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This module contains logical plan and query optimization parts.
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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.
 */

package org.apache.tajo.plan.rewrite.rules;

import org.apache.tajo.exception.TajoException;
import org.apache.tajo.plan.LogicalPlan;
import org.apache.tajo.plan.expr.*;
import org.apache.tajo.plan.logical.JoinNode;
import org.apache.tajo.plan.logical.LogicalNode;
import org.apache.tajo.plan.logical.NodeType;
import org.apache.tajo.plan.logical.SelectionNode;
import org.apache.tajo.plan.rewrite.LogicalPlanRewriteRule;
import org.apache.tajo.plan.rewrite.LogicalPlanRewriteRuleContext;
import org.apache.tajo.plan.visitor.BasicLogicalPlanVisitor;
import org.apache.tajo.util.TUtil;

import java.util.Set;
import java.util.Stack;

/**
 * Condition reduce rule reduces the query predicate based on distributivity.
 * For example, the query
 *
 * SELECT *
 * FROM t
 * WHERE (t.a = 1 OR t.b = 10) AND (t.a = 1 OR t.c = 100)
 *
 * is converted into
 *
 * SELECT *
 * FROM t
 * WHERE t.a = 1 OR (t.b = 10 AND t.c = 100).
 *
 */
public class CommonConditionReduceRule implements LogicalPlanRewriteRule {
  private Rewriter rewriter;

  @Override
  public String getName() {
    return "CommonConditionReduceRule";
  }

  @Override
  public boolean isEligible(LogicalPlanRewriteRuleContext context) {
    for (LogicalPlan.QueryBlock block : context.getPlan().getQueryBlocks()) {
      if (block.hasNode(NodeType.SELECTION) || block.hasNode(NodeType.JOIN)) {
        rewriter = new Rewriter(context.getPlan());
        return true;
      }
    }
    return false;
  }

  @Override
  public LogicalPlan rewrite(LogicalPlanRewriteRuleContext context) throws TajoException {
    rewriter.visit(null, context.getPlan(), context.getPlan().getRootBlock());
    return context.getPlan();
  }

  /**
   * Rewriter simply triggers rewriting evals while visiting logical nodes.
   */
  private final static class Rewriter extends BasicLogicalPlanVisitor {
    EvalRewriter evalRewriter;

    public Rewriter(LogicalPlan plan) {
      evalRewriter = new EvalRewriter(plan);
    }

    @Override
    public LogicalNode visitFilter(Object context, LogicalPlan plan, LogicalPlan.QueryBlock block,
                                   SelectionNode selNode, Stack stack) throws TajoException {
      selNode.setQual(evalRewriter.visit(null, selNode.getQual(), new Stack()));
      return null;
    }

    @Override
    public LogicalNode visitJoin(Object context, LogicalPlan plan, LogicalPlan.QueryBlock block,
                                 JoinNode joinNode, Stack stack) throws TajoException {
      if (joinNode.hasJoinQual()) {
        joinNode.setJoinQual(evalRewriter.visit(null, joinNode.getJoinQual(), new Stack()));
      }
      return null;
    }
  }

  /**
   * EvalRewriter is responsible for rewriting evals based on distributivity.
   */
  private static class EvalRewriter extends SimpleEvalNodeVisitor