/*
 * 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
 *
 *   https://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.
 *
 *   SPDX-License-Identifier: Apache-2.0
 */

package org.apache.jena.sparql.algebra.optimize;

import org.apache.jena.sparql.algebra.Op;
import org.apache.jena.sparql.algebra.TransformCopy;
import org.apache.jena.sparql.algebra.op.OpPath;
import org.apache.jena.sparql.core.PathBlock;
import org.apache.jena.sparql.path.PathCompiler;
import org.apache.jena.sparql.path.PathLib;

/**
 * Perform the equivalent of the transactions in the SPARQL 1.1 spec. ARQ regards
 * path transformation as an optimization. ARQ does not execute the exact
 * transformation as per spec as there are better ways to do it for ARQ. For example,
 * <ul>
 * <li>Path seq {@literal ->} BGPs or a (sequence)
 * <li>"|" is not expanded into a union.
 * </ul>
 */

public class TransformPathFlatten extends TransformCopy {
    // This transform is also used so programmatically built queries also get
    // converted.
    // Need previous BGP for merging? Do as a separate pass (sequence, BGP collapse)

    private PathCompiler pathCompiler;

    public TransformPathFlatten() {
        this(new PathCompiler());
    }

    public TransformPathFlatten(PathCompiler pathCompiler) {
        this.pathCompiler = pathCompiler;
    }

    @Override
    public Op transform(OpPath opPath) {
        // Flatten down to triples where possible.
        PathBlock pattern = pathCompiler.reduce(opPath.getTriplePath());
        // Any generated paths of exactly one to triple; convert to Op.
        return PathLib.pathToTriples(pattern);
    }
}
