import 'package:flutter/foundation.dart';

import 'license_service.dart';
import 'models.dart';
import 'order_api.dart';
import 'payment_service.dart';

enum PayState { idle, loading, success, failed }

@immutable
class PaywallUiState {
  final PayState state;
  final String? message;
  final Plan? selectedPlan;

  const PaywallUiState({
    this.state = PayState.idle,
    this.message,
    this.selectedPlan,
  });
}

class PaywallViewModel extends ChangeNotifier {
  final OrderApi orderApi;
  final LicenseService licenseService;
  final Map<PayChannel, PaymentService> services;

  PaywallUiState _state = const PaywallUiState();
  PaywallUiState get state => _state;

  List<Plan> _plans = const [];
  bool _plansLoading = false;
  String? _plansError;

  /// 套餐价格方案（来自后端，客户端不硬编码）
  List<Plan> get plans => _plans;
  bool get plansLoading => _plansLoading;
  String? get plansError => _plansError;

  PaywallViewModel({
    required this.orderApi,
    required this.licenseService,
    required this.services,
  });

  /// 进充值页时拉取套餐；已有数据或加载中跳过，失败可重试
  Future<void> loadPlans() async {
    if (_plans.isNotEmpty || _plansLoading) return;
    _plansLoading = true;
    _plansError = null;
    notifyListeners();
    try {
      _plans = await orderApi.fetchPlans();
    } on SessionExpiredException {
      _plansError = '登录已失效，请重新登录后再充值';
    } on OrderApiException catch (e) {
      _plansError = e.message;
    } finally {
      _plansLoading = false;
      notifyListeners();
    }
  }

  void selectPlan(Plan? plan) {
    _state = PaywallUiState(selectedPlan: plan);
    notifyListeners();
  }

  /// 发起支付；成功后刷新授权并通知页面进入相机
  Future<LicenseStatus?> pay(PayChannel channel) async {
    final plan = _state.selectedPlan;
    if (plan == null) return null;
    final service = services[channel];
    if (service == null) return null;

    _state = PaywallUiState(state: PayState.loading, selectedPlan: plan);
    notifyListeners();

    try {
      final result = await service.pay(plan, channel);
      if (!result.success) {
        _state = PaywallUiState(
          state: PayState.failed,
          message: result.message ?? '支付失败，请重试',
          selectedPlan: plan,
        );
        notifyListeners();
        return null;
      }
      final license = await licenseService.refresh();
      _state = PaywallUiState(
        state: PayState.success,
        selectedPlan: plan,
      );
      notifyListeners();
      return license;
    } on SessionExpiredException {
      _state = PaywallUiState(
        state: PayState.failed,
        message: '登录已失效，请重新登录后再充值',
        selectedPlan: plan,
      );
      notifyListeners();
      return null;
    } on OrderApiException catch (e) {
      _state = PaywallUiState(
        state: PayState.failed,
        message: '支付不可用: ${e.message}',
        selectedPlan: plan,
      );
      notifyListeners();
      return null;
    }
  }

  void reset() {
    _state = const PaywallUiState();
    notifyListeners();
  }
}