/*******************************************************************************
 * Copyright (c) 2013 Philip Collin.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the GNU Public License v3.0
 * which accompanies this distribution, and is available at
 * http://www.gnu.org/licenses/gpl.html
 * 
 * Contributors:
 *     Philip Collin - initial API and implementation
 ******************************************************************************/
package PaulChew;
/*
 * Copyright (c) 2007 by L. Paul Chew.
 *
 * Permission is hereby granted, without written agreement and without
 * license or royalty fees, to use, copy, modify, and distribute this
 * software and its documentation for any purpose, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

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

/**
 * Straightforward undirected graph implementation.
 * Nodes are generic type N.
 *
 * @author Paul Chew
 *
 * Created November, December 2007.  For use in Delaunay/Voronoi code.
 *
 */
public class Graph<N> {

    private Map<N, Set<N>> theNeighbors =    // Node -> adjacent nodes
        new HashMap<N, Set<N>>();
    private Set<N> theNodeSet =              // Set view of all nodes
        Collections.unmodifiableSet(theNeighbors.keySet());

    /**
     * Add a node.  If node is already in graph then no change.
     * @param node the node to add
     */
    public void add (N node) {
        if (theNeighbors.containsKey(node)) return;
        theNeighbors.put(node, new ArraySet<N>());
     }

    /**
     * Add a link. If the link is already in graph then no change.
     * @param nodeA one end of the link
     * @param nodeB the other end of the link
     * @throws NullPointerException if either endpoint is not in graph
     */
    public void add (N nodeA, N nodeB) throws NullPointerException {
        theNeighbors.get(nodeA).add(nodeB);
        theNeighbors.get(nodeB).add(nodeA);
    }

    /**
     * Remove node and any links that use node. If node not in graph, nothing
     * happens.
     * @param node the node to remove.
     */
    public void remove (N node) {
        if (!theNeighbors.containsKey(node)) return;
        for (N neighbor: theNeighbors.get(node))
            theNeighbors.get(neighbor).remove(node);    // Remove "to" links
        theNeighbors.get(node).clear();                 // Remove "from" links
        theNeighbors.remove(node);                      // Remove the node
    }

    /**
     * Remove the specified link. If link not in graph, nothing happens.
     * @param nodeA one end of the link
     * @param nodeB the other end of the link
     * @throws NullPointerException if either endpoint is not in graph
     */
    public void remove (N nodeA, N nodeB) throws NullPointerException {
        theNeighbors.get(nodeA).remove(nodeB);
        theNeighbors.get(nodeB).remove(nodeA);
    }

    /**
     * Report all the neighbors of node.
     * @param node the node
     * @return the neighbors of node
     * @throws NullPointerException if node does not appear in graph
     */
    public Set<N> neighbors (N node) throws NullPointerException {
        return Collections.unmodifiableSet(theNeighbors.get(node));
    }

    /**
     * Returns an unmodifiable Set view of the nodes contained in this graph.
     * The set is backed by the graph, so changes to the graph are reflected in
     * the set.
     * @return a Set view of the graph's node set
     */
    public Set<N> nodeSet () {
        return theNodeSet;
    }

}