'use strict';

/*
    2D Collision detection and performing
*/

class Collision{
	
	static ellipseToEllipse(e1, e2){
			
		//Colliding angle of ball 1 to ball 2 using arc tan of both x and y differences
		let collisionAngle = Math.atan2((e2.pos.y - e1.pos.y), (e2.pos.x - e1.pos.x));
			
		//Converting directions of velocity vector of balls into angles
		let d1 = Math.atan2(e1.vel.y, e1.vel.x);
		let d2 = Math.atan2(e2.vel.y, e2.vel.x);
			
		//Ignoring mass effects new velocites are simply magnitude multiplied with value of angle differences
		let newXspeed1 = e1.vel.mag() * Math.cos(d1 - collisionAngle);
		let newYspeed1 = e1.vel.mag() * Math.sin(d1 - collisionAngle);
		let newXspeed2 = e2.vel.mag() * Math.cos(d2 - collisionAngle);
		let newYspeed2 = e2.vel.mag() * Math.sin(d2 - collisionAngle);
	
		//According to the principle of linear momentum, kinetic energy stays the same after collision, so velocities are now related to masses
		let finalXspeed1 = ((e1.radius - e2.radius) * newXspeed1 + e2.radius * 2 * newXspeed2) / (e1.radius + e2.radius);
		let finalYspeed1 = newYspeed1;
		let finalXspeed2 = (e1.radius * 2 * newXspeed1 + (e2.radius - e1.radius) * newXspeed2) / (e1.radius + e2.radius);
		let finalYspeed2 = newYspeed2;
			
		//Values of collisionAngle
		let cosAngle = Math.cos(collisionAngle);
		let sinAngle = Math.sin(collisionAngle);
			
		//To also keep velocites relative to pure collisionAngle, subtract sin*x from cos*x and add sin*y to cos*y because coordSystem has y = 0 on the top
		let u1x = cosAngle * finalXspeed1 - sinAngle * finalYspeed1;
		let u1y = sinAngle * finalXspeed1 + cosAngle * finalYspeed1;
		let u2x = cosAngle * finalXspeed2 - sinAngle * finalYspeed2;
		let u2y = sinAngle * finalXspeed2 + cosAngle * finalYspeed2;
			
		//Set new velocities to both balls
		e1.vel.x = u1x;
		e1.vel.y = u1y;
		e2.vel.x = u2x;
		e2.vel.y = u2y;
		
		//Move balls one vx/vy forward to avoid double inverting collision detection
		e1.pos.x += e1.vel.x;
		e1.pos.y += e1.vel.y;
		e2.pos.x += e2.vel.x;
		e2.pos.y += e2.vel.y;
	}
	
}