use std::fs::read_to_string;

#[derive(Debug, PartialEq, Eq, Clone)]
struct Map {
    min_x: usize,
    width: usize,
    height: usize,
    map: Vec<bool>,
}

impl Map {
    fn new() -> Self {
        Self {
            min_x: 500,
            width: 0,
            height: 0,
            map: vec![],
        }
    }

    fn print(&self) {
        for y in 0..self.height {
            for x in 0..self.width {
                print!(
                    "{}",
                    if self.map[x + y * self.width] {
                        '#'
                    } else {
                        '.'
                    }
                );
            }
            println!();
        }
    }

    fn at(&self, position: (usize, usize)) -> bool {
        if !self.is_inside(position) {
            return false;
        }
        let x = position.0 - self.min_x;
        self.map[x + position.1 * self.width]
    }

    fn is_inside(&self, position: (usize, usize)) -> bool {
        position.0 >= self.min_x && position.0 < self.min_x + self.width && position.1 < self.height
    }

    fn add_obstacle(&mut self, position: (usize, usize)) {
        while self.min_x > position.0 {
            self.extend_left();
        }
        while self.min_x + self.width <= position.0 {
            self.extend_right();
        }
        while self.height <= position.1 {
            self.extend_down();
        }
        let x = position.0 - self.min_x;
        self.map[x + position.1 * self.width] = true;
    }

    fn extend_down(&mut self) {
        self.map.append(&mut vec![false; self.width]);
        self.height += 1;
    }

    fn extend_left(&mut self) {
        self.map.append(&mut vec![false; self.height]);
        for y in (0..self.height).rev() {
            for x in (0..self.width).rev() {
                self.map[(x + 1) + y * (self.width + 1)] = self.map[x + y * self.width];
            }
        }
        self.width += 1;
        self.min_x -= 1;
        for y in 0..self.height {
            self.map[y * self.width] = false;
        }
    }

    fn extend_right(&mut self) {
        self.map.append(&mut vec![false; self.height]);
        for y in (0..self.height).rev() {
            for x in (0..self.width).rev() {
                self.map[x + y * (self.width + 1)] = self.map[x + y * self.width];
            }
        }
        self.width += 1;
        for y in 0..self.height {
            self.map[self.width - 1 + y * self.width] = false;
        }
    }
}

fn add_sand(map: &Map) -> Option<(usize, usize)> {
    let mut sand = (500, 0);
    while map.is_inside(sand) {
        let x = sand.0;
        let y = sand.1;
        if !map.at((x, y + 1)) {
            sand.1 += 1;
            continue;
        }
        if !map.at((x - 1, y + 1)) {
            sand.1 += 1;
            sand.0 -= 1;
            continue;
        }
        if !map.at((x + 1, y + 1)) {
            sand.1 += 1;
            sand.0 += 1;
            continue;
        }
        return Some(sand);
    }
    None
}

fn add_sand_floor(map: &Map, floor: usize) -> Option<(usize, usize)> {
    let mut sand = (500, 0);
    while !map.at((500, 0)) {
        let x = sand.0;
        let y = sand.1;
        if y + 1 == floor {
            return Some(sand);
        }
        if !map.at((x, y + 1)) {
            sand.1 += 1;
            continue;
        }
        if !map.at((x - 1, y + 1)) {
            sand.1 += 1;
            sand.0 -= 1;
            continue;
        }
        if !map.at((x + 1, y + 1)) {
            sand.1 += 1;
            sand.0 += 1;
            continue;
        }
        return Some(sand);
    }
    None
}

fn main() {
    let input = "498,4 -> 498,6 -> 496,6
503,4 -> 502,4 -> 502,9 -> 494,9"
        .to_owned();
    let input = read_to_string("input.txt").unwrap_or(input);
    let mut map = Map::new();
    for line in input.lines() {
        let points = line.split(" -> ").map(|coord| {
            let [x, y] = coord.split(',').map(|n| n.parse::<usize>().unwrap()).collect::<Vec<_>>()[..] else {panic!()};
            (x, y)
        }).collect::<Vec<_>>();
        for line in points.windows(2) {
            let (x1, y1) = line[0];
            let (x2, y2) = line[1];
            let x_min = x1.min(x2);
            let x_max = x1.max(x2);
            let y_min = y1.min(y2);
            let y_max = y1.max(y2);
            for x in x_min..=x_max {
                for y in y_min..=y_max {
                    map.add_obstacle((x, y));
                }
            }
        }
    }
    println!("printing map:");
    map.print();
    let mut num_sand = 0;
    while let Some(sand) = add_sand(&map) {
        map.add_obstacle(sand);
        num_sand += 1;
    }
    println!();
    map.print();
    println!("needed {num_sand} sand particles");
    let floor = map.height + 1;
    println!("floor: {floor}");
    while let Some(sand) = add_sand_floor(&map, floor) {
        map.add_obstacle(sand);
        num_sand += 1;
    }
    println!();
    map.print();
    println!("needed {num_sand} sand particles");
}