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

namespace Ramitta.lib
{
    public class CryptoHelper
    {
        /// <summary>
        /// 通过OpenSSH格式私钥计算公钥（Base64格式）
        /// </summary>
        /// <param name="openSshPrivateKey">OpenSSH格式的Base64私钥（不带PEM头尾）</param>
        /// <returns>Base64格式的公钥，失败返回null</returns>
        public static string? GetPublicKeyFromPrivate(string openSshPrivateKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    // 解析OpenSSH私钥格式
                    ImportOpenSshPrivateKey(rsa, openSshPrivateKey);

                    // 导出公钥为Base64
                    byte[] publicKeyBytes = rsa.ExportRSAPublicKey();
                    return Convert.ToBase64String(publicKeyBytes);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show($"从私钥提取公钥失败: {ex.Message}");
                return null;
            }
        }

        /// <summary>
        /// 导入OpenSSH格式的私钥（纯Base64编码）
        /// </summary>
        private static void ImportOpenSshPrivateKey(RSA rsa, string openSshBase64)
        {
            byte[] keyData = Convert.FromBase64String(openSshBase64);

            using (var reader = new BinaryReader(new MemoryStream(keyData)))
            {
                // 读取魔术字
                var magic = reader.ReadBytes(15);
                string magicString = Encoding.ASCII.GetString(magic);
                if (magicString != "openssh-key-v1\0")
                    throw new FormatException("无效的OpenSSH私钥格式");

                // 读取加密信息
                var cipherName = ReadLengthPrefixedString(reader);
                var kdfName = ReadLengthPrefixedString(reader);
                var kdfOptions = ReadLengthPrefixedData(reader);

                // 检查是否加密
                if (cipherName != "none" || kdfName != "none")
                    throw new FormatException("不支持加密的OpenSSH私钥");

                // 读取密钥数量
                var keyCount = ReadUInt32BigEndian(reader);
                if (keyCount != 1)
                    throw new FormatException("不支持多个密钥");

                // 读取公钥（跳过）
                var publicKey = ReadLengthPrefixedData(reader);

                // 读取私钥数据
                var privateKeyData = ReadLengthPrefixedData(reader);

                // 解析私钥数据
                using (var privateReader = new BinaryReader(new MemoryStream(privateKeyData)))
                {
                    // 检查字节序标记
                    var check1 = privateReader.ReadUInt32();
                    var check2 = privateReader.ReadUInt32();
                    if (check1 != check2)
                        throw new FormatException("私钥检查值不匹配");

                    // 读取密钥类型
                    var keyType = ReadLengthPrefixedString(privateReader);
                    if (keyType != "ssh-rsa")
                        throw new FormatException("非RSA密钥");

                    // 读取RSA参数
                    var modulus = ReadLengthPrefixedData(privateReader);        // n
                    var publicExponent = ReadLengthPrefixedData(privateReader); // e
                    var privateExponent = ReadLengthPrefixedData(privateReader); // d
                    var coefficient = ReadLengthPrefixedData(privateReader);    // iqmp
                    var prime1 = ReadLengthPrefixedData(privateReader);         // p
                    var prime2 = ReadLengthPrefixedData(privateReader);         // q

                    // 创建RSA参数并导入
                    var rsaParameters = new RSAParameters
                    {
                        Modulus = modulus,
                        Exponent = publicExponent,
                        D = privateExponent,
                        P = prime1,
                        Q = prime2,
                        InverseQ = coefficient
                    };

                    rsa.ImportParameters(rsaParameters);
                }
            }
        }

        /// <summary>
        /// 读取长度前缀字符串
        /// </summary>
        private static string ReadLengthPrefixedString(BinaryReader reader)
        {
            var data = ReadLengthPrefixedData(reader);
            return Encoding.ASCII.GetString(data);
        }

        /// <summary>
        /// 读取长度前缀数据
        /// </summary>
        private static byte[] ReadLengthPrefixedData(BinaryReader reader)
        {
            var length = ReadUInt32BigEndian(reader);
            return reader.ReadBytes((int)length);
        }

        /// <summary>
        /// 以大端序读取uint32
        /// </summary>
        private static uint ReadUInt32BigEndian(BinaryReader reader)
        {
            var data = reader.ReadBytes(4);
            if (BitConverter.IsLittleEndian)
                Array.Reverse(data);
            return BitConverter.ToUInt32(data, 0);
        }

        /// <summary>
        /// 使用OpenSSH格式私钥对数据进行签名
        /// </summary>
        public static string? SignDataWithOpenSsh(string data, string openSshPrivateKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    ImportOpenSshPrivateKey(rsa, openSshPrivateKey);

                    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OpenSSH格式私钥解密数据
        /// </summary>
        public static string? DecryptWithOpenSsh(string encryptedData, string openSshPrivateKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    ImportOpenSshPrivateKey(rsa, openSshPrivateKey);

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

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

        /// <summary>
        /// 获取OpenSSH格式私钥的密钥长度
        /// </summary>
        public static int GetOpenSshKeySize(string openSshPrivateKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    ImportOpenSshPrivateKey(rsa, openSshPrivateKey);
                    return rsa.KeySize;
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show($"获取密钥长度失败: {ex.Message}");
                return -1;
            }
        }

        // 其他原有方法保持不变...
        public static (string publicKey, string privateKey) GenerateKeyPair(int keySize = 2048)
        {
            try
            {
                using (var rsa = RSA.Create(keySize))
                {
                    byte[] publicKeyBytes = rsa.ExportRSAPublicKey();
                    byte[] privateKeyBytes = rsa.ExportRSAPrivateKey();

                    string publicKey = Convert.ToBase64String(publicKeyBytes);
                    string privateKey = Convert.ToBase64String(privateKeyBytes);

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

        public static string? SignData(string data, string privateKey)
        {
            try
            {
                using (var rsa = RSA.Create())
                {
                    byte[] privateKeyBytes = Convert.FromBase64String(privateKey);

                    try
                    {
                        rsa.ImportRSAPrivateKey(privateKeyBytes, out _);
                    }
                    catch
                    {
                        rsa.ImportPkcs8PrivateKey(privateKeyBytes, out _);
                    }

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

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

        // 其他方法...
    }
}