package org.kuali.rice.krms.framework.engine;

 import java.util.Date;

 import java.util.Map;

 import org.kuali.rice.krms.api.Asset;

 import org.kuali.rice.krms.api.Context;

 import org.kuali.rice.krms.api.ContextProvider;

 import org.kuali.rice.krms.api.Engine;

 import org.kuali.rice.krms.api.EngineResults;

 import org.kuali.rice.krms.api.ExecutionEnvironment;

 import org.kuali.rice.krms.api.ResultEvent;

 import org.kuali.rice.krms.api.SelectionCriteria;

 import org.kuali.rice.krms.framework.engine.result.TimingResult;

 public class ProviderBasedEngine implements Engine {

         private static final Asset effectiveExecutionTimeAsset = new Asset("effectiveExecutionTime", "java.lang.Long");

         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<Asset, Object> facts, Map<String, String> executionOptions) {

                 Date start, end;

                 start = new Date();

                 ExecutionEnvironment environment = establishExecutionEnvironment(selectionCriteria, facts, executionOptions);

                 // set execution time

                 Long effectiveExecutionTime = environment.getSelectionCriteria().getEffectiveExecutionTime();

                 if (effectiveExecutionTime == null) { effectiveExecutionTime = System.currentTimeMillis(); }

                 environment.publishFact(effectiveExecutionTimeAsset, effectiveExecutionTime);

                 Context context = selectContext(selectionCriteria, facts, 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 Date();

                 if (KLog.isEnabled(environment)){

                         KLog.logResult(new TimingResult(ResultEvent.TimingEvent, this, environment, start, end));

                 }

                 return environment.getEngineResults();

         }

         protected ExecutionEnvironment establishExecutionEnvironment(SelectionCriteria selectionCriteria, Map<Asset, Object> facts, Map<String, String> executionOptions) {

                 return new BasicExecutionEnvironment(selectionCriteria, facts, executionOptions);

         }

         protected Context selectContext(SelectionCriteria selectionCriteria, Map<Asset, Object> facts, Map<String, String> executionOptions) {

                 if (contextProvider == null) {

                         throw new IllegalStateException("No ContextProvider was configured.");

                 }

                 return contextProvider.loadContext(selectionCriteria, facts, executionOptions);

         }

         public void setContextProvider(ContextProvider contextProvider) {

                 this.contextProvider = contextProvider;

         }

 }