/*
 * 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.iotdb.db.queryengine.plan.relational.planner.iterative.rule;

import org.apache.iotdb.db.queryengine.plan.planner.plan.node.PlanNode;
import org.apache.iotdb.db.queryengine.plan.relational.planner.Symbol;
import org.apache.iotdb.db.queryengine.plan.relational.planner.node.AggregationNode;

import com.google.common.collect.Maps;

import java.util.Map;
import java.util.Optional;
import java.util.Set;

import static org.apache.iotdb.db.queryengine.plan.relational.planner.node.Patterns.aggregation;

public class PruneAggregationColumns extends ProjectOffPushDownRule<AggregationNode> {
  public PruneAggregationColumns() {
    super(aggregation());
  }

  @Override
  protected Optional<PlanNode> pushDownProjectOff(
      Context context, AggregationNode aggregationNode, Set<Symbol> referencedOutputs) {
    Map<Symbol, AggregationNode.Aggregation> prunedAggregations =
        Maps.filterKeys(aggregationNode.getAggregations(), referencedOutputs::contains);

    if (prunedAggregations.size() == aggregationNode.getAggregations().size()) {
      return Optional.empty();
    }

    // PruneAggregationSourceColumns will subsequently project off any newly unused inputs.
    return Optional.of(
        AggregationNode.builderFrom(aggregationNode).setAggregations(prunedAggregations).build());
  }
}
