/*
 * 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 copyrightD
 *       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.
 *
 * 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
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;
using OpenSim.Framework;
using OpenSim.Framework.Monitoring;
using OpenSim.Region.Framework;
using OpenSim.Region.CoreModules;
using Logging = OpenSim.Region.CoreModules.Framework.Statistics.Logging;
using OpenSim.Region.Physics.Manager;
using Nini.Config;
using log4net;
using OpenMetaverse;

namespace OpenSim.Region.Physics.BulletSPlugin
{
public sealed class BSScene : PhysicsScene, IPhysicsParameters
{
    internal static readonly ILog m_log = LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
    internal static readonly string LogHeader = "[BULLETS SCENE]";

    // The name of the region we're working for.
    public string RegionName { get; private set; }

    public string BulletSimVersion = "?";

    // The handle to the underlying managed or unmanaged version of Bullet being used.
    public string BulletEngineName { get; private set; }
    public BSAPITemplate PE;

    // If the physics engine is running on a separate thread
    public Thread m_physicsThread;

    public Dictionary<uint, BSPhysObject> PhysObjects;
    public BSShapeCollection Shapes;

    // Keeping track of the objects with collisions so we can report begin and end of a collision
    public HashSet<BSPhysObject> ObjectsWithCollisions = new HashSet<BSPhysObject>();
    public HashSet<BSPhysObject> ObjectsWithNoMoreCollisions = new HashSet<BSPhysObject>();

    // All the collision processing is protected with this lock object
    public Object CollisionLock = new Object();

    // Properties are updated here
    public Object UpdateLock = new Object();
    public HashSet<BSPhysObject> ObjectsWithUpdates = new HashSet<BSPhysObject>();

    // Keep track of all the avatars so we can send them a collision event
    //    every tick so OpenSim will update its animation.
    private HashSet<BSPhysObject> m_avatars = new HashSet<BSPhysObject>();

    // let my minuions use my logger
    public ILog Logger { get { return m_log; } }

    public IMesher mesher;
    public uint WorldID { get; private set; }
    public BulletWorld World { get; private set; }

    // All the constraints that have been allocated in this instance.
    public BSConstraintCollection Constraints { get; private set; }

    // Simulation parameters
    //internal float m_physicsStepTime;   // if running independently, the interval simulated by default

    internal int m_maxSubSteps;
    internal float m_fixedTimeStep;

    internal float m_simulatedTime;     // the time simulated previously. Used for physics framerate calc.

    internal long m_simulationStep = 0; // The current simulation step.
    public long SimulationStep { get { return m_simulationStep; } }
    // A number to use for SimulationStep that is probably not any step value
    // Used by the collision code (which remembers the step when a collision happens) to remember not any simulation step.
    public static long NotASimulationStep = -1234;

    internal float LastTimeStep { get; private set; }   // The simulation time from the last invocation of Simulate()

    internal float NominalFrameRate { get; set; }       // Parameterized ideal frame rate that simulation is scaled to

    // Physical objects can register for prestep or poststep events
    public delegate void PreStepAction(float timeStep);
    public delegate void PostStepAction(float timeStep);
    public event PreStepAction BeforeStep;
    public event PostStepAction AfterStep;

    // A value of the time 'now' so all the collision and update routines do not have to get their own
    // Set to 'now' just before all the prims and actors are called for collisions and updates
    public int SimulationNowTime { get; private set; }

    // True if initialized and ready to do simulation steps
    private bool m_initialized = false;

    // Flag which is true when processing taints.
    // Not guaranteed to be correct all the time (don't depend on this) but good for debugging.
    public bool InTaintTime { get; private set; }

    // Pinned memory used to pass step information between managed and unmanaged
    internal int m_maxCollisionsPerFrame;
    internal CollisionDesc[] m_collisionArray;

    internal int m_maxUpdatesPerFrame;
    internal EntityProperties[] m_updateArray;

    public const uint TERRAIN_ID = 0;       // OpenSim senses terrain with a localID of zero
    public const uint GROUNDPLANE_ID = 1;
    public const uint CHILDTERRAIN_ID = 2;  // Terrain allocated based on our mega-prim childre start here

    public float SimpleWaterLevel { get; set; }
    public BSTerrainManager TerrainManager { get; private set; }

    public ConfigurationParameters Params
    {
        get { return UnmanagedParams[0]; }
    }
    public Vector3 DefaultGravity
    {
        get { return new Vector3(0f, 0f, Params.gravity); }
    }
    // Just the Z value of the gravity
    public float DefaultGravityZ
    {
        get { return Params.gravity; }
    }

    // When functions in the unmanaged code must be called, it is only
    //   done at a known time just before the simulation step. The taint
    //   system saves all these function calls and executes them in
    //   order before the simulation.
    public delegate void TaintCallback();
    private struct TaintCallbackEntry
    {
        public String originator;
        public String ident;
        public TaintCallback callback;
        public TaintCallbackEntry(string pIdent, TaintCallback pCallBack)
        {
            originator = BSScene.DetailLogZero;
            ident = pIdent;
            callback = pCallBack;
        }
        public TaintCallbackEntry(string pOrigin, string pIdent, TaintCallback pCallBack)
        {
            originator = pOrigin;
            ident = pIdent;
            callback = pCallBack;
        }
    }
    private Object _taintLock = new Object();   // lock for using the next object
    private List<TaintCallbackEntry> _taintOperations;
    private Dictionary<string, TaintCallbackEntry> _postTaintOperations;
    private List<TaintCallbackEntry> _postStepOperations;

    // A pointer to an instance if this structure is passed to the C++ code
    // Used to pass basic configuration values to the unmanaged code.
    internal ConfigurationParameters[] UnmanagedParams;

    // Sometimes you just have to log everything.
    public Logging.LogWriter PhysicsLogging;
    private bool m_physicsLoggingEnabled;
    private string m_physicsLoggingDir;
    private string m_physicsLoggingPrefix;
    private int m_physicsLoggingFileMinutes;
    private bool m_physicsLoggingDoFlush;
    private bool m_physicsPhysicalDumpEnabled;
    public int PhysicsMetricDumpFrames { get; set; }
    // 'true' of the vehicle code is to log lots of details
    public bool VehicleLoggingEnabled { get; private set; }
    public bool VehiclePhysicalLoggingEnabled { get; private set; }

    #region Construction and Initialization
    public BSScene(string engineType, string identifier)
    {
        m_initialized = false;

        // The name of the region we're working for is passed to us. Keep for identification.
        RegionName = identifier;

        // Set identifying variables in the PhysicsScene interface.
        EngineType = engineType;
        Name = EngineType + "/" + RegionName;
    }

    // Old version of initialization that assumes legacy sized regions (256x256)
    public override void Initialise(IMesher meshmerizer, IConfigSource config)
    {
        m_log.ErrorFormat("{0} WARNING WARNING WARNING! BulletSim initialized without region extent specification. Terrain will be messed up.");
        Vector3 regionExtent = new Vector3( Constants.RegionSize, Constants.RegionSize, Constants.RegionSize);
        Initialise(meshmerizer, config, regionExtent);
        
    }

    public override void Initialise(IMesher meshmerizer, IConfigSource config, Vector3 regionExtent)
    {
        mesher = meshmerizer;
        _taintOperations = new List<TaintCallbackEntry>();
        _postTaintOperations = new Dictionary<string, TaintCallbackEntry>();
        _postStepOperations = new List<TaintCallbackEntry>();
        PhysObjects = new Dictionary<uint, BSPhysObject>();
        Shapes = new BSShapeCollection(this);

        m_simulatedTime = 0f;
        LastTimeStep = 0.1f;

        // Allocate pinned memory to pass parameters.
        UnmanagedParams = new ConfigurationParameters[1];

        // Set default values for physics parameters plus any overrides from the ini file
        GetInitialParameterValues(config);

        // Force some parameters to values depending on other configurations
        // Only use heightmap terrain implementation if terrain larger than legacy size
        if ((uint)regionExtent.X > Constants.RegionSize || (uint)regionExtent.Y > Constants.RegionSize)
        {
            m_log.WarnFormat("{0} Forcing terrain implementation to heightmap for large region", LogHeader);
            BSParam.TerrainImplementation = (float)BSTerrainPhys.TerrainImplementation.Heightmap;
        }

        // Get the connection to the physics engine (could be native or one of many DLLs)
        PE = SelectUnderlyingBulletEngine(BulletEngineName);

        // Enable very detailed logging.
        // By creating an empty logger when not logging, the log message invocation code
        //     can be left in and every call doesn't have to check for null.
        if (m_physicsLoggingEnabled)
        {
            PhysicsLogging = new Logging.LogWriter(m_physicsLoggingDir, m_physicsLoggingPrefix, m_physicsLoggingFileMinutes, m_physicsLoggingDoFlush);
            PhysicsLogging.ErrorLogger = m_log; // for DEBUG. Let's the logger output its own error messages.
        }
        else
        {
            PhysicsLogging = new Logging.LogWriter();
        }

        // Allocate memory for returning of the updates and collisions from the physics engine
        m_collisionArray = new CollisionDesc[m_maxCollisionsPerFrame];
        m_updateArray = new EntityProperties[m_maxUpdatesPerFrame];

        // The bounding box for the simulated world. The origin is 0,0,0 unless we're
        //    a child in a mega-region.
        // Bullet actually doesn't care about the extents of the simulated
        //    area. It tracks active objects no matter where they are.
        Vector3 worldExtent = regionExtent;

        World = PE.Initialize(worldExtent, Params, m_maxCollisionsPerFrame, ref m_collisionArray, m_maxUpdatesPerFrame, ref m_updateArray);

        Constraints = new BSConstraintCollection(World);

        TerrainManager = new BSTerrainManager(this, worldExtent);
        TerrainManager.CreateInitialGroundPlaneAndTerrain();

        // Put some informational messages into the log file.
        m_log.InfoFormat("{0} Linksets implemented with {1}", LogHeader, (BSLinkset.LinksetImplementation)BSParam.LinksetImplementation);

        InTaintTime = false;
        m_initialized = true;

        // If the physics engine runs on its own thread, start same.
        if (BSParam.UseSeparatePhysicsThread)
        {
            // The physics simulation should happen independently of the heartbeat loop
            m_physicsThread 
                = Watchdog.StartThread(
                    BulletSPluginPhysicsThread, 
                    string.Format("{0} ({1})", BulletEngineName, RegionName), 
                    ThreadPriority.Normal, 
                    true, 
                    true);
        }
    }

    // All default parameter values are set here. There should be no values set in the
    // variable definitions.
    private void GetInitialParameterValues(IConfigSource config)
    {
        ConfigurationParameters parms = new ConfigurationParameters();
        UnmanagedParams[0] = parms;

        BSParam.SetParameterDefaultValues(this);

        if (config != null)
        {
            // If there are specifications in the ini file, use those values
            IConfig pConfig = config.Configs["BulletSim"];
            if (pConfig != null)
            {
                BSParam.SetParameterConfigurationValues(this, pConfig);

                // There are two Bullet implementations to choose from
                BulletEngineName = pConfig.GetString("BulletEngine", "BulletUnmanaged");

                // Very detailed logging for physics debugging
                // TODO: the boolean values can be moved to the normal parameter processing.
                m_physicsLoggingEnabled = pConfig.GetBoolean("PhysicsLoggingEnabled", false);
                m_physicsLoggingDir = pConfig.GetString("PhysicsLoggingDir", ".");
                m_physicsLoggingPrefix = pConfig.GetString("PhysicsLoggingPrefix", "physics-%REGIONNAME%-");
                m_physicsLoggingFileMinutes = pConfig.GetInt("PhysicsLoggingFileMinutes", 5);
                m_physicsLoggingDoFlush = pConfig.GetBoolean("PhysicsLoggingDoFlush", false);
                m_physicsPhysicalDumpEnabled = pConfig.GetBoolean("PhysicsPhysicalDumpEnabled", false);
                // Very detailed logging for vehicle debugging
                VehicleLoggingEnabled = pConfig.GetBoolean("VehicleLoggingEnabled", false);
                VehiclePhysicalLoggingEnabled = pConfig.GetBoolean("VehiclePhysicalLoggingEnabled", false);

                // Do any replacements in the parameters
                m_physicsLoggingPrefix = m_physicsLoggingPrefix.Replace("%REGIONNAME%", RegionName);
            }
            else
            {
                // Nothing in the configuration INI file so assume unmanaged and other defaults.
                BulletEngineName = "BulletUnmanaged";
                m_physicsLoggingEnabled = false;
                VehicleLoggingEnabled = false;
            }

            // The material characteristics.
            BSMaterials.InitializeFromDefaults(Params);
            if (pConfig != null)
            {
                // Let the user add new and interesting material property values.
                BSMaterials.InitializefromParameters(pConfig);
            }
        }
    }

    // A helper function that handles a true/false parameter and returns the proper float number encoding
    float ParamBoolean(IConfig config, string parmName, float deflt)
    {
        float ret = deflt;
        if (config.Contains(parmName))
        {
            ret = ConfigurationParameters.numericFalse;
            if (config.GetBoolean(parmName, false))
            {
                ret = ConfigurationParameters.numericTrue;
            }
        }
        return ret;
    }

    // Select the connection to the actual Bullet implementation.
    // The main engine selection is the engineName up to the first hypen.
    // So "Bullet-2.80-OpenCL-Intel" specifies the 'bullet' class here and the whole name
    //     is passed to the engine to do its special selection, etc.
    private BSAPITemplate SelectUnderlyingBulletEngine(string engineName)
    {
        // For the moment, do a simple switch statement.
        // Someday do fancyness with looking up the interfaces in the assembly.
        BSAPITemplate ret = null;

        string selectionName = engineName.ToLower();
        int hyphenIndex = engineName.IndexOf("-");
        if (hyphenIndex > 0)
            selectionName = engineName.ToLower().Substring(0, hyphenIndex - 1);

        switch (selectionName)
        {
            case "bullet":
            case "bulletunmanaged":
                ret = new BSAPIUnman(engineName, this);
                break;
            case "bulletxna":
                ret = new BSAPIXNA(engineName, this);
                // Disable some features that are not implemented in BulletXNA
                m_log.InfoFormat("{0} Disabling some physics features not implemented by BulletXNA", LogHeader);
                m_log.InfoFormat("{0}    Disabling ShouldUseBulletHACD", LogHeader);
                BSParam.ShouldUseBulletHACD = false;
                m_log.InfoFormat("{0}    Disabling ShouldUseSingleConvexHullForPrims", LogHeader);
                BSParam.ShouldUseSingleConvexHullForPrims = false;
                m_log.InfoFormat("{0}    Disabling ShouldUseGImpactShapeForPrims", LogHeader);
                BSParam.ShouldUseGImpactShapeForPrims = false;
                m_log.InfoFormat("{0}    Setting terrain implimentation to Heightmap", LogHeader);
                BSParam.TerrainImplementation = (float)BSTerrainPhys.TerrainImplementation.Heightmap;
                break;
        }

        if (ret == null)
        {
            m_log.ErrorFormat("{0) COULD NOT SELECT BULLET ENGINE: '[BulletSim]PhysicsEngine' must be either 'BulletUnmanaged-*' or 'BulletXNA-*'", LogHeader);
        }
        else
        {
            m_log.InfoFormat("{0} Selected bullet engine {1} -> {2}/{3}", LogHeader, engineName, ret.BulletEngineName, ret.BulletEngineVersion);
        }

        return ret;
    }

    public override void Dispose()
    {
        // m_log.DebugFormat("{0}: Dispose()", LogHeader);

        // make sure no stepping happens while we're deleting stuff
        m_initialized = false;

        foreach (KeyValuePair<uint, BSPhysObject> kvp in PhysObjects)
        {
            kvp.Value.Destroy();
        }
        PhysObjects.Clear();

        // Now that the prims are all cleaned up, there should be no constraints left
        if (Constraints != null)
        {
            Constraints.Dispose();
            Constraints = null;
        }

        if (Shapes != null)
        {
            Shapes.Dispose();
            Shapes = null;
        }

        if (TerrainManager != null)
        {
            TerrainManager.ReleaseGroundPlaneAndTerrain();
            TerrainManager.Dispose();
            TerrainManager = null;
        }

        // Anything left in the unmanaged code should be cleaned out
        PE.Shutdown(World);

        // Not logging any more
        PhysicsLogging.Close();
    }
    #endregion // Construction and Initialization

    #region Prim and Avatar addition and removal

    public override PhysicsActor AddAvatar(string avName, Vector3 position, Vector3 size, bool isFlying)
    {
        m_log.ErrorFormat("{0}: CALL TO AddAvatar in BSScene. NOT IMPLEMENTED", LogHeader);
        return null;
    }

    public override PhysicsActor AddAvatar(uint localID, string avName, Vector3 position, Vector3 size, bool isFlying)
    {
        // m_log.DebugFormat("{0}: AddAvatar: {1}", LogHeader, avName);

        if (!m_initialized) return null;

        BSCharacter actor = new BSCharacter(localID, avName, this, position, size, isFlying);
        lock (PhysObjects)
            PhysObjects.Add(localID, actor);

        // TODO: Remove kludge someday.
        // We must generate a collision for avatars whether they collide or not.
        // This is required by OpenSim to update avatar animations, etc.
        lock (m_avatars)
        {
            // The funky copy is because this list has few and infrequent changes but is
            //    read zillions of times. This allows the reader/iterator to use the
            //    list and this creates a new list with any updates.
            HashSet<BSPhysObject> avatarTemp = new HashSet<BSPhysObject>(m_avatars);
            avatarTemp.Add(actor);
            m_avatars = avatarTemp;
        }

        return actor;
    }

    public override void RemoveAvatar(PhysicsActor actor)
    {
        // m_log.DebugFormat("{0}: RemoveAvatar", LogHeader);

        if (!m_initialized) return;

        BSCharacter bsactor = actor as BSCharacter;
        if (bsactor != null)
        {
            try
            {
                lock (PhysObjects)
                    PhysObjects.Remove(bsactor.LocalID);
                // Remove kludge someday
                lock (m_avatars)
                {
                    HashSet<BSPhysObject> avatarTemp = new HashSet<BSPhysObject>(m_avatars);
                    avatarTemp.Remove(bsactor);
                    m_avatars = avatarTemp;
                }
            }
            catch (Exception e)
            {
                m_log.WarnFormat("{0}: Attempt to remove avatar that is not in physics scene: {1}", LogHeader, e);
            }
            bsactor.Destroy();
            // bsactor.dispose();
        }
        else
        {
            m_log.ErrorFormat("{0}: Requested to remove avatar that is not a BSCharacter. ID={1}, type={2}",
                                        LogHeader, actor.LocalID, actor.GetType().Name);
        }
    }

    public override void RemovePrim(PhysicsActor prim)
    {
        if (!m_initialized) return;

        BSPhysObject bsprim = prim as BSPhysObject;
        if (bsprim != null)
        {
            DetailLog("{0},RemovePrim,call", bsprim.LocalID);
            // m_log.DebugFormat("{0}: RemovePrim. id={1}/{2}", LogHeader, bsprim.Name, bsprim.LocalID);
            try
            {
                lock (PhysObjects) PhysObjects.Remove(bsprim.LocalID);
            }
            catch (Exception e)
            {
                m_log.ErrorFormat("{0}: Attempt to remove prim that is not in physics scene: {1}", LogHeader, e);
            }
            bsprim.Destroy();
            // bsprim.dispose();
        }
        else
        {
            m_log.ErrorFormat("{0}: Attempt to remove prim that is not a BSPrim type.", LogHeader);
        }
    }

    public override PhysicsActor AddPrimShape(string primName, PrimitiveBaseShape pbs, Vector3 position,
                                              Vector3 size, Quaternion rotation, bool isPhysical, uint localID)
    {
        // m_log.DebugFormat("{0}: AddPrimShape2: {1}", LogHeader, primName);

        if (!m_initialized) return null;

        // DetailLog("{0},BSScene.AddPrimShape,call", localID);

        BSPhysObject prim = new BSPrimLinkable(localID, primName, this, position, size, rotation, pbs, isPhysical);
        lock (PhysObjects) PhysObjects.Add(localID, prim);
        return prim;
    }

    // This is a call from the simulator saying that some physical property has been updated.
    // The BulletSim driver senses the changing of relevant properties so this taint
    // information call is not needed.
    public override void AddPhysicsActorTaint(PhysicsActor prim) { }

    #endregion // Prim and Avatar addition and removal

    #region Simulation

    // Call from the simulator to send physics information to the simulator objects.
    // This pushes all the collision and property update events into the objects in
    //    the simulator and, since it is on the heartbeat thread, there is an implicit
    //    locking of those data structures from other heartbeat events.
    // If the physics engine is running on a separate thread, the update information
    //    will be in the ObjectsWithCollions and ObjectsWithUpdates structures.
    public override float Simulate(float timeStep)
    {
        if (!BSParam.UseSeparatePhysicsThread)
        {
            DoPhysicsStep(timeStep);
        }
        return SendUpdatesToSimulator(timeStep);
    }

    // Call the physics engine to do one 'timeStep' and collect collisions and updates
    //    into ObjectsWithCollisions and ObjectsWithUpdates data structures.
    private void DoPhysicsStep(float timeStep)
    {
        // prevent simulation until we've been initialized
        if (!m_initialized) return;

        LastTimeStep = timeStep;

        int updatedEntityCount = 0;
        int collidersCount = 0;

        int beforeTime = Util.EnvironmentTickCount();
        int simTime = 0;

        int numTaints = _taintOperations.Count;
        InTaintTime = true; // Only used for debugging so locking is not necessary.

        // update the prim states while we know the physics engine is not busy
        ProcessTaints();

        // Some of the physical objects requre individual, pre-step calls
        //      (vehicles and avatar movement, in particular)
        TriggerPreStepEvent(timeStep);

        // the prestep actions might have added taints
        numTaints += _taintOperations.Count;
        ProcessTaints();

        InTaintTime = false; // Only used for debugging so locking is not necessary.

        // The following causes the unmanaged code to output ALL the values found in ALL the objects in the world.
        // Only enable this in a limited test world with few objects.
        if (m_physicsPhysicalDumpEnabled)
            PE.DumpAllInfo(World);

        // step the physical world one interval
        m_simulationStep++;
        int numSubSteps = 0;
        try
        {
            numSubSteps = PE.PhysicsStep(World, timeStep, m_maxSubSteps, m_fixedTimeStep, out updatedEntityCount, out collidersCount);

        }
        catch (Exception e)
        {
            m_log.WarnFormat("{0},PhysicsStep Exception: nTaints={1}, substeps={2}, updates={3}, colliders={4}, e={5}",
                        LogHeader, numTaints, numSubSteps, updatedEntityCount, collidersCount, e);
            DetailLog("{0},PhysicsStepException,call, nTaints={1}, substeps={2}, updates={3}, colliders={4}",
                        DetailLogZero, numTaints, numSubSteps, updatedEntityCount, collidersCount);
            updatedEntityCount = 0;
            collidersCount = 0;
        }

        // Make the physics engine dump useful statistics periodically
        if (PhysicsMetricDumpFrames != 0 && ((m_simulationStep % PhysicsMetricDumpFrames) == 0))
            PE.DumpPhysicsStatistics(World);

        // Get a value for 'now' so all the collision and update routines don't have to get their own.
        SimulationNowTime = Util.EnvironmentTickCount();

        // Send collision information to the colliding objects. The objects decide if the collision
        //     is 'real' (like linksets don't collide with themselves) and the individual objects
        //     know if the simulator has subscribed to collisions.
        lock (CollisionLock)
        {
            if (collidersCount > 0)
            {
                lock (PhysObjects)
                {
                    for (int ii = 0; ii < collidersCount; ii++)
                    {
                        uint cA = m_collisionArray[ii].aID;
                        uint cB = m_collisionArray[ii].bID;
                        Vector3 point = m_collisionArray[ii].point;
                        Vector3 normal = m_collisionArray[ii].normal;
                        float penetration = m_collisionArray[ii].penetration;
                        SendCollision(cA, cB, point, normal, penetration);
                        SendCollision(cB, cA, point, -normal, penetration);
                    }
                }
            }
        }

        // If any of the objects had updated properties, tell the managed objects about the update
        //     and remember that there was a change so it will be passed to the simulator.
        lock (UpdateLock)
        {
            if (updatedEntityCount > 0)
            {
                lock (PhysObjects)
                {
                    for (int ii = 0; ii < updatedEntityCount; ii++)
                    {
                        EntityProperties entprop = m_updateArray[ii];
                        BSPhysObject pobj;
                        if (PhysObjects.TryGetValue(entprop.ID, out pobj))
                        {
                            if (pobj.IsInitialized)
                                pobj.UpdateProperties(entprop);
                        }
                    }
                }
            }
        }

        // Some actors want to know when the simulation step is complete.
        TriggerPostStepEvent(timeStep);

        simTime = Util.EnvironmentTickCountSubtract(beforeTime);
        if (PhysicsLogging.Enabled)
        {
            DetailLog("{0},DoPhysicsStep,complete,frame={1}, nTaints={2}, simTime={3}, substeps={4}, updates={5}, colliders={6}, objWColl={7}",
                                    DetailLogZero, m_simulationStep, numTaints, simTime, numSubSteps,
                                    updatedEntityCount, collidersCount, ObjectsWithCollisions.Count);
        }

        // The following causes the unmanaged code to output ALL the values found in ALL the objects in the world.
        // Only enable this in a limited test world with few objects.
        if (m_physicsPhysicalDumpEnabled)
            PE.DumpAllInfo(World);

        // The physics engine returns the number of milliseconds it simulated this call.
        // These are summed and normalized to one second and divided by 1000 to give the reported physics FPS.
        // Multiply by a fixed nominal frame rate to give a rate similar to the simulator (usually 55).
        m_simulatedTime +=  (float)numSubSteps * m_fixedTimeStep * 1000f * NominalFrameRate;
    }

    // Called by a BSPhysObject to note that it has changed properties and this information
    //    should be passed up to the simulator at the proper time.
    // Note: this is called by the BSPhysObject from invocation via DoPhysicsStep() above so
    //    this is is under UpdateLock.
    public void PostUpdate(BSPhysObject updatee)
    {
        lock (UpdateLock)
        {
            ObjectsWithUpdates.Add(updatee);
        }
    }

    // The simulator thinks it is physics time so return all the collisions and position
    //     updates that were collected in actual physics simulation.
    private float SendUpdatesToSimulator(float timeStep)
    {
        if (!m_initialized) return 5.0f;

        DetailLog("{0},SendUpdatesToSimulator,collisions={1},updates={2},simedTime={3}",
            BSScene.DetailLogZero, ObjectsWithCollisions.Count, ObjectsWithUpdates.Count, m_simulatedTime);
        // Push the collisions into the simulator.
        lock (CollisionLock)
        {
            if (ObjectsWithCollisions.Count > 0)
            {
                foreach (BSPhysObject bsp in ObjectsWithCollisions)
                    if (!bsp.SendCollisions())
                    {
                        // If the object is done colliding, see that it's removed from the colliding list
                        ObjectsWithNoMoreCollisions.Add(bsp);
                    }
            }

            // This is a kludge to get avatar movement updates.
            // The simulator expects collisions for avatars even if there are have been no collisions.
            //    The event updates avatar animations and stuff.
            // If you fix avatar animation updates, remove this overhead and let normal collision processing happen.
            // Note that we copy the root of the list to search. Any updates will create a new list
            //    thus freeing this code from having to do an extra lock for every collision.
            HashSet<BSPhysObject> avatarTemp = m_avatars;
            foreach (BSPhysObject bsp in avatarTemp)
                if (!ObjectsWithCollisions.Contains(bsp))   // don't call avatars twice
                    bsp.SendCollisions();
            avatarTemp = null;

            // Objects that are done colliding are removed from the ObjectsWithCollisions list.
            // Not done above because it is inside an iteration of ObjectWithCollisions.
            // This complex collision processing is required to create an empty collision
            //     event call after all real collisions have happened on an object. This allows
            //     the simulator to generate the 'collision end' event.
            if (ObjectsWithNoMoreCollisions.Count > 0)
            {
                foreach (BSPhysObject po in ObjectsWithNoMoreCollisions)
                    ObjectsWithCollisions.Remove(po);
                ObjectsWithNoMoreCollisions.Clear();
            }
        }

        // Call the simulator for each object that has physics property updates.
        HashSet<BSPhysObject> updatedObjects = null;
        lock (UpdateLock)
        {
            if (ObjectsWithUpdates.Count > 0)
            {
                updatedObjects = ObjectsWithUpdates;
                ObjectsWithUpdates = new HashSet<BSPhysObject>();
            }
        }
        if (updatedObjects != null)
        {
            foreach (BSPhysObject obj in updatedObjects)
            {
                obj.RequestPhysicsterseUpdate();
            }
            updatedObjects.Clear();
        }

        // Return the framerate simulated to give the above returned results.
        // (Race condition here but this is just bookkeeping so rare mistakes do not merit a lock).
        float simTime = m_simulatedTime;
        m_simulatedTime = 0f;
        return simTime;
    }

    // Something has collided
    private void SendCollision(uint localID, uint collidingWith, Vector3 collidePoint, Vector3 collideNormal, float penetration)
    {
        if (localID <= TerrainManager.HighestTerrainID)
        {
            return;         // don't send collisions to the terrain
        }

        BSPhysObject collider;
        if (!PhysObjects.TryGetValue(localID, out collider))
        {
            // If the object that is colliding cannot be found, just ignore the collision.
            DetailLog("{0},BSScene.SendCollision,colliderNotInObjectList,id={1},with={2}", DetailLogZero, localID, collidingWith);
            return;
        }

        // Note: the terrain is not in the physical object list so 'collidee' can be null when Collide() is called.
        BSPhysObject collidee = null;
        PhysObjects.TryGetValue(collidingWith, out collidee);

        // DetailLog("{0},BSScene.SendCollision,collide,id={1},with={2}", DetailLogZero, localID, collidingWith);

        if (collider.IsInitialized)
        {
            if (collider.Collide(collidingWith, collidee, collidePoint, collideNormal, penetration))
            {
                // If a collision was 'good', remember to send it to the simulator
                lock (CollisionLock)
                {
                    ObjectsWithCollisions.Add(collider);
                }
            }
        }

        return;
    }

    public void BulletSPluginPhysicsThread()
    {
        while (m_initialized)
        {
            int beginSimulationRealtimeMS = Util.EnvironmentTickCount();

            if (BSParam.Active)
                DoPhysicsStep(BSParam.PhysicsTimeStep);

            int simulationRealtimeMS = Util.EnvironmentTickCountSubtract(beginSimulationRealtimeMS);
            int simulationTimeVsRealtimeDifferenceMS = ((int)(BSParam.PhysicsTimeStep*1000f)) - simulationRealtimeMS;

            if (simulationTimeVsRealtimeDifferenceMS > 0)
            {
                // The simulation of the time interval took less than realtime.
                // Do a sleep for the rest of realtime.
                Thread.Sleep(simulationTimeVsRealtimeDifferenceMS);
            }
            else
            {
                // The simulation took longer than realtime.
                // Do some scaling of simulation time.
                // TODO.
                DetailLog("{0},BulletSPluginPhysicsThread,longerThanRealtime={1}", BSScene.DetailLogZero, simulationTimeVsRealtimeDifferenceMS);
            }

            Watchdog.UpdateThread();
        }

        Watchdog.RemoveThread();
    }

    #endregion // Simulation

    public override void GetResults() { }

    #region Terrain

    public override void SetTerrain(float[] heightMap) {
        TerrainManager.SetTerrain(heightMap);
    }

    public override void SetWaterLevel(float baseheight)
    {
        SimpleWaterLevel = baseheight;
    }

    public override void DeleteTerrain()
    {
        // m_log.DebugFormat("{0}: DeleteTerrain()", LogHeader);
    }

    // Although no one seems to check this, I do support combining.
    public override bool SupportsCombining()
    {
        return TerrainManager.SupportsCombining();
    }
    // This call says I am a child to region zero in a mega-region. 'pScene' is that
    //    of region zero, 'offset' is my offset from regions zero's origin, and
    //    'extents' is the largest XY that is handled in my region.
    public override void Combine(PhysicsScene pScene, Vector3 offset, Vector3 extents)
    {
        TerrainManager.Combine(pScene, offset, extents);
    }

    // Unhook all the combining that I know about.
    public override void UnCombine(PhysicsScene pScene)
    {
        TerrainManager.UnCombine(pScene);
    }

    #endregion // Terrain

    public override Dictionary<uint, float> GetTopColliders()
    {
        Dictionary<uint, float> topColliders;

        lock (PhysObjects)
        {
            foreach (KeyValuePair<uint, BSPhysObject> kvp in PhysObjects)
            {
                kvp.Value.ComputeCollisionScore();
            }

            List<BSPhysObject> orderedPrims = new List<BSPhysObject>(PhysObjects.Values);
            orderedPrims.OrderByDescending(p => p.CollisionScore);
            topColliders = orderedPrims.Take(25).ToDictionary(p => p.LocalID, p => p.CollisionScore);
        }

        return topColliders;
    }

    public override bool IsThreaded { get { return false;  } }

    #region Extensions
    public override object Extension(string pFunct, params object[] pParams)
    {
        DetailLog("{0} BSScene.Extension,op={1}", DetailLogZero, pFunct);
        return base.Extension(pFunct, pParams);
    }
    #endregion // Extensions

    #region Taints
    // The simulation execution order is:
    // Simulate()
    //    DoOneTimeTaints
    //    TriggerPreStepEvent
    //    DoOneTimeTaints
    //    Step()
    //       ProcessAndSendToSimulatorCollisions
    //       ProcessAndSendToSimulatorPropertyUpdates
    //    TriggerPostStepEvent

    // Calls to the PhysicsActors can't directly call into the physics engine
    //       because it might be busy. We delay changes to a known time.
    // We rely on C#'s closure to save and restore the context for the delegate.
    public void TaintedObject(string pOriginator, string pIdent, TaintCallback pCallback)
    {
        TaintedObject(false /*inTaintTime*/, pOriginator, pIdent, pCallback);
    }
    public void TaintedObject(uint pOriginator, String pIdent, TaintCallback pCallback)
    {
        TaintedObject(false /*inTaintTime*/, m_physicsLoggingEnabled ? pOriginator.ToString() : BSScene.DetailLogZero, pIdent, pCallback);
    }
    public void TaintedObject(bool inTaintTime, String pIdent, TaintCallback pCallback)
    {
        TaintedObject(inTaintTime, BSScene.DetailLogZero, pIdent, pCallback);
    }
    public void TaintedObject(bool inTaintTime, uint pOriginator, String pIdent, TaintCallback pCallback)
    {
        TaintedObject(inTaintTime, m_physicsLoggingEnabled ? pOriginator.ToString() : BSScene.DetailLogZero, pIdent, pCallback);
    }
    // Sometimes a potentially tainted operation can be used in and out of taint time.
    // This routine executes the command immediately if in taint-time otherwise it is queued.
    public void TaintedObject(bool inTaintTime, string pOriginator, string pIdent, TaintCallback pCallback)
    {
        if (!m_initialized) return;

        if (inTaintTime)
            pCallback();
        else
        {
            lock (_taintLock)
            {
                _taintOperations.Add(new TaintCallbackEntry(pOriginator, pIdent, pCallback));
            }
        }
    }

    private void TriggerPreStepEvent(float timeStep)
    {
        PreStepAction actions = BeforeStep;
        if (actions != null)
            actions(timeStep);

    }

    private void TriggerPostStepEvent(float timeStep)
    {
        PostStepAction actions = AfterStep;
        if (actions != null)
            actions(timeStep);

    }

    // When someone tries to change a property on a BSPrim or BSCharacter, the object queues
    // a callback into itself to do the actual property change. That callback is called
    // here just before the physics engine is called to step the simulation.
    public void ProcessTaints()
    {
        ProcessRegularTaints();
        ProcessPostTaintTaints();
    }

    private void ProcessRegularTaints()
    {
        if (m_initialized && _taintOperations.Count > 0)  // save allocating new list if there is nothing to process
        {
            // swizzle a new list into the list location so we can process what's there
            List<TaintCallbackEntry> oldList;
            lock (_taintLock)
            {
                oldList = _taintOperations;
                _taintOperations = new List<TaintCallbackEntry>();
            }

            foreach (TaintCallbackEntry tcbe in oldList)
            {
                try
                {
                    DetailLog("{0},BSScene.ProcessTaints,doTaint,id={1}", tcbe.originator, tcbe.ident); // DEBUG DEBUG DEBUG
                    tcbe.callback();
                }
                catch (Exception e)
                {
                    m_log.ErrorFormat("{0}: ProcessTaints: {1}: Exception: {2}", LogHeader, tcbe.ident, e);
                }
            }
            oldList.Clear();
        }
    }

    // Schedule an update to happen after all the regular taints are processed.
    // Note that new requests for the same operation ("ident") for the same object ("ID")
    //     will replace any previous operation by the same object.
    public void PostTaintObject(String ident, uint ID, TaintCallback callback)
    {
        string IDAsString = ID.ToString();
        string uniqueIdent = ident + "-" + IDAsString;
        lock (_taintLock)
        {
            _postTaintOperations[uniqueIdent] = new TaintCallbackEntry(IDAsString, uniqueIdent, callback);
        }

        return;
    }

    // Taints that happen after the normal taint processing but before the simulation step.
    private void ProcessPostTaintTaints()
    {
        if (m_initialized && _postTaintOperations.Count > 0)
        {
            Dictionary<string, TaintCallbackEntry> oldList;
            lock (_taintLock)
            {
                oldList = _postTaintOperations;
                _postTaintOperations = new Dictionary<string, TaintCallbackEntry>();
            }

            foreach (KeyValuePair<string,TaintCallbackEntry> kvp in oldList)
            {
                try
                {
                    DetailLog("{0},BSScene.ProcessPostTaintTaints,doTaint,id={1}", DetailLogZero, kvp.Key); // DEBUG DEBUG DEBUG
                    kvp.Value.callback();
                }
                catch (Exception e)
                {
                    m_log.ErrorFormat("{0}: ProcessPostTaintTaints: {1}: Exception: {2}", LogHeader, kvp.Key, e);
                }
            }
            oldList.Clear();
        }
    }

    // Only used for debugging. Does not change state of anything so locking is not necessary.
    public bool AssertInTaintTime(string whereFrom)
    {
        if (!InTaintTime)
        {
            DetailLog("{0},BSScene.AssertInTaintTime,NOT IN TAINT TIME,Region={1},Where={2}", DetailLogZero, RegionName, whereFrom);
            m_log.ErrorFormat("{0} NOT IN TAINT TIME!! Region={1}, Where={2}", LogHeader, RegionName, whereFrom);
            // Util.PrintCallStack(DetailLog);
        }
        return InTaintTime;
    }

    #endregion // Taints

    #region IPhysicsParameters
    // Get the list of parameters this physics engine supports
    public PhysParameterEntry[] GetParameterList()
    {
        BSParam.BuildParameterTable();
        return BSParam.SettableParameters;
    }

    // Set parameter on a specific or all instances.
    // Return 'false' if not able to set the parameter.
    // Setting the value in the m_params block will change the value the physics engine
    //   will use the next time since it's pinned and shared memory.
    // Some of the values require calling into the physics engine to get the new
    //   value activated ('terrainFriction' for instance).
    public bool SetPhysicsParameter(string parm, string val, uint localID)
    {
        bool ret = false;

        BSParam.ParameterDefnBase theParam;
        if (BSParam.TryGetParameter(parm, out theParam))
        {
            // Set the value in the C# code
            theParam.SetValue(this, val);

            // Optionally set the parameter in the unmanaged code
            if (theParam.HasSetOnObject)
            {
                // update all the localIDs specified
                // If the local ID is APPLY_TO_NONE, just change the default value
                // If the localID is APPLY_TO_ALL change the default value and apply the new value to all the lIDs
                // If the localID is a specific object, apply the parameter change to only that object
                List<uint> objectIDs = new List<uint>();
                switch (localID)
                {
                    case PhysParameterEntry.APPLY_TO_NONE:
                        // This will cause a call into the physical world if some operation is specified (SetOnObject).
                        objectIDs.Add(TERRAIN_ID);
                        TaintedUpdateParameter(parm, objectIDs, val);
                        break;
                    case PhysParameterEntry.APPLY_TO_ALL:
                        lock (PhysObjects) objectIDs = new List<uint>(PhysObjects.Keys);
                        TaintedUpdateParameter(parm, objectIDs, val);
                        break;
                    default:
                        // setting only one localID
                        objectIDs.Add(localID);
                        TaintedUpdateParameter(parm, objectIDs, val);
                        break;
                }
            }

            ret = true;
        }
        return ret;
    }

    // schedule the actual updating of the paramter to when the phys engine is not busy
    private void TaintedUpdateParameter(string parm, List<uint> lIDs, string val)
    {
        string xval = val;
        List<uint> xlIDs = lIDs;
        string xparm = parm;
        TaintedObject(DetailLogZero, "BSScene.UpdateParameterSet", delegate() {
            BSParam.ParameterDefnBase thisParam;
            if (BSParam.TryGetParameter(xparm, out thisParam))
            {
                if (thisParam.HasSetOnObject)
                {
                    foreach (uint lID in xlIDs)
                    {
                        BSPhysObject theObject = null;
                        if (PhysObjects.TryGetValue(lID, out theObject))
                            thisParam.SetOnObject(this, theObject);
                    }
                }
            }
        });
    }

    // Get parameter.
    // Return 'false' if not able to get the parameter.
    public bool GetPhysicsParameter(string parm, out string value)
    {
        string val = String.Empty;
        bool ret = false;
        BSParam.ParameterDefnBase theParam;
        if (BSParam.TryGetParameter(parm, out theParam))
        {
            val = theParam.GetValue(this);
            ret = true;
        }
        value = val;
        return ret;
    }

    #endregion IPhysicsParameters

    // Invoke the detailed logger and output something if it's enabled.
    public void DetailLog(string msg, params Object[] args)
    {
        PhysicsLogging.Write(msg, args);
    }
    // Used to fill in the LocalID when there isn't one. It's the correct number of characters.
    public const string DetailLogZero = "0000000000";

}
}