str screen_namespace = "/dev/screen/0";
str mouse_namespace = "/dev/mouse/0";
byte BLACK = 0;
byte WHITE = 255;
byte DARK_GRAY = 73;
byte GRAY = 146;
byte LIGHT_GRAY = 182;
byte CHARCOAL = 36;
byte DARK_RED = 128;
byte RED = 224;
byte DARK_YELLOW = 144;
byte YELLOW = 252;
byte DARK_TEAL = 9;
byte TEAL = 18;
byte DARK_GREEN = 12;
byte GREEN = 16;
byte LIME = 28;
byte LIGHT_CYAN = 159;
byte NAVY = 2;
byte BLUE = 3;
byte DEEP_SKY_BLUE = 10;
byte LIGHT_BLUE = 19;
byte PURPLE = 131;
byte LIGHT_PURPLE = 147;
byte DARK_MAGENTA = 130;
byte MAGENTA = 227;
byte PLUM = 129;
byte PINK = 226;
byte SADDLE_BROWN = 72;
byte PERU = 141;
byte SIENNA = 136;
byte ORANGE = 241;
byte DARK_ORANGE = 208;
byte GOLD = 244;
byte SELECTED_COLOR = 255;

function main () {
  // Open screen
  int mode = 0;
  ptr screen = open(screen_namespace, mode);

  nat width = &screen + 8;
  nat size = &screen + 12;
  nat screen_buffer = &screen + 16;

  // open mouse
  ptr mouse = open(mouse_namespace, mode); // Mouse mouse = open("/dev/mouse/0", 0);

  byte color;
  nat x_pos;
  nat y_pos;

  color = BLACK;
  x_pos = 1;
  y_pos = 1;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = WHITE;
  x_pos = 21;
  y_pos = 1;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = CHARCOAL;
  x_pos = 1;
  y_pos = 21;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = DARK_GRAY;
  x_pos = 21;
  y_pos = 21;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = RED;
  x_pos = 1;
  y_pos = 41;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = ORANGE;
  x_pos = 21;
  y_pos = 41;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = YELLOW;
  x_pos = 1;
  y_pos = 61;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = GREEN;
  x_pos = 21;
  y_pos = 61;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = BLUE;
  x_pos = 1;
  y_pos = 81;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);

  color = PURPLE;
  x_pos = 21;
  y_pos = 81;
  draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
  
  // screen.draw
  write(screen, screen_buffer, size);

  nat zero = 0;

  loop draw_loop {
    // load mouse click data
    stat(mouse);

    byte left_down = &mouse + 16; // load btn1 pressed

    jump_eq_nat(draw_loop, left_down, zero); // if (!btn1.left) continue;

    nat mouse_x = &mouse + 8; // load x
    nat mouse_y = &mouse + 12; // load y

    nat box_size = 20;

    // first row
    color = BLACK;
    x_pos = 1;
    y_pos = 1;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = WHITE;
    x_pos = 21;
    y_pos = 1;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = CHARCOAL;
    x_pos = 1;
    y_pos = 21;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = DARK_GRAY;
    x_pos = 21;
    y_pos = 21;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = RED;
    x_pos = 1;
    y_pos = 41;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = ORANGE;
    x_pos = 21;
    y_pos = 41;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = YELLOW;
    x_pos = 1;
    y_pos = 61;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = GREEN;
    x_pos = 21;
    y_pos = 61;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = BLUE;
    x_pos = 1;
    y_pos = 81;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    color = PURPLE;
    x_pos = 21;
    y_pos = 81;
    draw_outlined_swatch (screen_buffer, color, x_pos, y_pos, width);
    set_color_if_clicked (mouse_x, mouse_y, x_pos, y_pos, color, box_size);

    write(screen, screen_buffer, size);

    byte selected_color = SELECTED_COLOR;
    nat brush_size = 5;

    draw_box(screen_buffer, width, selected_color, mouse_x, mouse_y, brush_size, brush_size);

    jump draw_loop;
  }

  // Flush and exit
  exit 0;
}

function set_color_if_clicked (int click_x, int click_y, int box_x, int box_y, byte check_color, int size) {

  // Compute right
  int right_edge = box_x + size;
  
  // Compute bottom = box_y + size  
  int bottom_edge = box_y + size;

  // Bounds check: x in [box_x, right] and y in [box_y, bottom]
  jump_lt_int(fail, click_x, box_x);
  jump_gt_int(fail, click_x, right_edge);
  jump_lt_int(fail, click_y, box_y);
  jump_gt_int(fail, click_y, bottom_edge);

  SELECTED_COLOR = check_color;

  else fail
    return;
}

function draw_outlined_swatch(nat base, byte color, int x, int y, int width) {

  // Constants
  const byte selected_color = SELECTED_COLOR;  
  byte background_color = GRAY;

  jump_eq_int set_selected color selected_color;
  jump end_set_selected;
  do set_selected
    background_color = DARK_GRAY;
  else end_set_selected

  const nat outline_size = 20;
  const nat fill_size = 17;

  draw_box(base, width, background_color, x, y, outline_size, outline_size);

  const nat offset = 2;
  int x_off = x + offset;
  int y_off = y + offset;

  draw_box(base, width, color, x_off, y_off, fill_size, fill_size);

  return;
}

function draw_box (nat db_base, nat screen_width, 
  byte box_color, nat x_start, nat y_start,
  nat db_width, nat height) {

  // Compute start address: base + y*640 + x
  nat fat_ptr_size = 4;

  nat offset = y_start * screen_width;
  offset = offset + x_start;
  offset = offset + db_base;  
  offset = offset + fat_ptr_size;      // need to add offset for fat pointer size

  int i = 0;
  const int zero = 0;

  loop draw_box_outer {
    memset_8 box_color db_width -> offset;  // draw row
    add_int offset screen_width -> offset;  // next row += 640
    sub_int height i -> height;             // decrement row count
    jump_gt_int draw_box_outer height zero;
  }
  return;
}