PlayJplEngineWrapper.java

package eu.play_project.dcep.distributedetalis;

import java.util.Hashtable;

import jpl.Atom;
import jpl.PrologException;
import jpl.Query;
import jpl.Term;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.jtalis.core.event.EtalisEventListener;
import com.jtalis.core.plengine.EngineOutputListener;
import com.jtalis.core.plengine.JPLEngineWrapper;
import com.jtalis.core.plengine.PrologEngineWrapper;

import eu.play_project.dcep.distributedetalis.api.DistributedEtalisException;
import eu.play_project.dcep.distributedetalis.api.PrologEngineWrapperPlayExtensions;

/**
 * To synchronize acces to JPL TODO synchronize it.
 * www.swi-prolog.org/packages/jpl/java_api/high-level_interface.html
 * 
 * Important: To execute goals related to SemWebLib use only
 * PrologEngineWrapperPlayExtensions.execute(String command). This method
 * guarantees exclusive access to db. (Only from Java side).
 * 
 * @author sobermeier
 * 
 */
public class PlayJplEngineWrapper implements PrologEngineWrapper<Object>, PrologEngineWrapperPlayExtensions {

	private final JPLEngineWrapper engine;
	private static PlayJplEngineWrapper localEngine = new PlayJplEngineWrapper();
	private final Logger logger = LoggerFactory.getLogger(PlayJplEngineWrapper.class);

	private PlayJplEngineWrapper(){
		engine = new JPLEngineWrapper();
	}
	
	public static PlayJplEngineWrapper getPlayJplEngineWrapper(){
		return localEngine;
	}

	@SuppressWarnings("unchecked")
	@Override
	public synchronized Hashtable<String, Object>[] execute(String command) throws DistributedEtalisException {
		try {
			// Get data from triplestore
			Query q = new Query(command);
			return q.allSolutions();
		} catch (PrologException e) {
			logger.error("Error shutting down Etalis. " + e.getMessage());
			return new Hashtable[0];
		}
	}

	@Override
	public synchronized boolean execute(com.jtalis.core.plengine.logic.Term term) {
		try {
			return engine.execute(term);
		} catch(PrologException e){
			logger.error("Error executing Prolog goal. " + e.getMessage());
			return false;
		}
	}

	@Override
	public boolean executeGoal(String goal) {
		try {
			Query q = new Query(goal);
			return q.hasSolution();
		} catch (PrologException e) {
			logger.error("Error executing Prolog goal. " + e.getMessage());
			return false;
		}
	}

	@Override
	public synchronized Object registerPushNotification(EtalisEventListener listener) {
		return engine.registerPushNotification(listener);
	}

	@Override
	public synchronized void unregisterPushNotification(EtalisEventListener listener) {
		engine.unregisterPushNotification(listener);
	}


	@Override
	public synchronized void shutdown() {
		try {
			engine.shutdown();
			//It is not possible to shutdown completly. We will clean up the database.
			//this.executeGoal("retractall(_)");
			this.executeGoal("rdf_retractall(_S,_P,_O,_DB)");
			this.executeGoal("reset_etalis");
		} catch (PrologException e) {
			logger.error("Error shutting down Etalis. " + e.getMessage());
		}
	}

	@Override
	public synchronized void addOutputListener(EngineOutputListener listener) {
		engine.addOutputListener(listener);
	}

	@Override
	public synchronized String getName() {
		return engine.getName();
	}

	@SuppressWarnings("unchecked")
	@Override
	public Hashtable<String, Object>[] getTriplestoreData(String triplestoreID) {
		
		Hashtable<String, Object>[] result;
		try {
			//Get data from triplestore
			result = this.execute("rdfTest(S,P,O, " + triplestoreID + ")");
		} catch (PrologException e) {
			logger.error("Error getting data from Prolog. " + e.getMessage());
			result = new Hashtable[0];
		} catch (DistributedEtalisException e) {
			logger.error("Error getting data from Prolog. " + e.getMessage());
			result = new Hashtable[0];
		} finally {
			try {
				// Free space
				this.executeGoal("retractall(rdfTest(_S,_P,_O, " + triplestoreID + "))");
				
			} catch (PrologException e) {}
		}
		return result;
	}
	
	@SuppressWarnings("unchecked")
	public Hashtable<String, Object>[] getVariableValues(String queryId){
		StringBuffer comand = new StringBuffer();
		
		comand.append("variableValues(");
		comand.append(queryId);
		comand.append(", _, Value)");
		
		try {
			// Get Variables and values
			return this.execute((comand.toString()));
		} catch (DistributedEtalisException e) {
			logger.error("Error getting values from Prolog. " + e.getMessage());
			return new Hashtable[0];
		} catch (PrologException e) {
			logger.error("Error getting values from Prolog. " + e.getMessage());
			return new Hashtable[0];
		}
	}
	
	@Override
	public synchronized boolean consult(String file) {
		try {
			Query consult_query = new Query("consult",
					new Term[] { new Atom(file) });
			return consult_query.hasSolution();
		} catch (PrologException e) {
			logger.error("Error consulting Prolog file. " + e.getMessage());
			return false;
		}
	}

	@Override
	public boolean assertFromFile(String file) {
		return false;
	}
}