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
  ptr screen;
  str screen_name;
  int mode;
  nat screen_buffer;

  // use load immediate because it a pointer to a string, not a value
  load_address screen_namespace -> screen_name;
  load_immediate 0 -> mode;
  syscall OPEN screen_name mode screen; // Screen screen = open("/dev/screen/0", 0);

  nat width;
  nat size;
  load_offset_32 screen 8 -> width; // load width
  load_offset_32 screen 12 -> size; // load size

  nat offset;
  load_immediate 16 -> offset; // offset for screen buffer
  add_nat screen offset -> screen_buffer;

  // open mouse
  ptr mouse;
  str mouse_name;
  load_address mouse_namespace -> mouse_name;
  syscall OPEN mouse_name mode mouse; // Mouse mouse = open("/dev/mouse/0", 0);

  byte color;
  nat x_pos;
  nat y_pos;

  load_absolute_8 BLACK -> color;
  load_immediate 1 -> x_pos;
  load_immediate 1 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 WHITE -> color;
  load_immediate 21 -> x_pos;
  load_immediate 1 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 CHARCOAL -> color;
  load_immediate 1 -> x_pos;
  load_immediate 21 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 DARK_GRAY -> color;
  load_immediate 21 -> x_pos;
  load_immediate 21 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 RED -> color;
  load_immediate 1 -> x_pos;
  load_immediate 41 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 ORANGE -> color;
  load_immediate 21 -> x_pos;
  load_immediate 41 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 YELLOW -> color;
  load_immediate 1 -> x_pos;
  load_immediate 61 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 GREEN -> color;
  load_immediate 21 -> x_pos;
  load_immediate 61 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 BLUE -> color;
  load_immediate 1 -> x_pos;
  load_immediate 81 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);

  load_absolute_8 PURPLE -> color;
  load_immediate 21 -> x_pos;
  load_immediate 81 -> y_pos;
  call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
  
  // screen.draw
  syscall WRITE screen screen_buffer size;

  nat zero;
  load_immediate 0 -> zero;

  loop draw_loop {
    // load mouse click data
    syscall REFRESH mouse;

    byte left_down;
    load_offset_8 mouse 16 -> left_down; // load btn1 pressed

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

    nat mouse_x;
    nat mouse_y;
    load_offset_32 mouse 8 -> mouse_x; // load x
    load_offset_32 mouse 12 -> mouse_y; // load y

    nat box_size;
    load_immediate 20 -> box_size;

    // first row
    load_absolute_8 BLACK -> color;
    load_immediate 1 -> x_pos;
    load_immediate 1 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 WHITE -> color;
    load_immediate 21 -> x_pos;
    load_immediate 1 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 CHARCOAL -> color;
    load_immediate 1 -> x_pos;
    load_immediate 21 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 DARK_GRAY -> color;
    load_immediate 21 -> x_pos;
    load_immediate 21 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 RED -> color;
    load_immediate 1 -> x_pos;
    load_immediate 41 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 ORANGE -> color;
    load_immediate 21 -> x_pos;
    load_immediate 41 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 YELLOW -> color;
    load_immediate 1 -> x_pos;
    load_immediate 61 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 GREEN -> color;
    load_immediate 21 -> x_pos;
    load_immediate 61 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 BLUE -> color;
    load_immediate 1 -> x_pos;
    load_immediate 81 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    load_absolute_8 PURPLE -> color;
    load_immediate 21 -> x_pos;
    load_immediate 81 -> y_pos;
    call draw_outlined_swatch (screen_buffer color x_pos y_pos width);
    call set_color_if_clicked (mouse_x mouse_y x_pos y_pos color box_size);

    syscall WRITE screen screen_buffer size;

    byte selected_color;
    load_absolute_8 SELECTED_COLOR -> selected_color;

    nat brush_size;
    load_immediate 5 -> brush_size;

    call 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;
  add_int box_x size -> right_edge;
  
  // Compute bottom = box_y + size  
  int bottom_edge;
  add_int box_y size -> bottom_edge;

  // 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;

  store_absolute_8 check_color -> SELECTED_COLOR;

  else fail
    return;
}

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

  // Constants
  nat background_color;
  load_absolute_8 GRAY -> background_color;
  
  byte selected_color;
  load_absolute_8 SELECTED_COLOR -> selected_color;

  jump_eq_int set_selected color selected_color;
  jump end_set_selected;
  do set_selected
    load_absolute_8 DARK_GRAY -> background_color;
  else end_set_selected

  nat outline_size;
  load_immediate 20 -> outline_size;

  nat fill_size;
  load_immediate 17 -> fill_size;

  nat offset;
  load_immediate 2 -> offset;

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

  int x_off;
  int y_off;
  add_int x offset -> x_off;   // x + 2
  add_int y offset -> y_off;   // y + 2

  call 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;
  load_immediate 4 -> fat_ptr_size;

  nat offset;
  mul_nat y_start screen_width -> offset;
  add_nat offset x_start -> offset;
  add_nat offset db_base -> offset;  
  add_nat offset fat_ptr_size -> offset;      // need to add offset for fat pointer size

  int i;
  load_immediate 1 -> i;

  int zero;
  load_immediate 0 -> zero;

  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;
}