/**
    * 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.kew.rule;
  
  import java.text.ParseException;
  
  import org.apache.commons.lang.StringUtils;
  import org.apache.log4j.Logger;
  import org.kuali.rice.core.api.exception.RiceIllegalStateException;
  import org.kuali.rice.kew.api.KewApiServiceLocator;
  import org.kuali.rice.kew.engine.RouteContext;
  
  /**
   * Implements the KRA meta-rule processing and state machine engine 
   * 
   * @author Kuali Rice Team (rice.collab@kuali.org)
   */
  public class KRAMetaRuleEngine {
      private static final Logger LOG = Logger.getLogger(KRAMetaRuleEngine.class);
  
      /**
       * KRA meta-rule processing flag
       */
      private static enum KRA_RULE_FLAG {
          NEXT, TRUE, FALSE
      }
  
      private final String expression;
      private final String[] statements;
      private int curStatement = 0;
      /**
       * Whether processing has indicated that we should stop
       */
      private boolean stop = false;
      
      public KRAMetaRuleEngine(String expression) throws ParseException {
          this.expression = expression;
          statements = expression.split("\\s*[;\r\n]\\s*");
          
          if (statements.length == 0) {
              throw new ParseException("No statements parsed in expression: " + expression, 0);
          }
      }
  
      /**
       * @return the expression the engine was initialized with
       */
      public String getExpression() {
          return expression;
      }
  
      /**
       * @return the parsed statements
       */
      public String[] getStatements() {
          return statements;
      }
  
      /**
       * @return the next statement the engine will process
       */
      public int getCurStatement() {
          return curStatement;
      }
  
      /**
       * @param statementNo the statement index at which to resume processing 
       */
      public void setCurStatement(int statementNo) {
          this.curStatement = statementNo;
      }
  
      /**
       * @return whether we are done processing
       */
      public boolean isDone() {
          return curStatement >= statements.length || stop;
      }
  
      /**
       * Processes a single statement and returns the result
       * @param context the current RouteContext
       * @return the expression result that resulted from the evaluation of a single statement
       * @throws ParseException if the statement could not be parsed
       */
      public RuleExpressionResult processSingleStatement(RouteContext context) throws ParseException {
         if (isDone()) {
             return null;
         }
 
         int stmtNum = curStatement + 1;
         String statement = statements[curStatement];
         LOG.debug("Processing statement: " + statement);
         String[] words = statement.split("\\s*:\\s*");
         if (words.length < 2) {
             throw new ParseException("Invalid statement (#" + stmtNum + "): " + statement, 0);
         }
         String ruleName = words[0];
         if (StringUtils.isEmpty(ruleName)) {
             throw new ParseException("Invalid rule in statement (#" + stmtNum + "): " + statement, 0);
         }
         String flag = words[1];
         LOG.debug(flag.toUpperCase());
         KRA_RULE_FLAG flagCode = KRA_RULE_FLAG.valueOf(flag.toUpperCase());
         if (flagCode == null) {
             throw new ParseException("Invalid flag in statement (#" + stmtNum + "): " + statement, 0);
         }
         org.kuali.rice.kew.api.rule.Rule nestedRule = KewApiServiceLocator.getRuleService().getRuleByName(ruleName);
         if (nestedRule == null) {
             throw new ParseException("Rule '" + ruleName + "' in statement (#" + stmtNum + ") not found: " + statement, 0);
         }
 
         Rule rule = new RuleImpl(nestedRule);
         RuleExpressionResult result;
         switch (flagCode) {
             case NEXT:
                 result = rule.evaluate(rule, context);
                 break;
             case TRUE:
                 result = rule.evaluate(rule, context);
                 if (!result.isSuccess()) {
                     stop = true;
                 }
                 break;
             case FALSE:
                 result = rule.evaluate(rule, context);
                 if (result.isSuccess()) {
                     stop = true;
                     // we need to just invert the ultimate expression result success, because in this case
                     // we wanted the expression to fail but it didn't
                     result = new RuleExpressionResult(rule, false, result.getResponsibilities());
                 }
                 break;
             default:
                 throw new RiceIllegalStateException("Unhandled statement flag: " + flagCode);
         }
 
         curStatement++;
         LOG.debug("Result of statement '" + statement + "': " + result);
         return result;
     }
 }