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#ifndef VGSTOOLS_CACHE_H
#define VGSTOOLS_CACHE_H
#include <algorithm>
#include <ctime>
#include <list>
#include <map>
#include <utility>
#include "stdext.h"
/* Interface for TValue:
* size_t weight()
* bool is_newer( time_t )
* bool load()
*
*/
namespace vgstools {
template< typename TKey, typename TValue >
class cache
{
public:
typedef TKey key_type;
typedef TValue value_type;
typedef std::tr1::shared_ptr< value_type > ptr_type;
private:
struct Value
{
ptr_type value;
std::time_t creation;
Value( key_type const& key )
: value( new value_type( key ) )
, creation( 0 ) {}
};
typedef std::list< Value > ValueList;
typedef std::map< TKey, typename ValueList::iterator > KeyMap;
public:
cache( size_t maxWeight )
: m_maxWeight( maxWeight )
, m_currentWeight( 0 ) {}
size_t weight() const { return m_currentWeight; }
size_t count() const { return m_values.size(); }
ptr_type get( key_type const& key )
{
typename KeyMap::iterator it = m_lookup.find( key );
if ( it == m_lookup.end() ) {
typename ValueList::iterator element = m_values.insert( m_values.begin(), Value( key ) );
std::pair< typename KeyMap::iterator, bool > result = m_lookup.insert( std::make_pair( key, element ) );
it = result.first;
}
Value* value = &*it->second;
std::time_t now = std::time( 0 );
if ( value->creation == 0 || !value->value->is_current() ) {
m_currentWeight -= value->value->weight();
if ( !value->value->load() ) {
m_values.erase( it->second );
m_lookup.erase( it );
return ptr_type();
}
m_currentWeight += value->value->weight();
value->creation = now;
}
if ( it->second != m_values.begin() ) {
typename ValueList::iterator element = m_values.insert( m_values.begin(), *it->second );
m_values.erase( it->second );
it->second = element;
value = &*element;
}
return value->value;
}
private:
std::size_t m_maxWeight;
std::size_t m_currentWeight;
ValueList m_values;
KeyMap m_lookup;
};
} // namespace vgstools
#endif // VGSTOOLS_CACHE_H
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