Only save annotations on changes

lib/features/sheet_viewer/drawing/drawing_controller.dart

@@ -51,6 +51,9 @@ class DrawingController extends ChangeNotifier {
   /// Maximum number of history steps to keep
   final int maxHistorySteps;
 
+  /// Whether there are unsaved changes since last load/clear
+  bool _hasUnsavedChanges = false;
+
   DrawingController({this.maxHistorySteps = 50});
 
   // ---------------------------------------------------------------------------
@@ -75,6 +78,9 @@ class DrawingController extends ChangeNotifier {
   /// Whether redo is available
   bool get canRedo => _redoStack.isNotEmpty;
 
+  /// Whether there are unsaved changes since last load/clear/markSaved
+  bool get hasUnsavedChanges => _hasUnsavedChanges;
+
   // ---------------------------------------------------------------------------
   // Drawing Operations
   // ---------------------------------------------------------------------------
@@ -120,6 +126,7 @@ class DrawingController extends ChangeNotifier {
         _redoStack.clear();
         _trimHistory();
         _currentErasedLines.clear();
+        _hasUnsavedChanges = true;
         notifyListeners(); // Update UI to enable undo button
       }
       return;
@@ -133,6 +140,7 @@ class DrawingController extends ChangeNotifier {
       _undoStack.add(AddLineAction(_currentLine!));
       _redoStack.clear();
       _trimHistory();
+      _hasUnsavedChanges = true;
     }
 
     _currentLine = null;
@@ -257,6 +265,7 @@ class DrawingController extends ChangeNotifier {
         _redoStack.add(action);
     }
 
+    _hasUnsavedChanges = true;
     notifyListeners();
   }
 
@@ -279,6 +288,7 @@ class DrawingController extends ChangeNotifier {
         _undoStack.add(action);
     }
 
+    _hasUnsavedChanges = true;
     notifyListeners();
   }
 
@@ -289,6 +299,7 @@ class DrawingController extends ChangeNotifier {
     _redoStack.clear();
     _currentLine = null;
     _currentErasedLines.clear();
+    _hasUnsavedChanges = false;
     notifyListeners();
   }
 
@@ -324,6 +335,7 @@ class DrawingController extends ChangeNotifier {
     _redoStack.clear();
     _currentLine = null;
     _currentErasedLines.clear();
+    _hasUnsavedChanges = false;
 
     for (final json in jsonList) {
       _lines.add(DrawingLine.fromJson(json));
@@ -354,6 +366,11 @@ class DrawingController extends ChangeNotifier {
     notifyListeners();
   }
 
+  /// Marks the current state as saved (resets unsaved changes flag).
+  void markSaved() {
+    _hasUnsavedChanges = false;
+  }
+
   @override
   void dispose() {
     _lines.clear();

lib/features/sheet_viewer/sheet_viewer_page.dart

@@ -103,7 +103,7 @@ class _SheetViewerPageState extends State<SheetViewerPage>
     });
 
     // Sync annotations from server (downloads newer versions)
-    await _syncService.syncAnnotationsFromServer(widget.sheet.uuid);
+    await _syncService.syncFromServer(widget.sheet.uuid);
 
     // Load annotations for current page(s)
     await _loadAnnotationsForCurrentPages();
@@ -143,10 +143,13 @@ class _SheetViewerPageState extends State<SheetViewerPage>
   }
 
   /// Saves the current page(s) annotations to storage and uploads to server.
+  ///
+  /// Only saves if there are actual changes to avoid unnecessary writes/uploads.
   Future<void> _saveCurrentAnnotations() async {
     final now = DateTime.now();
 
-    // Save left page
+    // Save left page only if changed
+    if (_leftDrawingController.hasUnsavedChanges) {
       final leftJson = _leftDrawingController.toJsonString();
       final leftHasContent = leftJson.isNotEmpty && leftJson != '[]';
 
@@ -167,8 +170,13 @@ class _SheetViewerPageState extends State<SheetViewerPage>
         );
       }
 
-    // Save right page (two-page mode)
-    if (widget.config.twoPageMode && _currentPage < _totalPages) {
+      _leftDrawingController.markSaved();
+    }
+
+    // Save right page (two-page mode) only if changed
+    if (widget.config.twoPageMode &&
+        _currentPage < _totalPages &&
+        _rightDrawingController.hasUnsavedChanges) {
       final rightJson = _rightDrawingController.toJsonString();
       final rightHasContent = rightJson.isNotEmpty && rightJson != '[]';
 
@@ -188,6 +196,8 @@ class _SheetViewerPageState extends State<SheetViewerPage>
           lastModified: now,
         );
       }
+
+      _rightDrawingController.markSaved();
     }
   }
 
@@ -290,9 +300,8 @@ class _SheetViewerPageState extends State<SheetViewerPage>
           icon: Icon(
             widget.config.fullscreen ? Icons.fullscreen_exit : Icons.fullscreen,
           ),
-          tooltip: widget.config.fullscreen
-              ? 'Exit Fullscreen'
-              : 'Enter Fullscreen',
+          tooltip:
+              widget.config.fullscreen ? 'Exit Fullscreen' : 'Enter Fullscreen',
           onPressed: _toggleFullscreen,
         ),
         IconButton(
@@ -304,9 +313,8 @@ class _SheetViewerPageState extends State<SheetViewerPage>
           icon: Icon(
             widget.config.twoPageMode ? Icons.filter_1 : Icons.filter_2,
           ),
-          tooltip: widget.config.twoPageMode
-              ? 'Single Page Mode'
-              : 'Two Page Mode',
+          tooltip:
+              widget.config.twoPageMode ? 'Single Page Mode' : 'Two Page Mode',
           onPressed: _toggleTwoPageMode,
         ),
       ],
@@ -338,9 +346,8 @@ class _SheetViewerPageState extends State<SheetViewerPage>
       currentPageNumber: _currentPage,
       config: widget.config,
       leftDrawingController: _leftDrawingController,
-      rightDrawingController: widget.config.twoPageMode
-          ? _rightDrawingController
-          : null,
+      rightDrawingController:
+          widget.config.twoPageMode ? _rightDrawingController : null,
       drawingEnabled: _isPaintMode,
     );