fn main() {
    let mut app = App::new();
    app.add_plugins(DefaultPlugins).add_systems(Startup, setup);
    physiks::enable(&mut app);
    app.run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    commands.spawn(Camera2dBundle {
        camera_2d: Camera2d {
            clear_color: ClearColorConfig::Custom(Color::BLACK),
        },
        ..default()
    });

    commands.spawn((
        RigidBody::new(1.0),
        MaterialMesh2dBundle {
            mesh: meshes.add(shape::Circle::new(50.0).into()).into(),
            material: materials.add(ColorMaterial::from(Color::PURPLE)),
            transform: Transform::from_translation(Vec3::new(0.0, 0.0, 0.0)),
            ..default()
        },
    ));

    commands.insert_resource(Time::new(Instant::now()));
    commands.insert_resource(FixedTime::new_from_secs(0.0));
    commands.insert_resource(PhysicsConfig {
        gravity: Vec3::NEG_Y * 9.8,
    });
}

pub fn enable(app: &mut App) {
    app.add_systems(FixedUpdate, systems::gravity::gravity)
        .add_systems(FixedUpdate, systems::movement::movement);
}

pub fn gravity(mut query: Query<&mut RigidBody>, config: Res<PhysicsConfig>) {
    for mut body in query.iter_mut() {
        body.velocity += config.gravity;
    }
}

pub fn movement(mut query: Query<(&mut Transform, &RigidBody)>, time: Res<FixedTime>) {
    for (mut transform, body) in query.iter_mut() {
        transform.translation += body.velocity * time.period.as_secs_f32();
    }
}