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

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

    let rad = 0.4;
    let num = 100;
    let shift = 1.0;

    let mut body_handles = Vec::new();

    for k in 0..num {
        for i in 0..num {
            let fk = k as f32;
            let fi = i as f32;

            let status = if i == 0 && (k % 4 == 0 || k == num - 1) {
                RigidBodyType::Fixed
            } else {
                RigidBodyType::Dynamic
            };

            let rigid_body =
                RigidBodyBuilder::new(status).translation(Vec3::new(fk * shift, 0.0, fi * shift));
            let collider = ColliderBuilder::ball(rad);
            let (child_handle, _) = world.insert(rigid_body, collider);

            // Vertical joint.
            if i > 0 {
                let parent_handle = *body_handles.last().unwrap();
                let joint = SphericalJointBuilder::new().local_anchor2(Vec3::new(0.0, 0.0, -shift));
                world.insert_impulse_joint(parent_handle, child_handle, joint);
            }

            // Horizontal joint.
            if k > 0 {
                let parent_index = body_handles.len() - num;
                let parent_handle = body_handles[parent_index];
                let joint = SphericalJointBuilder::new().local_anchor2(Vec3::new(-shift, 0.0, 0.0));
                world.insert_impulse_joint(parent_handle, child_handle, joint);
            }

            body_handles.push(child_handle);
        }
    }

    /*
     * Set up the testbed.
     */
    viewer.set_world(&mut world);
    viewer.look_at(
        Vec3::new(-110.0, -46.0, 170.0),
        Vec3::new(54.0, -38.0, 29.0),
    );

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