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

function main () 
  # open screen
  # use load immediate because it is a pointer to a string, not a value

  nat tmp_ptr = load_address screen_namespace
  int mode = load_immediate 0
  plex screen = open tmp_ptr, mode

  nat screen_handle = load_offset_32 screen, 4
  str tmp_str = nat_to_string screen_handle
  call pln tmp_str

  nat width = load_offset_32 screen, 8
  tmp_str = nat_to_string width
  call pln tmp_str

  nat buffer_size = load_offset_32 screen, 12
  tmp_str = nat_to_string buffer_size
  call pln tmp_str

  nat offset_temp = load_immediate 16
  nat screen_buffer = add_nat screen, offset_temp

  tmp_str = nat_to_string screen_buffer
  call pln tmp_str

  # open mouse
  tmp_ptr = load_address mouse_namespace
  plex mouse = open tmp_ptr, mode

  write screen, screen_buffer, buffer_size # redraw

  draw_loop:
    # load mouse click data
    stat mouse

    byte left_down = load_offset_8 mouse, 16 # load btn1 pressed

    jump_eq_nat draw_loop, left_down, mode # mode is 0 which is an alias for false

    nat x = load_offset_32 mouse, 8
    nat y = load_offset_32 mouse, 12

    # Compute start address: y*width + x
    nat pixel_pos = mul_nat y, width       # = y * width
    pixel_pos = add_nat x, pixel_pos # += x
    pixel_pos = add_nat screen_buffer, pixel_pos # += pixel_offset
    nat fat_ptr_size = load_immediate 4 # need to add offset for fat pointer size
    pixel_pos = add_nat pixel_pos, fat_ptr_size

    byte color = load_absolute_32 WHITE
    store_absolute_8 pixel_pos, color # draw color at screen [x,y]
    write screen, screen_buffer, buffer_size # redraw

    jump draw_loop
  exit 0

function pln (str message)
	nat term_ns = load_address terminal_namespace # get terminal device
	int mode = load_immediate 0
	plex term = open term_ns, mode
	int msg_length = strlen message
	write term, message, msg_length
	str nl = load_address new_line
	int nl_length = strlen nl
	write term, nl, nl_length
	return