/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
/*
 * Copyright (c) 2012 University of California, Los Angeles
 *
 * 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: Zhenkai Zhu <zhenkai@cs.ucla.edu>
 *         卞超轶 Chaoyi Bian <bcy@pku.edu.cn>
 *	   Alexander Afanasyev <alexander.afanasyev@ucla.edu>
 */

#ifndef SYNC_DIGEST_H
#define SYNC_DIGEST_H

#include <boost/exception/all.hpp>
#include <openssl/evp.h>
#include <boost/cstdint.hpp>

namespace Sync {

/**
 * @ingroup sync
 * @brief A simple wrapper for libcrypto hash functions
 */
class Digest
{
public:
  /**
   * @brief Default constructor.  Will initialize internal libssl structures
   */
  Digest ();

  /**
   * @brief Check if digest is empty
   */
  bool
  empty () const;
  
  /**
   * @brief Reset digest to the initial state
   */
  void
  reset ();

  /**
   * @brief Destructor
   */
  ~Digest ();

  /**
   * @brief Obtain a short version of the hash (just first sizeof(size_t) bytes
   *
   * Side effect: finalize() will be called on `this'
   */
  std::size_t
  getHash () const;

  /**
   * @brief Finalize digest. All subsequent calls to "operator <<" will fire an exception
   */
  void
  finalize ();

  /**
   * @brief Compare two full digests
   *
   * Side effect: Finalize will be called on `this' and `digest'
   */
  bool
  operator == (const Digest &digest) const;

  bool
  operator != (const Digest &digest) const
  { return ! (*this == digest); }
  

  /**
   * @brief Add existing digest to digest calculation
   * @param src digest to combine with
   *
   * The result of this combination is  hash (hash (...))
   */
  Digest &
  operator << (const Digest &src);

  /**
   * @brief Add string to digest calculation
   * @param str string to put into digest
   */
  inline Digest &
  operator << (const std::string &str);

  /**
   * @brief Add uint32_t value to digest calculation
   * @param value uint32_t value to put into digest
   */
  inline Digest &
  operator << (uint32_t value);

  /**
   * @brief Checks if the stored hash is zero-root hash
   *
   * Zero-root hash is a valid hash that optimally represents an empty state
   */
  bool
  isZero () const;
  
private:
  Digest &
  operator = (Digest &digest) { return *this; }
  
  /**
   * @brief Add size bytes of buffer to the hash
   */
  void
  update (const uint8_t *buffer, size_t size);

  friend std::ostream &
  operator << (std::ostream &os, const Digest &digest);

  friend std::istream &
  operator >> (std::istream &is, Digest &digest);
  
private:
  EVP_MD_CTX *m_context;
  uint8_t *m_buffer;
  uint32_t m_hashLength;
};

namespace Error {
struct DigestCalculationError : virtual boost::exception, virtual std::exception { };
}

typedef boost::shared_ptr<Digest> DigestPtr;
typedef boost::shared_ptr<const Digest> DigestConstPtr;

Digest &
Digest::operator << (const std::string &str)
{
  update (reinterpret_cast<const uint8_t*> (str.c_str ()), str.size ());
  return *this;
}

inline Digest &
Digest::operator << (uint32_t value)
{
  update (reinterpret_cast<const uint8_t*> (&value), sizeof (uint32_t));
  return *this;
}

std::ostream &
operator << (std::ostream &os, const Digest &digest);

std::istream &
operator >> (std::istream &is, Digest &digest);

// template<class INT>
// Digest &
// Digest::operator << (INT value)
// {
//   update (&value, sizeof (INT));
//   return *this;
// }


} // Sync

#endif // SYNC_DIGEST_H