Ensure offline support works in linux

Author: stnguyen90

templates/flutter/lib/src/client_offline_mixin.dart.twig

@@ -10,7 +10,9 @@ import 'package:sembast/utils/value_utils.dart';
 
 import 'enums.dart';
 import 'exception.dart';
-import 'offline_db.dart';
+import 'offline_db_stub.dart'
+    if (dart.library.html) 'offline_db_web.dart'
+    if (dart.library.io) 'offline_db_io.dart';
 import 'response.dart';
 
 class AccessTimestamp {

templates/flutter/lib/src/offline_db_io.dart.twig

@@ -0,0 +1,25 @@
+import 'dart:io';
+
+import 'package:sembast/sembast.dart';
+import 'package:sembast_sqflite/sembast_sqflite.dart';
+import 'package:sqflite/sqflite.dart' as sqflite;
+import 'package:sqflite_common_ffi/sqflite_ffi.dart';
+
+class OfflineDatabase {
+  static final OfflineDatabase instance = OfflineDatabase._internal();
+  Database? _db;
+
+  OfflineDatabase._internal();
+
+  Future<Database> db() async {
+    if (_db == null) {
+      final factory = getDatabaseFactorySqflite(
+        Platform.isLinux || Platform.isWindows
+            ? databaseFactoryFfi
+            : sqflite.databaseFactory,
+      );
+      _db = await factory.openDatabase('{{ spec.title | caseLower }}.db');
+    }
+    return _db!;
+  }
+}

templates/flutter/lib/src/offline_db_stub.dart.twig

@@ -0,0 +1,12 @@
+import 'package:sembast/sembast.dart';
+
+class OfflineDatabase {
+  static final OfflineDatabase instance = OfflineDatabase._internal();
+  Database? _db;
+
+  OfflineDatabase._internal();
+
+  Future<Database> db() async {
+    throw UnimplementedError();
+  }
+}

templates/flutter/lib/src/offline_db_web.dart.twig

@@ -0,0 +1,17 @@
+import 'package:sembast/sembast.dart';
+import 'package:sembast_web/sembast_web.dart';
+
+class OfflineDatabase {
+  static final OfflineDatabase instance = OfflineDatabase._internal();
+  Database? _db;
+
+  OfflineDatabase._internal();
+
+  Future<Database> db() async {
+    if (_db == null) {
+      final factory = databaseFactoryWeb;
+      _db = await factory.openDatabase('{{ spec.title | caseLower }}.db');
+    }
+    return _db!;
+  }
+}

templates/flutter/pubspec.yaml.twig

@@ -23,6 +23,7 @@ dependencies:
   path: ^1.8.2
   sembast: ^3.4.0+6
   sembast_sqflite: ^2.1.0+1
+  sqflite_common_ffi: ^2.2.2
   sembast_web: ^2.1.0+4
   sqflite: ^2.2.2