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.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<? extends RexNode> 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<RexNode> 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<Integer> projectedFields = getProjectFields(getProjects());
      if (projectedFields != null) {
        implementor.addProjectFields(projectedFields);
      }
    }
  
    static @Nullable List<Integer> getProjectFields(List<RexNode> exps) {
      final List<Integer> 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;
    }
  }
  