package com.learning;

import static org.junit.Assert.assertEquals;

import org.junit.Test;

public class RomanNumeralsTest {

	interface RomanNumber {

		int toNumeral();

		int value();

	}

	class NextEmptyNumber implements RomanNumber {

		@Override
		public int toNumeral() {
			return 0;
		}

		@Override
		public int value() {
			return 0;
		}

	}

	class V implements RomanNumber {

		private RomanNumber nextNumber;

		public V(RomanNumber nextNumber) {
			this.nextNumber = nextNumber;
		}

		public V() {
			this(new NextEmptyNumber());
		}

		@Override
		public int toNumeral() {
			if (nextNumber.value() == 5) {
				throw new IllegalArgumentException("VV is not valid");
			}
			return nextNumber.value() + value();
		}

		@Override
		public int value() {
			return 5;
		}

	}

	class I implements RomanNumber {

		private RomanNumber nextNumber;

		public I(RomanNumber nextNumber) {
			this.nextNumber = nextNumber;
		}

		public I() {
			this(new NextEmptyNumber());
		}

		public int toNumeral() {
			if (nextNumber.value() == 5) {
				return nextNumber.toNumeral() - value();
			}
			return nextNumber.toNumeral() + value();
		}

		public int value() {
			return 1;
		}

	}

	@Test
	public void I_is_1() throws Exception {
		assertEquals(1, new I().toNumeral());
	}

	@Test
	public void II_is_2() throws Exception {
		assertEquals(2, new I(new I()).toNumeral());

	}

	@Test
	public void III_is_3() throws Exception {
		assertEquals(3, new I(new I(new I())).toNumeral());
	}

	@Test
	public void IV_is_4() throws Exception {
		assertEquals(4, new I(new V()).toNumeral());
	}

	@Test
	public void VI_is_6() throws Exception {
		assertEquals(6, new V(new I()).toNumeral());
	}

	@Test(expected = IllegalArgumentException.class)
	public void VV_is_invalid() throws Exception {
		new V(new V()).toNumeral();
	}
}