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.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 Project}
   * on a {@link Join} and removes the join provided that the join is a left join
   * or right join and the join keys are unique.
   *
   * <p>For instance,
   *
   * <blockquote>
   * <pre>select s.product_id
   * from sales as s
   * left join product as p
   * on s.product_id = p.product_id</pre></blockquote>
   *
   * <p>becomes
   *
   * <blockquote>
   * <pre>select s.product_id from sales as s</pre></blockquote>
   */
  @Value.Enclosing
  public class ProjectJoinRemoveRule
      extends RelRule<ProjectJoinRemoveRule.Config>
      implements SubstitutionRule {
  
    /** Creates a ProjectJoinRemoveRule. */
    protected ProjectJoinRemoveRule(Config config) {
      super(config);
    }
  
    @Deprecated // to be removed before 2.0
    public ProjectJoinRemoveRule(
        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 join = call.rel(1);
      final boolean isLeftJoin = join.getJoinType() == JoinRelType.LEFT;
      int lower = isLeftJoin
          ? join.getLeft().getRowType().getFieldCount() : 0;
      int upper = isLeftJoin
          ? join.getRowType().getFieldCount()
          : join.getLeft().getRowType().getFieldCount();
  
      // Check whether the project uses columns whose index is between
      // lower(included) and upper(excluded).
      for (RexNode expr : project.getProjects()) {
        if (RelOptUtil.InputFinder.bits(expr).asList().stream().anyMatch(
            i -> i >= lower && i < upper)) {
          return;
        }
      }
  
      final List<Integer> leftKeys = new ArrayList<>();
      final List<Integer> rightKeys = new ArrayList<>();
      RelOptUtil.splitJoinCondition(join.getLeft(), join.getRight(),
          join.getCondition(), leftKeys, rightKeys,
          new ArrayList<>());
  
      final List<Integer> joinKeys = isLeftJoin ? rightKeys : leftKeys;
      final ImmutableBitSet.Builder columns = ImmutableBitSet.builder();
      joinKeys.forEach(columns::set);
  
      final RelMetadataQuery mq = call.getMetadataQuery();
      if (!Boolean.TRUE.equals(
          mq.areColumnsUnique(isLeftJoin ? join.getRight() : join.getLeft(),
          columns.build()))) {
        return;
      }
  
      RelNode node;
      if (isLeftJoin) {
        node = project
            .copy(project.getTraitSet(), join.getLeft(), project.getProjects(),
                project.getRowType());
      } else {
        final int offset = join.getLeft().getRowType().getFieldCount();
        final List<RexNode> newExprs = project.getProjects().stream()
            .map(expr -> RexUtil.shift(expr, -offset))
            .collect(Collectors.toList());
        node =
            project.copy(project.getTraitSet(), join.getRight(), newExprs,
                project.getRowType());
      }
      call.transformTo(node);
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableProjectJoinRemoveRule.Config.of()
          .withOperandFor(LogicalProject.class, LogicalJoin.class);
  
      @Override default ProjectJoinRemoveRule toRule() {
        return new ProjectJoinRemoveRule(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(join ->
                    join.getJoinType() == JoinRelType.LEFT
                        || join.getJoinType() == JoinRelType.RIGHT).anyInputs()))
            .as(Config.class);
      }
    }
  }
  