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   * Licensed to the Apache Software Foundation (ASF) under one
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   * distributed with this work for additional information
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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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   *
   *     http://www.apache.org/licenses/LICENSE-2.0
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   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
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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.Collections;
  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.planner.NodeStats;
  import org.apache.beam.sdk.extensions.sql.impl.utils.CalciteUtils;
  import org.apache.beam.sdk.schemas.Schema;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.transforms.ParDo;
  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.RelTraitSet;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.rel.RelNode;
  import org.apache.beam.vendor.calcite.v1_40_0.org.apache.calcite.rel.core.Uncollect;
  
  /** {@link BeamRelNode} to implement an uncorrelated {@link Uncollect}, aka UNNEST. */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class BeamUncollectRel extends Uncollect implements BeamRelNode {
  
    public BeamUncollectRel(
        RelOptCluster cluster, RelTraitSet traitSet, RelNode input, boolean withOrdinality) {
      super(cluster, traitSet, input, withOrdinality, Collections.emptyList());
    }
  
    @Override
    public RelNode copy(RelTraitSet traitSet, RelNode input) {
      return new BeamUncollectRel(getCluster(), traitSet, input, withOrdinality);
    }
  
    @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> pinput) {
        checkArgument(
            pinput.size() == 1,
            "Wrong number of inputs for %s: %s",
            BeamUncollectRel.class.getSimpleName(),
            pinput);
        PCollection<Row> upstream = pinput.get(0);
  
        // Each row of the input contains a single array of things to be emitted; Calcite knows
        // what the row looks like
        Schema outputSchema = CalciteUtils.toSchema(getRowType());
  
        PCollection<Row> uncollected =
            upstream.apply(ParDo.of(new UncollectDoFn(outputSchema))).setRowSchema(outputSchema);
  
        return uncollected;
      }
    }
  
    @Override
    public NodeStats estimateNodeStats(BeamRelMetadataQuery mq) {
      // We estimate the average length of each array by a constant.
      // We might be able to get an estimate of the length by making a MetadataHandler for this
      // purpose, and get the estimate by reading the first couple of the rows in the source.
      return BeamSqlRelUtils.getNodeStats(this.input, mq).multiply(2);
    }
  
    @Override
    public BeamCostModel beamComputeSelfCost(RelOptPlanner planner, BeamRelMetadataQuery mq) {
      NodeStats estimates = BeamSqlRelUtils.getNodeStats(this, mq);
      return BeamCostModel.FACTORY.makeCost(estimates.getRowCount(), estimates.getRate());
    }
  
    private static class UncollectDoFn extends DoFn<Row, Row> {
  
      private final Schema schema;
  
      private UncollectDoFn(Schema schema) {
        this.schema = schema;
      }
  
      @ProcessElement
      public void process(@Element Row inputRow, OutputReceiver<Row> output) {
        for (Object element : inputRow.getArray(0)) {
          if (element instanceof Row) {
            Row nestedRow = (Row) element;
            output.output(Row.withSchema(schema).addValues(nestedRow.getBaseValues()).build());
          } else {
            output.output(Row.withSchema(schema).addValue(element).build());
          }
        }
      }
    }
  }
  