/*
 * Copyright (c) Contributors, http://opensimulator.org/
 * See CONTRIBUTORS.TXT for a full list of copyright holders.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the OpenSimulator Project nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

using System;
using System.Collections.Concurrent;
using System.Reflection;
using System.Threading;
using log4net;
using OpenSim.Framework;
using OpenSim.Framework.Monitoring;
using OpenSim.Region.Framework.Scenes;

namespace OpenSim.Region.CoreModules.Framework.EntityTransfer
{
    public class Job
    {
        public string Name { get; private set; }
        public string CommonId { get; private set; }
        public WaitCallback Callback { get; private set; }
        public object O { get; private set; }

        public Job(string name, string commonId, WaitCallback callback, object o)
        {
            Name = name;
            CommonId = commonId;
            Callback = callback;
            O = o;
        }
    }

    // TODO: These kinds of classes MUST be generalized with JobEngine, etc.
    public class HGIncomingSceneObjectEngine
    {
        private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        public int LogLevel { get; set; }

        public bool IsRunning { get; private set; } 

        public string Name { get; set; }

        /// <summary>
        /// The timeout in milliseconds to wait for at least one event to be written when the recorder is stopping.
        /// </summary>
        public int RequestProcessTimeoutOnStop { get; set; }

        /// <summary>
        /// Controls whether we need to warn in the log about exceeding the max queue size.
        /// </summary>
        /// <remarks>
        /// This is flipped to false once queue max has been exceeded and back to true when it falls below max, in 
        /// order to avoid spamming the log with lots of warnings.
        /// </remarks>
        private bool m_warnOverMaxQueue = true;

        private BlockingCollection<Job> m_requestQueue;

        private CancellationTokenSource m_cancelSource = new CancellationTokenSource();

        private Stat m_requestsWaitingStat;

        private Job m_currentJob;

        /// <summary>
        /// Used to signal that we are ready to complete stop.
        /// </summary>
        private ManualResetEvent m_finishedProcessingAfterStop = new ManualResetEvent(false);

        public HGIncomingSceneObjectEngine(string name)
        {
//            LogLevel = 1;
            Name = name;
            RequestProcessTimeoutOnStop = 5000;

//            MainConsole.Instance.Commands.AddCommand(
//                "Debug",
//                false,
//                "debug jobengine",
//                "debug jobengine <start|stop|status>",
//                "Start, stop or get status of the job engine.",
//                "If stopped then all jobs are processed immediately.",
//                HandleControlCommand);
        }

        public void Start()
        {
            lock (this)
            {
                if (IsRunning)
                    return;

                IsRunning = true;

                m_finishedProcessingAfterStop.Reset();

                m_requestQueue = new BlockingCollection<Job>(new ConcurrentQueue<Job>(), 5000);

                m_requestsWaitingStat = 
                    new Stat(
                        "HGIncomingAttachmentsWaiting",
                        "Number of incoming attachments waiting for processing.",
                        "",
                        "",
                        "entitytransfer",
                        Name,
                        StatType.Pull,
                        MeasuresOfInterest.None,
                        stat => stat.Value = m_requestQueue.Count,
                        StatVerbosity.Debug);

                StatsManager.RegisterStat(m_requestsWaitingStat);

                WorkManager.StartThread(
                    ProcessRequests,
                    string.Format("HG Incoming Scene Object Engine Thread ({0})", Name),
                    ThreadPriority.Normal,
                    false,
                    true,
                    null,
                    int.MaxValue);
            }
        }

        public void Stop()
        {   
            lock (this)
            {
                try
                {
                    if (!IsRunning)
                        return;

                    IsRunning = false;

                    int requestsLeft = m_requestQueue.Count;

                    if (requestsLeft <= 0)
                    {
                        m_cancelSource.Cancel();
                    }
                    else 
                    {
                        m_log.InfoFormat("[HG INCOMING SCENE OBJECT ENGINE]: Waiting to write {0} events after stop.", requestsLeft);

                        while (requestsLeft > 0)
                        {
                            if (!m_finishedProcessingAfterStop.WaitOne(RequestProcessTimeoutOnStop))
                            {
                                // After timeout no events have been written
                                if (requestsLeft == m_requestQueue.Count)
                                {
                                    m_log.WarnFormat(
                                        "[HG INCOMING SCENE OBJECT ENGINE]: No requests processed after {0} ms wait.  Discarding remaining {1} requests", 
                                        RequestProcessTimeoutOnStop, requestsLeft);

                                    break;
                                }
                            }

                            requestsLeft = m_requestQueue.Count;
                        }
                    }
                }
                finally
                {
                    m_cancelSource.Dispose();
                    StatsManager.DeregisterStat(m_requestsWaitingStat);
                    m_requestsWaitingStat = null;
                    m_requestQueue = null;
                }
            }
        }

        public Job RemoveNextRequest()
        {
            Job nextRequest;
            m_requestQueue.TryTake(out nextRequest);

            return nextRequest;
        }

        public bool QueueRequest(string name, string commonId, WaitCallback req, object o)
        {
            return QueueRequest(new Job(name, commonId, req, o));
        }

        public bool QueueRequest(Job job)
        {
            if (LogLevel >= 1)
                m_log.DebugFormat(
                    "[HG INCOMING SCENE OBJECT ENGINE]: Queued job {0}, common ID {1}", job.Name, job.CommonId);

            if (m_requestQueue.Count < m_requestQueue.BoundedCapacity)
            {
                //                m_log.DebugFormat(
                //                    "[OUTGOING QUEUE REFILL ENGINE]: Adding request for categories {0} for {1} in {2}", 
                //                    categories, client.AgentID, m_udpServer.Scene.Name);

                m_requestQueue.Add(job);

                if (!m_warnOverMaxQueue)
                    m_warnOverMaxQueue = true;

                return true;
            }
            else
            {
                if (m_warnOverMaxQueue)
                {
                    //                    m_log.WarnFormat(
                    //                        "[JOB ENGINE]: Request queue at maximum capacity, not recording request from {0} in {1}", 
                    //                        client.AgentID, m_udpServer.Scene.Name);

                    m_log.WarnFormat("[HG INCOMING SCENE OBJECT ENGINE]: Request queue at maximum capacity, not recording job");

                    m_warnOverMaxQueue = false;
                }

                return false;
            }
        }

        private void ProcessRequests()
        {
            try
            {
                while (IsRunning || m_requestQueue.Count > 0)
                {
                    m_currentJob = m_requestQueue.Take(m_cancelSource.Token);

                    //                QueueEmpty callback = req.Client.OnQueueEmpty;                      
                    //
                    //                if (callback != null)
                    //                {               
                    //                    try 
                    //                    { 
                    //                        callback(req.Categories); 
                    //                    }
                    //                    catch (Exception e) 
                    //                    { 
                    //                        m_log.Error("[OUTGOING QUEUE REFILL ENGINE]: ProcessRequests(" + req.Categories + ") threw an exception: " + e.Message, e); 
                    //                    }
                    //                }

                    if (LogLevel >= 1)
                        m_log.DebugFormat("[HG INCOMING SCENE OBJECT ENGINE]: Processing job {0}", m_currentJob.Name);

                    try
                    {
                        m_currentJob.Callback.Invoke(m_currentJob.O);
                    }
                    catch (Exception e)
                    {
                        m_log.Error(
                            string.Format(
                            "[HG INCOMING SCENE OBJECT ENGINE]: Job {0} failed, continuing.  Exception  ", m_currentJob.Name), e);
                    }

                    if (LogLevel >= 1)
                        m_log.DebugFormat("[HG INCOMING SCENE OBJECT ENGINE]: Processed job {0}", m_currentJob.Name);

                    m_currentJob = null;
                }
            }
            catch (OperationCanceledException)
            {
            }

            m_finishedProcessingAfterStop.Set();
        }

//        private void HandleControlCommand(string module, string[] args)
//        {
//            //            if (SceneManager.Instance.CurrentScene != null && SceneManager.Instance.CurrentScene != m_udpServer.Scene)
//            //                return;
//
//            if (args.Length < 3)
//            {
//                MainConsole.Instance.Output("Usage: debug jobengine <stop|start|status|loglevel>");
//                return;
//            }
//
//            string subCommand = args[2];
//
//            if (subCommand == "stop")
//            {
//                Stop();
//                MainConsole.Instance.OutputFormat("Stopped job engine.");
//            }
//            else if (subCommand == "start")
//            {
//                Start();
//                MainConsole.Instance.OutputFormat("Started job engine.");
//            }
//            else if (subCommand == "status")
//            {
//                MainConsole.Instance.OutputFormat("Job engine running: {0}", IsRunning);
//                MainConsole.Instance.OutputFormat("Current job {0}", m_currentJob != null ? m_currentJob.Name : "none");
//                MainConsole.Instance.OutputFormat(
//                    "Jobs waiting: {0}", IsRunning ? m_requestQueue.Count.ToString() : "n/a");
//                MainConsole.Instance.OutputFormat("Log Level: {0}", LogLevel);
//            }
//
//            else if (subCommand == "loglevel")
//            {
//                //                int logLevel;
//                int logLevel = int.Parse(args[3]);
//                //                if (ConsoleUtil.TryParseConsoleInt(MainConsole.Instance, args[4], out logLevel))
//                //                {                 
//                LogLevel = logLevel;
//                MainConsole.Instance.OutputFormat("Set log level to {0}", LogLevel);
//                //                }
//            }
//            else 
//            {
//                MainConsole.Instance.OutputFormat("Unrecognized job engine subcommand {0}", subCommand);
//            }
//        }
    }
}