/*
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 * See CONTRIBUTORS.TXT for a full list of copyright holders.
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 * modification, are permitted provided that the following conditions are met:
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 *       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.
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 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
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 * 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
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

using System;
using System.Collections.Generic;

using libsecondlife;
using libsecondlife.Packets;

using OpenSim.Framework;
using OpenSim.Framework.Console;
using OpenSim.Region.Environment.Interfaces;
using OpenSim.Region.Environment.Scenes;

namespace OpenSim.Region.Environment.Modules
{
    /// <summary>
    /// This module sets up texture senders in response to client texture requests, and places them on a
    /// processing queue once those senders have the appropriate data (i.e. a texture retrieved from the 
    /// asset cache).
    /// </summary>
    public class UserTextureDownloadService
    {
        private static readonly log4net.ILog m_log 
            = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);

        /// <summary>
        /// We will allow the client to request the same texture n times before dropping further requests
        /// </summary>
        private static readonly int MAX_ALLOWED_TEXTURE_REQUESTS = 5;
        
        /// <summary>
        /// Holds texture senders before they have received the appropriate texture from the asset cache.
        /// </summary>
        private readonly Dictionary<LLUUID, TextureSender> m_textureSenders = new Dictionary<LLUUID, TextureSender>();
        
        /// <summary>
        /// Texture Senders are placed in this queue once they have received their texture from the asset
        /// cache.  Another module actually invokes the send.
        /// </summary>
        private readonly BlockingQueue<ITextureSender> m_sharedSendersQueue;
        
        /// <summary>
        /// We're going to record when we get a request for a particular missing texture for each client
        /// XXX This is really a temporary solution to deal with the situation where a client continually requests
        /// the same missing textures
        /// </summary>
        private readonly Dictionary<LLUUID, int> missingTextureRequestCounts = new Dictionary<LLUUID, int>();
        
        /// <summary>
        /// XXX Also going to record all the textures found and dispatched
        /// </summary>
        private readonly Dictionary<LLUUID, int> dispatchedTextureRequestCounts = new Dictionary<LLUUID, int>();
        
        private readonly Scene m_scene;
        
        private readonly IClientAPI m_client;

        public UserTextureDownloadService(
            IClientAPI client, Scene scene, BlockingQueue<ITextureSender> sharedQueue)
        {
            m_client = client;
            m_scene = scene;
            m_sharedSendersQueue = sharedQueue;
        }

        /// <summary>
        /// Handle a texture request.  This involves creating a texture sender and placing it on the 
        /// previously passed in shared queue.
        /// </summary>
        /// <param name="e"></param>
        public void HandleTextureRequest(TextureRequestArgs e)
        {
            TextureSender textureSender;

            //TODO: should be working out the data size/ number of packets to be sent for each discard level
            if ((e.DiscardLevel >= 0) || (e.Priority != 0))
            {
                lock (m_textureSenders)
                {
                    if (m_textureSenders.TryGetValue(e.RequestedAssetID, out textureSender))
                    {
                        // If we've received new non UUID information for this request and it hasn't dispatched 
                        // yet, then update the request accordingly.
                        textureSender.UpdateRequest(e.DiscardLevel, e.PacketNumber);                        
                    }
                    else
                    {                 
                        // If we've already told the client we're missing the texture, then don't ask the 
                        // asset server for it again - record the fact that it's missing instead.
                        // XXX This is to reduce (but not resolve) a current problem where some clients keep 
                        // requesting the same textures                        
                        if (missingTextureRequestCounts.ContainsKey(e.RequestedAssetID))
                        {
                            missingTextureRequestCounts[e.RequestedAssetID] += 1;
                            
                            if (missingTextureRequestCounts[e.RequestedAssetID] > MAX_ALLOWED_TEXTURE_REQUESTS)
                            {
                                if (MAX_ALLOWED_TEXTURE_REQUESTS + 1 == missingTextureRequestCounts[e.RequestedAssetID])
                                {
                                    m_log.DebugFormat(
                                        "[USER TEXTURE DOWNLOAD SERVICE]: Dropping requests for notified missing texture {0} for {1} since we have received more than {2} requests",
                                        e.RequestedAssetID, m_client.AgentId, MAX_ALLOWED_TEXTURE_REQUESTS);
                                }
                                
                                return;
                            }                                                         
                        }
                        else
                        {          
                            // If we keep receiving requests for textures we've already served to the client,
                            // then stop sending them.  This is a short term approach approach to the problem
                            // of clients which keep requesting the same texture - the long term approach
                            // will be to treat the cause (and possibly more generally cap the request 
                            // queues as well/instead)
                            if (dispatchedTextureRequestCounts.ContainsKey(e.RequestedAssetID))
                            {
                                dispatchedTextureRequestCounts[e.RequestedAssetID] += 1;                                
                                
                                if (dispatchedTextureRequestCounts[e.RequestedAssetID] > MAX_ALLOWED_TEXTURE_REQUESTS)
                                {
//                                    if (MAX_ALLOWED_TEXTURE_REQUESTS + 1 == dispatchedTextureRequestCounts[e.RequestedAssetID])
//                                    {
//                                        m_log.DebugFormat(
//                                            "[USER TEXTURE DOWNLOAD SERVICE]: Dropping further requests for dispatched/queued texture {0} for {1} since we have received more than {2} requests",
//                                            e.RequestedAssetID, m_client.AgentId, MAX_ALLOWED_TEXTURE_REQUESTS);
//                                    }
                                    
                                    return;
                                }                               
                            }
                        }
                
                        m_scene.AddPendingDownloads(1);
                
                        TextureSender requestHandler = new TextureSender(m_client, e.DiscardLevel, e.PacketNumber);                        
                        m_textureSenders.Add(e.RequestedAssetID, requestHandler);
                        
                        m_scene.AssetCache.GetAsset(e.RequestedAssetID, TextureCallback, true);                                                        
                    }
                }
            }
            else
            {
                lock (m_textureSenders)
                {
                    if (m_textureSenders.TryGetValue(e.RequestedAssetID, out textureSender))
                    {
                        textureSender.Cancel = true;
                    }
                }
            }
        }

        /// <summary>
        /// The callback for the asset cache when a texture has been retrieved.  This method queues the
        /// texture sender for processing.
        /// </summary>
        /// <param name="textureID"></param>
        /// <param name="texture"></param>
        public void TextureCallback(LLUUID textureID, AssetBase texture)
        {
            //m_log.DebugFormat("[USER TEXTURE DOWNLOAD SERVICE]: Calling TextureCallback with {0}, texture == null is {1}", textureID, (texture == null ? true : false));
            
            lock (m_textureSenders)
            {
                TextureSender textureSender;

                if (m_textureSenders.TryGetValue(textureID, out textureSender))
                {
                    // XXX It may be perfectly valid for a texture to have no data...  but if we pass
                    // this on to the TextureSender it will blow up, so just discard for now.
                    // Needs investigation.
                    if (texture == null || texture.Data == null)
                    {                        
                        if (!missingTextureRequestCounts.ContainsKey(textureID))
                        {
                            missingTextureRequestCounts.Add(textureID, 1);

                            m_log.DebugFormat(
                                "[USER TEXTURE DOWNLOAD SERVICE]: Queueing first TextureNotFoundSender for {0}, client {1}", 
                                textureID, m_client.AgentId);
                        }
                       
                        ITextureSender textureNotFoundSender = new TextureNotFoundSender(m_client, textureID);
                        EnqueueTextureSender(textureNotFoundSender);                  
                    }
                    else
                    {
                        if (!textureSender.ImageLoaded)
                        {
                            textureSender.TextureReceived(texture);
                            EnqueueTextureSender(textureSender);
                            
                            // Record the fact that we've put this texture in for dispatch
                            if (!dispatchedTextureRequestCounts.ContainsKey(textureID))
                            {
                                dispatchedTextureRequestCounts.Add(textureID, 1);
                            }
                        }
                    }

                    //m_log.InfoFormat("[TEXTURE SENDER] Removing texture sender with uuid {0}", textureID);
                    m_textureSenders.Remove(textureID);                    
                    //m_log.InfoFormat("[TEXTURE SENDER] Current texture senders in dictionary: {0}", m_textureSenders.Count);
                }
                else
                {
                    m_log.WarnFormat(
                       "Got a texture uuid {0} with no sender object to handle it, this shouldn't happen",
                       textureID);
                }
            }
        }

        /// <summary>
        /// Place a ready texture sender on the processing queue.
        /// </summary>
        /// <param name="textureSender"></param>
        private void EnqueueTextureSender(ITextureSender textureSender)
        {
            textureSender.Cancel = false;
            textureSender.Sending = true;

            if (!m_sharedSendersQueue.Contains(textureSender))
            {
                m_sharedSendersQueue.Enqueue(textureSender);
            }
        }

        /// <summary>
        /// Close this module.
        /// </summary>
        internal void Close()
        {
            lock (m_textureSenders)
            {
                foreach( TextureSender textureSender in m_textureSenders.Values )
                {
                    textureSender.Cancel = true;
                }

                m_textureSenders.Clear();
            }
        }
    }
}