//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2017 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    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 Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// A general-purpose circular list collection class.
// Used by the OpenVPN anti-replay logic.

#ifndef OPENVPN_COMMON_CIRC_LIST_H
#define OPENVPN_COMMON_CIRC_LIST_H

#include <vector>

#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>

namespace openvpn {

  template <typename T>
  class CircList
  {
  public:
    OPENVPN_SIMPLE_EXCEPTION(circ_list_reset);
    OPENVPN_SIMPLE_EXCEPTION(circ_list_index);
    OPENVPN_SIMPLE_EXCEPTION(circ_list_const_index);
    OPENVPN_SIMPLE_EXCEPTION(circ_list_push);

    CircList() { init(0); }

    explicit CircList(const size_t capacity) { init(capacity); }

    void init(const size_t capacity)
    {
      if (capacity)
	{
	  data_.reserve(capacity);
	  capacity_ = capacity;
	  reset();
	}
      else
	{
	  head_ = capacity_ = 0;
	  data_.clear();
	}
    }

    void reset()
    {
      if (capacity_)
	{
	  head_ = capacity_ - 1;
	  data_.clear();
	}
      else
	throw circ_list_reset();
    }

    size_t size() const
    {
      return data_.size();
    }

    bool defined() const
    {
      return capacity_ > 0;
    }

    void push(const T& item)
    {
      if (++head_ >= capacity_)
	head_ = 0;
      if (head_ < data_.size())
	data_[head_] = item;
      else if (head_ == data_.size() && data_.size() < capacity_)
	data_.push_back(item);
      else
	throw circ_list_push(); // could occur if object isn't properly initialized
    }

    T& operator[](const size_t index)
    {
      if (index >= data_.size())
	throw circ_list_index();
      else if (index <= head_)
	return data_[head_-index];
      else
	return data_[head_+capacity_-index];
    }

    const T& operator[](const size_t index) const
    {
      if (index >= data_.size())
	throw circ_list_const_index();
      else if (index <= head_)
	return data_[head_-index];
      else
	return data_[head_+capacity_-index];
    }

  private:
    size_t capacity_;
    size_t head_;
    std::vector<T> data_;
  };

} // namespace openvpn

#endif // OPENVPN_COMMON_CIRC_LIST_H