import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;

import java.math.BigInteger;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

public class FactTest {
    @Rule
    public ExpectedException thrown = ExpectedException.none();

    public static BigInteger factorial(int value) {
        if (value == 1) {
            return BigInteger.valueOf(value);
        } else {
            return BigInteger.valueOf(value).multiply(factorial(value - 1));
        }
    }

    public static BigInteger factorialNonRecursive(int value) {
        if (value == 1) {
            return BigInteger.ONE; // LOL, enterprise code!
        } else {
            BigInteger res = BigInteger.ONE;
            for (int i = 2; i <= value; i++) {
                res = res.multiply(BigInteger.valueOf(i));
            }
            return res;
        }
    }

    @Test
    public void countNonRecursive() {
        assertEquals(BigInteger.valueOf(6L), factorialNonRecursive(3));
        BigInteger largeFrac = factorialNonRecursive(50000);
        // assert that we managed to get very large number
        assertTrue(largeFrac.bitLength() > 700000);
    }

    @Test
    public void count() {
        thrown.expect(StackOverflowError.class);
        assertEquals(BigInteger.ONE, factorial(50000));
    }
}