/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading;
using Apache.NMS.Stomp.Commands;
using Apache.NMS.Stomp.State;
using Apache.NMS.Stomp.Threads;
using Apache.NMS.Util;

namespace Apache.NMS.Stomp.Transport.Failover
{
    /// <summary>
    /// A Transport that is made reliable by being able to fail over to another
    /// transport when a transport failure is detected.
    /// </summary>
    public class FailoverTransport : ICompositeTransport, IComparable
    {
        private static int idCounter = 0;
        private readonly int id;

        private bool disposed;
        private bool connected;
        private readonly List<Uri> uris = new List<Uri>();
        private CommandHandler commandHandler;
        private ExceptionHandler exceptionHandler;
        private InterruptedHandler interruptedHandler;
        private ResumedHandler resumedHandler;

        private readonly Mutex reconnectMutex = new Mutex();
        private readonly Mutex sleepMutex = new Mutex();
        private readonly ConnectionStateTracker stateTracker = new ConnectionStateTracker();
        private readonly Dictionary<int, Command> requestMap = new Dictionary<int, Command>();

        private Uri connectedTransportURI;
        private Uri failedConnectTransportURI;
        private readonly AtomicReference<ITransport> connectedTransport = new AtomicReference<ITransport>(null);
        private TaskRunner reconnectTask = null;
        private bool started;

        private int timeout = -1;
        private int initialReconnectDelay = 10;
        private int maxReconnectDelay = 1000 * 30;
        private int backOffMultiplier = 2;
        private bool useExponentialBackOff = true;
        private bool randomize = true;
        private int maxReconnectAttempts;
        private int connectFailures;
        private int reconnectDelay = 10;
        private Exception connectionFailure;
        private bool firstConnection = true;
        private volatile Exception failure;
        private readonly object mutex = new object();

        public FailoverTransport()
        {
            id = idCounter++;
        }

        ~FailoverTransport()
        {
            Dispose(false);
        }

        #region FailoverTask

        private class FailoverTask : Task
        {
            private readonly FailoverTransport parent;

            public FailoverTask(FailoverTransport p)
            {
                parent = p;
            }

            public bool Iterate()
            {
                bool result = false;
                bool doReconnect = !parent.disposed && parent.connectionFailure == null;
                try
                {
                    if(parent.ConnectedTransport == null && doReconnect)
                    {
                        result = parent.DoConnect();
                    }
                }
                finally
                {
                }

                return result;
            }
        }

        #endregion

        #region Property Accessors

        public CommandHandler Command
        {
            get { return commandHandler; }
            set { commandHandler = value; }
        }

        public ExceptionHandler Exception
        {
            get { return exceptionHandler; }
            set { exceptionHandler = value; }
        }

        public InterruptedHandler Interrupted
        {
            get { return interruptedHandler; }
            set { this.interruptedHandler = value; }
        }

        public ResumedHandler Resumed
        {
            get { return resumedHandler; }
            set { this.resumedHandler = value; }
        }

        internal Exception Failure
        {
            get{ return failure; }
            set
            {
                lock(mutex)
                {
                    failure = value;
                }
            }
        }

        public int Timeout
        {
            get { return this.timeout; }
            set { this.timeout = value; }
        }

        public int InitialReconnectDelay
        {
            get { return initialReconnectDelay; }
            set { initialReconnectDelay = value; }
        }

        public int MaxReconnectDelay
        {
            get { return maxReconnectDelay; }
            set { maxReconnectDelay = value; }
        }

        public int ReconnectDelay
        {
            get { return reconnectDelay; }
            set { reconnectDelay = value; }
        }

        public int ReconnectDelayExponent
        {
            get { return backOffMultiplier; }
            set { backOffMultiplier = value; }
        }

        public ITransport ConnectedTransport
        {
            get { return connectedTransport.Value; }
            set { connectedTransport.Value = value; }
        }

        public Uri ConnectedTransportURI
        {
            get { return connectedTransportURI; }
            set { connectedTransportURI = value; }
        }

        public int MaxReconnectAttempts
        {
            get { return maxReconnectAttempts; }
            set { maxReconnectAttempts = value; }
        }

        public bool Randomize
        {
            get { return randomize; }
            set { randomize = value; }
        }

        public bool UseExponentialBackOff
        {
            get { return useExponentialBackOff; }
            set { useExponentialBackOff = value; }
        }

        #endregion

        public bool IsFaultTolerant
        {
            get { return true; }
        }

        public bool IsDisposed
        {
            get { return disposed; }
        }

        public bool IsConnected
        {
            get { return connected; }
        }

        public bool IsStarted
        {
            get { return started; }
        }

        /// <summary>
        /// </summary>
        /// <param name="command"></param>
        /// <returns>Returns true if the command is one sent when a connection is being closed.</returns>
        private static bool IsShutdownCommand(Command command)
        {
            return (command != null && (command.IsShutdownInfo || command is RemoveInfo));
        }

        public void OnException(ITransport sender, Exception error)
        {
            try
            {
                HandleTransportFailure(error);
            }
            catch(Exception e)
            {
                e.GetType();
                // What to do here?
            }
        }

        public void disposedOnCommand(ITransport sender, Command c)
        {
        }

        public void disposedOnException(ITransport sender, Exception e)
        {
        }

        public void HandleTransportFailure(Exception e)
        {
            ITransport transport = connectedTransport.GetAndSet(null);
            if(transport != null)
            {
                transport.Command = new CommandHandler(disposedOnCommand);
                transport.Exception = new ExceptionHandler(disposedOnException);
                try
                {
                    transport.Stop();
                }
                catch(Exception ex)
                {
                    ex.GetType();	// Ignore errors but this lets us see the error during debugging
                }

                lock(reconnectMutex)
                {
                    bool reconnectOk = false;
                    if(started)
                    {
                        Tracer.WarnFormat("Transport failed to {0}, attempting to automatically reconnect due to: {1}", ConnectedTransportURI.ToString(), e.Message);
                        reconnectOk = true;
                    }

                    failedConnectTransportURI = ConnectedTransportURI;
                    ConnectedTransportURI = null;
                    connected = false;
                    if(reconnectOk)
                    {
                        reconnectTask.Wakeup();
                    }
                }

                if(this.Interrupted != null)
                {
                    this.Interrupted(transport);
                }
            }
        }

        public void Start()
        {
            lock(reconnectMutex)
            {
                if(started)
                {
                    Tracer.Debug("FailoverTransport Already Started.");
                    return;
                }

                Tracer.Debug("FailoverTransport Started.");
                started = true;
                if(ConnectedTransport != null)
                {
                    stateTracker.DoRestore(ConnectedTransport);
                }
                else
                {
                    Reconnect();
                }
            }
        }

        public virtual void Stop()
        {
            ITransport transportToStop = null;

            lock(reconnectMutex)
            {
                if(!started)
                {
                    Tracer.Debug("FailoverTransport Already Stopped.");
                    return;
                }

                Tracer.Debug("FailoverTransport Stopped.");
                started = false;
                disposed = true;
                connected = false;

                if(ConnectedTransport != null)
                {
                    transportToStop = connectedTransport.GetAndSet(null);
                }
            }

            try
            {
                sleepMutex.WaitOne();
            }
            finally
            {
                sleepMutex.ReleaseMutex();
            }

            if(reconnectTask != null)
            {
                reconnectTask.Shutdown();
            }

            if(transportToStop != null)
            {
                transportToStop.Stop();
            }
        }

        public FutureResponse AsyncRequest(Command command)
        {
            throw new ApplicationException("FailoverTransport does not implement AsyncRequest(Command)");
        }

        public Response Request(Command command)
        {
            throw new ApplicationException("FailoverTransport does not implement Request(Command)");
        }

        public Response Request(Command command, TimeSpan ts)
        {
            throw new ApplicationException("FailoverTransport does not implement Request(Command, TimeSpan)");
        }

        public void OnCommand(ITransport sender, Command command)
        {
            if(command != null)
            {
                if(command.IsResponse)
                {
                    Object oo = null;
                    lock(((ICollection) requestMap).SyncRoot)
                    {
                        int v = ((Response) command).CorrelationId;
                        try
                        {
                            if(requestMap.ContainsKey(v))
                            {
                                oo = requestMap[v];
                                requestMap.Remove(v);
                            }
                        }
                        catch
                        {
                        }
                    }

                    Tracked t = oo as Tracked;
                    if(t != null)
                    {
                        t.onResponses();
                    }
                }
            }

            this.Command(sender, command);
        }

        public void Oneway(Command command)
        {
            Exception error = null;

            lock(reconnectMutex)
            {
                if(IsShutdownCommand(command) && ConnectedTransport == null)
                {
                    if(command.IsShutdownInfo)
                    {
                        // Skipping send of ShutdownInfo command when not connected.
                        return;
                    }

                    if(command is RemoveInfo)
                    {
                        // Simulate response to RemoveInfo command
                        Response response = new Response();
                        response.CorrelationId = command.CommandId;
                        OnCommand(this, response);
                        return;
                    }
                }

                // Keep trying until the message is sent.
                for(int i = 0; !disposed; i++)
                {
                    try
                    {
                        // Wait for transport to be connected.
                        ITransport transport = ConnectedTransport;
                        DateTime start = DateTime.Now;
                        bool timedout = false;
                        while(transport == null && !disposed && connectionFailure == null)
                        {
                            int elapsed = (int)(DateTime.Now - start).TotalMilliseconds;
                            if( this.timeout > 0 && elapsed > timeout )
                            {
                                timedout = true;
                                Tracer.DebugFormat("FailoverTransport.oneway - timed out after {0} mills", elapsed );
                                break;
                            }

                            // Release so that the reconnect task can run
                            try
                            {
                                // This is a bit of a hack, what should be happening is that when
                                // there's a reconnect the reconnectTask should signal the Monitor
                                // or some other event object to indicate that we can wakeup right
                                // away here, instead of performing the full wait.
                                Monitor.Exit(reconnectMutex);
                                Thread.Sleep(100);
                                Monitor.Enter(reconnectMutex);
                            }
                            catch(Exception e)
                            {
                                Tracer.DebugFormat("Interrupted: {0}", e.Message);
                            }

                            transport = ConnectedTransport;
                        }

                        if(transport == null)
                        {
                            // Previous loop may have exited due to use being disposed.
                            if(disposed)
                            {
                                error = new IOException("Transport disposed.");
                            }
                            else if(connectionFailure != null)
                            {
                                error = connectionFailure;
                            }
                            else if(timedout)
                            {
                                error = new IOException("Failover oneway timed out after "+ timeout +" milliseconds.");
                            }
                            else
                            {
                                error = new IOException("Unexpected failure.");
                            }
                            break;
                        }

                        // If it was a request and it was not being tracked by
                        // the state tracker, then hold it in the requestMap so
                        // that we can replay it later.
                        Tracked tracked = stateTracker.track(command);
                        lock(((ICollection) requestMap).SyncRoot)
                        {
                            if(tracked != null && tracked.WaitingForResponse)
                            {
                                requestMap.Add(command.CommandId, tracked);
                            }
                            else if(tracked == null && command.ResponseRequired)
                            {
                                requestMap.Add(command.CommandId, command);
                            }
                        }

                        // Send the message.
                        try
                        {
                            transport.Oneway(command);
                            stateTracker.trackBack(command);
                        }
                        catch(Exception e)
                        {
                            // If the command was not tracked.. we will retry in
                            // this method
                            if(tracked == null)
                            {

                                // since we will retry in this method.. take it
                                // out of the request map so that it is not
                                // sent 2 times on recovery
                                if(command.ResponseRequired)
                                {
                                    lock(((ICollection) requestMap).SyncRoot)
                                    {
                                        requestMap.Remove(command.CommandId);
                                    }
                                }

                                // Rethrow the exception so it will handled by
                                // the outer catch
                                throw e;
                            }

                        }

                        return;

                    }
                    catch(Exception e)
                    {
                        Tracer.DebugFormat("Send Oneway attempt: {0} failed: Message = {1}", i, e.Message);
                        Tracer.DebugFormat("Failed Message Was: {0}", command);
                        HandleTransportFailure(e);
                    }
                }
            }

            if(!disposed)
            {
                if(error != null)
                {
                    throw error;
                }
            }
        }

        public void Add(Uri[] u)
        {
            lock(uris)
            {
                for(int i = 0; i < u.Length; i++)
                {
                    if(!uris.Contains(u[i]))
                    {
                        uris.Add(u[i]);
                    }
                }
            }

            Reconnect();
        }

        public void Remove(Uri[] u)
        {
            lock(uris)
            {
                for(int i = 0; i < u.Length; i++)
                {
                    uris.Remove(u[i]);
                }
            }

            Reconnect();
        }

        public void Add(String u)
        {
            try
            {
                Uri uri = new Uri(u);
                lock(uris)
                {
                    if(!uris.Contains(uri))
                    {
                        uris.Add(uri);
                    }
                }

                Reconnect();
            }
            catch(Exception e)
            {
                Tracer.ErrorFormat("Failed to parse URI '{0}': {1}", u, e.Message);
            }
        }

        public void Reconnect(Uri uri)
        {
            Add(new Uri[] { uri });
        }

        public void Reconnect()
        {
            lock(reconnectMutex)
            {
                if(started)
                {
                    if(reconnectTask == null)
                    {
                        Tracer.Debug("Creating reconnect task");
                        reconnectTask = new DedicatedTaskRunner(new FailoverTask(this));
                    }

                    Tracer.Debug("Waking up reconnect task");
                    try
                    {
                        reconnectTask.Wakeup();
                    }
                    catch(Exception)
                    {
                    }
                }
                else
                {
                    Tracer.Debug("Reconnect was triggered but transport is not started yet. Wait for start to connect the transport.");
                }
            }
        }

        private List<Uri> ConnectList
        {
            get
            {
                List<Uri> l = new List<Uri>(uris);
                bool removed = false;
                if(failedConnectTransportURI != null)
                {
                    removed = l.Remove(failedConnectTransportURI);
                }

                if(Randomize)
                {
                    // Randomly, reorder the list by random swapping
                    Random r = new Random(DateTime.Now.Millisecond);
                    for(int i = 0; i < l.Count; i++)
                    {
                        int p = r.Next(l.Count);
                        Uri t = l[p];
                        l[p] = l[i];
                        l[i] = t;
                    }
                }

                if(removed)
                {
                    l.Add(failedConnectTransportURI);
                }

                return l;
            }
        }

        protected void RestoreTransport(ITransport t)
        {
            Tracer.Info("Restoring previous transport connection.");
            t.Start();

            stateTracker.DoRestore(t);

            Tracer.Info("Sending queued commands...");
            Dictionary<int, Command> tmpMap = null;
            lock(((ICollection) requestMap).SyncRoot)
            {
                tmpMap = new Dictionary<int, Command>(requestMap);
            }

            foreach(Command command in tmpMap.Values)
            {
                t.Oneway(command);
            }
        }

        public Uri RemoteAddress
        {
            get
            {
                if(ConnectedTransport != null)
                {
                    return ConnectedTransport.RemoteAddress;
                }
                return null;
            }
        }

        public Object Narrow(Type type)
        {
            if(this.GetType().Equals(type))
            {
                return this;
            }
            else if(ConnectedTransport != null)
            {
                return ConnectedTransport.Narrow(type);
            }

            return null;
        }

        private bool DoConnect()
        {
            lock(reconnectMutex)
            {
                if(ConnectedTransport != null || disposed || connectionFailure != null)
                {
                    return false;
                }
                else
                {
                    List<Uri> connectList = ConnectList;
                    if(connectList.Count == 0)
                    {
                        Failure = new NMSConnectionException("No URIs available for connection.");
                    }
                    else
                    {
                        if(!UseExponentialBackOff)
                        {
                            ReconnectDelay = InitialReconnectDelay;
                        }

                        ITransport transport = null;
                        Uri chosenUri = null;

                        try
                        {
                            foreach(Uri uri in connectList)
                            {
                                if(ConnectedTransport != null || disposed)
                                {
                                    break;
                                }

                                Tracer.DebugFormat("Attempting connect to: {0}", uri);

                                // synchronous connect
                                try
                                {
                                    Tracer.DebugFormat("Attempting connect to: {0}", uri.ToString());
                                    transport = TransportFactory.CompositeConnect(uri);
                                    chosenUri = transport.RemoteAddress;
                                    break;
                                }
                                catch(Exception e)
                                {
                                    Failure = e;
                                    Tracer.DebugFormat("Connect fail to: {0}, reason: {1}", uri, e.Message);
                                }
                            }

                            if(transport != null)
                            {
                                transport.Command = new CommandHandler(OnCommand);
                                transport.Exception = new ExceptionHandler(OnException);
                                transport.Start();

                                if(started)
                                {
                                    RestoreTransport(transport);
                                }

                                if(this.Resumed != null)
                                {
                                    this.Resumed(transport);
                                }

                                Tracer.Debug("Connection established");
                                ReconnectDelay = InitialReconnectDelay;
                                ConnectedTransportURI = chosenUri;
                                ConnectedTransport = transport;
                                connectFailures = 0;
                                connected = true;

                                if(firstConnection)
                                {
                                    firstConnection = false;
                                    Tracer.InfoFormat("Successfully connected to: {0}", chosenUri.ToString());
                                }
                                else
                                {
                                    Tracer.InfoFormat("Successfully reconnected to: {0}", chosenUri.ToString());
                                }

                                return false;
                            }
                        }
                        catch(Exception e)
                        {
                            Failure = e;
                            Tracer.DebugFormat("Connect attempt failed.  Reason: {0}", e.Message);
                        }
                    }

                    if(MaxReconnectAttempts > 0 && ++connectFailures >= MaxReconnectAttempts)
                    {
                        Tracer.ErrorFormat("Failed to connect to transport after {0} attempt(s)", connectFailures);
                        connectionFailure = Failure;
                        this.Exception(this, connectionFailure);
                        return false;
                    }
                }
            }

            if(!disposed)
            {
                Tracer.DebugFormat("Waiting {0}ms before attempting connection.", ReconnectDelay);
                lock(sleepMutex)
                {
                    try
                    {
                        Thread.Sleep(ReconnectDelay);
                    }
                    catch(Exception)
                    {
                    }
                }

                if(UseExponentialBackOff)
                {
                    // Exponential increment of reconnect delay.
                    ReconnectDelay *= ReconnectDelayExponent;
                    if(ReconnectDelay > MaxReconnectDelay)
                    {
                        ReconnectDelay = MaxReconnectDelay;
                    }
                }
            }
            return !disposed;
        }

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

        public void Dispose(bool disposing)
        {
            if(disposing)
            {
                // get rid of unmanaged stuff
            }

            disposed = true;
        }

        public int CompareTo(Object o)
        {
            if(o is FailoverTransport)
            {
                FailoverTransport oo = o as FailoverTransport;

                return this.id - oo.id;
            }
            else
            {
                throw new ArgumentException();
            }
        }

        public override String ToString()
        {
            return ConnectedTransportURI == null ? "unconnected" : ConnectedTransportURI.ToString();
        }
    }
}