/*******************************************************************************
 * Copyright (c) 2013, Daniel Murphy
 * All rights reserved.
 * 
 * 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.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDER OR 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.
 ******************************************************************************/
/*
 * JBox2D - A Java Port of Erin Catto's Box2D
 * 
 * JBox2D homepage: http://jbox2d.sourceforge.net/
 * Box2D homepage: http://www.box2d.org
 * 
 * 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.
 */

package org.jbox2d.dynamics.joints;

import org.jbox2d.common.MathUtils;
import org.jbox2d.common.Rot;
import org.jbox2d.common.Settings;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.SolverData;
import org.jbox2d.pooling.IWorldPool;

//C = norm(p2 - p1) - L
//u = (p2 - p1) / norm(p2 - p1)
//Cdot = dot(u, v2 + cross(w2, r2) - v1 - cross(w1, r1))
//J = [-u -cross(r1, u) u cross(r2, u)]
//K = J * invM * JT
//= invMass1 + invI1 * cross(r1, u)^2 + invMass2 + invI2 * cross(r2, u)^2

/** A distance joint constrains two points on two bodies to remain at a fixed distance from each other. You can view this as a
 * massless, rigid rod. */
public class DistanceJoint extends Joint {

	private float m_frequencyHz;
	private float m_dampingRatio;
	private float m_bias;

	// Solver shared
	private final Vec2 m_localAnchorA;
	private final Vec2 m_localAnchorB;
	private float m_gamma;
	private float m_impulse;
	private float m_length;

	// Solver temp
	private int m_indexA;
	private int m_indexB;
	private final Vec2 m_u = new Vec2();
	private final Vec2 m_rA = new Vec2();
	private final Vec2 m_rB = new Vec2();
	private final Vec2 m_localCenterA = new Vec2();
	private final Vec2 m_localCenterB = new Vec2();
	private float m_invMassA;
	private float m_invMassB;
	private float m_invIA;
	private float m_invIB;
	private float m_mass;

	protected DistanceJoint (IWorldPool argWorld, final DistanceJointDef def) {
		super(argWorld, def);
		m_localAnchorA = def.localAnchorA.clone();
		m_localAnchorB = def.localAnchorB.clone();
		m_length = def.length;
		m_impulse = 0.0f;
		m_frequencyHz = def.frequencyHz;
		m_dampingRatio = def.dampingRatio;
		m_gamma = 0.0f;
		m_bias = 0.0f;
	}

	public void setFrequency (float hz) {
		m_frequencyHz = hz;
	}

	public float getFrequency () {
		return m_frequencyHz;
	}

	public float getLength () {
		return m_length;
	}

	public void setLength (float argLength) {
		m_length = argLength;
	}

	public void setDampingRatio (float damp) {
		m_dampingRatio = damp;
	}

	public float getDampingRatio () {
		return m_dampingRatio;
	}

	@Override
	public void getAnchorA (Vec2 argOut) {
		m_bodyA.getWorldPointToOut(m_localAnchorA, argOut);
	}

	@Override
	public void getAnchorB (Vec2 argOut) {
		m_bodyB.getWorldPointToOut(m_localAnchorB, argOut);
	}

	public Vec2 getLocalAnchorA () {
		return m_localAnchorA;
	}

	public Vec2 getLocalAnchorB () {
		return m_localAnchorB;
	}

	/** Get the reaction force given the inverse time step. Unit is N. */
	@Override
	public void getReactionForce (float inv_dt, Vec2 argOut) {
		argOut.x = m_impulse * m_u.x * inv_dt;
		argOut.y = m_impulse * m_u.y * inv_dt;
	}

	/** Get the reaction torque given the inverse time step. Unit is N*m. This is always zero for a distance joint. */
	@Override
	public float getReactionTorque (float inv_dt) {
		return 0.0f;
	}

	@Override
	public void initVelocityConstraints (final SolverData data) {

		m_indexA = m_bodyA.m_islandIndex;
		m_indexB = m_bodyB.m_islandIndex;
		m_localCenterA.set(m_bodyA.m_sweep.localCenter);
		m_localCenterB.set(m_bodyB.m_sweep.localCenter);
		m_invMassA = m_bodyA.m_invMass;
		m_invMassB = m_bodyB.m_invMass;
		m_invIA = m_bodyA.m_invI;
		m_invIB = m_bodyB.m_invI;

		Vec2 cA = data.positions[m_indexA].c;
		float aA = data.positions[m_indexA].a;
		Vec2 vA = data.velocities[m_indexA].v;
		float wA = data.velocities[m_indexA].w;

		Vec2 cB = data.positions[m_indexB].c;
		float aB = data.positions[m_indexB].a;
		Vec2 vB = data.velocities[m_indexB].v;
		float wB = data.velocities[m_indexB].w;

		final Rot qA = pool.popRot();
		final Rot qB = pool.popRot();

		qA.set(aA);
		qB.set(aB);

		// use m_u as temporary variable
		Rot.mulToOutUnsafe(qA, m_u.set(m_localAnchorA).subLocal(m_localCenterA), m_rA);
		Rot.mulToOutUnsafe(qB, m_u.set(m_localAnchorB).subLocal(m_localCenterB), m_rB);
		m_u.set(cB).addLocal(m_rB).subLocal(cA).subLocal(m_rA);

		pool.pushRot(2);

		// Handle singularity.
		float length = m_u.length();
		if (length > Settings.linearSlop) {
			m_u.x *= 1.0f / length;
			m_u.y *= 1.0f / length;
		} else {
			m_u.set(0.0f, 0.0f);
		}

		float crAu = Vec2.cross(m_rA, m_u);
		float crBu = Vec2.cross(m_rB, m_u);
		float invMass = m_invMassA + m_invIA * crAu * crAu + m_invMassB + m_invIB * crBu * crBu;

		// Compute the effective mass matrix.
		m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;

		if (m_frequencyHz > 0.0f) {
			float C = length - m_length;

			// Frequency
			float omega = 2.0f * MathUtils.PI * m_frequencyHz;

			// Damping coefficient
			float d = 2.0f * m_mass * m_dampingRatio * omega;

			// Spring stiffness
			float k = m_mass * omega * omega;

			// magic formulas
			float h = data.step.dt;
			m_gamma = h * (d + h * k);
			m_gamma = m_gamma != 0.0f ? 1.0f / m_gamma : 0.0f;
			m_bias = C * h * k * m_gamma;

			invMass += m_gamma;
			m_mass = invMass != 0.0f ? 1.0f / invMass : 0.0f;
		} else {
			m_gamma = 0.0f;
			m_bias = 0.0f;
		}
		if (data.step.warmStarting) {

			// Scale the impulse to support a variable time step.
			m_impulse *= data.step.dtRatio;

			Vec2 P = pool.popVec2();
			P.set(m_u).mulLocal(m_impulse);

			vA.x -= m_invMassA * P.x;
			vA.y -= m_invMassA * P.y;
			wA -= m_invIA * Vec2.cross(m_rA, P);

			vB.x += m_invMassB * P.x;
			vB.y += m_invMassB * P.y;
			wB += m_invIB * Vec2.cross(m_rB, P);

			pool.pushVec2(1);
		} else {
			m_impulse = 0.0f;
		}
// data.velocities[m_indexA].v.set(vA);
		data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v.set(vB);
		data.velocities[m_indexB].w = wB;
	}

	@Override
	public void solveVelocityConstraints (final SolverData data) {
		Vec2 vA = data.velocities[m_indexA].v;
		float wA = data.velocities[m_indexA].w;
		Vec2 vB = data.velocities[m_indexB].v;
		float wB = data.velocities[m_indexB].w;

		final Vec2 vpA = pool.popVec2();
		final Vec2 vpB = pool.popVec2();

		// Cdot = dot(u, v + cross(w, r))
		Vec2.crossToOutUnsafe(wA, m_rA, vpA);
		vpA.addLocal(vA);
		Vec2.crossToOutUnsafe(wB, m_rB, vpB);
		vpB.addLocal(vB);
		float Cdot = Vec2.dot(m_u, vpB.subLocal(vpA));

		float impulse = -m_mass * (Cdot + m_bias + m_gamma * m_impulse);
		m_impulse += impulse;

		float Px = impulse * m_u.x;
		float Py = impulse * m_u.y;

		vA.x -= m_invMassA * Px;
		vA.y -= m_invMassA * Py;
		wA -= m_invIA * (m_rA.x * Py - m_rA.y * Px);
		vB.x += m_invMassB * Px;
		vB.y += m_invMassB * Py;
		wB += m_invIB * (m_rB.x * Py - m_rB.y * Px);

// data.velocities[m_indexA].v.set(vA);
		data.velocities[m_indexA].w = wA;
// data.velocities[m_indexB].v.set(vB);
		data.velocities[m_indexB].w = wB;

		pool.pushVec2(2);
	}

	@Override
	public boolean solvePositionConstraints (final SolverData data) {
		if (m_frequencyHz > 0.0f) {
			return true;
		}
		final Rot qA = pool.popRot();
		final Rot qB = pool.popRot();
		final Vec2 rA = pool.popVec2();
		final Vec2 rB = pool.popVec2();
		final Vec2 u = pool.popVec2();

		Vec2 cA = data.positions[m_indexA].c;
		float aA = data.positions[m_indexA].a;
		Vec2 cB = data.positions[m_indexB].c;
		float aB = data.positions[m_indexB].a;

		qA.set(aA);
		qB.set(aB);

		Rot.mulToOutUnsafe(qA, u.set(m_localAnchorA).subLocal(m_localCenterA), rA);
		Rot.mulToOutUnsafe(qB, u.set(m_localAnchorB).subLocal(m_localCenterB), rB);
		u.set(cB).addLocal(rB).subLocal(cA).subLocal(rA);

		float length = u.normalize();
		float C = length - m_length;
		C = MathUtils.clamp(C, -Settings.maxLinearCorrection, Settings.maxLinearCorrection);

		float impulse = -m_mass * C;
		float Px = impulse * u.x;
		float Py = impulse * u.y;

		cA.x -= m_invMassA * Px;
		cA.y -= m_invMassA * Py;
		aA -= m_invIA * (rA.x * Py - rA.y * Px);
		cB.x += m_invMassB * Px;
		cB.y += m_invMassB * Py;
		aB += m_invIB * (rB.x * Py - rB.y * Px);

// data.positions[m_indexA].c.set(cA);
		data.positions[m_indexA].a = aA;
// data.positions[m_indexB].c.set(cB);
		data.positions[m_indexB].a = aB;

		pool.pushVec2(3);
		pool.pushRot(2);

		return MathUtils.abs(C) < Settings.linearSlop;
	}
}
