var vec2 = require('../math/vec2'); 
module.exports = Spring; 
function Spring(bodyA, bodyB, options){ 
options = options || { 
}
; 
this.restLength = typeof (options.restLength) == "number"? options.restLength: 1; 
this.stiffness = options.stiffness || 100; 
this.damping = options.damping || 1; 
this.bodyA = bodyA; 
this.bodyB = bodyB; 
this.localAnchorA = vec2.fromValues(0, 0); 
this.localAnchorB = vec2.fromValues(0, 0); 
if (options.localAnchorA) vec2.copy(this.localAnchorA, options.localAnchorA); 
if (options.localAnchorB) vec2.copy(this.localAnchorB, options.localAnchorB); 
if (options.worldAnchorA) this.setWorldAnchorA(options.worldAnchorA); 
if (options.worldAnchorB) this.setWorldAnchorB(options.worldAnchorB); 
} 
; 
Spring.prototype.setWorldAnchorA = function (worldAnchorA){ 
this.bodyA.toLocalFrame(this.localAnchorA, worldAnchorA); 
} 
; 
Spring.prototype.setWorldAnchorB = function (worldAnchorB){ 
this.bodyB.toLocalFrame(this.localAnchorB, worldAnchorB); 
} 
; 
Spring.prototype.getWorldAnchorA = function (result){ 
this.bodyA.toWorldFrame(result, this.localAnchorA); 
} 
; 
Spring.prototype.getWorldAnchorB = function (result){ 
this.bodyB.toWorldFrame(result, this.localAnchorB); 
} 
; 
var applyForce_r = vec2.create(), applyForce_r_unit = vec2.create(), applyForce_u = vec2.create(), applyForce_f = vec2.create(), applyForce_worldAnchorA = vec2.create(), applyForce_worldAnchorB = vec2.create(), applyForce_ri = vec2.create(), applyForce_rj = vec2.create(), applyForce_tmp = vec2.create(); 
Spring.prototype.applyForce = function (){ 
var k = this.stiffness, d = this.damping, l = this.restLength, bodyA = this.bodyA, bodyB = this.bodyB, r = applyForce_r, r_unit = applyForce_r_unit, u = applyForce_u, f = applyForce_f, tmp = applyForce_tmp; 
var worldAnchorA = applyForce_worldAnchorA, worldAnchorB = applyForce_worldAnchorB, ri = applyForce_ri, rj = applyForce_rj; 
this.getWorldAnchorA(worldAnchorA); 
this.getWorldAnchorB(worldAnchorB); 
vec2.sub(ri, worldAnchorA, bodyA.position); 
vec2.sub(rj, worldAnchorB, bodyB.position); 
vec2.sub(r, worldAnchorB, worldAnchorA); 
var rlen = vec2.len(r); 
vec2.normalize(r_unit, r); 
vec2.sub(u, bodyB.velocity, bodyA.velocity); 
vec2.crossZV(tmp, bodyB.angularVelocity, rj); 
vec2.add(u, u, tmp); 
vec2.crossZV(tmp, bodyA.angularVelocity, ri); 
vec2.sub(u, u, tmp); 
vec2.scale(f, r_unit, - k * (rlen - l) - d * vec2.dot(u, r_unit)); 
vec2.sub(bodyA.force, bodyA.force, f); 
vec2.add(bodyB.force, bodyB.force, f); 
var ri_x_f = vec2.crossLength(ri, f); 
var rj_x_f = vec2.crossLength(rj, f); 
bodyA.angularForce -= ri_x_f; 
bodyB.angularForce += rj_x_f; 
} 
;