 1
+		$query = $this->db->getQueryBuilder();
+		$query->select('userid')
+			->from($tableName)
+			->where($query->expr()->eq('appid', $query->createNamedParameter('owncloud')))
+			->andWhere($query->expr()->eq('configkey', $query->createNamedParameter('isGuest')))
+			->andWhere($query->expr()->eq('configvalue', $query->createNamedParameter('1')));
+
+		$result = $query->executeQuery();
+		$count = $result->rowCount();
+		if ($count === 0) {
+			return false;
+		}
+
+		$this->logger->info("Found $count owncloud guests to migrate");
+		$this->cachedUserIDs = $result->fetchAll();
+
+		return true;
+	}
+
+	/**
+	 * For each old guest user, we do the following:
+	 * 1. Create a new guest with the same username and password
+	 * 2. register a new transfer
+	 * 3. Delete the old user
+	 * 4. Delete the old preferences row
+	 */
+	protected function runStep() {
+
+	}
+}