/*
 * Created on Jul 12, 2007
 *
 * Copyright (c) 2007, the JUNG Project and the Regents of the University 
 * of California
 * All rights reserved.
 *
 * This software is open-source under the BSD license; see either
 * "license.txt" or
 * http://jung.sourceforge.net/license.txt for a description.
 */
package edu.uci.ics.jung.algorithms.scoring.util;

import java.util.Collection;

import org.apache.commons.collections15.Transformer;

import edu.uci.ics.jung.algorithms.scoring.HITS;

/**
 * Methods for assigning values (to be interpreted as prior probabilities) to
 * vertices in the context of random-walk-based scoring algorithms.
 */
public class ScoringUtils {
	/**
	 * Assigns a probability of 1/<code>roots.size()</code> to each of the
	 * elements of <code>roots</code>.
	 * 
	 * @param <V>
	 *            the vertex type
	 * @param roots
	 *            the vertices to be assigned nonzero prior probabilities
	 * @return
	 */
	public static <V> Transformer<V, Double> getUniformRootPrior(
			Collection<V> roots) {
		final Collection<V> inner_roots = roots;
		Transformer<V, Double> distribution = new Transformer<V, Double>() {
			@Override
			public Double transform(V input) {
				if (inner_roots.contains(input)) {
					return new Double(1.0 / inner_roots.size());
				}
				return 0.0;
			}
		};

		return distribution;
	}

	/**
	 * Returns a Transformer that hub and authority values of 1/
	 * <code>roots.size()</code> to each element of <code>roots</code>.
	 * 
	 * @param <V>
	 *            the vertex type
	 * @param roots
	 *            the vertices to be assigned nonzero scores
	 * @return a Transformer that assigns uniform prior hub/authority
	 *         probabilities to each root
	 */
	public static <V> Transformer<V, HITS.Scores> getHITSUniformRootPrior(
			Collection<V> roots) {
		final Collection<V> inner_roots = roots;
		Transformer<V, HITS.Scores> distribution = new Transformer<V, HITS.Scores>() {
			@Override
			public HITS.Scores transform(V input) {
				if (inner_roots.contains(input)) {
					return new HITS.Scores(1.0 / inner_roots.size(),
							1.0 / inner_roots.size());
				}
				return new HITS.Scores(0.0, 0.0);
			}
		};
		return distribution;
	}
}