/**
    * Copyright 2005-2013 The Kuali Foundation
    *
    * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
    *
   * 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.kuali.rice.ksb.api.bus.support;
  
  import org.apache.commons.lang.ArrayUtils;
  import org.apache.commons.lang.StringUtils;
  import org.kuali.rice.core.api.resourceloader.GlobalResourceLoader;
  import org.kuali.rice.core.api.resourceloader.ResourceLoaderException;
  import org.kuali.rice.ksb.api.KsbApiServiceLocator;
  import org.springframework.beans.factory.FactoryBean;
  import org.springframework.beans.factory.FactoryBeanNotInitializedException;
  import org.springframework.beans.factory.InitializingBean;
  
  import javax.xml.namespace.QName;
  import java.lang.reflect.InvocationHandler;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.lang.reflect.Proxy;
  
  /**
   * Loads a lazy proxy to a service from the {@link org.kuali.rice.ksb.api.bus.ServiceBus}.  This proxy is created based on either the
   * proxy interfaces that are injected into this bean, or derived from the objectType which is injected into this bean.
   * If neither of these are injected, then an exception will be through during bean initialization.
   *
   * The attempt to fetch the resource from the ServiceBus won't be attempted until a method on the resulting
   * proxy is invoked.  If it fails to locate the resource, it will throw a ResourceLoaderException indicating the service
   * could not be loaded.
   *
   * <p>This allows for referencing of a potentially remote service in the spring context during startup which won't get
   * used until after startup.  If the remote service gets used *during* startup, then it must be available from the GRL
   * during startup or else the ResourceLoaderException will be thrown.</p>
   *
   * @author Kuali Rice Team (rice.collab@kuali.org)
   *
   */
  public class LazyServiceFactoryBean implements FactoryBean<Object>, InitializingBean {
  
      private String serviceNamespace;
  	private String serviceName;
      private String applicationId;
      private Class<?> objectType;
      private Class<?>[] proxyInterfaces;
      private Object proxyObject;
  
  	public LazyServiceFactoryBean() {
          this.objectType = Object.class;
          this.proxyInterfaces = null;
  	}
  
      public void afterPropertiesSet() throws Exception {
          if (ArrayUtils.isEmpty(getProxyInterfaces())) {
              setProxyInterfaces(detectProxyInterfaces());
              if (ArrayUtils.isEmpty(getProxyInterfaces())) {
                  throw new FactoryBeanNotInitializedException("Failed to initialize factory bean because " +
                          "proxyInterfaces were not injected or could not be derived from object type.");
              }
          }
          this.proxyObject = Proxy.newProxyInstance(getClass().getClassLoader(), getProxyInterfaces(),
                  new LazyInvocationHandler());
  	}
  
      protected Class<?>[] detectProxyInterfaces() {
          Class<?> type = getObjectType();
          if (type != null && type.isInterface()) {
              return new Class<?>[] {type};
          } else if (type != null) {
              return type.getInterfaces();
          } else {
              return null;
          }
      }
  
      @Override
      public Object getObject() throws Exception {
          return this.proxyObject;
      }
  
      @Override
      public Class<?> getObjectType() {
          return this.objectType;
      }
  
      public void setObjectType(Class<?> objectType) {
          this.objectType = objectType;
      }
  
     @Override
     public boolean isSingleton() {
         return true;
     }
 
     public String getServiceNamespace() {
         return serviceNamespace;
     }
 
     public void setServiceNamespace(String serviceNamespace) {
         this.serviceNamespace = serviceNamespace;
     }
 
     public String getServiceName() {
         return serviceName;
     }
 
     public void setServiceName(String serviceName) {
         this.serviceName = serviceName;
     }
 
     public String getApplicationId() {
         return applicationId;
     }
 
     public void setApplicationId(String applicationId) {
         this.applicationId = applicationId;
     }
 
     public Class<?>[] getProxyInterfaces() {
         return proxyInterfaces;
     }
 
     public void setProxyInterfaces(Class<?>[] proxyInterfaces) {
         this.proxyInterfaces = proxyInterfaces;
     }
 
     private class LazyInvocationHandler implements InvocationHandler {
         private volatile Object service = null;
         public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
             try {
                 if (service == null) {
                     QName name = new QName(getServiceNamespace(), getServiceName());
                     if (StringUtils.isNotBlank(getApplicationId())) {
                         service = KsbApiServiceLocator.getServiceBus().getService(name, getApplicationId());
                     } else {
                         service = KsbApiServiceLocator.getServiceBus().getService(name);
                     }
                     if (service == null) {
                         throw new ResourceLoaderException("Failed to locate resource with name: " + name);
                     }
                 }
                 return method.invoke(service, args);
             } catch (InvocationTargetException e) {
                 throw e.getTargetException();
             }
         }
 
     }
 
 }