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 *       notice, this list of conditions and the following disclaimer in the
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 *       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
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 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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 */
using System;
using System.Collections.Generic;
using System.Text;

using OMV = OpenMetaverse;

namespace OpenSim.Region.Physics.BulletSPlugin
{

// A BSPrim can get individual information about its linkedness attached
//    to it through an instance of a subclass of LinksetInfo.
// Each type of linkset will define the information needed for its type.
public abstract class BSLinksetInfo
{
    public virtual void Clear() { }
}

public abstract class BSLinkset
{
    // private static string LogHeader = "[BULLETSIM LINKSET]";

    public enum LinksetImplementation
    {
        Constraint   = 0,   // linkset tied together with constraints
        Compound     = 1,   // linkset tied together as a compound object
        Manual       = 2    // linkset tied together manually (code moves all the pieces)
    }
    // Create the correct type of linkset for this child
    public static BSLinkset Factory(BSScene physScene, BSPhysObject parent)
    {
        BSLinkset ret = null;

        switch ((int)BSParam.LinksetImplementation)
        {
            case (int)LinksetImplementation.Constraint:
                ret = new BSLinksetConstraints(physScene, parent);
                break;
            case (int)LinksetImplementation.Compound:
                ret = new BSLinksetCompound(physScene, parent);
                break;
            case (int)LinksetImplementation.Manual:
                // ret = new BSLinksetManual(physScene, parent);
                break;
            default:
                ret = new BSLinksetCompound(physScene, parent);
                break;
        }
        return ret;
    }

    public BSPhysObject LinksetRoot { get; protected set; }

    public BSScene PhysicsScene { get; private set; }

    static int m_nextLinksetID = 1;
    public int LinksetID { get; private set; }

    // The children under the root in this linkset.
    protected HashSet<BSPhysObject> m_children;

    // We lock the diddling of linkset classes to prevent any badness.
    // This locks the modification of the instances of this class. Changes
    //    to the physical representation is done via the tainting mechenism.
    protected object m_linksetActivityLock = new Object();

    // Some linksets have a preferred physical shape.
    // Returns SHAPE_UNKNOWN if there is no preference. Causes the correct shape to be selected.
    public virtual BSPhysicsShapeType PreferredPhysicalShape(BSPhysObject requestor)
    {
        return BSPhysicsShapeType.SHAPE_UNKNOWN;
    }

    // We keep the prim's mass in the linkset structure since it could be dependent on other prims
    public float LinksetMass { get; protected set; }

    public virtual bool LinksetIsColliding { get { return false; } }

    public OMV.Vector3 CenterOfMass
    {
        get { return ComputeLinksetCenterOfMass(); }
    }

    public OMV.Vector3 GeometricCenter
    {
        get { return ComputeLinksetGeometricCenter(); }
    }

    protected BSLinkset(BSScene scene, BSPhysObject parent)
    {
        // A simple linkset of one (no children)
        LinksetID = m_nextLinksetID++;
        // We create LOTS of linksets.
        if (m_nextLinksetID <= 0)
            m_nextLinksetID = 1;
        PhysicsScene = scene;
        LinksetRoot = parent;
        m_children = new HashSet<BSPhysObject>();
        LinksetMass = parent.RawMass;
        Rebuilding = false;
    }

    // Link to a linkset where the child knows the parent.
    // Parent changing should not happen so do some sanity checking.
    // We return the parent's linkset so the child can track its membership.
    // Called at runtime.
    public BSLinkset AddMeToLinkset(BSPhysObject child)
    {
        lock (m_linksetActivityLock)
        {
            // Don't add the root to its own linkset
            if (!IsRoot(child))
                AddChildToLinkset(child);
            LinksetMass = ComputeLinksetMass();
        }
        return this;
    }

    // Remove a child from a linkset.
    // Returns a new linkset for the child which is a linkset of one (just the
    //    orphened child).
    // Called at runtime.
    public BSLinkset RemoveMeFromLinkset(BSPhysObject child)
    {
        lock (m_linksetActivityLock)
        {
            if (IsRoot(child))
            {
                // Cannot remove the root from a linkset.
                child.PositionDisplacement = OMV.Vector3.Zero;
                return this;
            }
            RemoveChildFromLinkset(child);
            LinksetMass = ComputeLinksetMass();
        }

        // The child is down to a linkset of just itself
        child.PositionDisplacement = OMV.Vector3.Zero;
        return BSLinkset.Factory(PhysicsScene, child);
    }

    // Return 'true' if the passed object is the root object of this linkset
    public bool IsRoot(BSPhysObject requestor)
    {
        return (requestor.LocalID == LinksetRoot.LocalID);
    }

    public int NumberOfChildren { get { return m_children.Count; } }

    // Return 'true' if this linkset has any children (more than the root member)
    public bool HasAnyChildren { get { return (m_children.Count > 0); } }

    // Return 'true' if this child is in this linkset
    public bool HasChild(BSPhysObject child)
    {
        bool ret = false;
        lock (m_linksetActivityLock)
        {
            ret = m_children.Contains(child);
            /* Safer version but the above should work
            foreach (BSPhysObject bp in m_children)
            {
                if (child.LocalID == bp.LocalID)
                {
                    ret = true;
                    break;
                }
            }
             */
        }
        return ret;
    }

    // Perform an action on each member of the linkset including root prim.
    // Depends on the action on whether this should be done at taint time.
    public delegate bool ForEachMemberAction(BSPhysObject obj);
    public virtual bool ForEachMember(ForEachMemberAction action)
    {
        bool ret = false;
        lock (m_linksetActivityLock)
        {
            action(LinksetRoot);
            foreach (BSPhysObject po in m_children)
            {
                if (action(po))
                    break;
            }
        }
        return ret;
    }

    // I am the root of a linkset and a new child is being added
    // Called while LinkActivity is locked.
    protected abstract void AddChildToLinkset(BSPhysObject child);
    
    // I am the root of a linkset and one of my children is being removed.
    // Safe to call even if the child is not really in my linkset.
    protected abstract void RemoveChildFromLinkset(BSPhysObject child);

    // When physical properties are changed the linkset needs to recalculate
    //   its internal properties.
    // May be called at runtime or taint-time.
    public virtual void Refresh(BSPhysObject requestor)
    {
        LinksetMass = ComputeLinksetMass();
    }

    // Flag denoting the linkset is in the process of being rebuilt.
    // Used to know not the schedule a rebuild in the middle of a rebuild.
    protected bool Rebuilding { get; set; }

    // The object is going dynamic (physical). Do any setup necessary
    //     for a dynamic linkset.
    // Only the state of the passed object can be modified. The rest of the linkset
    //     has not yet been fully constructed.
    // Return 'true' if any properties updated on the passed object.
    // Called at taint-time!
    public abstract bool MakeDynamic(BSPhysObject child);

    // The object is going static (non-physical). Do any setup necessary
    //     for a static linkset.
    // Return 'true' if any properties updated on the passed object.
    // Called at taint-time!
    public abstract bool MakeStatic(BSPhysObject child);

    // Called when a parameter update comes from the physics engine for any object
    //      of the linkset is received.
    // Passed flag is update came from physics engine (true) or the user (false).
    // Called at taint-time!!
    public abstract void UpdateProperties(UpdatedProperties whichUpdated, BSPhysObject physObject);

    // Routine used when rebuilding the body of the root of the linkset
    // Destroy all the constraints have have been made to root.
    // This is called when the root body is changing.
    // Returns 'true' of something was actually removed and would need restoring
    // Called at taint-time!!
    public abstract bool RemoveBodyDependencies(BSPrim child);

    // Companion to RemoveBodyDependencies(). If RemoveBodyDependencies() returns 'true',
    //     this routine will restore the removed constraints.
    // Called at taint-time!!
    public abstract void RestoreBodyDependencies(BSPrim child);

    // ================================================================
    protected virtual float ComputeLinksetMass()
    {
        float mass = LinksetRoot.RawMass;
        if (HasAnyChildren)
        {
            lock (m_linksetActivityLock)
            {
                foreach (BSPhysObject bp in m_children)
                {
                    mass += bp.RawMass;
                }
            }
        }
        return mass;
    }

    protected virtual OMV.Vector3 ComputeLinksetCenterOfMass()
    {
        OMV.Vector3 com;
        lock (m_linksetActivityLock)
        {
            com = LinksetRoot.Position * LinksetRoot.RawMass;
            float totalMass = LinksetRoot.RawMass;

            foreach (BSPhysObject bp in m_children)
            {
                com += bp.Position * bp.RawMass;
                totalMass += bp.RawMass;
            }
            if (totalMass != 0f)
                com /= totalMass;
        }

        return com;
    }

    protected virtual OMV.Vector3 ComputeLinksetGeometricCenter()
    {
        OMV.Vector3 com;
        lock (m_linksetActivityLock)
        {
            com = LinksetRoot.Position;

            foreach (BSPhysObject bp in m_children)
            {
                com += bp.Position;
            }
            com /= (m_children.Count + 1);
        }

        return com;
    }

    // Invoke the detailed logger and output something if it's enabled.
    protected void DetailLog(string msg, params Object[] args)
    {
        if (PhysicsScene.PhysicsLogging.Enabled)
            PhysicsScene.DetailLog(msg, args);
    }

}
}