// globals.cxx -- Global state that needs to be shared among the sim modules
//
// Written by Curtis Olson, started July 2000.
//
// SPDX-FileCopyrightText: 2000 Curtis L. Olson
// SPDX-License-Identifier: GPL-2.0-or-later

#include <config.h>

#include <algorithm>

#include <osgDB/Registry>
#include <osgViewer/Viewer>

#include <simgear/ephemeris/ephemeris.hxx>
#include <simgear/misc/sg_dir.hxx>
#include <simgear/misc/sg_path.hxx>
#include <simgear/structure/commands.hxx>
#include <simgear/structure/event_mgr.hxx>
#include <simgear/structure/exception.hxx>
#include <simgear/structure/subsystem_mgr.hxx>
#include <simgear/timing/sg_time.hxx>

#include <simgear/misc/ResourceManager.hxx>
#include <simgear/package/Root.hxx>
#include <simgear/props/AtomicChangeListener.hxx>
#include <simgear/props/propertyObject.hxx>
#include <simgear/props/props_io.hxx>
#include <simgear/scene/model/modellib.hxx>

#include <Add-ons/AddonResourceProvider.hxx>
#include <Aircraft/controls.hxx>
#include <Airports/runways.hxx>
#include <Autopilot/route_mgr.hxx>
#include <Navaids/navlist.hxx>

#include <GUI/gui.h>
#include <Main/sentryIntegration.hxx>
#include <Viewer/viewmgr.hxx>

#include <GUI/MessageBox.hxx>
#include <Scenery/scenery.hxx>
#include <Scenery/tilemgr.hxx>
#include <Viewer/VRManager.hxx>
#include <Viewer/renderer.hxx>

#include <simgear/scene/material/matlib.hxx>
#include <simgear/sound/soundmgr.hxx>

#include "globals.hxx"
#include "locale.hxx"

#include "fg_props.hxx"

class AircraftResourceProvider : public simgear::ResourceProvider
{
public:
    AircraftResourceProvider() : simgear::ResourceProvider(simgear::ResourceManager::PRIORITY_HIGH)
    {
    }

    virtual SGPath resolve(const std::string& aResource, SGPath&) const override
    {
        string_list pieces(sgPathBranchSplit(aResource));
        if ((pieces.size() < 3) || (pieces.front() != "Aircraft")) {
            return SGPath(); // not an Aircraft path
        }

        // test against the aircraft-dir property
        const std::string aircraftDir = fgGetString("/sim/aircraft-dir");
        string_list aircraftDirPieces(sgPathBranchSplit(aircraftDir));
        if (!aircraftDirPieces.empty() && (aircraftDirPieces.back() == pieces[1])) {
            // current aircraft-dir matches resource aircraft
            SGPath r(aircraftDir);
            for (unsigned int i = 2; i < pieces.size(); ++i) {
                r.append(pieces[i]);
            }

            if (r.exists()) {
                return r;
            } else {
                // Stop here, otherwise we could end up returning a resource that
                // belongs to an unrelated version of the same aircraft (from a
                // different aircraft directory).
                return SGPath();
            }
        }

        // try each aircraft dir in turn
        std::string res(aResource, 9); // resource path with 'Aircraft/' removed
        const PathList& dirs(globals->get_aircraft_paths());
        PathList::const_iterator it = dirs.begin();
        for (; it != dirs.end(); ++it) {
            SGPath p(*it);
            p.append(res);
            if (p.exists()) {
                return p;
            }
        } // of aircraft path iteration

        return SGPath(); // not found
    }

    virtual std::vector<SGPath> findAllOfType(simgear::ResourceManager::FileType type) const override
    {
        std::vector<SGPath> paths;
        for (const SGPath& path : globals->get_aircraft_paths()) {
            findAllOfTypeHelper(path, type, paths);
        }
        return paths;
    }
};

class CurrentAircraftDirProvider : public simgear::ResourceProvider
{
public:
    CurrentAircraftDirProvider() : simgear::ResourceProvider(simgear::ResourceManager::PRIORITY_HIGH)
    {
    }

    virtual SGPath resolve(const std::string& aResource, SGPath&) const override
    {
        SGPath p = SGPath::fromUtf8(fgGetString("/sim/aircraft-dir"));
        p.append(aResource);
        return p.exists() ? p : SGPath();
    }

    virtual std::vector<SGPath> findAllOfType(simgear::ResourceManager::FileType type) const override
    {
        std::vector<SGPath> paths;
        findAllOfTypeHelper(SGPath::fromUtf8(fgGetString("/sim/aircraft-dir")), type, paths);
        return paths;
    }
};

////////////////////////////////////////////////////////////////////////
// Implementation of FGGlobals.
////////////////////////////////////////////////////////////////////////

// global global :-)
FGGlobals* globals = NULL;


// Constructor
FGGlobals::FGGlobals() : renderer(NULL),
                         subsystem_mgr(new SGSubsystemMgr),
                         event_mgr(new SGEventMgr),
                         sim_time_sec(0.0),
                         time_params(NULL),
                         commands(SGCommandMgr::instance()),
                         channel_options_list(NULL),
                         initial_waypoints(NULL),
                         channellist(NULL),
                         haveUserSettings(false)
{
    SGPropertyNode* root = new SGPropertyNode;
    props = SGPropertyNode_ptr(root);
    locale = new FGLocale(props);

    auto resMgr = simgear::ResourceManager::instance();
    resMgr->addProvider(new AircraftResourceProvider());
    resMgr->addProvider(new CurrentAircraftDirProvider());
    resMgr->addProvider(new flightgear::addons::ResourceProvider());
    initProperties();
}

void FGGlobals::initProperties()
{
    simgear::PropertyObjectBase::setDefaultRoot(props);

    positionLon = props->getNode("position/longitude-deg", true);
    positionLat = props->getNode("position/latitude-deg", true);
    positionAlt = props->getNode("position/altitude-ft", true);

    viewLon = props->getNode("sim/current-view/viewer-lon-deg", true);
    viewLat = props->getNode("sim/current-view/viewer-lat-deg", true);
    viewAlt = props->getNode("sim/current-view/viewer-elev-ft", true);

    referenceOffsetX = props->getNode("sim/model/reference-offset-x", true);
    referenceOffsetY = props->getNode("sim/model/reference-offset-y", true);
    referenceOffsetZ = props->getNode("sim/model/reference-offset-z", true);

    orientPitch = props->getNode("orientation/pitch-deg", true);
    orientHeading = props->getNode("orientation/heading-deg", true);
    orientRoll = props->getNode("orientation/roll-deg", true);
}

// Destructor
FGGlobals::~FGGlobals()
{
    // save user settings (unless already saved)
    saveUserSettings();

    // stop OSG threading first, to avoid thread races while we tear down
    // scene-graph pieces
    // there are some scenarios where renderer is already gone.
    if (renderer) {
        osgViewer::ViewerBase* vb = renderer->getViewerBase();
        if (vb) {
            // https://code.google.com/p/flightgear-bugs/issues/detail?id=1291
            // explicitly stop trheading before we delete the renderer or
            // viewMgr (which ultimately holds refs to the CameraGroup, and
            // GraphicsContext)
            vb->stopThreading();
        }
    }

    subsystem_mgr->shutdown();
#ifdef ENABLE_OSGXR
    flightgear::VRManager::destroyInstance();
#endif
    subsystem_mgr->unbind();

    // don't cancel the pager until after shutdown, since AIModels (and
    // potentially others) can queue delete requests on the pager.
    if (renderer) {
        osgViewer::View* v = renderer->getView();
        if (v && v->getDatabasePager()) {
            v->getDatabasePager()->cancel();
            v->getDatabasePager()->clear();
        }
    }

    osgDB::Registry::instance()->clearObjectCache();
    if (subsystem_mgr->get_subsystem(FGScenery::staticSubsystemClassId())) {
        subsystem_mgr->remove(FGScenery::staticSubsystemClassId());
    }

    // renderer touches subsystems during its destruction
    set_renderer(nullptr);

    fgCancelSnapShot();

    delete subsystem_mgr;
    subsystem_mgr = nullptr; // important so ::get_subsystem returns NULL
    set_matlib(NULL);

    delete time_params;
    delete channel_options_list;
    delete initial_waypoints;
    delete channellist;

    // delete commands before we release the property root
    // this avoids crash where commands might be storing a property
    // ref/pointer.
    // see https://sentry.io/organizations/flightgear/issues/1890563449
    delete commands;
    commands = nullptr;

    simgear::PropertyObjectBase::setDefaultRoot(NULL);
    simgear::SGModelLib::resetPropertyRoot();
    delete locale;
    locale = NULL;

    cleanupListeners();

    props.clear();

    delete simgear::ResourceManager::instance();
}

// set the fg_root path
void FGGlobals::set_fg_root(const SGPath& root)
{
    SGPath tmp(root);
    fg_root = tmp.realpath();

    // append /data to root if it exists
    tmp.append("data");
    tmp.append("version");
    if (tmp.exists()) {
        fgGetNode("BAD_FG_ROOT", true)->setStringValue(fg_root.utf8Str());
        fg_root.append("data");
        fgGetNode("GOOD_FG_ROOT", true)->setStringValue(fg_root.utf8Str());
        SG_LOG(SG_GENERAL, SG_ALERT, "***\n***\n*** Warning: changing bad FG_ROOT/--fg-root to '" << fg_root << "'\n***\n***");
    }

    // deliberately not a tied property, for SGPath::validate() security
    // write-protect to avoid accidents
    SGPropertyNode* n = fgGetNode("/sim", true);
    n->removeChild("fg-root", 0);
    n = n->getChild("fg-root", 0, true);
    n->setStringValue(fg_root.utf8Str());
    n->setAttribute(SGPropertyNode::WRITE, false);

    simgear::ResourceManager::instance()->addBasePath(fg_root,
                                                      simgear::ResourceManager::PRIORITY_DEFAULT);
}

// set the fg_home path
void FGGlobals::set_fg_home(const SGPath& home)
{
    fg_home = home.realpath();
}

void FGGlobals::set_texture_cache_dir(const SGPath& textureCache)
{
    texture_cache_dir = textureCache.realpath();
    auto node = fgGetNode("/sim/rendering/texture-cache/dir", true);
    node->setAttribute(SGPropertyNode::WRITE, true);
    node->setStringValue(textureCache.utf8Str());
    node->setAttribute(SGPropertyNode::WRITE, false);
}


PathList FGGlobals::get_data_paths() const
{
    PathList r(additional_data_paths);
    r.push_back(fg_root);
    r.insert(r.end(), _dataPathsAfterFGRoot.begin(), _dataPathsAfterFGRoot.end());
    return r;
}

PathList FGGlobals::get_data_paths(const std::string& suffix) const
{
    PathList r;
    for (SGPath p : get_data_paths()) {
        p.append(suffix);
        if (p.exists()) {
            r.push_back(p);
        }
    }

    return r;
}

void FGGlobals::append_data_path(const SGPath& path, bool afterFGRoot)
{
    if (path.isNull()) {
        return;
    }

    if (!path.exists()) {
        SG_LOG(SG_GENERAL, SG_WARN, "adding non-existent data path:" << path);
    }

    using RM = simgear::ResourceManager;
    auto resManager = RM::instance();
    if (afterFGRoot) {
        _dataPathsAfterFGRoot.push_back(path);
        // after FG_ROOT
        resManager->addBasePath(path, static_cast<RM::Priority>(RM::PRIORITY_DEFAULT - 10));
    } else {
        additional_data_paths.push_back(path);
        // after NORMAL priority, but ahead of FG_ROOT
        resManager->addBasePath(path, static_cast<RM::Priority>(RM::PRIORITY_DEFAULT + 10));
    }
}

SGPath FGGlobals::findDataPath(const std::string& pathSuffix) const
{
    for (SGPath p : additional_data_paths) {
        p.append(pathSuffix);
        if (p.exists()) {
            return p;
        }
    }

    SGPath rootPath(fg_root);
    rootPath.append(pathSuffix);
    if (rootPath.exists()) {
        return rootPath;
    }

    for (SGPath p : _dataPathsAfterFGRoot) {
        p.append(pathSuffix);
        if (p.exists()) {
            return p;
        }
    }

    return SGPath{};
}

void FGGlobals::append_fg_scenery(const PathList& paths)
{
    for (const SGPath& path : paths) {
        append_fg_scenery(path);
    }
}

void FGGlobals::append_fg_scenery(const SGPath& path)
{
    SGPropertyNode* sim = fgGetNode("/sim", true);

    // find first unused fg-scenery property in /sim
    int propIndex = 0;
    while (sim->getChild("fg-scenery", propIndex) != NULL) {
        ++propIndex;
    }

    SGPath abspath(path.realpath());
    if (!abspath.exists()) {
        SG_LOG(SG_GENERAL, SG_WARN, "scenery path not found:" << abspath);
        return;
    }

    // check for duplicates
    PathList::const_iterator ex = std::find(fg_scenery.begin(), fg_scenery.end(), abspath);
    if (ex != fg_scenery.end()) {
        SG_LOG(SG_GENERAL, SG_INFO, "skipping duplicate add of scenery path:" << abspath);
        return;
    }

    // tell the ResourceManager about the scenery path
    // needed to load Models from this scenery path
    simgear::ResourceManager::instance()->addBasePath(abspath, simgear::ResourceManager::PRIORITY_DEFAULT);

    fg_scenery.push_back(abspath);
    extra_read_allowed_paths.push_back(abspath);

    // make scenery dirs available to Nasal
    SGPropertyNode* n = sim->getChild("fg-scenery", propIndex++, true);
    n->setStringValue(abspath.utf8Str());
    n->setAttribute(SGPropertyNode::WRITE, false);

    // temporary fix so these values survive reset
    n->setAttribute(SGPropertyNode::PRESERVE, true);

    // Add any sources.xml file to the property tree so we can provide attribution through the GUI
    SGPath sources = SGPath(abspath);
    sources.append("sources.xml");
    SG_LOG(SG_TERRAIN, SG_DEBUG, "Looking for source file " << sources << ". Exists ? " << sources.exists());
    if (sources.exists()) {
        // Determine the next free indice under /scenery/sources
        SGPropertyNode* sourcesProp = fgGetNode("/scenery/sources", true);
        int propIndex = 0;
        while (sourcesProp->getChild("directory", propIndex) != NULL) {
            ++propIndex;
        }

        sourcesProp = sourcesProp->getChild("directory", propIndex++, true);

        // Add a reference to the path itself
        sourcesProp->setStringValue("path", abspath.utf8Str());

        // Now load the sources file into /scenery/sources/source[n]
        if (!fgLoadProps(sources.utf8Str(), sourcesProp, false)) {
            SG_LOG(SG_TERRAIN, SG_ALERT, "Unable to load sources file " << sources.utf8Str());
        }

        // Ensure these properties cannot be over-ridden, and preserve them across a reset.
        sourcesProp->setAttribute(SGPropertyNode::WRITE, false);
        sourcesProp->setAttribute(SGPropertyNode::PRESERVE, true);
    }
}

void FGGlobals::append_read_allowed_paths(const SGPath& path)
{
    SGPath abspath(path.realpath());
    if (!abspath.exists()) {
        SG_LOG(SG_IO, SG_DEBUG, "read-allowed path not found:" << abspath);
        return;
    }
    extra_read_allowed_paths.push_back(abspath);
}

void FGGlobals::clear_fg_scenery()
{
    fg_scenery.clear();
    fgGetNode("/sim", true)->removeChildren("fg-scenery");
}

// The 'path' argument to this method must come from trustworthy code, because
// the method grants read permissions to Nasal code for many files beneath
// 'path'. In particular, don't call this method with a 'path' value taken
// from the property tree or any other Nasal-writable place.
void FGGlobals::set_download_dir(const SGPath& path)
{
    SGPath abspath(path.realpath());
    download_dir = abspath;

    append_read_allowed_paths(abspath / "Aircraft");
    append_read_allowed_paths(abspath / "AI");
    append_read_allowed_paths(abspath / "Liveries");
    // If in use, abspath / TerraSync will be added to 'extra_read_allowed_paths'
    // by FGGlobals::append_fg_scenery(), as any scenery path.

    SGPropertyNode* n = fgGetNode("/sim/paths/download-dir", true);
    n->setAttribute(SGPropertyNode::WRITE, true);
    n->setStringValue(abspath.utf8Str());
    n->setAttribute(SGPropertyNode::WRITE, false);
}

// The 'path' argument to this method must come from trustworthy code, because
// the method grants read permissions to Nasal code for all files beneath
// 'path'. In particular, don't call this method with a 'path' value taken
// from the property tree or any other Nasal-writable place.
void FGGlobals::set_terrasync_dir(const SGPath& path)
{
    if (terrasync_dir.realpath() != SGPath(fgGetString("/sim/terrasync/scenery-dir")).realpath()) {
        // if they don't match, /sim/terrasync/scenery-dir has been set by something else
        SG_LOG(SG_GENERAL, SG_WARN, "/sim/terrasync/scenery-dir is no longer stored across runs: if you wish to keep using a non-standard Terrasync directory, use --terrasync-dir or the launcher's settings");
    }
    SGPath abspath(path.realpath());
    terrasync_dir = abspath;
    // deliberately not a tied property, for SGPath::validate() security
    // write-protect to avoid accidents
    SGPropertyNode* n = fgGetNode("/sim/terrasync/scenery-dir", true);
    n->setAttribute(SGPropertyNode::WRITE, true);
    n->setStringValue(abspath.utf8Str());
    n->setAttribute(SGPropertyNode::WRITE, false);
    // don't add it to fg_scenery yet, as we want it ordered after explicit --fg-scenery
}


void FGGlobals::set_catalog_aircraft_path(const SGPath& path)
{
    catalog_aircraft_dir = path;
}

PathList FGGlobals::get_aircraft_paths() const
{
    PathList r;
    if (!catalog_aircraft_dir.isNull()) {
        r.push_back(catalog_aircraft_dir);
    }

    r.insert(r.end(), fg_aircraft_dirs.begin(), fg_aircraft_dirs.end());
    return r;
}

void FGGlobals::append_aircraft_path(const SGPath& path)
{
    SGPath dirPath(path);
    if (!dirPath.exists()) {
        SG_LOG(SG_GENERAL, SG_WARN, "aircraft path not found:" << path);
        return;
    }

    SGPath acSubdir(dirPath);
    acSubdir.append("Aircraft");
    if (acSubdir.exists()) {
        SG_LOG(
            SG_GENERAL,
            SG_WARN,
            "Specified an aircraft-dir with an 'Aircraft' subdirectory:" << dirPath
                                                                         << ", will instead use child directory:" << acSubdir);
        dirPath = acSubdir;
    }

    fg_aircraft_dirs.push_back(dirPath.realpath());
    extra_read_allowed_paths.push_back(dirPath.realpath());
}

void FGGlobals::append_aircraft_paths(const PathList& paths)
{
    for (unsigned int p = 0; p < paths.size(); ++p) {
        append_aircraft_path(paths[p]);
    }
}

SGPath FGGlobals::resolve_aircraft_path(const std::string& branch) const
{
    return simgear::ResourceManager::instance()->findPath(branch);
}

SGPath FGGlobals::resolve_maybe_aircraft_path(const std::string& branch) const
{
    return simgear::ResourceManager::instance()->findPath(branch);
}

SGPath FGGlobals::resolve_resource_path(const std::string& branch) const
{
    return simgear::ResourceManager::instance()
        ->findPath(branch, SGPath(fgGetString("/sim/aircraft-dir")));
}

FGRenderer*
FGGlobals::get_renderer() const
{
    return renderer;
}

void FGGlobals::set_renderer(FGRenderer* render)
{
    if (render == renderer) {
        return;
    }
    if (renderer) {
        delete renderer;
    }
    renderer = render;
}

SGSubsystemMgr*
FGGlobals::get_subsystem_mgr() const
{
    return subsystem_mgr;
}

SGSubsystem*
FGGlobals::get_subsystem(const char* name) const
{
    if (!subsystem_mgr) {
        return NULL;
    }

    return subsystem_mgr->get_subsystem(name);
}

SGEventMgr*
FGGlobals::get_event_mgr() const
{
    return event_mgr;
}

SGGeod
FGGlobals::get_aircraft_position() const
{
    return SGGeod::fromDegFt(positionLon->getDoubleValue(),
                             positionLat->getDoubleValue(),
                             positionAlt->getDoubleValue());
}

SGVec3d
FGGlobals::get_aircraft_position_cart() const
{
    return SGVec3d::fromGeod(get_aircraft_position());
}

void FGGlobals::get_aircraft_orientation(double& heading, double& pitch, double& roll)
{
    heading = orientHeading->getDoubleValue();
    pitch = orientPitch->getDoubleValue();
    roll = orientRoll->getDoubleValue();
}

SGGeod
FGGlobals::get_view_position() const
{
    return SGGeod::fromDegFt(viewLon->getDoubleValue(),
                             viewLat->getDoubleValue(),
                             viewAlt->getDoubleValue());
}

SGVec3d
FGGlobals::get_view_position_cart() const
{
    return SGVec3d::fromGeod(get_view_position());
}
SGVec3d FGGlobals::get_ownship_reference_position_cart() const
{
    SGVec3d pos = get_aircraft_position_cart();

    if (referenceOffsetX)
        pos[0] += referenceOffsetX->getDoubleValue();

    if (referenceOffsetY)
        pos[1] += referenceOffsetY->getDoubleValue();

    if (referenceOffsetZ)
        pos[2] += referenceOffsetZ->getDoubleValue();

    return pos;
}

static void treeDumpRefCounts(int depth, SGPropertyNode* n)
{
    for (int i = 0; i < n->nChildren(); ++i) {
        SGPropertyNode* cp = n->getChild(i);
        if (SGReferenced::count(cp) > 1) {
            SG_LOG(SG_GENERAL, SG_INFO, "\t" << cp->getPath() << " refcount:" << SGReferenced::count(cp));
        }

        treeDumpRefCounts(depth + 1, cp);
    }
}

static void treeClearAliases(SGPropertyNode* n)
{
    if (n->isAlias()) {
        n->unalias();
    }

    for (int i = 0; i < n->nChildren(); ++i) {
        SGPropertyNode* cp = n->getChild(i);
        treeClearAliases(cp);
    }
}

void FGGlobals::resetPropertyRoot()
{
    delete locale;

    // avoid a warning when we processOptions after reset
    terrasync_dir = SGPath{};

    cleanupListeners();

    // we don't strictly need to clear these (they will be reset when we
    // initProperties again), but trying to reduce false-positives when dumping
    // ref-counts.
    positionLon.clear();
    positionLat.clear();
    positionAlt.clear();
    viewLon.clear();
    viewLat.clear();
    viewAlt.clear();
    orientPitch.clear();
    orientHeading.clear();
    orientRoll.clear();

    // clear aliases so ref-counts are accurate when dumped
    treeClearAliases(props);

    SG_LOG(SG_GENERAL, SG_INFO, "root props refcount:" << props.getNumRefs());
    treeDumpRefCounts(0, props);

    //BaseStackSnapshot::dumpAll(std::cout);

    props = new SGPropertyNode;
    initProperties();
    locale = new FGLocale(props);

    // remove /sim/fg-root before writing to prevent hijacking
    SGPropertyNode* n = props->getNode("/sim", true);
    n->removeChild("fg-root", 0);
    n = n->getChild("fg-root", 0, true);
    n->setStringValue(fg_root.utf8Str());
    n->setAttribute(SGPropertyNode::WRITE, false);
}

static std::string autosaveName()
{
    std::ostringstream os;
    string_list versionParts = simgear::strutils::split(VERSION, ".");
    if (versionParts.size() < 2) {
        return "autosave.xml";
    }

    os << "autosave_" << versionParts[0] << "_" << versionParts[1] << ".xml";
    return os.str();
}

SGPath FGGlobals::autosaveFilePath(SGPath userDataPath) const
{
    if (userDataPath.isNull()) {
        userDataPath = get_fg_home();
    }

    return simgear::Dir(userDataPath).file(autosaveName());
}

static void deleteProperties(SGPropertyNode* props, const string_list& blacklist)
{
    const std::string path(props->getPath());
    auto it = std::find_if(blacklist.begin(), blacklist.end(), [path](const std::string& black) { return simgear::strutils::matchPropPathToTemplate(path, black); });
    if (it != blacklist.end()) {
        SGPropertyNode* pr = props->getParent();
        pr->removeChild(props);
        return;
    }

    // recurse
    for (int c = 0; c < props->nChildren(); ++c) {
        deleteProperties(props->getChild(c), blacklist);
    }
}

using VersionPair = std::pair<int, int>;

static bool operator<(const VersionPair& a, const VersionPair& b)
{
    if (a.first == b.first) {
        return a.second < b.second;
    }

    return a.first < b.first;
}

static void tryAutosaveMigration(const SGPath& userDataPath, SGPropertyNode* props)
{
    const string_list versionParts = simgear::strutils::split(VERSION, ".");
    if (versionParts.size() < 2) {
        return;
    }

    simgear::Dir userDataDir(userDataPath);
    SGPath migratePath;
    VersionPair foundVersion(0, 0);
    const VersionPair currentVersion(simgear::strutils::to_int(versionParts[0]),
                                     simgear::strutils::to_int(versionParts[1]));

    for (auto previousSave : userDataDir.children(simgear::Dir::TYPE_FILE, ".xml")) {
        const std::string base = previousSave.file_base();
        VersionPair v;
        // extract version from name
        const int matches = ::sscanf(base.c_str(), "autosave_%d_%d", &v.first, &v.second);
        if (matches != 2) {
            continue;
        }

        if (currentVersion < v) {
            // ignore autosaves from more recent versions; this happens when
            // running unstable and stable at the same time
            continue;
        }

        if (v.first < 2000) {
            // ignore autosaves from older versions, too much change to deal
            // with.
            continue;
        }

        if (foundVersion < v) {
            foundVersion = v;
            migratePath = previousSave;
        }
    }

    if (!migratePath.exists()) {
        return;
    }

    SG_LOG(SG_GENERAL, SG_INFO, "Migrating old autosave:" << migratePath);
    SGPropertyNode oldProps;

    try {
        readProperties(migratePath, &oldProps, SGPropertyNode::USERARCHIVE);
    } catch (sg_exception& e) {
        SG_LOG(SG_GENERAL, SG_WARN, "failed to read previous user settings:" << e.getMessage() << "(from " << e.getOrigin() << ")");
        return;
    }

    // read migration blacklist
    string_list blacklist;
    SGPropertyNode_ptr blacklistNode = fgGetNode("/sim/autosave-migration/blacklist", true);
    for (auto node : blacklistNode->getChildren("path")) {
        blacklist.push_back(node->getStringValue());
    }

    // apply migration filters for each property in turn
    deleteProperties(&oldProps, blacklist);

    // manual migrations
    // migrate pre-2019.1 sense of /sim/mouse/invert-mouse-wheel
    if (foundVersion.first < 2019) {
        SGPropertyNode_ptr wheelNode = oldProps.getNode("/sim/mouse/invert-mouse-wheel");
        if (wheelNode) {
            wheelNode->setBoolValue(!wheelNode->getBoolValue());
        }
    }
    // copy remaining props out
    copyProperties(&oldProps, props);

    // we can't inform the user yet, because embedded resources and the locale
    // are not done. So we set a flag and check it once those things are done.
    fgSetBool("/sim/autosave-migration/did-migrate", true);
}

// Load user settings from the autosave file (normally in $FG_HOME)
void FGGlobals::loadUserSettings(SGPath userDataPath)
{
    if (userDataPath.isNull()) {
        userDataPath = get_fg_home();
    }

    // Remember that we have (tried) to load any existing autosave file
    haveUserSettings = true;

    SGPath autosaveFile = autosaveFilePath(userDataPath);
    SGPropertyNode autosave;
    if (autosaveFile.exists()) {
        SG_LOG(SG_INPUT, SG_INFO,
               "Reading user settings from " << autosaveFile);
        try {
            readProperties(autosaveFile, &autosave, SGPropertyNode::USERARCHIVE);
        } catch (sg_exception& e) {
            SG_LOG(SG_INPUT, SG_WARN, "failed to read user settings:" << e.getMessage() << "(from " << e.getOrigin() << ")");
        }
    } else {
        tryAutosaveMigration(userDataPath, &autosave);
    }
    /* Before 2020-03-10, we could save portions of the /ai/models/ tree, which
    confuses things when loaded again. So delete any such items if they have
    been loaded. */
    SGPropertyNode* ai = autosave.getNode("ai");
    if (ai) {
        ai->removeChildren("models");
    }
    copyProperties(&autosave, globals->get_props());
}

// Save user settings to the autosave file.
//
// When calling this method, make sure the value of 'userDataPath' is
// trustworthy. In particular, make sure it can't be influenced by Nasal code,
// not even indirectly via a Nasal-writable place such as the property tree.
//
// Note: the default value, which causes the autosave file to be written to
//       $FG_HOME, is safe---if not, it would be a bug.
void FGGlobals::saveUserSettings(SGPath userDataPath)
{
    if (userDataPath.isNull()) userDataPath = get_fg_home();

    // only save settings when we have (tried) to load the previous
    // settings (otherwise user data was lost)
    if (!haveUserSettings)
        return;

    if (fgGetBool("/sim/startup/save-on-exit")) {
        // don't save settings more than once on shutdown
        haveUserSettings = false;

        SGPath autosaveFile = autosaveFilePath(userDataPath);
        autosaveFile.create_dir(0700);

        SGPath tmpFile = autosaveFile.dirPath() / "autosave.tmp";
        SG_LOG(SG_IO, SG_DEBUG, "Saving user settings to " << tmpFile);
        try {
            writeProperties(tmpFile, globals->get_props(), false, SGPropertyNode::USERARCHIVE);
            tmpFile.rename(autosaveFile);
            SG_LOG(SG_IO, SG_INFO, "Saved user settings to " << autosaveFile);
        } catch (const sg_exception& e) {
            guiErrorMessage("Error writing autosave:", e);
        }
    }
}

long int FGGlobals::get_warp() const
{
    return fgGetInt("/sim/time/warp");
}

void FGGlobals::set_warp(long int w)
{
    fgSetInt("/sim/time/warp", w);
}

long int FGGlobals::get_warp_delta() const
{
    return fgGetInt("/sim/time/warp-delta");
}

void FGGlobals::set_warp_delta(long int d)
{
    fgSetInt("/sim/time/warp-delta", d);
}

FGScenery* FGGlobals::get_scenery() const
{
    return subsystem_mgr->get_subsystem<FGScenery>();
}

FGViewMgr* FGGlobals::get_viewmgr() const
{
    return subsystem_mgr->get_subsystem<FGViewMgr>();
}

flightgear::View* FGGlobals::get_current_view() const
{
    FGViewMgr* vm = get_viewmgr();
    return vm ? vm->get_current_view() : 0;
}

void FGGlobals::set_matlib(SGMaterialLib* m)
{
    matlib = m;
}

FGControls* FGGlobals::get_controls() const
{
    return subsystem_mgr->get_subsystem<FGControls>();
}

void FGGlobals::addListenerToCleanup(SGPropertyChangeListener* l)
{
    _listeners_to_cleanup.push_back(l);
}

void FGGlobals::cleanupListeners()
{
    SGPropertyChangeListenerVec::iterator i = _listeners_to_cleanup.begin();
    for (; i != _listeners_to_cleanup.end(); ++i) {
        delete *i;
    }
    _listeners_to_cleanup.clear();

    simgear::AtomicChangeListener::clearPendingChanges();
}

simgear::pkg::Root* FGGlobals::packageRoot()
{
    return _packageRoot.get();
}

void FGGlobals::setPackageRoot(const SGSharedPtr<simgear::pkg::Root>& p)
{
    _packageRoot = p;
}

bool FGGlobals::is_headless()
{
    return flightgear::isHeadlessMode();
}

void FGGlobals::set_headless(bool mode)
{
    flightgear::setHeadlessMode(mode);
}

// end of globals.cxx
