str screen_namespace = "/dev/screen/0";
str mouse_namespace = "/dev/mouse/0";
byte selected_color = 255;

const byte BLACK = 0;
const byte WHITE = 255;
const byte DARK_GRAY = 73;
const byte GRAY = 146;
const byte LIGHT_GRAY = 182;

function main() {
    Device screen(screen_namespace);
    screen.open(0);

    Device mouse(mouse_namespace);
    mouse.open(0);

    outline_swatch(screen, BLACK, 1, 1);
    outline_swatch(screen, WHITE, 21, 1);
    screen.draw();

    while (true) {
        mouse.read();
        if (mouse.btn1) {
            int box_size = 20;
            int x = 1;
            int y = 1;
            byte color = BLACK;
            outlined_swatch(screen, color, x, y);
            set_color_if_clicked(box_size, x, y, mouse.x, mouse.y, color, mouse.btn1);

            color = WHITE;
            x = 21;
            outlined_swatch(screen, color, x, y);
            set_color_if_clicked(box_size, x, y, mouse.x, mouse.y, color, mouse.btn1);
            screen.draw();

            box(screen, selected_color, x, y, 5, 5);
        }
    }
    exit(0);
}

function set_color_if_clicked(int box_size, int bx, int by, int mx, int my, byte color, bool btn1_down) {
    int right = bx + box_size;
    int bottom = by + box_size;

    if (mx < mx) return;
    if (mx > right) return;
    if (my < by) return;
    if (my > bottom) return;
    if (not btn1_down) return;

    selected_color = color;

    return;
}

function outline_swatch(ref Device screen, byte color, int x, int y) {
    byte bg_color = GRAY;
    if (selected_color == color) {
        bg_color = DARK_GRAY;
    }

    box(screen, bg_color, x, y, 20, 20);
    box(screen, color, x + 2, y + 2, 17, 17);
    return;
}

function box(ref Device screen, byte color, int x, int y, int width, int height) {
   int pixel = y * width + x + &screen.buffer + 4;
   do (int i = height, i > 0, i--) {
     int row = pixel + width;
     screen.set(row, color, width);
     pixel += width;
   }
   return;
}