use winnow::{
    Parser, Result,
    ascii::{multispace0, newline},
    combinator::{alt, preceded, repeat, terminated},
};

use crate::{AoC, SimpleDay, WinnowDay};

fn day() -> impl WinnowDay {
    AoC::new(parse as _, part1 as _, part2 as _)
}

type Parsed = Vec<Vec<Cell>>;

#[derive(Debug, PartialEq, Eq)]
enum Cell {
    Empty,
    Paper,
}

impl Cell {
    fn is_empty(&self) -> bool {
        self == &Cell::Empty
    }

    fn is_paper(&self) -> bool {
        self == &Cell::Paper
    }
}

fn parse(input: &mut &str) -> Result<Parsed> {
    repeat(1.., preceded(multispace0, parse_line)).parse_next(input)
}

fn parse_line(input: &mut &str) -> Result<Vec<Cell>> {
    repeat(1.., parse_cell).parse_next(input)
}

fn parse_cell(input: &mut &str) -> Result<Cell> {
    alt((".".map(|_| Cell::Empty), "@".map(|_| Cell::Paper))).parse_next(input)
}

fn part1(input: Parsed) -> usize {
    let mut input = input;
    remove_paper(&mut input)
}

fn remove_paper(input: &mut [Vec<Cell>]) -> usize {
    let mut score = 0;
    let mut access = Vec::new();
    let h = input.len();
    let w = input[0].len();
    let directions = [
        (-1, -1),
        (0, -1),
        (1, -1),
        (1, 0),
        (1, 1),
        (0, 1),
        (-1, 1),
        (-1, 0),
    ];
    for y in 0..h {
        for x in 0..w {
            match input[y][x] {
                Cell::Empty => {}
                Cell::Paper => {
                    let count = directions
                        .iter()
                        .filter(|dir| {
                            let nx = x as isize + dir.0;
                            let ny = y as isize + dir.1;
                            nx >= 0
                                && nx < w as isize
                                && ny >= 0
                                && ny < h as isize
                                && input[ny as usize][nx as usize].is_paper()
                        })
                        .count();
                    if count < 4 {
                        score += 1;
                        access.push((x, y));
                    }
                }
            }
        }
    }
    access.iter().for_each(|(x, y)| {
        input[*y][*x] = Cell::Empty;
    });
    score
}

fn part2(input: Parsed) -> usize {
    let mut input = input;
    let mut score = 0;
    loop {
        let removed = remove_paper(&mut input);
        score += removed;
        if removed == 0 {
            return score;
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::Day;

    use super::*;

    #[test]
    fn part1_test() {
        day().assert1(
            "..@@.@@@@.
@@@.@.@.@@
@@@@@.@.@@
@.@@@@..@.
@@.@@@@.@@
.@@@@@@@.@
.@.@.@.@@@
@.@@@.@@@@
.@@@@@@@@.
@.@.@@@.@.",
            "13",
        );
    }

    #[test]
    fn part1_solve() {
        day().assert1(include_str!("../input/day4.txt"), "1356");
    }

    #[test]
    fn part2_test() {
        day().assert2(
            "..@@.@@@@.
@@@.@.@.@@
@@@@@.@.@@
@.@@@@..@.
@@.@@@@.@@
.@@@@@@@.@
.@.@.@.@@@
@.@@@.@@@@
.@@@@@@@@.
@.@.@@@.@.",
            "43",
        );
    }

    #[test]
    fn part2_solve() {
        day().assert2(include_str!("../input/day4.txt"), "8713");
    }
}