/*
    * 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.io.encoding;
  
  import java.io.DataInputStream;
  import java.io.DataOutputStream;
  import java.io.IOException;
  import java.nio.ByteBuffer;
  
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.CellComparator;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.KeyValue.KVComparator;
  import org.apache.hadoop.hbase.KeyValue.SamePrefixComparator;
  import org.apache.hadoop.hbase.KeyValue.Type;
  import org.apache.hadoop.hbase.KeyValueUtil;
  import org.apache.hadoop.hbase.SettableSequenceId;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.io.HeapSize;
  import org.apache.hadoop.hbase.io.TagCompressionContext;
  import org.apache.hadoop.hbase.io.util.LRUDictionary;
  import org.apache.hadoop.hbase.util.ByteBufferUtils;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.ClassSize;
  import org.apache.hadoop.io.WritableUtils;
  
  /**
   * Base class for all data block encoders that use a buffer.
   */
  @InterfaceAudience.Private
  abstract class BufferedDataBlockEncoder extends AbstractDataBlockEncoder {
    /**
     * TODO: This datablockencoder is dealing in internals of hfileblocks. Purge reference to HFBs
     */
    private static int INITIAL_KEY_BUFFER_SIZE = 512;
  
    @Override
    public ByteBuffer decodeKeyValues(DataInputStream source,
        HFileBlockDecodingContext blkDecodingCtx) throws IOException {
      if (blkDecodingCtx.getClass() != HFileBlockDefaultDecodingContext.class) {
        throw new IOException(this.getClass().getName() + " only accepts "
            + HFileBlockDefaultDecodingContext.class.getName() + " as the decoding context.");
      }
  
      HFileBlockDefaultDecodingContext decodingCtx =
          (HFileBlockDefaultDecodingContext) blkDecodingCtx;
      if (decodingCtx.getHFileContext().isIncludesTags()
          && decodingCtx.getHFileContext().isCompressTags()) {
        if (decodingCtx.getTagCompressionContext() != null) {
          // It will be overhead to create the TagCompressionContext again and again for every block
          // decoding.
          decodingCtx.getTagCompressionContext().clear();
        } else {
          try {
            TagCompressionContext tagCompressionContext = new TagCompressionContext(
                LRUDictionary.class, Byte.MAX_VALUE);
            decodingCtx.setTagCompressionContext(tagCompressionContext);
          } catch (Exception e) {
            throw new IOException("Failed to initialize TagCompressionContext", e);
          }
        }
      }
      return internalDecodeKeyValues(source, 0, 0, decodingCtx);
    }
  
    protected static class SeekerState implements Cell {
      protected ByteBuffer currentBuffer;
      protected TagCompressionContext tagCompressionContext;
      protected int valueOffset = -1;
      protected int keyLength;
      protected int valueLength;
      protected int lastCommonPrefix;
      protected int tagsLength = 0;
      protected int tagsOffset = -1;
      protected int tagsCompressedLength = 0;
      protected boolean uncompressTags = true;
  
      /** We need to store a copy of the key. */
      protected byte[] keyBuffer = HConstants.EMPTY_BYTE_ARRAY;
      protected byte[] tagsBuffer = HConstants.EMPTY_BYTE_ARRAY;
  
      protected long memstoreTS;
      protected int nextKvOffset;
     protected KeyValue.KeyOnlyKeyValue currentKey = new KeyValue.KeyOnlyKeyValue();
 
     public SeekerState() {
     }
 
     protected boolean isValid() {
       return valueOffset != -1;
     }
 
     protected void invalidate() {
       valueOffset = -1;
       tagsCompressedLength = 0;
       currentKey = new KeyValue.KeyOnlyKeyValue();
       uncompressTags = true;
       currentBuffer = null;
     }
 
     protected void ensureSpaceForKey() {
       if (keyLength > keyBuffer.length) {
         int newKeyBufferLength = Integer.highestOneBit(Math.max(
             INITIAL_KEY_BUFFER_SIZE, keyLength) - 1) << 1;
         byte[] newKeyBuffer = new byte[newKeyBufferLength];
         System.arraycopy(keyBuffer, 0, newKeyBuffer, 0, keyBuffer.length);
         keyBuffer = newKeyBuffer;
       }
     }
 
     protected void ensureSpaceForTags() {
       if (tagsLength > tagsBuffer.length) {
         int newTagsBufferLength = Integer.highestOneBit(Math.max(
             INITIAL_KEY_BUFFER_SIZE, tagsLength) - 1) << 1;
         byte[] newTagsBuffer = new byte[newTagsBufferLength];
         System.arraycopy(tagsBuffer, 0, newTagsBuffer, 0, tagsBuffer.length);
         tagsBuffer = newTagsBuffer;
       }
     }
 
     protected void setKey(byte[] keyBuffer, long memTS) {
       currentKey.setKey(keyBuffer, 0, keyLength);
       memstoreTS = memTS;
     }
 
     /**
      * Copy the state from the next one into this instance (the previous state
      * placeholder). Used to save the previous state when we are advancing the
      * seeker to the next key/value.
      */
     protected void copyFromNext(SeekerState nextState) {
       if (keyBuffer.length != nextState.keyBuffer.length) {
         keyBuffer = nextState.keyBuffer.clone();
       } else if (!isValid()) {
         // Note: we can only call isValid before we override our state, so this
         // comes before all the assignments at the end of this method.
         System.arraycopy(nextState.keyBuffer, 0, keyBuffer, 0,
              nextState.keyLength);
       } else {
         // don't copy the common prefix between this key and the previous one
         System.arraycopy(nextState.keyBuffer, nextState.lastCommonPrefix,
             keyBuffer, nextState.lastCommonPrefix, nextState.keyLength
                 - nextState.lastCommonPrefix);
       }
       currentKey = nextState.currentKey;
 
       valueOffset = nextState.valueOffset;
       keyLength = nextState.keyLength;
       valueLength = nextState.valueLength;
       lastCommonPrefix = nextState.lastCommonPrefix;
       nextKvOffset = nextState.nextKvOffset;
       memstoreTS = nextState.memstoreTS;
       currentBuffer = nextState.currentBuffer;
       tagsOffset = nextState.tagsOffset;
       tagsLength = nextState.tagsLength;
       if (nextState.tagCompressionContext != null) {
         tagCompressionContext = nextState.tagCompressionContext;
       }
     }
 
     @Override
     public byte[] getRowArray() {
       return currentKey.getRowArray();
     }
 
     @Override
     public int getRowOffset() {
       return Bytes.SIZEOF_SHORT;
     }
 
     @Override
     public short getRowLength() {
       return currentKey.getRowLength();
     }
 
     @Override
     public byte[] getFamilyArray() {
       return currentKey.getFamilyArray();
     }
 
     @Override
     public int getFamilyOffset() {
       return currentKey.getFamilyOffset();
     }
 
     @Override
     public byte getFamilyLength() {
       return currentKey.getFamilyLength();
     }
 
     @Override
     public byte[] getQualifierArray() {
       return currentKey.getQualifierArray();
     }
 
     @Override
     public int getQualifierOffset() {
       return currentKey.getQualifierOffset();
     }
 
     @Override
     public int getQualifierLength() {
       return currentKey.getQualifierLength();
     }
 
     @Override
     public long getTimestamp() {
       return currentKey.getTimestamp();
     }
 
     @Override
     public byte getTypeByte() {
       return currentKey.getTypeByte();
     }
 
     @Override
     public long getMvccVersion() {
       return memstoreTS;
     }
 
     @Override
     public long getSequenceId() {
       return memstoreTS;
     }
 
     @Override
     public byte[] getValueArray() {
       return currentBuffer.array();
     }
 
     @Override
     public int getValueOffset() {
       return currentBuffer.arrayOffset() + valueOffset;
     }
 
     @Override
     public int getValueLength() {
       return valueLength;
     }
 
     @Override
     public byte[] getTagsArray() {
       if (tagCompressionContext != null) {
         return tagsBuffer;
       }
       return currentBuffer.array();
     }
 
     @Override
     public int getTagsOffset() {
       if (tagCompressionContext != null) {
         return 0;
       }
       return currentBuffer.arrayOffset() + tagsOffset;
     }
 
     @Override
     public int getTagsLength() {
       return tagsLength;
     }
 
     @Override
     @Deprecated
     public byte[] getValue() {
       throw new UnsupportedOperationException("getValue() not supported");
     }
 
     @Override
     @Deprecated
     public byte[] getFamily() {
       throw new UnsupportedOperationException("getFamily() not supported");
     }
 
     @Override
     @Deprecated
     public byte[] getQualifier() {
       throw new UnsupportedOperationException("getQualifier() not supported");
     }
 
     @Override
     @Deprecated
     public byte[] getRow() {
       throw new UnsupportedOperationException("getRow() not supported");
     }
 
     @Override
     public String toString() {
       return KeyValue.keyToString(this.keyBuffer, 0, KeyValueUtil.keyLength(this)) + "/vlen="
           + getValueLength() + "/seqid=" + memstoreTS;
     }
 
     public Cell shallowCopy() {
       return new ClonedSeekerState(currentBuffer, keyBuffer, currentKey.getRowLength(),
           currentKey.getFamilyOffset(), currentKey.getFamilyLength(), keyLength, 
           currentKey.getQualifierOffset(), currentKey.getQualifierLength(),
           currentKey.getTimestamp(), currentKey.getTypeByte(), valueLength, valueOffset,
           memstoreTS, tagsOffset, tagsLength, tagCompressionContext, tagsBuffer);
     }
   }
 
   /**
    * Copies only the key part of the keybuffer by doing a deep copy and passes the 
    * seeker state members for taking a clone.
    * Note that the value byte[] part is still pointing to the currentBuffer and the 
    * represented by the valueOffset and valueLength
    */
   // We return this as a Cell to the upper layers of read flow and might try setting a new SeqId
   // there. So this has to be an instance of SettableSequenceId. SeekerState need not be
   // SettableSequenceId as we never return that to top layers. When we have to, we make
   // ClonedSeekerState from it.
   protected static class ClonedSeekerState implements Cell, HeapSize, SettableSequenceId {
     private static final long FIXED_OVERHEAD = ClassSize.align(ClassSize.OBJECT
         + (4 * ClassSize.REFERENCE) + (2 * Bytes.SIZEOF_LONG) + (7 * Bytes.SIZEOF_INT)
         + (Bytes.SIZEOF_SHORT) + (2 * Bytes.SIZEOF_BYTE) + (2 * ClassSize.ARRAY));
     private byte[] keyOnlyBuffer;
     private ByteBuffer currentBuffer;
     private short rowLength;
     private int familyOffset;
     private byte familyLength;
     private int qualifierOffset;
     private int qualifierLength;
     private long timestamp;
     private byte typeByte;
     private int valueOffset;
     private int valueLength;
     private int tagsLength;
     private int tagsOffset;
     private byte[] cloneTagsBuffer;
     private long seqId;
     private TagCompressionContext tagCompressionContext;
     
     protected ClonedSeekerState(ByteBuffer currentBuffer, byte[] keyBuffer, short rowLength,
         int familyOffset, byte familyLength, int keyLength, int qualOffset, int qualLength,
         long timeStamp, byte typeByte, int valueLen, int valueOffset, long seqId,
         int tagsOffset, int tagsLength, TagCompressionContext tagCompressionContext,
         byte[] tagsBuffer) {
       this.currentBuffer = currentBuffer;
       keyOnlyBuffer = new byte[keyLength];
       this.tagCompressionContext = tagCompressionContext;
       this.rowLength = rowLength;
       this.familyOffset = familyOffset;
       this.familyLength = familyLength;
       this.qualifierOffset = qualOffset;
       this.qualifierLength = qualLength;
       this.timestamp = timeStamp;
       this.typeByte = typeByte;
       this.valueLength = valueLen;
       this.valueOffset = valueOffset;
       this.tagsOffset = tagsOffset;
       this.tagsLength = tagsLength;
       System.arraycopy(keyBuffer, 0, keyOnlyBuffer, 0, keyLength);
       if (tagCompressionContext != null) {
         this.cloneTagsBuffer = new byte[tagsLength];
         System.arraycopy(tagsBuffer, 0, this.cloneTagsBuffer, 0, tagsLength);
       }
       setSequenceId(seqId);
     }
 
     @Override
     public byte[] getRowArray() {
       return keyOnlyBuffer;
     }
 
     @Override
     public byte[] getFamilyArray() {
       return keyOnlyBuffer;
     }
 
     @Override
     public byte[] getQualifierArray() {
       return keyOnlyBuffer;
     }
 
     @Override
     public int getRowOffset() {
       return Bytes.SIZEOF_SHORT;
     }
 
     @Override
     public short getRowLength() {
       return rowLength;
     }
 
     @Override
     public int getFamilyOffset() {
       return familyOffset;
     }
 
     @Override
     public byte getFamilyLength() {
       return familyLength;
     }
 
     @Override
     public int getQualifierOffset() {
       return qualifierOffset;
     }
 
     @Override
     public int getQualifierLength() {
       return qualifierLength;
     }
 
     @Override
     public long getTimestamp() {
       return timestamp;
     }
 
     @Override
     public byte getTypeByte() {
       return typeByte;
     }
 
     @Override
     @Deprecated
     public long getMvccVersion() {
       return getSequenceId();
     }
 
     @Override
     public long getSequenceId() {
       return seqId;
     }
 
     @Override
     public byte[] getValueArray() {
       return currentBuffer.array();
     }
 
     @Override
     public int getValueOffset() {
       return currentBuffer.arrayOffset() + valueOffset;
     }
 
     @Override
     public int getValueLength() {
       return valueLength;
     }
 
     @Override
     public byte[] getTagsArray() {
       if (tagCompressionContext != null) {
         return cloneTagsBuffer;
       }
       return currentBuffer.array();
     }
 
     @Override
     public int getTagsOffset() {
       if (tagCompressionContext != null) {
         return 0;
       }
       return currentBuffer.arrayOffset() + tagsOffset;
     }
 
     @Override
     public int getTagsLength() {
       return tagsLength;
     }
 
     @Override
     @Deprecated
     public byte[] getValue() {
       return CellUtil.cloneValue(this);
     }
 
     @Override
     @Deprecated
     public byte[] getFamily() {
       return CellUtil.cloneFamily(this);
     }
 
     @Override
     @Deprecated
     public byte[] getQualifier() {
       return CellUtil.cloneQualifier(this);
     }
 
     @Override
     @Deprecated
     public byte[] getRow() {
       return CellUtil.cloneRow(this);
     }
 
     @Override
     public String toString() {
       return KeyValue.keyToString(this.keyOnlyBuffer, 0, KeyValueUtil.keyLength(this)) + "/vlen="
           + getValueLength() + "/seqid=" + seqId;
     }
 
     @Override
     public void setSequenceId(long seqId) {
       this.seqId = seqId;
     }
 
     @Override
     public long heapSize() {
       return FIXED_OVERHEAD + rowLength + familyLength + qualifierLength + valueLength + tagsLength;
     }
   }
 
   protected abstract static class BufferedEncodedSeeker<STATE extends SeekerState>
       extends AbstractEncodedSeeker {
     protected final SamePrefixComparator<byte[]> samePrefixComparator;
     protected ByteBuffer currentBuffer;
     protected STATE current, previous;
     protected TagCompressionContext tagCompressionContext = null;
 
     public BufferedEncodedSeeker(KVComparator comparator,
         HFileBlockDecodingContext decodingCtx) {
       super(comparator, decodingCtx);
       this.samePrefixComparator = comparator;
       if (decodingCtx.getHFileContext().isCompressTags()) {
         try {
           tagCompressionContext = new TagCompressionContext(LRUDictionary.class, Byte.MAX_VALUE);
         } catch (Exception e) {
           throw new RuntimeException("Failed to initialize TagCompressionContext", e);
         }
       }
       current = createSeekerState(); // always valid
       previous = createSeekerState(); // may not be valid
     }
 
     @Override
     public int compareKey(KVComparator comparator, byte[] key, int offset, int length) {
       return comparator.compareFlatKey(key, offset, length,
           current.keyBuffer, 0, current.keyLength);
     }
 
     @Override
     public int compareKey(KVComparator comparator, Cell key) {
       return comparator.compareOnlyKeyPortion(key,
           new KeyValue.KeyOnlyKeyValue(current.keyBuffer, 0, current.keyLength));
     }
 
     @Override
     public void setCurrentBuffer(ByteBuffer buffer) {
       if (this.tagCompressionContext != null) {
         this.tagCompressionContext.clear();
       }
       currentBuffer = buffer;
       current.currentBuffer = currentBuffer;
       if(tagCompressionContext != null) {
         current.tagCompressionContext = tagCompressionContext;
       }
       decodeFirst();
       current.setKey(current.keyBuffer, current.memstoreTS);
       previous.invalidate();
     }
 
     @Override
     public ByteBuffer getKeyDeepCopy() {
       ByteBuffer keyBuffer = ByteBuffer.allocate(current.keyLength);
       keyBuffer.put(current.keyBuffer, 0, current.keyLength);
       keyBuffer.rewind();
       return keyBuffer;
     }
 
     @Override
     public ByteBuffer getValueShallowCopy() {
       ByteBuffer dup = currentBuffer.duplicate();
       dup.position(current.valueOffset);
       dup.limit(current.valueOffset + current.valueLength);
       return dup.slice();
     }
 
     @Override
     public Cell getKeyValue() {
       return current.shallowCopy();
     }
 
     @Override
     public void rewind() {
       currentBuffer.rewind();
       if (tagCompressionContext != null) {
         tagCompressionContext.clear();
       }
       decodeFirst();
       current.setKey(current.keyBuffer, current.memstoreTS);
       previous.invalidate();
     }
 
     @Override
     public boolean next() {
       if (!currentBuffer.hasRemaining()) {
         return false;
       }
       decodeNext();
       current.setKey(current.keyBuffer, current.memstoreTS);
       previous.invalidate();
       return true;
     }
 
     protected void decodeTags() {
       current.tagsLength = ByteBufferUtils.readCompressedInt(currentBuffer);
       if (tagCompressionContext != null) {
         if (current.uncompressTags) {
           // Tag compression is been used. uncompress it into tagsBuffer
           current.ensureSpaceForTags();
           try {
             current.tagsCompressedLength = tagCompressionContext.uncompressTags(currentBuffer,
                 current.tagsBuffer, 0, current.tagsLength);
           } catch (IOException e) {
             throw new RuntimeException("Exception while uncompressing tags", e);
           }
         } else {
           ByteBufferUtils.skip(currentBuffer, current.tagsCompressedLength);
           current.uncompressTags = true;// Reset this.
         }
         current.tagsOffset = -1;
       } else {
         // When tag compress is not used, let us not do copying of tags bytes into tagsBuffer.
         // Just mark the tags Offset so as to create the KV buffer later in getKeyValueBuffer()
         current.tagsOffset = currentBuffer.position();
         ByteBufferUtils.skip(currentBuffer, current.tagsLength);
       }
     }
 
     @Override
     public int seekToKeyInBlock(byte[] key, int offset, int length, boolean seekBefore) {
       return seekToKeyInBlock(new KeyValue.KeyOnlyKeyValue(key, offset, length), seekBefore);
     }
 
     @Override
     public int seekToKeyInBlock(Cell seekCell, boolean seekBefore) {
       int rowCommonPrefix = 0;
       int familyCommonPrefix = 0;
       int qualCommonPrefix = 0;
       previous.invalidate();
       KeyValue.KeyOnlyKeyValue currentCell = new KeyValue.KeyOnlyKeyValue();
       do {
         int comp;
         if (samePrefixComparator != null) {
           currentCell.setKey(current.keyBuffer, 0, current.keyLength);
           if (current.lastCommonPrefix != 0) {
             // The KV format has row key length also in the byte array. The
             // common prefix
             // includes it. So we need to subtract to find out the common prefix
             // in the
             // row part alone
             rowCommonPrefix = Math.min(rowCommonPrefix, current.lastCommonPrefix - 2);
           }
           if (current.lastCommonPrefix <= 2) {
             rowCommonPrefix = 0;
           }
           rowCommonPrefix += CellComparator.findCommonPrefixInRowPart(seekCell, currentCell,
               rowCommonPrefix);
           comp = CellComparator.compareCommonRowPrefix(seekCell, currentCell, rowCommonPrefix);
           if (comp == 0) {
             comp = compareTypeBytes(seekCell, currentCell);
             if (comp == 0) {
               // Subtract the fixed row key length and the family key fixed length
               familyCommonPrefix = Math.max(
                   0,
                   Math.min(familyCommonPrefix,
                       current.lastCommonPrefix - (3 + currentCell.getRowLength())));
               familyCommonPrefix += CellComparator.findCommonPrefixInFamilyPart(seekCell,
                   currentCell, familyCommonPrefix);
               comp = CellComparator.compareCommonFamilyPrefix(seekCell, currentCell,
                   familyCommonPrefix);
               if (comp == 0) {
                 // subtract the rowkey fixed length and the family key fixed
                 // length
                 qualCommonPrefix = Math.max(
                     0,
                     Math.min(
                         qualCommonPrefix,
                         current.lastCommonPrefix
                             - (3 + currentCell.getRowLength() + currentCell.getFamilyLength())));
                 qualCommonPrefix += CellComparator.findCommonPrefixInQualifierPart(seekCell,
                     currentCell, qualCommonPrefix);
                 comp = CellComparator.compareCommonQualifierPrefix(seekCell, currentCell,
                     qualCommonPrefix);
                 if (comp == 0) {
                   comp = CellComparator.compareTimestamps(seekCell, currentCell);
                   if (comp == 0) {
                     // Compare types. Let the delete types sort ahead of puts;
                     // i.e. types
                     // of higher numbers sort before those of lesser numbers.
                     // Maximum
                     // (255)
                     // appears ahead of everything, and minimum (0) appears
                     // after
                     // everything.
                     comp = (0xff & currentCell.getTypeByte()) - (0xff & seekCell.getTypeByte());
                   }
                 }
               }
             }
           }
         } else {
           Cell r = new KeyValue.KeyOnlyKeyValue(current.keyBuffer, 0, current.keyLength);
           comp = comparator.compareOnlyKeyPortion(seekCell, r);
         }
         if (comp == 0) { // exact match
           if (seekBefore) {
             if (!previous.isValid()) {
               // The caller (seekBefore) has to ensure that we are not at the
               // first key in the block.
               throw new IllegalStateException("Cannot seekBefore if "
                   + "positioned at the first key in the block: key="
                   + Bytes.toStringBinary(seekCell.getRowArray()));
             }
             moveToPrevious();
             return 1;
           }
           return 0;
         }
 
         if (comp < 0) { // already too large, check previous
           if (previous.isValid()) {
             moveToPrevious();
           } else {
             return HConstants.INDEX_KEY_MAGIC; // using optimized index key
           }
           return 1;
         }
 
         // move to next, if more data is available
         if (currentBuffer.hasRemaining()) {
           previous.copyFromNext(current);
           decodeNext();
           current.setKey(current.keyBuffer, current.memstoreTS);
         } else {
           break;
         }
       } while (true);
 
       // we hit the end of the block, not an exact match
       return 1;
     }
 
     private int compareTypeBytes(Cell key, Cell right) {
       if (key.getFamilyLength() + key.getQualifierLength() == 0
           && key.getTypeByte() == Type.Minimum.getCode()) {
         // left is "bigger", i.e. it appears later in the sorted order
         return 1;
       }
       if (right.getFamilyLength() + right.getQualifierLength() == 0
           && right.getTypeByte() == Type.Minimum.getCode()) {
         return -1;
       }
       return 0;
     }
 
 
     private void moveToPrevious() {
       if (!previous.isValid()) {
         throw new IllegalStateException(
             "Can move back only once and not in first key in the block.");
       }
 
       STATE tmp = previous;
       previous = current;
       current = tmp;
 
       // move after last key value
       currentBuffer.position(current.nextKvOffset);
       // Already decoded the tag bytes. We cache this tags into current state and also the total
       // compressed length of the tags bytes. For the next time decodeNext() we don't need to decode
       // the tags again. This might pollute the Data Dictionary what we use for the compression.
       // When current.uncompressTags is false, we will just reuse the current.tagsBuffer and skip
       // 'tagsCompressedLength' bytes of source stream.
       // See in decodeTags()
       current.tagsBuffer = previous.tagsBuffer;
       current.tagsCompressedLength = previous.tagsCompressedLength;
       current.uncompressTags = false;
       current.setKey(current.keyBuffer, current.memstoreTS);
       previous.invalidate();
     }
 
     @SuppressWarnings("unchecked")
     protected STATE createSeekerState() {
       // This will fail for non-default seeker state if the subclass does not
       // override this method.
       return (STATE) new SeekerState();
     }
 
     abstract protected void decodeFirst();
     abstract protected void decodeNext();
   }
 
   /**
    * @param cell
    * @param out
    * @param encodingCtx
    * @return unencoded size added
    * @throws IOException
    */
   protected final int afterEncodingKeyValue(Cell cell, DataOutputStream out,
       HFileBlockDefaultEncodingContext encodingCtx) throws IOException {
     int size = 0;
     if (encodingCtx.getHFileContext().isIncludesTags()) {
       int tagsLength = cell.getTagsLength();
       ByteBufferUtils.putCompressedInt(out, tagsLength);
       // There are some tags to be written
       if (tagsLength > 0) {
         TagCompressionContext tagCompressionContext = encodingCtx.getTagCompressionContext();
         // When tag compression is enabled, tagCompressionContext will have a not null value. Write
         // the tags using Dictionary compression in such a case
         if (tagCompressionContext != null) {
           tagCompressionContext
               .compressTags(out, cell.getTagsArray(), cell.getTagsOffset(), tagsLength);
         } else {
           out.write(cell.getTagsArray(), cell.getTagsOffset(), tagsLength);
         }
       }
       size += tagsLength + KeyValue.TAGS_LENGTH_SIZE;
     }
     if (encodingCtx.getHFileContext().isIncludesMvcc()) {
       // Copy memstore timestamp from the byte buffer to the output stream.
       long memstoreTS = cell.getSequenceId();
       WritableUtils.writeVLong(out, memstoreTS);
       // TODO use a writeVLong which returns the #bytes written so that 2 time parsing can be
       // avoided.
       size += WritableUtils.getVIntSize(memstoreTS);
     }
     return size;
   }
 
   protected final void afterDecodingKeyValue(DataInputStream source,
       ByteBuffer dest, HFileBlockDefaultDecodingContext decodingCtx) throws IOException {
     if (decodingCtx.getHFileContext().isIncludesTags()) {
       int tagsLength = ByteBufferUtils.readCompressedInt(source);
       // Put as unsigned short
       dest.put((byte) ((tagsLength >> 8) & 0xff));
       dest.put((byte) (tagsLength & 0xff));
       if (tagsLength > 0) {
         TagCompressionContext tagCompressionContext = decodingCtx.getTagCompressionContext();
         // When tag compression is been used in this file, tagCompressionContext will have a not
         // null value passed.
         if (tagCompressionContext != null) {
           tagCompressionContext.uncompressTags(source, dest, tagsLength);
         } else {
           ByteBufferUtils.copyFromStreamToBuffer(dest, source, tagsLength);
         }
       }
     }
     if (decodingCtx.getHFileContext().isIncludesMvcc()) {
       long memstoreTS = -1;
       try {
         // Copy memstore timestamp from the data input stream to the byte
         // buffer.
         memstoreTS = WritableUtils.readVLong(source);
         ByteBufferUtils.writeVLong(dest, memstoreTS);
       } catch (IOException ex) {
         throw new RuntimeException("Unable to copy memstore timestamp " +
             memstoreTS + " after decoding a key/value");
       }
     }
   }
 
   protected abstract ByteBuffer internalDecodeKeyValues(DataInputStream source,
       int allocateHeaderLength, int skipLastBytes, HFileBlockDefaultDecodingContext decodingCtx)
       throws IOException;
 
   /**
    * Asserts that there is at least the given amount of unfilled space
    * remaining in the given buffer.
    * @param out typically, the buffer we are writing to
    * @param length the required space in the buffer
    * @throws EncoderBufferTooSmallException If there are no enough bytes.
    */
   protected static void ensureSpace(ByteBuffer out, int length)
       throws EncoderBufferTooSmallException {
     if (out.position() + length > out.limit()) {
       throw new EncoderBufferTooSmallException(
           "Buffer position=" + out.position() +
           ", buffer limit=" + out.limit() +
           ", length to be written=" + length);
     }
   }
 
   @Override
   public void startBlockEncoding(HFileBlockEncodingContext blkEncodingCtx, DataOutputStream out)
       throws IOException {
     if (blkEncodingCtx.getClass() != HFileBlockDefaultEncodingContext.class) {
       throw new IOException (this.getClass().getName() + " only accepts "
           + HFileBlockDefaultEncodingContext.class.getName() + " as the " +
           "encoding context.");
     }
 
     HFileBlockDefaultEncodingContext encodingCtx =
         (HFileBlockDefaultEncodingContext) blkEncodingCtx;
     encodingCtx.prepareEncoding(out);
     if (encodingCtx.getHFileContext().isIncludesTags()
         && encodingCtx.getHFileContext().isCompressTags()) {
       if (encodingCtx.getTagCompressionContext() != null) {
         // It will be overhead to create the TagCompressionContext again and again for every block
         // encoding.
         encodingCtx.getTagCompressionContext().clear();
       } else {
         try {
           TagCompressionContext tagCompressionContext = new TagCompressionContext(
               LRUDictionary.class, Byte.MAX_VALUE);
           encodingCtx.setTagCompressionContext(tagCompressionContext);
         } catch (Exception e) {
           throw new IOException("Failed to initialize TagCompressionContext", e);
         }
       }
     }
     ByteBufferUtils.putInt(out, 0); // DUMMY length. This will be updated in endBlockEncoding()
     blkEncodingCtx.setEncodingState(new BufferedDataBlockEncodingState());
   }
 
   private static class BufferedDataBlockEncodingState extends EncodingState {
     int unencodedDataSizeWritten = 0;
   }
 
   @Override
   public int encode(Cell cell, HFileBlockEncodingContext encodingCtx, DataOutputStream out)
       throws IOException {
     BufferedDataBlockEncodingState state = (BufferedDataBlockEncodingState) encodingCtx
         .getEncodingState();
     int encodedKvSize = internalEncode(cell, (HFileBlockDefaultEncodingContext) encodingCtx, out);
     state.unencodedDataSizeWritten += encodedKvSize;
     return encodedKvSize;
   }
 
   public abstract int internalEncode(Cell cell, HFileBlockDefaultEncodingContext encodingCtx,
       DataOutputStream out) throws IOException;
 
   @Override
   public void endBlockEncoding(HFileBlockEncodingContext encodingCtx, DataOutputStream out,
       byte[] uncompressedBytesWithHeader) throws IOException {
     BufferedDataBlockEncodingState state = (BufferedDataBlockEncodingState) encodingCtx
         .getEncodingState();
     // Write the unencodedDataSizeWritten (with header size)
     Bytes.putInt(uncompressedBytesWithHeader,
       HConstants.HFILEBLOCK_HEADER_SIZE + DataBlockEncoding.ID_SIZE, state.unencodedDataSizeWritten
         );
     postEncoding(encodingCtx);
   }
 }