use std::f32::consts::PI;

use glam::{Mat2, Vec3, vec2, vec3};

pub struct Mesh {
	pub vertices: Vec<Vec3>,
	pub faces: Vec<[usize; 3]>,
}

pub fn shell(shape: &crate::ShapeArgs) -> Mesh {
	let mut vertices = Vec::<Vec3>::new();
	let mut faces = Vec::<[usize; 3]>::new();

	let sides = shape.sides as usize;
	let layers = (shape.layers_up + shape.layers_down) as usize;
	let base_layer = shape.layers_down;
	let diameter = shape.base_diameter;
	let radius = diameter / 2.;
	let height = shape.height;
	let bottom_angle = (PI / sides as f32) * -(base_layer as f32);
	let top_angle = (PI / sides as f32) * (layers as f32 - base_layer as f32);
	let bottom_y = radius * bottom_angle.tan();
	let top_y = radius * top_angle.tan();
	let incline = height / (top_y - bottom_y);
	let elevation = -height / 2. - incline * bottom_y;

	for layer in 0..=layers {
		let angle = (PI / sides as f32) * (layer as f32 - base_layer as f32);
		let x = radius;
		let y = angle.tan() * x;
		let z = elevation + incline * y;
		for side in 0..sides {
			let angle = (2. * PI / sides as f32) * side as f32;
			let rot = Mat2::from_angle(angle);
			let xy = rot * vec2(x, y);
			let v = vec3(xy.x, xy.y, z);
			vertices.push(v);
		}
	}
	for layer in 0..layers {
		let base = sides * layer;
		for side in 0..sides {
			let index = |layer, offset| base + sides * layer + (side + offset) % sides;
			faces.push([index(0, 0), index(0, 1), index(1, 0)]);
			faces.push([index(0, 1), index(1, 1), index(1, 0)]);
		}
	}

	Mesh { vertices, faces }
}

pub fn solid(shape: &crate::ShapeArgs) -> Mesh {
	let mut mesh = shell(shape);
	let sides = shape.sides as usize;
	for side in 0..(sides - 2) {
		mesh.faces.push([sides - 1, side + 1, side]);
	}
	let base = mesh.vertices.len() - sides;
	for side in 0..(sides - 2) {
		mesh.faces
			.push([base + sides - 1, base + side, base + side + 1]);
	}
	mesh
}