/**
 * Constants
 */
const byte BLACK = 0;
const byte WHITE = 255;
const byte DARK_GRAY = 73;
const byte GRAY = 146;

byte selected_color = 255;

plex System {
  ref function vector;
  byte wst;
  byte rst;
  u32 pad;
  nat r;
  nat g;
  nat b;
  byte debug;
  byte halt;
}

plex Screen {
  ref function vector;
  nat width;
  nat height;
  nat auto;
  nat x;
  nat y;
  nat addr;
  byte pixel;
  byte sprite;
}

plex Mouse {
  ref function vector;
  nat x;
  nat y;
  nat state;
  nat z;
  nat scrollx;
  nat scrolly;
  nat unused_;
}

System system = mmap(0x00, System);
Screen screen = mmap(0x20, Screen);
screen.vector = ref render_screen;
Mouse mouse = mmap(0x90, Mouse);
mouse.vector = ref render_screen;
halt;

function on_mouse_down() {
  int box_size = 20;
  int x = 1;
  int y = 1;
  byte color = BLACK;
  outlined_swatch(screen, color, x, y);
  set_color(box_size, x, y, mouse.x, mouse.y, color);
  
  color = WHITE;
  x = 21;
  outlined_swatch(screen, color, x, y);
  set_color(box_size, x, y, mouse.x, mouse.y, color);
  
  rectangle(screen, selected_color, x, y, 5, 5);
}

function render_screen() {
  outline_swatch(screen, BLACK, 1, 1);
  outline_swatch(screen, WHITE, 21, 1);
}

/**
 * Checks if the click is within the bound and update the selected color if so.
 */
function set_color(int box_size, int bx, int by, int mx, int my, byte color) {
    int right = bx + box_size;
    int bottom = by + box_size;

    if (mx < bx) return;
    if (mx > right) return;
    if (my < by) return;
    if (my > bottom) return;

    selected_color = color;
}

/**
 * Draw a color box with a grey outline, if selected use a darker color
 */
function outline_swatch(byte color, int x, int y) {
    byte bg_color = GRAY;
    if (selected_color == color) {
	    bg_color = DARK_GRAY;
    }

    rectangle(bg_color, x, y, 20, 20);
    rectangle(color, x + 2, y + 2, 17, 17);
}

/**
 * Draw a rectangle
 */ 
function rectangle(byte color, int x, int y, int width, int height) {
  int base = y * screen.width + x;

  for (int i = height; i > 0; i--) {
    int row = base + width;
    for (int j = width; j < row; j++) {
       screen.x = i;
       screen.y = j;
       screen.pixel = color;
    }
    base += screen.width;
  }
}