using System;
using System.Text;
using System.Security.Cryptography;
using Newtonsoft.Json.Linq;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Macs;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Crypto.Generators;
using Org.BouncyCastle.Crypto.Prng;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Crypto.Paddings;
using Org.BouncyCastle.Crypto.Modes;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Asn1.Sec;
using Org.BouncyCastle.Asn1.X9;
using Org.BouncyCastle.Asn1.X509;
using Org.BouncyCastle.Asn1.Pkcs;
using Org.BouncyCastle.Pkcs;
using Org.BouncyCastle.Utilities.Encoders;

namespace MySystem
{
    public class SMUtil
    {
        private const string KEY_ALGORITHM = "AES";
        public const string SM4_ECB_PKCS5PADDING = "SM4/ECB/PKCS5Padding";
        public const string ALGORITHM_NAME = "SM4";

        static SMUtil()
        {
            // 在 .NET 中不需要像 Java 那样显式注册提供者，BouncyCastle 通过 NuGet 引用即可使用
        }

        // 生成一个对称秘钥（返回字符串，行为与 Java 版保持一致：base64 后取前 16 个字符）
        public static string GetSymmetrickey()
        {
            try
            {
                byte[] keyBytes = new byte[32]; // 256 bits
                using (var rng = new RNGCryptoServiceProvider())
                {
                    rng.GetBytes(keyBytes);
                }
                string key = Convert.ToBase64String(keyBytes);
                if (key.Length >= 16)
                    key = key.Substring(0, 16);
                return key;
            }
            catch
            {
                return string.Empty;
            }
        }

        // 生成 SM2 公私钥对，返回 { publicKeyBase64, privateKeyBase64 }
        public static string[] GenerateSmKey()
        {
            try
            {
                X9ECParameters ecP = ECNamedCurveTable.GetByName("sm2p256v1");
                ECDomainParameters domainParams = new ECDomainParameters(ecP.Curve, ecP.G, ecP.N, ecP.H);

                var gen = new ECKeyPairGenerator();
                var secureRandom = new SecureRandom();
                var keyGenParam = new ECKeyGenerationParameters(domainParams, secureRandom);
                gen.Init(keyGenParam);
                AsymmetricCipherKeyPair pair = gen.GenerateKeyPair();

                // 构造 X.509 SubjectPublicKeyInfo（使用公钥点），以及 PKCS#8 PrivateKeyInfo
                var pubParam = pair.Public as ECPublicKeyParameters;
                var privInfo = PrivateKeyInfoFactory.CreatePrivateKeyInfo(pair.Private);
                // AlgorithmIdentifier: id-ecPublicKey + named curve OID
                var curveOid = ECNamedCurveTable.GetOid("sm2p256v1");
                var algId = new Org.BouncyCastle.Asn1.X509.AlgorithmIdentifier(X9ObjectIdentifiers.IdECPublicKey, curveOid);
                var spki = new SubjectPublicKeyInfo(algId, pubParam.Q.GetEncoded(false));
                byte[] pubBytes = spki.ToAsn1Object().GetEncoded();
                byte[] privBytes = privInfo.ToAsn1Object().GetEncoded();

                return new string[] { Convert.ToBase64String(pubBytes), Convert.ToBase64String(privBytes) };
            }
            catch (Exception)
            {
                return null;
            }
        }

        // 从 base64 字符串恢复公钥参数（AsymmetricKeyParameter）
        public static AsymmetricKeyParameter CreatePublicKey(string publicKeyBase64)
        {
            try
            {
                byte[] data = Convert.FromBase64String(publicKeyBase64);
                return PublicKeyFactory.CreateKey(data);
            }
            catch (Exception)
            {
                return null;
            }
        }

        // 从 base64 字符串恢复私钥参数
        public static AsymmetricKeyParameter CreatePrivateKey(string privateKeyBase64)
        {
            try
            {
                byte[] data = Convert.FromBase64String(privateKeyBase64);
                return PrivateKeyFactory.CreateKey(data);
            }
            catch (Exception)
            {
                return null;
            }
        }

        // SM2 加密（对称秘钥字符串使用 SM2 公钥加密，返回 base64）
        public static string Sm2Encrypt(string symmetrickey, string pubKeyBase64)
        {
            try
            {
                var pubParam = CreatePublicKey(pubKeyBase64) as ECPublicKeyParameters;
                if (pubParam == null) return null;
                var engine = new SM2Engine();
                engine.Init(true, new ParametersWithRandom(pubParam, new SecureRandom()));
                byte[] inBytes = Encoding.UTF8.GetBytes(symmetrickey);
                byte[] outBytes = engine.ProcessBlock(inBytes, 0, inBytes.Length);
                return Convert.ToBase64String(outBytes);
            }
            catch (Exception)
            {
                return null;
            }
        }

        // SM2 解密（传入 base64 密文和私钥 base64）
        public static string Sm2Decrypt(string cipherBase64, string priKeyBase64)
        {
            try
            {
                var priParam = CreatePrivateKey(priKeyBase64) as ECPrivateKeyParameters;
                if (priParam == null) return null;
                var engine = new SM2Engine();
                engine.Init(false, priParam);
                byte[] inBytes = Convert.FromBase64String(cipherBase64);
                byte[] outBytes = engine.ProcessBlock(inBytes, 0, inBytes.Length);
                return Encoding.UTF8.GetString(outBytes);
            }
            catch (Exception)
            {
                return null;
            }
        }

        // SM3 摘要
        public static byte[] Sm3(byte[] srcData)
        {
            var digest = new SM3Digest();
            digest.BlockUpdate(srcData, 0, srcData.Length);
            byte[] result = new byte[digest.GetDigestSize()];
            digest.DoFinal(result, 0);
            return result;
        }

        public static string Sm3Hex(string srcData)
        {
            byte[] hash = Sm3(Encoding.UTF8.GetBytes(srcData));
            return Hex.ToHexString(hash);
        }

        // HMAC-SM3
        public static byte[] HmacSm3(byte[] key, byte[] srcData)
        {
            var mac = new HMac(new SM3Digest());
            mac.Init(new KeyParameter(key));
            mac.BlockUpdate(srcData, 0, srcData.Length);
            byte[] result = new byte[mac.GetMacSize()];
            mac.DoFinal(result, 0);
            return result;
        }

        public static string HmacSm3Hex(string key, string srcData)
        {
            byte[] hash = HmacSm3(Encoding.UTF8.GetBytes(key), Encoding.UTF8.GetBytes(srcData));
            return Hex.ToHexString(hash);
        }

        // 另一种调用 MessageDigest 的 SM3 实现（使用 BouncyCastle 的 Digest 就足够了）
        public static byte[] Sm3Bc(byte[] srcData)
        {
            return Sm3(srcData);
        }

        public static string Sm3BcHex(string srcData)
        {
            return Sm3Hex(srcData);
        }

        // SM4 加解密（使用 BouncyCastle 的块加密器和填充）
        public static string Sm4Encrypt(string symmetrickey, string data)
        {
            string algorithmName = SM4_ECB_PKCS5PADDING;
            byte[] key = Encoding.UTF8.GetBytes(symmetrickey);
            byte[] iv = Encoding.UTF8.GetBytes(symmetrickey);
            byte[] cipher = Sm4Core(algorithmName, true, key, iv, Encoding.UTF8.GetBytes(data));
            return Convert.ToBase64String(cipher);
        }

        public static string Sm4Decrypt(string symmetrickey, string data)
        {
            string algorithmName = SM4_ECB_PKCS5PADDING;
            byte[] key = Encoding.UTF8.GetBytes(symmetrickey);
            byte[] iv = Encoding.UTF8.GetBytes(symmetrickey);
            byte[] plain = Sm4Core(algorithmName, false, key, iv, Convert.FromBase64String(data));
            return Encoding.UTF8.GetString(plain);
        }

        private static byte[] Sm4Core(string algorithmName, bool forEncrypt, byte[] key, byte[] iv, byte[] input)
        {
            try
            {
                // 将 Java 的 "SM4/ECB/PKCS5Padding" 换为 BouncyCastle 可识别的形式
                string bcName = algorithmName.Replace("PKCS5Padding", "PKCS7Padding");
                var cipher = CipherUtilities.GetCipher(bcName);
                ICipherParameters parameters = null;
                if (algorithmName.Contains("/ECB/"))
                {
                    parameters = new KeyParameter(key);
                }
                else
                {
                    parameters = new ParametersWithIV(new KeyParameter(key), iv);
                }
                cipher.Init(forEncrypt, parameters);
                byte[] outBytes = cipher.DoFinal(input);
                return outBytes;
            }
            catch (Exception ex)
            {
                throw new Exception("SM4 operation failed", ex);
            }
        }

        // 将 JObject 的 key 转为小写（null 或空值替换为 ""）
        public static JObject DealJSONObj(JObject jsonObj)
        {
            var result = new JObject();
            foreach (var prop in jsonObj.Properties())
            {
                JToken val = prop.Value;
                if (!HasValue(val))
                    val = "";
                result[prop.Name.ToLower()] = val;
            }
            return result;
        }

        public static JArray DealJSONArray(JArray jsonArray)
        {
            var arr = new JArray();
            foreach (var item in jsonArray)
            {
                if (item is JObject jo)
                {
                    arr.Add(DealJSONObj(jo));
                }
                else
                {
                    arr.Add(item);
                }
            }
            return arr;
        }

        private static bool HasValue(JToken token)
        {
            if (token == null) return false;
            if (token.Type == JTokenType.Null) return false;
            if (token.Type == JTokenType.String)
            {
                var s = token.ToString();
                return !string.IsNullOrWhiteSpace(s);
            }
            return true;
        }
    }
}