/*
Bullet Continuous Collision Detection and Physics Library
Copyright (c) 2003-2006 Erwin Coumans  http://continuousphysics.com/Bullet/

This software is provided 'as-is', without any express or implied warranty.
In no event will the authors be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software for any purpose, 
including commercial applications, and to alter it and redistribute it freely, 
subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
*/


#include "btContactConstraint.h"
#include "BulletDynamics/Dynamics/btRigidBody.h"
#include "LinearMath/btVector3.h"
#include "btJacobianEntry.h"
#include "btContactSolverInfo.h"
#include "LinearMath/btMinMax.h"
#include "BulletCollision/NarrowPhaseCollision/btManifoldPoint.h"

#define ASSERT2 assert

//some values to find stable tresholds

float useGlobalSettingContacts = false;//true;
btScalar contactDamping = 0.2f;
btScalar contactTau = .02f;//0.02f;//*0.02f;







//bilateral constraint between two dynamic objects
void resolveSingleBilateral(btRigidBody& body1, const btVector3& pos1,
                      btRigidBody& body2, const btVector3& pos2,
                      btScalar distance, const btVector3& normal,btScalar& impulse ,float timeStep)
{
	float normalLenSqr = normal.length2();
	ASSERT2(fabs(normalLenSqr) < 1.1f);
	if (normalLenSqr > 1.1f)
	{
		impulse = 0.f;
		return;
	}
	btVector3 rel_pos1 = pos1 - body1.getCenterOfMassPosition(); 
	btVector3 rel_pos2 = pos2 - body2.getCenterOfMassPosition();
	//this jacobian entry could be re-used for all iterations
	
	btVector3 vel1 = body1.getVelocityInLocalPoint(rel_pos1);
	btVector3 vel2 = body2.getVelocityInLocalPoint(rel_pos2);
	btVector3 vel = vel1 - vel2;
	

	  btJacobianEntry jac(body1.getCenterOfMassTransform().getBasis().transpose(),
		body2.getCenterOfMassTransform().getBasis().transpose(),
		rel_pos1,rel_pos2,normal,body1.getInvInertiaDiagLocal(),body1.getInvMass(),
		body2.getInvInertiaDiagLocal(),body2.getInvMass());

	btScalar jacDiagAB = jac.getDiagonal();
	btScalar jacDiagABInv = 1.f / jacDiagAB;
	
	  btScalar rel_vel = jac.getRelativeVelocity(
		body1.getLinearVelocity(),
		body1.getCenterOfMassTransform().getBasis().transpose() * body1.getAngularVelocity(),
		body2.getLinearVelocity(),
		body2.getCenterOfMassTransform().getBasis().transpose() * body2.getAngularVelocity()); 
	float a;
	a=jacDiagABInv;


	rel_vel = normal.dot(vel);
		

#ifdef ONLY_USE_LINEAR_MASS
	btScalar massTerm = 1.f / (body1.getInvMass() + body2.getInvMass());
	impulse = - contactDamping * rel_vel * massTerm;
#else	
	btScalar velocityImpulse = -contactDamping * rel_vel * jacDiagABInv;
	impulse = velocityImpulse;
#endif
}




//velocity + friction
//response  between two dynamic objects with friction
float resolveSingleCollision(
	btRigidBody& body1,
	btRigidBody& body2,
	btManifoldPoint& contactPoint,
	const btContactSolverInfo& solverInfo

		)
{

	const btVector3& pos1 = contactPoint.getPositionWorldOnA();
	const btVector3& pos2 = contactPoint.getPositionWorldOnB();
    
	
//	printf("distance=%f\n",distance);

	const btVector3& normal = contactPoint.m_normalWorldOnB;

	btVector3 rel_pos1 = pos1 - body1.getCenterOfMassPosition(); 
	btVector3 rel_pos2 = pos2 - body2.getCenterOfMassPosition();
	
	btVector3 vel1 = body1.getVelocityInLocalPoint(rel_pos1);
	btVector3 vel2 = body2.getVelocityInLocalPoint(rel_pos2);
	btVector3 vel = vel1 - vel2;
	btScalar rel_vel;
	rel_vel = normal.dot(vel);
	

	btScalar Kfps = 1.f / solverInfo.m_timeStep ;

	float damping = solverInfo.m_damping ;
	float Kerp = solverInfo.m_erp;
	
	if (useGlobalSettingContacts)
	{
		damping = contactDamping;
		Kerp = contactTau;
	} 

	float Kcor = Kerp *Kfps;

	//printf("dist=%f\n",distance);

		btConstraintPersistentData* cpd = (btConstraintPersistentData*) contactPoint.m_userPersistentData;
	assert(cpd);

	btScalar distance = cpd->m_penetration;//contactPoint.getDistance();
	

	//distance = 0.f;
	btScalar positionalError = Kcor *-distance;
	//jacDiagABInv;
	btScalar velocityError = cpd->m_restitution - rel_vel;// * damping;

	
	btScalar penetrationImpulse = positionalError * cpd->m_jacDiagABInv;

	btScalar	velocityImpulse = velocityError * cpd->m_jacDiagABInv;

	btScalar normalImpulse = penetrationImpulse+velocityImpulse;
	
	// See Erin Catto's GDC 2006 paper: Clamp the accumulated impulse
	float oldNormalImpulse = cpd->m_appliedImpulse;
	float sum = oldNormalImpulse + normalImpulse;
	cpd->m_appliedImpulse = 0.f > sum ? 0.f: sum;

	normalImpulse = cpd->m_appliedImpulse - oldNormalImpulse;

	body1.applyImpulse(normal*(normalImpulse), rel_pos1);
	body2.applyImpulse(-normal*(normalImpulse), rel_pos2);
	
	return normalImpulse;
}


float resolveSingleFriction(
	btRigidBody& body1,
	btRigidBody& body2,
	btManifoldPoint& contactPoint,
	const btContactSolverInfo& solverInfo

		)
{

	const btVector3& pos1 = contactPoint.getPositionWorldOnA();
	const btVector3& pos2 = contactPoint.getPositionWorldOnB();

	btVector3 rel_pos1 = pos1 - body1.getCenterOfMassPosition(); 
	btVector3 rel_pos2 = pos2 - body2.getCenterOfMassPosition();
	
	btConstraintPersistentData* cpd = (btConstraintPersistentData*) contactPoint.m_userPersistentData;
	assert(cpd);

	float combinedFriction = cpd->m_friction;
	
	btScalar limit = cpd->m_appliedImpulse * combinedFriction;
	//if (contactPoint.m_appliedImpulse>0.f)
	//friction
	{
		//apply friction in the 2 tangential directions
		
		{
			// 1st tangent
			btVector3 vel1 = body1.getVelocityInLocalPoint(rel_pos1);
			btVector3 vel2 = body2.getVelocityInLocalPoint(rel_pos2);
			btVector3 vel = vel1 - vel2;
			
			btScalar vrel = cpd->m_frictionWorldTangential0.dot(vel);

			// calculate j that moves us to zero relative velocity
			btScalar j = -vrel * cpd->m_jacDiagABInvTangent0;
			float total = cpd->m_accumulatedTangentImpulse0 + j;
			GEN_set_min(total, limit);
			GEN_set_max(total, -limit);
			j = total - cpd->m_accumulatedTangentImpulse0;
			cpd->m_accumulatedTangentImpulse0 = total;
			body1.applyImpulse(j * cpd->m_frictionWorldTangential0, rel_pos1);
			body2.applyImpulse(j * -cpd->m_frictionWorldTangential0, rel_pos2);
		}

				
		{
			// 2nd tangent
			btVector3 vel1 = body1.getVelocityInLocalPoint(rel_pos1);
			btVector3 vel2 = body2.getVelocityInLocalPoint(rel_pos2);
			btVector3 vel = vel1 - vel2;

			btScalar vrel = cpd->m_frictionWorldTangential1.dot(vel);
			
			// calculate j that moves us to zero relative velocity
			btScalar j = -vrel * cpd->m_jacDiagABInvTangent1;
			float total = cpd->m_accumulatedTangentImpulse1 + j;
			GEN_set_min(total, limit);
			GEN_set_max(total, -limit);
			j = total - cpd->m_accumulatedTangentImpulse1;
			cpd->m_accumulatedTangentImpulse1 = total;
			body1.applyImpulse(j * cpd->m_frictionWorldTangential1, rel_pos1);
			body2.applyImpulse(j * -cpd->m_frictionWorldTangential1, rel_pos2);
		}
	} 
	return cpd->m_appliedImpulse;
}