Added core data models, repositories, and utilities

lifetimer/lib/data/repositories/countdown_repository.dart

@@ -0,0 +1,62 @@
+import 'package:supabase_flutter/supabase_flutter.dart' as supabase;
+import '../models/user_model.dart' as app;
+import '../../core/utils/date_time_utils.dart';
+import '../../core/errors/failure.dart';
+
+class CountdownRepository {
+  final supabase.SupabaseClient _client;
+
+  CountdownRepository(this._client);
+
+  Future<app.User> startCountdown(String userId) async {
+    try {
+      final startDate = DateTime.now();
+      final endDate = DateTimeUtils.calculateEndDate(startDate);
+
+      final response = await _client
+          .from('users')
+          .update({
+            'countdown_start_date': startDate.toIso8601String(),
+            'countdown_end_date': endDate.toIso8601String(),
+            'updated_at': DateTime.now().toIso8601String(),
+          })
+          .eq('id', userId)
+          .select()
+          .single();
+
+      return app.User.fromJson(response);
+    } catch (e) {
+      throw _handleError(e);
+    }
+  }
+
+  Future<app.User> getCountdownInfo(String userId) async {
+    try {
+      final response = await _client
+          .from('users')
+          .select()
+          .eq('id', userId)
+          .single();
+
+      return app.User.fromJson(response);
+    } catch (e) {
+      throw _handleError(e);
+    }
+  }
+
+  Future<bool> hasCountdownStarted(String userId) async {
+    try {
+      final user = await getCountdownInfo(userId);
+      return user.countdownStartDate != null;
+    } catch (e) {
+      throw _handleError(e);
+    }
+  }
+
+  Failure _handleError(dynamic error) {
+    if (error is supabase.PostgrestException) {
+      return ServerFailure(error.message);
+    }
+    return UnknownFailure(error.toString());
+  }
+}