content: /*
   * 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.calcite.rel;
  
  import org.apache.calcite.linq4j.Ord;
  import org.apache.calcite.rel.core.TableFunctionScan;
  import org.apache.calcite.rel.core.TableScan;
  import org.apache.calcite.rel.logical.LogicalAggregate;
  import org.apache.calcite.rel.logical.LogicalAsofJoin;
  import org.apache.calcite.rel.logical.LogicalCalc;
  import org.apache.calcite.rel.logical.LogicalCorrelate;
  import org.apache.calcite.rel.logical.LogicalExchange;
  import org.apache.calcite.rel.logical.LogicalFilter;
  import org.apache.calcite.rel.logical.LogicalIntersect;
  import org.apache.calcite.rel.logical.LogicalJoin;
  import org.apache.calcite.rel.logical.LogicalMatch;
  import org.apache.calcite.rel.logical.LogicalMinus;
  import org.apache.calcite.rel.logical.LogicalProject;
  import org.apache.calcite.rel.logical.LogicalRepeatUnion;
  import org.apache.calcite.rel.logical.LogicalSort;
  import org.apache.calcite.rel.logical.LogicalTableModify;
  import org.apache.calcite.rel.logical.LogicalUnion;
  import org.apache.calcite.rel.logical.LogicalValues;
  
  import java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.Deque;
  import java.util.List;
  
  /**
   * Basic implementation of {@link RelShuttle} that calls
   * {@link RelNode#accept(RelShuttle)} on each child, and
   * {@link RelNode#copy(org.apache.calcite.plan.RelTraitSet, java.util.List)} if
   * any children change.
   */
  public class RelShuttleImpl implements RelShuttle {
    protected final Deque<RelNode> stack = new ArrayDeque<>();
  
    /**
     * Visits a particular child of a parent.
     */
    protected RelNode visitChild(RelNode parent, int i, RelNode child) {
      stack.push(parent);
      try {
        RelNode child2 = child.accept(this);
        if (child2 != child) {
          final List<RelNode> newInputs = new ArrayList<>(parent.getInputs());
          newInputs.set(i, child2);
          return parent.copy(parent.getTraitSet(), newInputs);
        }
        return parent;
      } finally {
        stack.pop();
      }
    }
  
    protected RelNode visitChildren(RelNode rel) {
      for (Ord<RelNode> input : Ord.zip(rel.getInputs())) {
        rel = visitChild(rel, input.i, input.e);
      }
      return rel;
    }
  
    @Override public RelNode visit(LogicalAggregate aggregate) {
      return visitChild(aggregate, 0, aggregate.getInput());
    }
  
    @Override public RelNode visit(LogicalMatch match) {
      return visitChild(match, 0, match.getInput());
    }
  
    @Override public RelNode visit(TableScan scan) {
      return scan;
    }
  
    @Override public RelNode visit(TableFunctionScan scan) {
      return visitChildren(scan);
    }
  
    @Override public RelNode visit(LogicalValues values) {
      return values;
    }
  
    @Override public RelNode visit(LogicalFilter filter) {
      return visitChild(filter, 0, filter.getInput());
    }
  
    @Override public RelNode visit(LogicalCalc calc) {
      return visitChildren(calc);
    }
  
    @Override public RelNode visit(LogicalProject project) {
      return visitChild(project, 0, project.getInput());
    }
  
    @Override public RelNode visit(LogicalJoin join) {
      return visitChildren(join);
    }
  
    @Override public RelNode visit(LogicalCorrelate correlate) {
      return visitChildren(correlate);
    }
  
    @Override public RelNode visit(LogicalUnion union) {
      return visitChildren(union);
    }
  
    @Override public RelNode visit(LogicalIntersect intersect) {
      return visitChildren(intersect);
    }
  
    @Override public RelNode visit(LogicalMinus minus) {
      return visitChildren(minus);
    }
  
    @Override public RelNode visit(LogicalSort sort) {
      return visitChildren(sort);
    }
  
    @Override public RelNode visit(LogicalExchange exchange) {
      return visitChildren(exchange);
    }
  
    @Override public RelNode visit(LogicalTableModify modify) {
      return visitChildren(modify);
    }
  
    @Override public RelNode visit(LogicalAsofJoin logicalAsofJoin) {
      return visitChildren(logicalAsofJoin);
    }
  
    @Override public RelNode visit(LogicalRepeatUnion logicalRepeatUnion) {
      return visitChildren(logicalRepeatUnion);
    }
  
    @Override public RelNode visit(RelNode other) {
      return visitChildren(other);
    }
  }
  