feat: add remote pull and push

lib/services/bar_tab_service.dart

@@ -87,6 +87,7 @@ class DriftBarTabService implements BarTabService {
       status: row.status,
       openedAt: row.openedAt,
       closedAt: row.closedAt,
+      version: row.version,
       items: items,
     );
   }
@@ -292,6 +293,7 @@ class DriftBarTabService implements BarTabService {
   @override
   Future<BarTab> createTab({required String customerName}) async {
     final id = _uuid.v4();
+    final now = DateTime.now();
 
     await database
         .into(database.barTabs)
@@ -300,7 +302,8 @@ class DriftBarTabService implements BarTabService {
             id: id,
             customerName: customerName,
             status: const Value('open'),
-            openedAt: DateTime.now(),
+            openedAt: now,
+            version: const Value(1),
           ),
         );
 
@@ -335,6 +338,8 @@ class DriftBarTabService implements BarTabService {
     if (updatedRows != 1) {
       throw StateError('Tab not found.');
     }
+
+    await _incrementTabVersion(tabId);
   }
 
   @override
@@ -368,6 +373,14 @@ class DriftBarTabService implements BarTabService {
     });
   }
 
+  Future<void> _incrementTabVersion(String tabId) async {
+    await database.customUpdate(
+      'UPDATE bar_tabs SET version = version + 1 WHERE id = ?',
+      variables: [Variable.withString(tabId)],
+      updates: {database.barTabs},
+    );
+  }
+
   @override
   Future<void> addProductToTab({
     required String tabId,
@@ -414,6 +427,8 @@ class DriftBarTabService implements BarTabService {
 
       await _recordPurchase(tabItemId: tabItemId);
     });
+
+    await _incrementTabVersion(tabId);
   }
 
   @override
@@ -421,7 +436,9 @@ class DriftBarTabService implements BarTabService {
     required String tabItemId,
     required int delta,
   }) async {
-    return database.transaction(() async {
+    String? tabId;
+
+    final actualDelta = await database.transaction(() async {
       final item = await (database.select(
         database.tabItems,
       )..where((row) => row.id.equals(tabItemId))).getSingleOrNull();
@@ -430,6 +447,8 @@ class DriftBarTabService implements BarTabService {
         return 0;
       }
 
+      tabId = item.tabId;
+
       final requestedQuantity = item.quantity + delta;
       final actualDelta = requestedQuantity <= 0 ? -item.quantity : delta;
 
@@ -483,6 +502,12 @@ class DriftBarTabService implements BarTabService {
 
       return actualDelta;
     });
+
+    if (tabId != null && actualDelta != 0) {
+      await _incrementTabVersion(tabId!);
+    }
+
+    return actualDelta;
   }
 
   @override
@@ -544,6 +569,8 @@ class DriftBarTabService implements BarTabService {
 
       await deleteQuery.go();
     });
+
+    await _incrementTabVersion(tabId);
   }
 
   @override