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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.druid.data.input.parquet;

import org.apache.druid.data.input.InputEntity;
import org.apache.druid.data.input.InputEntity.CleanableFile;
import org.apache.druid.data.input.InputRow;
import org.apache.druid.data.input.InputRowSchema;
import org.apache.druid.data.input.IntermediateRowParsingReader;
import org.apache.druid.data.input.impl.MapInputRowParser;
import org.apache.druid.data.input.parquet.simple.ParquetGroupFlattenerMaker;
import org.apache.druid.java.util.common.io.Closer;
import org.apache.druid.java.util.common.parsers.CloseableIterator;
import org.apache.druid.java.util.common.parsers.JSONPathSpec;
import org.apache.druid.java.util.common.parsers.ObjectFlattener;
import org.apache.druid.java.util.common.parsers.ObjectFlatteners;
import org.apache.druid.java.util.common.parsers.ParseException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.parquet.example.data.Group;
import org.apache.parquet.hadoop.example.GroupReadSupport;

import javax.annotation.Nullable;
import java.io.File;
import java.io.IOException;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;

public class ParquetReader extends IntermediateRowParsingReader
{
  private final Configuration conf;
  private final InputRowSchema inputRowSchema;
  private final InputEntity source;
  private final File temporaryDirectory;
  private final ObjectFlattener flattener;

  ParquetReader(
      Configuration conf,
      InputRowSchema inputRowSchema,
      InputEntity source,
      File temporaryDirectory,
      @Nullable JSONPathSpec flattenSpec,
      boolean binaryAsString
  )
  {
    this.conf = conf;
    this.inputRowSchema = inputRowSchema;
    this.source = source;
    this.temporaryDirectory = temporaryDirectory;
    this.flattener = ObjectFlatteners.create(
        flattenSpec,
        new ParquetGroupFlattenerMaker(
            binaryAsString,
            inputRowSchema.getDimensionsSpec().useSchemaDiscovery()
        )
    );
  }

  @Override
  protected CloseableIterator intermediateRowIterator() throws IOException
  {
    final Closer closer = Closer.create();
    byte[] buffer = new byte[InputEntity.DEFAULT_FETCH_BUFFER_SIZE];
    final ClassLoader currentClassLoader = Thread.currentThread().getContextClassLoader();
    final org.apache.parquet.hadoop.ParquetReader reader;
    try {
      final CleanableFile file = closer.register(source.fetch(temporaryDirectory, buffer));
      final Path path = new Path(file.file().toURI());

      Thread.currentThread().setContextClassLoader(getClass().getClassLoader());
      reader = closer.register(org.apache.parquet.hadoop.ParquetReader.builder(new GroupReadSupport(), path)
                                                                      .withConf(conf)
                                                                      .build());
    }
    catch (Exception e) {
      // We don't expect to see any exceptions thrown in the above try clause,
      // but we catch it just in case to avoid any potential resource leak.
      closer.close();
      throw new RuntimeException(e);
    }
    finally {
      Thread.currentThread().setContextClassLoader(currentClassLoader);
    }

    return new CloseableIterator()
    {
      Group value = null;

      @Override
      public boolean hasNext()
      {
        if (value == null) {
          try {
            value = reader.read();
          }
          catch (IOException e) {
            throw new RuntimeException(e);
          }
        }
        return value != null;
      }

      @Override
      public Group next()
      {
        if (value == null) {
          throw new NoSuchElementException();
        }
        Group currentValue = value;
        value = null;
        return currentValue;
      }

      @Override
      public void close() throws IOException
      {
        closer.close();
      }
    };
  }

  @Override
  protected InputEntity source()
  {
    return source;
  }

  @Override
  protected List parseInputRows(Group intermediateRow) throws ParseException
  {
    return Collections.singletonList(
        MapInputRowParser.parse(
            inputRowSchema,
            flattener.flatten(intermediateRow)
        )
    );
  }

  @Override
  protected List> toMap(Group intermediateRow)
  {
    return Collections.singletonList(flattener.toMap(intermediateRow));
  }
}