use glam::{bool, f32, Mat2, Vec2, vec2};

use coords::{FlatCoordinateSystem, InnerCS, OuterCS};
use metric::Tube;
use Subspace::{Boundary, Inner, Outer};

use crate::riemann;
use crate::tube::coords::FlatRegion;
use crate::types::{FlatTraceResult, Hit, Location, Object, Ray};

pub mod metric;
mod coords;

pub struct Space {
	pub tube: Tube,
	pub objs: Vec<Object>,
}

#[derive(PartialEq, Eq, Debug)]
pub enum Subspace {
	Outer,
	Boundary,
	Inner,
}

impl Space {
	pub fn which_subspace(&self, pt: Vec2) -> Subspace {
		if pt.y.abs() > self.tube.external_halflength {
			Outer
		} else if pt.x.abs() > self.tube.outer_radius {
			Outer
		} else if pt.x.abs() > self.tube.inner_radius {
			Boundary
		} else {
			Inner
		}
	}

	/// Выполняет один шаг трассировки. Работает в любой части пространства, но вне Boundary доступны более эффективные методы.
	/// ray задаётся в основной СК.
	pub fn trace_step(&self, ray: Ray) -> Ray {
		let a: Vec2 = -riemann::contract2(riemann::krist(&self.tube, ray.pos), ray.dir);
		let v = ray.dir + a;
		let p = ray.pos + v;
		Ray { pos: p, dir: v }
	}

	/// Выполняет один шаг перемещения. Работает в любой части пространства.
	/// off задаётся в локальной СК. Рекомендуется считать небольшими шагами.
	pub fn move_step(&self, loc: Location, off: Vec2) -> Location {
		let corr = Mat2::IDENTITY - riemann::contract(riemann::krist(&self.tube, loc.pos), loc.rot * off);
		let p = loc.pos + corr * loc.rot * off;
		Location { pos: p, rot: corr * loc.rot }
	}

	pub fn trace_iter(&self, ray: Ray) -> impl Iterator<Item=Ray> + '_ {
		std::iter::successors(Some(ray), |&ray| Some(self.trace_step(ray)))
	}

	pub fn trace_inner(&self, ray: Ray) -> FlatTraceResult {
		assert_eq!(self.which_subspace(ray.pos), Inner);
		self.trace_flat(InnerCS(self.tube), ray)
	}

	pub fn trace_outer(&self, ray: Ray) -> FlatTraceResult {
		assert_eq!(self.which_subspace(ray.pos), Outer);
		self.trace_flat(OuterCS(self.tube), ray)
	}

	fn trace_flat(&self, cs: impl FlatRegion, ray: Ray) -> FlatTraceResult {
		let ray = cs.global_to_flat(ray);
		let dist = cs.distance_to_boundary(ray);
		let objs = self.list_objects(|loc| cs.global_to_flat(loc));
		FlatTraceResult {
			end: dist.map(|dist| cs.flat_to_global(ray.forward(dist))),
			objects: Self::hit_objects(objs.as_slice(), ray, dist, |pos| cs.flat_to_global(pos)),
		}
	}

	fn trace_boundary(&self, ray: Ray) -> Ray {
		assert_eq!(self.which_subspace(ray.pos), Boundary);
		self.trace_iter(ray)
			.find(|&ray| self.which_subspace(ray.pos) != Boundary)
			.expect("Can't get outta the wall!")
	}

	fn list_objects(&self, tfm: impl Fn(Location) -> Location) -> Vec<Object> {
		self.objs.iter().map(|&Object { id, loc, r }| Object { id, loc: tfm(loc), r }).collect()
	}

	fn hit_objects(objs: &[Object], ray: Ray, limit: Option<f32>, globalize: impl Fn(Vec2) -> Vec2) -> Vec<Hit> {
		let limit = limit.unwrap_or(f32::INFINITY);
		objs.iter()
			.filter_map(|obj| {
				let rel = ray.pos - obj.loc.pos;
				let diff = rel.dot(ray.dir).powi(2) - ray.dir.length_squared() * (rel.length_squared() - obj.r.powi(2));
				if diff > 0.0 {
					let t = (-rel.dot(ray.dir) - diff.sqrt()) / ray.dir.length_squared();
					Some((obj, t))
				} else {
					None
				}
			})
			.filter(|&(_, t)| t >= 0.0 && t < limit)
			.map(|(obj, t)| {
				let pos = ray.forward(t).pos;
				let rel = obj.loc.rot.inverse() * Ray { pos: pos - obj.loc.pos, dir: ray.dir };
				Hit { id: obj.id, distance: t, pos: globalize(pos), rel }
			})
			.collect()
	}

	pub fn line(&self, a: Vec2, b: Vec2, step: f32) -> Vec<Vec2> {
		match self.which_subspace(a) {
			Outer => vec![b],
			Inner => {
				let cs = InnerCS(self.tube);
				let n = ((b - a).length() / step) as usize + 1;
				let a = cs.global_to_flat(a);
				let b = cs.global_to_flat(b);
				(1..=n).map(|k| cs.flat_to_global(a.lerp(b, k as f32 / n as f32))).collect()
			}
			Boundary => panic!("Can't draw a line here!"),
		}
	}
}

struct Rect {
	pub size: Vec2,
}

impl Rect {
	/// Отражает луч, чтобы все координаты направления были положительны (допустимо благодаря симметрии Rect).
	fn flip_ray(ray: Ray) -> Ray {
		Ray { pos: ray.pos * ray.dir.signum(), dir: ray.dir.abs() }
	}

	fn is_inside(&self, pt: Vec2) -> bool {
		pt.abs().cmplt(self.size).all()
	}

	fn trace_into(&self, ray: Ray) -> Option<f32> {
		let ray = Self::flip_ray(ray);
		// ray.pos.x + t * ray.dir.x = −size.x
		let ts = (-self.size - ray.pos) / ray.dir;
		let t = ts.max_element();
		let pt = ray.pos + t * ray.dir;
		if t < 0.0 { return None; }
		if pt.cmpgt(self.size).any() { return None; }
		Some(t)
	}

	fn trace_out_of(&self, ray: Ray) -> Option<f32> {
		let ray = Self::flip_ray(ray);
		// ray.pos.x + t * ray.dir.x = +size.x
		let ts = (self.size - ray.pos) / ray.dir;
		let t = ts.min_element();
		Some(t)
	}
}

#[test]
fn test_rect() {
	assert_eq!(Rect::flip_ray(Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, 5.0) }), Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, 5.0) });
	assert_eq!(Rect::flip_ray(Ray { pos: vec2(2.0, 3.0), dir: vec2(-4.0, 5.0) }), Ray { pos: vec2(-2.0, 3.0), dir: vec2(4.0, 5.0) });
	assert_eq!(Rect::flip_ray(Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, -5.0) }), Ray { pos: vec2(2.0, -3.0), dir: vec2(4.0, 5.0) });
	assert_eq!(Rect::flip_ray(Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, 0.0) }), Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, 0.0) });

	let r = Rect { size: vec2(2.0, 3.0) };

	assert_eq!(r.trace_into(Ray { pos: vec2(3.0, 3.0), dir: vec2(1.0, 1.0) }), None);
	assert_eq!(r.trace_into(Ray { pos: vec2(-3.0, 2.0), dir: vec2(1.0, 0.0) }), Some(1.0));
	assert_eq!(r.trace_into(Ray { pos: vec2(-3.0, 2.0), dir: vec2(-1.0, 0.0) }), None);
	assert_eq!(r.trace_into(Ray { pos: vec2(-3.0, 1.0), dir: vec2(2.0, 2.0) }), Some(0.5));
	assert_eq!(r.trace_into(Ray { pos: vec2(-3.0, 2.1), dir: vec2(2.0, 2.0) }), None);

	assert_eq!(r.trace_into(Ray { pos: vec2(2.0, 3.0), dir: vec2(1.0, 1.0) }), None);
	assert_eq!(r.trace_into(Ray { pos: vec2(-2.0, 3.0), dir: vec2(-1.0, 1.0) }), None);
	assert_eq!(r.trace_into(Ray { pos: vec2(2.0, 3.0), dir: vec2(-1.0, -1.0) }), Some(0.0));
	assert_eq!(r.trace_into(Ray { pos: vec2(2.0, -3.0), dir: vec2(-1.0, 1.0) }), Some(0.0));

	assert_eq!(r.trace_out_of(Ray { pos: vec2(0.0, 0.0), dir: vec2(1.0, 1.0) }), Some(2.0));
	assert_eq!(r.trace_out_of(Ray { pos: vec2(0.0, 0.0), dir: vec2(0.0, 1.0) }), Some(3.0));
	assert_eq!(r.trace_out_of(Ray { pos: vec2(0.0, 1.0), dir: vec2(0.0, -1.0) }), Some(4.0));
	assert_eq!(r.trace_out_of(Ray { pos: vec2(1.0, 1.0), dir: vec2(0.0, -1.0) }), Some(4.0));
	assert_eq!(r.trace_out_of(Ray { pos: vec2(2.0, 3.0), dir: vec2(1.0, 1.0) }), Some(0.0));
}