content: /*
   * 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 tech.mlsql.common;
  
  import org.apache.parquet.hadoop.ParquetReader;
  
  import java.io.IOException;
  import java.util.Iterator;
  
  
  public class ParquetReaderIterator<T> implements Iterator<T> {
  
      // Parquet reader for an existing parquet file
      private final ParquetReader<T> parquetReader;
      // Holds the next entry returned by the parquet reader
      private T next;
  
      public ParquetReaderIterator(ParquetReader<T> 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 RuntimeException("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 RuntimeException("No more records left to read from parquet file");
                  }
              }
              T retVal = this.next;
              this.next = parquetReader.read();
              return retVal;
          } catch (IOException io) {
              throw new RuntimeException("unable to read next record from parquet file ", io);
          }
      }
  
      public void close() throws IOException {
          parquetReader.close();
      }
  }
  
  