/*

 * Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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 General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package javax.imageio.spi;

import java.io.Serializable;

import java.util.HashSet;

import java.util.Iterator;

import java.util.Set;

/**

 * A node in a directed graph.  In addition to an arbitrary

 * {@code Object} containing user data associated with the node,

 * each node maintains a {@code Set}s of nodes which are pointed

 * to by the current node (available from {@code getOutNodes}).

 * The in-degree of the node (that is, number of nodes that point to

 * the current node) may be queried.

 *

 */

class DigraphNode<E> implements Cloneable, Serializable {

    private static final long serialVersionUID = 5308261378582246841L;

    /** The data associated with this node. */

    protected E data;

    /**

     * A {@code Set} of neighboring nodes pointed to by this

     * node.

     */

    protected Set<DigraphNode<E>> outNodes = new HashSet<>();

    /** The in-degree of the node. */

    protected int inDegree = 0;

    /**

     * A {@code Set} of neighboring nodes that point to this

     * node.

     */

    private Set<DigraphNode<E>> inNodes = new HashSet<>();

    public DigraphNode(E data) {

        this.data = data;

    }

    /** Returns the {@code Object} referenced by this node. */

    public E getData() {

        return data;

    }

    /**

     * Returns an {@code Iterator} containing the nodes pointed

     * to by this node.

     */

    public Iterator<DigraphNode<E>> getOutNodes() {

        return outNodes.iterator();

    }

    /**

     * Adds a directed edge to the graph.  The outNodes list of this

     * node is updated and the in-degree of the other node is incremented.

     *

     * @param node a {@code DigraphNode}.

     *

     * @return {@code true} if the node was not previously the

     * target of an edge.

     */

    public boolean addEdge(DigraphNode<E> node) {

        if (outNodes.contains(node)) {

            return false;

        }

        outNodes.add(node);

        node.inNodes.add(this);

        node.incrementInDegree();

        return true;

    }

    /**

     * Returns {@code true} if an edge exists between this node

     * and the given node.

     *

     * @param node a {@code DigraphNode}.

     *

     * @return {@code true} if the node is the target of an edge.

     */

    public boolean hasEdge(DigraphNode<E> node) {

        return outNodes.contains(node);

    }

    /**

     * Removes a directed edge from the graph.  The outNodes list of this

     * node is updated and the in-degree of the other node is decremented.

     *

     * @return {@code true} if the node was previously the target

     * of an edge.

     */

    public boolean removeEdge(DigraphNode<E> node) {

        if (!outNodes.contains(node)) {

            return false;

        }

        outNodes.remove(node);

        node.inNodes.remove(this);

        node.decrementInDegree();

        return true;

    }

    /**

     * Removes this node from the graph, updating neighboring nodes

     * appropriately.

     */

    public void dispose() {

        Object[] inNodesArray = inNodes.toArray();

        for(int i=0; i<inNodesArray.length; i++) {

            @SuppressWarnings("unchecked")

            DigraphNode<E> node = (DigraphNode<E>)inNodesArray[i];

            node.removeEdge(this);

        }

        Object[] outNodesArray = outNodes.toArray();

        for(int i=0; i<outNodesArray.length; i++) {

            @SuppressWarnings("unchecked")

            DigraphNode<E> node = (DigraphNode<E>)outNodesArray[i];

            removeEdge(node);

        }

    }

    /** Returns the in-degree of this node. */

    public int getInDegree() {

        return inDegree;

    }

    /** Increments the in-degree of this node. */

    private void incrementInDegree() {

        ++inDegree;

    }

    /** Decrements the in-degree of this node. */

    private void decrementInDegree() {

        --inDegree;

    }

}