use sdl2;


// 2d position, x and y
type pos = (int, int);

type drawing_state = struct {
	// is the mouse button held down?
	drawing: bool,
	pos: pos,
	picture: picture,
};

type picture = struct {
	d: *[*]u32,
	w: size,
	h: size,
};
// Returns array index of the pixel at position pos.
// Bounds check happens in here instead of using a slice type, so
// that it's easier to remove later.
fn pidx(pic: *picture, pos: pos) size = {
	const (x,y) = pos;
	const (xs,ys) = (x:size, y:size);
	assert(0 <= x, "x position must not be less than 0");
	assert(0 <= y, "y position must not be less than 0");
	assert(xs < pic.w, "x position must be less than picture width");
	assert(ys < pic.h, "y position must be less than picture height");

	return xs + pic.w*ys;
};
fn pic_set(pic: *picture, pos: pos, val: u32) void = pic.d[pidx(pic,pos)] = val;
fn picture_from_surface(surf: *sdl2::SDL_Surface) picture = picture {
	w = surf.w: size,
	h = surf.h: size,
	d = (surf.pixels as *opaque: *[*]u32),
};

fn min(a: int, b: int) int = if (a<b) a else b;
fn max(a: int, b: int) int = if (a<b) b else a;

fn circle(dstate: *drawing_state, c: pos, r: int, color: u32) void = {
	const (cx,cy) = c;
	const ymin = max(0, cy-r);
	const ymax = min(dstate.picture.h:int-1, cy+r);
	const xmin = max(0, cx-r);
	const xmax = min(dstate.picture.w:int-1, cx+r);

	const r2 = r*r + r;

	for (let y = ymin; y<=ymax; y+=1) {
		const yd = y-cy;
		for (let x = xmin; x<=xmax; x+=1) {
			const xd = x-cx;
			if (yd*yd + xd*xd <= r2) {
				pic_set(&dstate.picture, (x,y), color);
			};
		};
	};

};

fn do_drawing(dstate: *drawing_state) void = {
	if (dstate.drawing) circle(dstate, dstate.pos, 20, 0xff0088);
};