using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;

namespace UsdtPayment.SDK
{
    /// <summary>
    /// USDT支付网关 C# SDK v3.2.0
    /// 
    /// 接口说明:
    /// - /api/address/create  动态生成收款地址（支持多币种）
    /// - /api/pay/create      创建支付订单
    /// - /api/pay/query       查询订单状态
    ///
    /// 支持币种:
    /// - USDT-TRC20  (TRON网络USDT)
    /// - USDC-TRC20  (TRON网络USDC)
    /// - ETH         (以太坊)
    /// - USDT-ERC20  (ERC20 USDT)
    /// - USDC-ERC20  (ERC20 USDC)
    /// - BTC         (比特币)
    /// - BSC         (币安链)
    /// - USDT-BEP20  (BEP20 USDT)
    /// - USDC-BEP20  (BEP20 USDC)
    /// - POLYGON     (Polygon网络)
    /// - USDT-POLYGON(Polygon USDT)
    /// - USDC-POLYGON(Polygon USDC)
    /// </summary>
    public class UsdtPaySDK
    {
        private readonly string _baseUrl;
        private readonly string _merchantNo;
        private readonly string _apiKey;
        private readonly string _apiSecret;
        private readonly HttpClient _httpClient;

        public UsdtPaySDK(string baseUrl, string merchantNo, string apiKey, string apiSecret)
        {
            _baseUrl = baseUrl.TrimEnd('/');
            _merchantNo = merchantNo;
            _apiKey = apiKey;
            _apiSecret = apiSecret;
            _httpClient = new HttpClient { Timeout = TimeSpan.FromSeconds(30) };
        }

        /// <summary>
        /// 动态生成收款地址
        /// </summary>
        /// <param name="label">地址别名（可选）</param>
        /// <param name="coinType">币种类型: USDT-TRC20, ETH, USDT-ERC20, BTC, BSC, USDT-BEP20, POLYGON, USDT-POLYGON</param>
        /// <returns>响应JSON字符串</returns>
        public async Task<string> CreateAddressAsync(string label = null, string coinType = "USDT-TRC20")
        {
            long timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();

            var parameters = new Dictionary<string, object>
            {
                { "merchantNo", _merchantNo },
                { "timestamp", timestamp }
            };

            if (!string.IsNullOrEmpty(label))
            {
                parameters["label"] = label;
            }
            if (!string.IsNullOrEmpty(coinType))
            {
                parameters["coinType"] = coinType;
            }

            string sign = GenerateSign(parameters);
            parameters["sign"] = sign;

            return await RequestAsync("/api/address/create", parameters);
        }

        /// <summary>
        /// 创建支付订单
        /// </summary>
        public async Task<string> CreateOrderAsync(string payAddress, string productName, string productDescription = null)
        {
            long timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();

            var parameters = new Dictionary<string, object>
            {
                { "merchantNo", _merchantNo },
                { "payAddress", payAddress },
                { "productName", productName },
                { "timestamp", timestamp }
            };

            if (!string.IsNullOrEmpty(productDescription))
            {
                parameters["productDescription"] = productDescription;
            }

            string sign = GenerateSign(parameters);
            parameters["sign"] = sign;

            return await RequestAsync("/api/pay/create", parameters);
        }

        /// <summary>
        /// 查询订单状态
        /// </summary>
        public async Task<string> QueryOrderAsync(string orderNo)
        {
            long timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();

            var parameters = new Dictionary<string, object>
            {
                { "merchantNo", _merchantNo },
                { "orderNo", orderNo },
                { "timestamp", timestamp }
            };

            string sign = GenerateSign(parameters);
            parameters["sign"] = sign;

            return await RequestAsync("/api/pay/query", parameters);
        }

        /// <summary>
        /// 验证回调签名
        /// </summary>
        public bool VerifyCallback(Dictionary<string, object> data)
        {
            if (!data.ContainsKey("sign"))
                return false;

            string sign = data["sign"].ToString();

            var signData = new Dictionary<string, object>(data);
            signData.Remove("sign");

            string expectedSign = GenerateSign(signData);

            return sign.Equals(expectedSign, StringComparison.OrdinalIgnoreCase);
        }

        /// <summary>
        /// 生成签名
        /// 签名算法: SHA256(参数按键名排序拼接 + key=apiSecret)
        /// 拼接格式: key1=value1&key2=value2&...&key=apiSecret
        /// </summary>
        private string GenerateSign(Dictionary<string, object> parameters)
        {
            // 按键名排序
            var sortedParams = new SortedDictionary<string, object>(parameters);
            
            // 拼接参数
            var sb = new StringBuilder();
            foreach (var entry in sortedParams)
            {
                if (entry.Value != null && !string.IsNullOrEmpty(entry.Value.ToString()))
                {
                    sb.Append(entry.Key).Append("=").Append(entry.Value).Append("&");
                }
            }
            // 追加密钥
            sb.Append("key=").Append(_apiSecret);
            
            return Sha256Hex(sb.ToString());
        }

        private string Sha256Hex(string input)
        {
            using (var sha256 = SHA256.Create())
            {
                byte[] hash = sha256.ComputeHash(Encoding.UTF8.GetBytes(input));
                return BitConverter.ToString(hash).Replace("-", "").ToLower();
            }
        }

        private async Task<string> RequestAsync(string path, Dictionary<string, object> parameters)
        {
            string url = _baseUrl + path;
            string json = JsonSerializer.Serialize(parameters);

            var request = new HttpRequestMessage(HttpMethod.Post, url)
            {
                Content = new StringContent(json, Encoding.UTF8, "application/json")
            };
            request.Headers.Add("X-API-KEY", _apiKey);

            var response = await _httpClient.SendAsync(request);
            return await response.Content.ReadAsStringAsync();
        }
    }

    // ==================== 使用示例 ====================
    class Program
    {
        static async Task Main(string[] args)
        {
            var sdk = new UsdtPaySDK(
                "https://xxxx.com",
                "M203254xxxx1709440",  // 商户编号
                "AK_xxxxxxxx",            // API Key
                "AS_xxxxxxxx"             // API Secret
            );

            // 1. 动态生成收款地址（默认USDT-TRC20）
            string result = await sdk.CreateAddressAsync("用户充值-订单123");
            Console.WriteLine("生成TRC20地址: " + result);

            // 1.1 生成ETH地址
            result = await sdk.CreateAddressAsync("用户充值-ETH", "ETH");
            Console.WriteLine("生成ETH地址: " + result);

            // 1.2 生成USDT-ERC20地址
            result = await sdk.CreateAddressAsync("用户充值-ERC20", "USDT-ERC20");
            Console.WriteLine("生成ERC20地址: " + result);

            // 1.3 生成BTC地址
            result = await sdk.CreateAddressAsync("用户充值-BTC", "BTC");
            Console.WriteLine("生成BTC地址: " + result);

            // 1.4 生成BSC USDT地址
            result = await sdk.CreateAddressAsync("用户充值-BEP20", "USDT-BEP20");
            Console.WriteLine("生成BEP20地址: " + result);

            // 2. 创建支付订单
            result = await sdk.CreateOrderAsync(
                "T9xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
                "购买VIP会员",
                "购买1个月VIP会员服务"
            );
            Console.WriteLine("创建订单结果: " + result);

            // 3. 查询订单状态
            result = await sdk.QueryOrderAsync("P2032545595611709440");
            Console.WriteLine("查询订单结果: " + result);
        }
    }
}

/*
===================== 完整对接流程 =====================

1. 从商户后台获取凭证：
   - 商户编号 (merchantNo)
   - API Key
   - API Secret

2. 用户发起支付时：
   a) 调用 CreateAddressAsync() 动态生成收款地址
   b) 调用 CreateOrderAsync() 创建支付订单
   c) 展示收款地址给用户进行转账

3. 用户转账后：
   - 系统自动检测链上交易
   - 支付成功后回调您的通知地址

4. 验证回调签名，更新订单状态

=====================================================
*/