/// 券数据模型 — 对应后端 GET /api/v1/coupons 返回结构
class CouponModel {
  final String id;
  final String issuerId;
  final String name;
  final String? description;
  final String? imageUrl;
  final double faceValue;
  final double currentPrice;
  final double? issuePrice;
  final int totalSupply;
  final int remainingSupply;
  final String category;
  final String status;
  final String couponType;
  final DateTime expiryDate;
  final bool isTransferable;
  final int resaleCount;
  final int maxResaleCount;

  // Joined issuer fields
  final String? brandName;
  final String? brandLogoUrl;
  final String? creditRating;

  const CouponModel({
    required this.id,
    required this.issuerId,
    required this.name,
    this.description,
    this.imageUrl,
    required this.faceValue,
    required this.currentPrice,
    this.issuePrice,
    required this.totalSupply,
    required this.remainingSupply,
    required this.category,
    required this.status,
    required this.couponType,
    required this.expiryDate,
    required this.isTransferable,
    this.resaleCount = 0,
    this.maxResaleCount = 3,
    this.brandName,
    this.brandLogoUrl,
    this.creditRating,
  });

  factory CouponModel.fromJson(Map<String, dynamic> json) {
    final issuer = json['issuer'] as Map<String, dynamic>?;
    return CouponModel(
      id: json['id'] ?? '',
      issuerId: json['issuerId'] ?? '',
      name: json['name'] ?? '',
      description: json['description'],
      imageUrl: json['imageUrl'],
      faceValue: _toDouble(json['faceValue']),
      currentPrice: _toDouble(json['currentPrice']),
      issuePrice: json['issuePrice'] != null ? _toDouble(json['issuePrice']) : null,
      totalSupply: json['totalSupply'] ?? 0,
      remainingSupply: json['remainingSupply'] ?? 0,
      category: json['category'] ?? '',
      status: json['status'] ?? '',
      couponType: json['couponType'] ?? 'utility',
      expiryDate: DateTime.tryParse(json['expiryDate']?.toString() ?? '') ?? DateTime.now(),
      isTransferable: json['isTransferable'] ?? true,
      resaleCount: json['resaleCount'] ?? 0,
      maxResaleCount: json['maxResaleCount'] ?? 3,
      brandName: issuer?['companyName'],
      brandLogoUrl: issuer?['logoUrl'],
      creditRating: issuer?['creditRating'],
    );
  }

  /// 折扣率 (0~1)
  double get discount => faceValue > 0 ? 1 - currentPrice / faceValue : 0;

  /// 是否即将过期（7天内）
  bool get isExpiringSoon => expiryDate.difference(DateTime.now()).inDays <= 7;

  /// 是否已过期
  bool get isExpired => expiryDate.isBefore(DateTime.now());

  static double _toDouble(dynamic value) {
    if (value == null) return 0;
    if (value is num) return value.toDouble();
    return double.tryParse(value.toString()) ?? 0;
  }
}