Flutter Feature Flags

3. Evaluate flags

import 'dart:convert';
import 'package:http/http.dart' as http;

class FlagBit {
  static const String _url = 'https://flagbit.anethoth.com/api/v1/evaluate';
  static String sdkKey = const String.fromEnvironment('FLAGBIT_SDK_KEY');
  static final Map<String, bool> _cache = {};

  static Future<bool> isEnabled(String flagKey, {Map<String, String>? context}) async {
    final cacheKey = '\$flagKey:\${context.hashCode}';
    if (_cache.containsKey(cacheKey)) return _cache[cacheKey]!;

    try {
      final resp = await http.post(
        Uri.parse(_url),
        headers: {'Content-Type': 'application/json', 'X-SDK-Key': sdkKey},
        body: jsonEncode({'flag_key': flagKey, 'context': context ?? {}}),
      );
      final value = jsonDecode(resp.body)['value'] as bool;
      _cache[cacheKey] = value;
      return value;
    } catch (_) {
      return false;
    }
  }
}

// Widget usage
class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder<bool>(
      future: FlagBit.isEnabled('new-home-layout', context: {'user_id': userId}),
      builder: (ctx, snapshot) {
        if (snapshot.data == true) {
          return NewHomeLayout();
        }
        return ClassicHomeLayout();
      },
    );
  }
}

// Provider pattern for app-wide flags
class FeatureFlagProvider extends ChangeNotifier {
  final Map<String, bool> _flags = {};

  Future<void> loadFlags(List<String> keys) async {
    for (final key in keys) {
      _flags[key] = await FlagBit.isEnabled(key);
    }
    notifyListeners();
  }

  bool isEnabled(String key) => _flags[key] ?? false;
}