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Common functionality for HBase
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/**
 * 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.util;

import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;

import org.apache.hadoop.hbase.util.ByteBufferUtils;
import org.apache.yetus.audience.InterfaceAudience;

/**
 * Dictionary interface
 *
 * Dictionary indexes should be either bytes or shorts, only positive. (The
 * first bit is reserved for detecting whether something is compressed or not).
 */
@InterfaceAudience.Private
public interface Dictionary {
  byte NOT_IN_DICTIONARY = -1;

  void init(int initialSize);
  /**
   * Gets an entry from the dictionary.
   * 
   * @param idx index of the entry
   * @return the entry, or null if non existent
   */
  byte[] getEntry(short idx);

  /**
   * Finds the index of an entry.
   * If no entry found, we add it.
   * 
   * @param data the byte array that we're looking up
   * @param offset Offset into data to add to Dictionary.
   * @param length Length beyond offset that comprises entry; must be > 0.
   * @return the index of the entry, or {@link #NOT_IN_DICTIONARY} if not found
   */
  short findEntry(byte[] data, int offset, int length);

  /**
   * Finds the index of an entry.
   * If no entry found, we add it.
   * @param data the ByteBuffer that we're looking up
   * @param offset Offset into data to add to Dictionary.
   * @param length Length beyond offset that comprises entry; must be > 0.
   * @return the index of the entry, or {@link #NOT_IN_DICTIONARY} if not found
   */
  short findEntry(ByteBuffer data, int offset, int length);

  /**
   * Adds an entry to the dictionary.
   * Be careful using this method.  It will add an entry to the
   * dictionary even if it already has an entry for the same data.
   * Call {{@link #findEntry(byte[], int, int)}} to add without duplicating
   * dictionary entries.
   * 
   * @param data the entry to add
   * @param offset Offset into data to add to Dictionary.
   * @param length Length beyond offset that comprises entry; must be > 0.
   * @return the index of the entry
   */
  short addEntry(byte[] data, int offset, int length);

  /**
   * Flushes the dictionary, empties all values.
   */
  void clear();

  /**
   * Helper methods to write the dictionary data to the OutputStream
   * @param out the outputstream to which data needs to be written
   * @param data the data to be written in byte[]
   * @param offset the offset
   * @param length length to be written
   * @param dict the dictionary whose contents are to written
   * @throws IOException
   */
  public static void write(OutputStream out, byte[] data, int offset, int length, Dictionary dict)
      throws IOException {
    short dictIdx = Dictionary.NOT_IN_DICTIONARY;
    if (dict != null) {
      dictIdx = dict.findEntry(data, offset, length);
    }
    if (dictIdx == Dictionary.NOT_IN_DICTIONARY) {
      out.write(Dictionary.NOT_IN_DICTIONARY);
      StreamUtils.writeRawVInt32(out, length);
      out.write(data, offset, length);
    } else {
      StreamUtils.writeShort(out, dictIdx);
    }
  }

  /**
   * Helper methods to write the dictionary data to the OutputStream
   * @param out the outputstream to which data needs to be written
   * @param data the data to be written in ByteBuffer
   * @param offset the offset
   * @param length length to be written
   * @param dict the dictionary whose contents are to written
   * @throws IOException
   */
  public static void write(OutputStream out, ByteBuffer data, int offset, int length,
      Dictionary dict) throws IOException {
    short dictIdx = Dictionary.NOT_IN_DICTIONARY;
    if (dict != null) {
      dictIdx = dict.findEntry(data, offset, length);
    }
    if (dictIdx == Dictionary.NOT_IN_DICTIONARY) {
      out.write(Dictionary.NOT_IN_DICTIONARY);
      StreamUtils.writeRawVInt32(out, length);
      ByteBufferUtils.copyBufferToStream(out, data, offset, length);
    } else {
      StreamUtils.writeShort(out, dictIdx);
    }
  }
}