started improving exception handling

lib/Exceptions/NotFoundException.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace OCA\GroupfolderFilesystemSnapshots\Exceptions;
+
+class NotFoundException extends \RuntimeException {
+	public function __construct($entity, array|string $criteria) {
+		$message = sprintf(
+			"Could not find %s with criteria %s",
+			class_exists($entity) ? array_pop(explode('\\', $entity)) : $entity,
+			is_string($criteria) ? $criteria : json_encode($criteria),
+		);
+		parent::__construct($message);
+	}
+}