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.piglet;
  
  import org.apache.pig.impl.logicalLayer.FrontendException;
  import org.apache.pig.impl.util.Utils;
  import org.apache.pig.newplan.Operator;
  import org.apache.pig.newplan.OperatorPlan;
  import org.apache.pig.newplan.PlanVisitor;
  import org.apache.pig.newplan.PlanWalker;
  import org.apache.pig.newplan.logical.relational.LogicalRelationalNodesVisitor;
  import org.apache.pig.newplan.logical.relational.LogicalRelationalOperator;
  
  import java.util.Collection;
  
  /**
   * Post-order walker for Pig logical relational plans. Walks the plan
   * from sinks to sources.
   */
  class PigRelOpWalker extends PlanWalker {
    /**
     * Visitor that allow doing pre-visit.
     */
    abstract static class PlanPreVisitor extends LogicalRelationalNodesVisitor {
      PlanPreVisitor(OperatorPlan plan, PlanWalker walker) throws FrontendException {
        super(plan, walker);
      }
  
      /**
       * Called before a node.
       *
       * @param root Pig logical operator to check
       * @return Returns whether the node has been visited before
       */
      public abstract boolean preVisit(LogicalRelationalOperator root);
    }
  
    PigRelOpWalker(OperatorPlan plan) {
      super(plan);
    }
  
    @Override public void walk(PlanVisitor planVisitor) throws FrontendException {
      if (!(planVisitor instanceof PigRelOpVisitor)) {
        throw new FrontendException("Expected PigRelOpVisitor", 2223);
      }
  
      final PigRelOpVisitor pigRelVistor = (PigRelOpVisitor) planVisitor;
      postOrderWalk(pigRelVistor.getCurrentRoot(), pigRelVistor);
    }
  
    /**
     * Does post-order walk on the Pig logical relational plans from sinks to sources.
     *
     * @param root The root Pig logical relational operator
     * @param visitor The visitor of each Pig logical operator node
     * @throws FrontendException Exception during processing Pig operator
     */
    private void postOrderWalk(Operator root, PlanPreVisitor visitor) throws FrontendException {
      if (root == null || visitor.preVisit((LogicalRelationalOperator) root)) {
        return;
      }
  
      Collection<Operator> nexts =
          Utils.mergeCollection(plan.getPredecessors(root), plan.getSoftLinkPredecessors(root));
      if (nexts != null) {
        for (Operator op : nexts) {
          postOrderWalk(op, visitor);
        }
      }
      root.accept(visitor);
    }
  
    @Override public PlanWalker spawnChildWalker(OperatorPlan operatorPlan) {
      return new PigRelOpWalker(operatorPlan);
    }
  }
  