import 'package:flutter/foundation.dart';

import 'feature.dart';

/// Unveränderlicher Satz an Feature-Schaltern, geladen aus
/// `assets/feature_flags.json` (siehe [FeatureFlagsRepository]).
///
/// Erwartetes Format:
/// ```json
/// { "features": { "<key>": { "enabled": true, "description": "…" } } }
/// ```
/// `description` ist nur Doku für Menschen. Unbekannte Keys werden
/// ignoriert, fehlende fallen auf [Feature.defaultEnabled] zurück.
@immutable
class FeatureFlags {
  const FeatureFlags(this._enabledByKey);

  factory FeatureFlags.fromJson(Map<String, dynamic> json) {
    final features = json['features'];
    if (features is! Map<String, dynamic>) {
      throw const FormatException('feature_flags.json: "features" fehlt.');
    }
    final knownKeys = {for (final f in Feature.values) f.key};
    final enabledByKey = <String, bool>{};
    features.forEach((key, value) {
      final enabled = value is Map<String, dynamic> ? value['enabled'] : null;
      if (enabled is! bool) {
        throw FormatException(
          'feature_flags.json: "$key.enabled" muss true oder false sein.',
        );
      }
      if (!knownKeys.contains(key)) {
        debugPrint('FeatureFlags: unbekannter Key "$key" wird ignoriert.');
        return;
      }
      enabledByKey[key] = enabled;
    });
    return FeatureFlags(enabledByKey);
  }

  final Map<String, bool> _enabledByKey;

  bool isEnabled(Feature feature) =>
      _enabledByKey[feature.key] ?? feature.defaultEnabled;
}