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.rel.rules;
  
  import org.apache.calcite.plan.RelOptRuleCall;
  import org.apache.calcite.plan.RelOptUtil;
  import org.apache.calcite.plan.RelRule;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.Join;
  import org.apache.calcite.rel.core.JoinRelType;
  import org.apache.calcite.rel.core.Project;
  import org.apache.calcite.rel.logical.LogicalJoin;
  import org.apache.calcite.rel.logical.LogicalProject;
  import org.apache.calcite.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.rex.RexUtil;
  import org.apache.calcite.tools.RelBuilder;
  import org.apache.calcite.tools.RelBuilderFactory;
  import org.apache.calcite.util.ImmutableBitSet;
  
  import org.immutables.value.Value;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.stream.Collectors;
  
  /**
   * Planner rule that matches an {@link org.apache.calcite.rel.core.Project}
   * on a {@link org.apache.calcite.rel.core.Join} and removes the left input
   * of the join provided that the left input is also a left join if possible.
   *
   * <p>For instance,
   *
   * <blockquote>
   * <pre>select s.product_id, pc.product_id
   * from sales as s
   * left join product as p
   *   on s.product_id = p.product_id
   * left join product_class pc
   *   on s.product_id = pc.product_id</pre></blockquote>
   *
   * <p>becomes
   *
   * <blockquote>
   * <pre>select s.product_id, pc.product_id
   * from sales as s
   * left join product_class pc
   *   on s.product_id = pc.product_id</pre></blockquote>
   *
   * @see CoreRules#PROJECT_JOIN_JOIN_REMOVE
   */
  @Value.Enclosing
  public class ProjectJoinJoinRemoveRule
      extends RelRule<ProjectJoinJoinRemoveRule.Config>
      implements SubstitutionRule {
  
    /** Creates a ProjectJoinJoinRemoveRule. */
    protected ProjectJoinJoinRemoveRule(Config config) {
      super(config);
    }
  
    @Deprecated // to be removed before 2.0
    public ProjectJoinJoinRemoveRule(
        Class<? extends Project> projectClass,
        Class<? extends Join> joinClass, RelBuilderFactory relBuilderFactory) {
      this(Config.DEFAULT.withRelBuilderFactory(relBuilderFactory)
          .as(Config.class)
          .withOperandFor(projectClass, joinClass));
    }
  
    @Override public void onMatch(RelOptRuleCall call) {
      final Project project = call.rel(0);
      final Join topJoin = call.rel(1);
      final Join bottomJoin = call.rel(2);
      int leftBottomChildSize = bottomJoin.getLeft().getRowType().getFieldCount();
  
      // Check whether the project uses columns in the right input of bottom join.
      for (RexNode expr : project.getProjects()) {
        if (RelOptUtil.InputFinder.bits(expr).asList().stream().anyMatch(
            i -> i >= leftBottomChildSize
                && i < bottomJoin.getRowType().getFieldCount())) {
          return;
        }
      }
  
      // Check whether the top join uses columns in the right input of bottom join.
      final List<Integer> leftKeys = new ArrayList<>();
      RelOptUtil.splitJoinCondition(topJoin.getLeft(), topJoin.getRight(),
          topJoin.getCondition(), leftKeys, new ArrayList<>(),
          new ArrayList<>());
      if (leftKeys.stream().anyMatch(s -> s >= leftBottomChildSize)) {
        return;
      }
  
      // Check whether left join keys in top join and bottom join are equal.
      final List<Integer> leftChildKeys = new ArrayList<>();
      final List<Integer> rightChildKeys = new ArrayList<>();
      RelOptUtil.splitJoinCondition(bottomJoin.getLeft(), bottomJoin.getRight(),
          bottomJoin.getCondition(), leftChildKeys, rightChildKeys,
          new ArrayList<>());
      if (!leftKeys.equals(leftChildKeys)) {
        return;
      }
  
      // Make sure that right keys of bottom join are unique.
      final ImmutableBitSet.Builder columns = ImmutableBitSet.builder();
      rightChildKeys.forEach(columns::set);
      final RelMetadataQuery mq = call.getMetadataQuery();
      if (!Boolean.TRUE.equals(mq.areColumnsUnique(bottomJoin.getRight(), columns.build()))) {
        return;
      }
  
      int offset = bottomJoin.getRight().getRowType().getFieldCount();
      final RelBuilder relBuilder = call.builder();
  
      final RexNode condition =
          RexUtil.shift(topJoin.getCondition(), leftBottomChildSize, -offset);
      final RelNode join =
          relBuilder.push(bottomJoin.getLeft())
              .push(topJoin.getRight())
              .join(topJoin.getJoinType(), condition)
              .build();
  
      final List<RexNode> newExprs = project.getProjects().stream()
          .map(expr -> RexUtil.shift(expr, leftBottomChildSize, -offset))
          .collect(Collectors.toList());
      relBuilder.push(join).project(newExprs);
      call.transformTo(relBuilder.build());
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableProjectJoinJoinRemoveRule.Config.of()
          .withOperandFor(LogicalProject.class, LogicalJoin.class);
  
      @Override default ProjectJoinJoinRemoveRule toRule() {
        return new ProjectJoinJoinRemoveRule(this);
      }
  
      /** Defines an operand tree for the given classes. */
      default Config withOperandFor(Class<? extends Project> projectClass,
          Class<? extends Join> joinClass) {
        return withOperandSupplier(b0 ->
            b0.operand(projectClass).oneInput(b1 ->
                b1.operand(joinClass).predicate(j ->
                    j.getJoinType() == JoinRelType.LEFT)
                .inputs(b2 ->
                    b2.operand(joinClass).predicate(j ->
                        j.getJoinType() == JoinRelType.LEFT)
                    .anyInputs())))
            .as(Config.class);
      }
    }
  }
  