/*
 * 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.iotdb.db.query.reader.series;

import org.apache.iotdb.db.conf.IoTDBDescriptor;
import org.apache.iotdb.db.engine.querycontext.QueryDataSource;
import org.apache.iotdb.db.engine.storagegroup.TsFileResource;
import org.apache.iotdb.db.metadata.PartialPath;
import org.apache.iotdb.db.query.context.QueryContext;
import org.apache.iotdb.db.query.control.QueryResourceManager;
import org.apache.iotdb.db.query.control.QueryTimeManager;
import org.apache.iotdb.db.query.filter.TsFileFilter;
import org.apache.iotdb.db.query.reader.universal.DescPriorityMergeReader;
import org.apache.iotdb.db.query.reader.universal.PriorityMergeReader;
import org.apache.iotdb.db.query.reader.universal.PriorityMergeReader.MergeReaderPriority;
import org.apache.iotdb.db.utils.FileLoaderUtils;
import org.apache.iotdb.db.utils.QueryUtils;
import org.apache.iotdb.db.utils.TestOnly;
import org.apache.iotdb.tsfile.file.metadata.IChunkMetadata;
import org.apache.iotdb.tsfile.file.metadata.ITimeSeriesMetadata;
import org.apache.iotdb.tsfile.file.metadata.TimeseriesMetadata;
import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
import org.apache.iotdb.tsfile.file.metadata.statistics.Statistics;
import org.apache.iotdb.tsfile.read.TimeValuePair;
import org.apache.iotdb.tsfile.read.common.BatchData;
import org.apache.iotdb.tsfile.read.common.BatchDataFactory;
import org.apache.iotdb.tsfile.read.filter.basic.Filter;
import org.apache.iotdb.tsfile.read.filter.basic.UnaryFilter;
import org.apache.iotdb.tsfile.read.reader.IPageReader;

import java.io.IOException;
import java.io.Serializable;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import java.util.Objects;
import java.util.PriorityQueue;
import java.util.Set;
import java.util.function.ToLongFunction;
import java.util.stream.Collectors;

public class SeriesReader {

  // inner class of SeriesReader for order purpose
  protected TimeOrderUtils orderUtils;

  protected final PartialPath seriesPath;

  // all the sensors in this device;
  protected final Set<String> allSensors;
  protected final TSDataType dataType;
  protected final QueryContext context;

  /*
   * There is at most one is not null between timeFilter and valueFilter
   *
   * timeFilter is pushed down to all pages (seq, unseq) without correctness problem
   *
   * valueFilter is pushed down to non-overlapped page only
   */
  protected final Filter timeFilter;
  protected final Filter valueFilter;
  /*
   * file cache
   */
  protected final List<TsFileResource> seqFileResource;
  protected final List<TsFileResource> unseqFileResource;

  /*
   * TimeSeriesMetadata cache
   */
  protected ITimeSeriesMetadata firstTimeSeriesMetadata;
  protected final List<ITimeSeriesMetadata> seqTimeSeriesMetadata = new LinkedList<>();
  protected final PriorityQueue<ITimeSeriesMetadata> unSeqTimeSeriesMetadata;

  /*
   * chunk cache
   */
  protected IChunkMetadata firstChunkMetadata;
  protected final PriorityQueue<IChunkMetadata> cachedChunkMetadata;

  /*
   * page cache
   */
  protected VersionPageReader firstPageReader;
  protected final List<VersionPageReader> seqPageReaders = new LinkedList<>();
  protected final PriorityQueue<VersionPageReader> unSeqPageReaders;

  /*
   * point cache
   */
  protected final PriorityMergeReader mergeReader;

  /*
   * result cache
   */
  protected boolean hasCachedNextOverlappedPage;
  protected BatchData cachedBatchData;

  public SeriesReader(
      PartialPath seriesPath,
      Set<String> allSensors,
      TSDataType dataType,
      QueryContext context,
      QueryDataSource dataSource,
      Filter timeFilter,
      Filter valueFilter,
      TsFileFilter fileFilter,
      boolean ascending) {
    this.seriesPath = seriesPath;
    this.allSensors = allSensors;
    this.dataType = dataType;
    this.context = context;
    QueryUtils.filterQueryDataSource(dataSource, fileFilter);
    this.timeFilter = timeFilter;
    this.valueFilter = valueFilter;
    if (ascending) {
      this.orderUtils = new AscTimeOrderUtils();
      mergeReader = new PriorityMergeReader();
    } else {
      this.orderUtils = new DescTimeOrderUtils();
      mergeReader = new DescPriorityMergeReader();
    }

    this.seqFileResource = new LinkedList<>(dataSource.getSeqResources());
    this.unseqFileResource = sortUnSeqFileResources(dataSource.getUnseqResources());
    unSeqTimeSeriesMetadata =
        new PriorityQueue<>(
            orderUtils.comparingLong(
                timeSeriesMetadata -> orderUtils.getOrderTime(timeSeriesMetadata.getStatistics())));
    cachedChunkMetadata =
        new PriorityQueue<>(
            orderUtils.comparingLong(
                chunkMetadata -> orderUtils.getOrderTime(chunkMetadata.getStatistics())));
    unSeqPageReaders =
        new PriorityQueue<>(
            orderUtils.comparingLong(
                versionPageReader -> orderUtils.getOrderTime(versionPageReader.getStatistics())));
  }

  @TestOnly
  @SuppressWarnings("squid:S107")
  SeriesReader(
      PartialPath seriesPath,
      Set<String> allSensors,
      TSDataType dataType,
      QueryContext context,
      List<TsFileResource> seqFileResource,
      List<TsFileResource> unseqFileResource,
      Filter timeFilter,
      Filter valueFilter,
      boolean ascending) {
    this.seriesPath = seriesPath;
    this.allSensors = allSensors;
    this.dataType = dataType;
    this.context = context;
    this.timeFilter = timeFilter;
    this.valueFilter = valueFilter;
    if (ascending) {
      this.orderUtils = new AscTimeOrderUtils();
      mergeReader = new PriorityMergeReader();
    } else {
      this.orderUtils = new DescTimeOrderUtils();
      mergeReader = new DescPriorityMergeReader();
    }

    this.seqFileResource = new LinkedList<>(seqFileResource);
    this.unseqFileResource = sortUnSeqFileResources(unseqFileResource);
    unSeqTimeSeriesMetadata =
        new PriorityQueue<>(
            orderUtils.comparingLong(
                timeSeriesMetadata -> orderUtils.getOrderTime(timeSeriesMetadata.getStatistics())));
    cachedChunkMetadata =
        new PriorityQueue<>(
            orderUtils.comparingLong(
                chunkMetadata -> orderUtils.getOrderTime(chunkMetadata.getStatistics())));
    unSeqPageReaders =
        new PriorityQueue<>(
            orderUtils.comparingLong(
                versionPageReader -> orderUtils.getOrderTime(versionPageReader.getStatistics())));
  }

  public boolean isEmpty() throws IOException {
    return !(hasNextPage() || hasNextChunk() || hasNextFile());
  }

  boolean hasNextFile() throws IOException {
    QueryTimeManager.checkQueryAlive(context.getQueryId());

    if (!unSeqPageReaders.isEmpty()
        || firstPageReader != null
        || mergeReader.hasNextTimeValuePair()) {
      throw new IOException(
          "all cached pages should be consumed first cachedPageReaders.isEmpty() is "
              + unSeqPageReaders.isEmpty()
              + " firstPageReader != null is "
              + (firstPageReader != null)
              + " mergeReader.hasNextTimeValuePair() = "
              + mergeReader.hasNextTimeValuePair());
    }

    if (firstChunkMetadata != null || !cachedChunkMetadata.isEmpty()) {
      throw new IOException("all cached chunks should be consumed first");
    }

    if (firstTimeSeriesMetadata != null) {
      return true;
    }

    // init first time series metadata whose startTime is minimum
    tryToUnpackAllOverlappedFilesToTimeSeriesMetadata();

    return firstTimeSeriesMetadata != null;
  }

  boolean isFileOverlapped() throws IOException {
    if (firstTimeSeriesMetadata == null) {
      throw new IOException("no first file");
    }

    Statistics fileStatistics = firstTimeSeriesMetadata.getStatistics();
    return !seqTimeSeriesMetadata.isEmpty()
            && orderUtils.isOverlapped(fileStatistics, seqTimeSeriesMetadata.get(0).getStatistics())
        || !unSeqTimeSeriesMetadata.isEmpty()
            && orderUtils.isOverlapped(
                fileStatistics, unSeqTimeSeriesMetadata.peek().getStatistics());
  }

  Statistics currentFileStatistics() {
    return firstTimeSeriesMetadata.getStatistics();
  }

  boolean currentFileModified() throws IOException {
    if (firstTimeSeriesMetadata == null) {
      throw new IOException("no first file");
    }
    return firstTimeSeriesMetadata.isModified();
  }

  void skipCurrentFile() {
    firstTimeSeriesMetadata = null;
  }

  /**
   * This method should be called after hasNextFile() until no next chunk, make sure that all
   * overlapped chunks are consumed
   */
  boolean hasNextChunk() throws IOException {
    QueryTimeManager.checkQueryAlive(context.getQueryId());

    if (!unSeqPageReaders.isEmpty()
        || firstPageReader != null
        || mergeReader.hasNextTimeValuePair()) {
      throw new IOException(
          "all cached pages should be consumed first cachedPageReaders.isEmpty() is "
              + unSeqPageReaders.isEmpty()
              + " firstPageReader != null is "
              + (firstPageReader != null)
              + " mergeReader.hasNextTimeValuePair() = "
              + mergeReader.hasNextTimeValuePair());
    }

    if (firstChunkMetadata != null) {
      return true;
    }

    /*
     * construct first chunk metadata
     */
    if (firstTimeSeriesMetadata != null) {
      /*
       * try to unpack all overlapped TimeSeriesMetadata to cachedChunkMetadata
       */
      unpackAllOverlappedTsFilesToTimeSeriesMetadata(
          orderUtils.getOverlapCheckTime(firstTimeSeriesMetadata.getStatistics()));
      unpackAllOverlappedTimeSeriesMetadataToCachedChunkMetadata(
          orderUtils.getOverlapCheckTime(firstTimeSeriesMetadata.getStatistics()), true);
    } else {
      /*
       * first time series metadata is already unpacked, consume cached ChunkMetadata
       */
      if (!cachedChunkMetadata.isEmpty()) {
        firstChunkMetadata = cachedChunkMetadata.poll();
        unpackAllOverlappedTsFilesToTimeSeriesMetadata(
            orderUtils.getOverlapCheckTime(firstChunkMetadata.getStatistics()));
        unpackAllOverlappedTimeSeriesMetadataToCachedChunkMetadata(
            orderUtils.getOverlapCheckTime(firstChunkMetadata.getStatistics()), false);
      }
    }

    return firstChunkMetadata != null;
  }

  private void unpackAllOverlappedTimeSeriesMetadataToCachedChunkMetadata(
      long endpointTime, boolean init) throws IOException {
    while (!seqTimeSeriesMetadata.isEmpty()
        && orderUtils.isOverlapped(endpointTime, seqTimeSeriesMetadata.get(0).getStatistics())) {
      unpackOneTimeSeriesMetadata(seqTimeSeriesMetadata.remove(0));
    }
    while (!unSeqTimeSeriesMetadata.isEmpty()
        && orderUtils.isOverlapped(endpointTime, unSeqTimeSeriesMetadata.peek().getStatistics())) {
      unpackOneTimeSeriesMetadata(unSeqTimeSeriesMetadata.poll());
    }

    if (firstTimeSeriesMetadata != null
        && orderUtils.isOverlapped(endpointTime, firstTimeSeriesMetadata.getStatistics())) {
      unpackOneTimeSeriesMetadata(firstTimeSeriesMetadata);
      firstTimeSeriesMetadata = null;
    }

    if (init && firstChunkMetadata == null && !cachedChunkMetadata.isEmpty()) {
      firstChunkMetadata = cachedChunkMetadata.poll();
    }
  }

  protected void unpackOneTimeSeriesMetadata(ITimeSeriesMetadata timeSeriesMetadata)
      throws IOException {
    List<IChunkMetadata> chunkMetadataList =
        FileLoaderUtils.loadChunkMetadataList(timeSeriesMetadata);
    chunkMetadataList.forEach(chunkMetadata -> chunkMetadata.setSeq(timeSeriesMetadata.isSeq()));

    // try to calculate the total number of chunk and time-value points in chunk
    if (IoTDBDescriptor.getInstance().getConfig().isEnablePerformanceTracing()) {
      QueryResourceManager queryResourceManager = QueryResourceManager.getInstance();
      queryResourceManager
          .getChunkNumMap()
          .compute(
              context.getQueryId(),
              (k, v) -> v == null ? chunkMetadataList.size() : v + chunkMetadataList.size());

      long totalChunkSize =
          chunkMetadataList.stream()
              .mapToLong(chunkMetadata -> chunkMetadata.getStatistics().getCount())
              .sum();
      queryResourceManager
          .getChunkSizeMap()
          .compute(context.getQueryId(), (k, v) -> v == null ? totalChunkSize : v + totalChunkSize);
    }

    cachedChunkMetadata.addAll(chunkMetadataList);
  }

  boolean isChunkOverlapped() throws IOException {
    if (firstChunkMetadata == null) {
      throw new IOException("no first chunk");
    }

    Statistics chunkStatistics = firstChunkMetadata.getStatistics();
    return !cachedChunkMetadata.isEmpty()
        && orderUtils.isOverlapped(chunkStatistics, cachedChunkMetadata.peek().getStatistics());
  }

  Statistics currentChunkStatistics() {
    return firstChunkMetadata.getStatistics();
  }

  boolean currentChunkModified() throws IOException {
    if (firstChunkMetadata == null) {
      throw new IOException("no first chunk");
    }
    return firstChunkMetadata.isModified();
  }

  void skipCurrentChunk() {
    firstChunkMetadata = null;
  }

  /**
   * This method should be called after hasNextChunk() until no next page, make sure that all
   * overlapped pages are consumed
   */
  @SuppressWarnings("squid:S3776")
  // Suppress high Cognitive Complexity warning
  boolean hasNextPage() throws IOException {
    QueryTimeManager.checkQueryAlive(context.getQueryId());

    /*
     * has overlapped data before
     */
    if (hasCachedNextOverlappedPage) {
      return true;
    } else if (mergeReader.hasNextTimeValuePair()) {
      if (hasNextOverlappedPage()) {
        cachedBatchData = nextOverlappedPage();
        if (cachedBatchData != null && cachedBatchData.hasCurrent()) {
          hasCachedNextOverlappedPage = true;
          return true;
        }
      }
    }

    if (firstPageReader != null) {
      return true;
    }

    /*
     * construct first page reader
     */
    if (firstChunkMetadata != null) {
      /*
       * try to unpack all overlapped ChunkMetadata to cachedPageReaders
       */
      unpackAllOverlappedChunkMetadataToPageReaders(
          orderUtils.getOverlapCheckTime(firstChunkMetadata.getStatistics()), true);
    } else {
      /*
       * first chunk metadata is already unpacked, consume cached pages
       */
      unpackFirstPageReader();
    }

    if (isExistOverlappedPage()) {
      return true;
    }

    // make sure firstPageReader won't be null while the cachedPageReaders has more cached page
    // readers
    while (firstPageReader == null && (!seqPageReaders.isEmpty() || !unSeqPageReaders.isEmpty())) {

      unpackFirstPageReader();

      if (isExistOverlappedPage()) {
        return true;
      }
    }
    return firstPageReader != null;
  }

  private void unpackFirstPageReader() throws IOException {
    initFirstPageReader();
    if (firstPageReader != null) {
      long endpointTime = orderUtils.getOverlapCheckTime(firstPageReader.getStatistics());
      unpackAllOverlappedTsFilesToTimeSeriesMetadata(endpointTime);
      unpackAllOverlappedTimeSeriesMetadataToCachedChunkMetadata(endpointTime, false);
      unpackAllOverlappedChunkMetadataToPageReaders(endpointTime, false);
    }
  }

  private boolean isExistOverlappedPage() throws IOException {
    if (firstPageOverlapped()) {
      /*
       * next page is overlapped, read overlapped data and cache it
       */
      if (hasNextOverlappedPage()) {
        cachedBatchData = nextOverlappedPage();
        if (cachedBatchData != null && cachedBatchData.hasCurrent()) {
          hasCachedNextOverlappedPage = true;
          return true;
        }
      }
    }

    return false;
  }

  private boolean firstPageOverlapped() throws IOException {
    if (firstPageReader == null) {
      return false;
    }
    return (!seqPageReaders.isEmpty()
            && orderUtils.isOverlapped(
                firstPageReader.getStatistics(), seqPageReaders.get(0).getStatistics()))
        || (!unSeqPageReaders.isEmpty()
                && orderUtils.isOverlapped(
                    firstPageReader.getStatistics(), unSeqPageReaders.peek().getStatistics())
            || (mergeReader.hasNextTimeValuePair()
                && mergeReader.currentTimeValuePair().getTimestamp()
                    > firstPageReader.getStatistics().getStartTime()));
  }

  private void unpackAllOverlappedChunkMetadataToPageReaders(long endpointTime, boolean init)
      throws IOException {
    if (firstChunkMetadata != null
        && orderUtils.isOverlapped(endpointTime, firstChunkMetadata.getStatistics())) {
      unpackOneChunkMetaData(firstChunkMetadata);
      firstChunkMetadata = null;
    }
    // In case unpacking too many sequence chunks
    boolean hasMeetSeq = false;
    while (!cachedChunkMetadata.isEmpty()
        && orderUtils.isOverlapped(endpointTime, cachedChunkMetadata.peek().getStatistics())) {
      if (cachedChunkMetadata.peek().isSeq() && hasMeetSeq) {
        break;
      } else if (cachedChunkMetadata.peek().isSeq()) {
        hasMeetSeq = true;
      }
      unpackOneChunkMetaData(cachedChunkMetadata.poll());
    }
    if (init
        && firstPageReader == null
        && (!seqPageReaders.isEmpty() || !unSeqPageReaders.isEmpty())) {
      initFirstPageReader();
    }
  }

  private void unpackOneChunkMetaData(IChunkMetadata chunkMetaData) throws IOException {
    FileLoaderUtils.loadPageReaderList(chunkMetaData, timeFilter)
        .forEach(
            pageReader -> {
              if (chunkMetaData.isSeq()) {
                // addLast for asc; addFirst for desc
                if (orderUtils.getAscending()) {
                  seqPageReaders.add(
                      new VersionPageReader(
                          chunkMetaData.getVersion(),
                          chunkMetaData.getOffsetOfChunkHeader(),
                          pageReader,
                          true));
                } else {
                  seqPageReaders.add(
                      0,
                      new VersionPageReader(
                          chunkMetaData.getVersion(),
                          chunkMetaData.getOffsetOfChunkHeader(),
                          pageReader,
                          true));
                }

              } else {
                unSeqPageReaders.add(
                    new VersionPageReader(
                        chunkMetaData.getVersion(),
                        chunkMetaData.getOffsetOfChunkHeader(),
                        pageReader,
                        false));
              }
            });
  }

  /**
   * This method should be called after calling hasNextPage.
   *
   * <p>hasNextPage may cache firstPageReader if it is not overlapped or cached a BatchData if the
   * first page is overlapped
   */
  boolean isPageOverlapped() throws IOException {

    /*
     * has an overlapped page
     */
    if (hasCachedNextOverlappedPage) {
      return true;
    }

    /*
     * has a non-overlapped page in firstPageReader
     */
    if (mergeReader.hasNextTimeValuePair()
        && ((orderUtils.getAscending()
                && mergeReader.currentTimeValuePair().getTimestamp()
                    <= firstPageReader.getStatistics().getEndTime())
            || (!orderUtils.getAscending()
                && mergeReader.currentTimeValuePair().getTimestamp()
                    >= firstPageReader.getStatistics().getStartTime()))) {
      throw new IOException("overlapped data should be consumed first");
    }

    Statistics firstPageStatistics = firstPageReader.getStatistics();

    return !unSeqPageReaders.isEmpty()
        && orderUtils.isOverlapped(firstPageStatistics, unSeqPageReaders.peek().getStatistics());
  }

  Statistics currentPageStatistics() {
    if (firstPageReader == null) {
      return null;
    }
    return firstPageReader.getStatistics();
  }

  boolean currentPageModified() throws IOException {
    if (firstPageReader == null) {
      throw new IOException("no first page");
    }
    return firstPageReader.isModified();
  }

  void skipCurrentPage() {
    firstPageReader = null;
  }

  /** This method should only be used when the method isPageOverlapped() return true. */
  BatchData nextPage() throws IOException {

    if (!hasNextPage()) {
      throw new IOException("no next page, neither non-overlapped nor overlapped");
    }

    if (hasCachedNextOverlappedPage) {
      hasCachedNextOverlappedPage = false;
      return cachedBatchData;
    } else {

      /*
       * next page is not overlapped, push down value filter if it exists
       */
      if (valueFilter != null) {
        firstPageReader.setFilter(valueFilter);
      }
      BatchData batchData = firstPageReader.getAllSatisfiedPageData(orderUtils.getAscending());
      firstPageReader = null;

      return batchData;
    }
  }

  /**
   * read overlapped data till currentLargestEndTime in mergeReader, if current batch does not
   * contain data, read till next currentLargestEndTime again
   */
  @SuppressWarnings("squid:S3776") // Suppress high Cognitive Complexity warning
  private boolean hasNextOverlappedPage() throws IOException {

    if (hasCachedNextOverlappedPage) {
      return true;
    }

    tryToPutAllDirectlyOverlappedUnseqPageReadersIntoMergeReader();

    while (true) {

      // may has overlapped data
      if (mergeReader.hasNextTimeValuePair()) {

        cachedBatchData =
            BatchDataFactory.createBatchData(dataType, orderUtils.getAscending(), true);
        long currentPageEndPointTime = mergeReader.getCurrentReadStopTime();
        // get data as small as possible
        if (firstPageReader != null) {
          currentPageEndPointTime =
              orderUtils.getCurrentEndPoint(
                  currentPageEndPointTime, firstPageReader.getStatistics());
        }
        if (!seqPageReaders.isEmpty()) {
          currentPageEndPointTime =
              orderUtils.getCurrentEndPoint(
                  currentPageEndPointTime, seqPageReaders.get(0).getStatistics());
        }
        while (mergeReader.hasNextTimeValuePair()) {

          /*
           * get current first point in mergeReader, this maybe overlapped later
           */
          TimeValuePair timeValuePair = mergeReader.currentTimeValuePair();

          if (orderUtils.isExcessEndpoint(timeValuePair.getTimestamp(), currentPageEndPointTime)) {
            /*
             * when the merged point excesses the currentPageEndPointTime, we have read all overlapped data before currentPageEndPointTime
             * 1. has cached batch data, we don't need to read more data, just use the cached data later
             * 2. has first page reader, which means first page reader last endTime < currentTimeValuePair.getTimestamp(),
             * we could just use the first page reader later
             * 3. sequence page reader is not empty, which means first page reader last endTime < currentTimeValuePair.getTimestamp(),
             * we could use the first sequence page reader later
             */
            if (cachedBatchData.hasCurrent()
                || firstPageReader != null
                || !seqPageReaders.isEmpty()) {
              break;
            }
            // so, we don't have other data except mergeReader
            currentPageEndPointTime = mergeReader.getCurrentReadStopTime();
          }

          // unpack all overlapped data for the first timeValuePair
          unpackAllOverlappedTsFilesToTimeSeriesMetadata(timeValuePair.getTimestamp());
          unpackAllOverlappedTimeSeriesMetadataToCachedChunkMetadata(
              timeValuePair.getTimestamp(), false);
          unpackAllOverlappedChunkMetadataToPageReaders(timeValuePair.getTimestamp(), false);
          unpackAllOverlappedUnseqPageReadersToMergeReader(timeValuePair.getTimestamp());

          // from now, the unsequence reader is all unpacked, so we don't need to consider it
          // we has first page reader now
          if (firstPageReader != null) {
            // if current timeValuePair excesses the first page reader's end time, we just use the
            // cached data
            if ((orderUtils.getAscending()
                    && timeValuePair.getTimestamp() > firstPageReader.getStatistics().getEndTime())
                || (!orderUtils.getAscending()
                    && timeValuePair.getTimestamp()
                        < firstPageReader.getStatistics().getStartTime())) {
              hasCachedNextOverlappedPage = cachedBatchData.hasCurrent();
              return hasCachedNextOverlappedPage;
            } else {
              // current timeValuePair is overlapped with firstPageReader, add it to merged reader
              // and update endTime to the max end time
              mergeReader.addReader(
                  firstPageReader
                      .getAllSatisfiedPageData(orderUtils.getAscending())
                      .getBatchDataIterator(),
                  firstPageReader.version,
                  orderUtils.getOverlapCheckTime(firstPageReader.getStatistics()));
              currentPageEndPointTime =
                  updateEndPointTime(currentPageEndPointTime, firstPageReader);
              firstPageReader = null;
            }
          }

          // the seq page readers is not empty, just like first page reader
          if (!seqPageReaders.isEmpty()) {
            if ((orderUtils.getAscending()
                    && timeValuePair.getTimestamp()
                        > seqPageReaders.get(0).getStatistics().getEndTime())
                || (!orderUtils.getAscending()
                    && timeValuePair.getTimestamp()
                        < seqPageReaders.get(0).getStatistics().getStartTime())) {
              hasCachedNextOverlappedPage = cachedBatchData.hasCurrent();
              return hasCachedNextOverlappedPage;
            } else {
              VersionPageReader pageReader = seqPageReaders.remove(0);
              mergeReader.addReader(
                  pageReader
                      .getAllSatisfiedPageData(orderUtils.getAscending())
                      .getBatchDataIterator(),
                  pageReader.version,
                  orderUtils.getOverlapCheckTime(pageReader.getStatistics()));
              currentPageEndPointTime = updateEndPointTime(currentPageEndPointTime, pageReader);
            }
          }

          /*
           * get the latest first point in mergeReader
           */
          timeValuePair = mergeReader.nextTimeValuePair();

          Object valueForFilter =
              timeValuePair.getValue().getDataType() == TSDataType.VECTOR
                  ? timeValuePair.getValue().getVector()[0].getValue()
                  : timeValuePair.getValue().getValue();
          if (valueFilter == null
              || valueFilter.satisfy(timeValuePair.getTimestamp(), valueForFilter)) {
            cachedBatchData.putAnObject(
                timeValuePair.getTimestamp(), timeValuePair.getValue().getValue());
          }
        }
        cachedBatchData.flip();
        hasCachedNextOverlappedPage = cachedBatchData.hasCurrent();
        /*
         * if current overlapped page has valid data, return, otherwise read next overlapped page
         */
        if (hasCachedNextOverlappedPage) {
          return true;
        } else if (mergeReader.hasNextTimeValuePair()) {
          // condition: seqPage.endTime < mergeReader.currentTime
          return false;
        }
      } else {
        return false;
      }
    }
  }

  private long updateEndPointTime(long currentPageEndPointTime, VersionPageReader pageReader) {
    if (orderUtils.getAscending()) {
      return Math.min(currentPageEndPointTime, pageReader.getStatistics().getEndTime());
    } else {
      return Math.max(currentPageEndPointTime, pageReader.getStatistics().getStartTime());
    }
  }

  private void tryToPutAllDirectlyOverlappedUnseqPageReadersIntoMergeReader() throws IOException {

    /*
     * no cached page readers
     */
    if (firstPageReader == null && unSeqPageReaders.isEmpty() && seqPageReaders.isEmpty()) {
      return;
    }

    /*
     * init firstPageReader
     */
    if (firstPageReader == null) {
      initFirstPageReader();
    }

    long currentPageEndpointTime;
    if (mergeReader.hasNextTimeValuePair()) {
      currentPageEndpointTime = mergeReader.getCurrentReadStopTime();
    } else {
      currentPageEndpointTime = orderUtils.getOverlapCheckTime(firstPageReader.getStatistics());
    }

    /*
     * put all currently directly overlapped unseq page reader to merge reader
     */
    unpackAllOverlappedUnseqPageReadersToMergeReader(currentPageEndpointTime);
  }

  private void initFirstPageReader() {
    if (!seqPageReaders.isEmpty() && !unSeqPageReaders.isEmpty()) {
      if (orderUtils.isTakeSeqAsFirst(
          seqPageReaders.get(0).getStatistics(), unSeqPageReaders.peek().getStatistics())) {
        firstPageReader = seqPageReaders.remove(0);
      } else {
        firstPageReader = unSeqPageReaders.poll();
      }
    } else if (!seqPageReaders.isEmpty()) {
      firstPageReader = seqPageReaders.remove(0);
    } else if (!unSeqPageReaders.isEmpty()) {
      firstPageReader = unSeqPageReaders.poll();
    }
  }

  private void unpackAllOverlappedUnseqPageReadersToMergeReader(long endpointTime)
      throws IOException {
    while (!unSeqPageReaders.isEmpty()
        && orderUtils.isOverlapped(endpointTime, unSeqPageReaders.peek().data.getStatistics())) {
      putPageReaderToMergeReader(unSeqPageReaders.poll());
    }
    if (firstPageReader != null
        && !firstPageReader.isSeq()
        && orderUtils.isOverlapped(endpointTime, firstPageReader.getStatistics())) {
      putPageReaderToMergeReader(firstPageReader);
      firstPageReader = null;
    }
  }

  private void putPageReaderToMergeReader(VersionPageReader pageReader) throws IOException {
    mergeReader.addReader(
        pageReader.getAllSatisfiedPageData(orderUtils.getAscending()).getBatchDataIterator(),
        pageReader.version,
        orderUtils.getOverlapCheckTime(pageReader.getStatistics()));
  }

  private BatchData nextOverlappedPage() throws IOException {
    if (hasCachedNextOverlappedPage || hasNextOverlappedPage()) {
      hasCachedNextOverlappedPage = false;
      return cachedBatchData;
    }
    throw new IOException("No more batch data");
  }

  private LinkedList<TsFileResource> sortUnSeqFileResources(List<TsFileResource> tsFileResources) {
    return tsFileResources.stream()
        .sorted(orderUtils.comparingLong(tsFileResource -> orderUtils.getOrderTime(tsFileResource)))
        .collect(Collectors.toCollection(LinkedList::new));
  }

  /**
   * unpack all overlapped seq/unseq files and find the first TimeSeriesMetadata
   *
   * <p>Because there may be too many files in the scenario used by the user, we cannot open all the
   * chunks at once, which may cause OOM, so we can only unpack one file at a time when needed. This
   * approach is likely to be ubiquitous, but it keeps the system running smoothly
   */
  @SuppressWarnings("squid:S3776") // Suppress high Cognitive Complexity warning
  protected void tryToUnpackAllOverlappedFilesToTimeSeriesMetadata() throws IOException {
    /*
     * Fill sequence TimeSeriesMetadata List until it is not empty
     */
    while (seqTimeSeriesMetadata.isEmpty() && !seqFileResource.isEmpty()) {
      unpackSeqTsFileResource();
    }

    /*
     * Fill unSequence TimeSeriesMetadata Priority Queue until it is not empty
     */
    while (unSeqTimeSeriesMetadata.isEmpty() && !unseqFileResource.isEmpty()) {
      unpackUnseqTsFileResource();
    }

    /*
     * find end time of the first TimeSeriesMetadata
     */
    long endTime = -1L;
    if (!seqTimeSeriesMetadata.isEmpty() && unSeqTimeSeriesMetadata.isEmpty()) {
      // only has seq
      endTime = orderUtils.getOverlapCheckTime(seqTimeSeriesMetadata.get(0).getStatistics());
    } else if (seqTimeSeriesMetadata.isEmpty() && !unSeqTimeSeriesMetadata.isEmpty()) {
      // only has unseq
      endTime = orderUtils.getOverlapCheckTime(unSeqTimeSeriesMetadata.peek().getStatistics());
    } else if (!seqTimeSeriesMetadata.isEmpty()) {
      // has seq and unseq
      endTime =
          orderUtils.getCurrentEndPoint(
              seqTimeSeriesMetadata.get(0).getStatistics(),
              unSeqTimeSeriesMetadata.peek().getStatistics());
    }

    /*
     * unpack all directly overlapped seq/unseq files with first TimeSeriesMetadata
     */
    if (endTime != -1) {
      unpackAllOverlappedTsFilesToTimeSeriesMetadata(endTime);
    }

    /*
     * update the first TimeSeriesMetadata
     */
    if (!seqTimeSeriesMetadata.isEmpty() && unSeqTimeSeriesMetadata.isEmpty()) {
      // only has seq
      firstTimeSeriesMetadata = seqTimeSeriesMetadata.remove(0);
    } else if (seqTimeSeriesMetadata.isEmpty() && !unSeqTimeSeriesMetadata.isEmpty()) {
      // only has unseq
      firstTimeSeriesMetadata = unSeqTimeSeriesMetadata.poll();
    } else if (!seqTimeSeriesMetadata.isEmpty()) {
      // has seq and unseq
      if (orderUtils.isTakeSeqAsFirst(
          seqTimeSeriesMetadata.get(0).getStatistics(),
          unSeqTimeSeriesMetadata.peek().getStatistics())) {
        firstTimeSeriesMetadata = seqTimeSeriesMetadata.remove(0);
      } else {
        firstTimeSeriesMetadata = unSeqTimeSeriesMetadata.poll();
      }
    }
  }

  protected void unpackAllOverlappedTsFilesToTimeSeriesMetadata(long endpointTime)
      throws IOException {
    while (!unseqFileResource.isEmpty()
        && orderUtils.isOverlapped(endpointTime, unseqFileResource.get(0))) {
      unpackUnseqTsFileResource();
    }
    while (!seqFileResource.isEmpty()
        && orderUtils.isOverlapped(
            endpointTime, orderUtils.getNextSeqFileResource(seqFileResource, false))) {
      unpackSeqTsFileResource();
    }
  }

  protected void unpackSeqTsFileResource() throws IOException {
    TimeseriesMetadata timeseriesMetadata =
        FileLoaderUtils.loadTimeSeriesMetadata(
            orderUtils.getNextSeqFileResource(seqFileResource, true),
            seriesPath,
            context,
            getAnyFilter(),
            allSensors);
    if (timeseriesMetadata != null) {
      timeseriesMetadata.setSeq(true);
      seqTimeSeriesMetadata.add(timeseriesMetadata);
    }
  }

  protected void unpackUnseqTsFileResource() throws IOException {
    TimeseriesMetadata timeseriesMetadata =
        FileLoaderUtils.loadTimeSeriesMetadata(
            unseqFileResource.remove(0), seriesPath, context, getAnyFilter(), allSensors);
    if (timeseriesMetadata != null) {
      timeseriesMetadata.setModified(true);
      timeseriesMetadata.setSeq(false);
      unSeqTimeSeriesMetadata.add(timeseriesMetadata);
    }
  }

  protected Filter getAnyFilter() {
    return timeFilter != null ? timeFilter : valueFilter;
  }

  void setTimeFilter(long timestamp) {
    ((UnaryFilter) timeFilter).setValue(timestamp);
  }

  Filter getTimeFilter() {
    return timeFilter;
  }

  private class VersionPageReader {

    protected PriorityMergeReader.MergeReaderPriority version;
    protected IPageReader data;

    protected boolean isSeq;

    VersionPageReader(long version, long offset, IPageReader data, boolean isSeq) {
      this.version = new MergeReaderPriority(version, offset);
      this.data = data;
      this.isSeq = isSeq;
    }

    Statistics getStatistics() {
      return data.getStatistics();
    }

    BatchData getAllSatisfiedPageData(boolean ascending) throws IOException {
      return data.getAllSatisfiedPageData(ascending);
    }

    void setFilter(Filter filter) {
      data.setFilter(filter);
    }

    boolean isModified() {
      return data.isModified();
    }

    public boolean isSeq() {
      return isSeq;
    }
  }

  public interface TimeOrderUtils {

    long getOrderTime(Statistics<? extends Object> statistics);

    long getOrderTime(TsFileResource fileResource);

    long getOverlapCheckTime(Statistics<? extends Object> range);

    boolean isOverlapped(Statistics<? extends Object> left, Statistics<? extends Object> right);

    boolean isOverlapped(long time, Statistics<? extends Object> right);

    boolean isOverlapped(long time, TsFileResource right);

    TsFileResource getNextSeqFileResource(List<TsFileResource> seqResources, boolean isDelete);

    <T> Comparator<T> comparingLong(ToLongFunction<? super T> keyExtractor);

    long getCurrentEndPoint(long time, Statistics<? extends Object> statistics);

    long getCurrentEndPoint(
        Statistics<? extends Object> seqStatistics, Statistics<? extends Object> unseqStatistics);

    boolean isExcessEndpoint(long time, long endpointTime);

    /** Return true if taking first page reader from seq readers */
    boolean isTakeSeqAsFirst(
        Statistics<? extends Object> seqStatistics, Statistics<? extends Object> unseqStatistics);

    boolean getAscending();
  }

  class DescTimeOrderUtils implements TimeOrderUtils {

    @Override
    public long getOrderTime(Statistics statistics) {
      return statistics.getEndTime();
    }

    @Override
    public long getOrderTime(TsFileResource fileResource) {
      return fileResource.getEndTime(seriesPath.getDevice());
    }

    @Override
    public long getOverlapCheckTime(Statistics range) {
      return range.getStartTime();
    }

    @Override
    public boolean isOverlapped(Statistics left, Statistics right) {
      return left.getStartTime() <= right.getEndTime();
    }

    @Override
    public boolean isOverlapped(long time, Statistics right) {
      return time <= right.getEndTime();
    }

    @Override
    public boolean isOverlapped(long time, TsFileResource right) {
      return time <= right.getEndTime(seriesPath.getDevice());
    }

    @Override
    public TsFileResource getNextSeqFileResource(
        List<TsFileResource> seqResources, boolean isDelete) {
      if (isDelete) {
        return seqResources.remove(seqResources.size() - 1);
      }
      return seqResources.get(seqResources.size() - 1);
    }

    @Override
    public <T> Comparator<T> comparingLong(ToLongFunction<? super T> keyExtractor) {
      Objects.requireNonNull(keyExtractor);
      return (Comparator<T> & Serializable)
          (c1, c2) -> Long.compare(keyExtractor.applyAsLong(c2), keyExtractor.applyAsLong(c1));
    }

    @Override
    public long getCurrentEndPoint(long time, Statistics<? extends Object> statistics) {
      return Math.max(time, statistics.getStartTime());
    }

    @Override
    public long getCurrentEndPoint(
        Statistics<? extends Object> seqStatistics, Statistics<? extends Object> unseqStatistics) {
      return Math.max(seqStatistics.getStartTime(), unseqStatistics.getStartTime());
    }

    @Override
    public boolean isExcessEndpoint(long time, long endpointTime) {
      return time < endpointTime;
    }

    @Override
    public boolean isTakeSeqAsFirst(
        Statistics<? extends Object> seqStatistics, Statistics<? extends Object> unseqStatistics) {
      return seqStatistics.getEndTime() > unseqStatistics.getEndTime();
    }

    @Override
    public boolean getAscending() {
      return false;
    }
  }

  class AscTimeOrderUtils implements TimeOrderUtils {

    @Override
    public long getOrderTime(Statistics statistics) {
      return statistics.getStartTime();
    }

    @Override
    public long getOrderTime(TsFileResource fileResource) {
      return fileResource.getStartTime(seriesPath.getDevice());
    }

    @Override
    public long getOverlapCheckTime(Statistics range) {
      return range.getEndTime();
    }

    @Override
    public boolean isOverlapped(Statistics left, Statistics right) {
      return left.getEndTime() >= right.getStartTime();
    }

    @Override
    public boolean isOverlapped(long time, Statistics right) {
      return time >= right.getStartTime();
    }

    @Override
    public boolean isOverlapped(long time, TsFileResource right) {
      return time >= right.getStartTime(seriesPath.getDevice());
    }

    @Override
    public TsFileResource getNextSeqFileResource(
        List<TsFileResource> seqResources, boolean isDelete) {
      if (isDelete) {
        return seqResources.remove(0);
      }
      return seqResources.get(0);
    }

    @Override
    public <T> Comparator<T> comparingLong(ToLongFunction<? super T> keyExtractor) {
      Objects.requireNonNull(keyExtractor);
      return (Comparator<T> & Serializable)
          (c1, c2) -> Long.compare(keyExtractor.applyAsLong(c1), keyExtractor.applyAsLong(c2));
    }

    @Override
    public long getCurrentEndPoint(long time, Statistics<? extends Object> statistics) {
      return Math.min(time, statistics.getEndTime());
    }

    @Override
    public long getCurrentEndPoint(
        Statistics<? extends Object> seqStatistics, Statistics<? extends Object> unseqStatistics) {
      return Math.min(seqStatistics.getEndTime(), unseqStatistics.getEndTime());
    }

    @Override
    public boolean isExcessEndpoint(long time, long endpointTime) {
      return time > endpointTime;
    }

    @Override
    public boolean isTakeSeqAsFirst(
        Statistics<? extends Object> seqStatistics, Statistics<? extends Object> unseqStatistics) {
      return seqStatistics.getStartTime() < unseqStatistics.getStartTime();
    }

    @Override
    public boolean getAscending() {
      return true;
    }
  }

  public TimeOrderUtils getOrderUtils() {
    return orderUtils;
  }
}