/*
 * boing.cc
 *
 *  Created on: Dec 20, 2011
 *      Author: madura
 */

#include <iostream>
#include <list>

#define LEN 100

using namespace std;

struct ball{
	int code;
	float velocity; // S->N positive
	float position; // measured from south
	float time; // t=0, start
};

typedef list<ball>::iterator it_ball;
void print(list<ball>& balls){

	for (it_ball it=balls.begin();it!=balls.end();it++ ) {
		cout<< it->code<<" pos:"<<it->position<<" velo:"<<it->velocity<< " time:"<<it->time<<"\n";
	}
}
void update_position(ball& b, float time){
	b.position += b.velocity*time;
	b.time += time;
	if (b.position < 0)
		b.position = 0;
	else if (b.position > LEN)
		b.position = LEN;
}
float next_collision(ball& a, ball& b) {
	// Va > Vb && Sb > Sa
	return (b.position - a.position)/(a.velocity - b.velocity);

}
void swap(float& a, float& b){
	float temp = a;
	a = b;
	b = temp;
}
void update_all_positions(list<ball>& balls, float time){
	// only for no collisions
	it_ball it = balls.begin();
	while (it!=balls.end()) {
		update_position(*it,time );
		it++;
	}

}
void collide(list<ball>& balls, float time){
	it_ball it = balls.begin();
	it = balls.begin();
	float collide_in=-1;
	it_ball collidee;
	while (it!=--balls.end()) {
		//it->position +=  it->velocity*time;
		it_ball next = it;
		next++;
		if (  it->velocity > next->velocity ) {
			float t = next_collision(*it, *next);
			if (collide_in>t || collide_in < 0) {
				collidee = it;
				collide_in = t;
			}
		}
		it++;
	}

	if ( collide_in > 0 ) {
		if (time > collide_in) {  // >= may be? if you take t=collide_in as collided
			it_ball next=collidee;
			next++;
			update_position(*collidee, collide_in);
			update_position(*next, collide_in);
			swap(next->velocity,collidee->velocity);
			collide(balls, time - collide_in);
		} else {
			// no collision so update all positions and end
			update_all_positions(balls, time);

		}
	} else {//if ( collide_in < 0 || time <= 0) {
		// no collision so update all positions and end
		update_all_positions(balls, time);

	}
}

int main(){
	list<ball> balls;
	ball a;
	a.code = 1;
	a.velocity = 1;
	a.position = 10;
	a.time = 0;

	ball b;
	b.code = 2;
	b.velocity =-1;
	b.position = 95;
	b.time = 0;

	balls.push_back(a);
	balls.push_back(b);

	print(balls);
	collide(balls, 60);
	print(balls);
	return 0;

}