diff --git a/lib/Service/DiffTaskService.php b/lib/Service/DiffTaskService.php
index ec1a925..16ebb46 100644
--- a/lib/Service/DiffTaskService.php
+++ b/lib/Service/DiffTaskService.php
@@ -7,6 +7,7 @@ use OCP\AppFramework\Db\DoesNotExistException;
 use OCP\AppFramework\Db\MultipleObjectsReturnedException;
 
 use OCA\GroupfolderFilesystemSnapshots\Exceptions\NotFoundException;
+use OCA\GroupfolderFilesystemSnapshots\Exceptions\InvalidRelativePathException;
 use OCA\GroupfolderFilesystemSnapshots\Db\DiffTask;
 use OCA\GroupfolderFilesystemSnapshots\Db\DiffTaskMapper;
 use OCA\GroupfolderFilesystemSnapshots\Db\DiffTaskResult;
@@ -14,112 +15,120 @@ use OCA\GroupfolderFilesystemSnapshots\Db\DiffTaskResultMapper;
 use OCA\GroupfolderFilesystemSnapshots\Manager\PathManager;
 use OCA\GroupfolderFilesystemSnapshots\RecursiveDiff;
 
-
 class DiffTaskService {
 
-    private DiffTaskMapper $mapper;
-    private DiffTaskResultMapper $diffTaskResultMapper;
-    private PathManager $pathManager;
+	private DiffTaskMapper $mapper;
+	private DiffTaskResultMapper $diffTaskResultMapper;
+	private PathManager $pathManager;
 
-    public function __construct(DiffTaskMapper $mapper, DiffTaskResultMapper $diffTaskResultMapper, PathManager $pathManager){
-        $this->mapper = $mapper;
-        $this->diffTaskResultMapper = $diffTaskResultMapper;
-        $this->pathManager = $pathManager;
-    }
+	public function __construct(
+		DiffTaskMapper $mapper,
+		DiffTaskResultMapper $diffTaskResultMapper,
+		PathManager $pathManager,
+	){
+		$this->mapper = $mapper;
+		$this->diffTaskResultMapper = $diffTaskResultMapper;
+		$this->pathManager = $pathManager;
+	}
 
-    /**
-     * @return DiffTask[]
-     */
-    public function findAll(string $userId): array {
-        return $this->mapper->findAll($userId);
-    }
+	/**
+	 * @return DiffTask[]
+	 */
+	public function findAll(string $userId): array {
+		return $this->mapper->findAll($userId);
+	}
 
-    /**
-     * @return never
-     */
-    private function handleException ($e, $criteria) {
-        if ($e instanceof DoesNotExistException ||
-            $e instanceof MultipleObjectsReturnedException) {
-            throw new NotFoundException($e->getMessage(), $criteria);
-        } else {
-            throw $e;
-        }
-    }
+	/**
+	 * @return never
+	 */
+	private function handleException ($e, $criteria) {
+		if ($e instanceof DoesNotExistException ||
+			$e instanceof MultipleObjectsReturnedException) {
+			throw new NotFoundException($e->getMessage(), $criteria);
+		} else {
+			throw $e;
+		}
+	}
 
-    public function find(int $id, string $userId): DiffTask {
-        try {
-            return $this->mapper->find($id, $userId);
-        } catch(Exception $e) {
-            $this->handleException($e, ["userId" => $userId, "id" => $id]);
-        }
-    }
+	public function find(int $id, string $userId): DiffTask {
+		try {
+			return $this->mapper->find($id, $userId);
+		} catch(Exception $e) {
+			$this->handleException($e, ["userId" => $userId, "id" => $id]);
+		}
+	}
 
-    function create(int $groupfolderId, string $snapshotId, string $userId, Callable $progressCallback = null): DiffTask {
-        $snapshotPath = $this->pathManager->getGroupFolderSnapshotDirectory($groupfolderId, $snapshotId);
-        $groupfolderPath = $this->pathManager->getGroupFolderDirectory($groupfolderId);
+	function create(string $relativePathInGroupfolder, int $groupfolderId, string $snapshotId, string $userId, Callable $progressCallback = null): ?DiffTask {
+		$snapshotPath = $this->pathManager->getGroupFolderSnapshotDirectory($groupfolderId, $relativePathInGroupfolder, $snapshotId);
+		$groupfolderPath = $this->pathManager->getGroupFolderDirectory($groupfolderId, $relativePathInGroupfolder);
 
-        $newTask = new DiffTask();
-        $newTask->setGroupfolderId($groupfolderId);
-        $newTask->setSnapshotId($snapshotId);
-        $newTask->setTimestamp(time());
-        $newTask->setUserId($userId);
-        $task = $this->mapper->insert($newTask);
+		if(!($snapshotPath && $groupfolderPath)) {
+			throw new InvalidRelativePathException;
+		}
 
-        $numFiles = 0;
+		$newTask = new DiffTask();
+		$newTask->setGroupfolderId($groupfolderId);
+		$newTask->setRelativePath($relativePathInGroupfolder);
+		$newTask->setSnapshotId($snapshotId);
+		$newTask->setTimestamp(time());
+		$newTask->setUserId($userId);
+		$task = $this->mapper->insert($newTask);
 
-        $diffTask = new RecursiveDiff(
-            $snapshotPath,
-            $groupfolderPath,
-            "",
-            function(string $type, bool $beforeFileExists, ?string $beforePath, ?int $beforeSize, bool $currentFileExists, ?string $currentPath, ?int $currentSize) use ($task) {
-                $newResult = new DiffTaskResult();
-                $newResult->setTaskId($task->getId());
-                $newResult->setType($type);
-                $newResult->setBeforeFileExists($beforeFileExists);
-                $newResult->setBeforePath($beforePath);
-                $newResult->setBeforeSize($beforeSize);
-                $newResult->setCurrentFileExists($currentFileExists);
-                $newResult->setCurrentPath($currentPath);
-                $newResult->setCurrentSize($currentSize);
-                $newResult = $this->diffTaskResultMapper->insert($newResult);
-            },
-            function($numDoneFiles) use ($progressCallback, &$numFiles) {
-                if(isset($progressCallback) && ($numFiles != 0) && ($numFiles != $numDoneFiles)) {
-                    ($progressCallback)([
-                        "overallFiles" => $numFiles,
-                        "doneFiles" => $numDoneFiles,
-                        "progress" => number_format(($numDoneFiles / $numFiles),2),
-                        "progressPercent" => (number_format(($numDoneFiles / $numFiles),2) * 100) . "%",
-                    ]);
-                }
-            },
-        );
+		$numFiles = 0;
 
-        $numFiles = $diffTask->scan();
+		$diffTask = new RecursiveDiff(
+			$snapshotPath,
+			$groupfolderPath,
+			"",
+			function(string $type, bool $beforeFileExists, ?string $beforePath, ?int $beforeSize, bool $currentFileExists, ?string $currentPath, ?int $currentSize) use ($task) {
+				$newResult = new DiffTaskResult();
+				$newResult->setTaskId($task->getId());
+				$newResult->setType($type);
+				$newResult->setBeforeFileExists($beforeFileExists);
+				$newResult->setBeforePath($beforePath);
+				$newResult->setBeforeSize($beforeSize);
+				$newResult->setCurrentFileExists($currentFileExists);
+				$newResult->setCurrentPath($currentPath);
+				$newResult->setCurrentSize($currentSize);
+				$newResult = $this->diffTaskResultMapper->insert($newResult);
+			},
+			function($numDoneFiles) use ($progressCallback, &$numFiles) {
+				if(isset($progressCallback) && ($numFiles != 0) && ($numFiles != $numDoneFiles)) {
+					($progressCallback)([
+						"overallFiles" => $numFiles,
+						"doneFiles" => $numDoneFiles,
+						"progress" => number_format(($numDoneFiles / $numFiles),2),
+						"progressPercent" => (number_format(($numDoneFiles / $numFiles),2) * 100) . "%",
+					]);
+				}
+			},
+		);
 
-        $diffTask->diff();
+		$numFiles = $diffTask->scan();
 
-        if(isset($progressCallback)) {
-            ($progressCallback)([
-                "overallFiles" => $numFiles,
-                "doneFiles" => $numFiles,
-                "progress" => 1.0,
-                "progressPercent" => "100.00%",
-                "result" => $task,
-            ]);
-        }
+		$diffTask->diff();
 
-        return $task;
-    }
+		if(isset($progressCallback)) {
+			($progressCallback)([
+				"overallFiles" => $numFiles,
+				"doneFiles" => $numFiles,
+				"progress" => 1.0,
+				"progressPercent" => "100.00%",
+				"result" => $task,
+			]);
+		}
 
-    public function delete(int $id, string $userId): DiffTask {
-        try {
-            $task = $this->mapper->find($id, $userId);
-            $this->mapper->delete($task);
-            return $task;
-        } catch(Exception $e) {
-            $this->handleException($e);
-        }
-    }
+		return $task;
+	}
+
+	public function delete(int $id, string $userId): DiffTask {
+		try {
+			$task = $this->mapper->find($id, $userId);
+			$this->mapper->delete($task);
+			return $task;
+		} catch(Exception $e) {
+			$this->handleException($e);
+		}
+	}
 
 }
\ No newline at end of file