use glam::{bool, f32, vec3, Mat3, Vec3};

use crate::ifaces::{DebugTraceable, RayPath, Traceable};
use coords::{FlatCoordinateSystem, InnerCS, OuterCS};
use metric::Tube;
use Subspace::{Boundary, Inner, Outer};

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

mod coords;
pub mod metric;

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

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

impl Space {
	fn which_subspace(&self, pt: Vec3) -> 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 = -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: Vec3) -> Location {
		let corr =
			Mat3::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)))
	}

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

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

	fn obj_hitter(&self, pos: Vec3) -> Option<fn(&Self, ray: Ray) -> FlatTraceResult> {
		match self.which_subspace(pos) {
			Inner => Some(Self::trace_inner),
			Outer => Some(Self::trace_outer),
			Boundary => None,
		}
	}

	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(Vec3) -> Vec3,
	) -> 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: Vec3, b: Vec3, step: f32) -> Vec<Vec3> {
		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!"),
		}
	}

	fn camera_ray_to_abs(&self, camera: Location, ray: Ray) -> Ray {
		let pos = camera.pos;
		let dir = camera.rot * ray.dir;
		// TODO account for ray.pos
		let dir = DT * self.tube.normalize_vec_at(pos, dir);
		Ray { pos, dir }
	}
}

/// Like [`std::iter::successors`] but with an upper limit on iteration count.
///
/// # Panics
///
/// Panics if the sequence doesn’t terminate in `max_iters` calls of `succ`.
fn iterate_with_limit<T>(max_iters: usize, init: T, mut succ: impl FnMut(T) -> Option<T>) {
	let mut state = init;
	for _ in 0..max_iters {
		match succ(state) {
			Some(next) => state = next,
			None => return,
		}
	}
	panic!("iteration limit exceeded");
}

impl Traceable for Space {
	fn trace(&self, camera: Location, ray: Ray) -> Vec<Hit> {
		let ray = self.camera_ray_to_abs(camera, ray);
		let mut hits = vec![];
		iterate_with_limit(100, ray, |ray| {
			let ret = self
				.trace_iter(ray)
				.skip(1)
				.find_map(|ray| self.obj_hitter(ray.pos).map(|hitter| hitter(self, ray)))
				.expect("Space::trace_iter does not terminate");
			hits.extend(ret.objects); // TODO fix distance
			ret.end
		});
		hits
	}
}

impl DebugTraceable for Space {
	fn trace_dbg(&self, camera: Location, ray: Ray) -> (Vec<Hit>, RayPath) {
		let mut points = vec![];
		let mut hits = vec![];
		let mut ray = self.camera_ray_to_abs(camera, ray);

		let trace_to_flat = |points: &mut Vec<Vec3>, ray| {
			for ray in self.trace_iter(ray).skip(1) {
				points.push(ray.pos);
				if let Some(hitter) = self.obj_hitter(ray.pos) {
					return (ray, hitter(self, ray));
				}
			}
			unreachable!("Space::trace_iter terminated!")
		};

		points.push(ray.pos);
		for _ in 0..100 {
			let (ray_into_flat, ret) = trace_to_flat(&mut points, ray);
			hits.extend(ret.objects); // TODO fix distance
			let Some(ray_outta_flat) = ret.end else {
				return (
					hits,
					RayPath {
						points,
						end_dir: ray_into_flat.dir.normalize(),
					},
				);
			};
			points.extend(self.line(ray_into_flat.pos, ray_outta_flat.pos, 10.0));
			ray = ray_outta_flat;
		}
		panic!("tracing didn't terminate");
	}
}

struct Rect {
	pub size: Vec3,
}

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: Vec3) -> 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: vec3(2.0, 3.0, 2.0),
			dir: vec3(4.0, 5.0, 4.0)
		}),
		Ray {
			pos: vec3(2.0, 3.0, 2.0),
			dir: vec3(4.0, 5.0, 4.0)
		}
	);
	assert_eq!(
		Rect::flip_ray(Ray {
			pos: vec3(2.0, 3.0, 2.0),
			dir: vec3(-4.0, 5.0, -4.0)
		}),
		Ray {
			pos: vec3(-2.0, 3.0, -2.0),
			dir: vec3(4.0, 5.0, 4.0)
		}
	);
	assert_eq!(
		Rect::flip_ray(Ray {
			pos: vec3(2.0, 3.0, 2.0),
			dir: vec3(4.0, -5.0, 4.0)
		}),
		Ray {
			pos: vec3(2.0, -3.0, 2.0),
			dir: vec3(4.0, 5.0, 4.0)
		}
	);
	assert_eq!(
		Rect::flip_ray(Ray {
			pos: vec3(2.0, 3.0, 2.0),
			dir: vec3(4.0, 0.0, 4.0)
		}),
		Ray {
			pos: vec3(2.0, 3.0, 2.0),
			dir: vec3(4.0, 0.0, 4.0)
		}
	);

	let r = Rect {
		size: vec3(2.0, 3.0, 2.0),
	};

	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(3.0, 3.0, 3.0),
			dir: vec3(1.0, 1.0, 1.0)
		}),
		None
	);
	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(-3.0, 2.0, -3.0),
			dir: vec3(1.0, 0.0, 1.0)
		}),
		Some(1.0)
	);
	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(-3.0, 2.0, -3.0),
			dir: vec3(-1.0, 0.0, -1.0)
		}),
		None
	);
	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(-3.0, 1.0, -3.0),
			dir: vec3(2.0, 2.0, 2.0)
		}),
		Some(0.5)
	);
	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(-3.0, 2.1, -3.0),
			dir: vec3(2.0, 2.0, 2.0)
		}),
		None
	);

	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(2.0, 3.0, 2.0),
			dir: vec3(1.0, 1.0, 1.0)
		}),
		None
	);
	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(-2.0, 3.0, -2.0),
			dir: vec3(-1.0, 1.0, -1.0)
		}),
		None
	);
	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(2.0, 3.0, 2.0),
			dir: vec3(-1.0, -1.0, -1.0)
		}),
		Some(0.0)
	);
	assert_eq!(
		r.trace_into(Ray {
			pos: vec3(2.0, -3.0, 2.0),
			dir: vec3(-1.0, 1.0, -1.0)
		}),
		Some(0.0)
	);

	assert_eq!(
		r.trace_out_of(Ray {
			pos: vec3(0.0, 0.0, 0.0),
			dir: vec3(1.0, 1.0, 1.0)
		}),
		Some(2.0)
	);
	assert_eq!(
		r.trace_out_of(Ray {
			pos: vec3(0.0, 0.0, 0.0),
			dir: vec3(0.0, 1.0, 0.0)
		}),
		Some(3.0)
	);
	assert_eq!(
		r.trace_out_of(Ray {
			pos: vec3(0.0, 1.0, 0.0),
			dir: vec3(0.0, -1.0, 0.0)
		}),
		Some(4.0)
	);
	assert_eq!(
		r.trace_out_of(Ray {
			pos: vec3(1.0, 1.0, 1.0),
			dir: vec3(0.0, -1.0, 0.0)
		}),
		Some(4.0)
	);
	assert_eq!(
		r.trace_out_of(Ray {
			pos: vec3(2.0, 3.0, 2.0),
			dir: vec3(1.0, 1.0, 1.0)
		}),
		Some(0.0)
	);
}