/*
 * Copyright (C) 2014  The Async HBase Authors.  All rights reserved.
 * This file is part of Async HBase.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *   - Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   - Redistributions in binary form must reproduce the above copyright notice,
 *     this list of conditions and the following disclaimer in the documentation
 *     and/or other materials provided with the distribution.
 *   - Neither the name of the StumbleUpon nor the names of its contributors
 *     may be used to endorse or promote products derived from this software
 *     without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
package org.hbase.async;

import com.google.protobuf.ByteString;
import org.jboss.netty.buffer.ChannelBuffer;

import org.hbase.async.generated.ComparatorPB;

/**
 * Abstract base class for {@link ScanFilter} comparators.
 * <p>
 * These comparators are used by scan filters.
 * <p>
 * Subclasses are guaranteed to be immutable and are thus
 * thread-safe as well as usable concurrently on multiple
 * {@link Scanner} instances.
 * @since 1.6
 */
public abstract class FilterComparator {

  // This class is the equivalent of HBase's WritableByteArrayComparable.
  // We don't need this class to be Writable or Comparable, so
  // FilterComparator is a more appropriate name.

  final static byte CODE = 54;

  /**
   * Returns the name of this scanner on the wire.
   * <p>
   * This method is only used with HBase 0.95 and newer.
   * The contents of the array returned MUST NOT be modified.
   */
  abstract byte[] name();

  /**
   * Serializes the byte representation to a protobuf in a byte array.
   * <p>
   * This method is only used with HBase 0.95 and newer.
   */
  abstract ComparatorPB.Comparator toProtobuf();

  /**
   * Wraps the passed in serialized FilterComparator in a protobuf Comparator.
   *
   * @param comparator serialized FilterComparator.
   * @return a serialized protobuf Comparator
   */
  protected final ComparatorPB.Comparator toProtobuf(ByteString comparator) {
    return ComparatorPB
      .Comparator
      .newBuilder()
      .setNameBytes(Bytes.wrap(name()))
      .setSerializedComparator(comparator)
      .build();
  }

  /**
   * Serializes the byte representation to the RPC channel buffer.
   * <p>
   * This method is only used with HBase 0.94 and before.
   * @param buf The RPC channel buffer to which the byte array is serialized
   */
  void serializeOld(ChannelBuffer buf) {
    buf.writeByte(CODE);  // 1
  }

  /**
   * Returns the number of bytes that it will write to the RPC channel buffer
   * when {@code serialize} is called. This method helps predict the initial
   * size of the byte array
   * <p>
   * This method is only used with HBase 0.94 and before.
   * @return A strictly positive integer
   */
  int predictSerializedSize() {
    return 1;
  }
}