jena-arq/src/main/java/org/apache/jena/sparql/algebra/op/OpExt.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.sparql.algebra.op;

import org.apache.jena.atlas.io.IndentedWriter ;
import org.apache.jena.sparql.ARQNotImplemented ;
import org.apache.jena.sparql.algebra.Op ;
import org.apache.jena.sparql.algebra.OpVisitor ;
import org.apache.jena.sparql.algebra.Transform ;
import org.apache.jena.sparql.engine.ExecutionContext ;
import org.apache.jena.sparql.engine.QueryIterator ;
import org.apache.jena.sparql.serializer.SerializationContext ;
import org.apache.jena.sparql.sse.Tags ;
import org.apache.jena.sparql.sse.writers.WriterLib ;

/** Marker for extension points
 *  Execution will be per-engine specific */
public abstract class OpExt extends OpBase
{ 
    protected final String tag ;
    
    public OpExt(String name) { tag = name ; }
    
    /** Return an op that will used by query processing algorithms such as 
     *  optimization.  This method returns a non-extension Op expression that
     *  is the equivalent SPARQL expression.  For example, this is the Op replaced
     *  by this extension node.   
     */ 
    public abstract Op effectiveOp() ;
    
    /** Evaluate the op, given a stream of bindings as input 
     *  Throw UnsupportedOperationException if this OpExt is not executeable. 
     */
    public abstract QueryIterator eval(QueryIterator input, ExecutionContext execCxt) ;
    
    @Override
    public final String getName() { return tag ; }
    
    @Override
    public final void visit(OpVisitor opVisitor)
    { opVisitor.visit(this) ; }

    @Override
    public void output(IndentedWriter out, SerializationContext sCxt)
    {
        int line = out.getRow() ;
        
        if ( false )
        {
            // Write in (ext NAME ...) form.
            WriterLib.start(out, Tags.tagExt, WriterLib.NoNL) ;
            out.print(getName()) ;
            out.print(" ") ;
            outputArgs(out, sCxt) ;
            WriterLib.finish(out, Tags.tagExt) ;
        }
        else
        {
         // Write in (NAME ...) form.
            WriterLib.start(out, tag, WriterLib.NoNL) ;
            outputArgs(out, sCxt) ;
            WriterLib.finish(out, tag) ;
        }
        
        if ( line != out.getRow() )
            out.ensureStartOfLine() ;
    }
    
    public Op apply(Transform transform, OpVisitor before, OpVisitor after) {
        // Default behaviour is just to pass to apply(transform)
        return apply(transform) ;
    } 
    
    public Op apply(Transform transform) { throw new ARQNotImplemented("OpExt.apply(Transform)") ; }
    
//    /** Return the sub tag - must match the builder */ 
//    public abstract String getSubTag() ;

    /** Output the arguments in legal SSE format. Multiple items, whitespace separated */ 
    public abstract void outputArgs(IndentedWriter out, SerializationContext sCxt) ;
}