const KBD_STATUS 0x1ffc
const KBD_CODE 0x1ffe
const VCD 0x2000

const FL_EQ 0x2
const FL_EQ 0x4

const KBD_FLAG_IS_RELEASE 0x1

    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
    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 [0x600], r0

main_loop:
    hlt
    jmp main_loop
    
key_press_int:
    mov r0, [KBD_STATUS]
    and r0, r0, KBD_FLAG_IS_RELEASE
    jnz r0, .leave

    mov r0, [0x600]
    add r0, r0, VCD
    mov r1, [KBC_CODE]
    cmp r1, 44 ; spacebar
    mov r2, rfl
    and r2, r2, FL_EQ
    jnz r2, .incr
    add r1, r1, 61
    mov byte [r0], r1
.incr:
    mov r0, [0x600]
    add r0, r0, 1
    mov [0x600], r0
.leave:
    reti

;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