/*
 * Copyright (C) by Klaas Freitag <freitag@owncloud.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
#include "common/checksums.h"
#include "asserts.h"
#include "common/chronoelapsedtimer.h"
#include "common/utility.h"
#include "filesystembase.h"

#include <QCoreApplication>
#include <QCryptographicHash>
#include <QLoggingCategory>
#include <QScopeGuard>
#include <QtConcurrentRun>

#include <zlib.h>

/** \file checksums.cpp
 *
 * \brief Computing and validating file checksums
 *
 * Overview
 * --------
 *
 * Checksums are used in two distinct ways during synchronization:
 *
 * - to guard uploads and downloads against data corruption
 *   (transmission checksum)
 * - to quickly check whether the content of a file has changed
 *   to avoid redundant uploads (content checksum)
 *
 * In principle both are independent and different checksumming
 * algorithms can be used. To avoid redundant computations, it can
 * make sense to use the same checksum algorithm though.
 *
 * Transmission Checksums
 * ----------------------
 *
 * The usage of transmission checksums is currently optional and needs
 * to be explicitly enabled by adding 'transmissionChecksum=TYPE' to
 * the '[General]' section of the config file.
 *
 * When enabled, the checksum will be calculated on upload and sent to
 * the server in the OC-Checksum header with the format 'TYPE:CHECKSUM'.
 *
 * On download, the header with the same name is read and if the
 * received data does not have the expected checksum, the download is
 * rejected.
 *
 * Transmission checksums guard a specific sync action and are not stored
 * in the database.
 *
 * Content Checksums
 * -----------------
 *
 * Sometimes the metadata of a local file changes while the content stays
 * unchanged. Content checksums allow the sync client to avoid uploading
 * the same data again by comparing the file's actual checksum to the
 * checksum stored in the database.
 *
 * Content checksums are not sent to the server.
 *
 * Checksum Algorithms
 * -------------------
 *
 * - Adler32 (requires zlib)
 * - MD5
 * - SHA1
 * - SHA256
 * - SHA3-256 (requires Qt 5.9)
 *
 */


namespace {

QByteArray calcAdler32(QIODevice *device)
{
    const qint64 BUFSIZE(500 * 1024); // 500 KiB
    if (device->size() == 0) {
        return QByteArray();
    }
    QByteArray buf(BUFSIZE, Qt::Uninitialized);

    unsigned int adler = adler32(0L, nullptr, 0);
    qint64 size;
    while (!device->atEnd()) {
        size = device->read(buf.data(), BUFSIZE);
        if (size > 0)
            adler = adler32(adler, (const Bytef *)buf.data(), size);
    }

    return QByteArray::number(adler, 16);
}
}

namespace OCC {

Q_LOGGING_CATEGORY(lcChecksums, "sync.checksums", QtInfoMsg)
Q_LOGGING_CATEGORY(lcChecksumsHeader, "sync.checksums.header", QtInfoMsg)

ChecksumHeader ChecksumHeader::parseChecksumHeader(const QByteArray &header)
{
    if (header.isEmpty()) {
        return {};
    }
    ChecksumHeader out;
    const auto idx = header.indexOf(':');
    if (idx < 0) {
        out._error = QCoreApplication::translate("ChecksumHeader", "The checksum header is malformed: %1").arg(QString::fromUtf8(header));
    } else {
        out._checksumType = CheckSums::fromByteArray(header.left(idx));
        if (out._checksumType == CheckSums::Algorithm::PARSE_ERROR) {
            out._error = QCoreApplication::translate("ChecksumHeader", "The checksum header contained an unknown checksum type '%1'")
                             .arg(QString::fromUtf8(header.left(idx)));
        }
        out._checksum = header.mid(idx + 1);
    }
    if (!out.isValid()) {
        qCDebug(lcChecksumsHeader) << u"Failed to parse" << header << out.error();
    }
    return out;
}

ChecksumHeader::ChecksumHeader(CheckSums::Algorithm type, const QByteArray &checksum)
    : _checksumType(type)
    , _checksum(checksum)
{
}

QByteArray ChecksumHeader::makeChecksumHeader() const
{
    if (!isValid()) {
        return {};
    }
    return Utility::enumToString(_checksumType).toUtf8() + ':' + _checksum;
}

CheckSums::Algorithm ChecksumHeader::type() const
{
    return _checksumType;
}

QByteArray ChecksumHeader::checksum() const
{
    return _checksum;
}

bool ChecksumHeader::isValid() const
{
    return _checksumType != CheckSums::Algorithm::NONE && _checksumType != CheckSums::Algorithm::PARSE_ERROR && !_checksum.isEmpty();
}

QString ChecksumHeader::error() const
{
    return _error;
}

bool ChecksumHeader::operator==(const ChecksumHeader &other) const
{
    return _checksumType == other._checksumType && _checksum == other._checksum;
}

bool ChecksumHeader::operator!=(const ChecksumHeader &other) const
{
    return !(*this == other);
}

QByteArray findBestChecksum(const QByteArray &_checksums)
{
    if (_checksums.isEmpty()) {
        return {};
    }

    // The order of the searches here defines the preference ordering.
    // we assume _checksums to be utf-8 so toUpper is valid here
    const auto i = [checksums = _checksums.toUpper()]() -> qsizetype {
        for (const auto &algo : CheckSums::All) {
            auto i = checksums.indexOf(algo.second.data());
            if (i != -1) {
                return i;
            }
        }
        return -1;
    }();
    if (i != -1) {
        // Now i is the start of the best checksum
        // Grab it until the next space or end of xml or end of string.
        int end = _checksums.indexOf(' ', i);
        // workaround for https://github.com/owncloud/core/pull/38304
        if (end == -1) {
            end = _checksums.indexOf('<', i);
        }
        return _checksums.mid(i, end - i);
    }
    qCWarning(lcChecksums) << u"Failed to parse" << _checksums;
    return {};
}

ComputeChecksum::ComputeChecksum(QObject *parent)
    : QObject(parent)
{
}

ComputeChecksum::~ComputeChecksum() { }

void ComputeChecksum::setChecksumType(CheckSums::Algorithm type)
{
    Q_ASSERT(type != CheckSums::Algorithm::NONE && type != CheckSums::Algorithm::PARSE_ERROR);
    _checksumType = type;
}

CheckSums::Algorithm ComputeChecksum::checksumType() const
{
    return _checksumType;
}

void ComputeChecksum::start(const QString &filePath)
{
    qCInfo(lcChecksums) << u"Computing" << checksumType() << u"checksum of" << filePath << u"in a thread";
    startImpl(std::make_unique<QFile>(filePath));
}

void ComputeChecksum::start(std::unique_ptr<QIODevice> device)
{
    OC_ENFORCE(device);
    qCInfo(lcChecksums) << u"Computing" << checksumType() << u"checksum of device" << device.get() << u"in a thread";
    OC_ASSERT(!device->parent());

    startImpl(std::move(device));
}

void ComputeChecksum::startImpl(std::unique_ptr<QIODevice> device)
{
    connect(&_watcher, &QFutureWatcherBase::finished, this, &ComputeChecksum::slotCalculationDone, Qt::UniqueConnection);

    // We'd prefer to move the unique_ptr into the lambda, but that's
    // awkward with the C++ standard we're on
    auto sharedDevice = QSharedPointer<QIODevice>(device.release());

    // Bug: The thread will keep running even if ComputeChecksum is deleted.
    auto type = checksumType();
    _watcher.setFuture(QtConcurrent::run([sharedDevice, type]() {
        if (!sharedDevice->open(QIODevice::ReadOnly)) {
            if (auto file = qobject_cast<QFile *>(sharedDevice.data())) {
                qCWarning(lcChecksums) << u"Could not open file" << file->fileName() << u"for reading to compute a checksum" << file->errorString();
            } else {
                qCWarning(lcChecksums) << u"Could not open device" << sharedDevice.data() << u"for reading to compute a checksum"
                                       << sharedDevice->errorString();
            }
            return QByteArray();
        }
        auto result = ComputeChecksum::computeNow(sharedDevice.data(), type);
        sharedDevice->close();
        return result;
    }));
}

QByteArray ComputeChecksum::computeNowOnFile(const QString &filePath, CheckSums::Algorithm checksumType)
{
    QFile file(filePath);
    if (!file.open(QIODevice::ReadOnly)) {
        qCWarning(lcChecksums) << u"Could not open file" << filePath << u"for reading and computing checksum" << file.errorString();
        return QByteArray();
    }

    return computeNow(&file, checksumType);
}

QByteArray ComputeChecksum::computeNow(QIODevice *device, CheckSums::Algorithm algorithm)
{
    // const cast to prevent stream to "device"
    const auto log = qScopeGuard([device, algorithm, timer = Utility::ChronoElapsedTimer()] {
        if (auto file = qobject_cast<QFile *>(device)) {
            qCDebug(lcChecksums) << u"Finished" << algorithm << u"computation for" << file->fileName() << timer;
        } else {
            qCDebug(lcChecksums) << u"Finished" << algorithm << u"computation for" << device << timer;
        }
    });
    switch (algorithm) {
    case CheckSums::Algorithm::SHA3_256:
        [[fallthrough]];
    case CheckSums::Algorithm::SHA256:
        [[fallthrough]];
    case CheckSums::Algorithm::SHA1:
        [[fallthrough]];
    case CheckSums::Algorithm::MD5: {
        QCryptographicHash crypto(static_cast<QCryptographicHash::Algorithm>(algorithm));
        if (crypto.addData(device)) {
            return crypto.result().toHex();
        }
        qCWarning(lcChecksums) << u"Failed to compoute checksum" << Utility::enumToString(algorithm);
        return {};
    }
    case CheckSums::Algorithm::ADLER32:
        return calcAdler32(device);
    case CheckSums::Algorithm::DUMMY_FOR_TESTS:
        return QByteArrayLiteral("0x1");
    case CheckSums::Algorithm::PARSE_ERROR:
        return {};
    case CheckSums::Algorithm::NONE:
        Q_UNREACHABLE();
    }
    Q_UNREACHABLE();
}

void ComputeChecksum::slotCalculationDone()
{
    QByteArray checksum = _watcher.future().result();
    if (!checksum.isNull()) {
        Q_EMIT done(_checksumType, checksum);
    } else {
        Q_EMIT done(CheckSums::Algorithm::PARSE_ERROR, QByteArray());
    }
}


ValidateChecksumHeader::ValidateChecksumHeader(QObject *parent)
    : QObject(parent)
{
}

ComputeChecksum *ValidateChecksumHeader::prepareStart(const QByteArray &checksumHeader)
{
    // If the incoming header is empty no validation can happen. Just continue.
    if (checksumHeader.isEmpty()) {
        Q_EMIT validated(CheckSums::Algorithm::PARSE_ERROR, QByteArray());
        return nullptr;
    }
    _expectedChecksum = ChecksumHeader::parseChecksumHeader(checksumHeader);
    if (!_expectedChecksum.isValid()) {
        qCWarning(lcChecksums) << u"Checksum header malformed:" << checksumHeader;
        Q_EMIT validationFailed(_expectedChecksum.error());
        return nullptr;
    }

    auto calculator = new ComputeChecksum(this);
    calculator->setChecksumType(_expectedChecksum.type());
    connect(calculator, &ComputeChecksum::done, this, &ValidateChecksumHeader::slotChecksumCalculated);
    return calculator;
}

void ValidateChecksumHeader::start(const QString &filePath, const QByteArray &checksumHeader)
{
    if (auto calculator = prepareStart(checksumHeader))
        calculator->start(filePath);
}

void ValidateChecksumHeader::start(std::unique_ptr<QIODevice> device, const QByteArray &checksumHeader)
{
    if (auto calculator = prepareStart(checksumHeader))
        calculator->start(std::move(device));
}

void ValidateChecksumHeader::slotChecksumCalculated(CheckSums::Algorithm checksumType, const QByteArray &checksum)
{
    if (_expectedChecksum.type() == CheckSums::Algorithm::PARSE_ERROR) {
        Q_EMIT validationFailed(_expectedChecksum.error());
        return;
    }
    if (checksum != _expectedChecksum.checksum()) {
        Q_EMIT validationFailed(tr("The downloaded file does not match the checksum, it will be resumed. '%1' != '%2'")
                                    .arg(QString::fromUtf8(_expectedChecksum.checksum()), QString::fromUtf8(checksum)));
        return;
    }
    Q_EMIT validated(checksumType, checksum);
}
}
