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Arrow adapter for Calcite
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/*
 * 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.adapter.arrow;

import org.apache.calcite.plan.RelOptCluster;
import org.apache.calcite.plan.RelOptCost;
import org.apache.calcite.plan.RelOptPlanner;
import org.apache.calcite.plan.RelTraitSet;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.core.Project;
import org.apache.calcite.rel.metadata.RelMetadataQuery;
import org.apache.calcite.rel.type.RelDataType;
import org.apache.calcite.rex.RexInputRef;
import org.apache.calcite.rex.RexNode;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;

import org.checkerframework.checker.nullness.qual.Nullable;

import java.util.ArrayList;
import java.util.List;

import static java.util.Objects.requireNonNull;

/**
 * Implementation of {@link org.apache.calcite.rel.core.Project}
 * relational expression in Arrow.
 */
class ArrowProject extends Project implements ArrowRel {

  /** Creates an ArrowProject. */
  ArrowProject(RelOptCluster cluster, RelTraitSet traitSet,
      RelNode input, List projects, RelDataType rowType) {
    super(cluster, traitSet, ImmutableList.of(), input, projects, rowType, ImmutableSet.of());
    assert getConvention() == ArrowRel.CONVENTION;
    assert getConvention() == input.getConvention();
  }

  @Override public Project copy(RelTraitSet traitSet, RelNode input,
      List projects, RelDataType rowType) {
    return new ArrowProject(getCluster(), traitSet, input, projects,
        rowType);
  }

  @Override public RelOptCost computeSelfCost(RelOptPlanner planner,
      RelMetadataQuery mq) {
    final RelOptCost cost = super.computeSelfCost(planner, mq);
    return requireNonNull(cost, "cost").multiplyBy(0.1);
  }

  @Override public void implement(Implementor implementor) {
    implementor.visitInput(0, getInput());
    List projectedFields = getProjectFields(getProjects());
    if (projectedFields != null) {
      implementor.addProjectFields(projectedFields);
    }
  }

  static @Nullable List getProjectFields(List exps) {
    final List fields = new ArrayList<>();
    for (final RexNode exp : exps) {
      if (exp instanceof RexInputRef) {
        fields.add(((RexInputRef) exp).getIndex());
      } else {
        return null; // not a simple projection
      }
    }
    return fields;
  }
}