/*
  BUFFER-LOCAL-KEY.hpp  -  opaque data for BufferProvider implementation

  Copyright (C)         Lumiera.org
    2011,               Hermann Vosseler <Ichthyostega@web.de>

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License as
  published by the Free Software Foundation; either version 2 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 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., 675 Mass Ave, Cambridge, MA 02139, USA.

*/


#ifndef PROC_ENGINE_BUFFR_LOCAL_KEY_H
#define PROC_ENGINE_BUFFR_LOCAL_KEY_H


#include "lib/error.hpp"

#include <boost/functional/hash.hpp>


namespace lib {
  typedef size_t HashVal;
}

namespace engine {
  
  namespace metadata {
    class Key;
    class Entry;
  }
  class BufferMetadata;
  
  using lib::HashVal;
  
  
  
  /**
   * an opaque ID to be used by the BufferProvider implementation.
   * Typically this will be used, to set apart some pre-registered
   * kinds of buffers. It is treated as being part of the buffer type.
   * LocalKey objects may be copied but not re-assigned or changed.
   */
  class LocalKey
    {
      uint64_t privateID_;
      
    public:
      LocalKey (uint64_t opaqueValue=0)
        : privateID_(opaqueValue)
        { }
      
      operator uint64_t()  const { return privateID_; }
      
      bool isDefined()     const { return bool(privateID_); }
      
      friend size_t
      hash_value (LocalKey const& lkey)
      {
        boost::hash<uint64_t> hashFunction;
        return hashFunction(lkey.privateID_);
      }
      
    private:
      /** assignment usually prohibited */
      LocalKey& operator= (LocalKey const& o)
        {
          privateID_ = o.privateID_;
          return *this;
        }
      
      /** but Key assignments are acceptable */
      friend class metadata::Key;
    };
  
  
} // namespace engine
#endif