cpu 8086
bits 16

org 0x7c00

jmp 0:start
start:
	cld

	cli

	; Set up segments and stack
	mov ax, cs
	mov ds, ax
	mov es, ax
	mov ss, ax
	mov sp, $$

	sti

	; Clear BSS
	mov di, _bss_start
	mov cx, _bss_end - _bss_start
	xor al, al
	rep stosb

initialize_mouse:
	; Initialize mouse
	; https://www.ctyme.com/intr/rb-1601.htm
	mov ax, 0xc205
	mov bh, 3 ; TODO: This is the usual PS/2 mouse packet size, but is it correct here?
	int 0x15
	jc .error

	; Set handler address
	; https://www.ctyme.com/intr/rb-1603.htm
	mov ax, 0xc207
	; es is already set correctly
	mov bx, mouse_handler
	int 0x15
	jc .error

	; Enable mouse
	; https://www.ctyme.com/intr/rb-1596.htm
	mov ax, 0xc200
	mov bh, 1
	int 0x15
	jc .error

	jmp mainloop

	.error:
		; https://www.ctyme.com/intr/rb-1601.htm
		mov ax, 0xc201
		int 0x15
		jmp initialize_mouse

mainloop:
	; TODO: everything

hang:
	hlt
	;mov ax, 0x0e00 + '.'
	;int 0x10
	jmp hang

Y_OVERFLOW equ 0x80
X_OVERFLOW equ 0x40
Y_NEGATIVE equ 0x20
X_NEGATIVE equ 0x10
BUTTONS equ 0x03

COLUMNS equ 80
ROWS equ 25
X_MAX_VALUE equ COLUMNS-1
Y_MAX_VALUE equ ROWS-1

mouse_handler:
	push ax
	push bx
	push bp
	push ds

	mov ax, cs
	mov ds, ax

	mov bp, sp

	mov bx, [bp+18] ; status

	test bl, X_OVERFLOW
	jnz .x_end
	.x:
		mov ax, [bp+16] ; X

		test bl, X_NEGATIVE
		jnz .x_negative
		.x_nonnegative:
			add [mouse_x], ax
			cmp word [mouse_x], X_MAX_VALUE
			jb .x_end
			mov word [mouse_x], X_MAX_VALUE
			jmp .x_end

		.x_negative:
			neg al
			sub [mouse_x], ax
			jnc .x_end
			mov word [mouse_x], 0
	.x_end:
	mov ax, [mouse_x];debg
	call hexprint16;debg
	mov ax, 0x0e00 + ' ';debg
	int 0x10;debg

	test bl, Y_OVERFLOW
	jnz .y_end
	.y:
		mov ax, [bp+14] ; Y

		test bl, Y_NEGATIVE
		jnz .y_negative
		.y_nonnegative:
			; Y-axis is inverted
			sub [mouse_y], ax
			jnc .y_end
			mov word [mouse_y], 0
			jmp .y_end

		.y_negative:
			neg al
			add [mouse_y], ax
			cmp word [mouse_y], Y_MAX_VALUE
			jb .y_end
			mov word [mouse_y], Y_MAX_VALUE
	.y_end
	mov ax, [mouse_y];debg
	call hexprint16;debg
	mov ax, 0x0e00 + ' ';debg
	int 0x10;debg

	and bl, BUTTONS
	mov [mouse_buttons], bl

	mov al, [mouse_buttons];debg
	call hexprint8;debg
	mov ax, 0x0e00 + 13;debg
	int 0x10;debg
	mov ax, 0x0e00 + 10;debg
	int 0x10;debg

	pop ds
	pop bp
	pop bx
	pop ax
	retf

hexprint16:
	xchg ah, al
	call hexprint8
	xchg ah, al

hexprint8:
	push ax
	push cx
	mov cl, 4
	shr al, cl
	call hexprint4
	pop cx
	pop ax

hexprint4:
	push ax
	and al, 0xf
	cmp al, 10
	jb .digit09

	add al, 'a' - '0' - 10

	.digit09:
	add al, '0'
	mov ah, 0x0e
	int 0x10
	pop ax
	ret

times 510-($-$$) db 0
db 0x55
db 0xaa

section .bss
_bss_start:

mouse_x resw 1
mouse_y resw 1
mouse_buttons resb 1

_bss_end: