// Copyright (c) 2004, 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.IO;
using System.IO.Compression;
using MySql.Data.Common;
using System.Net;
using Sog.Properties;

namespace MySql.Data.MySqlClient
{
    /// <summary>
    /// Summary description for CompressedStream.
    /// </summary>
    internal class CompressedStream : Stream
    {
        // writing fields
        private Stream baseStream;
        private MemoryStream cache;

        // reading fields
        private byte[] localByte;
        private byte[] inBuffer;
        private byte[] lengthBytes;
        private WeakReference inBufferRef;
        private int inPos;
        private int maxInPos;
        private DeflateStream compInStream;

        public CompressedStream(Stream baseStream)
        {
            this.baseStream = baseStream;
            this.localByte = new byte[1];
            this.lengthBytes = new byte[7];
            this.cache = new MemoryStream();
            this.inBufferRef = new WeakReference(this.inBuffer, false);
        }

        #region Properties


        public override bool CanRead => this.baseStream.CanRead;

        public override bool CanWrite => this.baseStream.CanWrite;

        public override bool CanSeek => this.baseStream.CanSeek;

        public override long Length => this.baseStream.Length;

        public override long Position
        {
            get { return this.baseStream.Position; }
            set { this.baseStream.Position = value; }
        }

        #endregion

        public override void Close()
        {
            base.Close();
            this.baseStream.Close();
            this.cache.Dispose();
        }

        public override void SetLength(long value)
        {
            throw new NotSupportedException(Resources.CSNoSetLength);
        }

        public override int ReadByte()
        {
            try
            {
                this.Read(this.localByte, 0, 1);
                return this.localByte[0];
            }
            catch (EndOfStreamException)
            {
                return -1;
            }
        }

        public override bool CanTimeout => this.baseStream.CanTimeout;

        public override int ReadTimeout
        {
            get
            {
                return this.baseStream.ReadTimeout;
            }
            set
            {
                this.baseStream.ReadTimeout = value;
            }
        }

        public override int WriteTimeout
        {
            get
            {
                return this.baseStream.WriteTimeout;
            }
            set
            {
                this.baseStream.WriteTimeout = value;
            }
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            if (buffer == null)
            {
                throw new ArgumentNullException(nameof(buffer), Resources.BufferCannotBeNull);
            }

            if (offset < 0 || offset >= buffer.Length)
            {
                throw new ArgumentOutOfRangeException(nameof(offset), Resources.OffsetMustBeValid);
            }

            if ((offset + count) > buffer.Length)
            {
                throw new ArgumentException(Resources.BufferNotLargeEnough, nameof(buffer));
            }

            if (this.inPos == this.maxInPos)
            {
                this.PrepareNextPacket();
            }

            int countToRead = Math.Min(count, this.maxInPos - this.inPos);
            int countRead;

            if (this.compInStream != null)
            {
                countRead = this.compInStream.Read(buffer, offset, countToRead);
            }
            else
            {
                countRead = this.baseStream.Read(buffer, offset, countToRead);
            }

            this.inPos += countRead;

            // release the weak reference
            if (this.inPos == this.maxInPos)
            {
                this.compInStream = null;

                if (!Platform.IsMono())
                {
                    this.inBufferRef = new WeakReference(this.inBuffer, false);
                    this.inBuffer = null;
                }
            }

            return countRead;
        }

        private void PrepareNextPacket()
        {
            MySqlStream.ReadFully(this.baseStream, this.lengthBytes, 0, 7);
            int compressedLength = this.lengthBytes[0] + (this.lengthBytes[1] << 8) + (this.lengthBytes[2] << 16);

            // lengthBytes[3] is seq
            int unCompressedLength = this.lengthBytes[4] + (this.lengthBytes[5] << 8) +
                         (this.lengthBytes[6] << 16);

            if (unCompressedLength == 0)
            {
                unCompressedLength = compressedLength;
                this.compInStream = null;
            }
            else
            {
                this.ReadNextPacket(compressedLength);
                MemoryStream ms = new MemoryStream(this.inBuffer, 2, compressedLength - 2);
                this.compInStream = new DeflateStream(ms, CompressionMode.Decompress);
            }

            this.inPos = 0;
            this.maxInPos = unCompressedLength;
        }

        private void ReadNextPacket(int len)
        {
            this.inBuffer = this.inBufferRef.Target as byte[];

            if (this.inBuffer == null || this.inBuffer.Length < len)
            {
                this.inBuffer = new byte[len];
            }

            MySqlStream.ReadFully(this.baseStream, this.inBuffer, 0, len);
        }

        private MemoryStream CompressCache()
        {
            // small arrays almost never yeild a benefit from compressing
            if (this.cache.Length < 50)
            {
                return null;
            }

            byte[] cacheBytes = this.cache.GetBuffer();

            MemoryStream compressedBuffer = new MemoryStream();

            compressedBuffer.WriteByte(0x78);
            compressedBuffer.WriteByte(0x9c);
            var outCompStream = new DeflateStream(compressedBuffer, CompressionMode.Compress, true);
            outCompStream.Write(cacheBytes, 0, (int)this.cache.Length);
            outCompStream.Dispose();
            int adler = IPAddress.HostToNetworkOrder(this.Adler32(cacheBytes, 0, (int)this.cache.Length));
            compressedBuffer.Write(BitConverter.GetBytes(adler), 0, sizeof(uint));

            // if the compression hasn't helped, then just return null
            if (compressedBuffer.Length >= this.cache.Length)
            {
                return null;
            }

            return compressedBuffer;
        }

        int Adler32(byte[] bytes, int index, int length)
        {
            const uint a32mod = 65521;
            uint s1 = 1, s2 = 0;
            for (int i = index; i < length; i++)
            {
                byte b = bytes[i];
                s1 = (s1 + b) % a32mod;
                s2 = (s2 + s1) % a32mod;
            }

            return unchecked((int)((s2 << 16) + s1));
        }

        private void CompressAndSendCache()
        {
            long compressedLength, uncompressedLength;

            // we need to save the sequence byte that is written
            byte[] cacheBuffer = this.cache.GetBuffer();

            byte seq = cacheBuffer[3];
            cacheBuffer[3] = 0;

            // first we compress our current cache
            MemoryStream compressedBuffer = this.CompressCache();

            // now we set our compressed and uncompressed lengths
            // based on if our compression is going to help or not
            MemoryStream memStream;

            if (compressedBuffer == null)
            {
                compressedLength = this.cache.Length;
                uncompressedLength = 0;
                memStream = this.cache;
            }
            else
            {
                compressedLength = compressedBuffer.Length;
                uncompressedLength = this.cache.Length;
                memStream = compressedBuffer;
            }

            // Make space for length prefix (7 bytes) at the start of output
            long dataLength = memStream.Length;
            int bytesToWrite = (int)dataLength + 7;
            memStream.SetLength(bytesToWrite);
            byte[] buffer = memStream.GetBuffer();
            Array.Copy(buffer, 0, buffer, 7, (int)dataLength);

            // Write length prefix
            buffer[0] = (byte)(compressedLength & 0xff);
            buffer[1] = (byte)((compressedLength >> 8) & 0xff);
            buffer[2] = (byte)((compressedLength >> 16) & 0xff);
            buffer[3] = seq;
            buffer[4] = (byte)(uncompressedLength & 0xff);
            buffer[5] = (byte)((uncompressedLength >> 8) & 0xff);
            buffer[6] = (byte)((uncompressedLength >> 16) & 0xff);

            this.baseStream.Write(buffer, 0, bytesToWrite);
            this.baseStream.Flush();
            this.cache.SetLength(0);

            compressedBuffer?.Dispose();
        }

        public override void Flush()
        {
            if (!this.InputDone())
            {
                return;
            }

            this.CompressAndSendCache();
        }

        private bool InputDone()
        {
            // if we have not done so yet, see if we can calculate how many bytes we are expecting
            if (this.baseStream is TimedStream && ((TimedStream)this.baseStream).IsClosed)
            {
                return false;
            }

            if (this.cache.Length < 4)
            {
                return false;
            }

            byte[] buf = this.cache.GetBuffer();
            int expectedLen = buf[0] + (buf[1] << 8) + (buf[2] << 16);
            if (this.cache.Length < (expectedLen + 4))
            {
                return false;
            }

            return true;
        }

        public override void WriteByte(byte value)
        {
            this.cache.WriteByte(value);
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            this.cache.Write(buffer, offset, count);
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            return this.baseStream.Seek(offset, origin);
        }
    }
}