/*
* Copyright (c) 2006-2007 Erin Catto http:
*
* 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, and must not be
* misrepresented the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

/**
 * p = attached point, m = mouse point
 * C = p - m
 * Cdot = v
 *      = v + cross(w, r)
 * J = [I r_skew]
 * Identity used:
 * w k % (rx i + ry j) = w * (-ry i + rx j)
 * 
 * @class b2MouseJoint
 * @constructor
 */
var b2MouseJoint = function (def) {
    // The constructor for b2Joint
	// initialize instance variables for references
	this.m_node1 = new b2JointNode();
	this.m_node2 = new b2JointNode();
	//
	this.m_type = def.type;
	this.m_prev = null;
	this.m_next = null;
	this.m_body1 = def.body1;
	this.m_body2 = def.body2;
	this.m_collideConnected = def.collideConnected;
	this.m_islandFlag = false;
	this.m_userData = def.userData;
	//

	// initialize instance variables for references
	this.K = new b2Mat22();
	this.K1 = new b2Mat22();
	this.K2 = new b2Mat22();
	this.m_localAnchor = new b2Vec2();
	this.m_target = new b2Vec2();
	this.m_impulse = new b2Vec2();
	this.m_ptpMass = new b2Mat22();
	this.m_C = new b2Vec2();
	//

	//super(def);

	this.m_target.SetV(def.target);
	//this.m_localAnchor = b2Math.b2MulTMV(this.m_body2.m_R, b2Math.SubtractVV( this.m_target, this.m_body2.m_position ) );
	var tX = this.m_target.x - this.m_body2.m_position.x;
	var tY = this.m_target.y - this.m_body2.m_position.y;
	this.m_localAnchor.x = (tX * this.m_body2.m_R.col1.x + tY * this.m_body2.m_R.col1.y);
	this.m_localAnchor.y = (tX * this.m_body2.m_R.col2.x + tY * this.m_body2.m_R.col2.y);

	this.m_maxForce = def.maxForce;
	this.m_impulse.SetZero();

	var mass = this.m_body2.m_mass;

	// Frequency
	var omega = 2.0 * b2Settings.b2_pi * def.frequencyHz;

	// Damping coefficient
	var d = 2.0 * mass * def.dampingRatio * omega;

	// Spring stiffness
	var k = mass * omega * omega;

	// magic formulas
	this.m_gamma = 1.0 / (d + def.timeStep * k);
	this.m_beta = def.timeStep * k / (d + def.timeStep * k);
};
Object.extend(b2MouseJoint.prototype, b2Joint.prototype);
Object.extend(b2MouseJoint.prototype, 
{
	GetAnchor1: function(){
		return this.m_target;
	},
	GetAnchor2: function(){
		var tVec = b2Math.b2MulMV(this.m_body2.m_R, this.m_localAnchor);
		tVec.Add(this.m_body2.m_position);
		return tVec;
	},

	GetReactionForce: function(invTimeStep)
	{
		//b2Vec2 F = invTimeStep * this.m_impulse;
		var F = new b2Vec2();
		F.SetV(this.m_impulse);
		F.Multiply(invTimeStep);
		return F;
	},

	GetReactionTorque: function(invTimeStep)
	{
		//NOT_USED(invTimeStep);
		return 0.0;
	},

	SetTarget: function(target){
		this.m_body2.WakeUp();
		this.m_target = target;
	},

	//--------------- Internals Below -------------------

	// Presolve vars
	K: new b2Mat22(),
	K1: new b2Mat22(),
	K2: new b2Mat22(),
	PrepareVelocitySolver: function(){
		var b = this.m_body2;

		var tMat;

		// Compute the effective mass matrix.
		//b2Vec2 r = b2Mul(b.m_R, this.m_localAnchor);
		tMat = b.m_R;
		var rX = tMat.col1.x * this.m_localAnchor.x + tMat.col2.x * this.m_localAnchor.y;
		var rY = tMat.col1.y * this.m_localAnchor.x + tMat.col2.y * this.m_localAnchor.y;

		// this.K    = [(1/m1 + 1/m2) * eye(2) - skew(r1) * invI1 * skew(r1) - skew(r2) * invI2 * skew(r2)]
		//      = [1/m1+1/m2     0    ] + invI1 * [r1.y*r1.y -r1.x*r1.y] + invI2 * [r1.y*r1.y -r1.x*r1.y]
		//        [    0     1/m1+1/m2]           [-r1.x*r1.y r1.x*r1.x]           [-r1.x*r1.y r1.x*r1.x]
		var invMass = b.m_invMass;
		var invI = b.m_invI;

		//b2Mat22 this.K1;
		this.K1.col1.x = invMass;	this.K1.col2.x = 0.0;
		this.K1.col1.y = 0.0;		this.K1.col2.y = invMass;

		//b2Mat22 this.K2;
		this.K2.col1.x =  invI * rY * rY;	this.K2.col2.x = -invI * rX * rY;
		this.K2.col1.y = -invI * rX * rY;	this.K2.col2.y =  invI * rX * rX;

		//b2Mat22 this.K = this.K1 + this.K2;
		this.K.SetM(this.K1);
		this.K.AddM(this.K2);
		this.K.col1.x += this.m_gamma;
		this.K.col2.y += this.m_gamma;

		//this.m_ptpMass = this.K.Invert();
		this.K.Invert(this.m_ptpMass);

		//this.m_C = b.m_position + r - this.m_target;
		this.m_C.x = b.m_position.x + rX - this.m_target.x;
		this.m_C.y = b.m_position.y + rY - this.m_target.y;

		// Cheat with some damping
		b.m_angularVelocity *= 0.98;

		// Warm starting.
		//b2Vec2 P = this.m_impulse;
		var PX = this.m_impulse.x;
		var PY = this.m_impulse.y;
		//b.m_linearVelocity += invMass * P;
		b.m_linearVelocity.x += invMass * PX;
		b.m_linearVelocity.y += invMass * PY;
		//b.m_angularVelocity += invI * b2Cross(r, P);
		b.m_angularVelocity += invI * (rX * PY - rY * PX);
	},


	SolveVelocityConstraints: function(step){
		var body = this.m_body2;

		var tMat;

		// Compute the effective mass matrix.
		//b2Vec2 r = b2Mul(body.m_R, this.m_localAnchor);
		tMat = body.m_R;
		var rX = tMat.col1.x * this.m_localAnchor.x + tMat.col2.x * this.m_localAnchor.y;
		var rY = tMat.col1.y * this.m_localAnchor.x + tMat.col2.y * this.m_localAnchor.y;

		// Cdot = v + cross(w, r)
		//b2Vec2 Cdot = body->m_linearVelocity + b2Cross(body->m_angularVelocity, r);
		var CdotX = body.m_linearVelocity.x + (-body.m_angularVelocity * rY);
		var CdotY = body.m_linearVelocity.y + (body.m_angularVelocity * rX);
		//b2Vec2 impulse = -b2Mul(this.m_ptpMass, Cdot + (this.m_beta * step->inv_dt) * this.m_C + this.m_gamma * this.m_impulse);
		tMat = this.m_ptpMass;
		var tX = CdotX + (this.m_beta * step.inv_dt) * this.m_C.x + this.m_gamma * this.m_impulse.x;
		var tY = CdotY + (this.m_beta * step.inv_dt) * this.m_C.y + this.m_gamma * this.m_impulse.y;
		var impulseX = -(tMat.col1.x * tX + tMat.col2.x * tY);
		var impulseY = -(tMat.col1.y * tX + tMat.col2.y * tY);

		var oldImpulseX = this.m_impulse.x;
		var oldImpulseY = this.m_impulse.y;
		//this.m_impulse += impulse;
		this.m_impulse.x += impulseX;
		this.m_impulse.y += impulseY;
		var length = this.m_impulse.Length();
		if (length > step.dt * this.m_maxForce)
		{
			//this.m_impulse *= step.dt * this.m_maxForce / length;
			this.m_impulse.Multiply(step.dt * this.m_maxForce / length);
		}
		//impulse = this.m_impulse - oldImpulse;
		impulseX = this.m_impulse.x - oldImpulseX;
		impulseY = this.m_impulse.y - oldImpulseY;

		//body.m_linearVelocity += body->m_invMass * impulse;
		body.m_linearVelocity.x += body.m_invMass * impulseX;
		body.m_linearVelocity.y += body.m_invMass * impulseY;
		//body.m_angularVelocity += body->m_invI * b2Cross(r, impulse);
		body.m_angularVelocity += body.m_invI * (rX * impulseY - rY * impulseX);
	},
	SolvePositionConstraints: function(){
		return true;
	},

	m_localAnchor: new b2Vec2(),
	m_target: new b2Vec2(),
	m_impulse: new b2Vec2(),

	m_ptpMass: new b2Mat22(),
	m_C: new b2Vec2(),
	m_maxForce: null,
	m_beta: null,
	m_gamma: null
});