/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * The contents of this file are subject to the Netscape Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/NPL/
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express oqr
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is Netscape
 * Communications Corporation.  Portions created by Netscape are
 * Copyright (C) 1997-1999 Netscape Communications Corporation. All
 * Rights Reserved.
 *
 * Contributor(s):
 * Igor Bukanov
 *
 * Alternatively, the contents of this file may be used under the
 * terms of the GNU Public License (the "GPL"), in which case the
 * provisions of the GPL are applicable instead of those above.
 * If you wish to allow use of your version of this file only
 * under the terms of the GPL and not to allow others to use your
 * version of this file under the NPL, indicate your decision by
 * deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL.  If you do not delete
 * the provisions above, a recipient may use your version of this
 * file under either the NPL or the GPL.
 */

package org.mozilla.javascript;

import java.io.Serializable;

/**
 * Class instances represent serializable tags to mark special Object values.
 * <p>
 * Compatibility note: under jdk 1.1 use
 * org.mozilla.javascript.serialize.ScriptableInputStream to read serialized
 * instances of UniqueTag as under this JDK version the default
 * ObjectInputStream would not restore them correctly as it lacks support
 * for readResolve method
 */
public final class UniqueTag implements Serializable
{
    static final long serialVersionUID = -4320556826714577259L;

    private static final int ID_NOT_FOUND    = 1;
    private static final int ID_NULL_VALUE   = 2;
    private static final int ID_DOUBLE_MARK  = 3;

    /**
     * Tag to mark non-existing values.
     */
    public static final UniqueTag
        NOT_FOUND = new UniqueTag(ID_NOT_FOUND);

    /**
     * Tag to distinguish between uninitialized and null values.
     */
    public static final UniqueTag
        NULL_VALUE = new UniqueTag(ID_NULL_VALUE);

    /**
     * Tag to indicate that a object represents "double" with the real value
     * stored somewhere else.
     */
    public static final UniqueTag
        DOUBLE_MARK = new UniqueTag(ID_DOUBLE_MARK);

    private final int tagId;

    private UniqueTag(int tagId)
    {
        this.tagId = tagId;
    }

    public Object readResolve()
    {
        switch (tagId) {
          case ID_NOT_FOUND:
            return NOT_FOUND;
          case ID_NULL_VALUE:
            return NULL_VALUE;
          case ID_DOUBLE_MARK:
            return DOUBLE_MARK;
        }
        throw new IllegalStateException(String.valueOf(tagId));
    }

// Overridden for better debug printouts
    public String toString()
    {
        String name;
        switch (tagId) {
          case ID_NOT_FOUND:
            name = "NOT_FOUND";
            break;
          case ID_NULL_VALUE:
            name = "NULL_VALUE";
            break;
          case ID_DOUBLE_MARK:
            name = "DOUBLE_MARK";
            break;
          default:
            throw Kit.codeBug();
        }
        return super.toString()+": "+name;
    }

}

