/*
 *   Copyright (C) 2015 Christian Mollekopf <chrigi_1@fastmail.fm>
 *
 *   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.,
 *   51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA.
 */

#include "facade.h"

#include "commands.h"
#include "log.h"
#include "storage.h"
#include "definitions.h"

using namespace Akonadi2;

/**
 * A QueryRunner runs a query and updates the corresponding result set.
 * 
 * The lifetime of the QueryRunner is defined by the resut set (otherwise it's doing useless work),
 * and by how long a result set must be updated. If the query is one off the runner dies after the execution,
 * otherwise it lives on the react to changes and updates the corresponding result set.
 * 
 * QueryRunner has to keep ResourceAccess alive in order to keep getting updates.
 */
class QueryRunner : public QObject
{
    Q_OBJECT
public:
    typedef std::function<KAsync::Job<void>()> QueryFunction;

    QueryRunner(const Akonadi2::Query &query) {};
    /**
     * Starts query
     */
    KAsync::Job<void> run(qint64 newRevision = 0)
    {
        return queryFunction();
    }

    /**
     * Set the query to run
     */
    void setQuery(const QueryFunction &query)
    {
        queryFunction = query;
    }

public slots:
    /**
     * Rerun query with new revision
     */
    void revisionChanged(qint64 newRevision)
    {
        Trace() << "New revision: " << newRevision;
        run().exec();
    }

private:
    QueryFunction queryFunction;
};

static inline ResultSet fullScan(const Akonadi2::Storage::Transaction &transaction, const QByteArray &bufferType)
{
    //TODO use a result set with an iterator, to read values on demand
    QVector<QByteArray> keys;
    transaction.openDatabase(bufferType + ".main").scan(QByteArray(), [&](const QByteArray &key, const QByteArray &value) -> bool {
        //Skip internals
        if (Akonadi2::Storage::isInternalKey(key)) {
            return true;
        }
        keys << Akonadi2::Storage::uidFromKey(key);
        return true;
    },
    [](const Akonadi2::Storage::Error &error) {
        qWarning() << "Error during query: " << error.message;
    });

    Trace() << "Full scan found " << keys.size() << " results";
    return ResultSet(keys);
}



template<class DomainType>
GenericFacade<DomainType>::GenericFacade(const QByteArray &resourceIdentifier, const DomainTypeAdaptorFactoryInterface::Ptr &adaptorFactory , const QSharedPointer<Akonadi2::ResourceAccessInterface> resourceAccess)
    : Akonadi2::StoreFacade<DomainType>(),
    mResourceAccess(resourceAccess),
    mDomainTypeAdaptorFactory(adaptorFactory),
    mResourceInstanceIdentifier(resourceIdentifier)
{
    if (!mResourceAccess) {
        mResourceAccess = QSharedPointer<Akonadi2::ResourceAccess>::create(resourceIdentifier);
    }
}

template<class DomainType>
GenericFacade<DomainType>::~GenericFacade()
{
}

template<class DomainType>
QByteArray GenericFacade<DomainType>::bufferTypeForDomainType()
{
    //We happen to have a one to one mapping
    return Akonadi2::ApplicationDomain::getTypeName<DomainType>();
}

template<class DomainType>
KAsync::Job<void> GenericFacade<DomainType>::create(const DomainType &domainObject)
{
    if (!mDomainTypeAdaptorFactory) {
        Warning() << "No domain type adaptor factory available";
        return KAsync::error<void>();
    }
    flatbuffers::FlatBufferBuilder entityFbb;
    mDomainTypeAdaptorFactory->createBuffer(domainObject, entityFbb);
    return mResourceAccess->sendCreateCommand(bufferTypeForDomainType(), QByteArray::fromRawData(reinterpret_cast<const char*>(entityFbb.GetBufferPointer()), entityFbb.GetSize()));
}

template<class DomainType>
KAsync::Job<void> GenericFacade<DomainType>::modify(const DomainType &domainObject)
{
    if (!mDomainTypeAdaptorFactory) {
        Warning() << "No domain type adaptor factory available";
        return KAsync::error<void>();
    }
    flatbuffers::FlatBufferBuilder entityFbb;
    mDomainTypeAdaptorFactory->createBuffer(domainObject, entityFbb);
    return mResourceAccess->sendModifyCommand(domainObject.identifier(), domainObject.revision(), bufferTypeForDomainType(), QByteArrayList(), QByteArray::fromRawData(reinterpret_cast<const char*>(entityFbb.GetBufferPointer()), entityFbb.GetSize()));
}

template<class DomainType>
KAsync::Job<void> GenericFacade<DomainType>::remove(const DomainType &domainObject)
{
    return mResourceAccess->sendDeleteCommand(domainObject.identifier(), domainObject.revision(), bufferTypeForDomainType());
}

template<class DomainType>
KAsync::Job<void> GenericFacade<DomainType>::load(const Akonadi2::Query &query, Akonadi2::ResultProviderInterface<typename DomainType::Ptr> &resultProvider)
{
    //We delegate loading of initial data to the result provider, os it can decide for itself what it needs to load.
    resultProvider.setFetcher([this, query, &resultProvider](const typename DomainType::Ptr &parent) {
        const qint64 newRevision = executeInitialQuery(query, parent, resultProvider);
        mResourceAccess->sendRevisionReplayedCommand(newRevision);
    });


    //In case of a live query we keep the runner for as long alive as the result provider exists
    if (query.liveQuery) {
        auto runner = QSharedPointer<QueryRunner>::create(query);
        //Incremental updates are always loaded directly, leaving it up to the result to discard the changes if they are not interesting
        runner->setQuery([this, query, &resultProvider] () -> KAsync::Job<void> {
            return KAsync::start<void>([this, query, &resultProvider](KAsync::Future<void> &future) {
                const qint64 newRevision = executeIncrementalQuery(query, resultProvider);
                mResourceAccess->sendRevisionReplayedCommand(newRevision);
                future.setFinished();
            });
        });
        resultProvider.setQueryRunner(runner);
        //Ensure the connection is open, if it wasn't already opened
        //TODO If we are not connected already, we have to check for the latest revision once connected, otherwise we could miss some updates
        mResourceAccess->open();
        QObject::connect(mResourceAccess.data(), &Akonadi2::ResourceAccess::revisionChanged, runner.data(), &QueryRunner::revisionChanged);
    }
    return KAsync::null<void>();
}

    //TODO move into result provider?
template<class DomainType>
void GenericFacade<DomainType>::replaySet(ResultSet &resultSet, Akonadi2::ResultProviderInterface<typename DomainType::Ptr> &resultProvider)
{
    while (resultSet.next([&resultProvider](const Akonadi2::ApplicationDomain::ApplicationDomainType::Ptr &value, Akonadi2::Operation operation) -> bool {
        switch (operation) {
        case Akonadi2::Operation_Creation:
            Trace() << "Got creation";
            resultProvider.add(Akonadi2::ApplicationDomain::ApplicationDomainType::getInMemoryRepresentation<DomainType>(*value).template staticCast<DomainType>());
            break;
        case Akonadi2::Operation_Modification:
            Trace() << "Got modification";
            resultProvider.modify(Akonadi2::ApplicationDomain::ApplicationDomainType::getInMemoryRepresentation<DomainType>(*value).template staticCast<DomainType>());
            break;
        case Akonadi2::Operation_Removal:
            Trace() << "Got removal";
            resultProvider.remove(Akonadi2::ApplicationDomain::ApplicationDomainType::getInMemoryRepresentation<DomainType>(*value).template staticCast<DomainType>());
            break;
        }
        return true;
    })){};
}

template<class DomainType>
void GenericFacade<DomainType>::readEntity(const Akonadi2::Storage::Transaction &transaction, const QByteArray &key, const std::function<void(const Akonadi2::ApplicationDomain::ApplicationDomainType::Ptr &, Akonadi2::Operation)> &resultCallback)
{
    const auto bufferType = bufferTypeForDomainType();
    //This only works for a 1:1 mapping of resource to domain types.
    //Not i.e. for tags that are stored as flags in each entity of an imap store.
    //additional properties that don't have a 1:1 mapping (such as separately stored tags),
    //could be added to the adaptor.
    //
    // Akonadi2::Storage::getLatest(transaction, bufferTye, key);
    transaction.openDatabase(bufferType + ".main").findLatest(key, [=](const QByteArray &key, const QByteArray &value) -> bool {
        Akonadi2::EntityBuffer buffer(value.data(), value.size());
        const Akonadi2::Entity &entity = buffer.entity();
        const auto metadataBuffer = Akonadi2::EntityBuffer::readBuffer<Akonadi2::Metadata>(entity.metadata());
        Q_ASSERT(metadataBuffer);
        const qint64 revision = metadataBuffer ? metadataBuffer->revision() : -1;
        resultCallback(DomainType::Ptr::create(mResourceInstanceIdentifier, Akonadi2::Storage::uidFromKey(key), revision, mDomainTypeAdaptorFactory->createAdaptor(entity)), metadataBuffer->operation());
        return false;
    },
    [](const Akonadi2::Storage::Error &error) {
        qWarning() << "Error during query: " << error.message;
    });
}

template<class DomainType>
ResultSet GenericFacade<DomainType>::loadInitialResultSet(const Akonadi2::Query &query, Akonadi2::Storage::Transaction &transaction, QSet<QByteArray> &remainingFilters)
{
    QSet<QByteArray> appliedFilters;
    auto resultSet = Akonadi2::ApplicationDomain::TypeImplementation<DomainType>::queryIndexes(query, mResourceInstanceIdentifier, appliedFilters, transaction);
    remainingFilters = query.propertyFilter.keys().toSet() - appliedFilters;

    //We do a full scan if there were no indexes available to create the initial set.
    if (appliedFilters.isEmpty()) {
        //TODO this should be replaced by an index lookup as well
        resultSet = fullScan(transaction, bufferTypeForDomainType());
    }
    return resultSet;
}

template<class DomainType>
ResultSet GenericFacade<DomainType>::loadIncrementalResultSet(qint64 baseRevision, const Akonadi2::Query &query, Akonadi2::Storage::Transaction &transaction, QSet<QByteArray> &remainingFilters)
{
    const auto bufferType = bufferTypeForDomainType();
    auto revisionCounter = QSharedPointer<qint64>::create(baseRevision);
    remainingFilters = query.propertyFilter.keys().toSet();
    return ResultSet([bufferType, revisionCounter, &transaction]() -> QByteArray {
        const qint64 topRevision = Akonadi2::Storage::maxRevision(transaction);
        //Spit out the revision keys one by one.
        while (*revisionCounter <= topRevision) {
            const auto uid = Akonadi2::Storage::getUidFromRevision(transaction, *revisionCounter);
            const auto type = Akonadi2::Storage::getTypeFromRevision(transaction, *revisionCounter);
            Trace() << "Revision" << *revisionCounter << type << uid;
            if (type != bufferType) {
                //Skip revision
                *revisionCounter += 1;
                continue;
            }
            const auto key = Akonadi2::Storage::assembleKey(uid, *revisionCounter);
            *revisionCounter += 1;
            return key;
        }
        Trace() << "Finished reading incremental result set:" << *revisionCounter;
        //We're done
        return QByteArray();
    });
}

template<class DomainType>
ResultSet GenericFacade<DomainType>::filterSet(const ResultSet &resultSet, const std::function<bool(const Akonadi2::ApplicationDomain::ApplicationDomainType::Ptr &domainObject)> &filter, const Akonadi2::Storage::Transaction &transaction, bool initialQuery)
{
    auto resultSetPtr = QSharedPointer<ResultSet>::create(resultSet);

    //Read through the source values and return whatever matches the filter
    std::function<bool(std::function<void(const Akonadi2::ApplicationDomain::ApplicationDomainType::Ptr &, Akonadi2::Operation)>)> generator = [this, resultSetPtr, &transaction, filter, initialQuery](std::function<void(const Akonadi2::ApplicationDomain::ApplicationDomainType::Ptr &, Akonadi2::Operation)> callback) -> bool {
        while (resultSetPtr->next()) {
            //readEntity is only necessary if we actually want to filter or know the operation type (but not a big deal if we do it always I guess)
            readEntity(transaction, resultSetPtr->id(), [this, filter, callback, initialQuery](const Akonadi2::ApplicationDomain::ApplicationDomainType::Ptr &domainObject, Akonadi2::Operation operation) {
                //Always remove removals, they probably don't match due to non-available properties
                if (filter(domainObject) || operation == Akonadi2::Operation_Removal) {
                    if (initialQuery) {
                        //We're not interested in removals during the initial query
                        if (operation != Akonadi2::Operation_Removal) {
                            callback(domainObject, Akonadi2::Operation_Creation);
                        }
                    } else {
                        callback(domainObject, operation);
                    }
                }
            });
        }
        return false;
    };
    return ResultSet(generator);
}


template<class DomainType>
std::function<bool(const Akonadi2::ApplicationDomain::ApplicationDomainType::Ptr &domainObject)> GenericFacade<DomainType>::getFilter(const QSet<QByteArray> remainingFilters, const Akonadi2::Query &query)
{
    return [remainingFilters, query](const Akonadi2::ApplicationDomain::ApplicationDomainType::Ptr &domainObject) -> bool {
        for (const auto &filterProperty : remainingFilters) {
            const auto property = domainObject->getProperty(filterProperty);
            if (property.isValid()) {
                //TODO implement other comparison operators than equality
                if (property != query.propertyFilter.value(filterProperty)) {
                    Trace() << "Filtering entity due to property mismatch: " << domainObject->getProperty(filterProperty);
                    return false;
                }
            } else {
                Warning() << "Ignored property filter because value is invalid: " << filterProperty;
            }
        }
        return true;
    };
}

template<class DomainType>
qint64 GenericFacade<DomainType>::load(const Akonadi2::Query &query, const std::function<ResultSet(Akonadi2::Storage::Transaction &, QSet<QByteArray> &)> &baseSetRetriever, Akonadi2::ResultProviderInterface<typename DomainType::Ptr> &resultProvider)
{
    Akonadi2::Storage storage(Akonadi2::storageLocation(), mResourceInstanceIdentifier);
    storage.setDefaultErrorHandler([](const Akonadi2::Storage::Error &error) {
        Warning() << "Error during query: " << error.store << error.message;
    });
    auto transaction = storage.createTransaction(Akonadi2::Storage::ReadOnly);

    QSet<QByteArray> remainingFilters;
    auto resultSet = baseSetRetriever(transaction, remainingFilters);
    auto filteredSet = filterSet(resultSet, getFilter(remainingFilters, query), transaction, false);
    replaySet(filteredSet, resultProvider);
    resultProvider.setRevision(Akonadi2::Storage::maxRevision(transaction));
    return Akonadi2::Storage::maxRevision(transaction);
}


template<class DomainType>
qint64 GenericFacade<DomainType>::executeIncrementalQuery(const Akonadi2::Query &query, Akonadi2::ResultProviderInterface<typename DomainType::Ptr> &resultProvider)
{
    const qint64 baseRevision = resultProvider.revision() + 1;
    Trace() << "Running incremental query " << baseRevision;
    return load(query, [&](Akonadi2::Storage::Transaction &transaction, QSet<QByteArray> &remainingFilters) -> ResultSet {
        return loadIncrementalResultSet(baseRevision, query, transaction, remainingFilters);
    }, resultProvider);
}

template<class DomainType>
qint64 GenericFacade<DomainType>::executeInitialQuery(const Akonadi2::Query &query, const typename DomainType::Ptr &parent, Akonadi2::ResultProviderInterface<typename DomainType::Ptr> &resultProvider)
{
    auto modifiedQuery = query;
    if (parent) {
        Trace() << "Running initial query for parent:" << parent->identifier();
        modifiedQuery.propertyFilter.insert("parent", parent->identifier());
    } else {
        Trace() << "Running initial query for toplevel";
        modifiedQuery.propertyFilter.insert("parent", QVariant());
    }
    return load(modifiedQuery, [&](Akonadi2::Storage::Transaction &transaction, QSet<QByteArray> &remainingFilters) -> ResultSet {
        return loadInitialResultSet(modifiedQuery, transaction, remainingFilters);
    }, resultProvider);
}

template class Akonadi2::GenericFacade<Akonadi2::ApplicationDomain::Folder>;
template class Akonadi2::GenericFacade<Akonadi2::ApplicationDomain::Mail>;
template class Akonadi2::GenericFacade<Akonadi2::ApplicationDomain::Event>;
// template class Akonadi2::GenericFacade<Akonadi2::ApplicationDomain::AkonadiResource>;

#include "facade.moc"