!animation_states = 3


!ticks_next_bar = $0F00
!curr_bar_index = $0F02
!loop_bar_index = $0F03
init:
		REP #$20
		STZ !curr_bar_index
		; STZ !loop_bar_index
		LDA music_bars
		STA !ticks_next_bar
		SEP #$20

		
		
main:
		REP #$20
		; read apu i/o 0-1 again if it's fucked until it isn't
	-	LDA $2140
		CMP $2140
		BNE -
		CMP !ticks_next_bar
		BMI .return
		
		; flip on/off
		; SEP #$20
		; LDA $14AF
		; EOR #$01
		; STA $14AF
		; LDA #$0B
		; STA $1DF9
		; REP #$20
		
		; cycle through the animation states
		SEP #$20
		LDA $7FC070
		INC
		CMP.b #!animation_states
		BCC +
		TDC
	+
		STA $7FC070
		REP #$20
		
		; handle the next bar
		LDX !curr_bar_index
		INX
		INX
		LDA music_bars,x
		BNE .check_track_end
		
		; place song loop start on next bar
		INX
		INX
		STX !loop_bar_index
		LDA music_bars,x
		BRA .update_stuff
		
	.check_track_end:
		BPL .update_stuff
		
		; the track ended so go back to the loop point (or the start)
		LDX !loop_bar_index
		LDA music_bars,x
		
	.update_stuff:
		CLC
		ADC !ticks_next_bar
		STA !ticks_next_bar
		STX !curr_bar_index

	.return:
		SEP #$20
		RTL
		
		
; how to:
; the duration of each bar is expressed in ticks
; use $0000 at the start of the loop point (if there's one)
; use $FFFF at the end of the track so it can loop back

!quarter = $0030
!quarterdot = $0048

music_bars:
		dw !quarter, !quarter, !quarterdot
		dw $FFFF