/*
 *
 * Copyright (c) 2004
 * John Maddock
 *
 * Use, modification and distribution are subject to the
 * Boost Software License, Version 1.0. (See accompanying file
 * LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 *
 */

/*
 *   LOCATION:    see http://www.boost.org for most recent version.
 *   FILE         object_cache.hpp
 *   VERSION      see <boost/version.hpp>
 *   DESCRIPTION: Implements a generic object cache.
 */

#ifndef BOOST_REGEX_OBJECT_CACHE_HPP
#define BOOST_REGEX_OBJECT_CACHE_HPP

#include <boost/regex/config.hpp>
#include <boost/shared_ptr.hpp>
#include <map>
#include <list>
#include <stdexcept>
#include <string>
#ifdef BOOST_HAS_THREADS
#include <boost/regex/pending/static_mutex.hpp>
#endif

namespace boost {

template <class Key, class Object>
class object_cache
{
  public:
    typedef std::pair< ::boost::shared_ptr<Object const>, Key const*> value_type;
    typedef std::list<value_type> list_type;
    typedef typename list_type::iterator list_iterator;
    typedef std::map<Key, list_iterator> map_type;
    typedef typename map_type::iterator map_iterator;
    typedef typename list_type::size_type size_type;
    static boost::shared_ptr<Object const>
    get(const Key& k, size_type l_max_cache_size);

  private:
    static boost::shared_ptr<Object const>
    do_get(const Key& k, size_type l_max_cache_size);

    struct data
    {
        list_type   cont;
        map_type    index;
    };

    // Needed by compilers not implementing the resolution to DR45. For reference,
    // see http://www.open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#45.
    friend struct data;
};

#ifdef BOOST_MSVC
#pragma warning(push)
#pragma warning(disable: 4702)
#endif
template <class Key, class Object>
boost::shared_ptr<Object const>
object_cache<Key, Object>::get(const Key& k, size_type l_max_cache_size)
{
#ifdef BOOST_HAS_THREADS
    static boost::static_mutex mut = BOOST_STATIC_MUTEX_INIT;
    boost::static_mutex::scoped_lock l(mut);

    if (l)
    {
        return do_get(k, l_max_cache_size);
    }

    //
    // what do we do if the lock fails?
    // for now just throw, but we should never really get here...
    //
    ::boost::throw_exception(std::runtime_error("Error in thread safety code: could not acquire a lock"));
#if defined(BOOST_NO_UNREACHABLE_RETURN_DETECTION) || defined(BOOST_NO_EXCEPTIONS)
    return boost::shared_ptr<Object>();
#endif
#else
    return do_get(k, l_max_cache_size);
#endif
}
#ifdef BOOST_MSVC
#pragma warning(pop)
#endif

template <class Key, class Object>
boost::shared_ptr<Object const>
object_cache<Key, Object>::do_get(const Key& k, size_type l_max_cache_size)
{
    typedef typename object_cache<Key, Object>::data object_data;
    typedef typename map_type::size_type map_size_type;
    static object_data s_data;

    //
    // see if the object is already in the cache:
    //
    map_iterator mpos = s_data.index.find(k);

    if (mpos != s_data.index.end())
    {
        //
        // Eureka!
        // We have a cached item, bump it up the list and return it:
        //
        if (--(s_data.cont.end()) != mpos->second)
        {
            // splice out the item we want to move:
            list_type temp;
            temp.splice(temp.end(), s_data.cont, mpos->second);
            // and now place it at the end of the list:
            s_data.cont.splice(s_data.cont.end(), temp, temp.begin());
            BOOST_REGEX_ASSERT(*(s_data.cont.back().second) == k);
            // update index with new position:
            mpos->second = --(s_data.cont.end());
            BOOST_REGEX_ASSERT(&(mpos->first) == mpos->second->second);
            BOOST_REGEX_ASSERT(&(mpos->first) == s_data.cont.back().second);
        }

        return s_data.cont.back().first;
    }

    //
    // if we get here then the item is not in the cache,
    // so create it:
    //
    boost::shared_ptr<Object const> result(new Object(k));
    //
    // Add it to the list, and index it:
    //
    s_data.cont.push_back(value_type(result, static_cast<Key const*>(0)));
    s_data.index.insert(std::make_pair(k, --(s_data.cont.end())));
    s_data.cont.back().second = &(s_data.index.find(k)->first);
    map_size_type s = s_data.index.size();
    BOOST_REGEX_ASSERT(s_data.index[k]->first.get() == result.get());
    BOOST_REGEX_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
    BOOST_REGEX_ASSERT(s_data.index.find(k)->first == k);

    if (s > l_max_cache_size)
    {
        //
        // We have too many items in the list, so we need to start
        // popping them off the back of the list, but only if they're
        // being held uniquely by us:
        //
        list_iterator pos = s_data.cont.begin();
        list_iterator last = s_data.cont.end();

        while ((pos != last) && (s > l_max_cache_size))
        {
            if (pos->first.unique())
            {
                list_iterator condemmed(pos);
                ++pos;
                // now remove the items from our containers,
                // then order has to be as follows:
                BOOST_REGEX_ASSERT(s_data.index.find(*(condemmed->second)) != s_data.index.end());
                s_data.index.erase(*(condemmed->second));
                s_data.cont.erase(condemmed);
                --s;
            }

            else
            {
                ++pos;
            }
        }

        BOOST_REGEX_ASSERT(s_data.index[k]->first.get() == result.get());
        BOOST_REGEX_ASSERT(&(s_data.index.find(k)->first) == s_data.cont.back().second);
        BOOST_REGEX_ASSERT(s_data.index.find(k)->first == k);
    }

    return result;
}

}

#endif
