mod mesh_loader;

use std::fs::File;
use std::{env};
use std::error::Error;
use std::f32::consts::PI;
use std::io::{BufReader};
use glm::*;
use show_image::{ImageInfo, ImageView, WindowOptions};
use crate::mesh_loader::{Face, load_mesh};

const W: i32 = 320;
const H: i32 = 240;

#[derive(Copy, Clone)]
struct Color(u8, u8, u8);

struct Image {
	w: i32,
	h: i32,
	data: Vec<u8>,
}

impl Image {
	fn data(&self) -> &[u8] {
		self.data.as_slice()
	}

	fn put_pixel(&mut self, x: i32, y: i32, color: Color) {
		if x < 0 || x >= self.w || y < 0 || y > self.h {
			return;
		}
		let index = 3 * (x + self.w * y) as usize;
		self.data[index] = color.0;
		self.data[index + 1] = color.1;
		self.data[index + 2] = color.2;
	}
}

fn ypr_to_mat(ypr: Vec3) -> Mat3 {
	let Vec3 { x: yaw, y: pitch, z: roll } = ypr;
	let m_roll = mat3(
		roll.cos(), roll.sin(), 0.0,
		-roll.sin(), roll.cos(), 0.0,
		0.0, 0.0, 1.0);
	let m_yaw = mat3(
		yaw.cos(), 0.0, yaw.sin(),
		0.0, 1.0, 0.0,
		-yaw.sin(), 0.0, yaw.cos());
	let m_pitch = mat3(
		1.0, 0.0, 0.0,
		0.0, pitch.cos(), -pitch.sin(),
		0.0, pitch.sin(), pitch.cos());
	m_roll * m_pitch * m_yaw
}

struct TraceResult {
	distance: f32,
	normal: Vec3,
}

fn trace_to_mesh(mesh: &[Face], base: Vec3, ray: Vec3) -> Option<TraceResult> {
	let mut ret: Option<TraceResult> = None;
	let mut dist = f32::INFINITY;
	for f in mesh {
		let fs = (0..3).map(|k| edge_dist(f.vertices[k], f.vertices[(k + 1) % 3], base, ray));
		if fs.into_iter().all(|f| f >= 0.0) {
			let m = Mat3 { c0: f.vertices[1] - f.vertices[0], c1: f.vertices[2] - f.vertices[0], c2: -ray };
			if let Some(m) = m.inverse() {
				let rel = m * (base - f.vertices[0]);
				if rel.z > dist {
					continue;
				}
				dist = rel.z;
				ret = Some(TraceResult {
					distance: rel.z,
					normal: f.normal,
				});
			} else {
				continue;
			}
		}
	}
	ret
}

fn render(mesh: &[Face], camera: impl Fn(Vec2) -> (Vec3, Vec3)) -> Image {
	let mut img = Image {
		w: W,
		h: H,
		data: vec![0; (3 * W * H) as usize],
	};
	let img_size = vec2(W as f32, H as f32);
	for y in 0..H {
		for x in 0..W {
			let img_coords = vec2(x as f32, y as f32);
			let off = (img_coords - img_size * 0.5) / img_size.y;
			let (base, ray) = camera(off);
			if let Some(r) = trace_to_mesh(mesh, base, ray) {
				let color = clamp(to_ivec3(r.normal * 120.0 + 128.0), ivec3(0, 0, 0), ivec3(255, 255, 255));
				img.put_pixel(x, y, Color(color.x as u8, color.y as u8, color.z as u8));
			}
		}
	}
	img
}

#[show_image::main]
fn main() -> Result<(), Box<dyn Error>> {
	let args: Vec<String> = env::args().collect();
	let mesh = {
		let f = File::open(&args[1])?;
		let mut f = BufReader::new(f);
		load_mesh(&mut f)?
	};
	let window = show_image::create_window("Raytracing", WindowOptions::default())?;
	loop {
		for phi in 0..360 {
			let m_view = ypr_to_mat(vec3((135.0 + phi as f32) * PI / 180.0, -30.0 * PI / 180.0, 0.0f32));
			let m_camera = transpose(&m_view);
			let img = render(mesh.as_slice(), |off| {
				// perspective projection
				let base = vec3(0.0, 0.0, -40.0);
				let ray = vec3(off.x, off.y, 2.0);

				// orthographic projection
				// let base = vec3(off.x, off.y, -10.0);
				// let ray = vec3(0.0, 0.0, 1.0);

				(m_camera * base, m_camera * ray)
			});

			let image = ImageView::new(ImageInfo::rgb8(W as u32, H as u32), img.data());
			window.set_image("image", image)?;
		}
	}
}

fn edge_dist(a: Vec3, b: Vec3, base: Vec3, dir: Vec3) -> f32 {
	// Note: given that the input is not arbitrary but comes from a cartesian product of certain (a, b) pairs and certain (base, dir) pairs, this can be optimized from Cnm to an+bm+cnm with c<C.
	Mat3 { c0: b - a, c1: base - a, c2: -dir }.determinant()
}