/*

  * Copyright 2007 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.kew.rule;

 import org.kuali.rice.kew.api.WorkflowRuntimeException;

 import org.kuali.rice.kew.engine.RouteContext;

 import org.kuali.rice.kew.exception.WorkflowException;

 import org.kuali.rice.kew.service.KEWServiceLocator;

 import javax.script.ScriptEngine;

 import javax.script.ScriptEngineManager;

 import javax.script.ScriptException;

 /**

  * A rule expression implementation that uses Bean Scripting Framework.

  * The language is given by the type qualifier, e.g.:

  * <expression type="BSF:groovy">...

  *

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

  */

 //TODO: this should really be renamed since it is no longer using apache BSF

 public class BSFRuleExpression implements RuleExpression {

     public RuleExpressionResult evaluate(Rule rule, RouteContext context) throws WorkflowException {

         RuleBaseValues ruleDefinition = rule.getDefinition();

         String type = ruleDefinition.getRuleExpressionDef().getType();

         String lang = parseLang(type, "groovy");

         String expression = ruleDefinition.getRuleExpressionDef().getExpression();

         RuleExpressionResult result;

         ScriptEngineManager factory = new ScriptEngineManager();

         ScriptEngine engine = factory.getEngineByName(lang);

         try {

             declareBeans(engine, rule, context);

             result = (RuleExpressionResult) engine.eval(expression);

         } catch (ScriptException e) {

             throw new WorkflowException("Error evaluating " + type + " expression: '" + expression + "'", e);

         }

         if (result == null) {

             return new RuleExpressionResult(rule, false);

         } else {

             return result;

         }

     }

     /**

      * Parses the language component from the type string

      * @param type the type string

      * @param deflt the default language if none is present in the type string

      * @return the language component or null

      */

     protected String parseLang(String type, String deflt) {

         int colon = type.indexOf(':');

         if (colon > -1) {

             return type.substring(colon + 1);

         } else {

             return deflt;

         }

     }

     /**

      * Populates the BSFManager with beans that are accessible to BSF scripts.  May be overridden by

      * subclasses.  The standard implementation exposes the rule and routeContext

      * @param manager the BSFManager

      * @param rule the current Rule object

      * @param context the current RouteContext

      */

     protected void declareBeans(ScriptEngine engine, Rule rule, RouteContext context) throws ScriptException {

         engine.put("rule", rule);

         engine.put("routeContext", context);

         engine.put("workflow", new WorkflowRuleAPI(context));

     }

     /**

      * A helper bean that is declared for use by BSF scripts.

      * This functionality should really be part of a single internal API that can be exposed

      * to various pieces of code that are plugged into KEW.  For comparison EDocLite also

      * has its own such API that it exposes. 

      */

     protected static final class WorkflowRuleAPI {

         private final RouteContext context;

         WorkflowRuleAPI(RouteContext context) {

             this.context = context;

         }

         /**

          * Evaluates a named rule

          * @param name the rule name

          * @return the RuleExpressionResult

          * @throws WorkflowException 

          */

         public RuleExpressionResult invokeRule(String name) throws WorkflowException {

             RuleBaseValues rbv = KEWServiceLocator.getRuleService().getRuleByName(name);

             if (rbv == null) throw new WorkflowRuntimeException("Could not find rule named \"" + name + "\"");

             Rule r = new RuleImpl(rbv);

             return r.evaluate(r, context);

         }

     }

 }