/*
 * 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.OpVisitorByTypeBase;
import org.apache.jena.sparql.algebra.TransformCopy;
import org.apache.jena.sparql.algebra.Transformer;
import org.apache.jena.sparql.algebra.op.OpModifier;
import org.apache.jena.sparql.algebra.op.OpProject;
import org.apache.jena.sparql.engine.Rename;

/**
 * Rename variables so that names can be treated globally. (project) and (group) can
 * hide variables, but we only need to account for OpProject because group is never
 * executed linearly.
 */
public class TransformScopeRename {
    // Is there an OpProject before any pattern algebra operators?
    // We don't need to rename through this one.

    // Track OpProject

    public static Op transform(Op op) {
        return new TransformScopeRename$(op).work();
    }

    private static class TransformScopeRename$ {
        private boolean outerMostOpProject = false;
        private int projectRenameDepth = 0;
        private int projectCount = 0;

        private Op op;

        public TransformScopeRename$(Op op) {
            this.op = op;

            Op op2 = op;
            while (op2 instanceof OpModifier opMod) {
                // If already true ...
                if ( op2 instanceof OpProject ) {
                    outerMostOpProject = true;
                    break;
                }
                op2 = opMod.getSubOp();
            }
            // Set the project counter: renaming begins when this hits one.
            // Setting it to 2 here if it is a project in the top-most OpModifers.
            // This does not cause a rename so start renaming at depth.
            // otherwise rename from depth 1.
            if ( outerMostOpProject )
                projectRenameDepth = 2;
            else
                projectRenameDepth = 1;
        }

        public Op work() {
            // Before/after maintain the projectCount.
            // It can't be done in transform(OpProject) because it is not the walker step.
            return Transformer.transform(new RenameByScope(), op, new BeforeWalk(), new AfterWalk());
        }

        private class BeforeWalk extends OpVisitorByTypeBase {
            @Override
            public void visit(OpProject opProject) {
                projectCount++;
            }
        }

        private class AfterWalk extends OpVisitorByTypeBase {
            @Override
            public void visit(OpProject opProject) {
                --projectCount;
            }
        }

        private class RenameByScope extends TransformCopy {
            @Override
            public Op transform(OpProject opProject, Op subOp) {
                // Need to find the right project
                // We already stripped outer modifier.
                if ( projectCount >= projectRenameDepth )
                    // Inner ones already done.
                    subOp = Rename.renameVars(subOp, opProject.getVars());
                return super.transform(opProject, subOp);
            }
        }
    }
}
