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A table format for huge analytic datasets
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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.iceberg;

import com.github.benmanes.caffeine.cache.Caffeine;
import com.github.benmanes.caffeine.cache.LoadingCache;
import java.util.Map;
import org.apache.iceberg.expressions.ManifestEvaluator;
import org.apache.iceberg.io.CloseableIterable;
import org.apache.iceberg.io.FileIO;
import org.apache.iceberg.relocated.com.google.common.annotations.VisibleForTesting;
import org.apache.iceberg.relocated.com.google.common.collect.Maps;
import org.apache.iceberg.types.Types;

/** A {@link Table} implementation that exposes a table's partitions as rows. */
public class PartitionsTable extends BaseMetadataTable {

  private final Schema schema;
  static final boolean PLAN_SCANS_WITH_WORKER_POOL =
      SystemProperties.getBoolean(SystemProperties.SCAN_THREAD_POOL_ENABLED, true);

  PartitionsTable(Table table) {
    this(table, table.name() + ".partitions");
  }

  PartitionsTable(Table table, String name) {
    super(table, name);

    this.schema =
        new Schema(
            Types.NestedField.required(1, "partition", Partitioning.partitionType(table)),
            Types.NestedField.required(2, "record_count", Types.LongType.get()),
            Types.NestedField.required(3, "file_count", Types.IntegerType.get()),
            Types.NestedField.required(4, "spec_id", Types.IntegerType.get()));
  }

  @Override
  public TableScan newScan() {
    return new PartitionsScan(table());
  }

  @Override
  public Schema schema() {
    if (table().spec().fields().size() < 1) {
      return schema.select("record_count", "file_count");
    }
    return schema;
  }

  @Override
  MetadataTableType metadataTableType() {
    return MetadataTableType.PARTITIONS;
  }

  private DataTask task(StaticTableScan scan) {
    Iterable partitions = partitions(table(), scan);
    if (table().spec().fields().size() < 1) {
      // the table is unpartitioned, partitions contains only the root partition
      return StaticDataTask.of(
          io().newInputFile(table().operations().current().metadataFileLocation()),
          schema(),
          scan.schema(),
          partitions,
          root -> StaticDataTask.Row.of(root.recordCount, root.fileCount));
    } else {
      return StaticDataTask.of(
          io().newInputFile(table().operations().current().metadataFileLocation()),
          schema(),
          scan.schema(),
          partitions,
          PartitionsTable::convertPartition);
    }
  }

  private static StaticDataTask.Row convertPartition(Partition partition) {
    return StaticDataTask.Row.of(
        partition.key, partition.recordCount, partition.fileCount, partition.specId);
  }

  private static Iterable partitions(Table table, StaticTableScan scan) {
    CloseableIterable tasks = planFiles(scan);
    Types.StructType normalizedPartitionType = Partitioning.partitionType(table);
    PartitionMap partitions = new PartitionMap();

    // cache a position map needed by each partition spec to normalize partitions to final schema
    Map normalizedPositionsBySpec =
        Maps.newHashMapWithExpectedSize(table.specs().size());

    for (FileScanTask task : tasks) {
      PartitionData original = (PartitionData) task.file().partition();
      int[] normalizedPositions =
          normalizedPositionsBySpec.computeIfAbsent(
              task.spec().specId(),
              specId -> normalizedPositions(table, specId, normalizedPartitionType));
      PartitionData normalized =
          normalizePartition(original, normalizedPartitionType, normalizedPositions);
      partitions.get(normalized).update(task.file());
    }
    return partitions.all();
  }

  /**
   * Builds an array of the field position of positions in the normalized partition type indexed by
   * field position in the original partition type
   */
  private static int[] normalizedPositions(
      Table table, int specId, Types.StructType normalizedType) {
    Types.StructType originalType = table.specs().get(specId).partitionType();
    int[] normalizedPositions = new int[originalType.fields().size()];
    for (int originalIndex = 0; originalIndex < originalType.fields().size(); originalIndex++) {
      Types.NestedField normalizedField =
          normalizedType.field(originalType.fields().get(originalIndex).fieldId());
      normalizedPositions[originalIndex] = normalizedType.fields().indexOf(normalizedField);
    }
    return normalizedPositions;
  }

  /**
   * Convert a partition data written by an old spec, to table's normalized partition type, which is
   * a common partition type for all specs of the table.
   *
   * @param originalPartition un-normalized partition data
   * @param normalizedPartitionType table's normalized partition type {@link
   *     Partitioning#partitionType(Table)}
   * @param normalizedPositions field positions in the normalized partition type indexed by field
   *     position in the original partition type
   * @return the normalized partition data
   */
  private static PartitionData normalizePartition(
      PartitionData originalPartition,
      Types.StructType normalizedPartitionType,
      int[] normalizedPositions) {
    PartitionData normalizedPartition = new PartitionData(normalizedPartitionType);
    for (int originalIndex = 0; originalIndex < originalPartition.size(); originalIndex++) {
      normalizedPartition.put(
          normalizedPositions[originalIndex], originalPartition.get(originalIndex));
    }
    return normalizedPartition;
  }

  @VisibleForTesting
  static CloseableIterable planFiles(StaticTableScan scan) {
    Table table = scan.table();
    Snapshot snapshot = table.snapshot(scan.snapshot().snapshotId());
    boolean caseSensitive = scan.isCaseSensitive();

    LoadingCache evalCache =
        Caffeine.newBuilder()
            .build(
                specId -> {
                  PartitionSpec spec = table.specs().get(specId);
                  PartitionSpec transformedSpec = transformSpec(scan.tableSchema(), spec);
                  return ManifestEvaluator.forRowFilter(
                      scan.filter(), transformedSpec, caseSensitive);
                });

    FileIO io = table.io();
    ManifestGroup manifestGroup =
        new ManifestGroup(io, snapshot.dataManifests(io), snapshot.deleteManifests(io))
            .caseSensitive(caseSensitive)
            .filterManifests(m -> evalCache.get(m.partitionSpecId()).eval(m))
            .select(scan.scanColumns())
            .specsById(scan.table().specs())
            .ignoreDeleted();

    if (scan.shouldIgnoreResiduals()) {
      manifestGroup = manifestGroup.ignoreResiduals();
    }

    if (scan.snapshot().dataManifests(io).size() > 1
        && (PLAN_SCANS_WITH_WORKER_POOL || scan.context().planWithCustomizedExecutor())) {
      manifestGroup = manifestGroup.planWith(scan.context().planExecutor());
    }

    return manifestGroup.planFiles();
  }

  private class PartitionsScan extends StaticTableScan {
    PartitionsScan(Table table) {
      super(
          table,
          PartitionsTable.this.schema(),
          MetadataTableType.PARTITIONS,
          PartitionsTable.this::task);
    }
  }

  static class PartitionMap {
    private final Map partitions = Maps.newHashMap();

    Partition get(PartitionData key) {
      Partition partition = partitions.get(key);
      if (partition == null) {
        partition = new Partition(key);
        partitions.put(key, partition);
      }
      return partition;
    }

    Iterable all() {
      return partitions.values();
    }
  }

  static class Partition {
    private final StructLike key;
    private long recordCount;
    private int fileCount;
    private int specId;

    Partition(StructLike key) {
      this.key = key;
      this.recordCount = 0;
      this.fileCount = 0;
      this.specId = 0;
    }

    void update(DataFile file) {
      this.recordCount += file.recordCount();
      this.fileCount += 1;
      this.specId = file.specId();
    }
  }
}