added ad provider

filcnaplo/lib/api/providers/ad_provider.dart

@@ -0,0 +1,29 @@
+import 'package:filcnaplo/api/client.dart';
+import 'package:filcnaplo/models/ad.dart';
+import 'package:flutter/material.dart';
+
+class AdProvider extends ChangeNotifier {
+  // private
+  late List<Ad> _ads;
+  bool get available => _ads.isNotEmpty;
+
+  // public
+  List<Ad> get ads => _ads;
+
+  AdProvider({
+    List<Ad> initialAds = const [],
+    required BuildContext context,
+  }) {
+    _ads = List.castFrom(initialAds);
+  }
+
+  Future<void> fetch() async {
+    _ads = await FilcAPI.getAds() ?? [];
+    _ads.sort((a, b) => -a.date.compareTo(b.date));
+
+    // check for new ads
+    if (_ads.isNotEmpty) {
+      notifyListeners();
+    }
+  }
+}