global str screen_namespace = "/dev/screen/0";
global str mouse_namespace = "/dev/mouse/0";
global str terminal_namespace = "/dev/term/0";
global str new_line = "\n";
global byte white = 255;

function main ()
  plex screen $0;
  plex mouse $1;
  str tmp_str $2;
  byte color $3;
  bool left_down $4;
  int mode $5;
  nat offset_temp $6;
  nat x $7;
  nat y $8;
  nat width $9;
  nat screen_buffer $10;
  nat buffer_size $11;
  nat pixel_pos $12;

  load_immediate screen_namespace -> screen;
  load_immediate 0 -> mode;
  syscall OPEN screen mode -> screen;

  nat_to_string screen -> tmp_str;
  call pln tmp_str -> void;

  load_offset_32 screen 8 -> width;
  nat_to_string width -> tmp_str;
  call pln tmp_str -> void;

  load_offset_32 screen 12 -> buffer_size;
  nat_to_string buffer_size -> tmp_str;
  call pln tmp_str -> void;

  load_immediate 16 -> offset_temp;
  add_nat screen offset_temp -> screen_buffer;

  nat_to_string screen_buffer -> tmp_str;
  call pln tmp_str -> void;

  // open mouse
  load_immediate mouse_namespace -> mouse;
  syscall OPEN mouse mode -> mouse;

  syscall WRITE screen screen_buffer buffer_size; // redraw

  loop draw_loop
    // load mouse click data
    syscall STAT mouse;

    load_offset_8 mouse 16 -> left_down;

    jump_eq_nat draw_loop left_down mode; // mode = 0 / false

    load_offset_32 mouse 8 -> x;
    load_offset_32 mouse 12 -> y;

    // Compute start address: y *width + x
    mul_nat y width -> pixel_pos;
    add_nat x pixel_pos -> pixel_pos;
    add_nat screen_buffer pixel_pos -> pixel_pos;
    load_immediate 4 -> fat_ptr_size;
    add_nat pixel_pos fat_ptr_size -> pixel_pos;

    load_absolute_32 white -> color;
    store_absolute_8 pixel_pos color; // draw color at screen [x,y]
    syscall WRITE screen screen_buffer buffer_size; // redraw

    jump draw_loop;
  exit 0;

function pln (str message $0) 
	str ts $1; 
	int mode $5;
	int msg_length $2; 
	str nl $3; 
	int nl_length $4;

	load_immediate terminal_namespace -> ts;
	load_immediate 0 -> mode;
	syscall OPEN ts mode -> ts;
	string_length message -> msg_length;
	syscall WRITE ts message msg_length	;
	load_immediate new_line -> nl;
	string_length nl -> nl_length;
	syscall WRITE ts nl nl_length;
	return;