/*

 * Copyright (c) 1997, 2008, 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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 * questions.

 */

package javax.swing.undo;

import java.util.Enumeration;

import java.util.Hashtable;

import java.util.Vector;

/**

 * <P>StateEdit is a general edit for objects that change state.

 * Objects being edited must conform to the StateEditable interface.</P>

 *

 * <P>This edit class works by asking an object to store it's state in

 * Hashtables before and after editing occurs.  Upon undo or redo the

 * object is told to restore it's state from these Hashtables.</P>

 *

 * A state edit is used as follows:

 * <PRE>

 *      // Create the edit during the "before" state of the object

 *      StateEdit newEdit = new StateEdit(myObject);

 *      // Modify the object

 *      myObject.someStateModifyingMethod();

 *      // "end" the edit when you are done modifying the object

 *      newEdit.end();

 * </PRE>

 *

 * <P><EM>Note that when a StateEdit ends, it removes redundant state from

 * the Hashtables - A state Hashtable is not guaranteed to contain all

 * keys/values placed into it when the state is stored!</EM></P>

 *

 * @see StateEditable

 *

 * @author Ray Ryan

 */

public class StateEdit

        extends AbstractUndoableEdit {

    protected static final String RCSID = "$Id: StateEdit.java,v 1.6 1997/10/01 20:05:51 sandipc Exp $";

    //

    // Attributes

    //

    /**

     * The object being edited

     */

    protected StateEditable object;

    /**

     * The state information prior to the edit

     */

    protected Hashtable<Object,Object> preState;

    /**

     * The state information after the edit

     */

    protected Hashtable<Object,Object> postState;

    /**

     * The undo/redo presentation name

     */

    protected String undoRedoName;

    //

    // Constructors

    //

    /**

     * Create and return a new StateEdit.

     *

     * @param anObject The object to watch for changing state

     *

     * @see StateEdit

     */

    public StateEdit(StateEditable anObject) {

        super();

        init (anObject,null);

    }

    /**

     * Create and return a new StateEdit with a presentation name.

     *

     * @param anObject The object to watch for changing state

     * @param name The presentation name to be used for this edit

     *

     * @see StateEdit

     */

    public StateEdit(StateEditable anObject, String name) {

        super();

        init (anObject,name);

    }

    protected void init (StateEditable anObject, String name) {

        this.object = anObject;

        this.preState = new Hashtable<Object, Object>(11);

        this.object.storeState(this.preState);

        this.postState = null;

        this.undoRedoName = name;

    }

    //

    // Operation

    //

    /**

     * Gets the post-edit state of the StateEditable object and

     * ends the edit.

     */

    public void end() {

        this.postState = new Hashtable<Object, Object>(11);

        this.object.storeState(this.postState);

        this.removeRedundantState();

    }

    /**

     * Tells the edited object to apply the state prior to the edit

     */

    public void undo() {

        super.undo();

        this.object.restoreState(preState);

    }

    /**

     * Tells the edited object to apply the state after the edit

     */

    public void redo() {

        super.redo();

        this.object.restoreState(postState);

    }

    /**

     * Gets the presentation name for this edit

     */

    public String getPresentationName() {

        return this.undoRedoName;

    }

    //

    // Internal support

    //

    /**

     * Remove redundant key/values in state hashtables.

     */

    protected void removeRedundantState() {

        Vector<Object> uselessKeys = new Vector<Object>();

        Enumeration myKeys = preState.keys();

        // Locate redundant state

        while (myKeys.hasMoreElements()) {

            Object myKey = myKeys.nextElement();

            if (postState.containsKey(myKey) &&

                postState.get(myKey).equals(preState.get(myKey))) {

                uselessKeys.addElement(myKey);

            }

        }

        // Remove redundant state

        for (int i = uselessKeys.size()-1; i >= 0; i--) {

            Object myKey = uselessKeys.elementAt(i);

            preState.remove(myKey);

            postState.remove(myKey);

        }

    }

} // End of class StateEdit