lmdbal/cache.hpp

// Squawk messenger. 
// Copyright (C) 2019  Yury Gubich <blue@macaw.me>
// 
// 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 3 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, see <http://www.gnu.org/licenses/>.

#ifndef DATABASE_CACHE_HPP
#define DATABASE_CACHE_HPP

#include "cache.h"
#include "exceptions.h"

template<class K, class V>
DataBase::Cache<K, V>::Cache(const std::string& p_name, DataBase* parent):
    DataBase::Table<K, V>(p_name, parent),
    mode(new Mode),
    cache(new std::map<K, V>()),
    abscent(new std::set<K>()),
    sizeDifference(new uint32_t)
{
    *mode = Mode::nothing;
    *sizeDifference = 0;
}

template<class K, class V>
DataBase::Cache<K, V>::~Cache() {
    delete sizeDifference;
    delete mode;
    delete cache;
    delete abscent;
}

template<class K, class V>
void DataBase::Cache<K, V>::addRecord(const K& key, const V& value) {
    if (!DataBase::Table<K, V>::db->opened) {
        throw Closed("addRecord", DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
    }

    if (cache->count(key) > 0) {
        throw Exist(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
    }

    Table<K, V>::addRecord(key, value);
    cache->insert(std::make_pair(key, value));
}


template<class K, class V>
void DataBase::Cache<K, V>::changeRecord(const K& key, const V& value) {
    if (!DataBase::Table<K, V>::db->opened) {
        throw Closed("changeRecord", DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
    }

    if (*mode == Mode::full) {
        typename std::map<K, V>::iterator itr = cache->find(key);
        if (itr != cache->end()) {
            throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
        }
        Table<K, V>::changeRecord(key, value);
        itr->second = value;
    } else {
        if (abscent->count(key) > 0) {
            throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
        }

        try {
            Table<K, V>::changeRecord(key, value);
            typename std::map<K, V>::iterator itr = cache->find(key);
            if (itr != cache->end()) {
                itr->second = value;
            } else {
                cache->insert(std::make_pair(key, value));
                handleMode();
            }
        } catch (const NotFound& error) {
            abscent->insert(key);
            throw error;
        }
    }
}

template<class K, class V>
V DataBase::Cache<K, V>::getRecord(const K& key) const {
    if (!DataBase::Table<K, V>::db->opened) {
        throw Closed("getRecord", DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
    }

    typename std::map<K, V>::const_iterator itr = cache->find(key);
    if (itr != cache->end()) {
        return itr->second;
    }

    if (*mode == Mode::full || abscent->count(key) != 0) {
        throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
    }

    try {
        V value = Table<K, V>::getRecord(key);
        cache->insert(std::make_pair(key, value));
        handleMode();
        return value;
    } catch (const NotFound& error) {
        abscent->insert(key);
        throw error;
    }
}

template<class K, class V>
std::map<K, V> DataBase::Cache<K, V>::readAll() const {
    if (!DataBase::Table<K, V>::db->opened) {
        throw Closed("readAll", DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
    }

    if (*mode != Mode::full) {                      //there is a room for optimization
        *mode = Mode::full;                         //I can read and deserialize only those values
        *cache = DataBase::Table<K, V>::readAll();  //that are missing in the cache
        abscent->clear();
        *sizeDifference = 0;
    }

    return *cache;
}

template<class K, class V>
void DataBase::Cache<K, V>::removeRecord(const K& key) {
    if (!DataBase::Table<K, V>::db->opened) {
        throw Closed("removeRecord", DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
    }

    typename std::pair<typename std::set<K>::const_iterator, bool> pair = abscent->insert(key);
    if (!pair.second) {
        throw NotFound(DataBase::_Table::toString(key), DataBase::Table<K, V>::db->name, DataBase::Table<K, V>::name);
    }

    Table<K, V>::removeRecord(key);
    if (cache->erase(key) == 0) {   //if it was not cached and we are now in size mode then the sizeDifference would decrease
        handleMode();
    }
    if (*mode != Mode::full) {
        abscent->insert(key);
    }
}

template<class K, class V>
uint32_t DataBase::Cache<K, V>::count() const {
    switch (*mode) {
        case Mode::nothing:
        {
            uint32_t sz = DataBase::Table<K, V>::count();
            *sizeDifference = sz - cache->size();
            if (sz == 0) {
                *mode = Mode::full;
                abscent->clear();
            } else {
                *mode = Mode::size;
            }
            return sz;
        }
        case Mode::size:
            return cache->size() + *sizeDifference;
        case Mode::full:
            return cache->size();
    }
}

template<class K, class V>
void DataBase::Cache<K, V>::handleMode() const {
    if (*mode == Mode::size) {
        --(*sizeDifference);
        if (*sizeDifference == 0) {
            *mode = Mode::full;
            abscent->clear();
        }
    }
}

template<class K, class V>
int DataBase::Cache<K, V>::drop(MDB_txn * transaction) {
    int res = DataBase::Table<K, V>::drop(transaction);
    cache->clear();
    abscent->clear();
    *mode = Mode::full;
    *sizeDifference = 0;
    return res;
}

#endif //DATABASE_CACHE_HPP