/* ============================================================
 *
 * This file is a part of digiKam
 *
 * Date        : 2024-10-28
 * Description : Threadsafe queue for submitting face training removal requests.
 *
 * SPDX-FileCopyrightText: 2024      by Michael Miller <micahel underscore miller at msn dot com>
 * SPDX-FileCopyrightText: 2024      by Gilles Caulier <caulier dot gilles at gmail dot com>
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 *
 * ============================================================ */

#pragma once

// C++ includes

#include <queue>
#include <mutex>
#include <condition_variable>

// Qt includes

#include <QString>
#include <QThread>

// Local includes

#include "digikam_export.h"

namespace Digikam
{

// template <typename T>
// class SharedQueue
// {
// public:

//     SharedQueue();
//     ~SharedQueue();

//     T&   front();
//     void pop_front();

//     void push_back(T& item);
//     void push_back(T&& item);

//     int  size();
//     bool empty();

// private:

//     std::deque<T>           queue_;
//     std::mutex              mutex_;
//     std::condition_variable cond_;
// }; 

// template <typename T>
// SharedQueue<T>::SharedQueue()  {}

// template <typename T>
// SharedQueue<T>::~SharedQueue() {}

// template <typename T>
// T& SharedQueue<T>::front()
// {
//     std::unique_lock<std::mutex> mlock(mutex_);

//     while (queue_.empty())
//     {
//         cond_.wait(mlock);
//     }

//     return queue_.front();
// }

// template <typename T>
// void SharedQueue<T>::pop_front()
// {
//     std::unique_lock<std::mutex> mlock(mutex_);

//     while (queue_.empty())
//     {
//         cond_.wait(mlock);
//     }

//     queue_.pop_front();
// }

// template <typename T>
// void SharedQueue<T>::push_back(T& item)
// {
//     std::unique_lock<std::mutex> mlock(mutex_);
//     queue_.push_back(item);
//     mlock.unlock();         // Unlock before notificiation to minimize mutex con.
//     cond_.notify_one();     // Notify one waiting thread.
// }

// template <typename T>
// void SharedQueue<T>::push_back(T&& item)
// {
//     std::unique_lock<std::mutex> mlock(mutex_);
//     queue_.push_back(std::move(item));
//     mlock.unlock();         // Unlock before notificiation to minimize mutex con.
//     cond_.notify_one();     // Notify one waiting thread?
// }

// template <typename T>
// int SharedQueue<T>::size()
// {
//     std::unique_lock<std::mutex> mlock(mutex_);
//     int size = queue_.size();
//     mlock.unlock();

//     return size;
// }

// -----------------------------------------------------
template <typename T>
class SharedQueue;

class DIGIKAM_GUI_EXPORT RecognitionTrainingUpdateQueue
{
public:

    RecognitionTrainingUpdateQueue();
    ~RecognitionTrainingUpdateQueue();

public:

    void push(const QString& hash);
    void pop();
    QString front();

    QString endSignal();

    void registerReaderThread(const QThread* thread);
    void unregisterReaderThread(const QThread* thread);

private:

    static SharedQueue<QString>             queue;
    static QList<const QThread*>            readers;
    static int                              ref;

    Q_DISABLE_COPY(RecognitionTrainingUpdateQueue)
};

} // namespace Digikam
