use anyhow::{bail, Context, Result};
use cgmath::{Deg, Point3, Rad};
use std::collections::{HashMap, HashSet};

use crate::{handle::SpriteHandle, util::Polar, Content, ContentBuildContext};

pub(crate) mod syntax {
	use serde::Deserialize;
	use std::collections::HashMap;
	// Raw serde syntax structs.
	// These are never seen by code outside this crate.

	#[derive(Debug, Deserialize)]
	pub struct System {
		pub object: HashMap<String, Object>,
	}

	#[derive(Debug, Deserialize)]
	pub struct Object {
		pub sprite: String,
		pub position: Position,

		pub size: f32,

		pub radius: Option<f32>,
		pub angle: Option<f32>,
	}

	#[derive(Debug, Deserialize)]
	#[serde(untagged)]
	pub enum Position {
		Polar(PolarCoords),
		Cartesian(CoordinatesThree),
	}

	#[derive(Debug, Deserialize)]
	pub struct PolarCoords {
		pub center: CoordinatesTwo,
		pub radius: f32,
		pub angle: f32,
		pub z: f32,
	}

	#[derive(Debug, Deserialize)]
	#[serde(untagged)]
	pub enum CoordinatesTwo {
		Label(String),
		Coords([f32; 2]),
	}

	impl ToString for CoordinatesTwo {
		fn to_string(&self) -> String {
			match self {
				Self::Label(s) => s.to_owned(),
				Self::Coords(v) => format!("{:?}", v),
			}
		}
	}

	#[derive(Debug, Deserialize)]
	#[serde(untagged)]
	pub enum CoordinatesThree {
		Label(String),
		Coords([f32; 3]),
	}

	impl ToString for CoordinatesThree {
		fn to_string(&self) -> String {
			match self {
				Self::Label(s) => s.to_owned(),
				Self::Coords(v) => format!("{:?}", v),
			}
		}
	}
}

// Processed data structs.
// These are exported.

/// Represents a star system
#[derive(Debug)]
pub struct System {
	/// This star system's name
	pub name: String,

	/// Objects in this system
	pub objects: Vec<Object>,
}

/// Represents an orbiting body in a star system
/// (A star, planet, moon, satellite, etc)
/// These may be landable and may be decorative.
/// System objects to not interact with the physics engine.
#[derive(Debug)]
pub struct Object {
	/// This object's sprite
	pub sprite: SpriteHandle,

	/// This object's size.
	/// Measured as height in game units.
	/// This value is scaled for distance
	/// (i.e, the z-value of position)
	pub size: f32,

	/// This object's position, in game coordinates,
	/// relative to the system's center (0, 0).
	pub pos: Point3<f32>,

	/// This object's sprite's angle.
	pub angle: Rad<f32>,
}

/// Helper function for resolve_position, never called on its own.
fn resolve_coordinates(
	objects: &HashMap<String, syntax::Object>,
	cor: &syntax::CoordinatesThree,
	mut cycle_detector: HashSet<String>,
) -> Result<Point3<f32>> {
	match cor {
		syntax::CoordinatesThree::Coords(c) => Ok((*c).into()),
		syntax::CoordinatesThree::Label(l) => {
			if cycle_detector.contains(l) {
				bail!(
					"Found coordinate cycle: `{}`",
					cycle_detector.iter().fold(String::new(), |sum, a| {
						if sum.is_empty() {
							a.to_string()
						} else {
							sum + " -> " + a
						}
					})
				);
			}
			cycle_detector.insert(l.to_owned());

			let p = match objects.get(l) {
				Some(p) => p,
				None => bail!("Could not resolve coordinate label `{l}`"),
			};
			Ok(resolve_position(&objects, &p, cycle_detector)
				.with_context(|| format!("In object {:#?}", l))?)
		}
	}
}

/// Given an object, resolve its position as a Point3.
fn resolve_position(
	objects: &HashMap<String, syntax::Object>,
	obj: &syntax::Object,
	cycle_detector: HashSet<String>,
) -> Result<Point3<f32>> {
	match &obj.position {
		syntax::Position::Cartesian(c) => Ok(resolve_coordinates(objects, &c, cycle_detector)?),
		syntax::Position::Polar(p) => {
			let three = match &p.center {
				syntax::CoordinatesTwo::Label(s) => syntax::CoordinatesThree::Label(s.clone()),
				syntax::CoordinatesTwo::Coords(v) => {
					syntax::CoordinatesThree::Coords([v[0], v[1], f32::NAN])
				}
			};
			let r = resolve_coordinates(&objects, &three, cycle_detector)?;
			let plane = Polar {
				center: (r.x, r.y).into(),
				radius: p.radius,
				angle: Deg(p.angle).into(),
			}
			.to_cartesian();
			Ok(Point3 {
				x: plane.x,
				y: plane.y,
				z: p.z,
			})
		}
	}
}

impl crate::Build for System {
	type InputSyntaxType = HashMap<String, syntax::System>;

	fn build(
		system: Self::InputSyntaxType,
		_build_context: &mut ContentBuildContext,
		content: &mut Content,
	) -> Result<()> {
		for (system_name, system) in system {
			let mut objects = Vec::new();

			for (label, obj) in &system.object {
				let mut cycle_detector = HashSet::new();
				cycle_detector.insert(label.clone());

				let handle = match content.sprite_index.get(&obj.sprite) {
					None => bail!(
						"In system `{}`: sprite `{}` doesn't exist",
						system_name,
						obj.sprite
					),
					Some(t) => *t,
				};

				objects.push(Object {
					sprite: handle,
					pos: resolve_position(&system.object, &obj, cycle_detector)
						.with_context(|| format!("In object {:#?}", label))?,
					size: obj.size,
					angle: Deg(obj.angle.unwrap_or(0.0)).into(),
				});
			}

			objects.sort_by(|a, b| a.pos.z.total_cmp(&b.pos.z));
			content.systems.push(Self {
				name: system_name,
				objects,
			});
		}

		return Ok(());
	}
}