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   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
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  package org.apache.beam.sdk.extensions.sql.impl.rel;
  
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
  
  import java.util.List;
  import java.util.Map;
  import org.apache.beam.sdk.extensions.sql.impl.BeamCalciteTable;
  import org.apache.beam.sdk.extensions.sql.impl.planner.BeamCostModel;
  import org.apache.beam.sdk.extensions.sql.impl.planner.BeamRelMetadataQuery;
  import org.apache.beam.sdk.extensions.sql.impl.utils.CalciteUtils;
  import org.apache.beam.sdk.extensions.sql.meta.BeamSqlTable;
  import org.apache.beam.sdk.extensions.sql.meta.BeamSqlTableFilter;
  import org.apache.beam.sdk.extensions.sql.meta.DefaultTableFilter;
  import org.apache.beam.sdk.schemas.Schema;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.values.PBegin;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.PCollectionList;
  import org.apache.beam.sdk.values.Row;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.plan.RelOptCluster;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.plan.RelOptPlanner;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.plan.RelOptTable;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.plan.RelTraitSet;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.rel.RelWriter;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions;
  
  public class BeamPushDownIOSourceRel extends BeamIOSourceRel {
    private final List<String> usedFields;
    private final BeamSqlTableFilter tableFilters;
  
    public BeamPushDownIOSourceRel(
        RelOptCluster cluster,
        RelTraitSet traitSet,
        RelOptTable table,
        BeamSqlTable beamTable,
        List<String> usedFields,
        BeamSqlTableFilter tableFilters,
        Map<String, String> pipelineOptions,
        BeamCalciteTable calciteTable) {
      super(cluster, traitSet, table, beamTable, pipelineOptions, calciteTable);
      this.usedFields = usedFields;
      this.tableFilters = tableFilters;
    }
  
    @Override
    public RelWriter explainTerms(RelWriter pw) {
      super.explainTerms(pw);
  
      // This is done to tell Calcite planner that BeamIOSourceRel cannot be simply substituted by
      //  another BeamIOSourceRel, except for when they carry the same content.
      if (!usedFields.isEmpty()) {
        pw.item("usedFields", usedFields.toString());
      }
      if (!(tableFilters instanceof DefaultTableFilter)) {
        pw.item(tableFilters.getClass().getSimpleName(), tableFilters.toString());
      }
  
      return pw;
    }
  
    @Override
    public PTransform<PCollectionList<Row>, PCollection<Row>> buildPTransform() {
      return new Transform();
    }
  
    private class Transform extends PTransform<PCollectionList<Row>, PCollection<Row>> {
  
      @Override
      public PCollection<Row> expand(PCollectionList<Row> input) {
        checkArgument(
            input.size() == 0,
            "Should not have received input for %s: %s",
            BeamIOSourceRel.class.getSimpleName(),
            input);
  
        final PBegin begin = input.getPipeline().begin();
        final BeamSqlTable beamSqlTable = BeamPushDownIOSourceRel.this.getBeamSqlTable();
  
        if (usedFields.isEmpty() && tableFilters instanceof DefaultTableFilter) {
          return beamSqlTable.buildIOReader(begin);
        }
  
        final Schema newBeamSchema = CalciteUtils.toSchema(getRowType());
        return beamSqlTable
            .buildIOReader(begin, tableFilters, usedFields)
            .setRowSchema(newBeamSchema);
      }
    }
  
    @Override
    public BeamCostModel beamComputeSelfCost(RelOptPlanner planner, BeamRelMetadataQuery mq) {
      BeamCostModel parentCost = super.beamComputeSelfCost(planner, mq);
      Preconditions.checkArgument(parentCost.getCpu() >= 0, "Cpu cost must be zero or positive.");
      // Table schema will always contain all fields, while usedFields may contain less fields due to
      // push-down. Difference between the two will be the number of fields pushed-down. Bigger
      // difference - better.
      double projectBenefit = getBeamSqlTable().getSchema().getFieldCount() - usedFields.size();
      // Number of filters pushed-down should have a smaller impact.
      double filterBenefit = tableFilters.numSupported();
      // Normalize filterBenefit to be between 0.00 and (10% of projectBenefit).
      filterBenefit = (1.0 - (1.0 / (filterBenefit + 1))) * ((projectBenefit + 1) * 0.1);
      // Total totalBenefit of having push-down.
      double totalBenefit = projectBenefit + filterBenefit;
      // Normalize totalBenefit to be between 0.00 and 1.00.
      double normalizedBenefit = totalBenefit / (Math.max(totalBenefit, parentCost.getCpu()) + 1);
      BeamCostModel minus = BeamCostModel.FACTORY.makeTinyCost().multiplyBy(normalizedBenefit);
      return parentCost.minus(minus);
    }
  }
  