jena-arq/src/main/java/org/apache/jena/sparql/algebra/optimize/TransformExpandOneOf.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.optimize;

import static org.apache.jena.sparql.expr.NodeValue.FALSE;
import static org.apache.jena.sparql.expr.NodeValue.TRUE;

import org.apache.jena.sparql.ARQInternalErrorException;
import org.apache.jena.sparql.algebra.Op;
import org.apache.jena.sparql.algebra.TransformCopy;
import org.apache.jena.sparql.algebra.op.OpFilter;
import org.apache.jena.sparql.algebra.op.OpLeftJoin;
import org.apache.jena.sparql.expr.*;

public class TransformExpandOneOf extends TransformCopy
{
    public TransformExpandOneOf() {}
    
    // Expressions to expand can be in two places: OpFilter and the expr of OpLeftJoin. 
    
    @Override
    public Op transform(OpFilter opFilter, Op subOp) {
        ExprList exprList = opFilter.getExprs();
        ExprList exprList2 = process(exprList);
        if ( exprList2 == null )
            return super.transform(opFilter, subOp);
        Op opFilter2 = OpFilter.filterBy(exprList2, subOp);
        return opFilter2;
    }

    @Override
    public Op transform(OpLeftJoin opLeftJoin, Op opLeft, Op opRight) {
        ExprList exprList = opLeftJoin.getExprs();
        if ( exprList == null )
            return opLeftJoin;
        ExprList exprList2 = process(exprList);
        if ( exprList2 == null )
            return opLeftJoin;
        return OpLeftJoin.create(opLeft, opRight, exprList2);
    }

    private static ExprList process(ExprList exprList) {
        if ( !interesting(exprList) )
            return null;
        return expand(exprList);
    }
    
    /** Prescan to see if anything to consider */ 
    private static boolean interesting(ExprList exprList) {
        return exprList.getList().stream().anyMatch((e) -> processable(e));
    }

    /** Check whether the expression is to be processed here */ 
    private static boolean processable(Expr e) {
        return (e instanceof E_OneOfBase) && ((E_OneOfBase)e).getRHS().size() < REWRITE_LIMIT;
    }

    /*package*/ static int REWRITE_LIMIT = 250;

    private static ExprList expand(ExprList exprList) {
        ExprList exprList2 = new ExprList() ;
        
        for ( Expr e : exprList ) {

            if ( !processable(e) ) {
                exprList2.add(e);
                continue;
            }

            if ( e instanceof E_OneOf ) {
                // ?x IN (a,b) ===> (?x == a) || (?x == b)
                // ?x IN () ===> false

                E_OneOf exprOneOf = (E_OneOf)e ;
                if ( exprOneOf.getRHS().size() > REWRITE_LIMIT )
                    // Too large - leave it alone.
                    continue;
                Expr x = exprOneOf.getLHS();
                Expr disjunction = null;
                // if ?x IN () then it's false regardless.
                for ( Expr sub : exprOneOf.getRHS() ) {
                    Expr e2 = new E_Equals(x, sub);
                    if ( disjunction == null )
                        disjunction = e2;
                    else
                        disjunction = new E_LogicalOr(disjunction, e2);
                }

                if ( disjunction == null )
                    exprList2.add(FALSE);
                else
                    exprList2.add(disjunction);
                continue;
            }
            if ( e instanceof E_NotOneOf ) {
                // ?x NOT IN (a,b) ===> (?x != a) && (?x != b)
                // ?x NOT IN () ===> TRUE (or nothing)
                E_NotOneOf exprNotOneOf = (E_NotOneOf)e;
                if ( exprNotOneOf.getRHS().size() > REWRITE_LIMIT )
                    // Too large - leave it alone.
                    continue ;
                Expr x = exprNotOneOf.getLHS() ;
                if ( exprNotOneOf.getRHS().size() == 0 )
                    exprList2.add(TRUE) ;
                else
                {
                    for ( Expr sub : exprNotOneOf.getRHS() )
                        exprList2.add(new E_NotEquals(x, sub)) ;
                }
                continue ;
            }
            throw new ARQInternalErrorException() ;
        }

        return exprList2 ;
    }
}