/**
    * 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.filter;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Comparator;
  import java.util.List;
  import java.util.PriorityQueue;
  
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.KeyValueUtil;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.exceptions.DeserializationException;
  import org.apache.hadoop.hbase.protobuf.generated.FilterProtos;
  import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos.BytesBytesPair;
  import org.apache.hadoop.hbase.util.ByteStringer;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.Pair;
  import org.apache.hadoop.hbase.util.UnsafeAccess;
  import org.apache.hadoop.hbase.util.UnsafeAvailChecker;
  
  import com.google.common.annotations.VisibleForTesting;
  import com.google.protobuf.InvalidProtocolBufferException;
  
  /**
   * This is optimized version of a standard FuzzyRowFilter Filters data based on fuzzy row key.
   * Performs fast-forwards during scanning. It takes pairs (row key, fuzzy info) to match row keys.
   * Where fuzzy info is a byte array with 0 or 1 as its values:
   * <ul>
   * <li>0 - means that this byte in provided row key is fixed, i.e. row key's byte at same position
   * must match</li>
   * <li>1 - means that this byte in provided row key is NOT fixed, i.e. row key's byte at this
   * position can be different from the one in provided row key</li>
   * </ul>
   * Example: Let's assume row key format is userId_actionId_year_month. Length of userId is fixed and
   * is 4, length of actionId is 2 and year and month are 4 and 2 bytes long respectively. Let's
   * assume that we need to fetch all users that performed certain action (encoded as "99") in Jan of
   * any year. Then the pair (row key, fuzzy info) would be the following: row key = "????_99_????_01"
   * (one can use any value instead of "?") fuzzy info =
   * "\x01\x01\x01\x01\x00\x00\x00\x00\x01\x01\x01\x01\x00\x00\x00" I.e. fuzzy info tells the matching
   * mask is "????_99_????_01", where at ? can be any value.
   */
  @InterfaceAudience.Public
  @InterfaceStability.Evolving
  public class FuzzyRowFilter extends FilterBase {
    private static final boolean UNSAFE_UNALIGNED = UnsafeAvailChecker.unaligned();
    private List<Pair<byte[], byte[]>> fuzzyKeysData;
    private boolean done = false;
  
    /**
     * The index of a last successfully found matching fuzzy string (in fuzzyKeysData). We will start
     * matching next KV with this one. If they do not match then we will return back to the one-by-one
     * iteration over fuzzyKeysData.
     */
    private int lastFoundIndex = -1;
  
    /**
     * Row tracker (keeps all next rows after SEEK_NEXT_USING_HINT was returned)
     */
    private RowTracker tracker;
  
    public FuzzyRowFilter(List<Pair<byte[], byte[]>> fuzzyKeysData) {
      List<Pair<byte[], byte[]>> fuzzyKeyDataCopy = new ArrayList<>(fuzzyKeysData.size());
  
      for (Pair<byte[], byte[]> aFuzzyKeysData : fuzzyKeysData) {
        if (aFuzzyKeysData.getFirst().length != aFuzzyKeysData.getSecond().length) {
          Pair<String, String> readable =
            new Pair<>(Bytes.toStringBinary(aFuzzyKeysData.getFirst()), Bytes.toStringBinary(aFuzzyKeysData.getSecond()));
          throw new IllegalArgumentException("Fuzzy pair lengths do not match: " + readable);
        }
  
        Pair<byte[], byte[]> p = new Pair<>();
        // create a copy of pair bytes so that they are not modified by the filter.
        p.setFirst(Arrays.copyOf(aFuzzyKeysData.getFirst(), aFuzzyKeysData.getFirst().length));
        p.setSecond(Arrays.copyOf(aFuzzyKeysData.getSecond(), aFuzzyKeysData.getSecond().length));
  
        // update mask ( 0 -> -1 (0xff), 1 -> 2)
        p.setSecond(preprocessMask(p.getSecond()));
        preprocessSearchKey(p);
  
        fuzzyKeyDataCopy.add(p);
      }
     this.fuzzyKeysData = fuzzyKeyDataCopy;
     this.tracker = new RowTracker();
   }
 
   private void preprocessSearchKey(Pair<byte[], byte[]> p) {
     if (!UNSAFE_UNALIGNED) {
       return;
     }
     byte[] key = p.getFirst();
     byte[] mask = p.getSecond();
     for (int i = 0; i < mask.length; i++) {
       // set non-fixed part of a search key to 0.
       if (mask[i] == 2) {
         key[i] = 0;
       }
     }
   }
 
   /**
    * We need to preprocess mask array, as since we treat 2's as unfixed positions and -1 (0xff) as
    * fixed positions
    * @param mask
    * @return mask array
    */
   private byte[] preprocessMask(byte[] mask) {
     if (!UNSAFE_UNALIGNED) {
       return mask;
     }
     if (isPreprocessedMask(mask)) return mask;
     for (int i = 0; i < mask.length; i++) {
       if (mask[i] == 0) {
         mask[i] = -1; // 0 -> -1
       } else if (mask[i] == 1) {
         mask[i] = 2;// 1 -> 2
       }
     }
     return mask;
   }
 
   private boolean isPreprocessedMask(byte[] mask) {
     for (int i = 0; i < mask.length; i++) {
       if (mask[i] != -1 && mask[i] != 2) {
         return false;
       }
     }
     return true;
   }
 
   @Override
   public ReturnCode filterKeyValue(Cell c) {
     final int startIndex = lastFoundIndex >= 0 ? lastFoundIndex : 0;
     final int size = fuzzyKeysData.size();
     for (int i = startIndex; i < size + startIndex; i++) {
       final int index = i % size;
       Pair<byte[], byte[]> fuzzyData = fuzzyKeysData.get(index);
       // This shift is idempotent - always end up with 0 and -1 as mask values.
       for (int j = 0; j < fuzzyData.getSecond().length; j++) {
         fuzzyData.getSecond()[j] >>= 2;
       }
       SatisfiesCode satisfiesCode =
           satisfies(isReversed(), c.getRowArray(), c.getRowOffset(), c.getRowLength(),
             fuzzyData.getFirst(), fuzzyData.getSecond());
       if (satisfiesCode == SatisfiesCode.YES) {
         lastFoundIndex = index;
         return ReturnCode.INCLUDE;
       }
     }
     // NOT FOUND -> seek next using hint
     lastFoundIndex = -1;
 
     return ReturnCode.SEEK_NEXT_USING_HINT;
 
   }
 
   @Override
   public Cell getNextCellHint(Cell currentCell) {
     boolean result = tracker.updateTracker(currentCell);
     if (result == false) {
       done = true;
       return null;
     }
     byte[] nextRowKey = tracker.nextRow();
     return KeyValueUtil.createFirstOnRow(nextRowKey);
   }
 
   /**
    * If we have multiple fuzzy keys, row tracker should improve overall performance. It calculates
    * all next rows (one per every fuzzy key) and put them (the fuzzy key is bundled) into a priority
    * queue so that the smallest row key always appears at queue head, which helps to decide the
    * "Next Cell Hint". As scanning going on, the number of candidate rows in the RowTracker will
    * remain the size of fuzzy keys until some of the fuzzy keys won't possibly have matches any
    * more.
    */
   private class RowTracker {
     private final PriorityQueue<Pair<byte[], Pair<byte[], byte[]>>> nextRows;
     private boolean initialized = false;
 
     RowTracker() {
       nextRows =
           new PriorityQueue<Pair<byte[], Pair<byte[], byte[]>>>(fuzzyKeysData.size(),
               new Comparator<Pair<byte[], Pair<byte[], byte[]>>>() {
                 @Override
                 public int compare(Pair<byte[], Pair<byte[], byte[]>> o1,
                     Pair<byte[], Pair<byte[], byte[]>> o2) {
                   return isReversed()? Bytes.compareTo(o2.getFirst(), o1.getFirst()):
                     Bytes.compareTo(o1.getFirst(), o2.getFirst());
                 }
               });
     }
 
     byte[] nextRow() {
       if (nextRows.isEmpty()) {
         throw new IllegalStateException(
             "NextRows should not be empty, make sure to call nextRow() after updateTracker() return true");
       } else {
         return nextRows.peek().getFirst();
       }
     }
 
     boolean updateTracker(Cell currentCell) {
       if (!initialized) {
         for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
           updateWith(currentCell, fuzzyData);
         }
         initialized = true;
       } else {
         while (!nextRows.isEmpty() && !lessThan(currentCell, nextRows.peek().getFirst())) {
           Pair<byte[], Pair<byte[], byte[]>> head = nextRows.poll();
           Pair<byte[], byte[]> fuzzyData = head.getSecond();
           updateWith(currentCell, fuzzyData);
         }
       }
       return !nextRows.isEmpty();
     }
 
     boolean lessThan(Cell currentCell, byte[] nextRowKey) {
       int compareResult =
           Bytes.compareTo(currentCell.getRowArray(), currentCell.getRowOffset(),
             currentCell.getRowLength(), nextRowKey, 0, nextRowKey.length);
       return (!isReversed() && compareResult < 0) || (isReversed() && compareResult > 0);
     }
 
     void updateWith(Cell currentCell, Pair<byte[], byte[]> fuzzyData) {
       byte[] nextRowKeyCandidate =
           getNextForFuzzyRule(isReversed(), currentCell.getRowArray(), currentCell.getRowOffset(),
             currentCell.getRowLength(), fuzzyData.getFirst(), fuzzyData.getSecond());
       if (nextRowKeyCandidate != null) {
         nextRows.add(new Pair<byte[], Pair<byte[], byte[]>>(nextRowKeyCandidate, fuzzyData));
       }
     }
 
   }
 
   @Override
   public boolean filterAllRemaining() {
     return done;
   }
 
   /**
    * @return The filter serialized using pb
    */
   @Override
   public byte[] toByteArray() {
     FilterProtos.FuzzyRowFilter.Builder builder = FilterProtos.FuzzyRowFilter.newBuilder();
     for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
       BytesBytesPair.Builder bbpBuilder = BytesBytesPair.newBuilder();
       bbpBuilder.setFirst(ByteStringer.wrap(fuzzyData.getFirst()));
       bbpBuilder.setSecond(ByteStringer.wrap(fuzzyData.getSecond()));
       builder.addFuzzyKeysData(bbpBuilder);
     }
     return builder.build().toByteArray();
   }
 
   /**
    * @param pbBytes A pb serialized {@link FuzzyRowFilter} instance
    * @return An instance of {@link FuzzyRowFilter} made from <code>bytes</code>
    * @throws DeserializationException
    * @see #toByteArray
    */
   public static FuzzyRowFilter parseFrom(final byte[] pbBytes) throws DeserializationException {
     FilterProtos.FuzzyRowFilter proto;
     try {
       proto = FilterProtos.FuzzyRowFilter.parseFrom(pbBytes);
     } catch (InvalidProtocolBufferException e) {
       throw new DeserializationException(e);
     }
     int count = proto.getFuzzyKeysDataCount();
     ArrayList<Pair<byte[], byte[]>> fuzzyKeysData = new ArrayList<Pair<byte[], byte[]>>(count);
     for (int i = 0; i < count; ++i) {
       BytesBytesPair current = proto.getFuzzyKeysData(i);
       byte[] keyBytes = current.getFirst().toByteArray();
       byte[] keyMeta = current.getSecond().toByteArray();
       fuzzyKeysData.add(new Pair<byte[], byte[]>(keyBytes, keyMeta));
     }
     return new FuzzyRowFilter(fuzzyKeysData);
   }
 
   @Override
   public String toString() {
     final StringBuilder sb = new StringBuilder();
     sb.append("FuzzyRowFilter");
     sb.append("{fuzzyKeysData=");
     for (Pair<byte[], byte[]> fuzzyData : fuzzyKeysData) {
       sb.append('{').append(Bytes.toStringBinary(fuzzyData.getFirst())).append(":");
       sb.append(Bytes.toStringBinary(fuzzyData.getSecond())).append('}');
     }
     sb.append("}, ");
     return sb.toString();
   }
 
   // Utility methods
 
   static enum SatisfiesCode {
     /** row satisfies fuzzy rule */
     YES,
     /** row doesn't satisfy fuzzy rule, but there's possible greater row that does */
     NEXT_EXISTS,
     /** row doesn't satisfy fuzzy rule and there's no greater row that does */
     NO_NEXT
   }
 
   @VisibleForTesting
   static SatisfiesCode satisfies(byte[] row, byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
     return satisfies(false, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
   }
 
   @VisibleForTesting
   static SatisfiesCode satisfies(boolean reverse, byte[] row, byte[] fuzzyKeyBytes,
       byte[] fuzzyKeyMeta) {
     return satisfies(reverse, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
   }
 
   static SatisfiesCode satisfies(boolean reverse, byte[] row, int offset, int length,
       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
 
     if (!UNSAFE_UNALIGNED) {
       return satisfiesNoUnsafe(reverse, row, offset, length, fuzzyKeyBytes, fuzzyKeyMeta);
     }
 
     if (row == null) {
       // do nothing, let scan to proceed
       return SatisfiesCode.YES;
     }
     length = Math.min(length, fuzzyKeyBytes.length);
     int numWords = length / Bytes.SIZEOF_LONG;
     int offsetAdj = offset + UnsafeAccess.BYTE_ARRAY_BASE_OFFSET;
 
     int j = numWords << 3; // numWords * SIZEOF_LONG;
 
     for (int i = 0; i < j; i += Bytes.SIZEOF_LONG) {
 
       long fuzzyBytes =
           UnsafeAccess.theUnsafe.getLong(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
               + (long) i);
       long fuzzyMeta =
           UnsafeAccess.theUnsafe.getLong(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
               + (long) i);
       long rowValue = UnsafeAccess.theUnsafe.getLong(row, offsetAdj + (long) i);
       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
         // We always return NEXT_EXISTS
         return SatisfiesCode.NEXT_EXISTS;
       }
     }
 
     int off = j;
 
     if (length - off >= Bytes.SIZEOF_INT) {
       int fuzzyBytes =
           UnsafeAccess.theUnsafe.getInt(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
               + (long) off);
       int fuzzyMeta =
           UnsafeAccess.theUnsafe.getInt(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
               + (long) off);
       int rowValue = UnsafeAccess.theUnsafe.getInt(row, offsetAdj + (long) off);
       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
         // We always return NEXT_EXISTS
         return SatisfiesCode.NEXT_EXISTS;
       }
       off += Bytes.SIZEOF_INT;
     }
 
     if (length - off >= Bytes.SIZEOF_SHORT) {
       short fuzzyBytes =
           UnsafeAccess.theUnsafe.getShort(fuzzyKeyBytes, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
               + (long) off);
       short fuzzyMeta =
           UnsafeAccess.theUnsafe.getShort(fuzzyKeyMeta, UnsafeAccess.BYTE_ARRAY_BASE_OFFSET
               + (long) off);
       short rowValue = UnsafeAccess.theUnsafe.getShort(row, offsetAdj + (long) off);
       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
         // We always return NEXT_EXISTS
         // even if it does not (in this case getNextForFuzzyRule
         // will return null)
         return SatisfiesCode.NEXT_EXISTS;
       }
       off += Bytes.SIZEOF_SHORT;
     }
 
     if (length - off >= Bytes.SIZEOF_BYTE) {
       int fuzzyBytes = fuzzyKeyBytes[off] & 0xff;
       int fuzzyMeta = fuzzyKeyMeta[off] & 0xff;
       int rowValue = row[offset + off] & 0xff;
       if ((rowValue & fuzzyMeta) != (fuzzyBytes)) {
         // We always return NEXT_EXISTS
         return SatisfiesCode.NEXT_EXISTS;
       }
     }
     return SatisfiesCode.YES;
   }
 
   static SatisfiesCode satisfiesNoUnsafe(boolean reverse, byte[] row, int offset, int length,
       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
     if (row == null) {
       // do nothing, let scan to proceed
       return SatisfiesCode.YES;
     }
 
     Order order = Order.orderFor(reverse);
     boolean nextRowKeyCandidateExists = false;
 
     for (int i = 0; i < fuzzyKeyMeta.length && i < length; i++) {
       // First, checking if this position is fixed and not equals the given one
       boolean byteAtPositionFixed = fuzzyKeyMeta[i] == 0;
       boolean fixedByteIncorrect = byteAtPositionFixed && fuzzyKeyBytes[i] != row[i + offset];
       if (fixedByteIncorrect) {
         // in this case there's another row that satisfies fuzzy rule and bigger than this row
         if (nextRowKeyCandidateExists) {
           return SatisfiesCode.NEXT_EXISTS;
         }
 
         // If this row byte is less than fixed then there's a byte array bigger than
         // this row and which satisfies the fuzzy rule. Otherwise there's no such byte array:
         // this row is simply bigger than any byte array that satisfies the fuzzy rule
         boolean rowByteLessThanFixed = (row[i + offset] & 0xFF) < (fuzzyKeyBytes[i] & 0xFF);
         if (rowByteLessThanFixed && !reverse) {
           return SatisfiesCode.NEXT_EXISTS;
         } else if (!rowByteLessThanFixed && reverse) {
           return SatisfiesCode.NEXT_EXISTS;
         } else {
           return SatisfiesCode.NO_NEXT;
         }
       }
 
       // Second, checking if this position is not fixed and byte value is not the biggest. In this
       // case there's a byte array bigger than this row and which satisfies the fuzzy rule. To get
       // bigger byte array that satisfies the rule we need to just increase this byte
       // (see the code of getNextForFuzzyRule below) by one.
       // Note: if non-fixed byte is already at biggest value, this doesn't allow us to say there's
       // bigger one that satisfies the rule as it can't be increased.
       if (fuzzyKeyMeta[i] == 1 && !order.isMax(fuzzyKeyBytes[i])) {
         nextRowKeyCandidateExists = true;
       }
     }
     return SatisfiesCode.YES;
   }
 
   @VisibleForTesting
   static byte[] getNextForFuzzyRule(byte[] row, byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
     return getNextForFuzzyRule(false, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
   }
 
   @VisibleForTesting
   static byte[] getNextForFuzzyRule(boolean reverse, byte[] row, byte[] fuzzyKeyBytes,
       byte[] fuzzyKeyMeta) {
     return getNextForFuzzyRule(reverse, row, 0, row.length, fuzzyKeyBytes, fuzzyKeyMeta);
   }
 
   /** Abstracts directional comparisons based on scan direction. */
   private enum Order {
     ASC {
       @Override
       public boolean lt(int lhs, int rhs) {
         return lhs < rhs;
       }
 
       @Override
       public boolean gt(int lhs, int rhs) {
         return lhs > rhs;
       }
 
       @Override
       public byte inc(byte val) {
         // TODO: what about over/underflow?
         return (byte) (val + 1);
       }
 
       @Override
       public boolean isMax(byte val) {
         return val == (byte) 0xff;
       }
 
       @Override
       public byte min() {
         return 0;
       }
     },
     DESC {
       @Override
       public boolean lt(int lhs, int rhs) {
         return lhs > rhs;
       }
 
       @Override
       public boolean gt(int lhs, int rhs) {
         return lhs < rhs;
       }
 
       @Override
       public byte inc(byte val) {
         // TODO: what about over/underflow?
         return (byte) (val - 1);
       }
 
       @Override
       public boolean isMax(byte val) {
         return val == 0;
       }
 
       @Override
       public byte min() {
         return (byte) 0xFF;
       }
     };
 
     public static Order orderFor(boolean reverse) {
       return reverse ? DESC : ASC;
     }
 
     /** Returns true when {@code lhs < rhs}. */
     public abstract boolean lt(int lhs, int rhs);
 
     /** Returns true when {@code lhs > rhs}. */
     public abstract boolean gt(int lhs, int rhs);
 
     /** Returns {@code val} incremented by 1. */
     public abstract byte inc(byte val);
 
     /** Return true when {@code val} is the maximum value */
     public abstract boolean isMax(byte val);
 
     /** Return the minimum value according to this ordering scheme. */
     public abstract byte min();
   }
 
   /**
    * @return greater byte array than given (row) which satisfies the fuzzy rule if it exists, null
    *         otherwise
    */
   @VisibleForTesting
   static byte[] getNextForFuzzyRule(boolean reverse, byte[] row, int offset, int length,
       byte[] fuzzyKeyBytes, byte[] fuzzyKeyMeta) {
     // To find out the next "smallest" byte array that satisfies fuzzy rule and "greater" than
     // the given one we do the following:
     // 1. setting values on all "fixed" positions to the values from fuzzyKeyBytes
     // 2. if during the first step given row did not increase, then we increase the value at
     // the first "non-fixed" position (where it is not maximum already)
 
     // It is easier to perform this by using fuzzyKeyBytes copy and setting "non-fixed" position
     // values than otherwise.
     byte[] result =
         Arrays.copyOf(fuzzyKeyBytes, length > fuzzyKeyBytes.length ? length : fuzzyKeyBytes.length);
     if (reverse && length > fuzzyKeyBytes.length) {
       // we need trailing 0xff's instead of trailing 0x00's
       for (int i = fuzzyKeyBytes.length; i < result.length; i++) {
         result[i] = (byte) 0xFF;
       }
     }
     int toInc = -1;
     final Order order = Order.orderFor(reverse);
 
     boolean increased = false;
     for (int i = 0; i < result.length; i++) {
       if (i >= fuzzyKeyMeta.length || fuzzyKeyMeta[i] == 0 /* non-fixed */) {
         result[i] = row[offset + i];
         if (!order.isMax(row[offset + i])) {
           // this is "non-fixed" position and is not at max value, hence we can increase it
           toInc = i;
         }
       } else if (i < fuzzyKeyMeta.length && fuzzyKeyMeta[i] == -1 /* fixed */) {
         if (order.lt((row[i + offset] & 0xFF), (fuzzyKeyBytes[i] & 0xFF))) {
           // if setting value for any fixed position increased the original array,
           // we are OK
           increased = true;
           break;
         }
 
         if (order.gt((row[i + offset] & 0xFF), (fuzzyKeyBytes[i] & 0xFF))) {
           // if setting value for any fixed position makes array "smaller", then just stop:
           // in case we found some non-fixed position to increase we will do it, otherwise
           // there's no "next" row key that satisfies fuzzy rule and "greater" than given row
           break;
         }
       }
     }
 
     if (!increased) {
       if (toInc < 0) {
         return null;
       }
       result[toInc] = order.inc(result[toInc]);
 
       // Setting all "non-fixed" positions to zeroes to the right of the one we increased so
       // that found "next" row key is the smallest possible
       for (int i = toInc + 1; i < result.length; i++) {
         if (i >= fuzzyKeyMeta.length || fuzzyKeyMeta[i] == 0 /* non-fixed */) {
           result[i] = order.min();
         }
       }
     }
 
     return reverse? result: trimTrailingZeroes(result, fuzzyKeyMeta, toInc);
   }
 
   /**
    * For forward scanner, next cell hint should  not contain any trailing zeroes
    * unless they are part of fuzzyKeyMeta
    * hint = '\x01\x01\x01\x00\x00'
    * will skip valid row '\x01\x01\x01'
    * 
    * @param result
    * @param fuzzyKeyMeta
    * @param toInc - position of incremented byte
    * @return trimmed version of result
    */
   
   private static byte[] trimTrailingZeroes(byte[] result, byte[] fuzzyKeyMeta, int toInc) {
     int off = fuzzyKeyMeta.length >= result.length? result.length -1:
            fuzzyKeyMeta.length -1;  
     for( ; off >= 0; off--){
       if(fuzzyKeyMeta[off] != 0) break;
     }
     if (off < toInc)  off = toInc;
     byte[] retValue = new byte[off+1];
     System.arraycopy(result, 0, retValue, 0, retValue.length);
     return retValue;
   }
 
   /**
    * @return true if and only if the fields of the filter that are serialized are equal to the
    *         corresponding fields in other. Used for testing.
    */
   @Override
   boolean areSerializedFieldsEqual(Filter o) {
     if (o == this) return true;
     if (!(o instanceof FuzzyRowFilter)) return false;
 
     FuzzyRowFilter other = (FuzzyRowFilter) o;
     if (this.fuzzyKeysData.size() != other.fuzzyKeysData.size()) return false;
     for (int i = 0; i < fuzzyKeysData.size(); ++i) {
       Pair<byte[], byte[]> thisData = this.fuzzyKeysData.get(i);
       Pair<byte[], byte[]> otherData = other.fuzzyKeysData.get(i);
       if (!(Bytes.equals(thisData.getFirst(), otherData.getFirst()) && Bytes.equals(
         thisData.getSecond(), otherData.getSecond()))) {
         return false;
       }
     }
     return true;
   }
 }