/*
 * This file is part of ELKI:
 * Environment for Developing KDD-Applications Supported by Index-Structures
 *
 * Copyright (C) 2022
 * ELKI Development Team
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
package elki.index.tree.spatial.rstarvariants.rdknn;

import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

import elki.index.tree.TreeIndexHeader;

/**
 * Encapsulates the header information of a RDkNN-Tree. This information is
 * needed for persistent storage.
 * 
 * @author Elke Achtert
 * @since 0.1
 */
class RdKNNTreeHeader extends TreeIndexHeader {
  /**
   * The size of this header in Bytes, which is 4 Bytes (for {@link #k_max}).
   */
  private static int SIZE = 4;

  /**
   * The maximum number k of reverse kNN queries to be supported.
   */
  int k_max;

  /**
   * Empty constructor for serialization.
   */
  public RdKNNTreeHeader() {
    super();
  }

  /**
   * Creates a new header with the specified parameters.
   * 
   * @param pageSize the size of a page in bytes
   * @param dirCapacity the maximum number of entries in a directory node
   * @param leafCapacity the maximum number of entries in a leaf node
   * @param dirMinimum the minimum number of entries in a directory node
   * @param leafMinimum the minimum number of entries in a leaf node
   * @param k_max the maximum number k of reverse kNN queries to be supported
   */
  public RdKNNTreeHeader(int pageSize, int dirCapacity, int leafCapacity, int dirMinimum, int leafMinimum, int k_max) {
    super(pageSize, dirCapacity, leafCapacity, dirMinimum, leafMinimum);
    this.k_max = k_max;
  }

  /**
   * Initializes this header from the specified file. Calls
   * {@link elki.index.tree.TreeIndexHeader#readHeader(FileChannel)
   * TreeIndexHeader#readHeader(file)} and reads additionally the integer value
   * of {@link #k_max} from the file.
   */
  @Override
  public void readHeader(ByteBuffer buffer) {
    super.readHeader(buffer);
    this.k_max = buffer.getInt();
  }

  /**
   * Writes this header to the specified file. Calls
   * {@link elki.index.tree.TreeIndexHeader#writeHeader(FileChannel)}
   * and writes additionally the integer value of {@link #k_max} to the file.
   */
  @Override
  public void writeHeader(ByteBuffer buffer) {
    super.writeHeader(buffer);
    buffer.putInt(this.k_max);
  }

  /**
   * Returns {@link elki.index.tree.TreeIndexHeader#size()} plus
   * the value of {@link #SIZE}).
   */
  @Override
  public int size() {
    return super.size() + SIZE;
  }
}
