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/*
 * Copyright (c) 2018 Uber Technologies, Inc. ([email protected])
 *
 * Licensed 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 com.uber.hoodie.func;

import com.uber.hoodie.common.util.queue.BoundedInMemoryQueue;
import com.uber.hoodie.exception.HoodieIOException;
import java.io.IOException;
import java.util.Iterator;
import org.apache.parquet.hadoop.ParquetReader;

/**
 * This class wraps a parquet reader and provides an iterator based api to
 * read from a parquet file. This is used in {@link BoundedInMemoryQueue}
 */
public class ParquetReaderIterator implements Iterator {

  // Parquet reader for an existing parquet file
  private final ParquetReader parquetReader;
  // Holds the next entry returned by the parquet reader
  private T next;

  public ParquetReaderIterator(ParquetReader parquetReader) {
    this.parquetReader = parquetReader;
  }

  @Override
  public boolean hasNext() {
    try {
      // To handle when hasNext() is called multiple times for idempotency and/or the first time
      if (this.next == null) {
        this.next = parquetReader.read();
      }
      return this.next != null;
    } catch (IOException io) {
      throw new HoodieIOException("unable to read next record from parquet file ", io);
    }
  }

  @Override
  public T next() {
    try {
      // To handle case when next() is called before hasNext()
      if (this.next == null) {
        if (!hasNext()) {
          throw new HoodieIOException("No more records left to read from parquet file");
        }
      }
      T retVal = this.next;
      this.next = parquetReader.read();
      return retVal;
    } catch (IOException io) {
      throw new HoodieIOException("unable to read next record from parquet file ", io);
    }
  }

  public void close() throws IOException {
    parquetReader.close();
  }
}