((code
  (label main
    ; Open screen
    ; use load immediate because it is a pointer to a string, not a value
    (load-immediate $0 &screen-namespace)
    (load-immediate $11 0)
    (syscall OPEN $0 $18 $11) ; open(out Plex screen, in namespace, in flags)

    (load-offset-32 $20 $0 8) ; load width
    (load-offset-32 $22 $0 12) ; load size
    (load-immediate $1 16) ; offset for screen buffer
    (add-nat $21 $0 $1)

    ; open mouse
    (load-immediate $16 &mouse-namespace)
    (syscall OPEN $15 $16 $11) ; open(out Plex mouse, in namespace, in flags)

    ; outline_swatch(screen, BLACK, 1, 1);
    (load-absolute-32 $1 &BLACK)
    (load-immediate $12 1)
    (load-immediate $13 1)
    (call &draw-outlined-swatch ($21 $1 $12 $13 $20) nil)

    ; outline_swatch(screen, WHITE, 1, 1);
    (load-absolute-32 $1 &WHITE)
    (load-immediate $12 21)
    (load-immediate $13 1)
    (call &draw-outlined-swatch ($21 $1 $12 $13 $20) nil) 
    
    ; screen.draw();
    (syscall WRITE $0 $21 $22)

    (label draw-loop
      ; load mouse click data
      (syscall REFRESH $15)
      (load-offset-8 $9 $15 16) ; load btn1 pressed

      (jump-eq-nat &draw-loop $9 $11)

      (load-offset-32 $7 $15 8)  ; load x
      (load-offset-32 $8 $15 12) ; load y

      (load-immediate $14 20) ; box size

      ; first row
      (load-absolute-32 $1 &BLACK)
      (load-immediate $12 1)
      (load-immediate $13 1)
      (call &draw-outlined-swatch ($21 $1 $12 $13 $20) nil) 
      
      (call &set-color-if-clicked ($7 $8 $12 $13 $1 $14) nil)

      (load-absolute-32 $1 &WHITE)
      (load-immediate $12 21)
      (load-immediate $13 1)
      (call &draw-outlined-swatch ($21 $1 $12 $13 $20) nil) 

      (call &set-color-if-clicked ($7 $8 $12 $13 $1 $14) nil)

      (syscall WRITE $0 $21 $22)

      (load-absolute-32 $22 &SELECTED-COLOR) ; color
      (load-immediate $1 5) ; size of brush

      (call &draw-box ($21 $20 $22 $7 $8 $1 $1) nil)

      (jump &draw-loop))

    ; Flush and halt
    (halt 0))

  (label set-color-if-clicked 
    ; (click_x, click_y, box_x, box_y, color, box_size)

    ; Compute right = box_x + box_size
    (add-int $6 $2 $5)    ; $6 = right edge
    
    ; Compute bottom = box_y + box_size  
    (add-int $7 $3 $5)    ; $7 = bottom edge

    ; Bounds check: x in [box_x, right] and y in [box_y, bottom]
    (jump-lt-int &fail $0 $2)
    (jump-gt-int &fail $0 $6)
    (jump-lt-int &fail $1 $3)
    (jump-gt-int &fail $1 $7)

    (load-immediate $10 &SELECTED-COLOR)
    (store-absolute-8 $10 $4)

    (label fail)
    (return nil))

  (label draw-outlined-swatch
    ; (base, color, x, y, width)

    ; Constants
    (load-absolute-32 $5 &GRAY)
    (load-absolute-32 $10 &SELECTED-COLOR)
    (jump-eq-int &set-selected $10 $1)
    (jump-eq-int &end-set-selected $5 $5)
    (label set-selected)
    (load-absolute-32 $5 &DARK-GRAY)
    (label end-set-selected)

    (load-immediate $6 20)       ; outline size
    (load-immediate $7 17)       ; fill size
    (load-immediate $8 2)        ; offset

    (call &draw-box ($0 $4 $5 $2 $3 $6 $6) nil)

    (add-int $9 $2 $8)    ; x + 2
    (add-int $10 $3 $8)   ; y + 2

    (call &draw-box ($0 $4 $1 $9 $10 $7 $7) nil)

    (return nil))

  (label draw-box
    ; (base, screen_width, color, x_start, y_start, width, height)

    ; Compute start address: base + y*640 + x
    (mul-int $15 $4 $1)        ; $15 = y * 640
    (add-int $15 $15 $3)       ; $15 += x
    (add-nat $15 $0 $15)       ; $15 = base + pixel_offset
    (load-immediate $25 4)
    (add-nat $15 $15 $25)      ; need to add offset for fat pointer size

    ; Outer loop: height times
    (load-immediate $30 1)     ; increment

    (label draw-box-outer
      (add-int $27 $15 $5)     ; $27 = row end = current + width
      (register-move $29 $15)   ; $7 = pixel pointer
      (memset-8 $29 $2 $5)      ; draw row
      (add-int $15 $15 $1)     ; next row (+= 640)
      (sub-int $6 $6 $30)    ; decrement row count
      (jump-gt-int &draw-box-outer $6 0))
    (return nil)))
(data
	(label screen-namespace "/dev/screen/0")
  (label mouse-namespace "/dev/mouse/0")
  (label SELECTED-COLOR 255)
	(label BLACK 0)
	(label WHITE 255)
	(label DARK-GRAY 73)
	(label GRAY 146)
	(label LIGHT-GRAY 182)))