/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2019 Universita' degli Studi di Napoli Federico II
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Author: Stefano Avallone <stavallo@unina.it>
 */

#ifndef BLOCK_ACK_WINDOW_H
#define BLOCK_ACK_WINDOW_H

#include <vector>

namespace ns3 {

/**
 * \ingroup wifi
 * \brief Block ack window
 *
 * This class provides the basic functionalities of a window sliding over a
 * bitmap: accessing any element in the bitmap and moving the window forward
 * a given number of positions. This class can be used to implement both
 * an originator's window and a recipient's window.
 *
 * The window is implemented as a vector of bool and managed as a circular
 * queue. The window is moved forward by advancing the head of the queue and
 * clearing the elements that become part of the tail of the queue. Hence,
 * no element is required to be shifted when the window moves forward.
 *
 * Example:
 *
 * |0|1|1|0|1|1|1|0|1|1|1|1|1|1|1|0|
 *                      ^
 *                      |
 *                     HEAD
 *
 * After moving the window forward three positions:
 *
 * |0|1|1|0|1|1|1|0|1|1|0|0|0|1|1|0|
 *                            ^
 *                            |
 *                           HEAD
 */
class BlockAckWindow
{
public:
  /**
   * Constructor
   */
  BlockAckWindow ();
  /**
   * Initialize the window with the given starting sequence number and size
   *
   * \param winStart the window start
   * \param winSize the window size
   */
  void Init (uint16_t winStart, uint16_t winSize);
  /**
   * Reset the window by clearing all the elements and setting winStart to the
   * given value.
   *
   * \param winStart the window start
   */
  void Reset (uint16_t winStart);
  /**
   * Get the current winStart value.
   *
   * \return the current winStart value
   */
  uint16_t GetWinStart (void) const;
  /**
   * Get the current winEnd value.
   *
   * \return the current winEnd value
   */
  uint16_t GetWinEnd (void) const;
  /**
   * Get the window size.
   *
   * \return the window size
   */
  std::size_t GetWinSize (void) const;
  /**
   * Get a reference to the element in the window having the given distance from
   * the current winStart. Note that the given distance must be less than the
   * window size.
   *
   * \param distance the given distance
   * \return a reference to the element in the window having the given distance
   *         from the current winStart
   */
  std::vector<bool>::reference At (std::size_t distance);
  /**
   * Advance the current winStart by the given number of positions.
   *
   * \param count the number of positions the current winStart must be advanced by
   */
  void Advance (std::size_t count);

private:
  uint16_t m_winStart;         ///< window start (sequence number)
  std::vector<bool> m_window;  ///< window
  std::size_t m_head;          ///< index of winStart in the vector
};

} //namespace ns3

#endif /* BLOCK_ACK_WINDOW_H */
