/**
 * 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.drill.exec.store.parquet.columnreaders;

import com.google.common.base.Stopwatch;
import com.google.common.collect.Lists;
import org.apache.drill.common.exceptions.DrillRuntimeException;
import org.apache.drill.exec.vector.ValueVector;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

public class VarLenBinaryReader {

  ParquetRecordReader parentReader;
  final List<VarLengthColumn<? extends ValueVector>> columns;
  final boolean useAsyncTasks;
  private final long targetRecordCount;

  public VarLenBinaryReader(ParquetRecordReader parentReader, List<VarLengthColumn<? extends ValueVector>> columns) {
    this.parentReader = parentReader;
    this.columns = columns;
    useAsyncTasks = parentReader.useAsyncColReader;

    // Can't read any more records than fixed width fields will fit.
    // Note: this calculation is very likely wrong; it is a simplified
    // version of earlier code, but probably needs even more attention.

    int totalFixedFieldWidth = parentReader.getBitWidthAllFixedFields() / 8;
    if (totalFixedFieldWidth == 0) {
      targetRecordCount = 0;
    } else {
      targetRecordCount = parentReader.getBatchSize() / totalFixedFieldWidth;
    }
  }

  /**
   * Reads as many variable length values as possible.
   *
   * @param recordsToReadInThisPass - the number of records recommended for reading form the reader
   * @param firstColumnStatus - a reference to the first column status in the Parquet file to grab metatdata from
   * @return - the number of fixed length fields that will fit in the batch
   * @throws IOException
   */
  public long readFields(long recordsToReadInThisPass) throws IOException {

    // write the first 0 offset
    for (VarLengthColumn<?> columnReader : columns) {
      columnReader.reset();
    }
    Stopwatch timer = Stopwatch.createStarted();

    // Can't read any more records than fixed width fields will fit.

    if (targetRecordCount > 0) {
      recordsToReadInThisPass = Math.min(recordsToReadInThisPass, targetRecordCount);
    }
    long recordsReadInCurrentPass = determineSizesSerial(recordsToReadInThisPass);

    if(useAsyncTasks) {
      readRecordsParallel(recordsReadInCurrentPass);
    } else {
      readRecordsSerial(recordsReadInCurrentPass);
    }

    parentReader.parquetReaderStats.timeVarColumnRead.addAndGet(timer.elapsed(TimeUnit.NANOSECONDS));

    return recordsReadInCurrentPass;
  }

  private long determineSizesSerial(long recordsToReadInThisPass) throws IOException {

    int recordsReadInCurrentPass = 0;
    top: do {
      for (VarLengthColumn<?> columnReader : columns) {
        // Return status is "done reading", meaning stop if true.
        if (columnReader.determineSize(recordsReadInCurrentPass)) {
          break top;
        }
      }
      for (VarLengthColumn<?> columnReader : columns) {
        columnReader.updateReadyToReadPosition();
        columnReader.currDefLevel = -1;
      }
      recordsReadInCurrentPass++;
    } while (recordsReadInCurrentPass < recordsToReadInThisPass);

    return recordsReadInCurrentPass;
  }

  private void readRecordsSerial(long recordsReadInCurrentPass) {
    for (VarLengthColumn<?> columnReader : columns) {
      columnReader.readRecords(columnReader.pageReader.valuesReadyToRead);
    }
    for (VarLengthColumn<?> columnReader : columns) {
      columnReader.valueVec.getMutator().setValueCount((int)recordsReadInCurrentPass);
    }
  }

  private void readRecordsParallel(long recordsReadInCurrentPass){
    ArrayList<Future<Integer>> futures = Lists.newArrayList();
    for (VarLengthColumn<?> columnReader : columns) {
      Future<Integer> f = columnReader.readRecordsAsync(columnReader.pageReader.valuesReadyToRead);
      futures.add(f);
    }
    Exception exception = null;
    for(Future<Integer> f: futures){
      if(exception != null) {
        f.cancel(true);
      } else {
        try {
          f.get();
        } catch (Exception e) {
          f.cancel(true);
          exception = e;
        }
      }
    }
    for (VarLengthColumn<?> columnReader : columns) {
      columnReader.valueVec.getMutator().setValueCount((int)recordsReadInCurrentPass);
    }
  }

  protected void handleAndRaise(String s, Exception e) {
    String message = "Error in parquet record reader.\nMessage: " + s;
    throw new DrillRuntimeException(message, e);
  }

}