// terrasync.cxx -- scenery fetcher
//
// Started by Curtis Olson, November 2002.
//
// Copyright (C) 2002  Curtis L. Olson  - http://www.flightgear.org/~curt
// Copyright (C) 2008  Alexander R. Perry <alex.perry@ieee.org>
// Copyright (C) 2011  Thorsten Brehm <brehmt@gmail.com>
//
// 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.
//
// $Id$

#ifdef HAVE_CONFIG_H
#  include <simgear_config.h>
#endif

#include <simgear/compiler.h>

#ifdef HAVE_WINDOWS_H
#include <windows.h>
#endif

#ifdef __MINGW32__
#  include <time.h>
#  include <unistd.h>
#elif defined(_MSC_VER)
#   include <io.h>
#   include <time.h>
#   include <process.h>
#endif

#include <stdlib.h>             // atoi() atof() abs() system()
#include <signal.h>             // signal()
#include <string.h>

#include <iostream>
#include <fstream>
#include <string>
#include <map>

#include <simgear/compiler.h>

#include "terrasync.hxx"

#include <simgear/bucket/newbucket.hxx>
#include <simgear/misc/sg_path.hxx>
#include <simgear/misc/strutils.hxx>
#include <simgear/threads/SGQueue.hxx>
#include <simgear/misc/sg_dir.hxx>
#include <simgear/debug/BufferedLogCallback.hxx>
#include <simgear/props/props_io.hxx>
#include <simgear/io/HTTPClient.hxx>
#include <simgear/io/SVNRepository.hxx>
#include <simgear/structure/exception.hxx>

static const bool svn_built_in_available = true;

using namespace simgear;
using namespace std;

const char* rsync_cmd = 
        "rsync --verbose --archive --delete --perms --owner --group";

const char* svn_options =
        "checkout -q";

namespace UpdateInterval
{
    // interval in seconds to allow an update to repeat after a successful update (=daily)
    static const double SuccessfulAttempt = 24*60*60;
    // interval in seconds to allow another update after a failed attempt (10 minutes)
    static const double FailedAttempt     = 10*60;
}

typedef map<string,time_t> CompletedTiles;

///////////////////////////////////////////////////////////////////////////////
// helper functions ///////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
string stripPath(string path)
{
    // svn doesn't like trailing white-spaces or path separators - strip them!
    path = simgear::strutils::strip(path);
    size_t slen = path.length();
    while ((slen>0)&&
            ((path[slen-1]=='/')||(path[slen-1]=='\\')))
    {
        slen--;
    }
    return path.substr(0,slen);
}

bool hasWhitespace(string path)
{
    return path.find(' ')!=string::npos;
}

///////////////////////////////////////////////////////////////////////////////
// SyncItem ////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
class SyncItem
{
public:
    enum Type
    {
        Stop = 0,   ///< special item indicating to stop the SVNThread
        Tile,
        AirportData,
        SharedModels,
        AIData
    };
    
    enum Status
    {
        Invalid = 0,
        Waiting,
        Cached, ///< using already cached result
        Updated,
        NotFound, 
        Failed
    };
    
    SyncItem() :
        _dir(),
        _type(Stop),
        _status(Invalid)
    {
    }
    
    SyncItem(string dir, Type ty) :
        _dir(dir),
        _type(ty),
        _status(Waiting)
    {}
        
    string _dir;
    Type _type;
    Status _status;
};

///////////////////////////////////////////////////////////////////////////////

/**
 * @brief SyncSlot encapsulates a queue of sync items we will fetch
 * serially. Multiple slots exist to sync different types of item in
 * parallel.
 */
class SyncSlot
{
public:
    SyncSlot() :
        isNewDirectory(false),
        busy(false)
    {}
    
    SyncItem currentItem;
    bool isNewDirectory;
    std::queue<SyncItem> queue;
    std::auto_ptr<SVNRepository> repository;
    SGTimeStamp stamp;
    bool busy; ///< is the slot working or idle
    
    unsigned int nextWarnTimeout;
};

static const int SYNC_SLOT_TILES = 0; ///< Terrain and Objects sync
static const int SYNC_SLOT_SHARED_DATA = 1; /// shared Models and Airport data
static const int SYNC_SLOT_AI_DATA = 2; /// AI traffic and models
static const unsigned int NUM_SYNC_SLOTS = 3;

/**
 * @brief translate a sync item type into one of the available slots.
 * This provides the scheduling / balancing / prioritising between slots.
 */
static unsigned int syncSlotForType(SyncItem::Type ty)
{
    switch (ty) {
    case SyncItem::Tile: return SYNC_SLOT_TILES;
    case SyncItem::SharedModels:
    case SyncItem::AirportData:
        return SYNC_SLOT_SHARED_DATA;
    case SyncItem::AIData:
        return SYNC_SLOT_AI_DATA;
        
    default:
        return SYNC_SLOT_SHARED_DATA;
    }
}


///////////////////////////////////////////////////////////////////////////////
// SGTerraSync::SvnThread /////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
class SGTerraSync::SvnThread : public SGThread
{
public:
   SvnThread();
   virtual ~SvnThread( ) { stop(); }

   void stop();
   bool start();

    bool isIdle() {return !_busy; }
   void request(const SyncItem& dir) {waitingTiles.push_front(dir);}
   bool isDirty() { bool r = _is_dirty;_is_dirty = false;return r;}
   bool hasNewTiles() { return !_freshTiles.empty();}
   SyncItem getNewTile() { return _freshTiles.pop_front();}

   void   setSvnServer(string server)       { _svn_server   = stripPath(server);}
   void   setSvnDataServer(string server)   { _svn_data_server   = stripPath(server);}
    
   void   setExtSvnUtility(string svn_util) { _svn_command  = simgear::strutils::strip(svn_util);}
   void   setRsyncServer(string server)     { _rsync_server = simgear::strutils::strip(server);}
   void   setLocalDir(string dir)           { _local_dir    = stripPath(dir);}
   string getLocalDir()                     { return _local_dir;}
   void   setUseSvn(bool use_svn)           { _use_svn = use_svn;}
   void   setAllowedErrorCount(int errors)  {_allowed_errors = errors;}

   void   setCachePath(const SGPath& p)     {_persistentCachePath = p;}
   void   setCacheHits(unsigned int hits)   {_cache_hits = hits;}
   void   setUseBuiltin(bool built_in) { _use_built_in = built_in;}

   volatile bool _active;
   volatile bool _running;
   volatile bool _busy;
   volatile bool _stalled;
   volatile int  _fail_count;
   volatile int  _updated_tile_count;
   volatile int  _success_count;
   volatile int  _consecutive_errors;
   volatile int  _allowed_errors;
   volatile int  _cache_hits;
   volatile int _transfer_rate;
   // kbytes, not bytes, because bytes might overflow 2^31
   volatile int _total_kb_downloaded;
   
private:
   virtual void run();
    
    // external model run and helpers
    void runExternal();
    void syncPathExternal(const SyncItem& next);
    bool runExternalSyncCommand(const char* dir);

    // internal mode run and helpers
    void runInternal();
    void updateSyncSlot(SyncSlot& slot);

    // commond helpers between both internal and external models
    
    bool isPathCached(const SyncItem& next) const;
    void initCompletedTilesPersistentCache();
    void writeCompletedTilesPersistentCache() const;
    void updated(SyncItem item, bool isNewDirectory);
    void fail(SyncItem failedItem);
    
    bool _use_built_in;
    HTTP::Client _http;
    SyncSlot _syncSlots[NUM_SYNC_SLOTS];

   volatile bool _is_dirty;
   volatile bool _stop;
   SGBlockingDeque <SyncItem> waitingTiles;
   CompletedTiles _completedTiles;
   SGBlockingDeque <SyncItem> _freshTiles;
   bool _use_svn;
   string _svn_server;
   string _svn_data_server;
   string _svn_command;
   string _rsync_server;
   string _local_dir;
   SGPath _persistentCachePath;
};

SGTerraSync::SvnThread::SvnThread() :
    _active(false),
    _running(false),
    _busy(false),
    _stalled(false),
    _fail_count(0),
    _updated_tile_count(0),
    _success_count(0),
    _consecutive_errors(0),
    _allowed_errors(6),
    _cache_hits(0),
    _transfer_rate(0),
    _total_kb_downloaded(0),
    _use_built_in(true),
    _is_dirty(false),
    _stop(false),
    _use_svn(true)
{
    _http.setUserAgent("terrascenery-" SG_STRINGIZE(SG_VERSION));
}

void SGTerraSync::SvnThread::stop()
{
    // drop any pending requests
    waitingTiles.clear();

    if (!_running)
        return;

    // set stop flag and wake up the thread with an empty request
    _stop = true;
    SyncItem w(string(), SyncItem::Stop);
    request(w);
    join();
    _running = false;
}

bool SGTerraSync::SvnThread::start()
{
    if (_running)
        return false;

    if (_local_dir=="")
    {
        SG_LOG(SG_TERRAIN,SG_ALERT,
               "Cannot start scenery download. Local cache directory is undefined.");
        _fail_count++;
        _stalled = true;
        return false;
    }

    SGPath path(_local_dir);
    if (!path.exists())
    {
        SG_LOG(SG_TERRAIN,SG_ALERT,
               "Cannot start scenery download. Directory '" << _local_dir <<
               "' does not exist. Set correct directory path or create directory folder.");
        _fail_count++;
        _stalled = true;
        return false;
    }

    path.append("version");
    if (path.exists())
    {
        SG_LOG(SG_TERRAIN,SG_ALERT,
               "Cannot start scenery download. Directory '" << _local_dir <<
               "' contains the base package. Use a separate directory.");
        _fail_count++;
        _stalled = true;
        return false;
    }

    _use_svn |= _use_built_in;

    if ((_use_svn)&&(_svn_server==""))
    {
        SG_LOG(SG_TERRAIN,SG_ALERT,
               "Cannot start scenery download. Subversion scenery server is undefined.");
        _fail_count++;
        _stalled = true;
        return false;
    }
    if ((!_use_svn)&&(_rsync_server==""))
    {
        SG_LOG(SG_TERRAIN,SG_ALERT,
               "Cannot start scenery download. Rsync scenery server is undefined.");
        _fail_count++;
        _stalled = true;
        return false;
    }

    _fail_count = 0;
    _updated_tile_count = 0;
    _success_count = 0;
    _consecutive_errors = 0;
    _stop = false;
    _stalled = false;
    _running = true;

    string status;

    if (_use_svn && _use_built_in)
        status = "Using built-in SVN support. ";
    else if (_use_svn)
    {
        status = "Using external SVN utility '";
        status += _svn_command;
        status += "'. ";
    }
    else
    {
        status = "Using RSYNC. ";
    }

    // not really an alert - but we want to (always) see this message, so user is
    // aware we're downloading scenery (and using bandwidth).
    SG_LOG(SG_TERRAIN,SG_ALERT,
           "Starting automatic scenery download/synchronization. "
           << status
           << "Directory: '" << _local_dir << "'.");

    SGThread::start();
    return true;
}

bool SGTerraSync::SvnThread::runExternalSyncCommand(const char* dir)
{
    ostringstream buf;
    SGPath localPath( _local_dir );
    localPath.append( dir );

    if (_use_svn)
    {
        buf << "\"" << _svn_command << "\" "
            << svn_options << " "
            << "\"" << _svn_server << "/" << dir << "\" "
            << "\"" << localPath.str_native() << "\"";
    } else {
        buf << rsync_cmd << " "
            << "\"" << _rsync_server << "/" << dir << "/\" "
            << "\"" << localPath.str_native() << "/\"";
    }

    string command;
#ifdef SG_WINDOWS
        // windows command line parsing is just lovely...
        // to allow white spaces, the system call needs this:
        // ""C:\Program Files\something.exe" somearg "some other arg""
        // Note: whitespace strings quoted by a pair of "" _and_ the 
        //       entire string needs to be wrapped by "" too.
        // The svn url needs forward slashes (/) as a path separator while
        // the local path needs windows-native backslash as a path separator.
    command = "\"" + buf.str() + "\"";
#else
    command = buf.str();
#endif
    SG_LOG(SG_TERRAIN,SG_DEBUG, "sync command '" << command << "'");

#ifdef SG_WINDOWS
    // tbd: does Windows support "popen"?
    int rc = system( command.c_str() );
#else
    FILE* pipe = popen( command.c_str(), "r");
    int rc=-1;
    // wait for external process to finish
    if (pipe)
        rc = pclose(pipe);
#endif

    if (rc)
    {
        SG_LOG(SG_TERRAIN,SG_ALERT,
               "Failed to synchronize directory '" << dir << "', " <<
               "error code= " << rc);
        return false;
    }
    return true;
}

void SGTerraSync::SvnThread::run()
{
    _active = true;
    initCompletedTilesPersistentCache();
    
    if (_use_built_in) {
        runInternal();
    } else {
        runExternal();
    }
    
    _active = false;
    _running = false;
    _is_dirty = true;
}

void SGTerraSync::SvnThread::runExternal()
{
    while (!_stop)
    {
        SyncItem next = waitingTiles.pop_front();
        if (_stop)
           break;

        if (isPathCached(next)) {
            _cache_hits++;
            SG_LOG(SG_TERRAIN, SG_DEBUG,
                   "Cache hit for: '" << next._dir << "'");
            next._status = SyncItem::Cached;
            _freshTiles.push_back(next);
            _is_dirty = true;
            continue;
        }
        
        syncPathExternal(next);

        if ((_allowed_errors >= 0)&&
            (_consecutive_errors >= _allowed_errors))
        {
            _stalled = true;
            _stop = true;
        }
    } // of thread running loop
}

void SGTerraSync::SvnThread::syncPathExternal(const SyncItem& next)
{
    _busy = true;
    SGPath path( _local_dir );
    path.append( next._dir );
    bool isNewDirectory = !path.exists();
    
    try {
        if (isNewDirectory) {
            int rc = path.create_dir( 0755 );
            if (rc) {
                SG_LOG(SG_TERRAIN,SG_ALERT,
                       "Cannot create directory '" << path << "', return code = " << rc );
                throw sg_exception("Cannot create directory for terrasync", path.str());
            }
        }
        
        if (!runExternalSyncCommand(next._dir.c_str())) {
            throw sg_exception("Running external sync command failed");
        }
    } catch (sg_exception& e) {
        fail(next);
        _busy = false;
        return;
    }
    
    updated(next, isNewDirectory);
    _busy = false;
}

void SGTerraSync::SvnThread::updateSyncSlot(SyncSlot &slot)
{
    if (slot.repository.get()) {
        if (slot.repository->isDoingSync()) {
#if 0
            if (slot.stamp.elapsedMSec() > slot.nextWarnTimeout) {
                SG_LOG(SG_TERRAIN, SG_INFO, "sync taking a long time:" << slot.currentItem._dir << " taken " << slot.stamp.elapsedMSec());
                SG_LOG(SG_TERRAIN, SG_INFO, "HTTP status:" << _http.hasActiveRequests());
                slot.nextWarnTimeout += 10000;
            }
#endif
            return; // easy, still working
        }
        
        // check result
        SVNRepository::ResultCode res = slot.repository->failure();
        if (res == SVNRepository::SVN_ERROR_NOT_FOUND) {
            // this is fine, but maybe we should use a different return code
            // in the future to higher layers can distinguish this case
            slot.currentItem._status = SyncItem::NotFound;
            _freshTiles.push_back(slot.currentItem);
            _is_dirty = true;
        } else if (res != SVNRepository::SVN_NO_ERROR) {
            fail(slot.currentItem);
        } else {
            updated(slot.currentItem, slot.isNewDirectory);
            SG_LOG(SG_TERRAIN, SG_DEBUG, "sync of " << slot.repository->baseUrl() << " finished ("
                   << slot.stamp.elapsedMSec() << " msec");
        }

        // whatever happened, we're done with this repository instance
        slot.busy = false;
        slot.repository.reset();
    }
    
    // init and start sync of the next repository
    if (!slot.queue.empty()) {
        slot.currentItem = slot.queue.front();
        slot.queue.pop();
        
        SGPath path(_local_dir);
        path.append(slot.currentItem._dir);
        slot.isNewDirectory = !path.exists();
        if (slot.isNewDirectory) {
            int rc = path.create_dir( 0755 );
            if (rc) {
                SG_LOG(SG_TERRAIN,SG_ALERT,
                       "Cannot create directory '" << path << "', return code = " << rc );
                fail(slot.currentItem);
                return;
            }
        } // of creating directory step
        
        string serverUrl(_svn_server);
        if (slot.currentItem._type == SyncItem::AIData) {
            serverUrl = _svn_data_server;
        }
        
        slot.repository.reset(new SVNRepository(path, &_http));
        slot.repository->setBaseUrl(serverUrl + "/" + slot.currentItem._dir);
        slot.repository->update();
        
        slot.nextWarnTimeout = 20000;
        slot.stamp.stamp();
        slot.busy = true;
        SG_LOG(SG_TERRAIN, SG_DEBUG, "sync of " << slot.repository->baseUrl() << " started, queue size is " << slot.queue.size());
    }
}

void SGTerraSync::SvnThread::runInternal()
{
    while (!_stop) {
        _http.update(100);
        _transfer_rate = _http.transferRateBytesPerSec();
        // convert from bytes to kbytes
        _total_kb_downloaded = static_cast<int>(_http.totalBytesDownloaded() / 1024);
        
        if (_stop)
            break;
 
        // drain the waiting tiles queue into the sync slot queues.
        while (!waitingTiles.empty()) {
            SyncItem next = waitingTiles.pop_front();
            if (isPathCached(next)) {
                _cache_hits++;
                SG_LOG(SG_TERRAIN, SG_DEBUG, "TerraSync Cache hit for: '" << next._dir << "'");
                next._status = SyncItem::Cached;
                _freshTiles.push_back(next);
                _is_dirty = true;
                continue;
            }

            unsigned int slot = syncSlotForType(next._type);
            _syncSlots[slot].queue.push(next);
        }
       
        bool anySlotBusy = false;
        // update each sync slot in turn
        for (unsigned int slot=0; slot < NUM_SYNC_SLOTS; ++slot) {
            updateSyncSlot(_syncSlots[slot]);
            anySlotBusy |= _syncSlots[slot].busy;
        }

        _busy = anySlotBusy;
        if (!anySlotBusy) {
            // wait on the blocking deque here, otherwise we spin
            // the loop very fast, since _http::update with no connections
            // active returns immediately.
            waitingTiles.waitOnNotEmpty();
        }
    } // of thread running loop
}

bool SGTerraSync::SvnThread::isPathCached(const SyncItem& next) const
{
    CompletedTiles::const_iterator ii = _completedTiles.find( next._dir );
    if (ii == _completedTiles.end()) {
        return false;
    }
    
    // check if the path still physically exists
    SGPath p(_local_dir);
    p.append(next._dir);
    if (!p.exists()) {
        return false;
    }
    
    time_t now = time(0);
    return (ii->second > now);
}

void SGTerraSync::SvnThread::fail(SyncItem failedItem)
{
    time_t now = time(0);
    _consecutive_errors++;
    _fail_count++;
    failedItem._status = SyncItem::Failed;
    _freshTiles.push_back(failedItem);
    _completedTiles[ failedItem._dir ] = now + UpdateInterval::FailedAttempt;
    _is_dirty = true;
}

void SGTerraSync::SvnThread::updated(SyncItem item, bool isNewDirectory)
{
    time_t now = time(0);
    _consecutive_errors = 0;
    _success_count++;
    SG_LOG(SG_TERRAIN,SG_INFO,
           "Successfully synchronized directory '" << item._dir << "'");
    
    item._status = SyncItem::Updated;
    if (item._type == SyncItem::Tile) {
        _updated_tile_count++;
    }

    _freshTiles.push_back(item);
    _completedTiles[ item._dir ] = now + UpdateInterval::SuccessfulAttempt;
    _is_dirty = true;
    writeCompletedTilesPersistentCache();
}

void SGTerraSync::SvnThread::initCompletedTilesPersistentCache()
{
    if (!_persistentCachePath.exists()) {
        return;
    }
    
    SGPropertyNode_ptr cacheRoot(new SGPropertyNode);
    time_t now = time(0);
    
    try {
        readProperties(_persistentCachePath.str(), cacheRoot);
    } catch (sg_exception& e) {
        SG_LOG(SG_TERRAIN, SG_INFO, "corrupted persistent cache, discarding");
        return;
    }
    
    for (int i=0; i<cacheRoot->nChildren(); ++i) {
        SGPropertyNode* entry = cacheRoot->getChild(i);
        string tileName = entry->getStringValue("path");
        time_t stamp = entry->getIntValue("stamp");
        if (stamp < now) {
            continue;
        }
        
        _completedTiles[tileName] = stamp;
    }
}

void SGTerraSync::SvnThread::writeCompletedTilesPersistentCache() const
{
    // cache is disabled
    if (_persistentCachePath.isNull()) {
        return;
    }
    
    std::ofstream f(_persistentCachePath.c_str(), std::ios::trunc);
    if (!f.is_open()) {
        return;
    }
    
    SGPropertyNode_ptr cacheRoot(new SGPropertyNode);
    CompletedTiles::const_iterator it = _completedTiles.begin();
    for (; it != _completedTiles.end(); ++it) {
        SGPropertyNode* entry = cacheRoot->addChild("entry");
        entry->setStringValue("path", it->first);
        entry->setIntValue("stamp", it->second);
    }
    
    writeProperties(f, cacheRoot, true /* write_all */);
    f.close();
}

///////////////////////////////////////////////////////////////////////////////
// SGTerraSync ////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
SGTerraSync::SGTerraSync() :
    _svnThread(NULL),
    _bound(false),
    _inited(false)
{
    _svnThread = new SvnThread();
    _log = new BufferedLogCallback(SG_TERRAIN, SG_INFO);
    _log->truncateAt(255);
    
    sglog().addCallback(_log);
}

SGTerraSync::~SGTerraSync()
{
    delete _svnThread;
    _svnThread = NULL;
    sglog().removeCallback(_log);
    delete _log;
     _tiedProperties.Untie();
}

void SGTerraSync::setRoot(SGPropertyNode_ptr root)
{
    _terraRoot = root->getNode("/sim/terrasync",true);
}

void SGTerraSync::init()
{
    if (_inited) {
        return;
    }
    
    _inited = true;
    
    assert(_terraRoot);
    _terraRoot->setBoolValue("built-in-svn-available",svn_built_in_available);
        
    reinit();
}

void SGTerraSync::shutdown()
{
     _svnThread->stop();
}

void SGTerraSync::reinit()
{
    // do not reinit when enabled and we're already up and running
    if ((_terraRoot->getBoolValue("enabled",false))&&
         (_svnThread->_active && _svnThread->_running))
    {
        return;
    }
    
    _svnThread->stop();

    if (_terraRoot->getBoolValue("enabled",false))
    {
        _svnThread->setSvnServer(_terraRoot->getStringValue("svn-server",""));
        _svnThread->setSvnDataServer(_terraRoot->getStringValue("svn-data-server",""));
        _svnThread->setRsyncServer(_terraRoot->getStringValue("rsync-server",""));
        _svnThread->setLocalDir(_terraRoot->getStringValue("scenery-dir",""));
        _svnThread->setAllowedErrorCount(_terraRoot->getIntValue("max-errors",5));
        _svnThread->setUseBuiltin(_terraRoot->getBoolValue("use-built-in-svn",true));
        _svnThread->setCachePath(SGPath(_terraRoot->getStringValue("cache-path","")));
        _svnThread->setCacheHits(_terraRoot->getIntValue("cache-hit", 0));
        _svnThread->setUseSvn(_terraRoot->getBoolValue("use-svn",true));
        _svnThread->setExtSvnUtility(_terraRoot->getStringValue("ext-svn-utility","svn"));

        if (_svnThread->start())
        {
            syncAirportsModels();
        }
    }

    _stalledNode->setBoolValue(_svnThread->_stalled);
}

void SGTerraSync::bind()
{
    if (_bound) {
        return;
    }
    
    _bound = true;
    _tiedProperties.Tie( _terraRoot->getNode("busy", true), (bool*) &_svnThread->_busy );
    _tiedProperties.Tie( _terraRoot->getNode("active", true), (bool*) &_svnThread->_active );
    _tiedProperties.Tie( _terraRoot->getNode("update-count", true), (int*) &_svnThread->_success_count );
    _tiedProperties.Tie( _terraRoot->getNode("error-count", true), (int*) &_svnThread->_fail_count );
    _tiedProperties.Tie( _terraRoot->getNode("tile-count", true), (int*) &_svnThread->_updated_tile_count );
    _tiedProperties.Tie( _terraRoot->getNode("cache-hits", true), (int*) &_svnThread->_cache_hits );
    _tiedProperties.Tie( _terraRoot->getNode("transfer-rate-bytes-sec", true), (int*) &_svnThread->_transfer_rate );
    
    // use kbytes here because propety doesn't support 64-bit and we might conceivably
    // download more than 2G in a single session
    _tiedProperties.Tie( _terraRoot->getNode("downloaded-kbytes", true), (int*) &_svnThread->_total_kb_downloaded );
    
    _terraRoot->getNode("busy", true)->setAttribute(SGPropertyNode::WRITE,false);
    _terraRoot->getNode("active", true)->setAttribute(SGPropertyNode::WRITE,false);
    _terraRoot->getNode("update-count", true)->setAttribute(SGPropertyNode::WRITE,false);
    _terraRoot->getNode("error-count", true)->setAttribute(SGPropertyNode::WRITE,false);
    _terraRoot->getNode("tile-count", true)->setAttribute(SGPropertyNode::WRITE,false);
    _terraRoot->getNode("use-built-in-svn", true)->setAttribute(SGPropertyNode::USERARCHIVE,false);
    _terraRoot->getNode("use-svn", true)->setAttribute(SGPropertyNode::USERARCHIVE,false);
    // stalled is used as a signal handler (to connect listeners triggering GUI pop-ups)
    _stalledNode = _terraRoot->getNode("stalled", true);
    _stalledNode->setBoolValue(_svnThread->_stalled);
    _stalledNode->setAttribute(SGPropertyNode::PRESERVE,true);
}

void SGTerraSync::unbind()
{
    _svnThread->stop();
    _tiedProperties.Untie();
    _bound = false;
    _inited = false;
    
    _terraRoot.clear();
    _stalledNode.clear();
    _cacheHits.clear();
}

void SGTerraSync::update(double)
{
    static SGBucket bucket;
    if (_svnThread->isDirty())
    {
        if (!_svnThread->_active)
        {
            if (_svnThread->_stalled)
            {
                SG_LOG(SG_TERRAIN,SG_ALERT,
                       "Automatic scenery download/synchronization stalled. Too many errors.");
            }
            else
            {
                // not really an alert - just always show this message
                SG_LOG(SG_TERRAIN,SG_ALERT,
                        "Automatic scenery download/synchronization has stopped.");
            }
            _stalledNode->setBoolValue(_svnThread->_stalled);
        }

        while (_svnThread->hasNewTiles())
        {
            SyncItem next = _svnThread->getNewTile();
            
            if ((next._type == SyncItem::Tile) || (next._type == SyncItem::AIData)) {
                _activeTileDirs.erase(next._dir);
            }
        } // of freshly synced items
    }
}

bool SGTerraSync::isIdle() {return _svnThread->isIdle();}

void SGTerraSync::syncAirportsModels()
{
    static const char* bounds = "MZAJKL"; // airport sync order: K-L, A-J, M-Z
    // note "request" method uses LIFO order, i.e. processes most recent request first
    for( unsigned i = 0; i < strlen(bounds)/2; i++ )
    {
        for ( char synced_other = bounds[2*i]; synced_other <= bounds[2*i+1]; synced_other++ )
        {
            ostringstream dir;
            dir << "Airports/" << synced_other;
            SyncItem w(dir.str(), SyncItem::AirportData);
            _svnThread->request( w );
        }
    }
    
    SyncItem w("Models", SyncItem::SharedModels);
    _svnThread->request( w );
}

void SGTerraSync::syncAreaByPath(const std::string& aPath)
{
    const char* terrainobjects[3] = { "Terrain/", "Objects/",  0 };
    for (const char** tree = &terrainobjects[0]; *tree; tree++)
    {
        std::string dir = string(*tree) + aPath;
        if (_activeTileDirs.find(dir) != _activeTileDirs.end()) {
            continue;
        }
                
        _activeTileDirs.insert(dir);
        SyncItem w(dir, SyncItem::Tile);
        _svnThread->request( w );
    }
}

bool SGTerraSync::scheduleTile(const SGBucket& bucket)
{
    std::string basePath = bucket.gen_base_path();
    syncAreaByPath(basePath);
    return true;
}

bool SGTerraSync::isTileDirPending(const std::string& sceneryDir) const
{
    if (!_svnThread->_running) {
        return false;
    }
    
    const char* terrainobjects[3] = { "Terrain/", "Objects/",  0 };
    for (const char** tree = &terrainobjects[0]; *tree; tree++) {
        string s = *tree + sceneryDir;
        if (_activeTileDirs.find(s) != _activeTileDirs.end()) {
            return true;
        }
    }

    return false;
}

void SGTerraSync::scheduleDataDir(const std::string& dataDir)
{
    if (_activeTileDirs.find(dataDir) != _activeTileDirs.end()) {
        return;
    }
    
    _activeTileDirs.insert(dataDir);
    SyncItem w(dataDir, SyncItem::AIData);
    _svnThread->request( w );

}

bool SGTerraSync::isDataDirPending(const std::string& dataDir) const
{
    if (!_svnThread->_running) {
        return false;
    }
    
    return (_activeTileDirs.find(dataDir) != _activeTileDirs.end());
}

void SGTerraSync::reposition()
{
    // stub, remove
}