// Copyright (c) 2017, 2020, 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.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace MySql.Data.MySqlClient.Authentication
{
    /// <summary>
    /// Provides functionality to read, decode and convert PEM files to objects supported in .NET.
    /// </summary>
    public class MySqlPemReader
    {
        /// <summary>
        /// Converts the binary data of a PEM file to an <see cref="RSACryptoServiceProvider"/> object. 
        /// </summary>
        /// <param name="rawPublicKey">A binary representation of the public key provided by the server.</param>
        /// <returns>An <see cref="RSACryptoServiceProvider"/> object containing the data found in the public key.</returns>
        public static RSACryptoServiceProvider ConvertPemToRSAProvider(byte[] rawPublicKey)
        {
            byte[] decodedKey = DecodeOpenSslKey(rawPublicKey);
            return DecodeX509Key(decodedKey);
        }

        static RSACryptoServiceProvider DecodeX509Key(byte[] key)
        {
            if (key == null)
            {
                return null;
            }

            byte[] oidSequence = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
            using (var memoryStream = new MemoryStream(key))
            {
                using (var reader = new BinaryReader(memoryStream))
                {
                    try
                    {
                        var bytes = reader.ReadUInt16();
                        switch (bytes)
                        {
                            case 0x8130:
                                reader.ReadByte();
                                break;
                            case 0x8230:
                                reader.ReadInt16();
                                break;
                            default:
                                return null;
                        }

                        var sequence = reader.ReadBytes(15);

                        // Compare arrays.
                        bool arraysAreEqual = true;
                        if (sequence.Length == oidSequence.Length)
                        {
                            for (int i = 0; i < oidSequence.Length; i++)
                            {
                                if (sequence[i] != oidSequence[i])
                                {
                                    arraysAreEqual = false;
                                }
                            }
                        }

                        if (!arraysAreEqual)
                        {
                            return null;
                        }

                        bytes = reader.ReadUInt16();
                        if (bytes == 0x8103)
                        {
                            reader.ReadByte();
                        }
                        else if (bytes == 0x8203)
                        {
                            reader.ReadInt16();
                        }
                        else
                        {
                            return null;
                        }

                        if (reader.ReadByte() != 0x00)
                        {
                            return null;
                        }

                        bytes = reader.ReadUInt16();
                        if (bytes == 0x8130)
                        {
                            reader.ReadByte();
                        }
                        else if (bytes == 0x8230)
                        {
                            reader.ReadInt16();
                        }
                        else
                        {
                            return null;
                        }

                        bytes = reader.ReadUInt16();
                        byte lowByte = 0x00;
                        byte highByte = 0x00;
                        if (bytes == 0x8102)
                        {
                            lowByte = reader.ReadByte();
                        }
                        else if (bytes == 0x8202)
                        {
                            highByte = reader.ReadByte();
                            lowByte = reader.ReadByte();
                        }
                        else
                        {
                            return null;
                        }

                        int modulusSize = BitConverter.ToInt32(new byte[] { lowByte, highByte, 0x00, 0x00 }, 0);
                        byte firstByte = reader.ReadByte();
                        reader.BaseStream.Seek(-1, SeekOrigin.Current);

                        if (firstByte == 0x00)
                        {
                            reader.ReadByte();
                            modulusSize -= 1;
                        }

                        // Read modulus.
                        byte[] modulus = reader.ReadBytes(modulusSize);
                        if (reader.ReadByte() != 0x02)
                        {
                            return null;
                        }

                        // Read exponent.
                        byte[] exponent = reader.ReadBytes(reader.ReadByte());
                        RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
                        RSAParameters rsaKeyInfo = new RSAParameters
                        {
                            Modulus = modulus,
                            Exponent = exponent
                        };
                        rsa.ImportParameters(rsaKeyInfo);
                        return rsa;
                    }
                    catch (Exception)
                    {
                        return null;
                    }
                }
            }
        }

        static byte[] DecodeOpenSslKey(byte[] rawPublicKey)
        {
            if (rawPublicKey == null)
            {
                return null;
            }

            // Remove line breaks and carriage returns.
            rawPublicKey = rawPublicKey.Where(b => b != 0x0D).ToArray();
            rawPublicKey = rawPublicKey.Where(b => b != 0x0A).ToArray();

            // Trim.
            rawPublicKey = TrimByteArray(rawPublicKey);

            // Remove header and footer
            byte[] headerSequence = { 0x2D, 0x2D, 0x2D, 0x2D, 0x2D, 0x42, 0x45, 0x47, 0x49, 0x4E, 0x20, 0x50, 0x55, 0x42, 0x4C, 0x49, 0x43, 0x20, 0x4B, 0x45, 0x59, 0x2D, 0x2D, 0x2D, 0x2D, 0x2D };
            byte[] footerSequence = { 0x2D, 0x2D, 0x2D, 0x2D, 0x2D, 0x45, 0x4E, 0x44, 0x20, 0x50, 0x55, 0x42, 0x4C, 0x49, 0x43, 0x20, 0x4B, 0x45, 0x59, 0x2D, 0x2D, 0x2D, 0x2D, 0x2D };
            if (!StartsWith(rawPublicKey, headerSequence) || !EndsWith(rawPublicKey, footerSequence))
            {
                return null;
            }

            byte[] formattedRawPublicKey = new byte[rawPublicKey.Length - headerSequence.Length - footerSequence.Length];
            Array.Copy(rawPublicKey, headerSequence.Length, formattedRawPublicKey, 0, formattedRawPublicKey.Length);
            byte[] binaryKey;

            try
            {
                binaryKey = Convert.FromBase64String(Encoding.Default.GetString(formattedRawPublicKey));
            }
            catch (FormatException)
            {
                return null;
            }

            return binaryKey;
        }

        private static byte[] TrimByteArray(byte[] array)
        {
            List<byte> trimmedArray = new List<byte>();
            bool startCopying = false;

            foreach (var item in array)
            {
                if (!startCopying)
                {
                    if (item == 0x20)
                    {
                        continue;
                    }
                    else
                    {
                        startCopying = true;
                    }
                }

                trimmedArray.Add(item);
            }

            array = trimmedArray.ToArray();
            trimmedArray = new List<byte>();

            for (int i = array.Length - 1; i >= 0; i--)
            {
                if (!startCopying)
                {
                    if (array[i] == 0x20)
                    {
                        continue;
                    }
                    else
                    {
                        startCopying = true;
                    }
                }

                trimmedArray.Add(array[i]);
            }

            return trimmedArray.ToArray().Reverse().ToArray();
        }

        private static bool StartsWith(byte[] array, byte[] containedArray)
        {
            for (int i = 0; i < array.Length; i++)
            {
                if (i == containedArray.Length)
                {
                    break;
                }

                if (array[i] != containedArray[i])
                {
                    return false;
                }
            }

            return true;
        }

        private static bool EndsWith(byte[] array, byte[] containedArray)
        {
            for (int i = array.Length - 1, j = 0; i >= 0; i--, j++)
            {
                if (j == containedArray.Length)
                {
                    break;
                }

                if (array[i] != containedArray[containedArray.Length - j - 1])
                {
                    return false;
                }
            }

            return true;
        }
    }
}