#include "gravity.h"
#include "consts.h"
#include "vec_utils.h"
#include <raylib.h>

void gravity(universe_t *uni) {
  const float dt = PHYSICS_TIMESTEP;
  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];
      Vector2 separation = vec2_diff(body_2->position, body_1->position);
      float distance_squared = vec2_dot(separation, separation);
      if (distance_squared == 0.0f) {
        continue;
      }
      Vector2 direction = vec2_normalize(separation);
      float factor = SIMULATION_G * dt / distance_squared;
      body_1->speed =
          vec2_sum(body_1->speed, vec2_scale(direction, factor * body_2->mass));
      body_2->speed = vec2_sum(body_2->speed,
                               vec2_scale(direction, -factor * body_1->mass));
    }
  }
}