// Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License, version 2.0, as
// published by the Free Software Foundation.
//
// This program is also distributed with certain software (including
// but not limited to OpenSSL) that is licensed under separate terms,
// as designated in a particular file or component or in included license
// documentation.  The authors of MySQL hereby grant you an
// additional permission to link the program and your derivative works
// with the separately licensed software that they have included with
// MySQL.
//
// Without limiting anything contained in the foregoing, this file,
// which is part of MySQL Connector/NET, is also subject to the
// Universal FOSS Exception, version 1.0, a copy of which can be found at
// http://oss.oracle.com/licenses/universal-foss-exception.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
// See the GNU General Public License, version 2.0, for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software Foundation, Inc.,
// 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA

using System;
using System.Text;
using System.Security.Cryptography;
using Sog.Properties;

namespace MySql.Data.MySqlClient.Authentication
{
    /// <summary>
    /// The implementation of the caching_sha2_password authentication plugin.
    /// </summary>
    internal class CachingSha2AuthenticationPlugin : Sha256AuthenticationPlugin
    {
        internal static AuthStage _authStage;

        public override string PluginName => "caching_sha2_password";

        protected override void SetAuthData(byte[] data)
        {
            // If the data given to us is a null terminated string, we need to trim off the trailing zero.
            if (data[data.Length - 1] == 0)
            {
                byte[] b = new byte[data.Length - 1];
                Buffer.BlockCopy(data, 0, b, 0, data.Length - 1);
                base.SetAuthData(b);
            }
            else
            {
                base.SetAuthData(data);
            }
        }

        protected override byte[] MoreData(byte[] data)
        {
            this.rawPubkey = data;

            // Generate scramble.
            if (data == null)
            {
                byte[] scramble = this.GetPassword() as byte[];
                byte[] buffer = new byte[scramble.Length - 1];
                Array.Copy(scramble, 1, buffer, 0, scramble.Length - 1);
                return buffer;
            }

            // Fast authentication.
            else if (data[0] == 3)
            {
                _authStage = AuthStage.FAST_AUTH;
                return null;
            }
            else
            {
                return this.GeneratePassword() as byte[];
            }
        }

        /// <summary>
        /// Generates a byte array set with the password of the user in the expected format based on the
        /// SSL settings of the current connection.
        /// </summary>
        /// <returns>A byte array that contains the password of the user in the expected format.</returns>
        protected byte[] GeneratePassword()
        {
            // If connection is secure perform full authentication.
            if (this.Settings.SslMode != MySqlSslMode.None)
            {
                _authStage = AuthStage.FULL_AUTH;

                // Send as clear text since the channel is already encrypted.
                byte[] passBytes = this.Encoding.GetBytes(this.Settings.Password);
                byte[] buffer = new byte[passBytes.Length + 1];
                Array.Copy(passBytes, 0, buffer, 0, passBytes.Length);
                buffer[passBytes.Length] = 0;
                return buffer;
            }
            else
            {
                // Request RSA key from server.
                if (this.rawPubkey != null && this.rawPubkey[0] == 4)
                {
                    _authStage = AuthStage.REQUEST_RSA_KEY;
                    return new byte[] { 0x02 };
                }
                else if (!this.Settings.AllowPublicKeyRetrieval)
                {
                    throw new MySqlException(Resources.RSAPublicKeyRetrievalNotEnabled);
                }

                // Full authentication.
                else
                {
                    _authStage = AuthStage.FULL_AUTH;
                    byte[] bytes = this.GetRsaPassword(this.Settings.Password, this.AuthenticationData, this.rawPubkey);
                    if (bytes != null && bytes.Length == 1 && bytes[0] == 0)
                    {
                        return null;
                    }

                    return bytes;
                }
            }
        }

        private byte[] GetRsaPassword(string password, byte[] seedBytes, byte[] rawPublicKey)
        {
            if (password.Length == 0)
            {
                return new byte[1];
            }

            if (this.rawPubkey == null)
            {
                return null;
            }

            // Obfuscate the plain text password with the session scramble.
            byte[] obfuscated = this.GetXor(Encoding.Default.GetBytes(password), seedBytes);

            // Encrypt the password and send it to the server.
            if (this.ServerVersion >= new Version("8.0.5"))
            {
                RSACryptoServiceProvider rsa = MySqlPemReader.ConvertPemToRSAProvider(rawPublicKey);
                if (rsa == null)
                {
                    throw new MySqlException(Resources.UnableToReadRSAKey);
                }

                return rsa.Encrypt(obfuscated, true);
            }
            else
            {
                RSACryptoServiceProvider rsa = MySqlPemReader.ConvertPemToRSAProvider(rawPublicKey);
                if (rsa == null)
                {
                    throw new MySqlException(Resources.UnableToReadRSAKey);
                }

                return rsa.Encrypt(obfuscated, false);
            }
        }

        public override object GetPassword()
        {
            _authStage = AuthStage.GENERATE_SCRAMBLE;

            // If we have no password then we just return 1 zero byte.
            if (this.Settings.Password.Length == 0)
            {
                return new byte[1];
            }

            SHA256 sha = SHA256.Create();

            byte[] firstHash = sha.ComputeHash(Encoding.Default.GetBytes(this.Settings.Password));
            byte[] secondHash = sha.ComputeHash(firstHash);

            byte[] input = new byte[this.AuthenticationData.Length + secondHash.Length];
            Array.Copy(secondHash, 0, input, 0, secondHash.Length);
            Array.Copy(this.AuthenticationData, 0, input, secondHash.Length, this.AuthenticationData.Length);
            byte[] thirdHash = sha.ComputeHash(input);

            byte[] finalHash = new byte[thirdHash.Length];
            for (int i = 0; i < firstHash.Length; i++)
            {
                finalHash[i] = (byte)(firstHash[i] ^ thirdHash[i]);
            }

            byte[] buffer = new byte[finalHash.Length + 1];
            Array.Copy(finalHash, 0, buffer, 1, finalHash.Length);
            buffer[0] = 0x20;
            return buffer;
        }
    }

    /// <summary>
    /// Defines the stage of the authentication.
    /// </summary>
    internal enum AuthStage
    {
        GENERATE_SCRAMBLE = 0,
        REQUEST_RSA_KEY = 1,
        FAST_AUTH = 2,
        FULL_AUTH = 3
    }
}