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/*
 * (C) Copyright 2003-2016, by John V Sichi and Contributors.
 *
 * JGraphT : a free Java graph-theory library
 *
 * This program and the accompanying materials are dual-licensed under
 * either
 *
 * (a) the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation, or (at your option) any
 * later version.
 *
 * or (per the licensee's choosing)
 *
 * (b) the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation.
 */
package org.jgrapht.graph;

import java.io.*;
import java.util.*;

import org.jgrapht.*;
import org.jgrapht.util.*;

/**
 * An undirected view of the backing directed graph specified in the constructor. This graph allows
 * modules to apply algorithms designed for undirected graphs to a directed graph by simply ignoring
 * edge direction. If the backing directed graph is an
 * oriented graph, then the view will
 * be a simple graph; otherwise, it will be a multigraph. Query operations on this graph "read
 * through" to the backing graph. Attempts to add edges will result in an
 * UnsupportedOperationException, but vertex addition/removal and edge removal are all
 * supported (and immediately reflected in the backing graph).
 *
 * 
 * Note that edges returned by this graph's accessors are really just the edges of the underlying
 * directed graph. Since there is no interface distinction between directed and undirected edges,
 * this detail should be irrelevant to algorithms.
 * 
 *
 * 
 * This graph does not pass the hashCode and equals operations through to the backing graph,
 * but relies on Object's equals and hashCode methods. This graph will be
 * serializable if the backing graph is serializable.
 * 
 *
 * @param  the graph vertex type
 * @param  the graph edge type
 *
 * @author John V. Sichi
 * @since Aug 14, 2003
 */
public class AsUndirectedGraph
    extends GraphDelegator
    implements Serializable, UndirectedGraph
{
    private static final long serialVersionUID = 3257845485078065462L; // @todo renew
    private static final String NO_EDGE_ADD = "this graph does not support edge addition";
    private static final String UNDIRECTED = "this graph only supports undirected operations";

    /**
     * Constructor for AsUndirectedGraph.
     *
     * @param g the backing directed graph over which an undirected view is to be created.
     */
    public AsUndirectedGraph(DirectedGraph g)
    {
        super(g);
    }

    /**
     * @see Graph#getAllEdges(Object, Object)
     */
    @Override
    public Set getAllEdges(V sourceVertex, V targetVertex)
    {
        Set forwardList = super.getAllEdges(sourceVertex, targetVertex);

        if (sourceVertex.equals(targetVertex)) {
            // avoid duplicating loops
            return forwardList;
        }

        Set reverseList = super.getAllEdges(targetVertex, sourceVertex);
        Set list = new ArrayUnenforcedSet<>(forwardList.size() + reverseList.size());
        list.addAll(forwardList);
        list.addAll(reverseList);

        return list;
    }

    /**
     * @see Graph#getEdge(Object, Object)
     */
    @Override
    public E getEdge(V sourceVertex, V targetVertex)
    {
        E edge = super.getEdge(sourceVertex, targetVertex);

        if (edge != null) {
            return edge;
        }

        // try the other direction
        return super.getEdge(targetVertex, sourceVertex);
    }

    /**
     * @see Graph#addEdge(Object, Object)
     */
    @Override
    public E addEdge(V sourceVertex, V targetVertex)
    {
        throw new UnsupportedOperationException(NO_EDGE_ADD);
    }

    /**
     * @see Graph#addEdge(Object, Object, Object)
     */
    @Override
    public boolean addEdge(V sourceVertex, V targetVertex, E e)
    {
        throw new UnsupportedOperationException(NO_EDGE_ADD);
    }

    /**
     * @see UndirectedGraph#degreeOf(Object)
     */
    @Override
    public int degreeOf(V vertex)
    {
        // this counts loops twice, which is consistent with AbstractBaseGraph
        return super.inDegreeOf(vertex) + super.outDegreeOf(vertex);
    }

    /**
     * @see DirectedGraph#inDegreeOf(Object)
     */
    @Override
    public int inDegreeOf(V vertex)
    {
        throw new UnsupportedOperationException(UNDIRECTED);
    }

    /**
     * @see DirectedGraph#incomingEdgesOf(Object)
     */
    @Override
    public Set incomingEdgesOf(V vertex)
    {
        throw new UnsupportedOperationException(UNDIRECTED);
    }

    /**
     * @see DirectedGraph#outDegreeOf(Object)
     */
    @Override
    public int outDegreeOf(V vertex)
    {
        throw new UnsupportedOperationException(UNDIRECTED);
    }

    /**
     * @see DirectedGraph#outgoingEdgesOf(Object)
     */
    @Override
    public Set outgoingEdgesOf(V vertex)
    {
        throw new UnsupportedOperationException(UNDIRECTED);
    }

    /**
     * @see AbstractBaseGraph#toString()
     */
    @Override
    public String toString()
    {
        return super.toStringFromSets(vertexSet(), edgeSet(), false);
    }
}

// End AsUndirectedGraph.java