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.csv;
  
  import org.apache.calcite.adapter.enumerable.EnumerableConvention;
  import org.apache.calcite.adapter.enumerable.EnumerableRel;
  import org.apache.calcite.adapter.enumerable.EnumerableRelImplementor;
  import org.apache.calcite.adapter.enumerable.PhysType;
  import org.apache.calcite.adapter.enumerable.PhysTypeImpl;
  import org.apache.calcite.linq4j.tree.Blocks;
  import org.apache.calcite.linq4j.tree.Expressions;
  import org.apache.calcite.linq4j.tree.Primitive;
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelOptCost;
  import org.apache.calcite.plan.RelOptPlanner;
  import org.apache.calcite.plan.RelOptTable;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.RelWriter;
  import org.apache.calcite.rel.core.TableScan;
  import org.apache.calcite.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.rel.type.RelDataTypeFactory;
  import org.apache.calcite.rel.type.RelDataTypeField;
  
  import com.google.common.collect.ImmutableList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Relational expression representing a scan of a CSV file.
   *
   * <p>Like any table scan, it serves as a leaf node of a query tree.
   */
  public class CsvTableScan extends TableScan implements EnumerableRel {
    final CsvTranslatableTable csvTable;
    final int[] fields;
  
    protected CsvTableScan(RelOptCluster cluster, RelOptTable table,
        CsvTranslatableTable csvTable, int[] fields) {
      super(cluster, cluster.traitSetOf(EnumerableConvention.INSTANCE), ImmutableList.of(), table);
      this.csvTable = requireNonNull(csvTable, "csvTable");
      this.fields = fields;
    }
  
    @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
      assert inputs.isEmpty();
      return new CsvTableScan(getCluster(), table, csvTable, fields);
    }
  
    @Override public RelWriter explainTerms(RelWriter pw) {
      return super.explainTerms(pw)
          .item("fields", Primitive.asList(fields));
    }
  
    @Override public RelDataType deriveRowType() {
      final List<RelDataTypeField> fieldList = table.getRowType().getFieldList();
      final RelDataTypeFactory.Builder builder =
          getCluster().getTypeFactory().builder();
      for (int field : fields) {
        builder.add(fieldList.get(field));
      }
      return builder.build();
    }
  
    @Override public void register(RelOptPlanner planner) {
      planner.addRule(CsvRules.PROJECT_SCAN);
    }
  
    @Override public @Nullable RelOptCost computeSelfCost(RelOptPlanner planner,
        RelMetadataQuery mq) {
      // Multiply the cost by a factor that makes a scan more attractive if it
      // has significantly fewer fields than the original scan.
      //
      // The "+ 2D" on top and bottom keeps the function fairly smooth.
      //
      // For example, if table has 3 fields, project has 1 field,
      // then factor = (1 + 2) / (3 + 2) = 0.6
      final RelOptCost cost = requireNonNull(super.computeSelfCost(planner, mq));
      return cost
          .multiplyBy(((double) fields.length + 2D)
              / ((double) table.getRowType().getFieldCount() + 2D));
    }
  
    @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
      PhysType physType =
          PhysTypeImpl.of(
              implementor.getTypeFactory(),
              getRowType(),
              pref.preferArray());
  
      return implementor.result(
          physType,
          Blocks.toBlock(
              Expressions.call(
                  requireNonNull(table.getExpression(CsvTranslatableTable.class)),
                  "project", implementor.getRootExpression(),
                  Expressions.constant(fields))));
    }
  }
  