/*
 * LMDB Abstraction Layer.
 * Copyright (C) 2023  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 LMDBAL_STORAGE_HPP
#define LMDBAL_STORAGE_HPP

#include "storage.h"
#include "exceptions.h"

#define UNUSED(x) (void)(x)

/**
 * \class LMDBAL::Storage
 * \brief This is a basic key value storage.
 *
 * \tparam K type of the keys of the storage
 * \tparam V type of the values of the storage
 *
 * You can receive an instance of this class calling LMDBAL::Base::addStorage(const std::string&)
 * if the database is yet closed and you're defining the storages you're going to need.
 * Or you can call LMDBAL::Base::getStorage(const std::string&) if you didn't save a pointer to the storage at first
 *
 * You are not supposed to instantiate or destory instances of this class yourself!
 */

/**
 * \brief Creates a storage
 *
 * \param[in]   parent      - LMDBAL::Base pointer for the owning database (borrowed)
 * \param[in]   name        - the name of the storage
 * \param[in]   duplicates  - true if storage supports duplicates, false otherwise (false by default)
 */
template<class K, class V>
LMDBAL::Storage<K, V>::Storage(Base* parent, const std::string& name, bool duplicates):
    iStorage(parent, name, duplicates),
    keySerializer(),
    valueSerializer(),
    cursors()
{}

/**
 * \brief Destroys a storage
 */
template<class K, class V>
LMDBAL::Storage<K, V>::~Storage() {
    for (Cursor<K, V>* cursor : cursors)
        delete cursor;
}

/**
 * \brief Adds a key-value record to the storage
 *
 * Take a note that if the storage already had a record you want to add LMDBAL::Exist is thrown
 *
 * \param[in] key      key of the record
 * \param[in] value    value of the record
 *
 * \exception LMDBAL::Exist     thrown if the storage already has a record with the given key
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::addRecord(const K& key, const V& value) {
    ensureOpened(addRecordMethodName);
    TransactionID txn = beginTransaction();
    try {
        Storage<K, V>::addRecord(key, value, txn);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    commitTransaction(txn);
}

/**
 * \brief Adds a key-value record to the storage (transaction variant)
 *
 * This function schedules an addition of a key-value record, but doesn't immidiately adds it.
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginTransaction().
 *
 * Take a note that if the storage already had a record you want to add LMDBAL::Exist is thrown
 *
 * \param[in] key      key of the record
 * \param[in] value    value of the record
 * \param[in] txn      transaction ID, needs to be a writable transaction!
 *
 * \exception LMDBAL::Exist     thrown if the storage already has a record with the given key
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::addRecord(const K& key, const V& value, TransactionID txn) {
    ensureOpened(addRecordMethodName);

    MDB_val lmdbKey = keySerializer.setData(key);
    MDB_val lmdbData = valueSerializer.setData(value);

    int rc = mdb_put(txn, dbi, &lmdbKey, &lmdbData, MDB_NOOVERWRITE);
    if (rc != MDB_SUCCESS)
        throwDuplicateOrUnknown(rc, toString(key));
}

/**
 * \brief Adds a key-value record to the storage, overwrites if it already exists
 * \param[in] key      key of the record
 * \param[in] value    value of the record
 * \returns true if the record was added, false otherwise
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
bool LMDBAL::Storage<K, V>::forceRecord(const K& key, const V& value) {
    ensureOpened(forceRecordMethodName);

    TransactionID txn = beginTransaction();
    bool added;
    try {
        added = Storage<K, V>::forceRecord(key, value, txn);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    commitTransaction(txn);
    return added;
}

/**
 * \brief Adds a key-value record to the storage, overwrites if it already exists (transaction variant)
 *
 * This function schedules an addition of a key-value record, but doesn't immidiately adds it.
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginTransaction().
 * If the record did already exist in the database the actual overwrite will be done only after calling LMDBAL::Base::commitTransaction().
 *
 * \param[in] key      key of the record
 * \param[in] value    value of the record
 * \param[in] txn      transaction ID, needs to be a writable transaction!
 * \returns true if the record was added, false otherwise
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
bool LMDBAL::Storage<K, V>::forceRecord(const K& key, const V& value, TransactionID txn) {
    ensureOpened(forceRecordMethodName);

    bool added;
    MDB_val lmdbKey = keySerializer.setData(key);
    MDB_val lmdbData;

    int rc = mdb_get(txn, dbi, &lmdbKey, &lmdbData);
    switch (rc) {
        case MDB_SUCCESS:
            added = false;
            break;
        case MDB_NOTFOUND:
            added = true;
            break;
        default:
            added = false;
            throwUnknown(rc);
    }

    lmdbData = valueSerializer.setData(value);
    rc = mdb_put(txn, dbi, &lmdbKey, &lmdbData, 0);
    if (rc != MDB_SUCCESS)
        throwUnknown(rc);

    return added;
}

/**
 * \brief Changes key-value record to the storage.
 *
 * Take a note that if the storage didn't have a record you want to change LMDBAL::NotFound is thrown
 *
 * \param[in] key      key of the record
 * \param[in] value    new value of the record
 *
 * \exception LMDBAL::NotFound  thrown if the storage doesn't have a record with the given key
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::changeRecord(const K& key, const V& value) {
    ensureOpened(changeRecordMethodName);

    TransactionID txn = beginTransaction();
    try {
        Storage<K, V>::changeRecord(key, value, txn);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    commitTransaction(txn);
}

/**
 * \brief Changes key-value record to the storage (transaction variant)
 *
 * This function schedules a modification of a key-value record, but doesn't immidiately changes it.
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginTransaction().
 *
 * Take a note that if the storage didn't have a record you want to change LMDBAL::NotFound is thrown
 *
 * \param[in] key      key of the record
 * \param[in] value    new value of the record
 * \param[in] txn      transaction ID, needs to be a writable transaction!
 *
 * \exception LMDBAL::NotFound  thrown if the storage doesn't have a record with the given key
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::changeRecord(const K& key, const V& value, TransactionID txn) {
    ensureOpened(changeRecordMethodName);

    MDB_cursor* cursor;
    int rc = mdb_cursor_open(txn, dbi, &cursor);
    if (rc != MDB_SUCCESS)
        throwUnknown(rc);

    MDB_val lmdbKey = keySerializer.setData(key);
    rc = mdb_cursor_get(cursor, &lmdbKey, nullptr, MDB_SET);
    if (rc != MDB_SUCCESS)
        throwNotFoundOrUnknown(rc, toString(key));

    MDB_val lmdbData = valueSerializer.setData(value);
    rc = mdb_cursor_put(cursor, &lmdbKey, &lmdbData, MDB_CURRENT);
    mdb_cursor_close(cursor);
    if (rc != MDB_SUCCESS)
        throwUnknown(rc);
}

/**
 * \brief Gets the record from the database

 * Take a note that if the storage didn't have a record you want to change LMDBAL::NotFound is thrown
 *
 * \param[in] key      key of the record you look for
 * \returns the value from the storage
 *
 * \exception LMDBAL::NotFound  thrown if the storage doesn't have a record with the given key
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
V LMDBAL::Storage<K, V>::getRecord(const K& key) const {
    ensureOpened(getRecordMethodName);

    V value;
    Storage<K, V>::getRecord(key, value);
    return value;
}

/**
 * \brief Gets the record from the database (reference variant)

 * Take a note that if the storage didn't have a record you want to change LMDBAL::NotFound is thrown
 *
 * \param[in] key      key of the record you look for
 * \param[out] value   the value from the storage
 *
 * \exception LMDBAL::NotFound  thrown if the storage doesn't have a record with the given key
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::getRecord(const K& key, V& value) const {
    ensureOpened(getRecordMethodName);

    TransactionID txn = beginReadOnlyTransaction();
    try {
        Storage<K, V>::getRecord(key, value, txn);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    abortTransaction(txn);
}

/**
 * \brief Gets the record from the database (transaction variant)
 *
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginReadOnlyTransaction() or LMDBAL::Base::beginTransaction().
 * If you just want to read data you should prefer LMDBAL::Base::beginReadOnlyTransaction().
 *
 * Take a note that if the storage didn't have a record you want to change LMDBAL::NotFound is thrown
 *
 * \param[in] key      key of the record you look for
 * \param[in] txn      transaction ID, can be read only transaction
 * \returns the value from the storage
 *
 * \exception LMDBAL::NotFound  thrown if the storage doesn't have a record with the given key
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
V LMDBAL::Storage<K, V>::getRecord(const K& key, TransactionID txn) const {
    ensureOpened(getRecordMethodName);

    V value;
    Storage<K, V>::getRecord(key, value, txn);
    return value;
}

/**
 * \brief Gets the record from the database (transaction, reference variant)
 *
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginReadOnlyTransaction() or LMDBAL::Base::beginTransaction().
 * If you just want to read data you should prefer LMDBAL::Base::beginReadOnlyTransaction().
 *
 * Take a note that if the storage didn't have a record you want to change LMDBAL::NotFound is thrown
 *
 * \param[in] key      key of the record you look for
 * \param[out] value   the value from the storage
 * \param[in] txn      transaction ID, can be read only transaction
 *
 * \exception LMDBAL::NotFound  thrown if the storage doesn't have a record with the given key
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::getRecord(const K& key, V& value, TransactionID txn) const {
    ensureOpened(getRecordMethodName);

    MDB_val lmdbKey = keySerializer.setData(key);
    MDB_val lmdbData;

    int rc = mdb_get(txn, dbi, &lmdbKey, &lmdbData);
    if (rc != MDB_SUCCESS)
        throwNotFoundOrUnknown(rc, toString(key));

    valueSerializer.deserialize(lmdbData, value);
}

/**
 * \brief Chechs if storage has value
 *
 * \param[in] key      key of the record you look for
 * \returns true if there was a record with given key, false otherwise
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
bool LMDBAL::Storage<K, V>::checkRecord(const K& key) const {
    ensureOpened(checkRecordMethodName);

    TransactionID txn = beginReadOnlyTransaction();
    bool result;
    try {
        result = Storage<K, V>::checkRecord(key, txn);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    abortTransaction(txn);
    return result;
}

/**
 * \brief Chechs if storage has value (transaction variant)
 *
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginReadOnlyTransaction() or LMDBAL::Base::beginTransaction().
 * If you just want to read data you should prefer LMDBAL::Base::beginReadOnlyTransaction().
 *
 * \param[in] key      key of the record you look for
 * \param[in] txn      transaction ID, can be read only transaction
 * \returns true if there was a record with given key, false otherwise
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
bool LMDBAL::Storage<K, V>::checkRecord(const K& key, TransactionID txn) const {
    ensureOpened(checkRecordMethodName);

    MDB_val lmdbKey = keySerializer.setData(key);
    MDB_val lmdbData;

    int rc = mdb_get(txn, dbi, &lmdbKey, &lmdbData);
    if (rc == MDB_SUCCESS)
        return true;

    if (rc != MDB_NOTFOUND)
        throwUnknown(rc);

    return false;
}

/**
 * \brief Reads whole storage into a map
 *
 * Basically just reads all database in an std::map, usefull when you store small storages
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
std::map<K, V> LMDBAL::Storage<K, V>::readAll() const {
    ensureOpened(readAllMethodName);

    std::map<K, V> result;
    Storage<K, V>::readAll(result);
    return result;
}

/**
 * \brief Reads whole storage into a map (reference variant)
 *
 * Basically just reads all database in an std::map, usefull when you store small storages
 *
 * \param[out] result   a map that is going to contain all data
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::readAll(std::map<K, V>& result) const {
    ensureOpened(readAllMethodName);

    TransactionID txn = beginReadOnlyTransaction();
    try {
        Storage<K, V>::readAll(result, txn);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    abortTransaction(txn);
}

/**
 * \brief Reads whole storage into a map (transaction variant)
 *
 * Basically just reads all database in an std::map, usefull when you store small storages
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginReadOnlyTransaction() or LMDBAL::Base::beginTransaction().
 * If you just want to read data you should prefer LMDBAL::Base::beginReadOnlyTransaction().
 *
 * \param[in] txn      transaction ID, can be read only transaction
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
std::map<K, V> LMDBAL::Storage<K, V>::readAll(TransactionID txn) const {
    ensureOpened(readAllMethodName);

    std::map<K, V> result;
    Storage<K, V>::readAll(result, txn);
    return result;
}

/**
 * \brief Reads whole storage into a map (transaction, reference variant)
 *
 * Basically just reads all database in an std::map, usefull when you store small storages
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginReadOnlyTransaction() or LMDBAL::Base::beginTransaction().
 * If you just want to read data you should prefer LMDBAL::Base::beginReadOnlyTransaction().
 *
 * \param[out] result   a map that is going to contain all data
 * \param[in] txn      transaction ID, can be read only transaction
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::readAll(std::map<K, V>& result, TransactionID txn) const {
    ensureOpened(readAllMethodName);

    MDB_cursor* cursor;
    MDB_val lmdbKey, lmdbData;

    int rc = mdb_cursor_open(txn, dbi, &cursor);
    if (rc != MDB_SUCCESS)
        throwUnknown(rc);

    rc = mdb_cursor_get(cursor, &lmdbKey, &lmdbData, MDB_FIRST);
    while (rc == MDB_SUCCESS) {
        K key;
        keySerializer.deserialize(lmdbKey, key);
        V& value = result[key];
        valueSerializer.deserialize(lmdbData, value);
        rc = mdb_cursor_get(cursor, &lmdbKey, &lmdbData, MDB_NEXT);
    }
    mdb_cursor_close(cursor);
    if (rc != MDB_NOTFOUND)
        throwUnknown(rc);
}

/**
 * \brief Replaces the content of the whole storage with the given
 *
 * Basically this function drops the database and adds all the records from the given map
 *
 * \param[in] data      new data of the storage
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::replaceAll(const std::map<K, V>& data) {
    ensureOpened(replaceAllMethodName);

    TransactionID txn = beginTransaction();
    try {
        Storage<K, V>::replaceAll(data, txn);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    commitTransaction(txn);
}

/**
 * \brief Replaces the content of the whole storage with the given (transaction variant)
 *
 * Basically this function drops the database and adds all the records from the given map
 * This function schedules a data replacement, but doesn't immidiately execute it.
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginTransaction().
 *
 * \param[in] data      new data of the storage
 * \param[in] txn       transaction ID, needs to be a writable transaction!
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::replaceAll(const std::map<K, V>& data, TransactionID txn) {
    ensureOpened(replaceAllMethodName);

    int rc = drop(txn);
    if (rc != MDB_SUCCESS)
        throwUnknown(rc);

    MDB_val lmdbKey, lmdbData;
    for (const std::pair<const K, V>& pair : data) {
        lmdbKey = keySerializer.setData(pair.first);
        lmdbData = valueSerializer.setData(pair.second);

        rc = mdb_put(txn, dbi, &lmdbKey, &lmdbData, MDB_NOOVERWRITE);   //TODO may be appending with cursor makes sence here?
        if (rc != MDB_SUCCESS)
            throwUnknown(rc);
    }
}

/**
 * \brief Adds records in bulk
 *
 * \param[in]       data        the data to be added
 * \param[in]       overwrite   if false function throws LMDBAL::Exist on repeated key, if true - overwrites it
 * \returns         new actual amount of records in the storage
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Exist     thrown if overwrite==false and at least one of the keys of data already exists in the storage
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
uint32_t LMDBAL::Storage<K, V>::addRecords(const std::map<K, V>& data, bool overwrite) {
    ensureOpened(addRecordsMethodName);

    TransactionID txn = beginTransaction();
    uint32_t amount;
    try {
        amount = Storage<K, V>::addRecords(data, txn, overwrite);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    commitTransaction(txn);
    return amount;
}

/**
 * \brief Adds records in bulk (transaction variant)
 *
 * This function schedules a data addition, but doesn't immidiately execute it.
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginTransaction().
 *
 * \param[in]       data        the data to be added
 * \param[in]       txn         transaction ID, needs to be a writable transaction!
 * \param[in]       overwrite   if false function throws LMDBAL::Exist on repeated key, if true - overwrites it
 * \returns         new actual amount of records in the storage
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Exist     thrown if overwrite==false and at least one of the keys of data already exists in the storage
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
uint32_t LMDBAL::Storage<K, V>::addRecords(const std::map<K, V>& data, TransactionID txn, bool overwrite) {
    ensureOpened(addRecordsMethodName);

    MDB_val lmdbKey, lmdbData;
    int rc;
    for (const std::pair<const K, V>& pair : data) {
        lmdbKey = keySerializer.setData(pair.first);
        lmdbData = valueSerializer.setData(pair.second);

        rc = mdb_put(txn, dbi, &lmdbKey, &lmdbData, overwrite ? 0 : MDB_NOOVERWRITE);
        if (rc == MDB_KEYEXIST)
            throwDuplicate(toString(pair.first));

        if (rc != MDB_SUCCESS)
            throwUnknown(rc);
    }

    MDB_stat stat;
    rc = mdb_stat(txn, dbi, &stat);
    if (rc != MDB_SUCCESS)
        throwUnknown(rc);

    return stat.ms_entries;
}

/**
 * \brief Removes one of the records
 *
 * Take a note that if the storage didn't have a record you want to remove LMDBAL::NotFound is thrown
 *
 * \param[in]       key     key of the record you wish to be removed
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::NotFound  thrown if the record with given key wasn't found
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::removeRecord(const K& key) {
    ensureOpened(removeRecordMethodName);

    TransactionID txn = beginTransaction();
    try {
        Storage<K, V>::removeRecord(key, txn);
    } catch (...) {
        abortTransaction(txn);
        throw;
    }

    commitTransaction(txn);
}

/**
 * \brief Removes one of the records (transaction variant)
 *
 * Take a note that if the storage didn't have a record you want to remove LMDBAL::NotFound is thrown
 * This function schedules a record removal, but doesn't immidiately execute it.
 * You can obtain LMDBAL::TransactionID calling LMDBAL::Base::beginTransaction().
 *
 * \param[in]       key         key of the record you wish to be removed
 * \param[in]       txn         transaction ID, needs to be a writable transaction!
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::NotFound  thrown if the record with given key wasn't found
 * \exception LMDBAL::Unknown   thrown if something unexpected happend within lmdb
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::removeRecord(const K& key, TransactionID txn) {
    ensureOpened(removeRecordMethodName);

    MDB_val lmdbKey = keySerializer.setData(key);
    int rc = mdb_del(txn, dbi, &lmdbKey, NULL);
    if (rc != MDB_SUCCESS)
        throwNotFoundOrUnknown(rc, toString(key));
}

/**
 * \brief A private virtual function I need to open each storage in the database
 *
 * \param[in] transaction   - lmdb transaction to call <a class="el" href="http://www.lmdb.tech/doc/group__mdb.html#gac08cad5b096925642ca359a6d6f0562a">mdb_dbi_open</a>
 * \returns MDB_SUCCESS if everything went smooth or MDB_<error> -like error code
 */
template<class K, class V>
int LMDBAL::Storage<K, V>::open(MDB_txn* transaction) {
    return makeStorage<K, V>(transaction, duplicates);
}

/**
 * \brief A private virtual function I need to close each storage in the database
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::close() {
    for (Cursor<K, V>* cursor : cursors)
        cursor->terminated();

    iStorage::close();
}

/**
 * \brief Creates cursor
 *
 * \returns LMDBAL::Cursor for this storage and returs you a pointer to a created cursor
 */
template<class K, class V>
LMDBAL::Cursor<K, V>* LMDBAL::Storage<K, V>::createCursor() {
    Cursor<K, V>* cursor = new Cursor<K, V>(this);
    cursors.insert(cursor);

    return cursor;
}

/**
 * \brief Reads current storage flags it was opened with
 *
 * This function exists mostly for testing purposes
 *
 * \returns Third out parameter of <a href="http://www.lmdb.tech/doc/group__internal.html#ga95ba4cb721035478a8705e57b91ae4d4">mdb_dbi_flags</a> function
 *
 * \exception LMDBAL::Closed    thrown if the database was not opened
 * \exception LMDBAL::Unknown   if the result of <a href="http://www.lmdb.tech/doc/group__internal.html#ga95ba4cb721035478a8705e57b91ae4d4">mdb_dbi_flags</a> was not successfull
 */
template<class K, class V>
uint32_t LMDBAL::Storage<K, V>::flags() const {
    ensureOpened(flagsMethodName);
    uint32_t result;
    TransactionID txn = beginReadOnlyTransaction();

    int res = mdb_dbi_flags(txn, dbi, &result);
    abortTransaction(txn);
    if (res != MDB_SUCCESS)
        throwUnknown(res);

    return result;
}

/**
 * \brief Destroys cursor
 *
 * This a normal way to discard a cursor you don't need anymore
 *
 * \param[in] cursor    a pointer to a cursor you want to destroy
 *
 * \exception LMDBAL::Unknown  thrown if you try to destroy something that this storage didn't create
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::destroyCursor(Cursor<K, V>* cursor) {
    typename std::set<Cursor<K, V>*>::const_iterator itr = cursors.find(cursor);
    if (itr == cursors.end())
        throwUnknown("An attempt to destroy a cursor the storage doesn't own");

    cursors.erase(itr);
    delete cursor;
}

/**
 * \brief A private virtual function that cursor calls when he reads a record, does nothing here but populates the LMDBAL::Cache
 *
 * \param[in]   key     a key of discovered record
 * \param[in]   value   a value of discovered record
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::discoveredRecord(const K& key, const V& value) const {
    UNUSED(key);
    UNUSED(value);
}

/**
 * \brief A private virtual function that cursor calls when he reads a record, does nothing here but populates the LMDBAL::Cache
 *
 * \param[in]   key     a key of discovered record
 * \param[in]   value   a value of discovered record
 * \param[in]   txn     TransactionID under which the dicovery happened, to avoid not commited changes collisions
 */
template<class K, class V>
void LMDBAL::Storage<K, V>::discoveredRecord(const K& key, const V& value, TransactionID txn) const {
    UNUSED(key);
    UNUSED(value);
    UNUSED(txn);
}

/**
 * \brief A functiion to actually open <a class="el" href="http://www.lmdb.tech/doc/group__mdb.html#gadbe68a06c448dfb62da16443d251a78b">MDB_dbi</a> storage
 *
 * \tparam K type of keys in opening storage
 *
 * \param[in] transaction   - lmdb transaction to call <a class="el" href="http://www.lmdb.tech/doc/group__mdb.html#gac08cad5b096925642ca359a6d6f0562a">mdb_dbi_open</a>, must be a writable transaction!
 * \param[in] duplicates    - true if you wish to enable duplicates support for the storage
 *
 * \returns MDB_SUCCESS if everything went smooth or MDB_<error> -like error code
 *
 * This is a way to optimise database using MDB_INTEGERKEY flag,
 * when the key is actually kind of an integer
 * This infrastructure also allowes us to customize mdb_dbi_open call in the future
 */
template<class K, class V>
inline int LMDBAL::iStorage::makeStorage(MDB_txn* transaction, bool duplicates) {
    unsigned int flags = MDB_CREATE;
    if constexpr (std::is_integral<K>::value)
        flags |= MDB_INTEGERKEY;

    if (duplicates) {
        flags |= MDB_DUPSORT;

        if constexpr (std::is_integral<V>::value)
            flags |= MDB_INTEGERDUP | MDB_DUPFIXED;
    }

    return mdb_dbi_open(transaction, name.c_str(), flags, &dbi);
}

/**
 * \brief A method to cast a value (which can be a value or a key) to string.
 *
 * This function is mainly used in exceptions, to report which key was duplicated or not found.
 * You can define your own specializations to this function in case std::to_string doesn't cover your case
 *
 * \param[in]   value   a value that should be converted to string
 * \returns     a string presentation of value
 */
template<class T>
inline std::string LMDBAL::iStorage::toString(const T& value) {
    return std::to_string(value);
}

/**
 * \brief A method to cast a value (which can be a value or a key) to string.
 *
 * QString spectialization
 *
 * \param[in]   value   a value that should be converted to string
 * \returns     a string presentation of value
 */
template<>
inline std::string LMDBAL::iStorage::toString(const QString& value) {
    return value.toStdString();
}

/**
 * \brief A method to cast a value (which can be a value or a key) to string.
 *
 * std::string spectialization
 *
 * \param[in]   value   a value that should be converted to string
 * \returns     a string presentation of value
 */
template<>
inline std::string LMDBAL::iStorage::toString(const std::string& value) {
    return value;
}

#endif //LMDBAL_STORAGE_HPP