/*
 * Copyright (c) 2003, 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.
 */
/*
 * Created on Feb 3, 2004
 */
package edu.uci.ics.jung.algorithms.blockmodel;

import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import edu.uci.ics.jung.graph.Graph;

/**
 * Maintains information about a vertex partition of a graph. This can be built
 * from a map from vertices to vertex sets or from a collection of (disjoint)
 * vertex sets, such as those created by various clustering methods.
 */
public class VertexPartition<V, E> {
	private Map<V, Set<V>> vertex_partition_map;
	private Collection<Set<V>> vertex_sets;
	private Graph<V, E> graph;

	/**
	 * Creates an instance based on the specified graph and mapping from
	 * vertices to vertex sets, and generates a set of partitions based on this
	 * mapping.
	 * 
	 * @param g
	 *            the graph over which the vertex partition is defined
	 * @param partition_map
	 *            the mapping from vertices to vertex sets (partitions)
	 */
	public VertexPartition(Graph<V, E> g, Map<V, Set<V>> partition_map) {
		this.vertex_partition_map = Collections.unmodifiableMap(partition_map);
		this.graph = g;
	}

	/**
	 * Creates an instance based on the specified graph, vertex-set mapping, and
	 * set of disjoint vertex sets. The vertex-set mapping and vertex partitions
	 * must be consistent; that is, the mapping must reflect the division of
	 * vertices into partitions, and each vertex must appear in exactly one
	 * partition.
	 * 
	 * @param g
	 *            the graph over which the vertex partition is defined
	 * @param partition_map
	 *            the mapping from vertices to vertex sets (partitions)
	 * @param vertex_sets
	 *            the set of disjoint vertex sets
	 */
	public VertexPartition(Graph<V, E> g, Map<V, Set<V>> partition_map,
			Collection<Set<V>> vertex_sets) {
		this.vertex_partition_map = Collections.unmodifiableMap(partition_map);
		this.vertex_sets = vertex_sets;
		this.graph = g;
	}

	/**
	 * Creates an instance based on the specified graph and set of disjoint
	 * vertex sets, and generates a vertex-to-partition map based on these sets.
	 * 
	 * @param g
	 *            the graph over which the vertex partition is defined
	 * @param vertex_sets
	 *            the set of disjoint vertex sets
	 */
	public VertexPartition(Graph<V, E> g, Collection<Set<V>> vertex_sets) {
		this.vertex_sets = vertex_sets;
		this.graph = g;
	}

	/**
	 * Returns the graph on which the partition is defined.
	 * 
	 * @return the graph on which the partition is defined
	 */
	public Graph<V, E> getGraph() {
		return graph;
	}

	/**
	 * Returns a map from each vertex in the input graph to its partition. This
	 * map is generated if it does not already exist.
	 * 
	 * @return a map from each vertex in the input graph to a vertex set
	 */
	public Map<V, Set<V>> getVertexToPartitionMap() {
		if (vertex_partition_map == null) {
			this.vertex_partition_map = new HashMap<V, Set<V>>();
			for (Set<V> set : this.vertex_sets) {
				for (V v : set) {
					this.vertex_partition_map.put(v, set);
				}
			}
		}
		return vertex_partition_map;
	}

	/**
	 * Returns a collection of vertex sets, where each vertex in the input graph
	 * is in exactly one set. This collection is generated based on the
	 * vertex-to-partition map if it does not already exist.
	 * 
	 * @return a collection of vertex sets such that each vertex in the
	 *         instance's graph is in exactly one set
	 */
	public Collection<Set<V>> getVertexPartitions() {
		if (vertex_sets == null) {
			this.vertex_sets = new HashSet<Set<V>>();
			this.vertex_sets.addAll(vertex_partition_map.values());
		}
		return vertex_sets;
	}

	/**
	 * Returns the number of partitions.
	 */
	public int numPartitions() {
		return vertex_sets.size();
	}

	@Override
	public String toString() {
		return "Partitions: " + vertex_partition_map;
	}
}