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/*
 * Licensed 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 io.trino.sql.planner.iterative.rule;

import com.google.common.collect.Maps;
import io.trino.sql.planner.Symbol;
import io.trino.sql.planner.plan.AggregationNode;
import io.trino.sql.planner.plan.PlanNode;

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

import static io.trino.sql.planner.plan.Patterns.aggregation;

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

    @Override
    protected Optional pushDownProjectOff(
            Context context,
            AggregationNode aggregationNode,
            Set referencedOutputs)
    {
        Map 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());
    }
}