onedirve and google drive

lib/screens/add_edit_vehicle_screen.dart

@@ -9,6 +9,7 @@ import '../services/app_state.dart';
 import '../services/ocr_service.dart';
 import '../services/vin_parser.dart';
 import '../widgets/image_source_sheet.dart';
+import 'vehicle_detail_screen.dart';
 
 /// Add/edit form for a vehicle. Pass an existing [vehicle] to edit it, or
 /// omit it to create a new one.
@@ -28,6 +29,7 @@ class _AddEditVehicleScreenState extends State<AddEditVehicleScreen> {
 
   bool _saving = false;
   bool _scanningVin = false;
+  bool _checkingDuplicateVin = false;
   String? _error;
 
   bool get _isEditing => widget.vehicle != null;
@@ -84,6 +86,7 @@ class _AddEditVehicleScreenState extends State<AddEditVehicleScreen> {
 
     if (vin != null) {
       _vinController.text = vin;
+      await _checkForExistingVin();
     } else if (mounted) {
       ScaffoldMessenger.of(context).showSnackBar(
         const SnackBar(
@@ -93,6 +96,62 @@ class _AddEditVehicleScreenState extends State<AddEditVehicleScreen> {
     }
   }
 
+  /// Field-level counterpart to [_checkForExistingVin]'s dialog: catches
+  /// "Required" as before, plus flags the field itself as invalid when the
+  /// VIN belongs to another active vehicle — excluding this vehicle's own
+  /// id while editing, same as [AppState.updateVehicle]'s check, so editing
+  /// a vehicle without touching its VIN doesn't flag itself.
+  String? _validateVin(String? value) {
+    final vin = value?.trim() ?? '';
+    if (vin.isEmpty) return 'Required';
+
+    final existing = context.read<AppState>().vehicleByVin(vin);
+    if (existing != null && existing.id != widget.vehicle?.id) {
+      return 'A vehicle with VIN "$vin" already exists.';
+    }
+    return null;
+  }
+
+  /// Only relevant when adding a new vehicle — editing one already starts
+  /// with its own VIN pre-filled, which would trivially "match itself".
+  /// Guarded against overlapping calls so rapid edits (or the scan-fill
+  /// path firing right after `onChanged`) can't stack multiple dialogs.
+  Future<void> _checkForExistingVin() async {
+    if (_isEditing || _checkingDuplicateVin) return;
+
+    final vin = _vinController.text.trim();
+    if (vin.isEmpty) return;
+    final existing = context.read<AppState>().vehicleByVin(vin);
+    if (existing == null) return;
+
+    _checkingDuplicateVin = true;
+    final openExisting = await showDialog<bool>(
+      context: context,
+      builder: (context) => AlertDialog(
+        title: const Text('Vehicle already exists'),
+        content: Text('Vehicle with the VIN $vin already exists, would you like to open that vehicle?'),
+        actions: [
+          TextButton(onPressed: () => Navigator.of(context).pop(false), child: const Text('No')),
+          TextButton(onPressed: () => Navigator.of(context).pop(true), child: const Text('Yes')),
+        ],
+      ),
+    );
+    _checkingDuplicateVin = false;
+    if (!mounted) return;
+
+    if (openExisting != true) {
+      // Declining to open the existing vehicle leaves them here with a
+      // still-duplicate VIN — surface that on the field itself rather than
+      // only catching it later at Save.
+      _formKey.currentState?.validate();
+      return;
+    }
+
+    Navigator.of(context)
+      ..pop()
+      ..push(MaterialPageRoute(builder: (_) => VehicleDetailScreen(vehicleId: existing.id)));
+  }
+
   Future<void> _save() async {
     if (!_formKey.currentState!.validate()) return;
 
@@ -205,7 +264,8 @@ class _AddEditVehicleScreenState extends State<AddEditVehicleScreen> {
                       ),
               ),
               textCapitalization: TextCapitalization.characters,
-              validator: (v) => (v == null || v.trim().isEmpty) ? 'Required' : null,
+              validator: _validateVin,
+              onChanged: _isEditing ? null : (_) => _checkForExistingVin(),
             ),
             if (_error != null) ...[
               const SizedBox(height: 12),