// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0

#include "settingsdatabase.h"

#include "qtcsettings.h"

#include <QCoreApplication>
#include <QDebug>
#include <QDir>
#include <QMap>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>
#include <QString>
#include <QStringList>
#include <QVariant>

#include <chrono>

/*!
    \namespace Utils::SettingsDatabase
    \inheaderfile utils/settingsdatabase.h
    \inmodule QtCreator

    \brief The SettingsDatabase namespace offers an alternative to the
    application-wide QSettings that is more
    suitable for storing large amounts of data.

    The settings database is SQLite based, and lazily retrieves data when it
    is asked for. It also does incremental updates of the database rather than
    rewriting the whole file each time one of the settings change.

    The SettingsDatabase API mimics that of QSettings.

    \sa settings()
*/

namespace Utils::SettingsDatabase {

enum { debug_settings = 0 };

using SettingsMap = QMap<QString, QVariant>;
using LastUsageMap = QMap<QString, std::chrono::system_clock::time_point>;

class SettingsDatabaseImpl
{
public:
    QString effectiveGroup() const
    {
        return m_groups.join(QString(QLatin1Char('/')));
    }

    QString effectiveKey(const QString &key) const
    {
        QString g = effectiveGroup();
        if (!g.isEmpty() && !key.isEmpty())
            g += QLatin1Char('/');
        g += key;
        return g;
    }

    SettingsMap m_settings;
    LastUsageMap m_lastUsage;

    QStringList m_groups;

    QSqlDatabase m_db;
};

static SettingsDatabaseImpl *d;

void ensureImpl()
{
    if (d)
        return;

    d = new SettingsDatabaseImpl;

    const QString path = QFileInfo(Utils::userSettings().fileName()).path();
    const QString application =  QCoreApplication::applicationName();
    const QLatin1Char slash('/');

    // TODO: Don't rely on a path, but determine automatically
    QDir pathDir(path);
    if (!pathDir.exists())
        pathDir.mkpath(pathDir.absolutePath());

    QString fileName = path;
    if (!fileName.endsWith(slash))
        fileName += slash;
    fileName += application;
    fileName += QLatin1String(".db");

    d->m_db = QSqlDatabase::addDatabase(QLatin1String("QSQLITE"), QLatin1String("settings"));
    d->m_db.setDatabaseName(fileName);
    if (!d->m_db.open()) {
        qWarning().nospace() << "Warning: Failed to open settings database at " << fileName << " ("
                             << d->m_db.lastError().driverText() << ")";
    } else {
        // Create the settings table if it doesn't exist yet
        QSqlQuery query(d->m_db);
        query.prepare(QLatin1String("CREATE TABLE IF NOT EXISTS settings ("
                                    "key PRIMARY KEY ON CONFLICT REPLACE, "
                                    "value)"));
        if (!query.exec())
            qWarning().nospace() << "Warning: Failed to prepare settings database! ("
                                 << query.lastError().driverText() << ")";

        // Retrieve all available keys (values are retrieved lazily)
        if (query.exec(QLatin1String("SELECT key FROM settings"))) {
            while (query.next()) {
                d->m_settings.insert(query.value(0).toString(), QVariant());
            }
        }

        QVariantMap lastUsages = value("SettingsDataBaseLastUsages").toMap();
        for (auto it = d->m_settings.begin(); it != d->m_settings.constEnd(); ++it) {
            auto lastUsageIt = lastUsages.find(it.key());
            std::chrono::system_clock::time_point lastUsage;
            if (lastUsageIt != lastUsages.end())
                lastUsage = std::chrono::system_clock::from_time_t(lastUsageIt.value().toLongLong());
            else
                lastUsage = std::chrono::system_clock::now();
            d->m_lastUsage.insert(it.key(), lastUsage);
        }

        // syncing can be slow, especially on Linux and Windows
        d->m_db.exec(QLatin1String("PRAGMA synchronous = OFF;"));
    }
}

void destroy()
{
    if (!d)
        return;

    // TODO: Delay writing of dirty keys and save them here

    QVariantMap lastUsages;
    const std::chrono::system_clock::time_point now = std::chrono::system_clock::now();
    for (auto it = d->m_lastUsage.begin(); it != d->m_lastUsage.end(); ++it) {
        if (now - it.value() > std::chrono::months(1))
            remove(it.key());
        else
            lastUsages.insert(it.key(), static_cast<qint64>(std::chrono::system_clock::to_time_t(it.value())));
    }
    setValue("SettingsDataBaseLastUsages", lastUsages);

    delete d;
    d = nullptr;
    QSqlDatabase::removeDatabase(QLatin1String("settings"));
}

void setValue(const QString &key, const QVariant &value)
{
    ensureImpl();
    const QString effectiveKey = d->effectiveKey(key);

    // Add to cache
    d->m_settings.insert(effectiveKey, value);
    d->m_lastUsage.insert(effectiveKey, std::chrono::system_clock::now());

    if (!d->m_db.isOpen())
        return;

    // Instant apply (TODO: Delay writing out settings)
    QSqlQuery query(d->m_db);
    query.prepare(QLatin1String("INSERT INTO settings VALUES (?, ?)"));
    query.addBindValue(effectiveKey);
    query.addBindValue(value);
    query.exec();

    if (debug_settings)
        qDebug() << "Stored:" << effectiveKey << "=" << value;
}

QVariant value(const QString &key, const QVariant &defaultValue)
{
    ensureImpl();
    const QString effectiveKey = d->effectiveKey(key);
    QVariant value = defaultValue;

    SettingsMap::const_iterator i = d->m_settings.constFind(effectiveKey);
    if (i != d->m_settings.constEnd() && i.value().isValid()) {
        value = i.value();
    } else if (d->m_db.isOpen()) {
        // Try to read the value from the database
        QSqlQuery query(d->m_db);
        query.prepare(QLatin1String("SELECT value FROM settings WHERE key = ?"));
        query.addBindValue(effectiveKey);
        query.exec();
        if (query.next()) {
            value = query.value(0);

            if (debug_settings)
                qDebug() << "Retrieved:" << effectiveKey << "=" << value;
        }

        // Cache the result
        d->m_settings.insert(effectiveKey, value);
    }

    d->m_lastUsage.insert(effectiveKey, std::chrono::system_clock::now());
    return value;
}

bool contains(const QString &key)
{
    ensureImpl();
    // check exact key
    // this already caches the value
    if (value(key).isValid())
        return true;
    // check for group
    if (d->m_db.isOpen()) {
        const QString glob = d->effectiveKey(key) + "/?*";
        QSqlQuery query(d->m_db);
        query.prepare(
            QLatin1String("SELECT value FROM settings WHERE key GLOB '%1' LIMIT 1").arg(glob));
        query.exec();
        if (query.next())
            return true;
    }
    return false;
}

void remove(const QString &key)
{
    ensureImpl();
    const QString effectiveKey = d->effectiveKey(key);

    // Remove keys from the cache
    for (auto it = d->m_settings.cbegin(); it != d->m_settings.cend(); ) {
        // Either it's an exact match, or it matches up to a /
        const QString k = it.key();
        if (k.startsWith(effectiveKey)
            && (k.size() == effectiveKey.size()
                || k.at(effectiveKey.size()) == QLatin1Char('/'))) {
            it = d->m_settings.erase(it);
        } else {
            ++it;
        }
    }

    if (!d->m_db.isOpen())
        return;

    // Delete keys from the database
    QSqlQuery query(d->m_db);
    query.prepare(QLatin1String("DELETE FROM settings WHERE key = ? OR key LIKE ?"));
    query.addBindValue(effectiveKey);
    query.addBindValue(QString(effectiveKey + QLatin1String("/%")));
    query.exec();
}

void beginGroup(const QString &prefix)
{
    ensureImpl();
    d->m_groups.append(prefix);
}

void endGroup()
{
    ensureImpl();
    d->m_groups.removeLast();
}

QString group()
{
    ensureImpl();
    return d->effectiveGroup();
}

QStringList childKeys()
{
    ensureImpl();
    QStringList children;

    const QString g = group();
    for (auto i = d->m_settings.cbegin(), end = d->m_settings.cend(); i != end; ++i) {
        const QString &key = i.key();
        if (key.startsWith(g) && key.indexOf(QLatin1Char('/'), g.size() + 1) == -1)
            children.append(key.mid(g.size() + 1));
    }

    return children;
}

void beginTransaction()
{
    ensureImpl();
    if (!d->m_db.isOpen())
        return;
    d->m_db.transaction();
}

void endTransaction()
{
    ensureImpl();
    if (!d->m_db.isOpen())
        return;
    d->m_db.commit();
}

} // Utils::SettingsDatabase