using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace YD_WeChatApplet.Commons.Utils
{
    public static class SaTokenSignHelper
    {
        /// <summary>
        /// 根据业务参数生成 Java Sa-Token Sign 兼容的 QueryString
        /// 自动生成 timestamp 和 nonce，如果外部未提供
        /// </summary>
        /// <param name="paramMap">业务参数字典（可包含 teacherNo 等）</param>
        /// <param name="secretKey">应用密钥</param>
        /// <param name="channel">应用编码，例如 sk-yuedong</param>
        /// <returns>带 sign 的完整 QueryString</returns>
        public static string BuildQueryString(Dictionary<string, object> paramMap, string secretKey)
        {
            if (paramMap == null)
                paramMap = new Dictionary<string, object>();

            // 1️⃣ TreeMap 排序（ASCII 升序）
            var sorted = new SortedDictionary<string, string>(StringComparer.Ordinal);
            foreach (var kv in paramMap)
                sorted[kv.Key] = kv.Value.ToString();

            // 2️⃣ 拼接签名字符串 k=v&k=v&...&key=secretKey
            var sbSign = new StringBuilder();
            foreach (var kv in sorted)
                sbSign.Append(kv.Key).Append("=").Append(kv.Value).Append("&");
            sbSign.Append("key=").Append(secretKey.Trim());

            string sign = Md5(sbSign.ToString());

            // 3️⃣ 拼接 QueryString（保留外部字典原顺序）
            var sbQuery = new StringBuilder();
            foreach (var kv in paramMap)
                sbQuery.Append(Uri.EscapeDataString(kv.Key))
                       .Append("=")
                       .Append(Uri.EscapeDataString(kv.Value.ToString()))
                       .Append("&");

            sbQuery.Append("sign=").Append(sign);

            return sbQuery.ToString();
        }

        /// <summary>
        /// MD5 小写 32 位
        /// </summary>
        private static string Md5(string input)
        {
            using var md5 = MD5.Create();
            var bytes = md5.ComputeHash(Encoding.UTF8.GetBytes(input));
            var sb = new StringBuilder();
            foreach (var b in bytes)
                sb.Append(b.ToString("x2"));
            return sb.ToString();
        }

        /// <summary>
        /// 生成随机字符串 nonce，可指定长度
        /// </summary>
        public static string RandomString(int length = 20)
        {
            const string chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
            var random = new Random();
            return new string(Enumerable.Repeat(chars, length).Select(s => s[random.Next(s.Length)]).ToArray());
        }
    }
}