jena-extras/jena-querybuilder/src/main/java/org/apache/jena/arq/querybuilder/rewriters/BuildElementVisitor.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.jena.arq.querybuilder.rewriters;

import java.util.List;

import org.apache.jena.arq.querybuilder.handlers.WhereHandler;
import org.apache.jena.sparql.syntax.*;

/**
 * An element visitor that does an in-place modification of the elements to 
 * fix union-of-one and similar issues.
 *
 */
public class BuildElementVisitor implements ElementVisitor {
	private Element result;


	public Element getResult()
	{
		return result;
	}

	public void setResult(Element result)
	{
		this.result = result;
	}

	@Override
	public void visit(ElementTriplesBlock el) {
		// no changes
		result=el;
	}

	@Override
	public void visit(ElementPathBlock el) {
		// no changes
		result=el;
	}

	@Override
	public void visit(ElementFilter el) {
		// no changes
		result=el;
	}

	@Override
	public void visit(ElementAssign el) {
		// no change
		result=el;
	}

	@Override
	public void visit(ElementBind el) {
		// no change
		result=el;
	}

	@Override public void visit(ElementFind el) {
        // no change
        result=el;
	}
	
	@Override
	public void visit(ElementData el) {
		// no change
		result=el;
	}

	private void updateList( List<Element> lst )
	{
		 for (int i=0;i<lst.size();i++)
    	 {
    		 lst.get(i).visit( this );
    		 lst.set(i, result);
    	 }
	}
	
	@Override
	public void visit(ElementUnion el) {
		List<Element> lst = el.getElements();
         if ( lst.size() <= 1 ) {
        	 ElementGroup eg = new ElementGroup();
             if ( lst.size() == 1)
             {
            	 el.getElements().get(0).visit( this );
        	   	 eg.addElement(result);
             }
        	 result = eg;
         } else {
        	 updateList( lst );
        	 result = el;
         }
	}

	@Override
	public void visit(ElementOptional el) {
		el.getOptionalElement().visit(this);
		if (result == el.getOptionalElement())
		{
			result = el;
		} else {
			result = new ElementOptional( result );
		}
	}

	@Override
	public void visit(ElementGroup el) {
		List<Element> lst = el.getElements();
		if (lst.isEmpty())
		{
			// noting to do
			result = el;
		} else if (lst.size() == 1)
		{
			lst.get(0).visit( this );
			// result is now set properly
		} else {
		updateList( lst );
		result = el;
		}
	}
	
	@Override
	public void visit(ElementDataset el) {
		// noting to do
		result = el;
	}

	@Override
	public void visit(ElementNamedGraph el) {
		el.getElement().visit( this );
		if (result == el.getElement())
		{
			// nothing to do
			result = el;
		}
		else {
			result = new ElementNamedGraph( el.getGraphNameNode(), result);
		}
	}

	@Override
	public void visit(ElementExists el) {
		el.getElement().visit(this);
		if (result == el.getElement())
		{
			// nothing to do
			result = el;
		}
		else {
			result = new ElementExists( result);
		}			
	}

	@Override
	public void visit(ElementNotExists el) {
		el.getElement().visit(this);
		if (result == el.getElement())
		{
			// nothing to do
			result = el;
		}
		else {
			result = new ElementNotExists( result);
		}
	}

	@Override
	public void visit(ElementMinus el) {
		el.getMinusElement().visit(this);
		if (result == el.getMinusElement())
		{
			// nothing to do
			result = el;
		}
		else {
			result = new ElementMinus( result);
		}
	}

	@Override
	public void visit(ElementService el) {
		el.getElement().visit(this);
		if (result == el.getElement())
		{
			// nothing to do
			result = el;
		}
		else {
			result = new ElementService( el.getServiceNode(), result, el.getSilent());
		}
		
	}

	@Override
	public void visit(ElementSubQuery el) {
		WhereHandler other = new WhereHandler( el.getQuery() );
		other.build();
		if (other.getElement() != el.getQuery().getQueryPattern())
		{
			el.getQuery().setQueryPattern( other.getQuery().getQueryPattern() );
		}
		result = el;
	}
	
}