/*
  SPDX-FileCopyrightText: 2000, 2001, 2004 Cornelius Schumacher <schumacher@kde.org>
  SPDX-FileCopyrightText: 2010 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
  SPDX-FileCopyrightText: 2010 Andras Mantia <andras@kdab.com>
  SPDX-FileCopyrightText: 2010 Casey Link <casey@kdab.com>

  SPDX-License-Identifier: LGPL-2.0-or-later
*/

#include "conflictresolver.h"
#include "incidenceeditor_debug.h"
#include <CalendarSupport/FreeBusyItemModel>

#include <QDate>

static const int DEFAULT_RESOLUTION_SECONDS = 15 * 60; // 15 minutes, 1 slot = 15 minutes

using namespace IncidenceEditorNG;

ConflictResolver::ConflictResolver(QWidget *parentWidget, QObject *parent)
    : QObject(parent)
    , mFBModel(new CalendarSupport::FreeBusyItemModel(this))
    , mParentWidget(parentWidget)
    , mWeekdays(7)
    , mSlotResolutionSeconds(DEFAULT_RESOLUTION_SECONDS)
{
    const QDateTime currentLocalDateTime = QDateTime::currentDateTime();
    mTimeframeConstraint = KCalendarCore::Period(currentLocalDateTime, currentLocalDateTime);

    // trigger a reload in case any attendees were inserted before
    // the connection was made
    // triggerReload();

    // set default values, all the days
    mWeekdays.setBit(0); // Monday
    mWeekdays.setBit(1);
    mWeekdays.setBit(2);
    mWeekdays.setBit(3);
    mWeekdays.setBit(4);
    mWeekdays.setBit(5);
    mWeekdays.setBit(6); // Sunday

    mMandatoryRoles.reserve(4);
    mMandatoryRoles << KCalendarCore::Attendee::ReqParticipant << KCalendarCore::Attendee::OptParticipant << KCalendarCore::Attendee::NonParticipant
                    << KCalendarCore::Attendee::Chair;

    connect(mFBModel, &CalendarSupport::FreeBusyItemModel::dataChanged, this, &ConflictResolver::freebusyDataChanged);

    connect(&mCalculateTimer, &QTimer::timeout, this, &ConflictResolver::findAllFreeSlots);
    mCalculateTimer.setSingleShot(true);
}

void ConflictResolver::insertAttendee(const KCalendarCore::Attendee &attendee)
{
    if (!mFBModel->containsAttendee(attendee)) {
        mFBModel->addItem(CalendarSupport::FreeBusyItem::Ptr(new CalendarSupport::FreeBusyItem(attendee, mParentWidget)));
    }
}

void ConflictResolver::insertAttendee(const CalendarSupport::FreeBusyItem::Ptr &freebusy)
{
    if (!mFBModel->containsAttendee(freebusy->attendee())) {
        mFBModel->addItem(freebusy);
    }
}

void ConflictResolver::removeAttendee(const KCalendarCore::Attendee &attendee)
{
    mFBModel->removeAttendee(attendee);
    calculateConflicts();
}

void ConflictResolver::clearAttendees()
{
    mFBModel->clear();
}

bool ConflictResolver::containsAttendee(const KCalendarCore::Attendee &attendee)
{
    return mFBModel->containsAttendee(attendee);
}

void ConflictResolver::setEarliestDate(QDate newDate)
{
    QDateTime newStart = mTimeframeConstraint.start();
    newStart.setDate(newDate);
    mTimeframeConstraint = KCalendarCore::Period(newStart, mTimeframeConstraint.end());
    calculateConflicts();
}

void ConflictResolver::setEarliestTime(QTime newTime)
{
    QDateTime newStart = mTimeframeConstraint.start();
    newStart.setTime(newTime);
    mTimeframeConstraint = KCalendarCore::Period(newStart, mTimeframeConstraint.end());
    calculateConflicts();
}

void ConflictResolver::setLatestDate(QDate newDate)
{
    QDateTime newEnd = mTimeframeConstraint.end();
    newEnd.setDate(newDate);
    mTimeframeConstraint = KCalendarCore::Period(mTimeframeConstraint.start(), newEnd);
    calculateConflicts();
}

void ConflictResolver::setLatestTime(QTime newTime)
{
    QDateTime newEnd = mTimeframeConstraint.end();
    newEnd.setTime(newTime);
    mTimeframeConstraint = KCalendarCore::Period(mTimeframeConstraint.start(), newEnd);
    calculateConflicts();
}

void ConflictResolver::setEarliestDateTime(const QDateTime &newDateTime)
{
    mTimeframeConstraint = KCalendarCore::Period(newDateTime, mTimeframeConstraint.end());
    calculateConflicts();
}

void ConflictResolver::setLatestDateTime(const QDateTime &newDateTime)
{
    mTimeframeConstraint = KCalendarCore::Period(mTimeframeConstraint.start(), newDateTime);
    calculateConflicts();
}

void ConflictResolver::freebusyDataChanged()
{
    calculateConflicts();
}

int ConflictResolver::tryDate(QDateTime &tryFrom, QDateTime &tryTo)
{
    int conflicts_count = 0;
    for (int i = 0; i < mFBModel->rowCount(); ++i) {
        QModelIndex index = mFBModel->index(i);
        auto attendee = mFBModel->data(index, CalendarSupport::FreeBusyItemModel::AttendeeRole).value<KCalendarCore::Attendee>();
        if (!matchesRoleConstraint(attendee)) {
            continue;
        }
        auto freebusy = mFBModel->data(index, CalendarSupport::FreeBusyItemModel::FreeBusyRole).value<KCalendarCore::FreeBusy::Ptr>();
        if (!tryDate(freebusy, tryFrom, tryTo)) {
            ++conflicts_count;
        }
    }
    return conflicts_count;
}

bool ConflictResolver::tryDate(const KCalendarCore::FreeBusy::Ptr &fb, QDateTime &tryFrom, QDateTime &tryTo)
{
    // If we don't have any free/busy information, assume the
    // participant is free. Otherwise a participant without available
    // information would block the whole allocation.
    if (!fb) {
        return true;
    }

    KCalendarCore::Period::List busyPeriods = fb->busyPeriods();
    for (auto it = busyPeriods.begin(); it != busyPeriods.end(); ++it) {
        if ((*it).end() <= tryFrom // busy period ends before try period
            || (*it).start() >= tryTo) { // busy period starts after try period
            continue;
        } else {
            // the current busy period blocks the try period, try
            // after the end of the current busy period
            const qint64 secsDuration = tryFrom.secsTo(tryTo);
            tryFrom = (*it).end();
            tryTo = tryFrom.addSecs(secsDuration);
            // try again with the new try period
            tryDate(fb, tryFrom, tryTo);
            // we had to change the date at least once
            return false;
        }
    }
    return true;
}

bool ConflictResolver::findFreeSlot(const KCalendarCore::Period &dateTimeRange)
{
    QDateTime dtFrom = dateTimeRange.start();
    QDateTime dtTo = dateTimeRange.end();
    if (tryDate(dtFrom, dtTo)) {
        // Current time is acceptable
        return true;
    }

    QDateTime tryFrom = dtFrom;
    QDateTime tryTo = dtTo;

    // Make sure that we never suggest a date in the past, even if the
    // user originally scheduled the meeting to be in the past.
    QDateTime now = QDateTime::currentDateTimeUtc();
    if (tryFrom < now) {
        // The slot to look for is at least partially in the past.
        const qint64 secs = tryFrom.secsTo(tryTo);
        tryFrom = now;
        tryTo = tryFrom.addSecs(secs);
    }

    bool found = false;
    while (!found) {
        found = tryDate(tryFrom, tryTo);
        // PENDING(kalle) Make the interval configurable
        if (!found && dtFrom.daysTo(tryFrom) > 365) {
            break; // don't look more than one year in the future
        }
    }

    dtFrom = tryFrom;
    dtTo = tryTo;

    return found;
}

void ConflictResolver::findAllFreeSlots()
{
    // Uses an O(p*n) (n number of attendees, p timeframe range / timeslot resolution ) algorithm to
    // locate all free blocks in a given timeframe that match the search constraints.
    // Does so by:
    // 1. convert each attendees schedule for the timeframe into a bitarray according to
    //    the time resolution, where each time slot has a value of 1 = busy, 0 = free.
    // 2. align the arrays vertically, and sum the columns
    // 3. the resulting summation indicates # of conflicts at each timeslot
    // 4. locate contiguous timeslots with a values of 0. these are the free time blocks.

    // define these locally for readability
    const QDateTime begin = mTimeframeConstraint.start();
    const QDateTime end = mTimeframeConstraint.end();

    // calculate the time resolution
    // each timeslot in the arrays represents a unit of time
    // specified here.
    if (mSlotResolutionSeconds < 1) {
        // fallback to default, if the user's value is invalid
        mSlotResolutionSeconds = DEFAULT_RESOLUTION_SECONDS;
    }

    // calculate the length of the timeframe in terms of the amount of timeslots.
    // Example: 1 week timeframe, with resolution of 15 minutes
    //          1 week = 10080 minutes / 15 = 672 15 min timeslots
    //          So, the array would have a length of 672
    const int range = begin.secsTo(end) / mSlotResolutionSeconds;
    if (range <= 0) {
        qCWarning(INCIDENCEEDITOR_LOG) << "free slot calculation: invalid range. range( " << begin.secsTo(end) << ") / mSlotResolutionSeconds("
                                       << mSlotResolutionSeconds << ") = " << range;
        return;
    }

    qCDebug(INCIDENCEEDITOR_LOG) << "from " << begin << " to " << end << "; mSlotResolutionSeconds = " << mSlotResolutionSeconds << "; range = " << range;
    // filter out attendees for which we don't have FB data
    // and which don't match the mandatory role constraint
    QList<KCalendarCore::FreeBusy::Ptr> filteredFBItems;
    for (int i = 0; i < mFBModel->rowCount(); ++i) {
        QModelIndex index = mFBModel->index(i);
        auto attendee = mFBModel->data(index, CalendarSupport::FreeBusyItemModel::AttendeeRole).value<KCalendarCore::Attendee>();
        if (!matchesRoleConstraint(attendee)) {
            continue;
        }
        auto freebusy = mFBModel->data(index, CalendarSupport::FreeBusyItemModel::FreeBusyRole).value<KCalendarCore::FreeBusy::Ptr>();
        if (freebusy) {
            filteredFBItems << freebusy;
        }
    }

    // now we know the number of attendees we are calculating for
    const int number_attendees = filteredFBItems.size();
    if (number_attendees <= 0) {
        qCDebug(INCIDENCEEDITOR_LOG) << "no attendees match search criteria";
        return;
    }
    qCDebug(INCIDENCEEDITOR_LOG) << "num attendees: " << number_attendees;
    // this is a 2 dimensional array where the rows are attendees
    // and the columns are 0 or 1 denoting free or busy respectively.
    QVector<QVector<int>> fbTable;

    // Explanation of the following loop:
    // iterate: through each attendee
    //   allocate: an array of length <range> and fill it with 0s
    //   iterate: through each attendee's busy period
    //     if: the period lies inside our timeframe
    //     then:
    //       calculate the array index within the timeframe range of the beginning of the busy period
    //       fill from that index until the period ends with a 1, representing busy
    //     fi
    //   etareti
    // append the allocated array to <fbTable>
    // etareti
    for (const KCalendarCore::FreeBusy::Ptr &currentFB : std::as_const(filteredFBItems)) {
        Q_ASSERT(currentFB); // sanity check
        const KCalendarCore::Period::List busyPeriods = currentFB->busyPeriods();
        QVector<int> fbArray(range);
        fbArray.fill(0); // initialize to zero
        for (const auto &period : busyPeriods) {
            if (period.end() >= begin && period.start() <= end) {
                int start_index = -1; // Initialize it to an invalid value.
                int duration = -1; // Initialize it to an invalid value.
                // case1: the period is completely in our timeframe
                if (period.end() <= end && period.start() >= begin) {
                    start_index = begin.secsTo(period.start()) / mSlotResolutionSeconds;
                    duration = period.start().secsTo(period.end()) / mSlotResolutionSeconds;
                    duration -= 1; // vector starts at 0
                    // case2: the period begins before our timeframe begins
                } else if (period.start() <= begin && period.end() <= end) {
                    start_index = 0;
                    duration = (begin.secsTo(period.end()) / mSlotResolutionSeconds) - 1;
                    // case3: the period ends after our timeframe ends
                } else if (period.end() >= end && period.start() >= begin) {
                    start_index = begin.secsTo(period.start()) / mSlotResolutionSeconds;
                    duration = range - start_index - 1;
                    // case4: case2+case3: our timeframe is inside the period
                } else if (period.start() <= begin && period.end() >= end) {
                    start_index = 0;
                    duration = range - 1;
                } else {
                    // QT5
                    // qCCritical(INCIDENCEEDITOR_LOG) << "impossible condition reached" << period.start() << period.end();
                }
                //      qCDebug(INCIDENCEEDITOR_LOG) << start_index << "+" << duration << "="
                //               << start_index + duration << "<=" << range;
                Q_ASSERT((start_index + duration) < range); // sanity check
                for (int i = start_index; i <= start_index + duration; ++i) {
                    fbArray[i] = 1;
                }
            }
        }
        Q_ASSERT(fbArray.size() == range); // sanity check
        fbTable.append(fbArray);
    }

    Q_ASSERT(fbTable.size() == number_attendees);

    // Now, create another array to represent the allowed weekdays constraints
    // All days which are not allowed, will be marked as busy
    QVector<int> fbArray(range);
    fbArray.fill(0); // initialize to zero
    for (int slot = 0; slot < fbArray.size(); ++slot) {
        const QDateTime dateTime = begin.addSecs(slot * mSlotResolutionSeconds);
        const int dayOfWeek = dateTime.date().dayOfWeek() - 1; // bitarray is 0 indexed
        if (!mWeekdays[dayOfWeek]) {
            fbArray[slot] = 1;
        }
    }
    fbTable.append(fbArray);

    // Create the composite array that will hold the sums for
    // each 15 minute timeslot
    QVector<int> summed(range);
    summed.fill(0); // initialize to zero

    // Sum the columns of the table
    for (int i = 0; i < fbTable.size(); ++i) {
        for (int j = 0; j < range; ++j) {
            summed[j] += fbTable[i][j];
        }
    }

    // Finally, iterate through the composite array locating contiguous free timeslots
    int free_count = 0;
    bool free_found = false;
    mAvailableSlots.clear();
    for (int i = 0; i < range; ++i) {
        // free timeslot encountered, increment counter
        if (summed[i] == 0) {
            ++free_count;
        }
        if (summed[i] != 0 || (i == (range - 1) && summed[i] == 0)) {
            // current slot is not free, so push the previous free blocks
            // OR we are in the last slot and it is free
            if (free_count > 0) {
                int free_start_i; // start index of the free block
                int free_end_i; // end index of the free block
                if (summed[i] == 0) {
                    // special case: we are on the last slot and it is free
                    //               so we want to include this slot in the free block
                    free_start_i = i - free_count + 1; // add one, to set us back inside the array because
                    // free_count was incremented already this iteration
                    free_end_i = i + 1; // add one to compensate for the fact that the array is 0 indexed
                } else {
                    free_start_i = i - free_count;
                    free_end_i = i - 1 + 1; // add one to compensate for the fact that the array is 0 indexed
                    // compiler will optimize out the -1+1, but I leave it here to make the reasoning apparent.
                }
                // convert from our timeslot interval back into to normal seconds
                // then calculate the date times of the free block based on
                // our initial timeframe
                const QDateTime freeBegin = begin.addSecs(free_start_i * mSlotResolutionSeconds);
                const QDateTime freeEnd = freeBegin.addSecs((free_end_i - free_start_i) * mSlotResolutionSeconds);
                // push the free block onto the list
                mAvailableSlots << KCalendarCore::Period(freeBegin, freeEnd);
                free_count = 0;
                if (!free_found) {
                    free_found = true;
                }
            }
        }
    }
    if (free_found) {
        Q_EMIT freeSlotsAvailable(mAvailableSlots);
    }
#if 0
    //DEBUG, dump the arrays. very helpful for debugging
    QTextStream dump(stdout);
    dump << "    ";
    dump.setFieldWidth(3);
    for (int i = 0; i < range; ++i) {   // header
        dump << i;
    }
    dump.setFieldWidth(1);
    dump << "\n\n";
    for (int i = 0; i < number_attendees; ++i) {
        dump.setFieldWidth(1);
        dump << i << ":  ";
        dump.setFieldWidth(3);
        for (int j = 0; j < range; ++j) {
            dump << fbTable[i][j];
        }
        dump << "\n\n";
    }
    dump.setFieldWidth(1);
    dump << "    ";
    dump.setFieldWidth(3);
    for (int i = 0; i < range; ++i) {
        dump << summed[i];
    }
    dump << "\n";
#endif
}

void ConflictResolver::calculateConflicts()
{
    QDateTime start = mTimeframeConstraint.start();
    QDateTime end = mTimeframeConstraint.end();
    const int count = tryDate(start, end);
    Q_EMIT conflictsDetected(count);

    if (!mCalculateTimer.isActive()) {
        mCalculateTimer.start(0);
    }
}

void ConflictResolver::setAllowedWeekdays(const QBitArray &weekdays)
{
    mWeekdays = weekdays;
    calculateConflicts();
}

void ConflictResolver::setMandatoryRoles(const QSet<KCalendarCore::Attendee::Role> &roles)
{
    mMandatoryRoles = roles;
    calculateConflicts();
}

bool ConflictResolver::matchesRoleConstraint(const KCalendarCore::Attendee &attendee)
{
    return mMandatoryRoles.contains(attendee.role());
}

KCalendarCore::Period::List ConflictResolver::availableSlots() const
{
    return mAvailableSlots;
}

void ConflictResolver::setResolution(int seconds)
{
    mSlotResolutionSeconds = seconds;
}

CalendarSupport::FreeBusyItemModel *ConflictResolver::model() const
{
    return mFBModel;
}
