/*
 * Copyright (c) 2009 The Georgia Institute of Technology
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Authors: Josh Pelkey <jpelkey@gatech.edu>
 */

#ifndef NIX_VECTOR_H
#define NIX_VECTOR_H

#include "buffer.h"

#include "ns3/ptr.h"
#include "ns3/simple-ref-count.h"

namespace ns3
{

/**
 * @ingroup packet
 *
 * @brief Neighbor-index data structure for nix-vector routing
 *
 * This data structure holds a vector of "neighbor-indexes" for
 * a simulation specific routing protocol, nix-vector routing.
 * These neighbor-indexes correspond to the net-device which a
 * node should use to route a packet.  A nix-vector is built
 * (or fetched from a cache) on-demand. The nix-vector is
 * transmitted with the packet, and along each hop of the
 * route, the current node extracts the appropriate
 * neighbor-index and routes the packet.
 *
 * @internal
 * The implementation of NixVector uses a vector to store
 * the neighbor-indexes.  Each entry in the vector is 32
 * bits long and can store multiple neighbor-indexes.  A
 * fair amount of bit manipulation is used to store these
 * neighbor-indexes efficiently.  A vector is used so that
 * the nix-vector can grow arbitrarily if the topology and
 * route requires a large number of neighbor-indexes.
 *
 * As the nix-vector travels along the route, an internal
 * private member variable keeps track of how many bits
 * have been used.  At a particular node, the nix-vector
 * is used to return the next neighbor-index. This
 * neighbor-index is used to determine which net-device
 * to use.  The number of bits used would then be
 * incremented accordingly, and the packet would be
 * routed.
 */

class NixVector : public SimpleRefCount<NixVector>
{
  public:
    NixVector();
    ~NixVector();
    /**
     * @return a copy of this nix-vector
     */
    Ptr<NixVector> Copy() const;
    /**
     * @param o the NixVector to copy to a new NixVector
     *          using a constructor
     */
    NixVector(const NixVector& o);
    /**
     * @return a reference to the assignee
     *
     * @param o the NixVector to copy to a new NixVector using the
     *          equals operator
     */
    NixVector& operator=(const NixVector& o);
    /**
     * @param newBits the neighbor-index to be added to the vector
     * @param numberOfBits the number of bits that newBits contains
     *
     * Adds the neighbor index to the vector using a fair amount of
     * bit manipulation to pack everything in efficiently.
     *
     * Note: This function assumes that the number of bits to be added
     * is always less than or equal to 32, ie., you can only span one
     * entry of a nix-vector at a time.  This is reasonable, since 32
     * bits gives you 2^32 possible neighbors.
     */
    void AddNeighborIndex(uint32_t newBits, uint32_t numberOfBits);
    /**
     * @return the neighbor index
     *
     * @param numberOfBits the number of bits to extract from the vector
     *
     * Extracts the number of bits specified from
     * the vector and returns the value extracted
     *
     * Note: This function assumes that the number of bits to be extracted
     * is always less than or equal to 32, ie., you can only span one
     * entry of a nix-vector at a time.  This is reasonable, since 32
     * bits gives you 2^32 possible neighbors.
     */
    uint32_t ExtractNeighborIndex(uint32_t numberOfBits);
    /**
     * @return number of bits remaining in the
     *         nix-vector (ie m_total - m_used)
     */
    uint32_t GetRemainingBits() const;
    /**
     * @return the number of bytes required for serialization
     */
    uint32_t GetSerializedSize() const;
    /**
     * @return zero if buffer not large enough
     *
     * @param buffer points to serialization buffer
     *
     * @param maxSize max number of bytes to write
     *
     * This nix-vector is serialized into the raw character
     * buffer parameter.
     */
    uint32_t Serialize(uint32_t* buffer, uint32_t maxSize) const;
    /**
     * @return zero if a complete nix-vector is not deserialized
     *
     * @param buffer points to buffer for deserialization
     *
     * @param size number of bytes to deserialize
     *
     * The raw character buffer containing all the nix-vector
     * information is deserialized into this nix-vector.
     */
    uint32_t Deserialize(const uint32_t* buffer, uint32_t size);
    /**
     * @return number of bits of numberOfNeighbors
     *
     * @param numberOfNeighbors the total number of neighbors
     *
     * This function is used to determine the number of bits of
     * numberOfNeighbors so that this value can be passed in to
     * AddNeighborIndex or ExtractNeighborIndex.
     */
    uint32_t BitCount(uint32_t numberOfNeighbors) const;

    /**
     * Set the NixVector Epoch
     * @param epoch the NixVector Epoch
     */
    void SetEpoch(uint32_t epoch);

    /**
     * Get the NixVector Epoch
     * @return the NixVector Epoch
     */
    uint32_t GetEpoch() const;

  private:
    /// Typedef: the NixVector bits storage.
    typedef std::vector<uint32_t> NixBits_t;

    /**
     * @brief Print the NixVector.
     *
     * @param os the output stream
     *
     * \note: this could be greatly simplified by using std::format (but it's C++20).
     */
    void DumpNixVector(std::ostream& os) const;

    /**
     * @brief Stream insertion operator.
     *
     * @param os the stream
     * @param nix the Nixvector
     * @returns a reference to the stream
     */
    friend std::ostream& operator<<(std::ostream& os, const NixVector& nix);

    NixBits_t m_nixVector; //!< the actual nix-vector
    uint32_t m_used;       //!< For tracking where we are in the nix-vector

    /**
     * A counter of how total bits are in
     * the nix-vector
     */
    uint32_t m_totalBitSize;

    uint32_t m_epoch; //!< Epoch of the Nix-vector creation

    /**
     * Internal for pretty printing of nix-vector (no fill)
     * @param decimalNum decimal divider
     * @param bitCount bit counter
     * @param os output stream
     */
    void PrintDec2BinNix(uint32_t decimalNum, uint32_t bitCount, std::ostream& os) const;
};
} // namespace ns3

#endif /* NIX_VECTOR_H */