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   * 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.
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  package org.apache.asterix.optimizer.rules;
  
  import org.apache.commons.lang3.mutable.Mutable;
  import org.apache.commons.lang3.mutable.MutableObject;
  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.IOptimizationContext;
  import org.apache.hyracks.algebricks.core.algebra.base.LogicalOperatorTag;
  import org.apache.hyracks.algebricks.core.algebra.base.LogicalVariable;
  import org.apache.hyracks.algebricks.core.algebra.expressions.VariableReferenceExpression;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AssignOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.SelectOperator;
  import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
  
  public class IntroduceTransactionCommitByAssignOpRule implements IAlgebraicRewriteRule {
  
      @Override
      public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          return false;
      }
  
      @Override
      public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
  
          AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
          if (op.getOperatorTag() != LogicalOperatorTag.SELECT) {
              return false;
          }
          SelectOperator selectOperator = (SelectOperator) op;
  
          Mutable<ILogicalOperator> childOfSelect = selectOperator.getInputs().get(0);
  
          //[Direction] SelectOp(cond1)<--ChildOps... ==> SelectOp(booleanValue of cond1)<--NewAssignOp(cond1)<--ChildOps...
          //#. Create an assign-operator with a new local variable and the condition of the select-operator.
          //#. Set the input(child operator) of the new assign-operator to input(child operator) of the select-operator.
          //   (Later, the newly created assign-operator will apply the condition on behalf of the select-operator,
          //    and set the variable of the assign-operator to a boolean value according to the condition evaluation.)
          //#. Give the select-operator the result boolean value created by the newly created child assign-operator.
  
          //create an assignOp with a variable and the condition of the select-operator.
          LogicalVariable v = context.newVar();
          AssignOperator assignOperator =
                  new AssignOperator(v, new MutableObject<ILogicalExpression>(selectOperator.getCondition().getValue()));
          assignOperator.setSourceLocation(selectOperator.getSourceLocation());
          //set the input of the new assign-operator to the input of the select-operator.
          assignOperator.getInputs().add(childOfSelect);
  
          //set the result value of the assign-operator to the condition of the select-operator
          VariableReferenceExpression varRef = new VariableReferenceExpression(v);
          varRef.setSourceLocation(selectOperator.getSourceLocation());
          selectOperator.getCondition().setValue(varRef);//scalarFunctionCallExpression);
          selectOperator.getInputs().set(0, new MutableObject<ILogicalOperator>(assignOperator));
  
          context.computeAndSetTypeEnvironmentForOperator(assignOperator);
  
          //Once this rule is fired, don't apply again.
          context.addToDontApplySet(this, selectOperator);
          return true;
      }
  }
  