/*

 * Copyright (c) 2000, 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

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 */

package javax.imageio.spi;

import java.util.AbstractSet;

import java.util.HashMap;

import java.util.Iterator;

import java.util.LinkedList;

import java.util.Map;

import java.util.Set;

/**

 * A set of <code>Object</code>s with pairwise orderings between them.

 * The <code>iterator</code> method provides the elements in

 * topologically sorted order.  Elements participating in a cycle

 * are not returned.

 *

 * Unlike the <code>SortedSet</code> and <code>SortedMap</code>

 * interfaces, which require their elements to implement the

 * <code>Comparable</code> interface, this class receives ordering

 * information via its <code>setOrdering</code> and

 * <code>unsetPreference</code> methods.  This difference is due to

 * the fact that the relevant ordering between elements is unlikely to

 * be inherent in the elements themselves; rather, it is set

 * dynamically accoring to application policy.  For example, in a

 * service provider registry situation, an application might allow the

 * user to set a preference order for service provider objects

 * supplied by a trusted vendor over those supplied by another.

 *

 */

class PartiallyOrderedSet extends AbstractSet {

    // The topological sort (roughly) follows the algorithm described in

    // Horowitz and Sahni, _Fundamentals of Data Structures_ (1976),

    // p. 315.

    // Maps Objects to DigraphNodes that contain them

    private Map poNodes = new HashMap();

    // The set of Objects

    private Set nodes = poNodes.keySet();

    /**

     * Constructs a <code>PartiallyOrderedSet</code>.

     */

    public PartiallyOrderedSet() {}

    public int size() {

        return nodes.size();

    }

    public boolean contains(Object o) {

        return nodes.contains(o);

    }

    /**

     * Returns an iterator over the elements contained in this

     * collection, with an ordering that respects the orderings set

     * by the <code>setOrdering</code> method.

     */

    public Iterator iterator() {

        return new PartialOrderIterator(poNodes.values().iterator());

    }

    /**

     * Adds an <code>Object</code> to this

     * <code>PartiallyOrderedSet</code>.

     */

    public boolean add(Object o) {

        if (nodes.contains(o)) {

            return false;

        }

        DigraphNode node = new DigraphNode(o);

        poNodes.put(o, node);

        return true;

    }

    /**

     * Removes an <code>Object</code> from this

     * <code>PartiallyOrderedSet</code>.

     */

    public boolean remove(Object o) {

        DigraphNode node = (DigraphNode)poNodes.get(o);

        if (node == null) {

            return false;

        }

        poNodes.remove(o);

        node.dispose();

        return true;

    }

    public void clear() {

        poNodes.clear();

    }

    /**

     * Sets an ordering between two nodes.  When an iterator is

     * requested, the first node will appear earlier in the

     * sequence than the second node.  If a prior ordering existed

     * between the nodes in the opposite order, it is removed.

     *

     * @return <code>true</code> if no prior ordering existed

     * between the nodes, <code>false</code>otherwise.

     */

    public boolean setOrdering(Object first, Object second) {

        DigraphNode firstPONode =

            (DigraphNode)poNodes.get(first);

        DigraphNode secondPONode =

            (DigraphNode)poNodes.get(second);

        secondPONode.removeEdge(firstPONode);

        return firstPONode.addEdge(secondPONode);

    }

    /**

     * Removes any ordering between two nodes.

     *

     * @return true if a prior prefence existed between the nodes.

     */

    public boolean unsetOrdering(Object first, Object second) {

        DigraphNode firstPONode =

            (DigraphNode)poNodes.get(first);

        DigraphNode secondPONode =

            (DigraphNode)poNodes.get(second);

        return firstPONode.removeEdge(secondPONode) ||

            secondPONode.removeEdge(firstPONode);

    }

    /**

     * Returns <code>true</code> if an ordering exists between two

     * nodes.

     */

    public boolean hasOrdering(Object preferred, Object other) {

        DigraphNode preferredPONode =

            (DigraphNode)poNodes.get(preferred);

        DigraphNode otherPONode =

            (DigraphNode)poNodes.get(other);

        return preferredPONode.hasEdge(otherPONode);

    }

}

class PartialOrderIterator implements Iterator {

    LinkedList zeroList = new LinkedList();

    Map inDegrees = new HashMap(); // DigraphNode -> Integer

    public PartialOrderIterator(Iterator iter) {

        // Initialize scratch in-degree values, zero list

        while (iter.hasNext()) {

            DigraphNode node = (DigraphNode)iter.next();

            int inDegree = node.getInDegree();

            inDegrees.put(node, new Integer(inDegree));

            // Add nodes with zero in-degree to the zero list

            if (inDegree == 0) {

                zeroList.add(node);

            }

        }

    }

    public boolean hasNext() {

        return !zeroList.isEmpty();

    }

    public Object next() {

        DigraphNode first = (DigraphNode)zeroList.removeFirst();

        // For each out node of the output node, decrement its in-degree

        Iterator outNodes = first.getOutNodes();

        while (outNodes.hasNext()) {

            DigraphNode node = (DigraphNode)outNodes.next();

            int inDegree = ((Integer)inDegrees.get(node)).intValue() - 1;

            inDegrees.put(node, new Integer(inDegree));

            // If the in-degree has fallen to 0, place the node on the list

            if (inDegree == 0) {

                zeroList.add(node);

            }

        }

        return first.getData();

    }

    public void remove() {

        throw new UnsupportedOperationException();

    }

}