solar-sim/src/main.rs

use bevy::{math::DVec3, prelude::*};
use bevy_panorbit_camera::{PanOrbitCamera, PanOrbitCameraPlugin};

// Unit wrapper types - all distances in AU
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct DistanceAu(pub f64);

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct PositionAu(pub DVec3);

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct VelocityAuPerDay(pub DVec3);

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct MassKg(pub f64);

#[derive(Clone, Debug, PartialEq)]
pub struct ObjectName(pub String);

// Component wrappers
#[derive(Component)]
struct Position(PositionAu);

#[derive(Component)]
struct Velocity(VelocityAuPerDay);

#[derive(Component)]
struct Mass(MassKg);

#[derive(Component)]
struct Radius(DistanceAu);

#[derive(Component)]
struct Name(ObjectName);

#[derive(Bundle)]
struct ObjectBundle {
    name: Name,
    position: Position,
    mass: Mass,
    radius: Radius,
    velocity: Velocity,
}

pub struct SolarRenderingPlugin;

impl Plugin for SolarRenderingPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Startup, setup_rendering)
            .add_systems(
                FixedPostUpdate,
                (sync_radius_to_mesh, sync_position_to_transform),
            );
    }
}

fn sync_radius_to_mesh(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    query: Query<(Entity, &Radius, Option<&Mesh3d>), Changed<Radius>>,
) {
    for (entity, radius, existing_mesh) in query.iter() {
        // Radius is already in AU, use directly for rendering
        let render_radius = radius.0.0;

        // Create or update sphere mesh
        let sphere_mesh = meshes.add(Sphere::new(render_radius as f32));
        let material = materials.add(StandardMaterial {
            base_color: Color::WHITE,
            ..default()
        });

        if existing_mesh.is_none() {
            // Add mesh and material components if they don't exist
            commands
                .entity(entity)
                .insert((Mesh3d(sphere_mesh), MeshMaterial3d(material)));
        } else {
            // Update existing mesh
            commands.entity(entity).insert(Mesh3d(sphere_mesh));
        }
    }
}

fn sync_position_to_transform(mut query: Query<(&Position, &mut Transform), Changed<Position>>) {
    for (position, mut transform) in query.iter_mut() {
        // Convert AU to rendering units (1 AU = 1 unit for simplicity)
        transform.translation = position.0.0.as_vec3();
    }
}

fn setup_rendering(mut commands: Commands) {
    // Spawn camera with pan/orbit/zoom controls
    // Place it at a good distance to view the solar system
    commands.spawn((
        Camera3d::default(),
        Transform::from_translation(Vec3::new(2.0, 1.5, 2.0)),
        PanOrbitCamera {
            focus: Vec3::ZERO,
            radius: Some(3.0),
            is_upside_down: false,
            ..default()
        },
    ));

    // Spawn directional light from the sun's position
    // This simulates sunlight illuminating the planets
    commands.spawn((
        DirectionalLight {
            color: Color::WHITE,
            illuminance: 10000.0, // Bright like the sun
            shadows_enabled: true,
            ..default()
        },
        Transform::from_xyz(0.0, 0.0, 0.0).looking_at(Vec3::new(1.0, 0.0, 0.0), Vec3::Y),
    ));
}

fn setup_solar_system(mut commands: Commands) {
    // Sun - From NASA JPL Horizons data (J2000.0 epoch)
    // Physical properties: Mass = 1988410 x 10^24 kg, Radius = 695700 km = 0.00465 AU
    commands.spawn(ObjectBundle {
        name: Name(ObjectName("Sun".to_string())),
        position: Position(PositionAu(DVec3::new(0.0, 0.0, 0.0))), // At barycenter
        velocity: Velocity(VelocityAuPerDay(DVec3::new(0.0, 0.0, 0.0))), // Stationary relative to barycenter
        mass: Mass(MassKg(1.988410e30)),                                 // Solar mass in kg
        radius: Radius(DistanceAu(0.00465)), // Solar radius in AU (695700 km / 149597870.691)
    });

    // Earth - From NASA JPL Horizons data (A.D. 2000-Jan-01 12:00:00.0000 TDB)
    // Position and velocity vectors in ecliptic J2000.0 frame relative to Sun
    // Mass = 5.97219 x 10^24 kg, Mean radius = 6371.01 km = 0.0000426 AU
    commands.spawn(ObjectBundle {
        name: Name(ObjectName("Earth".to_string())),
        position: Position(PositionAu(DVec3::new(
            -1.771350992727098e-1, // X = -0.177135 AU
            9.672416867665306e-1,  // Y = 0.967242 AU
            -4.085281582511366e-6, // Z = -4.085e-6 AU
        ))),
        velocity: Velocity(VelocityAuPerDay(DVec3::new(
            -1.720762506872895e-2, // VX = -0.0172076 AU/day
            -3.158782144324866e-3, // VY = -0.00315878 AU/day
            1.049888594613343e-7,  // VZ = 1.04989e-7 AU/day
        ))),
        mass: Mass(MassKg(5.97219e24)),        // Earth mass in kg
        radius: Radius(DistanceAu(0.0000426)), // Mean radius in AU (6371.01 km / 149597870.691)
    });

    // Moon - From NASA JPL Horizons data (A.D. 2000-Jan-01 12:00:00.0000 TDB)
    // Position and velocity vectors in ecliptic J2000.0 frame relative to Sun
    // Mass = 7.349 x 10^22 kg, Mean radius = 1737.53 km = 0.0000116 AU
    commands.spawn(ObjectBundle {
        name: Name(ObjectName("Moon".to_string())),
        position: Position(PositionAu(DVec3::new(
            -1.790843809223965e-1, // X = -0.179084 AU
            9.654035607264573e-1,  // Y = 0.965404 AU
            2.383726922995396e-4,  // Z = 0.000238373 AU
        ))),
        velocity: Velocity(VelocityAuPerDay(DVec3::new(
            -1.683595459141215e-2, // VX = -0.0168360 AU/day
            -3.580960720855671e-3, // VY = -0.00358096 AU/day
            -6.540550604528720e-6, // VZ = -6.54055e-6 AU/day
        ))),
        mass: Mass(MassKg(7.349e22)),          // Moon mass in kg
        radius: Radius(DistanceAu(0.0000116)), // Mean radius in AU (1737.53 km / 149597870.691)
    });
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugins(PanOrbitCameraPlugin)
        .add_plugins(SolarRenderingPlugin)
        .add_systems(Startup, setup_solar_system)
        .run();
}