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.Aggregate;
  import org.apache.calcite.rel.core.Aggregate.Group;
  import org.apache.calcite.rel.core.AggregateCall;
  import org.apache.calcite.rel.core.Project;
  import org.apache.calcite.rex.RexInputRef;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.tools.RelBuilder;
  import org.apache.calcite.tools.RelBuilderFactory;
  import org.apache.calcite.util.ImmutableBitSet;
  import org.apache.calcite.util.Util;
  import org.apache.calcite.util.mapping.Mappings;
  
  import com.google.common.collect.ImmutableList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.immutables.value.Value;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Planner rule that recognizes a {@link org.apache.calcite.rel.core.Aggregate}
   * on top of a {@link org.apache.calcite.rel.core.Project} and if possible
   * aggregate through the project or removes the project.
   *
   * <p>This is only possible when the grouping expressions and arguments to
   * the aggregate functions are field references (i.e. not expressions).
   *
   * <p>In some cases, this rule has the effect of trimming: the aggregate will
   * use fewer columns than the project did.
   *
   * @see CoreRules#AGGREGATE_PROJECT_MERGE
   */
  @Value.Enclosing
  public class AggregateProjectMergeRule
      extends RelRule<AggregateProjectMergeRule.Config>
      implements TransformationRule {
  
    /** Creates an AggregateProjectMergeRule. */
    protected AggregateProjectMergeRule(Config config) {
      super(config);
    }
  
    @Deprecated // to be removed before 2.0
    public AggregateProjectMergeRule(
        Class<? extends Aggregate> aggregateClass,
        Class<? extends Project> projectClass,
        RelBuilderFactory relBuilderFactory) {
      this(CoreRules.AGGREGATE_PROJECT_MERGE.config
          .withRelBuilderFactory(relBuilderFactory)
          .as(Config.class)
          .withOperandFor(aggregateClass, projectClass));
    }
  
    @Override public void onMatch(RelOptRuleCall call) {
      final Aggregate aggregate = call.rel(0);
      final Project project = call.rel(1);
      RelNode x = apply(call, aggregate, project);
      if (x != null) {
        call.transformTo(x);
      }
    }
  
    public static @Nullable RelNode apply(RelOptRuleCall call, Aggregate aggregate,
        Project project) {
      // Find all fields which we need to be straightforward field projections.
      final Set<Integer> interestingFields = RelOptUtil.getAllFields(aggregate);
  
      // Build the map from old to new; abort if any entry is not a
      // straightforward field projection.
      final Map<Integer, Integer> map = new HashMap<>();
      for (int source : interestingFields) {
        final RexNode rex = project.getProjects().get(source);
        if (!(rex instanceof RexInputRef)) {
          return null;
        }
        map.put(source, ((RexInputRef) rex).getIndex());
      }
  
      final ImmutableBitSet newGroupSet = aggregate.getGroupSet().permute(map);
      ImmutableList<ImmutableBitSet> newGroupingSets = null;
      if (aggregate.getGroupType() != Group.SIMPLE) {
        newGroupingSets =
            ImmutableBitSet.ORDERING.immutableSortedCopy(
                ImmutableBitSet.permute(aggregate.getGroupSets(), map));
      }
  
      final ImmutableList.Builder<AggregateCall> aggCalls =
          ImmutableList.builder();
      final int sourceCount = aggregate.getInput().getRowType().getFieldCount();
      final int targetCount = project.getInput().getRowType().getFieldCount();
      final Mappings.TargetMapping targetMapping =
          Mappings.target(map, sourceCount, targetCount);
      for (AggregateCall aggregateCall : aggregate.getAggCallList()) {
        aggCalls.add(aggregateCall.transform(targetMapping));
      }
  
      final Aggregate newAggregate =
          aggregate.copy(aggregate.getTraitSet(), project.getInput(),
              newGroupSet, newGroupingSets, aggCalls.build());
  
      // Add a project if the group set is not in the same order or
      // contains duplicates.
      final RelBuilder relBuilder = call.builder();
      relBuilder.push(newAggregate);
      final List<Integer> newKeys =
          Util.transform(aggregate.getGroupSet().asList(),
              key -> requireNonNull(map.get(key),
                  () -> "no value found for key " + key + " in " + map));
      if (!newKeys.equals(newGroupSet.asList())) {
        final List<Integer> posList = new ArrayList<>();
        for (int newKey : newKeys) {
          posList.add(newGroupSet.indexOf(newKey));
        }
        for (int i = newAggregate.getGroupCount();
             i < newAggregate.getRowType().getFieldCount(); i++) {
          posList.add(i);
        }
        relBuilder.project(relBuilder.fields(posList));
      }
  
      return relBuilder.build();
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableAggregateProjectMergeRule.Config.of()
          .withOperandFor(Aggregate.class, Project.class);
  
      @Override default AggregateProjectMergeRule toRule() {
        return new AggregateProjectMergeRule(this);
      }
  
      /** Defines an operand tree for the given classes. */
      default Config withOperandFor(Class<? extends Aggregate> aggregateClass,
          Class<? extends Project> projectClass) {
        return withOperandSupplier(b0 ->
            b0.operand(aggregateClass).oneInput(b1 ->
                b1.operand(projectClass).anyInputs())).as(Config.class);
      }
    }
  }
  