/**
    * 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.krms.impl.provider.repository;
  
  import org.kuali.rice.krms.api.engine.ExecutionEnvironment;
  import org.kuali.rice.krms.api.repository.action.ActionDefinition;
  import org.kuali.rice.krms.framework.engine.Action;
  import org.kuali.rice.krms.framework.type.ActionTypeService;
  import org.kuali.rice.krms.impl.type.KrmsTypeResolver;
  
  /**
   * An {@link Action} that doesn't load its members until execution.
   *
   * @author Kuali Rice Team (rice.collab@kuali.org)
   *
   */
  final class LazyAction implements Action {
  
  	private final ActionDefinition actionDefinition;
  	private final KrmsTypeResolver typeResolver;
  
  	private final Object mutex = new Object();
  	
  	// volatile for double-checked locking idiom
  	private volatile Action action;
  
      /**
       *
       * @param actionDefinition ActionDefinition
       * @param typeResolver KrmsTypeResolver
       */
  	LazyAction(ActionDefinition actionDefinition, KrmsTypeResolver typeResolver) {
  		this.actionDefinition = actionDefinition;
  		this.typeResolver = typeResolver;
  		this.action = null;
  	}
  	
  	@Override
  	public void execute(ExecutionEnvironment environment) {
  		getAction().execute(environment);
  	}
  
  	@Override
  	public void executeSimulation(ExecutionEnvironment environment) {
  		getAction().executeSimulation(environment);
  	}
  	
  	/**
  	 * Gets the action using a lazy double-checked locking mechanism as documented in Effective Java Item 71.
       * @return Action
  	 */
  	private Action getAction() {
  		Action localAction = action;
  		if (localAction == null) {
  			synchronized (mutex) {
  				localAction = action;
  				if (localAction == null) {
  					action = localAction = constructAction();
  				}
  			}
  		}
  		return localAction;
  	}
  
      /**
       * builder method
       * @return Action
       */
  	private Action constructAction() {
  		ActionTypeService actionTypeService = typeResolver.getActionTypeService(actionDefinition);
  		Action action = actionTypeService.loadAction(actionDefinition);
  		if (action == null) {
  			action = new Action() {
  				@Override
  				public void execute(ExecutionEnvironment environment) {
  				}
  				public void executeSimulation(ExecutionEnvironment environment) {
  				}
  			};
  		}
  		return action;
  	}
  
  	
  }