; SuBAsm
; The Sux Bootstrapped Assembler.
;
; by mr b0nk 500 <b0nk@b0nk.xyz>

; Variables
.org $1000
prg_name:
	.byte "SuBAsm"
ver_txt:
	.byte ", version "
ver_num:
	.byte "0.1"
x:
	.word $0
y:
	.word $0

str_buf:

; Input buffer.
.org $2000
buf:

; Control Register.
.org $C000
ctrl_reg:

; Screen.
.org $C001
scr:

; Keyboard.
.org $C002
kbd:

; Main program.
.org $0
reset:
	cps
	ldx.w #$FFFF
	txs
	ldy #$0
	jsr clr_buf
	ldx.w #$0	; Reset x.
	ldy #$0		; Reset y.
	jmp print_title

read:
	lda ctrl_reg	; Is the keyboard ready?
	beq read	; Loop until the keyboard is ready.
	lda #$0		; Start resetting the control register.
	sta ctrl_reg	; Reset the control register.
	jmp getchar	; We got a key.

rset_x:

	ldx #$0		; Reset x.
	stx.w x
	rts

print_title:
	lda prg_name, x
	beq print_ver	; Did we find a null terminator?
	sta		; Print character.
	inx		; Increment offset.
	inc x
	jmp print_title	; Keep printing more characters.

print_ver
	jsr rset_x
	lda ver_txt, x
	beq print_num	; Did we find a null terminator?
	sta scr		; Print character.
	inx		; Increment offset.
	jmp print_ver	; Keep printing more characters.

print_num:
	lda ver_num, x
	beq getline	; Did we find a null terminator?
	sta scr		; Print character.
	inx		; Increment offset.
	jmp print_num	; Keep printing more characters.
getline:
	lda #$A
	sta scr		; Print newline
	inc y
	jsr rset_x
	jmp read

getchar:
	lda kbd		; Get typed character.
	cmp #$1B	; Did the user type an escape?
	beq esc		; Yes, so start getting the escape code.
	cmp #$A		; Did the user type a newline?
	beq nl		; Yes, so start parsing the input.
	cmp #$8		; Did the user type a backspace?
	beq bs		; Yes, so start checking the buffer.
	jsr echo	; Print character to screen.

store_char:
	sta buf, y	; Store typed character into the input buffer.
	iny		; Increment buffer offset.
	jmp read	; Get another character.

esc:
	lda ctrl_reg	; Skip the '['.
	lda ctrl_reg	; Get the next character.
	beq read	; We have an error, so discard it, and read the next character.
	lda kbd		; Get the escape code.
	cmp #$41	; Did the user press the up arrow?
	beq up		; Yes, so move the cursor up.
	cmp #$42	; Did the user press the down arrow?
	beq down	; Yes, so move the cursor down.
	cmp #$43	; Did the user press the left arrow?
	beq left	; Yes, so move the cursor left.
	cmp #$44	; Did the user press the right arrow?
	beq right	; Yes, so move the cursor right.

up:
	lda #$1B
	sta scr
	lda #$5B
	sta scr
	lda #$41
	sta scr
	jmp read
down:
	lda #$1B
	sta scr
	lda #$5B
	sta scr
	lda #$42
	sta scr
	jmp read
left:
	lda #$1B
	sta scr
	lda #$5B
	sta scr
	lda #$43
	sta scr
	jmp read
right:
	lda #$1B
	sta scr
	lda #$5B
	sta scr
	lda #$44
	sta scr
	jmp read



nl:
	sta scr		; Print newline.
	lda #$0		; Put a null terminator, in place of the newline.
	sta buf, y	; Place it into the input buffer.
	ldy.w #$0	; Reset y, to parse the input.
	jmp parse

back:
	jsr echo	; Print backspace.
	lda #$0		; Put a null terminator, in place of the backspace.
	sta buf, y	; Place it into the input buffer.
	dey		; Decrement buffer offset.
	jmp read	; Get next character.

bs:
	cpy #$0		; Are we at the start of the buffer?
	beq read	; We are, so do not store the backspace into the buffer.
	jmp back	; We are not, so add the backspace to the buffer.

parse:
	lda buf, y
	beq clr_buf	; Reset y, if we hit the null terminator.
	sta scr		; Print 'You have typed, '
	iny		; Increment offset.
	jmp result	; Keep printing.

rset_y:
	ldy.w #$0
	jmp print_buf	; Print the input buffer.

print_buf:
	lda buf, y	; Get a character from the input buffer.
	beq fin		; Are we done with printing the buffer?
	sta scr		; Print said character.
	iny
	jmp print_buf	; Keep printing the buffer.

spin:
	nop
	nop
	nop
	jmp spin

clr_buf:
	lda #$0
	cpy.w #$1000
	beq clr_end
	sta buf, y
	iny
	jmp clr_buf
clr_sbuf:
	lda #$0
	cpy.w #$40
	beq clr_end
	sta str_buf, y
	iny
	jmp clr_sbuf

clr_end:
	rts

echo:
	sta scr		; Echo typed character.
	rts		; Return.

.org $FFC0
.qword reset

.org $FF50
.qword spin
.qword spin
.qword spin
.qword spin
.qword spin
.qword spin
.qword spin

.org $FFA0
.qword irq_routine
;.org $0
;viewmem
;.org $100
;viewmem
;q
done