/*

  * 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.myfaces.el.unified.resolver;

 import javax.el.ELContext;

 import javax.el.ELException;

 import javax.el.PropertyNotFoundException;

 import javax.faces.FacesException;

 import javax.faces.context.ExternalContext;

 import javax.faces.context.FacesContext;

 import org.apache.myfaces.config.element.ManagedBean;

 import com.google.inject.Injector;

 /**

  * <p>Register this ELResolver in faces-config.xml.</p>

  * 

  *     &ltapplication>

  *        &ltel-resolver>org.apache.myfaces.el.unified.resolver.GuiceResolver&lt/el-resolver>

  *    &lt/application>

  *

  * <p>Implement and configure a ServletContextListener in web.xml .</p>

  * 

  *  &ltlistener>

  *      <listener-class>com.your_company.GuiceServletContextListener&lt/listener-class>

  *  &lt/listener>

  * 

  * <p>Configure Guice in your ServletContextListener implementation, and place the 

  * Injector in application scope.</p>

  * 

  * public class GuiceServletContextListener implements ServletContextListener {

  *

  *    public void contextInitialized(ServletContextEvent event) {

  *        ServletContext ctx = event.getServletContext();

  *              //when on Java6, use ServiceLoader.load(com.google.inject.Module.class);

  *        Injector injector = Guice.createInjector(new YourModule());

  *        ctx.setAttribute(GuiceResolver.KEY, injector);

  *    }

  *

  *    public void contextDestroyed(ServletContextEvent event) {

  *        ServletContext ctx = event.getServletContext();

  *        ctx.removeAttribute(GuiceResolver.KEY);

  *    }

  *

  *}

  * 

  * @author Dennis Byrne

  */

 public class GuiceResolver extends ManagedBeanResolver {

     public static final String KEY = "oam." + Injector.class.getName();

     @Override

     public Object getValue(ELContext ctx, Object base, Object property) 

         throws NullPointerException, PropertyNotFoundException, ELException {

         if (base != null || !(property instanceof String)) 

             return null;

         if (property == null)

             throw new PropertyNotFoundException();

         FacesContext fctx = (FacesContext) ctx.getContext(FacesContext.class);

         if(fctx == null)

             return null;

         ExternalContext ectx = fctx.getExternalContext();

         if (ectx == null || 

             ectx.getRequestMap().containsKey(property) || 

             ectx.getSessionMap().containsKey(property) ||

             ectx.getApplicationMap().containsKey(property) ) 

             return null;

         ManagedBean managedBean = runtimeConfig(ctx).getManagedBean((String)property);

         return managedBean == null ? null : getValue(ctx, ectx, managedBean.getManagedBeanClass());

     }

     private Object getValue(ELContext ctx, ExternalContext ectx, Class managedBeanClass) {

         Injector injector = (Injector) ectx.getApplicationMap().get(KEY);

         if(injector == null)

             throw new FacesException("Could not find an instance of " + Injector.class.getName() 

                     + " in application scope using key '" + KEY + "'");

         Object value = injector.getInstance(managedBeanClass);

         ctx.setPropertyResolved(true);

         return value;

     }

 }