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.asterix.optimizer.rules.pushdown.visitor;
  
  import java.util.List;
  
  import org.apache.asterix.optimizer.rules.pushdown.PushdownContext;
  import org.apache.commons.lang3.mutable.Mutable;
  import org.apache.hyracks.algebricks.common.exceptions.AlgebricksException;
  import org.apache.hyracks.algebricks.core.algebra.base.ILogicalExpression;
  import org.apache.hyracks.algebricks.core.algebra.base.ILogicalOperator;
  import org.apache.hyracks.algebricks.core.algebra.base.LogicalVariable;
  import org.apache.hyracks.algebricks.core.algebra.visitors.ILogicalExpressionReferenceTransform;
  
  public class DefUseChainComputerVisitor implements ILogicalExpressionReferenceTransform {
      private final PushdownContext pushdownContext;
      private ILogicalOperator operator;
      private List<LogicalVariable> producedVariables;
      private int expressionIndex;
  
      public DefUseChainComputerVisitor(PushdownContext pushdownContext) {
          this.pushdownContext = pushdownContext;
      }
  
      public void init(ILogicalOperator operator, List<LogicalVariable> producedVariables) {
          this.operator = operator;
          this.producedVariables = producedVariables;
          expressionIndex = 0;
      }
  
      @Override
      public boolean transform(Mutable<ILogicalExpression> exprRef) throws AlgebricksException {
          ILogicalExpression expression = exprRef.getValue();
          // compute use chain first
          LogicalVariable producedVariable = producedVariables != null ? producedVariables.get(expressionIndex) : null;
          pushdownContext.use(operator, expression, expressionIndex, producedVariable);
          if (producedVariable != null) {
              // then define the produced variable
              pushdownContext.define(producedVariable, operator, expression, expressionIndex);
          }
          expressionIndex++;
          return false;
      }
  }
  