/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Creator:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2008, by Barak Naveh and Contributors.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */
/* --------------------------
 * ConnectivityInspector.java
 * --------------------------
 * (C) Copyright 2003-2008, by Barak Naveh and Contributors.
 *
 * Original Author:  Barak Naveh
 * Contributor(s):   John V. Sichi
 *                   Christian Hammer
 *
 * $Id: ConnectivityInspector.java 645 2008-09-30 19:44:48Z perfecthash $
 *
 * Changes
 * -------
 * 06-Aug-2003 : Initial revision (BN);
 * 10-Aug-2003 : Adaptation to new event model (BN);
 * 07-Jun-2005 : Made generic (CH);
 *
 */
package org.jgrapht.alg;

import java.util.*;

import org.jgrapht.*;
import org.jgrapht.event.*;
import org.jgrapht.graph.*;
import org.jgrapht.traverse.*;


/**
 * Allows obtaining various connectivity aspects of a graph. The <i>inspected
 * graph</i> is specified at construction time and cannot be modified.
 * Currently, the inspector supports connected components for an undirected
 * graph and weakly connected components for a directed graph. To find strongly
 * connected components, use {@link StrongConnectivityInspector} instead.
 *
 * <p>The inspector methods work in a lazy fashion: no computation is performed
 * unless immediately necessary. Computation are done once and results and
 * cached within this class for future need.</p>
 *
 * <p>The inspector is also a {@link org.jgrapht.event.GraphListener}. If added
 * as a listener to the inspected graph, the inspector will amend internal
 * cached results instead of recomputing them. It is efficient when a few
 * modifications are applied to a large graph. If many modifications are
 * expected it will not be efficient due to added overhead on graph update
 * operations. If inspector is added as listener to a graph other than the one
 * it inspects, results are undefined.</p>
 *
 * @author Barak Naveh
 * @author John V. Sichi
 * @since Aug 6, 2003
 */
public class ConnectivityInspector<V, E>
    implements GraphListener<V, E>
{
    //~ Instance fields --------------------------------------------------------

    List<Set<V>> connectedSets;
    Map<V, Set<V>> vertexToConnectedSet;
    private Graph<V, E> graph;

    //~ Constructors -----------------------------------------------------------

    /**
     * Creates a connectivity inspector for the specified undirected graph.
     *
     * @param g the graph for which a connectivity inspector to be created.
     */
    public ConnectivityInspector(UndirectedGraph<V, E> g)
    {
        init();
        this.graph = g;
    }

    /**
     * Creates a connectivity inspector for the specified directed graph.
     *
     * @param g the graph for which a connectivity inspector to be created.
     */
    public ConnectivityInspector(DirectedGraph<V, E> g)
    {
        init();
        this.graph = new AsUndirectedGraph<V, E>(g);
    }

    //~ Methods ----------------------------------------------------------------

    /**
     * Test if the inspected graph is connected. An empty graph is <i>not</i>
     * considered connected.
     *
     * @return <code>true</code> if and only if inspected graph is connected.
     */
    public boolean isGraphConnected()
    {
        return lazyFindConnectedSets().size() == 1;
    }

    /**
     * Returns a set of all vertices that are in the maximally connected
     * component together with the specified vertex. For more on maximally
     * connected component, see <a
     * href="http://www.nist.gov/dads/HTML/maximallyConnectedComponent.html">
     * http://www.nist.gov/dads/HTML/maximallyConnectedComponent.html</a>.
     *
     * @param vertex the vertex for which the connected set to be returned.
     *
     * @return a set of all vertices that are in the maximally connected
     * component together with the specified vertex.
     */
    public Set<V> connectedSetOf(V vertex)
    {
        Set<V> connectedSet = vertexToConnectedSet.get(vertex);

        if (connectedSet == null) {
            connectedSet = new HashSet<V>();

            BreadthFirstIterator<V, E> i =
                new BreadthFirstIterator<V, E>(graph, vertex);

            while (i.hasNext()) {
                connectedSet.add(i.next());
            }

            vertexToConnectedSet.put(vertex, connectedSet);
        }

        return connectedSet;
    }

    /**
     * Returns a list of <code>Set</code> s, where each set contains all
     * vertices that are in the same maximally connected component. All graph
     * vertices occur in exactly one set. For more on maximally connected
     * component, see <a
     * href="http://www.nist.gov/dads/HTML/maximallyConnectedComponent.html">
     * http://www.nist.gov/dads/HTML/maximallyConnectedComponent.html</a>.
     *
     * @return Returns a list of <code>Set</code> s, where each set contains all
     * vertices that are in the same maximally connected component.
     */
    public List<Set<V>> connectedSets()
    {
        return lazyFindConnectedSets();
    }

    /**
     * @see GraphListener#edgeAdded(GraphEdgeChangeEvent)
     */
    public void edgeAdded(GraphEdgeChangeEvent<V, E> e)
    {
        init(); // for now invalidate cached results, in the future need to
                // amend them.
    }

    /**
     * @see GraphListener#edgeRemoved(GraphEdgeChangeEvent)
     */
    public void edgeRemoved(GraphEdgeChangeEvent<V, E> e)
    {
        init(); // for now invalidate cached results, in the future need to
                // amend them.
    }

    /**
     * Tests if there is a path from the specified source vertex to the
     * specified target vertices. For a directed graph, direction is ignored for
     * this interpretation of path.
     *
     * <p>Note: Future versions of this method might not ignore edge directions
     * for directed graphs.</p>
     *
     * @param sourceVertex one end of the path.
     * @param targetVertex another end of the path.
     *
     * @return <code>true</code> if and only if there is a path from the source
     * vertex to the target vertex.
     */
    public boolean pathExists(V sourceVertex, V targetVertex)
    {
        /*
         * TODO: Ignoring edge direction for directed graph may be
         * confusing. For directed graphs, consider Dijkstra's algorithm.
         */
        Set<V> sourceSet = connectedSetOf(sourceVertex);

        return sourceSet.contains(targetVertex);
    }

    /**
     * @see VertexSetListener#vertexAdded(GraphVertexChangeEvent)
     */
    public void vertexAdded(GraphVertexChangeEvent<V> e)
    {
        init(); // for now invalidate cached results, in the future need to
                // amend them.
    }

    /**
     * @see VertexSetListener#vertexRemoved(GraphVertexChangeEvent)
     */
    public void vertexRemoved(GraphVertexChangeEvent<V> e)
    {
        init(); // for now invalidate cached results, in the future need to
                // amend them.
    }

    private void init()
    {
        connectedSets = null;
        vertexToConnectedSet = new HashMap<V, Set<V>>();
    }

    private List<Set<V>> lazyFindConnectedSets()
    {
        if (connectedSets == null) {
            connectedSets = new ArrayList<Set<V>>();

            Set<V> vertexSet = graph.vertexSet();

            if (vertexSet.size() > 0) {
                BreadthFirstIterator<V, E> i =
                    new BreadthFirstIterator<V, E>(graph, null);
                i.addTraversalListener(new MyTraversalListener());

                while (i.hasNext()) {
                    i.next();
                }
            }
        }

        return connectedSets;
    }

    //~ Inner Classes ----------------------------------------------------------

    /**
     * A traversal listener that groups all vertices according to to their
     * containing connected set.
     *
     * @author Barak Naveh
     * @since Aug 6, 2003
     */
    private class MyTraversalListener
        extends TraversalListenerAdapter<V, E>
    {
        private Set<V> currentConnectedSet;

        /**
         * @see TraversalListenerAdapter#connectedComponentFinished(ConnectedComponentTraversalEvent)
         */
        public void connectedComponentFinished(
            ConnectedComponentTraversalEvent e)
        {
            connectedSets.add(currentConnectedSet);
        }

        /**
         * @see TraversalListenerAdapter#connectedComponentStarted(ConnectedComponentTraversalEvent)
         */
        public void connectedComponentStarted(
            ConnectedComponentTraversalEvent e)
        {
            currentConnectedSet = new HashSet<V>();
        }

        /**
         * @see TraversalListenerAdapter#vertexTraversed(VertexTraversalEvent)
         */
        public void vertexTraversed(VertexTraversalEvent<V> e)
        {
            V v = e.getVertex();
            currentConnectedSet.add(v);
            vertexToConnectedSet.put(v, currentConnectedSet);
        }
    }
}

// End ConnectivityInspector.java