.CR 6502             ; Assemble 6502
    .LI on,toff          ; Listing on, no timings included
    .TF winner.prg, BIN ; Object filename and format

paddleIndexL  = $00
paddleIndexH  = $01
paddleOriginL = $03
paddleOriginH = $04
loopCnt       = $02


jsr init
jsr loop



init:
  lda #$00
  sta paddleIndexL
  lda #$02
  sta paddleIndexH
  lda #$00
  sta paddleOriginL
  lda #$02
  sta paddleOriginH
  lda #$00
  sta loopCnt
  rts

loop:
  lda paddleOriginL  ;reset paddle draw indexs
  sta paddleIndexL   
  lda paddleOriginH 
  sta paddleIndexH   
  jsr drawPaddle
  jsr readKeys
  jmp loop


drawPaddle:
  ldy #2
  lda #3       ;set color of player 1
  sta ($00),y  ;write that bit to display

  ldy #29
  lda #4       ;set color of player 2
  sta ($00),y

  lda paddleIndexL
  adc #$20     ;incr to next pixel of paddle
  sta paddleIndexL
  lda #$00
  adc paddleIndexH
  sta paddleIndexH
  ldx loopCnt  ;makes the paddle be 5 pixels long
  inx
  stx loopCnt
  cpx #5
  bne drawPaddle
  lda #$00     ;reset counter for next time
  sta loopCnt
  rts

readKeys:
  lda $ff
  cmp #$77
  beq upKey
  cmp #$73
  beq downKey
  rts

upKey:
  clc
  lda paddleOriginL ;checks if the paddle is near the edge
  adc paddleOriginH
  cmp #$02         
  clc
  beq onEdge

;decrement paddle draw index
  clc
  lda paddleIndexL
  sbc #$1f
  sta paddleIndexL
  lda paddleIndexH
  sbc #$00
  sta paddleIndexH
  clc
;clear previous pixel
  ldy #$02
  lda #$00
  sta ($00),y

  ldy #29
  lda #$00
  sta ($00),y

;decrement paddle origin
  lda paddleOriginL
  sbc #$1f
  sta paddleOriginL
  lda paddleOriginH
  sbc #$00
  sta paddleOriginH
  clc
  lda #$00
  sta $ff
  lda $ff
  rts

downKey:
  clc
  lda $03     ;checks is paddle is at the edge of the screen
  adc $04     
  cmp #$65   
  clc
  beq onEdge
 
  clc
;clear previous pixel when its moved
  ldy #$02
  lda #$00
  sta ($03),y

  ldy #29
  lda #$00
  sta ($03),y

;change the paddle location
  lda #$20
  adc paddleOriginL
  sta paddleOriginL


  lda #$00
  adc paddleOriginH
  sta paddleOriginH

;clear the keyboard buffer
  lda #$00
  sta $ff
  lda $ff
  rts

onEdge:       ;ends the program when the paddle goes off the edge of the screen
  rts         ;the edge of the screen
 
 

gameover:
  brk