export type world = struct {
	dead: uint,
	alive: uint,
	rows: uint,
	cols: uint,
	cells: *[*]uint,
};

fn cb(r: uint, c: uint) void;

fn cell(w: *world, r: uint, c: uint) *uint = &w.cells[(r * w.rows) + c];

fn isalive(w: *world, r: uint, c: uint) bool = *cell(w, r, c) == w.alive;

fn next(i: uint, n: uint) uint = (i + 1) & (n - 1);

fn prev(i: uint, n: uint) uint = (i - 1) & (n - 1);

fn live_neighbors(w: *world, r: uint, c: uint) uint = {
	const nc = next(c, w.cols);
	const pc = prev(c, w.cols);
	const nr = next(r, w.rows);
	const pr = prev(r, w.rows);
	let n = 0u;

	if (isalive(w, pr, pc)) n += 1;
	if (isalive(w, pr, c)) n += 1;
	if (isalive(w, pr, nc)) n += 1;
	if (isalive(w, r, pc)) n += 1;
	if (isalive(w, r, nc)) n += 1;
	if (isalive(w, nr, pc)) n += 1;
	if (isalive(w, nr, c)) n += 1;
	if (isalive(w, nr, nc)) n += 1;

	return n;
};

fn live(w: *world, r: uint, c: uint) bool = {
	const ln = live_neighbors(w, r, c);

	return ln == 3 || (ln == 2 && isalive(w, r, c));
};

export fn mutate(w: *world) void = {
	for (let r = 0u; r < w.rows; r += 1)
		for (let c = 0u; c < w.cols; c += 1)
			*cell(w, r, c) = if (live(w, r, c)) {
				yield w.alive;
			} else {
				yield w.dead;
			};
};