/**
 * PODD is an OWL ontology database used for scientific project management
 *
 * Copyright (C) 2009-2013 The University Of Queensland
 *
 * This program is free software: you can redistribute it and/or modify it under the terms of the
 * GNU Affero General Public License as published by the Free Software Foundation, either version 3
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
 * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License along with this program.
 * If not, see <http://www.gnu.org/licenses/>.
 */
package com.github.podd.impl.data;

import java.util.Collections;
import java.util.Set;

import org.openrdf.model.vocabulary.RDF;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.github.podd.api.PoddProcessorStage;
import com.github.podd.api.data.DataReferenceProcessor;
import com.github.podd.api.data.SPARQLDataReferenceProcessorFactory;
import com.github.podd.utils.PODD;

/**
 * An SPARQL Data Reference Processor Factory that creates {@link SPARQLDataReferenceProcessorImpl}
 * instances.
 *
 * @author Peter Ansell p_ansell@yahoo.com
 */
public class SPARQLDataReferenceProcessorFactoryImpl implements SPARQLDataReferenceProcessorFactory
{
    
    protected final Logger log = LoggerFactory.getLogger(this.getClass());
    
    /* The fixed set of stages supported by this Factory */
    private static final Set<PoddProcessorStage> STAGES = Collections.singleton(PoddProcessorStage.RDF_PARSING);
    
    @Override
    public boolean canHandleStage(final PoddProcessorStage stage)
    {
        if(stage == null)
        {
            throw new NullPointerException("Cannot handle NULL stage");
        }
        return SPARQLDataReferenceProcessorFactoryImpl.STAGES.contains(stage);
    }
    
    @Override
    public String getKey()
    {
        return this.getClass().getName();
    }
    
    @Override
    public String getParentSPARQLVariable()
    {
        // to find all file references directly under a given object, parent could be bound
        return "parent";
    }
    
    @Override
    public DataReferenceProcessor getProcessor()
    {
        return new SPARQLDataReferenceProcessorImpl();
    }
    
    @Override
    public String getSPARQLConstructBGP()
    {
        return " ?subject ?predicate ?object . ?parent ?containsPredicate ?subject . ";
    }
    
    @Override
    public String getSPARQLConstructWhere()
    {
        final StringBuilder builder = new StringBuilder();
        
        // match all triples about a subject whose TYPE is poddBase:SSHFileReference
        builder.append(" ?")
                .append(this.getSPARQLVariable())
                .append(" <" + RDF.TYPE.stringValue() + "> <" + PODD.PODD_BASE_DATA_REFERENCE_TYPE_SPARQL.stringValue()
                        + "> . ");
        
        builder.append(" ?").append(this.getSPARQLVariable()).append(" ?predicate ?object . ");
        
        builder.append(" ?").append(this.getParentSPARQLVariable()).append(" ?containsPredicate ").append(" ?")
                .append(this.getSPARQLVariable());
        
        return builder.toString();
    }
    
    @Override
    public String getSPARQLGroupBy()
    {
        // an empty GROUP BY clause
        return "";
    }
    
    @Override
    public String getSPARQLVariable()
    {
        // to find ALL file references, subject should not be bound
        return "subject";
    }
    
    @Override
    public Set<PoddProcessorStage> getStages()
    {
        return SPARQLDataReferenceProcessorFactoryImpl.STAGES;
    }
    
}