package com.tdudzik.testproject;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class TestProjectApp {

    public static void main(String[] args) throws Exception {

        while (true) {
            System.out.println("Podaj liczbę:");

            Scanner in = new Scanner(System.in);
            String number = in.next();

            if (isDivisibleByThree(number)) {
                System.out.println("Podzielne.");
            } else {
                System.out.println("Niepodzielne.");
            }
        }

    }

    public static boolean isDivisibleByThree(String number) {
        List<Integer> digitsDivisibleByThree = Arrays.asList(0, 3, 6, 9);
        int digit = reduceToOneDigit(number);

        return digitsDivisibleByThree.contains(digit);
    }

    public static int reduceToOneDigit(String number) {
        while (number.length() != 1) {
            number = sumDigits(number);
        }

        return Character.getNumericValue(number.charAt(0));
    }

    public static String sumDigits(String number) {
        List<Integer> digits = new ArrayList<>();
        for (char ch : number.toCharArray()) {
            digits.add(Character.getNumericValue(ch));
        }

        return digits
                .stream()
                .map(Integer::valueOf)
                .reduce(0, Integer::sum)
                .toString();
    }

}