// Copyright (c) 2009, 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 MySql.Data.Common;
using System;
using System.IO;

namespace MySql.Data.MySqlClient
{
    /// <summary>
    /// Stream that supports timeout of IO operations.
    /// This class is used is used to support timeouts for SQL command, where a 
    /// typical operation involves several network reads/writes. 
    /// Timeout here is defined as the accumulated duration of all IO operations.
    /// </summary>

    internal class TimedStream : Stream
    {
        readonly Stream _baseStream;

        int _timeout;
        int _lastReadTimeout;
        int _lastWriteTimeout;
        readonly LowResolutionStopwatch _stopwatch;

        internal bool IsClosed { get; private set; }

        enum IOKind
        {
            Read,
            Write
        }
    ;

        /// <summary>
        /// Construct a TimedStream
        /// </summary>
        /// <param name="baseStream"> Undelying stream</param>
        public TimedStream(Stream baseStream)
        {
            this._baseStream = baseStream;
            this._timeout = baseStream.CanTimeout ? baseStream.ReadTimeout : System.Threading.Timeout.Infinite;
            this.IsClosed = false;
            this._stopwatch = new LowResolutionStopwatch();
        }


        /// <summary>
        /// Figure out whether it is necessary to reset timeout on stream.
        /// We track the current value of timeout and try to avoid
        /// changing it too often, because setting Read/WriteTimeout property
        /// on network stream maybe a slow operation that involves a system call 
        /// (setsockopt). Therefore, we allow a small difference, and do not 
        /// reset timeout if current value is slightly greater than the requested
        /// one (within 0.1 second).
        /// </summary>

        private bool ShouldResetStreamTimeout(int currentValue, int newValue)
        {
            if (!this._baseStream.CanTimeout)
            {
                return false;
            }

            if (newValue == System.Threading.Timeout.Infinite
                && currentValue != newValue)
            {
                return true;
            }

            if (newValue > currentValue)
            {
                return true;
            }

            return currentValue >= newValue + 100;
        }

        private void StartTimer(IOKind op)
        {

            int streamTimeout;

            if (this._timeout == System.Threading.Timeout.Infinite)
            {
                streamTimeout = System.Threading.Timeout.Infinite;
            }
            else
            {
                streamTimeout = this._timeout - (int)this._stopwatch.ElapsedMilliseconds;
            }

            if (op == IOKind.Read)
            {
                if (this.ShouldResetStreamTimeout(this._lastReadTimeout, streamTimeout))
                {
                    this._baseStream.ReadTimeout = streamTimeout;
                    this._lastReadTimeout = streamTimeout;
                }
            }
            else
            {
                if (this.ShouldResetStreamTimeout(this._lastWriteTimeout, streamTimeout))
                {
                    this._baseStream.WriteTimeout = streamTimeout;
                    this._lastWriteTimeout = streamTimeout;
                }
            }

            if (this._timeout == System.Threading.Timeout.Infinite)
            {
                return;
            }

            this._stopwatch.Start();
        }

        private void StopTimer()
        {
            if (this._timeout == System.Threading.Timeout.Infinite)
            {
                return;
            }

            this._stopwatch.Stop();

            // Normally, a timeout exception would be thrown  by stream itself, 
            // since we set the read/write timeout  for the stream.  However 
            // there is a gap between  end of IO operation and stopping the 
            // stop watch,  and it makes it possible for timeout to exceed 
            // even after IO completed successfully.
            if (this._stopwatch.ElapsedMilliseconds > this._timeout)
            {
                this.ResetTimeout(System.Threading.Timeout.Infinite);
                throw new TimeoutException("Timeout in IO operation");
            }
        }

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

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

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

        public override void Flush()
        {
            try
            {
                this.StartTimer(IOKind.Write);
                this._baseStream.Flush();
                this.StopTimer();
            }
            catch (Exception e)
            {
                this.HandleException(e);
                throw;
            }
        }

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

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

        public override int Read(byte[] buffer, int offset, int count)
        {
            try
            {
                this.StartTimer(IOKind.Read);
                int retval = this._baseStream.Read(buffer, offset, count);
                this.StopTimer();
                return retval;
            }
            catch (Exception e)
            {
                this.HandleException(e);
                throw;
            }
        }

        public override int ReadByte()
        {
            try
            {
                this.StartTimer(IOKind.Read);
                int retval = this._baseStream.ReadByte();
                this.StopTimer();
                return retval;
            }
            catch (Exception e)
            {
                this.HandleException(e);
                throw;
            }
        }

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

        public override void SetLength(long value)
        {
            this._baseStream.SetLength(value);
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            try
            {
                this.StartTimer(IOKind.Write);
                this._baseStream.Write(buffer, offset, count);
                this.StopTimer();
            }
            catch (Exception e)
            {
                this.HandleException(e);
                throw;
            }
        }

        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 void Close()
        {
            if (this.IsClosed)
            {
                return;
            }

            this.IsClosed = true;
            this._baseStream.Close();
            this._baseStream.Dispose();
        }

        public void ResetTimeout(int newTimeout)
        {
            if (newTimeout == System.Threading.Timeout.Infinite || newTimeout == 0)
            {
                this._timeout = System.Threading.Timeout.Infinite;
            }
            else
            {
                this._timeout = newTimeout;
            }

            this._stopwatch.Reset();
        }


        /// <summary>
        /// Common handler for IO exceptions.
        /// Resets timeout to infinity if timeout exception is 
        /// detected and stops the times.
        /// </summary>
        /// <param name="e">original exception</param>
        void HandleException(Exception e)
        {
            this._stopwatch.Stop();
            this.ResetTimeout(-1);
        }
    }
}