using System.Security.Cryptography;
using System.Text;

namespace TrackCenter.Application.Helpers;

/// <summary>
/// API签名工具类
/// </summary>
public static class SignatureHelper
{
    /// <summary>
    /// 生成API签名
    /// </summary>
    /// <param name="appKey">应用唯一标识</param>
    /// <param name="timestamp">时间戳(Unix时间戳，单位：秒)</param>
    /// <param name="appSecret">应用密钥</param>
    /// <returns>MD5签名结果(大写)</returns>
    public static string GenerateSign(string appKey, long timestamp, string appSecret)
    {
        // 1. 排序后拼接：appKey, timestamp
        var sortedParams = $"appKey={appKey}&timestamp={timestamp}";
        
        // 2. 拼接密钥：添加appSecret
        var signString = $"{sortedParams}&appSecret={appSecret}";
        
        // 3. 计算MD5并转大写
        return CalculateMd5Hash(signString);
    }

    /// <summary>
    /// 验证签名
    /// </summary>
    /// <param name="appKey">应用唯一标识</param>
    /// <param name="timestamp">时间戳</param>
    /// <param name="sign">待验证的签名</param>
    /// <param name="appSecret">应用密钥</param>
    /// <param name="maxTimeDifferenceMinutes">允许的最大时间差(分钟)，默认5分钟</param>
    /// <returns>签名是否有效</returns>
    public static bool VerifySign(string appKey, long timestamp, string sign, string appSecret, int maxTimeDifferenceMinutes = 5)
    {
        // 1. 验证时间戳(防止重放攻击)
        var currentTimestamp = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
        var timeDifference = Math.Abs(currentTimestamp - timestamp);
        
        if (timeDifference > maxTimeDifferenceMinutes * 60)
        {
            return false;
        }
        
        // 2. 生成签名并比较
        var expectedSign = GenerateSign(appKey, timestamp, appSecret);
        return string.Equals(expectedSign, sign, StringComparison.OrdinalIgnoreCase);
    }

    /// <summary>
    /// 计算MD5哈希值(大写)
    /// </summary>
    /// <param name="input">输入字符串</param>
    /// <returns>MD5哈希值(大写)</returns>
    private static string CalculateMd5Hash(string input)
    {
        using var md5 = MD5.Create();
        var inputBytes = Encoding.UTF8.GetBytes(input);
        var hashBytes = md5.ComputeHash(inputBytes);
        
        var sb = new StringBuilder();
        foreach (var b in hashBytes)
        {
            sb.Append(b.ToString("X2"));
        }
        
        return sb.ToString();
    }
}