/*
 * 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
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.felix.http.proxy;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionIdListener;
import javax.servlet.http.HttpSessionListener;

import org.apache.felix.http.proxy.impl.EventDispatcherTracker;
import org.osgi.framework.BundleContext;

/**
 * The <code>ProxyListener</code> implements a Servlet API listener for HTTP
 * Session related events. These events are provided by the servlet container
 * and forwarded to the event dispatcher.
 *
 * @since 3.1.0
 */
public abstract class AbstractProxyListener
    implements HttpSessionListener,
               HttpSessionIdListener,
               HttpSessionAttributeListener,
               ServletContextAttributeListener
{

    private static final String ATTR_BUNDLE_CONTEXT = BundleContext.class.getName();
    
    // ---------- HttpSessionListener

    @Override
    public void sessionCreated(final HttpSessionEvent se)
    {
        final HttpSessionListener sessionDispatcher = getSessionDispatcher();
        if (sessionDispatcher != null)
        {
            sessionDispatcher.sessionCreated(se);
        }
    }

    @Override
    public void sessionDestroyed(final HttpSessionEvent se)
    {
        final HttpSessionListener sessionDispatcher = getSessionDispatcher();
        if (sessionDispatcher != null)
        {
            sessionDispatcher.sessionDestroyed(se);
        }
    }

    // ---------- HttpSessionIdListener

    @Override
    public void sessionIdChanged(final HttpSessionEvent event, final String oldSessionId)
    {
        final HttpSessionIdListener sessionIdDispatcher = getSessionIdDispatcher();
        if (sessionIdDispatcher != null)
        {
            sessionIdDispatcher.sessionIdChanged(event, oldSessionId);
        }
    }

    // ---------- HttpSessionAttributeListener

    @Override
    public void attributeAdded(final HttpSessionBindingEvent se)
    {
        final HttpSessionAttributeListener attributeDispatcher = getAttributeDispatcher();
        if (attributeDispatcher != null)
        {
            attributeDispatcher.attributeAdded(se);
        }
    }

    @Override
    public void attributeRemoved(final HttpSessionBindingEvent se)
    {
        final HttpSessionAttributeListener attributeDispatcher = getAttributeDispatcher();
        if (attributeDispatcher != null)
        {
            attributeDispatcher.attributeRemoved(se);
        }
    }

    @Override
    public void attributeReplaced(final HttpSessionBindingEvent se)
    {
        final HttpSessionAttributeListener attributeDispatcher = getAttributeDispatcher();
        if (attributeDispatcher != null)
        {
            attributeDispatcher.attributeReplaced(se);
        }
    }

    // ServletContextAttributeListener
    
    @Override
    public void attributeAdded(final ServletContextAttributeEvent event)
    {
        if ( event.getName().equals(ATTR_BUNDLE_CONTEXT) )
        {
            startTracking(event.getValue());
        }
    }

    @Override
    public void attributeRemoved(final ServletContextAttributeEvent event)
    {
        if ( event.getName().equals(ATTR_BUNDLE_CONTEXT) )
        {
            stopTracking();
        }
    }

    @Override
    public void attributeReplaced(final ServletContextAttributeEvent event)
    {
        if ( event.getName().equals(ATTR_BUNDLE_CONTEXT) )
        {
            stopTracking();
            startTracking(event.getServletContext().getAttribute(event.getName()));
        }
    }
    
    // ---------- internal

    protected abstract EventDispatcherTracker getEventDispatcherTracker();
    
    protected abstract void stopTracking();
    
    protected abstract void startTracking(Object bundleContext);
    
    private HttpSessionListener getSessionDispatcher()
    {
        final EventDispatcherTracker eventDispatcherTracker = getEventDispatcherTracker();
        if (eventDispatcherTracker != null)
        {
            return eventDispatcherTracker.getHttpSessionListener();
        }
        return null;
    }

    private HttpSessionIdListener getSessionIdDispatcher()
    {
        final EventDispatcherTracker eventDispatcherTracker = getEventDispatcherTracker();
        if (eventDispatcherTracker != null)
        {
            return eventDispatcherTracker.getHttpSessionIdListener();
        }
        return null;
    }

    private HttpSessionAttributeListener getAttributeDispatcher()
    {
        final EventDispatcherTracker eventDispatcherTracker = getEventDispatcherTracker();
        if (eventDispatcherTracker != null)
        {
            return eventDispatcherTracker.getHttpSessionAttributeListener();
        }
        return null;
    }
}