package net.sourceforge.fenixedu.commons;

import java.util.ArrayList;
import java.util.List;

public class Combinations implements java.util.Enumeration {
    protected List inArray;

    protected int n, m;

    protected int[] index;

    protected boolean hasMore = true;

    public Combinations(List inArray, int m) {

	this.inArray = inArray;
	this.n = inArray.size();
	this.m = m;

	check(n, m);

	index = new int[m];
	for (int i = 0; i < m; i++) {
	    index[i] = i;
	}
    }

    public void check(int n, int m) {
	if (n < 0) {
	    throw new RuntimeException("n, the number of items, must be " + "greater than 0");
	}
	if (n < m) {
	    throw new RuntimeException("n, the number of items, must be >= m, " + "the number selected");
	}
	if (m < 0) {
	    throw new RuntimeException("m, the number of selected items, must be >= 0");
	}
    }

    public boolean hasMoreElements() {
	return hasMore;
    }

    protected void moveIndex() {
	int i = rightmostIndexBelowMax();
	if (i >= 0) {
	    index[i] = index[i] + 1;
	    for (int j = i + 1; j < m; j++) {
		index[j] = index[j - 1] + 1;
	    }
	} else {
	    hasMore = false;
	}
    }

    public List nextElement() {
	if (!hasMore) {
	    return null;
	}

	List out = new ArrayList(m);
	for (int i = 0; i < m; i++) {
	    out.add(i, inArray.get(index[i]));
	}

	moveIndex();
	return out;
    }

    protected int rightmostIndexBelowMax() {

	for (int i = m - 1; i >= 0; i--) {
	    if (index[i] < n - m + i) {
		return i;
	    }
	}
	return -1;
    }
}