/**

  * Copyright 2005-2011 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.rule.RuleDefinition;

 import org.kuali.rice.krms.framework.engine.Rule;

 import org.kuali.rice.krms.framework.type.RuleTypeService;

 import org.kuali.rice.krms.impl.type.KrmsTypeResolver;

 /**

  * TODO... 

  * 

  * @author Kuali Rice Team (rice.collab@kuali.org)

  *

  */

 final class LazyRule implements Rule {

         private final RuleDefinition ruleDefinition;

         private final KrmsTypeResolver typeResolver;

         private final Object mutex = new Object();

         // volatile for double-checked locking idiom

         private volatile Rule rule;

         LazyRule(RuleDefinition ruleDefinition, KrmsTypeResolver typeResolver) {

                 this.ruleDefinition = ruleDefinition;

                 this.typeResolver = typeResolver;

                 this.rule = null;

         }

         @Override

         public boolean evaluate(ExecutionEnvironment environment) {

                 return getRule().evaluate(environment);

         }

         /**

          * Gets the rule using a lazy double-checked locking mechanism as documented in Effective Java Item 71.

          */

         private Rule getRule() {

                 Rule localRule = rule;

                 if (localRule == null) {

                         synchronized (mutex) {

                                 localRule = rule;

                                 if (localRule == null) {

                                         rule = localRule = constructRule();

                                 }

                         }

                 }

                 return localRule;

         }

         private Rule constructRule() {

                 RuleTypeService ruleTypeService = typeResolver.getRuleTypeService(ruleDefinition);

                 Rule rule = ruleTypeService.loadRule(ruleDefinition);

                 if (rule == null) {

                         rule = new Rule() {

                                 @Override

                                 public boolean evaluate(ExecutionEnvironment environment) {

                     return false;

                                 }

                         };

                 }

                 return rule;

         }

 }