use itertools::Itertools;

fn neighbors(grid: &Vec<Vec<char>>, position: (isize, isize)) -> i32 {
    let width = grid[0].len() as isize;
    let height = grid.len() as isize;
    let mut num_tp = 0;
    for y_offset in -1..=1 {
        for x_offset in -1..=1 {
            let search_position = (position.0 + x_offset, position.1 + y_offset);
            if search_position == position
                || search_position.0 < 0
                || search_position.0 >= width
                || search_position.1 < 0
                || search_position.1 >= height
            {
                continue;
            }
            let cell = grid[search_position.1 as usize][search_position.0 as usize];
            if cell == '@' {
                num_tp += 1;
            }
        }
    }
    num_tp
}

pub fn process_part1(input: &str) -> i32 {
    let grid = input
        .lines()
        .map(|line| line.chars().collect_vec())
        .collect_vec();
    let width = grid[0].len() as isize;
    let height = grid.len() as isize;
    let mut accessible_tp = 0;
    for y in 0..height {
        for x in 0..width {
            if grid[y as usize][x as usize] != '@' {
                continue;
            }
            let neighbors = neighbors(&grid, (x, y));
            if neighbors < 4 {
                accessible_tp += 1;
            }
        }
    }
    accessible_tp
}

pub fn process_part2(input: &str) -> i32 {
    let mut grid = input
        .lines()
        .map(|line| line.chars().collect_vec())
        .collect_vec();
    let width = grid[0].len() as isize;
    let height = grid.len() as isize;
    let mut accessible_tp_total = 0;
    loop {
        let mut accessible_tp = 0;
        let mut new_grid = grid.clone();
        for y in 0..height {
            for x in 0..width {
                if grid[y as usize][x as usize] != '@' {
                    continue;
                }
                let neighbors = neighbors(&grid, (x, y));
                if neighbors < 4 {
                    accessible_tp += 1;
                    new_grid[y as usize][x as usize] = '.';
                } else {
                    new_grid[y as usize][x as usize] = '@';
                }
            }
        }
        if accessible_tp == 0 {
            break;
        }
        grid = new_grid;
        accessible_tp_total += accessible_tp;
    }
    accessible_tp_total
}

#[cfg(test)]
mod tests {
    use super::*;

    const INPUT: &str = "..@@.@@@@.
@@@.@.@.@@
@@@@@.@.@@
@.@@@@..@.
@@.@@@@.@@
.@@@@@@@.@
.@.@.@.@@@
@.@@@.@@@@
.@@@@@@@@.
@.@.@@@.@.";

    #[test]
    fn part1() {
        let result = process_part1(INPUT);
        assert_eq!(result, 13);
    }

    #[test]
    fn part2() {
        let result = process_part2(INPUT);
        assert_eq!(result, 43);
    }
}