core/src/main/java/org/apache/accumulo/core/client/lexicoder/ReverseLexicoder.java

/*
 * 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.accumulo.core.client.lexicoder;

import static org.apache.accumulo.core.client.lexicoder.impl.ByteUtils.escape;
import static org.apache.accumulo.core.client.lexicoder.impl.ByteUtils.unescape;

import org.apache.accumulo.core.client.lexicoder.impl.AbstractLexicoder;

/**
 * A lexicoder that flips the sort order from another lexicoder. If this is applied to
 * {@link DateLexicoder}, the most recent date will be sorted first and the oldest date will be
 * sorted last. If it's applied to {@link LongLexicoder}, the Long.MAX_VALUE will be sorted first
 * and Long.MIN_VALUE will be sorted last, etc...
 *
 * @since 1.6.0
 */
public class ReverseLexicoder<T> extends AbstractLexicoder<T> {

  private Lexicoder<T> lexicoder;

  /**
   * @param lexicoder
   *          The lexicoder who's sort order will be flipped.
   */
  public ReverseLexicoder(Lexicoder<T> lexicoder) {
    this.lexicoder = lexicoder;
  }

  @Override
  public byte[] encode(T data) {
    byte[] bytes = escape(lexicoder.encode(data));
    byte[] ret = new byte[bytes.length + 1];

    for (int i = 0; i < bytes.length; i++)
      ret[i] = (byte) (0xff - (0xff & bytes[i]));

    ret[bytes.length] = (byte) 0xff;

    return ret;
  }

  @Override
  protected T decodeUnchecked(byte[] data, int offset, int len) {
    byte ret[] = new byte[len - 1];

    int dataIndex;
    for (int i = 0; i < ret.length; i++) {
      dataIndex = offset + i;
      ret[i] = (byte) (0xff - (0xff & data[dataIndex]));
    }

    return lexicoder.decode(unescape(ret));
  }
}