// **************************************************************************
// * This file is part of the FreeFileSync project. It is distributed under *
// * GNU General Public License: http://www.gnu.org/licenses/gpl.html       *
// * Copyright (C) Zenju (zenju AT gmx DOT de) - All Rights Reserved        *
// **************************************************************************

#include "monitor.h"
#include <ctime>
#include <set>
#include <zen/file_handling.h>
#include <zen/dir_watcher.h>
#include <zen/thread.h>
#include <zen/tick_count.h>
#include <wx/utils.h>
#include "../lib/resolve_path.h"
//#include "../library/db_file.h"     //SYNC_DB_FILE_ENDING -> complete file too much of a dependency; file ending too little to decouple into single header
//#include "../library/lock_holder.h" //LOCK_FILE_ENDING

using namespace zen;


namespace
{
const int CHECK_DIR_INTERVAL = 1; //unit: [s]


std::vector<Zstring> getFormattedDirs(const std::vector<Zstring>& dirs) //throw FileError
{
    std::set<Zstring, LessFilename> tmp; //make unique

    std::transform(dirs.begin(), dirs.end(), std::inserter(tmp, tmp.end()),
    [](const Zstring& dirnameNonFmt) { return getFormattedDirectoryName(dirnameNonFmt); });

    return std::vector<Zstring>(tmp.begin(), tmp.end());
}


//wait until changes are detected or if a directory is not available (anymore)
struct WaitResult
{
    enum ChangeType
    {
        CHANGE_DETECTED,
        CHANGE_DIR_MISSING
    };

    WaitResult(const zen::DirWatcher::Entry& changedItem) : type(CHANGE_DETECTED), changedItem_(changedItem) {}
    WaitResult(const Zstring& dirname) : type(CHANGE_DIR_MISSING), dirname_(dirname) {}

    ChangeType type;
    zen::DirWatcher::Entry changedItem_; //for type == CHANGE_DETECTED: file or directory
    Zstring dirname_;                    //for type == CHANGE_DIR_MISSING
};


WaitResult waitForChanges(const std::vector<Zstring>& dirNamesNonFmt, //throw FileError
                          const std::function<void(bool)>& onRefreshGui)  //bool: readyForSync
{
    const std::vector<Zstring> dirNamesFmt = getFormattedDirs(dirNamesNonFmt); //throw FileError
    if (dirNamesFmt.empty()) //pathological case, but we have to check else this function will wait endlessly
        throw zen::FileError(_("A folder input field is empty.")); //should have been checked by caller!

    //detect when volumes are removed/are not available anymore
    std::vector<std::pair<Zstring, std::shared_ptr<DirWatcher>>> watches;

    for (auto it = dirNamesFmt.begin(); it != dirNamesFmt.end(); ++it)
    {
        const Zstring& dirnameFmt = *it;
        try
        {
            //a non-existent network path may block, so check existence asynchronously!
            auto ftDirExists = async([=] { return zen::dirExists(dirnameFmt); });
            //we need to check dirExists(), not somethingExists(): it's not clear if DirWatcher detects a type clash (file instead of directory!)
            while (!ftDirExists.timed_wait(boost::posix_time::milliseconds(rts::UI_UPDATE_INTERVAL / 2)))
                onRefreshGui(false); //may throw!
            if (!ftDirExists.get())
                return WaitResult(dirnameFmt);

            watches.push_back(std::make_pair(dirnameFmt, std::make_shared<DirWatcher>(dirnameFmt))); //throw FileError
        }
        catch (FileError&)
        {
            if (!somethingExists(dirnameFmt)) //a benign(?) race condition with FileError
                return WaitResult(dirnameFmt);
            throw;
        }
    }

    const std::int64_t TICKS_DIR_CHECK_INTERVAL = CHECK_DIR_INTERVAL * ticksPerSec(); //0 on error
    TickVal lastCheck = getTicks(); //0 on error
    while (true)
    {
        const bool checkDirExistNow = [&]() -> bool //checking once per sec should suffice
        {
            const TickVal now = getTicks(); //0 on error
            if (dist(lastCheck, now) >= TICKS_DIR_CHECK_INTERVAL)
            {
                lastCheck = now;
                return true;
            }
            return false;
        }();


        for (auto it = watches.begin(); it != watches.end(); ++it)
        {
            const Zstring& dirname = it->first;
            DirWatcher& watcher = *(it->second);

            //IMPORTANT CHECK: dirwatcher has problems detecting removal of top watched directories!
            if (checkDirExistNow)
                if (!dirExists(dirname)) //catch errors related to directory removal, e.g. ERROR_NETNAME_DELETED -> somethingExists() is NOT sufficient here!
                    return WaitResult(dirname);
            try
            {
                std::vector<DirWatcher::Entry> changedItems = watcher.getChanges([&] { onRefreshGui(false); /*may throw!*/ }); //throw FileError

                //remove to be ignored changes
                vector_remove_if(changedItems, [](const DirWatcher::Entry& e)
                {
                    return endsWith(e.filename_, Zstr(".ffs_lock")) || //sync.ffs_lock, sync.Del.ffs_lock
                           endsWith(e.filename_, Zstr(".ffs_db"));     //sync.ffs_db, .sync.tmp.ffs_db
                    //no need to ignore temporal recycle bin directory: this must be caused by a file deletion anyway
                });

                if (!changedItems.empty())
                {
                    /*
                                    std::for_each(changedItems.begin(), changedItems.end(),
                                    [](const Zstring& fn) { wxMessageBox(toWx(fn));});
                    */
                    return WaitResult(changedItems[0]); //directory change detected
                }

            }
            catch (FileError&)
            {
                if (!somethingExists(dirname)) //a benign(?) race condition with FileError
                    return WaitResult(dirname);
                throw;
            }
        }

        boost::this_thread::sleep(boost::posix_time::milliseconds(rts::UI_UPDATE_INTERVAL / 2));
        onRefreshGui(true); //throw ?: may start sync at this presumably idle time
    }
}


//wait until all directories become available (again) + logs in network share
void waitForMissingDirs(const std::vector<Zstring>& dirNamesNonFmt, //throw FileError
                        const std::function<void(const Zstring&)>& onRefreshGui) //Zstring: the directory that is currently being waited for
{
    while (true)
    {
        //support specifying volume by name => call getFormattedDirectoryName() repeatedly
        const std::vector<Zstring>& dirNamesFmt = getFormattedDirs(dirNamesNonFmt); //throw FileError

        bool allExisting = true;
        for (auto it = dirNamesFmt.begin(); it != dirNamesFmt.end(); ++it)
        {
            const Zstring dirnameFmt = *it;
            auto ftDirExisting = async([=]() -> bool
            {
#ifdef ZEN_WIN
                //1. login to network share, if necessary -> we probably do NOT want multiple concurrent runs: GUI!?
                loginNetworkShare(dirnameFmt, false); //login networks shares, no PW prompt -> is this really RTS's job?
#endif
                //2. check dir existence
                return zen::dirExists(dirnameFmt);
            });
            while (!ftDirExisting.timed_wait(boost::posix_time::milliseconds(rts::UI_UPDATE_INTERVAL / 2)))
                onRefreshGui(dirnameFmt); //may throw!

            if (!ftDirExisting.get())
            {
                allExisting = false;
                //wait some time...
                const int refreshInterval = rts::UI_UPDATE_INTERVAL / 2;
                assert_static(CHECK_DIR_INTERVAL * 1000 % refreshInterval == 0);
                for (int i = 0; i < CHECK_DIR_INTERVAL * 1000 / refreshInterval; ++i)
                {
                    onRefreshGui(dirnameFmt); //may throw!
                    boost::this_thread::sleep(boost::posix_time::milliseconds(refreshInterval));
                }
                break;
            }
        }
        if (allExisting)
            return;
    }
}


inline
wxString toString(DirWatcher::ActionType type)
{
    switch (type)
    {
        case DirWatcher::ACTION_CREATE:
            return L"CREATE";
        case DirWatcher::ACTION_UPDATE:
            return L"UPDATE";
        case DirWatcher::ACTION_DELETE:
            return L"DELETE";
    }
    return L"ERROR";
}

struct ExecCommandNowException {};
}


void rts::monitorDirectories(const std::vector<Zstring>& dirNamesNonFmt, unsigned int delay, rts::MonitorCallback& callback)
{
    if (dirNamesNonFmt.empty())
    {
        assert(false);
        return;
    }

    auto execMonitoring = [&] //throw FileError
    {
        callback.setPhase(MonitorCallback::MONITOR_PHASE_WAITING);
        waitForMissingDirs(dirNamesNonFmt, [&](const Zstring& dirname) { callback.requestUiRefresh(); }); //throw FileError
        callback.setPhase(MonitorCallback::MONITOR_PHASE_ACTIVE);

        //schedule initial execution (*after* all directories have arrived, which could take some time which we don't want to include)
        time_t nextExecDate = std::time(nullptr) + delay;

        while (true) //loop over command invocations
        {
            DirWatcher::Entry lastChangeDetected;
            try
            {
                while (true) //loop over detected changes
                {
                    //wait for changes (and for all directories to become available)
                    WaitResult res = waitForChanges(dirNamesNonFmt, [&](bool readyForSync) //throw FileError, ExecCommandNowException
                    {
                        if (readyForSync)
                            if (nextExecDate <= std::time(nullptr))
                                throw ExecCommandNowException(); //abort wait and start sync
                        callback.requestUiRefresh();
                    });
                    switch (res.type)
                    {
                        case WaitResult::CHANGE_DIR_MISSING: //don't execute the command before all directories are available!
                            callback.setPhase(MonitorCallback::MONITOR_PHASE_WAITING);
                            waitForMissingDirs(dirNamesNonFmt, [&](const Zstring& dirname) { callback.requestUiRefresh(); }); //throw FileError
                            callback.setPhase(MonitorCallback::MONITOR_PHASE_ACTIVE);
                            break;

                        case WaitResult::CHANGE_DETECTED:
                            lastChangeDetected = res.changedItem_;
                            break;
                    }
                    nextExecDate = std::time(nullptr) + delay;
                }
            }
            catch (ExecCommandNowException&) {}

            ::wxSetEnv(L"change_path", utfCvrtTo<wxString>(lastChangeDetected.filename_)); //some way to output what file changed to the user
            ::wxSetEnv(L"change_action", toString(lastChangeDetected.action_)); //

            //execute command
            callback.executeExternalCommand();
            nextExecDate = std::numeric_limits<time_t>::max();
        }
    };

    while (true)
        try
        {
            execMonitoring(); //throw FileError
        }
        catch (const zen::FileError& e)
        {
            callback.reportError(e.toString());
        }
}