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

byte selected_color = 255;

interface Device {
  nat handle;
}

plex Screen implements Device {
  nat handle;
  nat width;
  nat height;
  nat buffer_size;
  byte[] buffer;

  draw() {
    unsafe {
      write(this, this.buffer, this.buffer_size);
    }
  }
}

plex Mouse implements Device {
  nat handle;
  nat x;
  nat y;
  bool left;
  bool right;
  bool middle;
  bool btn4;
}

/**
 * Main function
 */
function main() {
    Screen screen = open("/dev/screen/0", 0);
    Mouse mouse = open("/dev/mouse/0", 0);

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

    loop {
      mouse.refresh();
	    if (not mouse.left) continue; 

	    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);
	    screen.draw();

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

/**
 * 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;

    return;
}

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

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

/**
 * Draw a rectangle
 */ 
function rectangle(Device screen, byte color, int x, int y, int width, int height) {
   // we need unsafe because we are using pointers `&` and `memset` directly
   // unsafe takes the guardrails off and allows you to access/modify memory directly
   unsafe {
    int pixel = y * width + x + &screen.buffer + 4;
    do (int i = height; i > 0; i--) {
      int row = pixel + width;
      memset(screen.buffer, row, color, width);
      pixel += width;
    }
   }
   return;
}