.include "defs.s"

                DIRECTION = $2000

                .segment "VECTORS"

                .word nmi
                .word reset
                .word irq

                .code

reset:          jmp main
nmi:            rti
irq:            rti

main:           lda IO_MODEFLAG_VTERM
                sta IO_MODEFLAGS

                lda #(IO_PAINT_RED | IO_PAINT_BOLD)
                sta IO_PAINT

                lda #0
                sta DIRECTION

                ldx #0

loop:           jsr blank
                jsr draw
                jsr move
                jsr check
                jsr delay
                jmp loop

blank:          lda #' '
                ldy #39
:               sta IO_VTERM_START,y
                dey
                bmi :+
                jmp :-
:               rts

draw:           lda #'+'
                sta IO_VTERM_START,x
                rts

move:           lda DIRECTION
                cmp #0
                beq :+
                dex
                rts
:               inx
                rts

check:          txa
                cpx #0
                beq :+
                cpx #39
                bne :++
                lda #1
                sta DIRECTION
                rts
:               lda #0
                sta DIRECTION
:               rts

delay:          lda #$30
:               cmp #0
                beq :+++
                ldy #$FF
:               cpy #0
                beq :+
                nop
                nop
                nop
                nop
                nop
                dey
                jmp :-
:               sbc #1
                jmp :---
:               rts