/**
    * 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.krms.framework.engine;
  
  import java.util.Map;
  
  import org.joda.time.DateTime;
  import org.kuali.rice.krms.api.engine.Engine;
  import org.kuali.rice.krms.api.engine.EngineResults;
  import org.kuali.rice.krms.api.engine.ExecutionEnvironment;
  import org.kuali.rice.krms.api.engine.ExecutionOptions;
  import org.kuali.rice.krms.api.engine.Facts;
  import org.kuali.rice.krms.api.engine.ResultEvent;
  import org.kuali.rice.krms.api.engine.SelectionCriteria;
  import org.kuali.rice.krms.api.engine.Term;
  import org.kuali.rice.krms.framework.engine.result.TimingResult;
  
  /**
   * An implementation of {@link Engine}
   * @author Kuali Rice Team (rice.collab@kuali.org)
   */
  public class ProviderBasedEngine implements Engine {
  
  	private static final Term effectiveExecutionTimeTerm = new Term("effectiveExecutionTime", null);
  	
  	private static final org.apache.log4j.Logger LOG = org.apache.log4j.Logger.getLogger(ProviderBasedEngine.class);
  	private static final ResultLogger KLog = ResultLogger.getInstance();
  
  	private ContextProvider contextProvider;
  
      @Override
      public EngineResults execute(SelectionCriteria selectionCriteria, Map<String, Object> facts,
              ExecutionOptions executionOptions) {
          return execute(selectionCriteria,
                  Facts.Builder.create().addFactsByName(facts).build(),
                  executionOptions);
      }
  
      @Override
  	public EngineResults execute(SelectionCriteria selectionCriteria, Facts facts, ExecutionOptions executionOptions) {
  		DateTime start, end;
  		start = new DateTime();
  		ExecutionEnvironment environment = establishExecutionEnvironment(selectionCriteria, facts.getFactMap(), executionOptions);
  		
  		// set execution time
  		Long effectiveExecutionTime = environment.getSelectionCriteria().getEffectiveExecutionTime();
  		if (effectiveExecutionTime == null) { effectiveExecutionTime = System.currentTimeMillis(); }
  		environment.publishFact(effectiveExecutionTimeTerm, effectiveExecutionTime);
  
  		Context context = selectContext(selectionCriteria, facts.getFactMap(), executionOptions);
  		if (context == null) {
  			LOG.info("Failed to locate a Context for the given qualifiers, skipping rule engine execution: " + selectionCriteria.getContextQualifiers());
  			return null;
  		}
  		context.execute(environment);
  		end = new DateTime();
  		if (KLog.isEnabled(environment)){
  			KLog.logResult(new TimingResult(ResultEvent.TIMING_EVENT, this, environment, start, end));
  		}
  		return environment.getEngineResults();
  	}
  
      /**
       * Return a {@link BasicExecutionEnvironment} using the given parameters
       * @param selectionCriteria {@link SelectionCriteria}
       * @param facts
       * @param executionOptions {@link ExecutionOptions}
       * @return {@link ExecutionEnvironment} created with the given parameters
       */
  	protected ExecutionEnvironment establishExecutionEnvironment(SelectionCriteria selectionCriteria, Map<Term, Object> facts, ExecutionOptions executionOptions) {
  		return new BasicExecutionEnvironment(selectionCriteria, facts, executionOptions, new TermResolutionEngineImpl());
  	}
  
      /**
       * Load a Context from the contextProvider using the given parameters
       * @see ContextProvider loadContext
       * @param selectionCriteria
       * @param facts
       * @param executionOptions
       * @return {@link Context}
       * @throws IllegalStateException if the contextProvider is null;
       */
  	protected Context selectContext(SelectionCriteria selectionCriteria, Map<Term, Object> facts, ExecutionOptions executionOptions) {
  		if (contextProvider == null) {
  			throw new IllegalStateException("No ContextProvider was configured.");
  		}
 		return contextProvider.loadContext(selectionCriteria, facts, executionOptions);
 	}
 
     /**
      * Set the {@link ContextProvider}
      * @param contextProvider to loadContext from.
      */
 	public void setContextProvider(ContextProvider contextProvider) {
 		this.contextProvider = contextProvider;
 	}
 	
 }