/*
    * RDFpro - An extensible tool for building stream-oriented RDF processing libraries.
    * 
    * Written in 2015 by Francesco Corcoglioniti with support by Alessio Palmero Aprosio and Marco
    * Rospocher. Contact info on http://rdfpro.fbk.eu/
    * 
    * To the extent possible under law, the authors have dedicated all copyright and related and
    * neighboring rights to this software to the public domain worldwide. This software is
    * distributed without any warranty.
   * 
   * You should have received a copy of the CC0 Public Domain Dedication along with this software.
   * If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
   */
  package eu.fbk.rdfpro.internal;
  
  import org.openrdf.model.Value;
  import org.openrdf.model.ValueFactory;
  import org.openrdf.model.vocabulary.RDF;
  import org.openrdf.query.algebra.evaluation.ValueExprEvaluationException;
  import org.openrdf.query.algebra.evaluation.function.Function;
  
  import eu.fbk.rdfpro.vocab.RR;
  
  public class FunctionStarSelectGraph implements Function {
  
      @Override
      public String getURI() {
          return RR.STAR_SELECT_GRAPH.stringValue();
      }
  
      @Override
      public Value evaluate(final ValueFactory valueFactory, final Value... args)
              throws ValueExprEvaluationException {
  
          final Value global = args[0];
  
          Value result = null;
          for (int i = 1; i < args.length; ++i) {
              final Value graph = args[i];
              if (!graph.equals(global)) {
                  if (result == null) {
                      result = graph;
                  } else {
                      return RDF.NIL;
                  }
              }
          }
  
          return result != null ? result : global;
      }
  
  }