const XMAS: &str = "XMAS";
const MAS: &str = "MAS";

type Matrix = Vec<Vec<char>>;
type Position = (usize, usize);
type RowXmas = [Position; XMAS.len()];
type RowMas = [Position; MAS.len()];

fn check_xmas<'a, I>(m: &Matrix, it: I) -> bool
where
    I: Iterator<Item = &'a Position>,
{
    for (c, (i, j)) in XMAS.chars().zip(it) {
        if m[*i][*j] != c {
            return false;
        }
    }

    true
}

fn offplus(x: usize, y: isize) -> usize {
    (x as isize + y) as usize
}

fn rows_latdiag_from(p: Position, max_x: usize, max_y: usize) -> Vec<RowXmas> {
    let mut rs: Vec<RowXmas> = vec![];

    // Horizontal / vertical / diagonal
    for (p0, (di, dj)) in [
        (p, (0, 1)),                                   // horizontal, left-to-right
        (p, (1, 0)),                                   // vertical, top-down
        (p, (1, 1)),                                   // diag from p, top-down and left-to-right
        ((p.0, p.1 + XMAS.len() - 1), (1, -1isize)), // the other diag, top-down and right-to-left
    ] {
        // Bounds check
        let max_off = XMAS.len();
        if p0.0 + di * max_off > max_x
            || (dj > 0 && offplus(p0.1, dj * max_off as isize) > max_y)
            || p0.1 >= max_y
        {
            continue;
        }

        let mut p_acc = p0;
        let mut ps = [(0, 0); XMAS.len()];
        for idx in 0..ps.len() {
            ps[idx].0 = p_acc.0;
            ps[idx].1 = p_acc.1;
            p_acc = (p_acc.0 + di, offplus(p_acc.1, dj));
        }
        rs.push(ps);
    }

    rs
}

pub fn p1(input: &str) -> String {
    let m: Matrix = input.lines().map(|row| row.chars().collect()).collect();
    let mut result = 0;

    for i in 0..m.len() {
        for j in 0..m[i].len() {
            let p = (i, j);
            for row in rows_latdiag_from(p, m.len(), m[i].len()) {
                if check_xmas(&m, row.iter()) || check_xmas(&m, row.iter().rev()) {
                    result += 1;
                }
            }
        }
    }

    result.to_string()
}

fn check_mas<'a, I>(m: &Matrix, it: I) -> bool
where
    I: Iterator<Item = &'a Position>,
{
    for (c, (i, j)) in MAS.chars().zip(it) {
        if m[*i][*j] != c {
            return false;
        }
    }

    true
}

fn rows_diag_from(p: Position, max_x: usize, max_y: usize) -> Vec<RowMas> {
    let mut rs: Vec<RowMas> = vec![];

    // Horizontal / vertical / diagonal
    for (p0, (di, dj)) in [
        (p, (1, 1)),                                   // diag from p, top-down and left-to-right
        ((p.0, p.1 + MAS.len() - 1), (1, -1isize)), // the other diag, top-down and right-to-left
    ] {
        // Bounds check
        let max_off = MAS.len();
        if p0.0 + di * max_off > max_x
            || (dj > 0 && offplus(p0.1, dj * max_off as isize) > max_y)
            || p0.1 >= max_y
        {
            continue;
        }

        let mut p_acc = p0;
        let mut ps = [(0, 0); MAS.len()];
        for idx in 0..ps.len() {
            ps[idx].0 = p_acc.0;
            ps[idx].1 = p_acc.1;
            p_acc = (p_acc.0 + di, offplus(p_acc.1, dj));
        }
        rs.push(ps);
    }

    rs
}

pub fn p2(input: &str) -> String {
    let m: Matrix = input.lines().map(|row| row.chars().collect()).collect();
    let mut result = 0;

    for i in 0..=m.len() - MAS.len() {
        for j in 0..=m[i].len() - MAS.len() {
            let p = (i, j);
            let rows = rows_diag_from(p, m.len(), m[i].len());
            if rows.iter().all(|r| check_mas(&m, r.iter()) || check_mas(&m, r.iter().rev())) {
                result += 1;
            }
        }
    }

    result.to_string()
}