/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the QtConcurrent module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 3 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL3 included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 3 requirements
** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 2.0 or (at your option) the GNU General
** Public license version 3 or any later version approved by the KDE Free
** Qt Foundation. The licenses are as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
** included in the packaging of this file. Please review the following
** information to ensure the GNU General Public License requirements will
** be met: https://www.gnu.org/licenses/gpl-2.0.html and
** https://www.gnu.org/licenses/gpl-3.0.html.
**
** $QT_END_LICENSE$
**
****************************************************************************/

#ifndef QTCONCURRENT_REDUCEKERNEL_H
#define QTCONCURRENT_REDUCEKERNEL_H

#include <QtConcurrent/qtconcurrent_global.h>

#if !defined(QT_NO_CONCURRENT) || defined(Q_CLANG_QDOC)

#include <QtCore/qatomic.h>
#include <QtCore/qlist.h>
#include <QtCore/qmap.h>
#include <QtCore/qmutex.h>
#include <QtCore/qthread.h>
#include <QtCore/qthreadpool.h>
#include <QtCore/qvector.h>

#include <mutex>

QT_BEGIN_NAMESPACE


namespace QtConcurrent {

/*
    The ReduceQueueStartLimit and ReduceQueueThrottleLimit constants
    limit the reduce queue size for MapReduce. When the number of
    reduce blocks in the queue exceeds ReduceQueueStartLimit,
    MapReduce won't start any new threads, and when it exceeds
    ReduceQueueThrottleLimit running threads will be stopped.
*/
#ifdef Q_CLANG_QDOC
enum ReduceQueueLimits {
    ReduceQueueStartLimit = 20,
    ReduceQueueThrottleLimit = 30
};
#else
enum {
    ReduceQueueStartLimit = 20,
    ReduceQueueThrottleLimit = 30
};
#endif

// IntermediateResults holds a block of intermediate results from a
// map or filter functor. The begin/end offsets indicates the origin
// and range of the block.
template <typename T>
class IntermediateResults
{
public:
    int begin, end;
    QVector<T> vector;
};

enum ReduceOption {
    UnorderedReduce = 0x1,
    OrderedReduce = 0x2,
    SequentialReduce = 0x4
    // ParallelReduce = 0x8
};
Q_DECLARE_FLAGS(ReduceOptions, ReduceOption)
#ifndef Q_CLANG_QDOC
Q_DECLARE_OPERATORS_FOR_FLAGS(ReduceOptions)
#endif
// supports both ordered and out-of-order reduction
template <typename ReduceFunctor, typename ReduceResultType, typename T>
class ReduceKernel
{
    typedef QMap<int, IntermediateResults<T> > ResultsMap;

    const ReduceOptions reduceOptions;

    QMutex mutex;
    int progress, resultsMapSize, threadCount;
    ResultsMap resultsMap;

    bool canReduce(int begin) const
    {
        return (((reduceOptions & UnorderedReduce)
                 && progress == 0)
                || ((reduceOptions & OrderedReduce)
                    && progress == begin));
    }

    void reduceResult(ReduceFunctor &reduce,
                      ReduceResultType &r,
                      const IntermediateResults<T> &result)
    {
        for (int i = 0; i < result.vector.size(); ++i) {
            reduce(r, result.vector.at(i));
        }
    }

    void reduceResults(ReduceFunctor &reduce,
                       ReduceResultType &r,
                       ResultsMap &map)
    {
        typename ResultsMap::iterator it = map.begin();
        while (it != map.end()) {
            reduceResult(reduce, r, it.value());
            ++it;
        }
    }

public:
    ReduceKernel(ReduceOptions _reduceOptions)
        : reduceOptions(_reduceOptions), progress(0), resultsMapSize(0),
          threadCount(QThreadPool::globalInstance()->maxThreadCount())
    { }

    void runReduce(ReduceFunctor &reduce,
                   ReduceResultType &r,
                   const IntermediateResults<T> &result)
    {
        std::unique_lock<QMutex> locker(mutex);
        if (!canReduce(result.begin)) {
            ++resultsMapSize;
            resultsMap.insert(result.begin, result);
            return;
        }

        if (reduceOptions & UnorderedReduce) {
            // UnorderedReduce
            progress = -1;

            // reduce this result
            locker.unlock();
            reduceResult(reduce, r, result);
            locker.lock();

            // reduce all stored results as well
            while (!resultsMap.isEmpty()) {
                ResultsMap resultsMapCopy = resultsMap;
                resultsMap.clear();

                locker.unlock();
                reduceResults(reduce, r, resultsMapCopy);
                locker.lock();

                resultsMapSize -= resultsMapCopy.size();
            }

            progress = 0;
        } else {
            // reduce this result
            locker.unlock();
            reduceResult(reduce, r, result);
            locker.lock();

            // OrderedReduce
            progress += result.end - result.begin;

            // reduce as many other results as possible
            typename ResultsMap::iterator it = resultsMap.begin();
            while (it != resultsMap.end()) {
                if (it.value().begin != progress)
                    break;

                locker.unlock();
                reduceResult(reduce, r, it.value());
                locker.lock();

                --resultsMapSize;
                progress += it.value().end - it.value().begin;
                it = resultsMap.erase(it);
            }
        }
    }

    // final reduction
    void finish(ReduceFunctor &reduce, ReduceResultType &r)
    {
        reduceResults(reduce, r, resultsMap);
    }

    inline bool shouldThrottle()
    {
        return (resultsMapSize > (ReduceQueueThrottleLimit * threadCount));
    }

    inline bool shouldStartThread()
    {
        return (resultsMapSize <= (ReduceQueueStartLimit * threadCount));
    }
};

template <typename Sequence, typename Base, typename Functor1, typename Functor2>
struct SequenceHolder2 : public Base
{
    SequenceHolder2(const Sequence &_sequence,
                    Functor1 functor1,
                    Functor2 functor2,
                    ReduceOptions reduceOptions)
        : Base(_sequence.begin(), _sequence.end(), functor1, functor2, reduceOptions),
          sequence(_sequence)
    { }

    Sequence sequence;

    void finish() override
    {
        Base::finish();
        // Clear the sequence to make sure all temporaries are destroyed
        // before finished is signaled.
        sequence = Sequence();
    }
};

} // namespace QtConcurrent

QT_END_NAMESPACE

#endif // QT_NO_CONCURRENT

#endif