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

  load_address &screen_namespace -> tmp_str
  load_immediate 0 -> mode
  syscall OPEN tmp_str mode -> screen # openout Plex screen, in namespace, in flags

  nat_to_string screen -> tmp_str
  call &pln tmp_str

  load_offset_32 screen 8 -> width # load width
  nat_to_string width -> tmp_str
  call &pln tmp_str

  load_offset_32 screen 12 -> buffer_size # load size   
  nat_to_string buffer_size -> tmp_str
  call &pln tmp_str

  load_immediate 16 -> offset_temp # offset for screen buffer
  add_nat screen offset_temp -> screen_buffer

  nat_to_string screen_buffer -> tmp_str
  call &pln tmp_str

  # open mouse
  load_address &mouse_namespace -> tmp_str
  syscall OPEN tmp_str mode -> mouse # openout Plex mouse, in namespace, in flags

  syscall WRITE screen screen_buffer buffer_size # redraw

  draw_loop:
    # load mouse click data
    syscall STAT mouse

    load_offset_8 mouse 16 -> left_down # load btn1 pressed

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

    load_offset_32 mouse 8 -> x   # load x
    load_offset_32 mouse 12 -> y # load y

    # Compute start address: y*width + x
    mul_nat y width -> pixel_pos       # = y * width
    add_nat x pixel_pos -> pixel_pos # += x
    add_nat screen_buffer pixel_pos -> pixel_pos # += pixel_offset
    load_immediate 4 -> fat_ptr_size # need to add offset for fat pointer 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 is $0) 
	str term is $1 
	int msg_length is $2 
	str nl is $3 
	int nl_length is $4
	int mode is $5

	load_address &terminal_namespace -> term # get terminal device
	load_immediate 0 -> mode
	syscall OPEN term mode -> term
	strlen message -> msg_length
	syscall WRITE term message msg_length	
	load_address &new_line -> nl
	strlen nl -> nl_length
	syscall WRITE term nl nl_length
	return