.model small
.stack 100h

.data
    input_prompt    db  'Iveskite sesioliktaini skaiciu: $'
    help_text       db  'Programa konvertuoja ivesta sesioliktaini skaiciu i dvejetaini.$'
    invalid_input   db  'Neteisinga ivestis!$'
    new_line        db  13,10,'$'
    result          db  'Dvejetainis atitikmuo: $'
    input           db  100, 0, dup(0)

.code
program:

;load ds
mov ax,@data
mov ds,ax

;check if help text needs to be printed
mov bx,81h
argv:
    mov ax,es:[bx]
    inc bx
    cmp al,13
    je print_input_prompt
    cmp al,' '
    je argv
    cmp ax,'?/'
    jne argv
    mov ax,es:[bx]
    cmp ah,13
    je help
    cmp al,' '
    je help
    jmp print_input_prompt

;print help text
help:
    mov ah,9h
    mov dx,offset help_text
    int 21h
    jmp finish
;print input prompt
print_input_prompt:
    mov dx,offset input_prompt
    mov ah,9h
    int 21h

;ask user for input
collect_input:
    mov ah,0Ah
    mov dx,offset input
    int 21h
    ;move carret to a new line
    mov ah,9h
    mov dx,offset new_line
    int 21h

;validates input and prints error if input is invalid
mov bx,offset input
add bx,2
validate_input:
    mov ax,ds:[bx]
    inc bx
    ;if not end of input
    cmp al,13
    je print_result_msg
    ;if number
    cmp al,30h
    jb error
    cmp al,39h
    jbe validate_input
    ;if letter
    cmp al,41h
    jb error
    cmp al,46h
    jbe validate_input
    jmp error

;print error msg
error:
    mov dx,offset invalid_input
    mov ah,9h
    int 21h
    jmp finish

;print result msg
print_result_msg:
    mov dx,offset result
    mov ah,9h
    int 21h

;convert hex to bin
mov bx,offset input
add bx,2h
convert:
    mov ax,ds:[bx]
    inc bx
    cmp al,13
    je finish
    cmp al,39h
    jbe convert_number
    jmp convert_letter

;convert number character in al to number
convert_number:
    sub al,30h
    jmp print_binary

;convert letter to number
convert_letter:
    sub al,55d
    jmp print_binary

print_binary:
    mov ch,4;how many chars will be shown
    mov cl,3;how many rotates will be made

process:
    push ax
    ;convert bit to char
    mov dl,al
    ror dl,cl
    and dl,01
    add dl,30h
    ;print 0 or 1
    mov ah, 02h
    int 21h
    ;proceed if ch
    pop ax
    dec cl
    dec ch
    jnz process
    ;space after every 4 bits
    mov dl,' '
    mov ah,2h
    int 21h
    jmp convert

;finish program
finish:
    mov ax,4c00h
    int 21h

end program