module env = import "../futhark_mpi/envelope"

-- type envelope_1d_t [n] = env.envelope_1d_t [n]
-- type envelope_2d_t [n][m][ty][tx] = env.envelope_2d_t [n][m][ty][tx]

entry get_envelope_1d = env.get_envelope_1d
entry get_envelope_2d = env.get_envelope_2d

let count_neighbours [n][m] (board: [n][m]i8) : [n][m]i8 =
    let north = rotate (-1) board
    let south = rotate 1 board
    let east = map(rotate 1) board
    let west = map(rotate (-1)) board

    let north_east = map(rotate 1) north
    let north_west = map(rotate (-1)) north
    let south_east = map(rotate 1) south
    let south_west = map(rotate (-1)) south

    in map3 (\(nwr,nr,ner) (wr, br, er) (swr, sr, ser) ->
        map3 (\(nw,n,ne) (w, _, e) (sw, s, se) -> nw + n + ne + w + e + sw + s + se)
        (zip3 nwr nr ner) (zip3 wr br er) (zip3 swr sr ser))
    (zip3 north_west north north_east) (zip3 west board east) (zip3 south_west south south_east)

let augment_board [n][m] (chunk_board:[n][m]i8)
                         (nw:[1][1]i8) (no:[1][m]i8) (ne:[1][1]i8)
                                 (we:[n][1]i8) (ea:[n][1]i8)
                         (sw:[1][1]i8) (so:[1][m]i8) (se:[1][1]i8) :[][]i8 =
    tabulate_2d (n+2) (m+2) (\i j ->
            -- North-West
            if (i == 0 && j == 0) then nw[0,0]
            -- North-East
            else if (i == 0 && j == m+1) then ne[0,0]
            -- South-West
            else if (i == n+1 && j == 0) then sw[0,0]
            -- South-East
            else if (i == n+1 && j == m+1) then se[0,0]
            -- North
            else if (i == 0) then no[0, j-1]
            -- West
            else if (j == 0) then we[i-1, 0]
            -- East
            else if (j == m + 1) then ea[i-1, 0]
            -- South
            else if (i == n+1) then so[0,j-1]
            else chunk_board[i-1, j-1]
        )

entry next_chunk_board [n][m] (chunk_board :[n][m]i8)
                              (nw:[1][1]i8) (no:[1][m]i8) (ne:[1][1]i8)
                                   (we:[n][1]i8) (ea:[n][1]i8)
                              (sw:[1][1]i8) (so:[1][m]i8) (se:[1][1]i8) :[n][m]i8 =
    let augmented_board = augment_board chunk_board nw no ne we ea sw so se
    let neighbours = count_neighbours augmented_board
    let next_board = map2 (\augmented_board_r neighbours_r ->
        map2(\cell nb_alive_cells ->
            if (cell == 1 && (nb_alive_cells == 2 || nb_alive_cells == 3)) || (cell == 0 && nb_alive_cells == 3)
            then 1
            else 0)
        augmented_board_r neighbours_r)
      augmented_board neighbours
    in next_board[1:n+1, 1:m+1] :> [n][m]i8