logical/src/main/java/org/apache/drill/common/expression/visitors/ConditionalExprOptimizer.java

/*
 * 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.drill.common.expression.visitors;

import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import org.apache.drill.common.expression.AnyValueExpression;
import org.apache.drill.common.expression.BooleanOperator;
import org.apache.drill.common.expression.CastExpression;
import org.apache.drill.common.expression.ConvertExpression;
import org.apache.drill.common.expression.FunctionCall;
import org.apache.drill.common.expression.FunctionHolderExpression;
import org.apache.drill.common.expression.IfExpression;
import org.apache.drill.common.expression.IfExpression.IfCondition;
import org.apache.drill.common.expression.LogicalExpression;

import com.google.common.collect.Lists;

public class ConditionalExprOptimizer extends AbstractExprVisitor<LogicalExpression, Void, RuntimeException> {

  public static ConditionalExprOptimizer INSTANCE = new ConditionalExprOptimizer();

  @Override
  public LogicalExpression visitBooleanOperator(BooleanOperator op, Void value) throws RuntimeException {
    List<LogicalExpression> newArgs = Lists.newArrayList();
    newArgs.addAll(op.args());
    Collections.sort(newArgs, costComparator);

    return new BooleanOperator(op.getName(), newArgs, op.getPosition());
  }

  @Override
  public LogicalExpression visitFunctionHolderExpression(FunctionHolderExpression holder, Void value) throws RuntimeException {
    List<LogicalExpression> args = Lists.newArrayList();
    for (int i = 0; i < holder.args.size(); ++i) {
      LogicalExpression newExpr = holder.args.get(i).accept(this, value);
      assert newExpr != null;
      args.add(newExpr);
    }

    // Replace with a new function call, since its argument could be changed.
    return holder.copy(args);
  }

  @Override
  public LogicalExpression visitUnknown(LogicalExpression e, Void value) throws RuntimeException {
    return e;
  }

  @Override
  public LogicalExpression visitIfExpression(IfExpression ifExpr, Void value) throws RuntimeException{
    LogicalExpression newElseExpr = ifExpr.elseExpression.accept(this, value);
    IfCondition conditions = ifExpr.ifCondition;

    LogicalExpression newCondition = conditions.condition.accept(this, value);
    LogicalExpression newExpr = conditions.expression.accept(this, value);
    conditions = new IfExpression.IfCondition(newCondition, newExpr);

    return IfExpression.newBuilder().setElse(newElseExpr).setIfCondition(conditions).build();
  }

  @Override
  public LogicalExpression visitFunctionCall(FunctionCall call, Void value) throws RuntimeException {
    throw new UnsupportedOperationException("FunctionCall is not expected here. "
        + "It should have been converted to FunctionHolderExpression in materialization");
  }

  @Override
  public LogicalExpression visitCastExpression(CastExpression cast, Void value) throws RuntimeException {
    throw new UnsupportedOperationException("CastExpression is not expected here. "
        + "It should have been converted to FunctionHolderExpression in materialization");
  }

  @Override
  public LogicalExpression visitConvertExpression(ConvertExpression cast, Void value) throws RuntimeException {
    throw new UnsupportedOperationException("ConvertExpression is not expected here. "
        + "It should have been converted to FunctionHolderExpression in materialization");
  }

  @Override
  public LogicalExpression visitAnyValueExpression(AnyValueExpression cast, Void value) throws RuntimeException {
    throw new UnsupportedOperationException("AnyValueExpression is not expected here. "
        + "It should have been converted to FunctionHolderExpression in materialization");
  }

  private static Comparator<LogicalExpression> costComparator = new Comparator<LogicalExpression> () {
    @Override
    public int compare(LogicalExpression e1, LogicalExpression e2) {
      return e1.getCumulativeCost() <= e2.getCumulativeCost() ? -1 : 1;
    }
  };
}