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

/// <summary>
/// 签名算法：MD5(content + keys) 然后转base64
/// </summary>
public class SignatureHelper
{
    /// <summary>
    /// 生成签名
    /// </summary>
    /// <param name="content">待签名的内容</param>
    /// <param name="charset">字符编码，通常为 "UTF-8"</param>
    /// <param name="keys">密钥</param>
    /// <returns>Base64编码的签名</returns>
    public static string DoSign(string content, string charset, string keys)
    {
        try
        {
            // 拼接内容和密钥
            string signContent = content + keys;
            
            // 根据字符集获取编码
            Encoding encoding = GetEncoding(charset);
            
            // 计算MD5哈希
            byte[] signBytes = encoding.GetBytes(signContent);
            byte[] md5Hash = MD5.HashData(signBytes);
            
            // 转换为Base64字符串
            string sign = Convert.ToBase64String(md5Hash);
            
            return sign;
        }
        catch (Exception ex)
        {
            throw new Exception($"签名失败: {ex.Message}", ex);
        }
    }
    
    /// <summary>
    /// 根据字符集名称获取编码对象
    /// </summary>
    private static Encoding GetEncoding(string charset)
    {
        if (string.IsNullOrEmpty(charset))
        {
            return Encoding.UTF8;
        }
        
        switch (charset.ToUpper())
        {
            case "UTF-8":
            case "UTF8":
                return Encoding.UTF8;
            case "GBK":
                return Encoding.GetEncoding("GBK");
            case "GB2312":
                return Encoding.GetEncoding("GB2312");
            default:
                try
                {
                    return Encoding.GetEncoding(charset);
                }
                catch
                {
                    return Encoding.UTF8;
                }
        }
    }
}