#!/usr/bin/env python
# Luhn Algorithm Example - Developed by acidvegas in Python (https://git.acid.vegas/msr90)

def modulus10(card_number: str) -> str:
    '''
    Validate a card number using the Luhn Algorithm

    :param card_number: The card number to validate
    '''
   
    digits = [int(d) for d in card_number]
    total_sum = 0
    reversed_digits = digits[::-1]

    for i in range(len(reversed_digits)):
        digit = reversed_digits[i]

        if i % 2 != 0:
            digit = digit * 2

        if digit > 9:
            digit -= 9

        total_sum += digit

    check_digit = (10 - (total_sum % 10)) % 10
    full_card_number = card_number + str(check_digit)
    
    if (total_sum + check_digit) % 10 != 0:
        raise ValueError('failed luhn check (non-divisible by 10)')

    return full_card_number


if __name__ == '__main__':
    card_number = input('Enter your card number without the last digit:')

    if not card_number.isdigit():
        raise ValueError('invalid card number')
    
    print(f'Full card number: {modulus10(card_number)}')