ListItemLabel.java

package uk.me.kissy.document.templateMethod;

import java.util.List;
import java.util.TreeMap;

import freemarker.template.SimpleNumber;
import freemarker.template.SimpleScalar;
import freemarker.template.TemplateMethodModelEx;
import freemarker.template.TemplateModelException;

public class ListItemLabel implements TemplateMethodModelEx {
	private final static TreeMap<Integer, String> map = new TreeMap<>();

	static {
		map.put(1000, "M");
		map.put(900, "CM");
		map.put(500, "D");
		map.put(400, "CD");
		map.put(100, "C");
		map.put(90, "XC");
		map.put(50, "L");
		map.put(40, "XL");
		map.put(10, "X");
		map.put(9, "IX");
		map.put(5, "V");
		map.put(4, "IV");
		map.put(1, "I");
	}

	// Copied from Stackoverflow https://stackoverflow.com/a/19759564/2735286
	private static String toRoman(int number) {
		int l = map.floorKey(number);
		if (number == l) {
			return map.get(number);
		}
		return map.get(l) + toRoman(number - l);
	}

	// Copied from
	// https://stackoverflow.com/questions/10813154/how-do-i-convert-a-number-to-a-letter-in-java
	private static String toAlphabetic(int i) {
		if (i < 0) {
			return "-" + toAlphabetic(-i - 1);
		}
		int quot = i / 26;
		int rem = i % 26;
		char letter = (char) ((int) 'A' + rem);
		if (quot == 0) {
			return "" + letter;
		} else {
			return toAlphabetic(quot - 1) + letter;
		}
	}

	@Override
	public Object exec(List arguments) throws TemplateModelException {
		final String typeOrdered = ((SimpleScalar) arguments.get(0)).getAsString();
		final Integer number = ((SimpleNumber) arguments.get(1)).getAsNumber().intValue();
		if ("A".equals(typeOrdered)) {
			String value = toAlphabetic(number);
			return new SimpleScalar(value.toLowerCase());
		} else if ("a".equals(typeOrdered)) {
			String value = toAlphabetic(number);
			return new SimpleScalar(value.toLowerCase());
		} else if ("I".equals(typeOrdered)) {
			String value = toRoman(number);
			return new SimpleScalar(value);
		} else if ("i".equals(typeOrdered)) {
			String value = toRoman(number);
			return new SimpleScalar(value.toLowerCase());
		} else {
			// default numeric
			return new SimpleNumber(number);
		}
	}
}