define movingUp      1
define movingRight   2
define movingDown    4
define movingLeft    8
define movingUpLeft  9
define movingUpRight 3
define movingDownLeft 12
define movingDownRight 6

define AREA_MAX_X $1F
define AREA_MAX_Y $1F

define ballDirection $00

define ballX $20
define ballY $21

define ballL $10 ; screen location of the ball
define ballH $11 ; screen location of the ball

lda #$16
sta ballX
lda #$1b
sta ballY

lda #$1a ;red
sta $410

ldx #$18 ;number of blocks

lda #movingUpRight
sta ballDirection

loop:
lda #movingUp
bit ballDirection
bne up
lda #movingDown
bit ballDirection
bne down
up:
dec ballY
jmp checkLeftRight
down:
inc ballY
checkLeftRight:
lda #movingLeft
bit ballDirection
bne left
lda #movingRight
bit ballDirection
bne right
left:
dec ballX
jmp end_direction_check
right:
;tya
;pha
lda ballX
cmp #AREA_MAX_X
beq switch_to_left
inc ballX ;not a wall, move to right
jmp end_direction_check
switch_to_left:
;hit a wall - reverse direction
;brk
lda ballDirection; #$fd ; !2
and #$fd ; !2
;sta ballDirection
ora #movingLeft
sta ballDirection
jmp checkLeftRight
end_direction_check:
jsr ballCoordinatesToScreen
;draw new position
lda #3 ;different color
sta (ballL),y
dex
bne loop
brk

ballCoordinatesToScreen:
  ;ball = ballY * 32 + ballX + 0x0200
  lda #0
  sta ballH ; clear ballH as we'll be shifting later
  lda ballY
  sta ballL
  asl ballL ;*2 max 3E
  asl ballL ;*4 max 7C
  asl ballL ;*8 max F8
  asl ballL ;*16, can carry
  rol ballH ;rotate high byte left
  asl ballL; *32, can carry
  rol ballH ;rotate high byte left
  clc ;clear carry before the addition
  lda ballL ; ballL = ballL + ballX
  adc ballX
  sta ballL
  inc ballH ;increment by 2 to offset by 0x200
  inc ballH
  rts