/**
 * 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[] screen_buffer;

  init() {
    this.handle = open("/dev/screen/0", 0); 
  }
}

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

  init() {
    this.handle = open("/dev/mouse/0", 0); 
  }
}

/**
 * Main function
 */
function main() {
    Screen screen();
    Mouse mouse();

    outline_swatch(screen, BLACK, 1, 1, 8);
    outline_swatch(screen, WHITE, 21, 1, 8);
    screen.draw();

    loop {
	    mouse.read();
	    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();

	    draw_box(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 mouse_x, int mouse_y, int box_x, int box_y, nat color, nat box_size) {
    int right = box_x + box_size;
    int bottom = box_y + box_size;

    if (mouse_x < box_x) return;
    if (mouse_x > right) return;
    if (mouse_y < box_y) return;
    if (mouse_y > bottom) return;

    selected_color = color;
}

/**
 * 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;
    }

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

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