Add functionality to edit sheets with save and restore

lib/storage_helper.dart

@@ -1,5 +1,6 @@
 import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 import 'package:hive/hive.dart';
+import 'package:sheetless/upload_queue.dart';
 
 enum SecureStorageKey { url, jwt, email }
 
@@ -18,6 +19,7 @@ class Config {
 class StorageHelper {
   final sheetAccessTimesBox = "sheetAccessTimes";
   final configBox = "config";
+  final changeQueueBox = "changeQueue";
 
   late FlutterSecureStorage secureStorage;
 
@@ -60,4 +62,23 @@ class StorageHelper {
     final box = await Hive.openBox(sheetAccessTimesBox);
     await box.put(uuid, datetime.toIso8601String());
   }
+
+  Future<void> writeChange(Change change) async {
+    final box = await Hive.openBox(changeQueueBox);
+    box.add(change.toMap());
+  }
+
+  Future<ChangeQueue> readChangeQueue() async {
+    final box = await Hive.openBox(changeQueueBox);
+    ChangeQueue queue = ChangeQueue();
+    for (Map<dynamic, dynamic> map in box.values) {
+      queue.addChange(Change.fromMap(map));
+    }
+    return queue;
+  }
+
+  Future<void> deleteOldestChange(Change change) async {
+    final box = await Hive.openBox(changeQueueBox);
+    box.deleteAt(0);
+  }
 }