/**
    * Copyright 2005-2012 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.messaging;
  
  import org.apache.commons.lang.StringUtils;
  import org.apache.log4j.Logger;
  import org.kuali.rice.core.api.resourceloader.GlobalResourceLoader;
  
  import javax.xml.namespace.QName;
  import java.lang.reflect.InvocationHandler;
  import java.lang.reflect.Method;
  import java.lang.reflect.Proxy;
  
  /**
   * This class creates a proxy for services deployed on KSB. A 
   * reference to the service is obtained only upon the first method
   * invocation.
   * 
   * @author Kuali Rice Team (rice.collab@kuali.org)
   *
   */
  public class KSBClientProxy implements InvocationHandler {
  
  private static final Logger LOG = Logger.getLogger(KSBClientProxy.class);
      
      private QName serviceName;
      private volatile Object service;
  
  
      public static <T> T newInstance(String serviceQName, Class<T> interfaceClass) throws InstantiationException, IllegalAccessException {
          if (StringUtils.isBlank(serviceQName)) {
              throw new IllegalArgumentException("the qname was blank");
          }
  
          if (interfaceClass == null) {
              throw new IllegalArgumentException("the interfaceClass was null");
          }
  
          @SuppressWarnings("unchecked")
          final T t = (T)Proxy.newProxyInstance(interfaceClass.getClassLoader(), new Class[] { interfaceClass }, new KSBClientProxy(serviceQName));
          return t;
      }
  
      public KSBClientProxy(String serviceQName){
          if (StringUtils.isBlank(serviceQName)) {
              throw new IllegalArgumentException("the qname was blank");
          }
  
          this.serviceName = QName.valueOf(serviceQName);
      }
      
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
          //using DCL idiom
          //see effective java 2nd ed. pg. 71
          Object s = service;
          if (s == null) {
              synchronized (this) {
                  s = service;
                  if (s == null) {
                      service = s = GlobalResourceLoader.getService(serviceName);
                  }
              }
          }
  
          if (s != null) {
              return method.invoke(s, args);
          }
  
          LOG.warn("serviceName: " + serviceName + " was not found");
          return null;
      }
  }