remove simulation dependencies from physics module

- Remove CelestialBody and SimulationState forward declarations from physics.h
- Rename evaluate_acceleration_direct to evaluate_acceleration
- Update rk4_step to accept Vec3* and mass parameters directly
- Remove unused evaluate_acceleration function with SimulationState dependency
- Update simulation.cpp to extract and pass masses to rk4_step

Claude: partial refactoring cleanup

src/physics.cpp

@@ -1,5 +1,4 @@
 #include "physics.h"
-#include "simulation.h"
 #include <cmath>
 
 // Vector addition
@@ -54,52 +53,30 @@ Vec3 calculate_acceleration(Vec3 force, double mass) {
     return {0.0, 0.0, 0.0};
 }
 
-Vec3 evaluate_acceleration(Vec3 pos, Vec3 vel, AccelerationContext* ctx) {
+void rk4_step(Vec3* position, Vec3* velocity, double dt,
-    CelestialBody temp_body = *ctx->current_body;
+              double body_mass, double parent_mass) {
-    temp_body.local_position = pos;
-    temp_body.local_velocity = vel;
-
-    Vec3 total_force = {0.0, 0.0, 0.0};
-
-    if (temp_body.parent_index >= 0 && temp_body.parent_index < ctx->sim->body_count) {
-        CelestialBody* parent = &ctx->sim->bodies[temp_body.parent_index];
-
-        double distance = vec3_magnitude(pos);
-        if (distance < 1.0) {
-            distance = 1.0;
-        }
-
-        double force_magnitude = G * temp_body.mass * parent->mass / (distance * distance);
-        Vec3 direction = vec3_normalize(vec3_scale(pos, -1.0));
-        total_force = vec3_scale(direction, force_magnitude);
-    }
-
-    return calculate_acceleration(total_force, temp_body.mass);
-}
-
-void rk4_step(CelestialBody* body, AccelerationContext* ctx, double dt) {
     Vec3 k1_vel, k2_vel, k3_vel, k4_vel;
     Vec3 k1_pos, k2_pos, k3_pos, k4_pos;
 
-    Vec3 pos0 = body->local_position;
+    Vec3 pos0 = *position;
-    Vec3 vel0 = body->local_velocity;
+    Vec3 vel0 = *velocity;
 
-    k1_vel = evaluate_acceleration(pos0, vel0, ctx);
+    k1_vel = evaluate_acceleration(pos0, body_mass, parent_mass);
     k1_pos = vel0;
 
     Vec3 pos1 = vec3_add(pos0, vec3_scale(k1_pos, dt * 0.5));
     Vec3 vel1 = vec3_add(vel0, vec3_scale(k1_vel, dt * 0.5));
-    k2_vel = evaluate_acceleration(pos1, vel1, ctx);
+    k2_vel = evaluate_acceleration(pos1, body_mass, parent_mass);
     k2_pos = vel1;
 
     Vec3 pos2 = vec3_add(pos0, vec3_scale(k2_pos, dt * 0.5));
     Vec3 vel2 = vec3_add(vel0, vec3_scale(k2_vel, dt * 0.5));
-    k3_vel = evaluate_acceleration(pos2, vel2, ctx);
+    k3_vel = evaluate_acceleration(pos2, body_mass, parent_mass);
     k3_pos = vel2;
 
     Vec3 pos3 = vec3_add(pos0, vec3_scale(k3_pos, dt));
     Vec3 vel3 = vec3_add(vel0, vec3_scale(k3_vel, dt));
-    k4_vel = evaluate_acceleration(pos3, vel3, ctx);
+    k4_vel = evaluate_acceleration(pos3, body_mass, parent_mass);
     k4_pos = vel3;
 
     Vec3 k_vel_sum = vec3_add(vec3_add(k1_vel, vec3_scale(k2_vel, 2.0)),
@@ -107,6 +84,21 @@ void rk4_step(CelestialBody* body, AccelerationContext* ctx, double dt) {
     Vec3 k_pos_sum = vec3_add(vec3_add(k1_pos, vec3_scale(k2_pos, 2.0)),
                               vec3_add(vec3_scale(k3_pos, 2.0), k4_pos));
 
-    body->local_velocity = vec3_add(vel0, vec3_scale(k_vel_sum, dt / 6.0));
+    *velocity = vec3_add(vel0, vec3_scale(k_vel_sum, dt / 6.0));
-    body->local_position = vec3_add(pos0, vec3_scale(k_pos_sum, dt / 6.0));
+    *position = vec3_add(pos0, vec3_scale(k_pos_sum, dt / 6.0));
+}
+
+Vec3 evaluate_acceleration(Vec3 relative_pos, double body_mass, double parent_mass) {
+    Vec3 total_force = {0.0, 0.0, 0.0};
+
+    double distance = vec3_magnitude(relative_pos);
+    if (distance < 1.0) {
+        distance = 1.0;
+    }
+
+    double force_magnitude = G * body_mass * parent_mass / (distance * distance);
+    Vec3 direction = vec3_normalize(vec3_scale(relative_pos, -1.0));
+    total_force = vec3_scale(direction, force_magnitude);
+
+    return calculate_acceleration(total_force, body_mass);
 }

src/physics.h

@@ -1,9 +1,6 @@
 #ifndef PHYSICS_H
 #define PHYSICS_H
 
-// Forward declaration
-struct CelestialBody;
-
 // 3D Vector
 struct Vec3 {
     double x, y, z;
@@ -24,15 +21,9 @@ Vec3 vec3_normalize(Vec3 v);
 // Physics functions
 Vec3 calculate_acceleration(Vec3 force, double mass);
 
-// Forward declaration for RK4 context
+// Physics integration functions
-struct SimulationState;
+void rk4_step(Vec3* position, Vec3* velocity, double dt,
-
+              double body_mass, double parent_mass);
-struct AccelerationContext {
+Vec3 evaluate_acceleration(Vec3 relative_pos, double body_mass, double parent_mass);
-    SimulationState* sim;
-    CelestialBody* current_body;
-    int body_index;
-};
-
-void rk4_step(CelestialBody* body, AccelerationContext* ctx, double dt);
 
 #endif

src/simulation.cpp

@@ -104,12 +104,9 @@ void update_simulation(SimulationState* sim) {
         }
 
         if (body->parent_index >= 0 && body->parent_index < sim->body_count) {
-            AccelerationContext ctx;
+            CelestialBody* parent = &sim->bodies[body->parent_index];
-            ctx.sim = sim;
+            rk4_step(&body->local_position, &body->local_velocity,
-            ctx.current_body = body;
+                     sim->dt, body->mass, parent->mass);
-            ctx.body_index = i;
-
-            rk4_step(body, &ctx, sim->dt);
         }
     }