#include "magnetism.h"
#include "consts.h"
#include "vec_utils.h"
#include <math.h>

#define EPSILON 8.85418782E-12

void magnetism(universe_t* uni){
  for (unsigned int i = 0; i < uni->num_bodies; i++) {
    mass_body_t *body_1 = &uni->bodies[i];
    for (unsigned int y = i + 1; y < uni->num_bodies; y++) {
      mass_body_t *body_2 = &uni->bodies[y];
      if (body_1->charge == 0 || body_2->charge == 0) {
        continue;
      }
      Vector2 diff = vec2_diff(body_2->position, body_1->position);
      float distance_squared = vec2_dot(diff, diff);
      if (distance_squared == 0) {
        continue;
      }
      // Charges are in coulombs; convert acceleration to Earth radii/s^2.
      float factor = PHYSICS_TIMESTEP * body_1->charge * body_2->charge /
                     (4 * PI * EPSILON * EARTH_MASS * DISTANCE_UNIT_METERS *
                      DISTANCE_UNIT_METERS * DISTANCE_UNIT_METERS * distance_squared);
      Vector2 impulse = vec2_scale(vec2_normalize(diff), factor);
      body_1->speed = vec2_diff(body_1->speed,
                               vec2_scale(impulse, 1 / body_1->mass));
      body_2->speed = vec2_sum(body_2->speed,
                              vec2_scale(impulse, 1 / body_2->mass));
    }
  }
}