const fl_zero 0x1
const fl_eq 0x2
const fl_be 0x4
const fl_lt 0x8
const fl_err 0xa

const vcd_base 0x2000

const kbd_status 0x1ffc
const kbd_code 0x1ffe
const kbd_flag_is_release 0x1

const counter 0x600

_start:
    mov rsp, 0x1000
    mov rbp, rsp

    mov r0, 512
    mov r1, 1
    dskr r0, r1

    ; setup video character display (VCD)
    ; descriptor table structure:
    ;   [addr + 0] memory map base
    mov r0, vcd_base
    mov [0x700], r0
    lvcd 0x700

    ; setup keyboard (KBD)
    ; descriptor table structure:
    ;   [addr + 0] status address
    ;   [addr + 2] keycode address
    ;   [addr + 4] keyboard interrupt handler
    mov r0, kbd_status
    mov [0x702], r0
    mov r0, kbd_code
    mov [0x704], r0
    mov r0, key_press_int
    mov [0x706], r0
    lkbd 0x702

    ; character counter
    mov r0, 0
    mov [counter], r0

main_loop:
    hlt
    jmp main_loop
    
key_press_int:
    mov r0, [kbd_status]
    and r0, kbd_flag_is_release
    jnz r0, .leave

    mov r0, [counter]
    add r0, vcd_base
    mov r1, [kbd_code]
    cmp r1, 44 ; spacebar
    mov r2, rfl
    and r2, fl_eq
;    jnz r2, .incr
;    add r1, 61
;    mov byte [r0], r1
;.incr:
;    mov r0, [counter]
;    add r0, 1
;    mov [counter], r0

    jnz r2, .print_space
    add r1, 61 ; scancode letter -> ascii
    mov [rsp], r0
    add rsp, 2
    call print_char
    jmp .leave
.print_space:
    mov r0, ' '
    mov [rsp], r0
    add rsp, 2
    call print_char
.leave:
    reti

print_char:
    mov [rsp], rbp
    mov rbp, rsp
    add rsp, 2

    mov r1, [rbp-6]

    add r0, vcd_base
    mov r1, [kbd_code]
    cmp r1, ' '
    mov r2, rfl
    and r2, fl_eq
    jnz r2, .incr
    add r1, 61
    mov byte [r0], r1
.incr:
    mov r0, [counter]
    add r0, 1
    mov [counter], r0
.leave:
    sub rsp, 2
    mov rbp, [rsp]
    ret

;print_int:
;    mov [rsp], rbp
;    add rsp, 2
;    mov rbp, rsp
;    add rsp, rsp, 2
;
;    mov r1, [rbp-2]
;
;    mov r2, 10000
;    mov r3, 0
;    jmp .c_10000
;.b_10000:
;    add r3, 1
;    sub r1, r2
;.c_10000:
;    cmp r2, r1
;    mov r0, rfl
;    and r0, fl_eq | fl_lt
;    jnz r0, .b_10000
;    add r3, 48


;scancode_to_char:
;    cmp r1, 61
;
;    mov r2, rfl
;    and r2, r2, FL_LT
;    jnz .not_letter
;
;    ; if r1 > 86 { goto .not_letter }
;    cmp r1, 86
;    mov r2, rfl
;    xor r2, 0xffff
;    and r2, r2, FL_EQ | FL_LT
;
;
;    mov r4, rfl
;    and r4, r4, FL_EQ
;    shr r4, r4, 2