/**
    * 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;
  	}
  
  	
  }