//algorytm Verhoeff'a
//www.algorytm.org
//(c)2007 by Tomasz Lubinski

public class Verhoeff {
	
	private static final byte d[][] = 
	   {{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, 
		{1, 2, 3, 4, 0, 6, 7, 8, 9, 5}, 
		{2, 3, 4, 0, 1, 7, 8, 9, 5, 6}, 
		{3, 4, 0, 1, 2, 8, 9, 5, 6, 7}, 
		{4, 0, 1, 2, 3, 9, 5, 6, 7, 8}, 
		{5, 9, 8, 7, 6, 0, 4, 3, 2, 1}, 
		{6, 5, 9, 8, 7, 1, 0, 4, 3, 2}, 
		{7, 6, 5, 9, 8, 2, 1, 0, 4, 3}, 
		{8, 7, 6, 5, 9, 3, 2, 1, 0, 4}, 
		{9, 8, 7, 6, 5, 4, 3, 2, 1, 0}}; 

	private static final byte p[][] =
		{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, 
		 {1, 5, 7, 6, 2, 8, 3, 0, 9, 4}, 
		 {5, 8, 0, 3, 7, 9, 6, 1, 4, 2}, 
		 {8, 9, 1, 6, 0, 4, 3, 5, 2, 7}, 
		 {9, 4, 5, 3, 1, 2, 6, 8, 7, 0}, 
		 {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
		 {2, 7, 9, 3, 8, 0, 6, 4, 1, 5}, 
		 {7, 0, 4, 6, 9, 1, 3, 2, 5, 8}};
	
	private static final byte inv[] =
		{0, 4, 3, 2, 1, 5, 6, 7, 8, 9};

	/**
	 * Check number
	 * @param number
	 * @return true if check digit in number is correct, false otherwise
	 */
	public static boolean verhoeffCheck(String number) {
		int c = 0;
		int digit;
		for (int i=0; i<number.length(); i++) {
			digit = Integer.parseInt(number.charAt(number.length() - i - 1) + "");
			c = d[c][p[i%8][digit]]; 
		}
		
		if (c == 0) {
			return true;
		}
		return false;
	}
	
	/**
	 * Calculate check digit for a given number
	 * @param number (with check digit with any value)
	 * @return check digit
	 */
	public static byte verhoeffCheckDigit(String number) {
		int c = 0;
		int digit;
		for (int i=1; i<number.length(); i++) {
			digit = Integer.parseInt(number.charAt(number.length() - i - 1) + "");
			c = d[c][p[i%8][digit]]; 
		}

		return inv[c];
	}	

	/**
	 * Get number and check it
	 * 
	 * @param args
	 */
	public static void main(String[] args) {
		String number;
		
		System.out.println("Podaj numer do sprawdzenia");
		number = Console.readString();
		
		if (verhoeffCheck(number)) {
			System.out.println("Numer jest prawidłowy");
		} else {
			System.out.println("Numer jest nieprawidłowy");
			System.out.println("Dla tego numeru prawidlowa cyfra kontrolna to " + verhoeffCheckDigit(number));
		}
	}

}