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

namespace Estsh.Core.Util
{
    /// <summary>
    /// RSA加解密 使用OpenSSL的公钥加密/私钥解密
    /// 公私钥请使用openssl生成  ssh-keygen -t rsa 命令生成的公钥私钥是不行的
    /// </summary>
    public class RsaHelper 
    {
        private readonly RSA _privateKeyRsaProvider;
        private readonly RSA _publicKeyRsaProvider;
        private readonly HashAlgorithmName _hashAlgorithmName;
        private readonly Encoding _encoding;

        /// <summary>
        /// 实例化RSAHelper
        /// </summary>
        /// <param name="rsaType">加密算法类型 RSA SHA1;RSA2 SHA256 密钥长度至少为2048</param>
        /// <param name="encoding">编码类型</param>
        /// <param name="privateKey">私钥</param>
        /// <param name="publicKey">公钥</param>
        public RsaHelper( RSAType rsaType, Encoding encoding, string privateKey = null, string publicKey = null ) 
        {
            _encoding = encoding;
            if( !string.IsNullOrEmpty( privateKey ) ) 
            {
                _privateKeyRsaProvider = CreateRsaProviderFromPrivateKey( privateKey );
            }

            if( !string.IsNullOrEmpty( publicKey ) ) 
            {
                _publicKeyRsaProvider = CreateRsaProviderFromPublicKey( publicKey );
            }

            _hashAlgorithmName = rsaType == RSAType.RSA ? HashAlgorithmName.SHA1 : HashAlgorithmName.SHA256;
        }

        #region 使用私钥签名

        /// <summary>
        /// 使用私钥签名
        /// </summary>
        /// <param name="data">原始数据</param>
        /// <returns></returns>
        public string Sign( string data ) 
        {
            byte[] dataBytes = _encoding.GetBytes( data );

            var signatureBytes = _privateKeyRsaProvider.SignData( dataBytes, _hashAlgorithmName, RSASignaturePadding.Pkcs1 );

            return System.Convert.ToBase64String( signatureBytes );
        }

        #endregion

        #region 使用公钥验证签名

        /// <summary>
        /// 使用公钥验证签名
        /// </summary>
        /// <param name="data">原始数据</param>
        /// <param name="sign">签名</param>
        /// <returns></returns>
        public bool Verify( string data, string sign ) 
        {
            byte[] dataBytes = _encoding.GetBytes( data );
            byte[] signBytes = System.Convert.FromBase64String( sign );

            var verify = _publicKeyRsaProvider.VerifyData( dataBytes, signBytes, _hashAlgorithmName, RSASignaturePadding.Pkcs1 );

            return verify;
        }

        #endregion

        #region 解密

        public string Decrypt( string cipherText ) 
        {
            if( _privateKeyRsaProvider == null ) 
            {
                throw new Exception( "_privateKeyRsaProvider is null" );
            }
            return Encoding.UTF8.GetString( _privateKeyRsaProvider.Decrypt( System.Convert.FromBase64String( cipherText ), RSAEncryptionPadding.Pkcs1 ) );
        }

        public string SubDecrypt(string cipherText)
        {
            if (_privateKeyRsaProvider == null)
            {
                throw new Exception("_privateKeyRsaProvider is null");
            }
            byte[] cipherByte = Convert.FromBase64String( cipherText );
            int maxBlockSize = _publicKeyRsaProvider.KeySize / 8;
            if (cipherByte.Length <= maxBlockSize)
            {
                return Encoding.UTF8.GetString(_privateKeyRsaProvider.Decrypt(cipherByte, RSAEncryptionPadding.Pkcs1));
            }

            using (MemoryStream ms = new MemoryStream(cipherByte))
            {
                using (MemoryStream crypStream = new MemoryStream())
                {
                    Byte[] bufferByte = new Byte[maxBlockSize];
                    int blockSize = ms.Read(bufferByte, 0, maxBlockSize);

                    while (blockSize > 0)
                    {
                        Byte[] ToEncrypt = new Byte[blockSize];
                        Array.Copy(bufferByte, 0, ToEncrypt, 0, blockSize);

                        Byte[] cryptograph = _privateKeyRsaProvider.Decrypt(ToEncrypt, RSAEncryptionPadding.Pkcs1);
                        crypStream.Write(cryptograph, 0, cryptograph.Length);

                        blockSize = ms.Read(bufferByte, 0, maxBlockSize);
                    }

                    return Encoding.UTF8.GetString(crypStream.ToArray());
                }
            }
        }

        #endregion

        #region 加密

        public string Encrypt( string text ) 
        {
            if( _publicKeyRsaProvider == null ) 
            {
                throw new Exception( "_publicKeyRsaProvider is null" );
            }
            return Convert.ToBase64String( _publicKeyRsaProvider.Encrypt( Encoding.UTF8.GetBytes( text ), RSAEncryptionPadding.Pkcs1 ) );
        }

        public string SubEncrypt(string text)
        {

            if (_publicKeyRsaProvider == null)
            {
                throw new Exception("_publicKeyRsaProvider is null");
            }
            byte[] textBytes = Encoding.UTF8.GetBytes( text );
            int maxBlockSize = _publicKeyRsaProvider.KeySize / 8 - 11;
            if (textBytes.Length <= maxBlockSize)
            {
                return Convert.ToBase64String(_publicKeyRsaProvider.Encrypt(textBytes, RSAEncryptionPadding.Pkcs1));
            }

            using (MemoryStream ms = new MemoryStream(textBytes))
            {
                using (MemoryStream crypStream = new MemoryStream())
                {
                    Byte[] bufferByte = new Byte[maxBlockSize];
                    int blockSize = ms.Read(bufferByte, 0, maxBlockSize);

                    while (blockSize > 0)
                    {
                        Byte[] ToEncrypt = new Byte[blockSize];
                        Array.Copy(bufferByte, 0, ToEncrypt, 0, blockSize);

                        Byte[] cryptograph = _publicKeyRsaProvider.Encrypt(ToEncrypt, RSAEncryptionPadding.Pkcs1);
                        crypStream.Write(cryptograph, 0, cryptograph.Length);

                        blockSize = ms.Read(bufferByte, 0, maxBlockSize);
                    }

                    return Convert.ToBase64String(crypStream.ToArray(), Base64FormattingOptions.None);
                }
            }
        }

        #endregion

        #region 使用私钥创建RSA实例

        public RSA CreateRsaProviderFromPrivateKey( string privateKey ) 
        {
            var privateKeyBits = System.Convert.FromBase64String( privateKey );

            var rsa = RSA.Create();
            var rsaParameters = new RSAParameters();

            using( BinaryReader binr = new BinaryReader( new MemoryStream( privateKeyBits ) ) ) 
            {
                byte bt = 0;
                ushort twobytes = 0;
                twobytes = binr.ReadUInt16();
                if( twobytes == 0x8130 )
                    binr.ReadByte();
                else if( twobytes == 0x8230 )
                    binr.ReadInt16();
                else
                    throw new Exception( "Unexpected value read binr.ReadUInt16()" );

                twobytes = binr.ReadUInt16();
                if( twobytes != 0x0102 )
                    throw new Exception( "Unexpected version" );

                bt = binr.ReadByte();
                if( bt != 0x00 )
                    throw new Exception( "Unexpected value read binr.ReadByte()" );

                rsaParameters.Modulus = binr.ReadBytes( GetIntegerSize( binr ) );
                rsaParameters.Exponent = binr.ReadBytes( GetIntegerSize( binr ) );
                rsaParameters.D = binr.ReadBytes( GetIntegerSize( binr ) );
                rsaParameters.P = binr.ReadBytes( GetIntegerSize( binr ) );
                rsaParameters.Q = binr.ReadBytes( GetIntegerSize( binr ) );
                rsaParameters.DP = binr.ReadBytes( GetIntegerSize( binr ) );
                rsaParameters.DQ = binr.ReadBytes( GetIntegerSize( binr ) );
                rsaParameters.InverseQ = binr.ReadBytes( GetIntegerSize( binr ) );
            }

            rsa.ImportParameters( rsaParameters );
            return rsa;
        }

        #endregion

        #region 使用公钥创建RSA实例

        public RSA CreateRsaProviderFromPublicKey( string publicKeyString ) 
        {
            // encoded OID sequence for  PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"
            byte[] seqOid = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
            byte[] seq = new byte[15];

            var x509Key = System.Convert.FromBase64String( publicKeyString );

            // ---------  Set up stream to read the asn.1 encoded SubjectPublicKeyInfo blob  ------
            using( MemoryStream mem = new MemoryStream( x509Key ) ) 
            {
                using( BinaryReader binr = new BinaryReader( mem ) )  //wrap Memory Stream with BinaryReader for easy reading
                {
                    byte bt = 0;
                    ushort twobytes = 0;

                    twobytes = binr.ReadUInt16();
                    if( twobytes == 0x8130 ) //data read as little endian order (actual data order for Sequence is 30 81)
                        binr.ReadByte();    //advance 1 byte
                    else if( twobytes == 0x8230 )
                        binr.ReadInt16();   //advance 2 bytes
                    else
                        return null;

                    seq = binr.ReadBytes( 15 );       //read the Sequence OID
                    if( !CompareBytearrays( seq, seqOid ) )    //make sure Sequence for OID is correct
                        return null;

                    twobytes = binr.ReadUInt16();
                    if( twobytes == 0x8103 ) //data read as little endian order (actual data order for Bit String is 03 81)
                        binr.ReadByte();    //advance 1 byte
                    else if( twobytes == 0x8203 )
                        binr.ReadInt16();   //advance 2 bytes
                    else
                        return null;

                    bt = binr.ReadByte();
                    if( bt != 0x00 )     //expect null byte next
                        return null;

                    twobytes = binr.ReadUInt16();
                    if( twobytes == 0x8130 ) //data read as little endian order (actual data order for Sequence is 30 81)
                        binr.ReadByte();    //advance 1 byte
                    else if( twobytes == 0x8230 )
                        binr.ReadInt16();   //advance 2 bytes
                    else
                        return null;

                    twobytes = binr.ReadUInt16();
                    byte lowbyte = 0x00;
                    byte highbyte = 0x00;

                    if( twobytes == 0x8102 ) //data read as little endian order (actual data order for Integer is 02 81)
                        lowbyte = binr.ReadByte();  // read next bytes which is bytes in modulus
                    else if( twobytes == 0x8202 ) {
                        highbyte = binr.ReadByte(); //advance 2 bytes
                        lowbyte = binr.ReadByte();
                    }
                    else
                        return null;
                    byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };   //reverse byte order since asn.1 key uses big endian order
                    int modsize = BitConverter.ToInt32( modint, 0 );

                    int firstbyte = binr.PeekChar();
                    if( firstbyte == 0x00 ) {   //if first byte (highest order) of modulus is zero, don't include it
                        binr.ReadByte();    //skip this null byte
                        modsize -= 1;   //reduce modulus buffer size by 1
                    }

                    byte[] modulus = binr.ReadBytes( modsize );   //read the modulus bytes

                    if( binr.ReadByte() != 0x02 )            //expect an Integer for the exponent data
                        return null;
                    int expbytes = (int)binr.ReadByte();        // should only need one byte for actual exponent data (for all useful values)
                    byte[] exponent = binr.ReadBytes( expbytes );

                    // ------- create RSACryptoServiceProvider instance and initialize with public key -----
                    var rsa = RSA.Create();
                    RSAParameters rsaKeyInfo = new RSAParameters {
                        Modulus = modulus,
                        Exponent = exponent
                    };
                    rsa.ImportParameters( rsaKeyInfo );

                    return rsa;
                }

            }
        }

        #endregion

        #region 导入密钥算法

        private int GetIntegerSize( BinaryReader binr ) 
        {
            byte bt = 0;
            int count = 0;
            bt = binr.ReadByte();
            if( bt != 0x02 )
                return 0;
            bt = binr.ReadByte();

            if( bt == 0x81 )
                count = binr.ReadByte();
            else
            if( bt == 0x82 ) 
            {
                var highbyte = binr.ReadByte();
                var lowbyte = binr.ReadByte();
                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
                count = BitConverter.ToInt32( modint, 0 );
            }
            else 
            {
                count = bt;
            }

            while( binr.ReadByte() == 0x00 ) 
            {
                count -= 1;
            }
            binr.BaseStream.Seek( -1, SeekOrigin.Current );
            return count;
        }

        private bool CompareBytearrays( byte[] a, byte[] b ) 
        {
            if( a.Length != b.Length )
                return false;
            int i = 0;
            foreach( byte c in a ) 
            {
                if( c != b[i] )
                    return false;
                i++;
            }
            return true;
        }

        #endregion

    }

    /// <summary>
    /// RSA算法类型
    /// </summary>
    public enum RSAType 
    {
        /// <summary>
        /// SHA1
        /// </summary>
        RSA = 0,
        /// <summary>
        /// RSA2 密钥长度至少为2048
        /// SHA256
        /// </summary>
        RSA2
    }
}