/**     MidTerm Project
 * Created by Tseliso on 2/21/2017.
 *
 *  new StringBuilder()
 */
import java.util.Scanner;
public class Banker {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        long card;
        do {
            System.out.println("Please enter a valid credit card number. Enter the number '0' to end.");
            card = input.nextLong();

            if (isValid(card)) {
                System.out.println("This is a valid card.");
            } else {
                System.out.println("Card invalid, please try again.");
            }
        } while (card != 0);
    }


    /**
     * Return true if the card number is valid
     */
    public static boolean isValid(long number) {
        int evenSpots = 0;
        int oddSpots = 0;
        boolean length = false;
        boolean numbers = false;

        //Check Card length
        if (getSize(number) > 0) {
            System.out.println("Size GOOD");

            //Check for correct starting numbers, using OR instead of a bunch of if
            if (prefixMatched(number, 37) || prefixMatched(number, 6)
                    || prefixMatched(number, 5) || prefixMatched(number, 4)) {
                System.out.println("Starting number GOOD");
                //check to see if the card starts with the appropriate number THEN a
                evenSpots = sumOfDoubleEvenPlace(number);
                oddSpots = sumOfOddPlace(number);
                int total = evenSpots + oddSpots;
                if (total % 10 == 0)
                {
                    numbers = true;
                    length = true;
                }
                else
                {
                    System.out.println("Fail");
                }


            }


        }
        //System.out.print("Invalid Card length!");


        // Full validation Check
        if (length && numbers) {
            return true;
        } else {
            System.out.println("length: " + length + ", numbers: " + numbers);
            return false;
        }
    }

    /** Get the result from Step 2 */
    public static int sumOfDoubleEvenPlace(long number){
        int sum = 0;

        String numToString = Long.toString(number);
        int amtDigits = String.valueOf(number).length();
        System.out.println(amtDigits);
        for (int i = 1; i < numToString.length(); i+=2 /*decrement by two to skip the odd places.*/)
        {
            System.out.println("adding " + (getDigit(Character.getNumericValue(numToString.charAt(i)))) *2);

            sum += (getDigit(Character.getNumericValue(numToString.charAt(i)))*2);
        }

        System.out.println("SumOfDoubleEvenPlace: " + sum);

        return sum;
    }

    /** Return this number if it is a single digit, otherwise,
     * return the sum of the two digits */
    public static int getDigit(int number) {
        //int num = Integer.toString(number).length();
        // Big fail, lots of errors
        if ( Integer.toString(number).length() == 1) {
            //System.out.println("Get digit" + number);

            return number;
        }
        else {
            //System.out.println("Get digit" + number);

            return ((number % 10) + 1);
        }
    }
//////////////////////////////////////////////////////////////////////////////////////////////////////
    /** Return sum of odd-place digits in number */
    public static int sumOfOddPlace(long number){
        int sum = 0;
        String numToString = Long.toString(number);

        for (int i = 0; i < numToString.length(); i +=2 /*increment by two to skip the even places.*/)
            sum += getDigit(Character.getNumericValue(numToString.charAt(i)));
        System.out.println("SumOfOddPlace: " + sum);
        return sum;
    }

    /** Return true if the digit d is a prefix for number */
    public static boolean prefixMatched(long number, int d){
        int numLength = new StringBuilder(Integer.toString(d)).length();
        String numberString = Long.toString(number);
        String dString = Integer.toString(d);

        //increment through the length of the number
        for (int i = 0; i < numLength; i++)
            // if the number isn't one of the 4 acceptable then return false.
            if(numberString.charAt(i) != dString.charAt(i))
                return false;

        return true;
    }

    /** Return the number of digits in d */
    public static int getSize(long d){
        int numL = Long.toString(d).length();
        if (numL > 13 && numL <= 16 ) {
            return numL;
        }
        else
            return 0;
    }

    /** Return the first k number of digits from number. If the
     * number of digits in number is less than k, return number. */
    public static long getPrefix(long number, int k) {
        long ans = number;
        for (int i = 0; i < getSize(number) - (k); i++)
            ans /= 10;
        return ans;
    }


}