/*
 * @(#)StateEdit.java	1.10 00/02/02
 *
 * Copyright 1997-2000 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

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
 *
 * @version 1.10 02/02/00
 * @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 preState;

    /**
     * The state information after the edit
     */
    protected Hashtable 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(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(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 uselessKeys = new Vector();
	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