/*
 * 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.hadoop.hbase.client;

import java.io.IOException;
import java.nio.BufferOverflowException;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NavigableMap;
import java.util.NoSuchElementException;
import java.util.TreeMap;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellComparator;
import org.apache.hadoop.hbase.CellScanner;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.ExtendedCell;
import org.apache.hadoop.hbase.ExtendedCellScannable;
import org.apache.hadoop.hbase.ExtendedCellScanner;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.KeyValue;
import org.apache.hadoop.hbase.KeyValueUtil;
import org.apache.hadoop.hbase.PrivateCellUtil;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.yetus.audience.InterfaceAudience;

/**
 * Single row result of a {@link Get} or {@link Scan} query.
 * <p>
 * This class is <b>NOT THREAD SAFE</b>.
 * <p>
 * Convenience methods are available that return various {@link Map} structures and values directly.
 * <p>
 * To get a complete mapping of all cells in the Result, which can include multiple families and
 * multiple versions, use {@link #getMap()}.
 * <p>
 * To get a mapping of each family to its columns (qualifiers and values), including only the latest
 * version of each, use {@link #getNoVersionMap()}. To get a mapping of qualifiers to latest values
 * for an individual family use {@link #getFamilyMap(byte[])}.
 * <p>
 * To get the latest value for a specific family and qualifier use
 * {@link #getValue(byte[], byte[])}. A Result is backed by an array of {@link Cell} objects, each
 * representing an HBase cell defined by the row, family, qualifier, timestamp, and value.
 * <p>
 * The underlying {@link Cell} objects can be accessed through the method {@link #listCells()}. This
 * will create a List from the internal Cell []. Better is to exploit the fact that a new Result
 * instance is a primed {@link CellScanner}; just call {@link #advance()} and {@link #current()} to
 * iterate over Cells as you would any {@link CellScanner}. Call {@link #cellScanner()} to reset
 * should you need to iterate the same Result over again ({@link CellScanner}s are one-shot). If you
 * need to overwrite a Result with another Result instance -- as in the old 'mapred' RecordReader
 * next invocations -- then create an empty Result with the null constructor and in then use
 * {@link #copyFrom(Result)}
 */
@InterfaceAudience.Public
public class Result implements ExtendedCellScannable, ExtendedCellScanner {
  private ExtendedCell[] cells;
  private Boolean exists; // if the query was just to check existence.
  private boolean stale = false;

  /**
   * See {@link #mayHaveMoreCellsInRow()}.
   */
  private boolean mayHaveMoreCellsInRow = false;
  // We're not using java serialization. Transient here is just a marker to say
  // that this is where we cache row if we're ever asked for it.
  private transient byte[] row = null;
  // Ditto for familyMap. It can be composed on fly from passed in kvs.
  private transient NavigableMap<byte[],
    NavigableMap<byte[], NavigableMap<Long, byte[]>>> familyMap = null;

  private static ThreadLocal<byte[]> localBuffer = new ThreadLocal<>();
  private static final int PAD_WIDTH = 128;
  public static final Result EMPTY_RESULT = new Result(true);

  private final static int INITIAL_CELLSCANNER_INDEX = -1;

  /**
   * Index for where we are when Result is acting as a {@link CellScanner}.
   */
  private int cellScannerIndex = INITIAL_CELLSCANNER_INDEX;
  private RegionLoadStats stats;

  private final boolean readonly;

  private Cursor cursor = null;

  /**
   * Creates an empty Result w/ no KeyValue payload; returns null if you call {@link #rawCells()}.
   * Use this to represent no results if {@code null} won't do or in old 'mapred' as opposed to
   * 'mapreduce' package MapReduce where you need to overwrite a Result instance with a
   * {@link #copyFrom(Result)} call.
   */
  public Result() {
    this(false);
  }

  /**
   * Allows to construct special purpose immutable Result objects, such as EMPTY_RESULT.
   * @param readonly whether this Result instance is readonly
   */
  private Result(boolean readonly) {
    this.readonly = readonly;
  }

  /**
   * Instantiate a Result with the specified List of KeyValues. <br>
   * <strong>Note:</strong> You must ensure that the keyvalues are already sorted.
   * @param cells List of cells
   */
  public static Result create(List<? extends Cell> cells) {
    return create(cells, null);
  }

  public static Result create(List<? extends Cell> cells, Boolean exists) {
    return create(cells, exists, false);
  }

  public static Result create(List<? extends Cell> cells, Boolean exists, boolean stale) {
    return create(cells, exists, stale, false);
  }

  public static Result create(List<? extends Cell> cells, Boolean exists, boolean stale,
    boolean mayHaveMoreCellsInRow) {
    if (exists != null) {
      return new Result(null, exists, stale, mayHaveMoreCellsInRow);
    }
    return new Result(cells.toArray(new ExtendedCell[cells.size()]), null, stale,
      mayHaveMoreCellsInRow);
  }

  /**
   * Instantiate a Result with the specified array of KeyValues. <br>
   * <strong>Note:</strong> You must ensure that the keyvalues are already sorted.
   * @param cells array of cells
   */
  public static Result create(Cell[] cells) {
    return create(cells, null, false);
  }

  public static Result create(Cell[] cells, Boolean exists, boolean stale) {
    return create(cells, exists, stale, false);
  }

  public static Result create(Cell[] cells, Boolean exists, boolean stale,
    boolean mayHaveMoreCellsInRow) {
    if (exists != null) {
      return new Result(null, exists, stale, mayHaveMoreCellsInRow);
    }
    ExtendedCell[] extendCells = cells instanceof ExtendedCell[]
      ? (ExtendedCell[]) cells
      : Arrays.copyOf(cells, cells.length, ExtendedCell[].class);
    return new Result(extendCells, null, stale, mayHaveMoreCellsInRow);
  }

  // prefer these below methods inside hbase to avoid casting or copying
  static Result create(ExtendedCell[] cells) {
    return create(cells, null, false);
  }

  static Result create(ExtendedCell[] cells, Boolean exists, boolean stale) {
    return create(cells, exists, stale, false);
  }

  static Result create(ExtendedCell[] cells, Boolean exists, boolean stale,
    boolean mayHaveMoreCellsInRow) {
    if (exists != null) {
      return new Result(null, exists, stale, mayHaveMoreCellsInRow);
    }
    return new Result(cells, null, stale, mayHaveMoreCellsInRow);
  }

  public static Result createCursorResult(Cursor cursor) {
    return new Result(cursor);
  }

  private Result(Cursor cursor) {
    this.cursor = cursor;
    this.readonly = false;
  }

  /** Private ctor. Use {@link #create(Cell[])}. */
  private Result(ExtendedCell[] cells, Boolean exists, boolean stale,
    boolean mayHaveMoreCellsInRow) {
    this.cells = cells;
    this.exists = exists;
    this.stale = stale;
    this.mayHaveMoreCellsInRow = mayHaveMoreCellsInRow;
    this.readonly = false;
  }

  /**
   * Method for retrieving the row key that corresponds to the row from which this Result was
   * created.
   */
  public byte[] getRow() {
    if (this.row == null) {
      this.row =
        (this.cells == null || this.cells.length == 0) ? null : CellUtil.cloneRow(this.cells[0]);
    }
    return this.row;
  }

  /**
   * Return the array of Cells backing this Result instance. The array is sorted from smallest -&gt;
   * largest using the {@link CellComparator}. The array only contains what your Get or Scan
   * specifies and no more. For example if you request column "A" 1 version you will have at most 1
   * Cell in the array. If you request column "A" with 2 version you will have at most 2 Cells, with
   * the first one being the newer timestamp and the second being the older timestamp (this is the
   * sort order defined by {@link CellComparator}). If columns don't exist, they won't be present in
   * the result. Therefore if you ask for 1 version all columns, it is safe to iterate over this
   * array and expect to see 1 Cell for each column and no more. This API is faster than using
   * getFamilyMap() and getMap()
   * @return array of Cells; can be null if nothing in the result
   */
  public Cell[] rawCells() {
    return cells;
  }

  ExtendedCell[] rawExtendedCells() {
    return cells;
  }

  /**
   * Create a sorted list of the Cell's in this result. Since HBase 0.20.5 this is equivalent to
   * raw().
   * @return sorted List of Cells; can be null if no cells in the result
   */
  public List<Cell> listCells() {
    return isEmpty() ? null : Arrays.asList(rawCells());
  }

  /**
   * Return the Cells for the specific column. The Cells are sorted in the {@link CellComparator}
   * order. That implies the first entry in the list is the most recent column. If the query (Scan
   * or Get) only requested 1 version the list will contain at most 1 entry. If the column did not
   * exist in the result set (either the column does not exist or the column was not selected in the
   * query) the list will be empty. Also see getColumnLatest which returns just a Cell
   * @param family the family
   * @return a list of Cells for this column or empty list if the column did not exist in the result
   *         set
   */
  public List<Cell> getColumnCells(byte[] family, byte[] qualifier) {
    List<Cell> result = new ArrayList<>();

    Cell[] kvs = rawCells();

    if (kvs == null || kvs.length == 0) {
      return result;
    }
    int pos = binarySearch(kvs, family, qualifier);
    if (pos == -1) {
      return result; // cant find it
    }

    for (int i = pos; i < kvs.length; i++) {
      if (CellUtil.matchingColumn(kvs[i], family, qualifier)) {
        result.add(kvs[i]);
      } else {
        break;
      }
    }

    return result;
  }

  private byte[] notNullBytes(final byte[] bytes) {
    if (bytes == null) {
      return HConstants.EMPTY_BYTE_ARRAY;
    } else {
      return bytes;
    }
  }

  private int binarySearch(final Cell[] kvs, final byte[] family, final byte[] qualifier) {
    byte[] familyNotNull = notNullBytes(family);
    byte[] qualifierNotNull = notNullBytes(qualifier);
    Cell searchTerm = PrivateCellUtil.createFirstOnRow(kvs[0].getRowArray(), kvs[0].getRowOffset(),
      kvs[0].getRowLength(), familyNotNull, 0, (byte) familyNotNull.length, qualifierNotNull, 0,
      qualifierNotNull.length);

    // pos === ( -(insertion point) - 1)
    int pos = Arrays.binarySearch(kvs, searchTerm, CellComparator.getInstance());
    // never will exact match
    if (pos < 0) {
      pos = (pos + 1) * -1;
      // pos is now insertion point
    }
    if (pos == kvs.length) {
      return -1; // doesn't exist
    }
    return pos;
  }

  /**
   * Searches for the latest value for the specified column.
   * @param kvs       the array to search
   * @param family    family name
   * @param foffset   family offset
   * @param flength   family length
   * @param qualifier column qualifier
   * @param qoffset   qualifier offset
   * @param qlength   qualifier length
   * @return the index where the value was found, or -1 otherwise
   */
  private int binarySearch(final Cell[] kvs, final byte[] family, final int foffset,
    final int flength, final byte[] qualifier, final int qoffset, final int qlength) {

    double keyValueSize =
      (double) KeyValue.getKeyValueDataStructureSize(kvs[0].getRowLength(), flength, qlength, 0);

    byte[] buffer = localBuffer.get();
    if (buffer == null || keyValueSize > buffer.length) {
      // pad to the smallest multiple of the pad width
      buffer = new byte[(int) Math.ceil(keyValueSize / PAD_WIDTH) * PAD_WIDTH];
      localBuffer.set(buffer);
    }

    Cell searchTerm =
      KeyValueUtil.createFirstOnRow(buffer, 0, kvs[0].getRowArray(), kvs[0].getRowOffset(),
        kvs[0].getRowLength(), family, foffset, flength, qualifier, qoffset, qlength);

    // pos === ( -(insertion point) - 1)
    int pos = Arrays.binarySearch(kvs, searchTerm, CellComparator.getInstance());
    // never will exact match
    if (pos < 0) {
      pos = (pos + 1) * -1;
      // pos is now insertion point
    }
    if (pos == kvs.length) {
      return -1; // doesn't exist
    }
    return pos;
  }

  /**
   * The Cell for the most recent timestamp for a given column.
   * @return the Cell for the column, or null if no value exists in the row or none have been
   *         selected in the query (Get/Scan)
   */
  public Cell getColumnLatestCell(byte[] family, byte[] qualifier) {
    Cell[] kvs = rawCells(); // side effect possibly.
    if (kvs == null || kvs.length == 0) {
      return null;
    }
    int pos = binarySearch(kvs, family, qualifier);
    if (pos == -1) {
      return null;
    }
    if (CellUtil.matchingColumn(kvs[pos], family, qualifier)) {
      return kvs[pos];
    }
    return null;
  }

  /**
   * The Cell for the most recent timestamp for a given column.
   * @param family    family name
   * @param foffset   family offset
   * @param flength   family length
   * @param qualifier column qualifier
   * @param qoffset   qualifier offset
   * @param qlength   qualifier length
   * @return the Cell for the column, or null if no value exists in the row or none have been
   *         selected in the query (Get/Scan)
   */
  public Cell getColumnLatestCell(byte[] family, int foffset, int flength, byte[] qualifier,
    int qoffset, int qlength) {

    Cell[] kvs = rawCells(); // side effect possibly.
    if (kvs == null || kvs.length == 0) {
      return null;
    }
    int pos = binarySearch(kvs, family, foffset, flength, qualifier, qoffset, qlength);
    if (pos == -1) {
      return null;
    }
    if (
      PrivateCellUtil.matchingColumn(kvs[pos], family, foffset, flength, qualifier, qoffset,
        qlength)
    ) {
      return kvs[pos];
    }
    return null;
  }

  /**
   * Get the latest version of the specified column. Note: this call clones the value content of the
   * hosting Cell. See {@link #getValueAsByteBuffer(byte[], byte[])}, etc., or {@link #listCells()}
   * if you would avoid the cloning.
   * @param family    family name
   * @param qualifier column qualifier
   * @return value of latest version of column, null if none found
   */
  public byte[] getValue(byte[] family, byte[] qualifier) {
    Cell kv = getColumnLatestCell(family, qualifier);
    if (kv == null) {
      return null;
    }
    return CellUtil.cloneValue(kv);
  }

  /**
   * Returns the value wrapped in a new <code>ByteBuffer</code>.
   * @param family    family name
   * @param qualifier column qualifier
   * @return the latest version of the column, or <code>null</code> if none found
   */
  public ByteBuffer getValueAsByteBuffer(byte[] family, byte[] qualifier) {

    Cell kv = getColumnLatestCell(family, 0, family.length, qualifier, 0, qualifier.length);

    if (kv == null) {
      return null;
    }
    return ByteBuffer.wrap(kv.getValueArray(), kv.getValueOffset(), kv.getValueLength())
      .asReadOnlyBuffer();
  }

  /**
   * Returns the value wrapped in a new <code>ByteBuffer</code>.
   * @param family    family name
   * @param foffset   family offset
   * @param flength   family length
   * @param qualifier column qualifier
   * @param qoffset   qualifier offset
   * @param qlength   qualifier length
   * @return the latest version of the column, or <code>null</code> if none found
   */
  public ByteBuffer getValueAsByteBuffer(byte[] family, int foffset, int flength, byte[] qualifier,
    int qoffset, int qlength) {

    Cell kv = getColumnLatestCell(family, foffset, flength, qualifier, qoffset, qlength);

    if (kv == null) {
      return null;
    }
    return ByteBuffer.wrap(kv.getValueArray(), kv.getValueOffset(), kv.getValueLength())
      .asReadOnlyBuffer();
  }

  /**
   * Loads the latest version of the specified column into the provided <code>ByteBuffer</code>.
   * <p>
   * Does not clear or flip the buffer.
   * @param family    family name
   * @param qualifier column qualifier
   * @param dst       the buffer where to write the value
   * @return <code>true</code> if a value was found, <code>false</code> otherwise
   * @throws BufferOverflowException there is insufficient space remaining in the buffer
   */
  public boolean loadValue(byte[] family, byte[] qualifier, ByteBuffer dst)
    throws BufferOverflowException {
    return loadValue(family, 0, family.length, qualifier, 0, qualifier.length, dst);
  }

  /**
   * Loads the latest version of the specified column into the provided <code>ByteBuffer</code>.
   * <p>
   * Does not clear or flip the buffer.
   * @param family    family name
   * @param foffset   family offset
   * @param flength   family length
   * @param qualifier column qualifier
   * @param qoffset   qualifier offset
   * @param qlength   qualifier length
   * @param dst       the buffer where to write the value
   * @return <code>true</code> if a value was found, <code>false</code> otherwise
   * @throws BufferOverflowException there is insufficient space remaining in the buffer
   */
  public boolean loadValue(byte[] family, int foffset, int flength, byte[] qualifier, int qoffset,
    int qlength, ByteBuffer dst) throws BufferOverflowException {
    Cell kv = getColumnLatestCell(family, foffset, flength, qualifier, qoffset, qlength);

    if (kv == null) {
      return false;
    }
    dst.put(kv.getValueArray(), kv.getValueOffset(), kv.getValueLength());
    return true;
  }

  /**
   * Checks if the specified column contains a non-empty value (not a zero-length byte array).
   * @param family    family name
   * @param qualifier column qualifier
   * @return whether or not a latest value exists and is not empty
   */
  public boolean containsNonEmptyColumn(byte[] family, byte[] qualifier) {

    return containsNonEmptyColumn(family, 0, family.length, qualifier, 0, qualifier.length);
  }

  /**
   * Checks if the specified column contains a non-empty value (not a zero-length byte array).
   * @param family    family name
   * @param foffset   family offset
   * @param flength   family length
   * @param qualifier column qualifier
   * @param qoffset   qualifier offset
   * @param qlength   qualifier length
   * @return whether or not a latest value exists and is not empty
   */
  public boolean containsNonEmptyColumn(byte[] family, int foffset, int flength, byte[] qualifier,
    int qoffset, int qlength) {

    Cell kv = getColumnLatestCell(family, foffset, flength, qualifier, qoffset, qlength);

    return (kv != null) && (kv.getValueLength() > 0);
  }

  /**
   * Checks if the specified column contains an empty value (a zero-length byte array).
   * @param family    family name
   * @param qualifier column qualifier
   * @return whether or not a latest value exists and is empty
   */
  public boolean containsEmptyColumn(byte[] family, byte[] qualifier) {

    return containsEmptyColumn(family, 0, family.length, qualifier, 0, qualifier.length);
  }

  /**
   * Checks if the specified column contains an empty value (a zero-length byte array).
   * @param family    family name
   * @param foffset   family offset
   * @param flength   family length
   * @param qualifier column qualifier
   * @param qoffset   qualifier offset
   * @param qlength   qualifier length
   * @return whether or not a latest value exists and is empty
   */
  public boolean containsEmptyColumn(byte[] family, int foffset, int flength, byte[] qualifier,
    int qoffset, int qlength) {
    Cell kv = getColumnLatestCell(family, foffset, flength, qualifier, qoffset, qlength);

    return (kv != null) && (kv.getValueLength() == 0);
  }

  /**
   * Checks for existence of a value for the specified column (empty or not).
   * @param family    family name
   * @param qualifier column qualifier
   * @return true if at least one value exists in the result, false if not
   */
  public boolean containsColumn(byte[] family, byte[] qualifier) {
    Cell kv = getColumnLatestCell(family, qualifier);
    return kv != null;
  }

  /**
   * Checks for existence of a value for the specified column (empty or not).
   * @param family    family name
   * @param foffset   family offset
   * @param flength   family length
   * @param qualifier column qualifier
   * @param qoffset   qualifier offset
   * @param qlength   qualifier length
   * @return true if at least one value exists in the result, false if not
   */
  public boolean containsColumn(byte[] family, int foffset, int flength, byte[] qualifier,
    int qoffset, int qlength) {

    return getColumnLatestCell(family, foffset, flength, qualifier, qoffset, qlength) != null;
  }

  /**
   * Map of families to all versions of its qualifiers and values.
   * <p>
   * Returns a three level Map of the form:
   * <code>Map&amp;family,Map&lt;qualifier,Map&lt;timestamp,value&gt;&gt;&gt;</code>
   * <p>
   * Note: All other map returning methods make use of this map internally.
   * @return map from families to qualifiers to versions
   */
  public NavigableMap<byte[], NavigableMap<byte[], NavigableMap<Long, byte[]>>> getMap() {
    if (this.familyMap != null) {
      return this.familyMap;
    }
    if (isEmpty()) {
      return null;
    }
    this.familyMap = new TreeMap<>(Bytes.BYTES_COMPARATOR);
    for (Cell kv : this.cells) {
      byte[] family = CellUtil.cloneFamily(kv);
      NavigableMap<byte[], NavigableMap<Long, byte[]>> columnMap = familyMap.get(family);
      if (columnMap == null) {
        columnMap = new TreeMap<>(Bytes.BYTES_COMPARATOR);
        familyMap.put(family, columnMap);
      }
      byte[] qualifier = CellUtil.cloneQualifier(kv);
      NavigableMap<Long, byte[]> versionMap = columnMap.get(qualifier);
      if (versionMap == null) {
        versionMap = new TreeMap<>(new Comparator<Long>() {
          @Override
          public int compare(Long l1, Long l2) {
            return l2.compareTo(l1);
          }
        });
        columnMap.put(qualifier, versionMap);
      }
      Long timestamp = kv.getTimestamp();
      byte[] value = CellUtil.cloneValue(kv);

      versionMap.put(timestamp, value);
    }
    return this.familyMap;
  }

  /**
   * Map of families to their most recent qualifiers and values.
   * <p>
   * Returns a two level Map of the form: <code>Map&amp;family,Map&lt;qualifier,value&gt;&gt;</code>
   * <p>
   * The most recent version of each qualifier will be used.
   * @return map from families to qualifiers and value
   */
  public NavigableMap<byte[], NavigableMap<byte[], byte[]>> getNoVersionMap() {
    if (this.familyMap == null) {
      getMap();
    }
    if (isEmpty()) {
      return null;
    }
    NavigableMap<byte[], NavigableMap<byte[], byte[]>> returnMap =
      new TreeMap<>(Bytes.BYTES_COMPARATOR);
    for (Map.Entry<byte[], NavigableMap<byte[], NavigableMap<Long, byte[]>>> familyEntry : familyMap
      .entrySet()) {
      NavigableMap<byte[], byte[]> qualifierMap = new TreeMap<>(Bytes.BYTES_COMPARATOR);
      for (Map.Entry<byte[], NavigableMap<Long, byte[]>> qualifierEntry : familyEntry.getValue()
        .entrySet()) {
        byte[] value = qualifierEntry.getValue().get(qualifierEntry.getValue().firstKey());
        qualifierMap.put(qualifierEntry.getKey(), value);
      }
      returnMap.put(familyEntry.getKey(), qualifierMap);
    }
    return returnMap;
  }

  /**
   * Map of qualifiers to values.
   * <p>
   * Returns a Map of the form: <code>Map&lt;qualifier,value&gt;</code>
   * @param family column family to get
   * @return map of qualifiers to values
   */
  public NavigableMap<byte[], byte[]> getFamilyMap(byte[] family) {
    if (this.familyMap == null) {
      getMap();
    }
    if (isEmpty()) {
      return null;
    }
    NavigableMap<byte[], byte[]> returnMap = new TreeMap<>(Bytes.BYTES_COMPARATOR);
    NavigableMap<byte[], NavigableMap<Long, byte[]>> qualifierMap = familyMap.get(family);
    if (qualifierMap == null) {
      return returnMap;
    }
    for (Map.Entry<byte[], NavigableMap<Long, byte[]>> entry : qualifierMap.entrySet()) {
      byte[] value = entry.getValue().get(entry.getValue().firstKey());
      returnMap.put(entry.getKey(), value);
    }
    return returnMap;
  }

  /**
   * Returns the value of the first column in the Result.
   * @return value of the first column
   */
  public byte[] value() {
    if (isEmpty()) {
      return null;
    }
    return CellUtil.cloneValue(cells[0]);
  }

  /**
   * Check if the underlying Cell [] is empty or not
   * @return true if empty
   */
  public boolean isEmpty() {
    return this.cells == null || this.cells.length == 0;
  }

  /** Returns the size of the underlying Cell [] */
  public int size() {
    return this.cells == null ? 0 : this.cells.length;
  }

  /**
   *   */
  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("keyvalues=");
    if (isEmpty()) {
      sb.append("NONE");
      return sb.toString();
    }
    sb.append("{");
    boolean moreThanOne = false;
    for (Cell kv : this.cells) {
      if (moreThanOne) {
        sb.append(", ");
      } else {
        moreThanOne = true;
      }
      sb.append(kv.toString());
    }
    sb.append("}");
    return sb.toString();
  }

  /**
   * Does a deep comparison of two Results, down to the byte arrays.
   * @param res1 first result to compare
   * @param res2 second result to compare
   * @throws Exception Every difference is throwing an exception
   */
  public static void compareResults(Result res1, Result res2) throws Exception {
    compareResults(res1, res2, true);
  }

  /**
   * Does a deep comparison of two Results, down to the byte arrays.
   * @param res1    first result to compare
   * @param res2    second result to compare
   * @param verbose includes string representation for all cells in the exception if true; otherwise
   *                include rowkey only
   * @throws Exception Every difference is throwing an exception
   */
  public static void compareResults(Result res1, Result res2, boolean verbose) throws Exception {
    if (res2 == null) {
      throw new Exception(
        "There wasn't enough rows, we stopped at " + Bytes.toStringBinary(res1.getRow()));
    }
    if (res1.size() != res2.size()) {
      if (verbose) {
        throw new Exception(
          "This row doesn't have the same number of KVs: " + res1 + " compared to " + res2);
      } else {
        throw new Exception(
          "This row doesn't have the same number of KVs: row=" + Bytes.toStringBinary(res1.getRow())
            + ", " + res1.size() + " cells are compared to " + res2.size() + " cells");
      }
    }
    ExtendedCell[] ourKVs = res1.cells;
    ExtendedCell[] replicatedKVs = res2.cells;
    for (int i = 0; i < res1.size(); i++) {
      if (
        !ourKVs[i].equals(replicatedKVs[i]) || !CellUtil.matchingValue(ourKVs[i], replicatedKVs[i])
          || !PrivateCellUtil.matchingTags(ourKVs[i], replicatedKVs[i])
      ) {
        if (verbose) {
          throw new Exception("This result was different: " + res1 + " compared to " + res2);
        } else {
          throw new Exception(
            "This result was different: row=" + Bytes.toStringBinary(res1.getRow()));
        }
      }
    }
  }

  /**
   * Forms a single result from the partial results in the partialResults list. This method is
   * useful for reconstructing partial results on the client side.
   * @param partialResults list of partial results
   * @return The complete result that is formed by combining all of the partial results together
   * @throws IOException A complete result cannot be formed because the results in the partial list
   *                     come from different rows
   */
  public static Result createCompleteResult(Iterable<Result> partialResults) throws IOException {
    if (partialResults == null) {
      return Result.create(Collections.emptyList(), null, false);
    }
    List<Cell> cells = new ArrayList<>();
    boolean stale = false;
    byte[] prevRow = null;
    byte[] currentRow = null;
    for (Iterator<Result> iter = partialResults.iterator(); iter.hasNext();) {
      Result r = iter.next();
      currentRow = r.getRow();
      if (prevRow != null && !Bytes.equals(prevRow, currentRow)) {
        throw new IOException("Cannot form complete result. Rows of partial results do not match."
          + " Partial Results: " + partialResults);
      }
      // Ensure that all Results except the last one are marked as partials. The last result
      // may not be marked as a partial because Results are only marked as partials when
      // the scan on the server side must be stopped due to reaching the maxResultSize.
      // Visualizing it makes it easier to understand:
      // maxResultSize: 2 cells
      // (-x-) represents cell number x in a row
      // Example: row1: -1- -2- -3- -4- -5- (5 cells total)
      // How row1 will be returned by the server as partial Results:
      // Result1: -1- -2- (2 cells, size limit reached, mark as partial)
      // Result2: -3- -4- (2 cells, size limit reached, mark as partial)
      // Result3: -5- (1 cell, size limit NOT reached, NOT marked as partial)
      if (iter.hasNext() && !r.mayHaveMoreCellsInRow()) {
        throw new IOException("Cannot form complete result. Result is missing partial flag. "
          + "Partial Results: " + partialResults);
      }
      prevRow = currentRow;
      stale = stale || r.isStale();
      Collections.addAll(cells, r.rawCells());
    }

    return Result.create(cells, null, stale);
  }

  /**
   * Get total size of raw cells
   * @return Total size.
   */
  public static long getTotalSizeOfCells(Result result) {
    long size = 0;
    if (result.isEmpty()) {
      return size;
    }
    for (Cell c : result.rawCells()) {
      size += c.heapSize();
    }
    return size;
  }

  /**
   * Copy another Result into this one. Needed for the old Mapred framework
   * @throws UnsupportedOperationException if invoked on instance of EMPTY_RESULT (which is supposed
   *                                       to be immutable).
   */
  public void copyFrom(Result other) {
    checkReadonly();
    this.row = null;
    this.familyMap = null;
    this.cells = other.cells;
  }

  /**
   * For client users: You should only use the return value as a
   * {@link org.apache.hadoop.hbase.CellScanner}, {@link ExtendedCellScanner} is marked as
   * IA.Private which means there is no guarantee about its API stability.
   */
  @Override
  public ExtendedCellScanner cellScanner() {
    // Reset
    this.cellScannerIndex = INITIAL_CELLSCANNER_INDEX;
    return this;
  }

  /**
   * For client users: You should only use the return value as a {@link Cell}, {@link ExtendedCell}
   * is marked as IA.Private which means there is no guarantee about its API stability.
   */
  @Override
  public ExtendedCell current() {
    if (
      isEmpty() || cellScannerIndex == INITIAL_CELLSCANNER_INDEX || cellScannerIndex >= cells.length
    ) {
      return null;
    }
    return this.cells[cellScannerIndex];
  }

  @Override
  public boolean advance() {
    if (isEmpty()) {
      return false;
    }
    cellScannerIndex++;
    if (cellScannerIndex < this.cells.length) {
      return true;
    } else if (cellScannerIndex == this.cells.length) {
      return false;
    }
    throw new NoSuchElementException("Cannot advance beyond the last cell");
  }

  public Boolean getExists() {
    return exists;
  }

  public void setExists(Boolean exists) {
    checkReadonly();
    this.exists = exists;
  }

  /**
   * Whether or not the results are coming from possibly stale data. Stale results might be returned
   * if {@link Consistency} is not STRONG for the query.
   * @return Whether or not the results are coming from possibly stale data.
   */
  public boolean isStale() {
    return stale;
  }

  /**
   * For scanning large rows, the RS may choose to return the cells chunk by chunk to prevent OOM or
   * timeout. This flag is used to tell you if the current Result is the last one of the current
   * row. False means this Result is the last one. True means there MAY be more cells belonging to
   * the current row. If you don't use {@link Scan#setAllowPartialResults(boolean)} or
   * {@link Scan#setBatch(int)}, this method will always return false because the Result must
   * contains all cells in one Row.
   */
  public boolean mayHaveMoreCellsInRow() {
    return mayHaveMoreCellsInRow;
  }

  /**
   * Set load information about the region to the information about the result
   * @param loadStats statistics about the current region from which this was returned
   */
  @InterfaceAudience.Private
  public void setStatistics(RegionLoadStats loadStats) {
    this.stats = loadStats;
  }

  /**
   * Returns the associated statistics about the region from which this was returned. Can be
   * <tt>null</tt> if stats are disabled.
   */
  public RegionLoadStats getStats() {
    return stats;
  }

  /**
   * All methods modifying state of Result object must call this method to ensure that special
   * purpose immutable Results can't be accidentally modified.
   */
  private void checkReadonly() {
    if (readonly == true) {
      throw new UnsupportedOperationException("Attempting to modify readonly EMPTY_RESULT!");
    }
  }

  /**
   * Return true if this Result is a cursor to tell users where the server has scanned. In this
   * Result the only meaningful method is {@link #getCursor()}. {@code
   *  while (r = scanner.next() && r != null) {
   *    if(r.isCursor()){
   *    // scanning is not end, it is a cursor, save its row key and close scanner if you want, or
   * // just continue the loop to call next(). } else { // just like before } } // scanning is end }
   * {@link Scan#setNeedCursorResult(boolean)} {@link Cursor} {@link #getCursor()}
   */
  public boolean isCursor() {
    return cursor != null;
  }

  /**
   * Return the cursor if this Result is a cursor result. {@link Scan#setNeedCursorResult(boolean)}
   * {@link Cursor} {@link #isCursor()}
   */
  public Cursor getCursor() {
    return cursor;
  }
}