use rapier_testbed3d::TestbedViewer;
use rapier3d::prelude::*;

fn create_pyramid(
    bodies: &mut RigidBodySet,
    colliders: &mut ColliderSet,
    offset: Vec3,
    stack_height: usize,
    rad: f32,
) {
    let shift = rad * 2.0;

    for i in 0usize..stack_height {
        for j in i..stack_height {
            let fj = j as f32;
            let fi = i as f32;
            let x = (fi * shift / 2.0) + (fj - fi) * shift;
            let y = fi * shift;

            // Build the rigid body.
            let rigid_body = RigidBodyBuilder::dynamic().translation(Vec3::new(x, y, 0.0) + offset);
            let handle = bodies.insert(rigid_body);
            let collider = ColliderBuilder::cuboid(rad, rad, rad);
            colliders.insert_with_parent(collider, handle, bodies);
        }
    }
}

pub async fn run(viewer: &mut TestbedViewer) -> anyhow::Result<()> {
    /*
     * World
     */
    let mut world = PhysicsWorld::new();

    let rad = 0.5;
    let pyramid_count = 40;
    let spacing = 4.0;

    /*
     * Ground
     */
    let ground_size = 50.0;
    let ground_height = 0.1;

    let rigid_body = RigidBodyBuilder::fixed().translation(Vec3::new(0.0, -ground_height, 0.0));
    let collider = ColliderBuilder::cuboid(
        ground_size,
        ground_height,
        pyramid_count as f32 * spacing / 2.0 + ground_size,
    );
    let _ = world.insert(rigid_body, collider);

    /*
     * Create the cubes
     */
    for pyramid_index in 0..pyramid_count {
        let bottomy = rad;
        create_pyramid(
            &mut world.bodies,
            &mut world.colliders,
            Vec3::new(
                0.0,
                bottomy,
                (pyramid_index as f32 - pyramid_count as f32 / 2.0) * spacing,
            ),
            20,
            rad,
        );
    }

    /*
     * Set up the viewer.
     */
    viewer.set_world(&mut world);
    viewer.look_at(Vec3::new(100.0, 100.0, 100.0), Vec3::ZERO);

    while viewer.render_frame(&mut world).await {
        if viewer.simulating() {
            world.step();
        }
    }
    Ok(())
}
