fix(mobile): keep timezone when editing asset date time (#28978)

* fix(mobile): keep timezone when editing asset date time

* fix(mobile): negative utc offsets with minutes off by an hour

mobile/lib/infrastructure/repositories/remote_asset.repository.dart

@@ -194,12 +194,15 @@ class RemoteAssetRepository extends DriftDatabaseRepository {
     });
   }
 
-  Future<void> updateDateTime(List<String> ids, DateTime dateTime) {
+  Future<void> updateDateTime(List<String> ids, DateTime dateTime, {String? timeZone}) {
     return _db.batch((batch) async {
       for (final id in ids) {
         batch.update(
           _db.remoteExifEntity,
-          RemoteExifEntityCompanion(dateTimeOriginal: Value(dateTime)),
+          RemoteExifEntityCompanion(
+            dateTimeOriginal: Value(dateTime),
+            timeZone: timeZone == null ? const Value.absent() : Value(timeZone),
+          ),
           where: (e) => e.assetId.equals(id),
         );
         batch.update(

mobile/lib/repositories/asset_api.repository.dart

@@ -59,10 +59,8 @@ class AssetApiRepository extends ApiRepository {
     );
   }
 
-  Future<void> updateDateTime(List<String> ids, DateTime dateTime) async {
-    return _api.updateAssets(
-      AssetBulkUpdateDto(ids: ids, dateTimeOriginal: Optional.present(dateTime.toIso8601String())),
-    );
+  Future<void> updateDateTime(List<String> ids, String dateTime) async {
+    return _api.updateAssets(AssetBulkUpdateDto(ids: ids, dateTimeOriginal: Optional.present(dateTime)));
   }
 
   Future<StackResponse> stack(List<String> ids) async {

mobile/lib/services/action.service.dart

@@ -206,15 +206,24 @@ class ActionService {
       return false;
     }
 
-    // convert dateTime to DateTime object
-    final parsedDateTime = DateTime.parse(dateTime);
-
-    await _assetApiRepository.updateDateTime(remoteIds, parsedDateTime);
-    await _remoteAssetRepository.updateDateTime(remoteIds, parsedDateTime);
+    await applyDateTime(remoteIds, dateTime);
 
     return true;
   }
 
+  @visibleForTesting
+  Future<void> applyDateTime(List<String> remoteIds, String dateTime) async {
+    final parsedDateTime = DateTime.parse(dateTime);
+    final offset = RegExp(r'[+-]\d{2}:\d{2}$').firstMatch(dateTime)?.group(0);
+
+    await _assetApiRepository.updateDateTime(remoteIds, dateTime);
+    await _remoteAssetRepository.updateDateTime(
+      remoteIds,
+      parsedDateTime,
+      timeZone: offset == null ? null : 'UTC$offset',
+    );
+  }
+
   Future<int> removeFromAlbum(List<String> remoteIds, String albumId) async {
     final result = await _albumApiRepository.removeAssets(albumId, remoteIds);
     if (result.removed.isNotEmpty) {

mobile/lib/utils/timezone.dart

@@ -24,7 +24,9 @@ import 'package:timezone/timezone.dart';
     RegExp re = RegExp(r'^utc(?:([+-]\d{1,2})(?::(\d{2}))?)?$', caseSensitive: false);
     final m = re.firstMatch(timeZone);
     if (m != null) {
-      final duration = Duration(hours: int.parse(m.group(1) ?? '0'), minutes: int.parse(m.group(2) ?? '0'));
+      final hours = int.parse(m.group(1) ?? '0');
+      final minutes = int.parse(m.group(2) ?? '0');
+      final duration = Duration(hours: hours, minutes: hours.isNegative ? -minutes : minutes);
       dt = dt.add(duration);
       return (dt, duration);
     }

mobile/test/services/action.service_test.dart

@@ -99,6 +99,49 @@ void main() {
     });
   });
 
+  group('ActionService.applyDateTime', () {
+    const ids = ['asset_id_1'];
+
+    test('sends the picked value to the api with its offset intact', () async {
+      const picked = '2026-06-10T19:15:00.000+06:00';
+      when(() => assetApiRepository.updateDateTime(ids, picked)).thenAnswer((_) async {});
+      when(
+        () => remoteAssetRepository.updateDateTime(ids, DateTime.parse(picked), timeZone: 'UTC+06:00'),
+      ).thenAnswer((_) async {});
+
+      await sut.applyDateTime(ids, picked);
+
+      verify(() => assetApiRepository.updateDateTime(ids, picked)).called(1);
+      verify(() => remoteAssetRepository.updateDateTime(ids, DateTime.parse(picked), timeZone: 'UTC+06:00')).called(1);
+    });
+
+    test('handles negative offsets', () async {
+      const picked = '2026-01-05T08:00:00.000-05:30';
+      when(() => assetApiRepository.updateDateTime(ids, picked)).thenAnswer((_) async {});
+      when(
+        () => remoteAssetRepository.updateDateTime(ids, DateTime.parse(picked), timeZone: 'UTC-05:30'),
+      ).thenAnswer((_) async {});
+
+      await sut.applyDateTime(ids, picked);
+
+      verify(() => assetApiRepository.updateDateTime(ids, picked)).called(1);
+      verify(() => remoteAssetRepository.updateDateTime(ids, DateTime.parse(picked), timeZone: 'UTC-05:30')).called(1);
+    });
+
+    test('writes no timezone when the value has no offset', () async {
+      const picked = '2026-06-10T13:15:00.000Z';
+      when(() => assetApiRepository.updateDateTime(ids, picked)).thenAnswer((_) async {});
+      when(
+        () => remoteAssetRepository.updateDateTime(ids, DateTime.parse(picked), timeZone: null),
+      ).thenAnswer((_) async {});
+
+      await sut.applyDateTime(ids, picked);
+
+      verify(() => assetApiRepository.updateDateTime(ids, picked)).called(1);
+      verify(() => remoteAssetRepository.updateDateTime(ids, DateTime.parse(picked), timeZone: null)).called(1);
+    });
+  });
+
   group('ActionService.deleteLocal', () {
     test('routes deleted ids to trashed repository when Android trash handling is enabled', () async {
       await Store.put(StoreKey.manageLocalMediaAndroid, true);

mobile/test/unit/utils/timezone_test.dart

@@ -177,6 +177,32 @@ void main() {
         expect(adjustedTime.minute, 30);
         expect(offset, const Duration(hours: 5, minutes: 30));
       });
+
+      test('should handle UTC-05:30 format (negative offset with minutes)', () {
+        final utcTime = DateTime.utc(2024, 6, 15, 12, 0, 0);
+
+        final (adjustedTime, offset) = applyTimezoneOffset(
+          dateTime: utcTime,
+          timeZone: 'UTC-05:30',
+        );
+
+        expect(adjustedTime.hour, 6);
+        expect(adjustedTime.minute, 30); // 12:00 UTC - 5:30 = 06:30
+        expect(offset, const Duration(hours: -5, minutes: -30));
+      });
+
+      test('should handle UTC-3:30 format (single digit hour with minutes)', () {
+        final utcTime = DateTime.utc(2024, 6, 15, 12, 0, 0);
+
+        final (adjustedTime, offset) = applyTimezoneOffset(
+          dateTime: utcTime,
+          timeZone: 'UTC-3:30',
+        );
+
+        expect(adjustedTime.hour, 8);
+        expect(adjustedTime.minute, 30); // 12:00 UTC - 3:30 = 08:30
+        expect(offset, const Duration(hours: -3, minutes: -30));
+      });
     });
 
     group('with null or invalid timezone', () {