use packed_simd::{m8x64, shuffle, u8x64};

fn shuffle_right(v: u8x64) -> u8x64 {
    shuffle!(
        v,
        [
            63, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,
            23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,
            45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62
        ]
    )
}

fn shuffle_left(v: u8x64) -> u8x64 {
    shuffle!(
        v,
        [
            1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
            25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46,
            47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 0
        ]
    )
}

fn step(src: &[u8x64; 52], dst: &mut [u8x64; 52]) {
    let mask = m8x64::new(
        false, true, true, true, true, true, true, true, true, true, true, true, true, true, true,
        true, true, true, true, true, true, true, true, true, true, true, true, true, true, true,
        true, true, true, true, true, true, true, true, true, true, true, true, true, true, true,
        true, true, true, true, true, true, false, false, false, false, false, false, false, false,
        false, false, false, false, false,
    );
    let open = u8x64::splat(0);
    let tree = u8x64::splat(1);
    let lumber = u8x64::splat(2);

    for (dst, src) in dst[1..51].iter_mut().zip(src.windows(3)) {
        let t = src[0];
        let c = src[1];
        let b = src[2];

        let tl = shuffle_left(t);
        let tr = shuffle_right(t);
        let l = shuffle_left(c);
        let r = shuffle_right(c);
        let bl = shuffle_left(b);
        let br = shuffle_right(b);

        let tree_tl = tl & tree;
        let tree_tr = tr & tree;
        let tree_l = l & tree;
        let tree_r = r & tree;
        let tree_bl = bl & tree;
        let tree_br = br & tree;
        let tree_t = t & tree;
        let tree_b = b & tree;

        let tree_counts = tree_tl + tree_tr + tree_l + tree_r + tree_bl + tree_br + tree_t + tree_b;
        let new_open = tree_counts.ge(u8x64::splat(3)).select(tree, open);

        let lumber_tl = tl & lumber;
        let lumber_tr = tr & lumber;
        let lumber_l = l & lumber;
        let lumber_r = r & lumber;
        let lumber_bl = bl & lumber;
        let lumber_br = br & lumber;
        let lumber_t = t & lumber;
        let lumber_b = b & lumber;

        let lumber_counts_times_two = lumber_tl
            + lumber_tr
            + lumber_l
            + lumber_r
            + lumber_bl
            + lumber_br
            + lumber_t
            + lumber_b;

        let new_tree = lumber_counts_times_two
            .ge(u8x64::splat(6))
            .select(lumber, tree);

        let new_lumber = (tree_counts.ge(u8x64::splat(1))
            | lumber_counts_times_two.ge(u8x64::splat(2)))
        .select(lumber, open);

        let is_lumber = c.eq(lumber);
        let is_tree = c.eq(tree);

        let new_cells = is_tree.select(new_tree, is_lumber.select(new_lumber, new_open));

        *dst = mask.select(new_cells, u8x64::splat(0));
    }
}