/*
 *  Copyright (c) 1998-2009, The University of Sheffield.
 *
 *  This file is part of GATE (see http://gate.ac.uk/), and is free
 *  software, licenced under the GNU Library General Public License,
 *  Version 2, June 1991 (in the distribution as file licence.html,
 *  and also available at http://gate.ac.uk/gate/licence.html).
 *
 *  Johann Petrak 2009-08-13
 *
 *  $Id: UtilBooleanQuery.java 11598 2009-10-13 13:44:17Z johann_p $
 */
package gate.creole.ontology.impl.sesame;

import gate.creole.ontology.GateOntologyException;
import gate.creole.ontology.LiteralOrONodeID;
import gate.creole.ontology.OntologyBooleanQuery;
import gate.creole.ontology.OConstants;
import java.util.Vector;
import org.apache.log4j.Logger;
import org.openrdf.model.Value;
import org.openrdf.query.QueryLanguage;
import org.openrdf.query.BooleanQuery;
import org.openrdf.repository.RepositoryConnection;

/**
 * A class representing a Sesame ASK Query. This class makes it easy to
 * use a boolean query and reuse a query with different variable
 * bindings.
 * <p>
 * The following steps should be carried out when using this class:
 * <ol>
 * <li>Create an object and pass on the repository connection, query string,
 * and query language constant
 * <li>Set any variables for the query using {@link #setBinding} one or more times
 * <li>Evaluate the query using {@link evaluate} and retrieve the boolean result.
 * <li>To reuse the query, repeat from step 2
 * </ol>
 *
 * @author Johann Petrak
 */
 public class UtilBooleanQuery implements OntologyBooleanQuery {

    private RepositoryConnection mRepositoryConnection;
    private String mQuery;
    private BooleanQuery mBooleanQuery;
    private QueryLanguage mLang = QueryLanguage.SERQL;
    private Logger logger;
    private boolean mIsPrepared = false;

    public UtilBooleanQuery(RepositoryConnection repositoryConnection,
        String query, OConstants.QueryLanguage lang) {
      logger = Logger.getLogger(this.getClass().getName());
      mRepositoryConnection = repositoryConnection;
      logger.debug("Creating query: " + query);
      mQuery = query;
      if(lang == OConstants.QueryLanguage.SPARQL) {
        mLang = QueryLanguage.SPARQL;
      } else if(lang == OConstants.QueryLanguage.SERQL) {
        mLang = QueryLanguage.SERQL;
      } else {
        throw new GateOntologyException("Query language not supported: "+lang);
      }
      prepare();
    }


    public void prepare() {
      try {
        mBooleanQuery = mRepositoryConnection.prepareBooleanQuery(mLang, mQuery);
        mIsPrepared = true;
      } catch (Exception e) {
        throw new GateOntologyException("Cannot prepare boolean query: "+mQuery, e);
      }
    }

    /**
     *
     * @param name
     * @param value
     */
    public void setBinding(String name, LiteralOrONodeID value) {
      mBooleanQuery.setBinding(name, UtilConvert.toSesameValue(value));
    }

    public void setBinding(String name, Value value) {
      mBooleanQuery.setBinding(name, value);
    }

    /**
     * 
     * @return 
     */
    public boolean evaluate() {
      boolean ret;
      if(!mIsPrepared) {
        prepare();
      }
      try {
        ret = mBooleanQuery.evaluate();
      } catch (Exception e) {
        throw new GateOntologyException("Cannot evaluate query: "+mQuery, e);
      }
      return ret;
    }

  }