/*
Copyright (c) Contributors, http://osflotsam.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 Flotsam 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. */

// Uncomment to make asset Get requests for existing 
// #define WAIT_ON_INPROGRESS_REQUESTS

using System;
using System.IO;
using System.Collections.Generic;
using System.Reflection;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;
using System.Threading;
using System.Timers;

using log4net;
using Nini.Config;
using Mono.Addins;
using OpenMetaverse;

using OpenSim.Framework;
using OpenSim.Region.Framework.Interfaces;
using OpenSim.Region.Framework.Scenes;
using OpenSim.Services.Interfaces;


[assembly: Addin("FlotsamAssetCache", "1.1")]
[assembly: AddinDependency("OpenSim", "0.5")]

namespace Flotsam.RegionModules.AssetCache
{
    /// <summary>
    /// OpenSim.ini Options:
    /// -------
    /// [Modules]
    ///     AssetCaching = "FlotsamAssetCache"
    ///
    /// [AssetCache]
    ///    ; cache directory can be shared by multiple instances
    ///    CacheDirectory = /directory/writable/by/OpenSim/instance
    ///    
    ///    ; Log level
    ///    ; 0 - (Error) Errors only
    ///    ; 1 - (Info)  Hit Rate Stats + Level 0
    ///    ; 2 - (Debug) Cache Activity (Reads/Writes) + Level 1
    ///    ;
    ///    LogLevel = 1
    /// 
    ///    ; How often should hit rates be displayed (given in AssetRequests)
    ///    ; 0 to disable
    ///    HitRateDisplay = 100
    /// 
    ///    ; Set to false for disk cache only.
    ///    MemoryCacheEnabled = true
    ///    
    ///    ; How long {in hours} to keep assets cached in memory, .5 == 30 minutes
    ///    MemoryCacheTimeout = 2
    ///    
    ///    ; How long {in hours} to keep assets cached on disk, .5 == 30 minutes
    ///    ; Specify 0 if you do not want your disk cache to expire
    ///    FileCacheTimeout = 0
    ///    
    ///    ; How often {in hours} should the disk be checked for expired filed
    ///    ; Specify 0 to disable expiration checking
    ///    FileCleanupTimer = .166  ;roughly every 10 minutes
    ///    
    ///    ; If WAIT_ON_INPROGRESS_REQUESTS has been defined then this specifies how 
    ///    ; long (in miliseconds) to block a request thread while trying to complete 
    ///    ; writing to disk.
    ///    WaitOnInprogressTimeout = 3000
    /// -------
    /// </summary>

    [Extension(Path = "/OpenSim/RegionModules", NodeName = "RegionModule")]
    public class FlotsamAssetCache : ISharedRegionModule, IImprovedAssetCache
    {
        private static readonly ILog m_log =
                LogManager.GetLogger(
                MethodBase.GetCurrentMethod().DeclaringType);

        private bool m_Enabled = false;

        private const string m_ModuleName = "FlotsamAssetCache";
        private const string m_DefaultCacheDirectory = m_ModuleName;
        private string m_CacheDirectory = m_DefaultCacheDirectory;


        private List<char> m_InvalidChars = new List<char>();

        private int m_LogLevel = 1;
        private ulong m_HitRateDisplay = 1; // How often to display hit statistics, given in requests

        private static ulong m_Requests = 0;
        private static ulong m_RequestsForInprogress = 0;
        private static ulong m_DiskHits = 0;
        private static ulong m_MemoryHits = 0;
        private static double m_HitRateMemory = 0.0;
        private static double m_HitRateFile = 0.0;

#if WAIT_ON_INPROGRESS_REQUESTS
        private Dictionary<string, ManualResetEvent> m_CurrentlyWriting = new Dictionary<string, ManualResetEvent>();
        private int m_WaitOnInprogressTimeout = 3000;
#else
        private List<string> m_CurrentlyWriting = new List<string>();
#endif

        private ExpiringCache<string, AssetBase> m_MemoryCache = new ExpiringCache<string, AssetBase>();
        private bool m_MemoryCacheEnabled = true;

        // Expiration is expressed in hours.
        private const double m_DefaultMemoryExpiration = 1.0; 
        private const double m_DefaultFileExpiration = 48;
        private TimeSpan m_MemoryExpiration = TimeSpan.Zero;
        private TimeSpan m_FileExpiration = TimeSpan.Zero;
        private TimeSpan m_FileExpirationCleanupTimer = TimeSpan.Zero;

        private System.Timers.Timer m_CachCleanTimer = new System.Timers.Timer();

        public FlotsamAssetCache()
        {
            m_InvalidChars.AddRange(Path.GetInvalidPathChars());
            m_InvalidChars.AddRange(Path.GetInvalidFileNameChars());
        }

        public Type ReplacableInterface 
        {
            get { return null; }
        }

        public string Name
        {
            get { return m_ModuleName; }
        }

        public void Initialise(IConfigSource source)
        {
            IConfig moduleConfig = source.Configs["Modules"];

            if (moduleConfig != null)
            {
                string name = moduleConfig.GetString("AssetCaching", "");

                if (name == Name)
                {
                    m_Enabled = true;
                    m_log.InfoFormat("[ASSET CACHE]: {0} enabled", this.Name);

                    IConfig assetConfig = source.Configs["AssetCache"];
                    if (assetConfig == null)
                    {
                        m_log.Warn("[ASSET CACHE]: AssetCache missing from OpenSim.ini, using defaults.");
                        m_log.InfoFormat("[ASSET CACHE]: Cache Directory", m_DefaultCacheDirectory);
                        return;
                    }

                    m_CacheDirectory = assetConfig.GetString("CacheDirectory", m_DefaultCacheDirectory);
                    m_log.InfoFormat("[ASSET CACHE]: Cache Directory", m_DefaultCacheDirectory);

                    m_MemoryCacheEnabled = assetConfig.GetBoolean("MemoryCacheEnabled", true);
                    m_MemoryExpiration = TimeSpan.FromHours(assetConfig.GetDouble("MemoryCacheTimeout", m_DefaultMemoryExpiration));

#if WAIT_ON_INPROGRESS_REQUESTS
                    m_WaitOnInprogressTimeout = assetConfig.GetInt("WaitOnInprogressTimeout", 3000);
#endif

                    m_LogLevel = assetConfig.GetInt("LogLevel", 1);
                    m_HitRateDisplay = (ulong)assetConfig.GetInt("HitRateDisplay", 1);

                    m_FileExpiration = TimeSpan.FromHours(assetConfig.GetDouble("FileCacheTimeout", m_DefaultFileExpiration));
                    m_FileExpirationCleanupTimer = TimeSpan.FromHours(assetConfig.GetDouble("FileCleanupTimer", m_DefaultFileExpiration));
                    if ((m_FileExpiration > TimeSpan.Zero) && (m_FileExpirationCleanupTimer > TimeSpan.Zero))
                    {
                        m_CachCleanTimer.Interval = m_FileExpirationCleanupTimer.TotalMilliseconds;
                        m_CachCleanTimer.AutoReset = true;
                        m_CachCleanTimer.Elapsed += CleanupExpiredFiles;
                        m_CachCleanTimer.Enabled = true;
                        m_CachCleanTimer.Start();
                    }
                    else
                    {
                        m_CachCleanTimer.Enabled = false;
                    }
                }
            }
        }

        public void PostInitialise()
        {
        }

        public void Close()
        {
        }

        public void AddRegion(Scene scene)
        {
            if (m_Enabled)
                scene.RegisterModuleInterface<IImprovedAssetCache>(this);
        }

        public void RemoveRegion(Scene scene)
        {
        }

        public void RegionLoaded(Scene scene)
        {
        }

        ////////////////////////////////////////////////////////////
        // IImprovedAssetCache
        //

        private void UpdateMemoryCache(string key, AssetBase asset)
        {
            if (m_MemoryCacheEnabled)
            {
                if (m_MemoryExpiration > TimeSpan.Zero)
                {
                    m_MemoryCache.AddOrUpdate(key, asset, m_MemoryExpiration);
                }
                else
                {
                    m_MemoryCache.AddOrUpdate(key, asset, DateTime.MaxValue);
                }
            }
        }

        public void Cache(AssetBase asset)
        {
            // TODO: Spawn this off to some seperate thread to do the actual writing
            if (asset != null)
            {
                UpdateMemoryCache(asset.ID, asset);

                string filename = GetFileName(asset.ID);

                try
                {
                    // If the file is already cached, don't cache it, just touch it so access time is updated
                    if (File.Exists(filename))
                    {
                        File.SetLastAccessTime(filename, DateTime.Now);
                    } else { 
                        
                        // Once we start writing, make sure we flag that we're writing
                        // that object to the cache so that we don't try to write the 
                        // same file multiple times.
                        lock (m_CurrentlyWriting)
                        {
#if WAIT_ON_INPROGRESS_REQUESTS
                            if (m_CurrentlyWriting.ContainsKey(filename))
                            {
                                return;
                            }
                            else
                            {
                                m_CurrentlyWriting.Add(filename, new ManualResetEvent(false));
                            }

#else
                            if (m_CurrentlyWriting.Contains(filename))
                            {
                                return;
                            }
                            else
                            {
                                m_CurrentlyWriting.Add(filename);
                            }
#endif

                        }

                        ThreadPool.QueueUserWorkItem(
                            delegate
                            {
                                WriteFileCache(filename, asset);
                            }
                        );
                    }
                }
                catch (Exception e)
                {
                    LogException(e);
                }
            }
        }

        public AssetBase Get(string id)
        {
            m_Requests++;

            AssetBase asset = null;

            if (m_MemoryCacheEnabled && m_MemoryCache.TryGetValue(id, out asset))
            {
                m_MemoryHits++;
            }
            else
            {
                string filename = GetFileName(id);
                if (File.Exists(filename))
                {
                    try
                    {
                        FileStream stream = File.Open(filename, FileMode.Open);
                        BinaryFormatter bformatter = new BinaryFormatter();

                        asset = (AssetBase)bformatter.Deserialize(stream);
                        stream.Close();

                        UpdateMemoryCache(id, asset);

                        m_DiskHits++;
                    }
                    catch (System.Runtime.Serialization.SerializationException e)
                    {
                        LogException(e);

                        // If there was a problem deserializing the asset, the asset may 
                        // either be corrupted OR was serialized under an old format 
                        // {different version of AssetBase} -- we should attempt to
                        // delete it and re-cache
                        File.Delete(filename);
                    }
                    catch (Exception e)
                    {
                        LogException(e);
                    }
                }


#if WAIT_ON_INPROGRESS_REQUESTS
                // Check if we're already downloading this asset.  If so, try to wait for it to 
                // download.
                if (m_WaitOnInprogressTimeout > 0)
                {
                    m_RequestsForInprogress++;

                    ManualResetEvent waitEvent;
                    if (m_CurrentlyWriting.TryGetValue(filename, out waitEvent))
                    {
                        waitEvent.WaitOne(m_WaitOnInprogressTimeout);
                        return Get(id);
                    }
                }
#else
                // Track how often we have the problem that an asset is requested while
                // it is still being downloaded by a previous request.
                if (m_CurrentlyWriting.Contains(filename))
                {
                    m_RequestsForInprogress++;
                }
#endif
            }

            if (((m_LogLevel >= 1)) && (m_HitRateDisplay != 0) && (m_Requests % m_HitRateDisplay == 0))
            {
                m_HitRateFile = (double)m_DiskHits / m_Requests * 100.0;

                m_log.InfoFormat("[ASSET CACHE]: Cache Get :: {0} :: {1}", id, asset == null ? "Miss" : "Hit");
                m_log.InfoFormat("[ASSET CACHE]: File Hit Rate {0}% for {1} requests", m_HitRateFile.ToString("0.00"), m_Requests);

                if (m_MemoryCacheEnabled)
                {
                    m_HitRateMemory = (double)m_MemoryHits / m_Requests * 100.0;
                    m_log.InfoFormat("[ASSET CACHE]: Memory Hit Rate {0}% for {1} requests", m_HitRateMemory.ToString("0.00"), m_Requests);
                }

                m_log.InfoFormat("[ASSET CACHE]: {0} unnessesary requests due to requests for assets that are currently downloading.", m_RequestsForInprogress);
                
            }

            return asset;
        }

        public void Expire(string id)
        {
            if (m_LogLevel >= 2)
                m_log.DebugFormat("[ASSET CACHE]: Expiring Asset {0}.", id);

            try
            {
                string filename = GetFileName(id);
                if (File.Exists(filename))
                {
                    File.Delete(filename);
                }

                if (m_MemoryCacheEnabled)
                    m_MemoryCache.Remove(id);
            }
            catch (Exception e)
            {
                LogException(e);
            }
        }

        public void Clear()
        {
            if (m_LogLevel >= 2)
                m_log.Debug("[ASSET CACHE]: Clearing Cache.");

            foreach (string dir in Directory.GetDirectories(m_CacheDirectory))
            {
                Directory.Delete(dir);
            }

            if (m_MemoryCacheEnabled)
                m_MemoryCache.Clear();
        }

        private void CleanupExpiredFiles(object source, ElapsedEventArgs e)
        {
            if (m_LogLevel >= 2)
                m_log.DebugFormat("[ASSET CACHE]: Checking for expired files older then {0}.", m_FileExpiration.ToString());

            foreach (string dir in Directory.GetDirectories(m_CacheDirectory))
            {
                foreach (string file in Directory.GetFiles(dir))
                {
                    if (DateTime.Now - File.GetLastAccessTime(file) > m_FileExpiration)
                    {
                        File.Delete(file);
                    }
                }
            }
        }

        private string GetFileName(string id)
        {
            // Would it be faster to just hash the darn thing?
            foreach (char c in m_InvalidChars)
            {
                id = id.Replace(c, '_');
            }

            string p = id.Substring(id.Length - 4);
            p = Path.Combine(p, id);
            return Path.Combine(m_CacheDirectory, p);
        }

        private void WriteFileCache(string filename, AssetBase asset)
        {
            try
            {
                // Make sure the target cache directory exists
                string directory = Path.GetDirectoryName(filename);
                if (!Directory.Exists(directory))
                {
                    Directory.CreateDirectory(directory);
                }

                // Write file first to a temp name, so that it doesn't look 
                // like it's already cached while it's still writing.
                string tempname = Path.Combine(directory, Path.GetRandomFileName());
                Stream stream = File.Open(tempname, FileMode.Create);
                BinaryFormatter bformatter = new BinaryFormatter();
                bformatter.Serialize(stream, asset);
                stream.Close();

                // Now that it's written, rename it so that it can be found.
                File.Move(tempname, filename);

                if (m_LogLevel >= 2)
                    m_log.DebugFormat("[ASSET CACHE]: Cache Stored :: {0}", asset.ID);
            }
            catch (Exception e)
            {
                LogException(e);
            }
            finally
            {
                // Even if the write fails with an exception, we need to make sure
                // that we release the lock on that file, otherwise it'll never get
                // cached
                lock (m_CurrentlyWriting)
                {
#if WAIT_ON_INPROGRESS_REQUESTS
                    ManualResetEvent waitEvent;
                    if (m_CurrentlyWriting.TryGetValue(filename, out waitEvent))
                    {
                        m_CurrentlyWriting.Remove(filename);
                        waitEvent.Set();
                    }
#else
                    if (m_CurrentlyWriting.Contains(filename))
                    {
                        m_CurrentlyWriting.Remove(filename);
                    }
#endif
                }

            }
        }

        private static void LogException(Exception e)
        {
            string[] text = e.ToString().Split(new char[] { '\n' });
            foreach (string t in text)
            {
                m_log.ErrorFormat("[ASSET CACHE]: {0} ", t);
            }
        }
    }
}