use bevy::{prelude::*, render::render_resource::PrimitiveTopology};
use opensimplex_noise_rs::OpenSimplexNoise;
use rand::Rng;

pub fn planet() -> Mesh {
	let mut rng = rand::thread_rng();
	let simplex = OpenSimplexNoise::new(Some(rng.gen()));
	let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
	let perimeter: u32 = 1000;
	mesh.insert_attribute(
		Mesh::ATTRIBUTE_POSITION,
		(0..perimeter)
			.map(|i| {
				let mut r = simplex.eval_2d(i as f64 * 0.02, 0.) as f32 * 20.0 + 100.0;
				r += simplex.eval_2d(i as f64 * 0.05, 10.) as f32 * 10.0;
				r += simplex.eval_2d(i as f64 * 0.2, 10.) as f32 * 4.0;
				let a = std::f32::consts::TAU * i as f32 / perimeter as f32;
				[r * a.cos(), r * a.sin(), 0.]
			})
			.chain([[0., 0., 0.]].into_iter())
			.collect::<Vec<_>>(),
	);
	let mut triangles = Vec::new();
	for i in 0..perimeter {
		triangles.extend_from_slice(&[i, perimeter, (i + 1) % perimeter]);
	}
	mesh.set_indices(Some(bevy::render::mesh::Indices::U32(triangles)));
	mesh
}