use std::hint::unreachable_unchecked;

use raylib::prelude::*;

pub mod board;
pub mod pos;
pub mod tile;
use board::Board;
use pos::*;
use tile::*;

use crate::{draw_usize_small, Textures};

#[derive(Debug)]
pub struct Machine {
	board: Board,
	marbles: Vec<Pos>,
	powered: Vec<Pos>,

	input: Vec<u8>,
	input_index: usize,
	output: Vec<u8>,
	steps: usize,
}

impl Machine {
	pub fn new_empty(input: Vec<u8>, width: usize) -> Self {
		Self {
			board: Board::new_empty(width, width),
			marbles: Vec::new(),
			powered: Vec::new(),
			input,
			input_index: 0,
			output: Vec::new(),
			steps: 0,
		}
	}

	pub fn reset(&mut self) {
		self.steps = 0;
		self.input_index = 0;
		self.output.clear();
	}

	pub fn set_board(&mut self, board: Board) {
		self.marbles = board.get_marbles();
		self.board = board;
	}

	pub fn board(&self) -> &Board {
		&self.board
	}

	pub fn output(&self) -> &[u8] {
		&self.output
	}

	pub fn input(&self) -> &[u8] {
		&self.input
	}

	pub fn input_index(&self) -> usize {
		self.input_index
	}

	pub fn step_count(&self) -> usize {
		self.steps
	}

	pub fn set_input(&mut self, bytes: Vec<u8>) {
		self.input_index = self.input_index.min(bytes.len());
		self.input = bytes;
	}

	pub fn draw_marble_values(
		&self,
		d: &mut RaylibDrawHandle,
		textures: &Textures,
		offset: Vector2,
		zoom: i32,
	) {
		let tile_size = 16 << zoom;
		let scale = (1 << zoom) as f32;
		for marble in &self.marbles {
			let x = marble.x;
			let y = marble.y;
			if let Some(tile) = self.board.get(*marble) {
				let px = x as i32 * tile_size + offset.x as i32;
				let py = y as i32 * tile_size + offset.y as i32;
				if let Tile::Marble { value, dir } = tile {
					let texture = textures.get(dir.arrow_texture_name());
					let pos = Vector2::new(px as f32, py as f32);
					let faded_white = Color::new(255, 255, 255, 100);
					d.draw_texture_ex(texture, pos, 0., scale, faded_white);
					draw_usize_small(d, textures, value as usize, px, py, scale);
				}
			}
		}
	}

	pub fn step(&mut self) {
		self.steps += 1;
		// reset wires
		for &p in &self.powered {
			let Some(Tile::Powerable(_, state)) = self.board.get_mut(p) else {
				unsafe { unreachable_unchecked() }
			};
			*state = false;
		}
		self.powered.clear();

		if self.marbles.is_empty() {
			return;
		}

		#[derive(Debug, Clone, Copy)]
		enum Event {
			Stay,
			/// (new_pos, new_dir)
			MoveTo(Pos, Direction),
			/// (new_pos, new_dir, trigger_pos)
			Trigger(Pos, Direction, Pos),
			/// (other, new_dir)
			/// other marble should be set to reverse of new_dir
			/// and should be cancelled if it had a movement event planned
			Bounce(usize, Direction),
			Remove,
		}

		let mut marble_events: Vec<Event> = self
			.marbles
			.iter()
			.map(|&pos| {
				let marble = self.board.get(pos).unwrap();
				let Tile::Marble { value, dir } = marble else {
					panic!("broken marble");
				};
				let front_pos = dir.step(pos);
				let Some(front_tile) = self.board.get(front_pos) else {
					return Event::Stay;
				};

				if let Tile::Powerable(PTile::Bag, _) = front_tile {
					return Event::Remove;
				}
				if let Tile::Powerable(PTile::IO, _) = front_tile {
					self.output.push(value as u8);
					return Event::Remove;
				}

				let can_move_to = |tile| matches!(tile, Some(Tile::Blank | Tile::Digit(_)));

				let can_move_over = |tile| match tile {
					Tile::Mirror(mirror) => {
						let new_dir = mirror.new_dir(dir);
						let target_pos = new_dir.step(front_pos);
						let target = self.board.get(target_pos);
						if can_move_to(target) {
							Some((target_pos, new_dir))
						} else {
							None
						}
					}
					Tile::Arrow(new_dir) => {
						let target_pos = new_dir.step(front_pos);
						let target = self.board.get(target_pos);
						if target_pos == pos || can_move_to(target) {
							Some((target_pos, new_dir))
						} else {
							None
						}
					}
					_ => None,
				};

				if can_move_to(Some(front_tile)) {
					Event::MoveTo(front_pos, dir)
				} else if let Tile::Powerable(PTile::Trigger, _) = front_tile {
					let target_pos = dir.step(front_pos);
					let target = self.board.get(target_pos);
					if can_move_to(target) {
						Event::Trigger(target_pos, dir, front_pos)
					} else {
						Event::Stay
					}
				} else if let Some((new_pos, new_dir)) = can_move_over(front_tile) {
					Event::MoveTo(new_pos, new_dir)
				} else if let Tile::Marble {
					value: _,
					dir: other_dir,
				} = front_tile
				{
					if other_dir != dir {
						Event::Bounce(
							self.marbles.iter().position(|m| m == &front_pos).unwrap(),
							dir.opposite(),
						)
					} else {
						Event::Stay
					}
				} else {
					Event::Stay
				}
			})
			.collect();

		// resolve bounces
		for i in 0..marble_events.len() {
			let event = marble_events[i];
			if let Event::Bounce(other_index, dir) = event {
				match marble_events[other_index] {
					// cancel bounces on marble that are about to disappear
					Event::Remove => {
						marble_events[i] = Event::MoveTo(self.marbles[other_index], dir.opposite())
					}
					// let already bouncing marbles continue
					Event::Bounce(_, _) => (),
					// interrupt any other movement/staying to bounce
					_ => marble_events[other_index] = Event::Bounce(i, dir.opposite()),
				}
			}
		}

		// resolve deletions of tiles
		for (i, event) in marble_events.iter().enumerate() {
			if let Event::Remove = event {
				self.board.set(self.marbles[i], Tile::Blank);
			}
		}

		// resolve triggers
		let mut triggers_activated = Vec::new();
		for event in &mut marble_events {
			if let Event::Trigger(new_pos, dir, trigger_pos) = event {
				triggers_activated.push(*trigger_pos);
				*event = Event::MoveTo(*new_pos, *dir);
			}
		}

		// resolve collisions (multiple marbles entering the same space)
		for i in 0..(marble_events.len() - 1) {
			let event = marble_events[i];
			if let Event::MoveTo(new_pos, _dir) = event {
				for other_event in &mut marble_events[(i + 1)..] {
					if let Event::MoveTo(other_pos, _other_dir) = other_event {
						// todo: maybe sort by direction so the sucessful direction is consistent
						if other_pos == &new_pos {
							*other_event = Event::Stay;
						}
					}
				}
			}
		}

		// resolve movement
		for (i, &event) in marble_events.iter().enumerate() {
			if let Event::Remove = event {
				continue;
			}
			let marble = self.board.get_mut(self.marbles[i]).unwrap();
			let Tile::Marble { value, dir } = marble else {
				panic!("invalid marble");
			};
			match event {
				Event::MoveTo(new_pos, new_dir) => {
					let mut value = *value;
					self.board.set(self.marbles[i], Tile::Blank);
					self.marbles[i] = new_pos;
					let new_tile = self.board.get_mut(new_pos).unwrap();
					if let Tile::Digit(n) = new_tile {
						value = value.wrapping_mul(10).wrapping_add(*n as MarbleValue);
					}
					*new_tile = Tile::Marble {
						value,
						dir: new_dir,
					};
				}
				Event::Bounce(_other, new_dir) => *dir = new_dir,
				_ => (),
			}
		}

		// resolve deletions of marbles
		for (i, event) in marble_events.iter().enumerate().rev() {
			if let Event::Remove = event {
				self.marbles.remove(i);
			}
		}

		// process triggers
		for pos in triggers_activated {
			for dir in Direction::ALL {
				self.propagate_power(dir, dir.step(pos));
			}
		}
	}

	fn propagate_power(&mut self, dir: Direction, pos: Pos) {
		let Some(tile) = self.board.get_mut(pos) else {
			return;
		};
		let front_pos = dir.step(pos);
		if let Tile::Powerable(tile, state) = tile {
			if let PTile::Trigger = tile {
				return;
			}
			let was_powered = *state;
			*state = true;
			self.powered.push(pos);
			match tile {
				PTile::Wire(wiretype) => {
					if was_powered {
						return;
					}
					let dirs = wiretype.directions();
					for d in dirs {
						self.propagate_power(*d, d.step(pos));
					}
				}
				PTile::Bag => {
					if let Some(front) = self.board.get_blank_mut(front_pos) {
						*front = Tile::Marble { value: 0, dir };
						self.marbles.push(front_pos);
					}
				}
				PTile::IO => {
					if let Some(front) = self.board.get_blank_mut(front_pos) {
						if self.input_index < self.input.len() {
							let value = self.input[self.input_index] as MarbleValue;
							self.input_index += 1;
							*front = Tile::Marble { value, dir };
							self.marbles.push(front_pos);
						}
					}
				}
				PTile::Math(op) => {
					let op = *op;
					let pos_a = dir.left().step(pos);
					let pos_b = dir.right().step(pos);
					let val_a = self.board.get_or_blank(pos_a).read_value();
					let val_b = self.board.get_or_blank(pos_b).read_value();
					if !self.board.get_or_blank(pos_a).is_blank()
						|| !self.board.get_or_blank(pos_b).is_blank()
					{
						let value = match op {
							MathOp::Add => val_a.wrapping_add(val_b),
							MathOp::Sub => val_a.wrapping_sub(val_b),
							MathOp::Mul => val_a.wrapping_mul(val_b),
							MathOp::Div => val_a.checked_div(val_b).unwrap_or_default(),
							MathOp::Rem => val_a.checked_rem(val_b).unwrap_or_default(),
						};
						// println!("{op:?} a:{val_a} b:{val_b}");
						if let Some(front) = self.board.get_blank_mut(front_pos) {
							*front = Tile::Marble { value, dir };
							self.marbles.push(front_pos);
						}
					}
				}
				PTile::Flipper => {
					let Some(target) = self.board.get_mut(front_pos) else {
						return;
					};
					match target {
						Tile::Powerable(PTile::Wire(wire_type), _) => {
							*wire_type = match *wire_type {
								WireType::Vertical => WireType::Horizontal,
								WireType::Horizontal => WireType::Vertical,
								WireType::Cross => WireType::Cross,
							}
						}
						Tile::Mirror(mirror) => mirror.flip(),
						Tile::Arrow(dir) => *dir = dir.opposite(),
						_ => (),
					};
				}
				PTile::Gate(gate) => {
					let gate = *gate;
					let pos_a = dir.left().step(pos);
					let pos_b = dir.right().step(pos);
					let val_a = self.board.get_or_blank(pos_a).read_value();
					let val_b = self.board.get_or_blank(pos_b).read_value();

					let result = match gate {
						GateType::LessThan => val_a < val_b,
						GateType::GreaterThan => val_a > val_b,
						GateType::Equal => val_a == val_b,
						GateType::NotEqual => val_a != val_b,
					};
					if result {
						self.propagate_power(dir, dir.step(pos));
					}
				}
				PTile::Trigger => (),
			}
		}
	}
}