using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using System.Windows;

namespace Ramitta.lib
{
    public class CryptoHelper
    {
        /// <summary>
        /// 生成RSA密钥对
        /// </summary>
        /// <param name="keySize">密钥长度（通常为2048、4096）</param>
        /// <returns>包含公钥和私钥的元组</returns>
        public static (string publicKey, string privateKey) GenerateKeyPair(int keySize = 2048)
        {
            try
            {
                using (var rsa = RSA.Create(keySize))
                {
                    string publicKey = rsa.ToXmlString(false);
                    string privateKey = rsa.ToXmlString(true);

                    return (publicKey, privateKey);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show($"密钥生成失败: {ex.Message}");
                return (null, null);
            }
        }

        /// <summary>
        /// 使用私钥对数据进行签名
        /// </summary>
        public static string? SignData(string data, string privateKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    rsa.FromXmlString(privateKey);

                    byte[] dataBytes = Encoding.UTF8.GetBytes(data);
                    byte[] signature = rsa.SignData(dataBytes, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);

                    return Convert.ToBase64String(signature);
                }
            }
            catch (Exception ex)
            {
                return null;
            }
        }

        /// <summary>
        /// 使用公钥验证签名
        /// </summary>
        public static bool? VerifySignature(string data, string signature, string publicKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    rsa.FromXmlString(publicKey);

                    byte[] dataBytes = Encoding.UTF8.GetBytes(data);
                    byte[] signatureBytes = Convert.FromBase64String(signature);

                    return rsa.VerifyData(dataBytes, signatureBytes, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
                }
            }
            catch (Exception ex)
            {
                return false;
            }
        }

        /// <summary>
        /// 使用公钥加密数据
        /// </summary>
        public static string? Encrypt(string data, string publicKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    rsa.FromXmlString(publicKey);

                    byte[] dataBytes = Encoding.UTF8.GetBytes(data);
                    byte[] encryptedBytes = rsa.Encrypt(dataBytes, RSAEncryptionPadding.OaepSHA256);

                    return Convert.ToBase64String(encryptedBytes);
                }
            }
            catch (Exception ex)
            {
                return null;
            }
        }

        /// <summary>
        /// 使用私钥解密数据
        /// </summary>
        public static string? Decrypt(string encryptedData, string privateKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    rsa.FromXmlString(privateKey);

                    byte[] encryptedBytes = Convert.FromBase64String(encryptedData);
                    byte[] decryptedBytes = rsa.Decrypt(encryptedBytes, RSAEncryptionPadding.OaepSHA256);

                    return Encoding.UTF8.GetString(decryptedBytes);
                }
            }
            catch (Exception ex)
            {
                return null;
            }
        }
    }
}