mod utils;
use std::{
    cmp::min,
    collections::{HashSet, VecDeque},
    time::Duration,
};

use egui::{Color32, Sense, Stroke};
use utils::{iter_pair, read_input};

#[cfg(target_arch = "wasm32")]
fn main() {
    console_error_panic_hook::set_once();

    let input = include_str!("../fake_inputs/day9");
    let input = parse_moves(&input).collect();

    let options = eframe::WebOptions::default();
    wasm_bindgen_futures::spawn_local(async {
        eframe::start_web("canvas", options, Box::new(|_cc| Box::new(App::new(input))))
            .await
            .expect("unable to start eframe");
    });
}

#[cfg(not(target_arch = "wasm32"))]
fn main() {
    let input = read_input();

    println!("Part 1: {}", visited_from_moves::<2>(parse_moves(&input)));
    println!("Part 2: {}", visited_from_moves::<10>(parse_moves(&input)));
}

type Pos = (i32, i32);
type Move = (Direction, u8);

fn visited_from_moves<const N: usize>(moves: impl Iterator<Item = Move>) -> usize {
    let mut tail_visited = HashSet::new();
    tail_visited.insert((0, 0));
    let mut knots = [(0, 0); N];
    for mv in moves {
        make_move(mv, &mut knots, &mut tail_visited);
    }

    tail_visited.len()
}

fn make_move(mv: Move, knots: &mut [Pos], tail_visited: &mut HashSet<Pos>) {
    let (dir, count) = mv;

    for _ in 0..count {
        // Move head of rope
        match dir {
            Direction::Up => knots[0].1 += 1,
            Direction::Down => knots[0].1 -= 1,
            Direction::Right => knots[0].0 += 1,
            Direction::Left => knots[0].0 -= 1,
        };

        for front_idx in 0..knots.len() - 1 {
            let (fx, fy) = knots[front_idx];
            let (bx, by) = &mut knots[front_idx + 1];
            let (dx, dy) = (fx - *bx, fy - *by);
            if (dx.abs() == 2 && dy == 0) || (dy.abs() == 2 && dx == 0) || (dy.abs() + dx.abs() > 2)
            {
                *bx += (dx.signum()) * min(dx.abs(), 1);
                *by += (dy.signum()) * min(dy.abs(), 1);
            }
        }
        tail_visited.insert(knots[knots.len() - 1]);
    }
}

fn parse_moves(input: &str) -> impl Iterator<Item = Move> + '_ {
    input.lines().map(|x| {
        let (dir, count) = iter_pair(x.split(' '));
        let count = count.parse().unwrap();

        (
            match dir {
                "L" => Direction::Left,
                "R" => Direction::Right,
                "U" => Direction::Up,
                "D" => Direction::Down,
                _ => panic!("invalid direction, {}", dir),
            },
            count,
        )
    })
}

#[derive(Debug, Clone, Copy)]
enum Direction {
    Up,
    Down,
    Left,
    Right,
}

struct App {
    orig_input: VecDeque<Move>,
    input: VecDeque<Move>,
    knots: Vec<Pos>,
    tail_visited: HashSet<Pos>,
    desired_knot_count: usize,
    speed: usize,
}

impl App {
    fn new(input: VecDeque<Move>) -> Self {
        App {
            orig_input: input.clone(),
            input,
            knots: vec![],
            tail_visited: HashSet::new(),
            desired_knot_count: 2,
            speed: 0,
        }
    }

    fn reset_knots(&mut self) {
        self.input = self.orig_input.clone();
        self.knots = vec![(0, 0); self.desired_knot_count];
        self.tail_visited.clear();
        self.tail_visited.insert((0, 0));
    }

    fn step(&mut self) {
        match self.input.pop_front() {
            Some(mv) => make_move(mv, &mut self.knots, &mut self.tail_visited),
            None => (),
        }
    }
}

impl eframe::App for App {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        if self.desired_knot_count != self.knots.len() {
            self.reset_knots()
        }
        egui::SidePanel::right("instructions").show(ctx, |ui| {
            egui::ScrollArea::vertical().show(ui, |ui| {
                if ui.button("Step").clicked() {
                    self.step();
                }
                if ui.button("Reset").clicked() {
                    self.reset_knots()
                }
                ui.label(format!("Tail Visited: {}", self.tail_visited.len()));
                ui.add(egui::Slider::new(&mut self.desired_knot_count, 2..=20).text("Knot count"));
                ui.add(egui::Slider::new(&mut self.speed, 0..=20).text("Speed"));
                ui.heading("Instructions:");
                for (i, ins) in self.input.iter().take(20).enumerate() {
                    let arrow = match ins.0 {
                        Direction::Up => "⬆",
                        Direction::Down => "⬇",
                        Direction::Right => "➡",
                        Direction::Left => "⬅",
                    };
                    if i == 0 {
                        ui.colored_label(Color32::YELLOW, arrow.repeat(ins.1 as _));
                    } else {
                        ui.label(arrow.repeat(ins.1 as _));
                    }
                }
                if self.input.len() > 20 {
                    ui.label(format!("+ {} more", self.input.len() - 20));
                }
            })
        });

        if self.speed > 0 && self.input.len() > 0 {
            for _ in 0..self.speed {
                self.step();
            }
            ctx.request_repaint_after(Duration::from_millis(100))
        }

        egui::CentralPanel::default().show(ctx, |ui| {
            let mut painter_size = ui.available_size_before_wrap();
            if !painter_size.is_finite() {
                painter_size = egui::vec2(500.0, 500.0);
            }

            const SIDE: f32 = 5.0;

            let (res, painter) = ui.allocate_painter(painter_size, Sense::hover());
            let center = res.rect.center().to_vec2();

            let to_panel_pos = |pos: &Pos| {
                (egui::vec2(pos.0 as f32 * SIDE, pos.1 as f32 * SIDE) + center).to_pos2()
            };

            let half_width = (painter_size.x / SIDE).floor() as i32;
            let half_height = (painter_size.y / SIDE).floor() as i32;

            for x in -half_width..half_width {
                for y in -half_height..half_height {
                    let dot = (x, y);
                    let color = if dot == (0, 0) {
                        Color32::WHITE
                    } else if self.tail_visited.contains(&dot) {
                        Color32::DARK_RED
                    } else {
                        continue;
                    };

                    let dot_pos = to_panel_pos(&dot);
                    painter.circle_stroke(dot_pos, 1.0, Stroke::new(1.0, color));
                }
            }

            // paint the head
            painter.circle_stroke(
                to_panel_pos(&self.knots[0]),
                SIDE / 2.0,
                Stroke::new(SIDE / 2.0, Color32::GREEN),
            );
            for knot in self.knots.iter().skip(1) {
                painter.circle_stroke(
                    to_panel_pos(knot),
                    SIDE / 2.0,
                    Stroke::new(SIDE / 2.0, Color32::YELLOW),
                );
            }

            for (a, b) in self.knots.iter().zip(self.knots.iter().skip(1)) {
                let head_pos = to_panel_pos(a);
                let tail_pos = to_panel_pos(b);
                painter.arrow(
                    tail_pos,
                    head_pos - tail_pos,
                    Stroke::new(1.0, Color32::YELLOW),
                )
            }
        });
    }
}