/*
 * This file is part of the LibreOffice project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * This file incorporates work covered by the following license notice:
 *
 *   Licensed to the Apache Software Foundation (ASF) under one or more
 *   contributor license agreements. See the NOTICE file distributed
 *   with this work for additional information regarding copyright
 *   ownership. The ASF licenses this file to you under the Apache
 *   License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0 .
 */

package com.sun.star.uno;

import com.sun.star.uno.XWeak;
import com.sun.star.uno.UnoRuntime;
import com.sun.star.uno.XAdapter;
import com.sun.star.uno.XReference;

/** This class holds weak reference to an object. It actually holds a reference to a
    com.sun.star.XAdapter implementation and obtains a hard reference if necessary.
 */
public class WeakReference
{
    private final boolean DEBUG= false;
    private OWeakRefListener m_listener;
    // There is no default constructor. Every instance must register itself with the
    // XAdapter interface, which is done in the constructors. Assume we have this code
    // WeakReference ref= new WeakReference();
    // ref = someOtherWeakReference;
    //
    // ref would not be notified (XReference.dispose()) because it did not register
    // itself. Therefore the XAdapter would be kept aliver although this is not
    // necessary.

    /** Creates an instance of this class.
     *@param obj - another instance that is to be copied
     */
    public WeakReference(WeakReference obj)
    {
        if (obj != null)
        {
            Object weakImpl= obj.get();
            if (weakImpl != null)
            {
                XWeak weak= UnoRuntime.queryInterface(XWeak.class, weakImpl);
                if (weak != null)
                {
                    XAdapter adapter= weak.queryAdapter();
                    if (adapter != null)
                        m_listener= new OWeakRefListener(adapter);
                }
            }
        }
    }

    /** Creates an instance of this class.
     *@param obj XWeak implementation
     */
    public WeakReference(Object obj)
    {
        XWeak weak= UnoRuntime.queryInterface(XWeak.class, obj);
        if (weak != null)
        {
            XAdapter adapter= weak.queryAdapter();
            if (adapter != null)
                m_listener= new OWeakRefListener(adapter);
        }
    }
    /** Returns a hard reference to the object that is kept weak by this class.
     *@return a hard reference to the XWeak implementation.
     */
    public Object get()
    {
        if (m_listener != null)
            return m_listener.get();
        return null;
    }
}

/** Implementation of com.sun.star.uno.XReference for use with WeakReference.
 *  It keeps the XAdapter implementation and registers always with it. Deregistering
 *  occurs on notification by the adapter and the adapter is released.
 */
class OWeakRefListener implements XReference
{
    private final boolean DEBUG= false;
    private XAdapter m_adapter;

    /** The constructor registered this object with adapter.
     *@param adapter the XAdapter implementation.
     */
    OWeakRefListener( XAdapter adapter)
    {
        m_adapter= adapter;
        m_adapter.addReference(this);
    }
    /** Method of com.sun.star.uno.XReference. When called, it deregisteres this
     *  object with the adapter and releases the reference to it.
     */
    synchronized public void dispose()
    {
        if (m_adapter != null)
        {
            m_adapter.removeReference(this);
            m_adapter= null;
        }
    }

    /** Obtains a hard reference to the object which is kept weak by the adapter
     *  and returns it.
     *  @return hard reference to the otherwise weakly kept object.
     */
    synchronized Object get()
    {
        Object retVal= null;
        if (m_adapter != null)
        {
            retVal= m_adapter.queryAdapted();
            if (retVal == null)
            {
                // If this object registered as listener with XAdapter while it was notifying
                // the listeners then this object might not have been notified. If queryAdapted
                // returned null then the weak kept object is dead and the listeners have already
                // been notified. And we missed it.
                m_adapter.removeReference(this);
                m_adapter= null;
            }
        }
        return retVal;
    }
}