// Copyright (c) 2014, 2021, Oracle and/or its affiliates.
//
// 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 MySql.Data.MySqlClient;
using System;
using System.Diagnostics;
using System.IO;
using System.Runtime.InteropServices;
using System.Threading;

namespace MySql.Data.Common
{
    /// <summary>
    /// Helper class to encapsulate shared memory functionality
    /// Also cares of proper cleanup of file mapping object and cew
    /// </summary>
    internal class SharedMemory : IDisposable
    {
        private const uint FILE_MAP_WRITE = 0x0002;

        IntPtr fileMapping;
        IntPtr view;

        public SharedMemory(string name, IntPtr size)
        {
            this.fileMapping = NativeMethods.OpenFileMapping(FILE_MAP_WRITE, false,
                name);
            if (this.fileMapping == IntPtr.Zero)
            {
                throw new MySqlException("Cannot open file mapping " + name);
            }

            this.view = NativeMethods.MapViewOfFile(this.fileMapping, FILE_MAP_WRITE, 0, 0, size);
        }

        #region Destructor
        ~SharedMemory()
        {
            this.Dispose(false);
        }
        #endregion

        public IntPtr View
        {
            get { return this.view; }
        }

        public void Dispose()
        {
            this.Dispose(true);
            GC.SuppressFinalize(this);
        }


        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                if (this.view != IntPtr.Zero)
                {
                    NativeMethods.UnmapViewOfFile(this.view);
                    this.view = IntPtr.Zero;
                }

                if (this.fileMapping != IntPtr.Zero)
                {
                    // Free the handle
                    NativeMethods.CloseHandle(this.fileMapping);
                    this.fileMapping = IntPtr.Zero;
                }
            }
        }

    }

    /// <summary>
    /// Summary description for SharedMemoryStream.
    /// </summary>
    internal class SharedMemoryStream : Stream
    {
        private string memoryName;
        private EventWaitHandle serverRead;
        private EventWaitHandle serverWrote;
        private EventWaitHandle clientRead;
        private EventWaitHandle clientWrote;
        private EventWaitHandle connectionClosed;
        private SharedMemory data;
        private int bytesLeft;
        private int position;
        private int connectNumber;

        private const int BUFFERLENGTH = 16004;

        private int readTimeout = System.Threading.Timeout.Infinite;
        private int writeTimeout = System.Threading.Timeout.Infinite;

        public SharedMemoryStream(string memName)
        {
            this.memoryName = memName;
        }

        public void Open(uint timeOut)
        {
            if (this.connectionClosed != null)
            {
                Debug.Assert(false, "Connection is already open");
            }

            this.GetConnectNumber(timeOut);
            this.SetupEvents();
        }

        public override void Close()
        {
            if (this.connectionClosed != null)
            {
                bool isClosed = this.connectionClosed.WaitOne(0);
                if (!isClosed)
                {
                    this.connectionClosed.Set();
                    this.connectionClosed.Close();
                }

                this.connectionClosed = null;
                EventWaitHandle[] handles = { this.serverRead, this.serverWrote, this.clientRead, this.clientWrote };

                for (int i = 0; i < handles.Length; i++)
                {
                    if (handles[i] != null)
                    {
                        handles[i].Close();
                    }
                }

                if (this.data != null)
                {
                    this.data.Dispose();
                    this.data = null;
                }
            }
        }

        private void GetConnectNumber(uint timeOut)
        {
            EventWaitHandle connectRequest;
            try
            {
                connectRequest =
                    EventWaitHandle.OpenExisting(this.memoryName + "_CONNECT_REQUEST");

            }
            catch (Exception)
            {
                // If server runs as service, its shared memory is global 
                // And if connector runs in user session, it needs to prefix
                // shared memory name with "Global\"
                string prefixedMemoryName = @"Global\" + this.memoryName;
                connectRequest =
                    EventWaitHandle.OpenExisting(prefixedMemoryName + "_CONNECT_REQUEST");
                this.memoryName = prefixedMemoryName;
            }

            EventWaitHandle connectAnswer =
               EventWaitHandle.OpenExisting(this.memoryName + "_CONNECT_ANSWER");
            using (SharedMemory connectData =
                new SharedMemory(this.memoryName + "_CONNECT_DATA", (IntPtr)4))
            {
                // now start the connection
                if (!connectRequest.Set())
                {
                    throw new MySqlException("Failed to open shared memory connection");
                }

                if (!connectAnswer.WaitOne((int)(timeOut * 1000), false))
                {
                    throw new MySqlException("Timeout during connection");
                }

                this.connectNumber = Marshal.ReadInt32(connectData.View);
            }
        }


        private void SetupEvents()
        {
            string prefix = this.memoryName + "_" + this.connectNumber;
            this.data = new SharedMemory(prefix + "_DATA", (IntPtr)BUFFERLENGTH);
            this.serverWrote = EventWaitHandle.OpenExisting(prefix + "_SERVER_WROTE");
            this.serverRead = EventWaitHandle.OpenExisting(prefix + "_SERVER_READ");
            this.clientWrote = EventWaitHandle.OpenExisting(prefix + "_CLIENT_WROTE");
            this.clientRead = EventWaitHandle.OpenExisting(prefix + "_CLIENT_READ");
            this.connectionClosed = EventWaitHandle.OpenExisting(prefix + "_CONNECTION_CLOSED");

            // tell the server we are ready
            this.serverRead.Set();
        }

        #region Properties
        public override bool CanRead
        {
            get { return true; }
        }

        public override bool CanSeek
        {
            get { return false; }
        }

        public override bool CanWrite
        {
            get { return true; }
        }

        public override long Length
        {
            get { throw new NotSupportedException("SharedMemoryStream does not support seeking - length"); }
        }

        public override long Position
        {
            get { throw new NotSupportedException("SharedMemoryStream does not support seeking - position"); }
            set { }
        }

        #endregion

        public override void Flush()
        {
            // No need to flush anything to disk ,as our shared memory is backed 
            // by the page file
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            int timeLeft = this.readTimeout;
            WaitHandle[] waitHandles = { this.serverWrote, this.connectionClosed };
            LowResolutionStopwatch stopwatch = new LowResolutionStopwatch();
            while (this.bytesLeft == 0)
            {
                stopwatch.Start();
                int index = WaitHandle.WaitAny(waitHandles, timeLeft);
                stopwatch.Stop();
                if (index == WaitHandle.WaitTimeout)
                {
                    throw new TimeoutException("Timeout when reading from shared memory");
                }

                if (waitHandles[index] == this.connectionClosed)
                {
                    throw new MySqlException("Connection to server lost", true, null);
                }

                if (this.readTimeout != System.Threading.Timeout.Infinite)
                {
                    timeLeft = this.readTimeout - (int)stopwatch.ElapsedMilliseconds;
                    if (timeLeft < 0)
                    {
                        throw new TimeoutException("Timeout when reading from shared memory");
                    }
                }

                this.bytesLeft = Marshal.ReadInt32(this.data.View);
                this.position = 4;
            }

            int len = Math.Min(count, this.bytesLeft);
            long baseMem = this.data.View.ToInt64() + this.position;

            for (int i = 0; i < len; i++, this.position++)
            {
                buffer[offset + i] = Marshal.ReadByte((IntPtr)(baseMem + i));
            }

            this.bytesLeft -= len;
            if (this.bytesLeft == 0)
            {
                this.clientRead.Set();
            }

            return len;
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            throw new NotSupportedException("SharedMemoryStream does not support seeking");
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            int leftToDo = count;
            int buffPos = offset;
            WaitHandle[] waitHandles = { this.serverRead, this.connectionClosed };
            LowResolutionStopwatch stopwatch = new LowResolutionStopwatch();
            int timeLeft = this.writeTimeout;

            while (leftToDo > 0)
            {
                stopwatch.Start();
                int index = WaitHandle.WaitAny(waitHandles, timeLeft);
                stopwatch.Stop();

                if (waitHandles[index] == this.connectionClosed)
                {
                    throw new MySqlException("Connection to server lost", true, null);
                }

                if (index == WaitHandle.WaitTimeout)
                {
                    throw new TimeoutException("Timeout when reading from shared memory");
                }

                if (this.writeTimeout != System.Threading.Timeout.Infinite)
                {
                    timeLeft = this.writeTimeout - (int)stopwatch.ElapsedMilliseconds;
                    if (timeLeft < 0)
                    {
                        throw new TimeoutException("Timeout when writing to shared memory");
                    }
                }

                int bytesToDo = Math.Min(leftToDo, BUFFERLENGTH);
                long baseMem = this.data.View.ToInt64() + 4;
                Marshal.WriteInt32(this.data.View, bytesToDo);
                Marshal.Copy(buffer, buffPos, (IntPtr)baseMem, bytesToDo);
                buffPos += bytesToDo;
                leftToDo -= bytesToDo;
                if (!this.clientWrote.Set())
                {
                    throw new MySqlException("Writing to shared memory failed");
                }
            }
        }

        public override void SetLength(long value)
        {
            throw new NotSupportedException("SharedMemoryStream does not support seeking");
        }

        public override bool CanTimeout
        {
            get
            {
                return true;
            }
        }

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

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

    }
}