// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0

#pragma once

#include "tasking_global.h"

#include "tasktree.h"

namespace Tasking {

class TASKING_EXPORT Barrier final : public QObject
{
    Q_OBJECT

public:
    void setLimit(int value);
    int limit() const { return m_limit; }

    void start();
    void advance(); // If limit reached, stops with true
    void stopWithResult(bool success); // Ignores limit

    bool isRunning() const { return m_current >= 0; }
    int current() const { return m_current; }
    std::optional<bool> result() const { return m_result; }

signals:
    void done(bool success);

private:
    std::optional<bool> m_result = {};
    int m_limit = 1;
    int m_current = -1;
};

class TASKING_EXPORT BarrierTaskAdapter : public TaskAdapter<Barrier>
{
public:
    BarrierTaskAdapter() { connect(task(), &Barrier::done, this, &TaskInterface::done); }
    void start() final { task()->start(); }
};

} // namespace Tasking

TASKING_DECLARE_TASK(BarrierTask, Tasking::BarrierTaskAdapter);

namespace Tasking {

template <int Limit = 1>
class SharedBarrier
{
public:
    static_assert(Limit > 0, "SharedBarrier's limit should be 1 or more.");
    SharedBarrier() : m_barrier(new Barrier) {
        m_barrier->setLimit(Limit);
        m_barrier->start();
    }
    Barrier *barrier() const { return m_barrier.get(); }

private:
    std::shared_ptr<Barrier> m_barrier;
};

template <int Limit = 1>
using MultiBarrier = TreeStorage<SharedBarrier<Limit>>;

// Can't write: "MultiBarrier barrier;". Only "MultiBarrier<> barrier;" would work.
// Can't have one alias with default type in C++17, getting the following error:
// alias template deduction only available with C++20.
using SingleBarrier = MultiBarrier<1>;

class TASKING_EXPORT WaitForBarrierTask : public BarrierTask
{
public:
    template <int Limit>
    WaitForBarrierTask(const MultiBarrier<Limit> &sharedBarrier)
        : BarrierTask([sharedBarrier](Barrier &barrier) {
            SharedBarrier<Limit> *activeBarrier = sharedBarrier.activeStorage();
            if (!activeBarrier) {
                qWarning("The barrier referenced from WaitForBarrier element "
                         "is not reachable in the running tree. "
                         "It is possible that no barrier was added to the tree, "
                         "or the storage is not reachable from where it is referenced. "
                         "The WaitForBarrier task will finish with error. ");
                return TaskAction::StopWithError;
            }
            Barrier *activeSharedBarrier = activeBarrier->barrier();
            const std::optional<bool> result = activeSharedBarrier->result();
            if (result.has_value())
                return result.value() ? TaskAction::StopWithDone : TaskAction::StopWithError;
            QObject::connect(activeSharedBarrier, &Barrier::done, &barrier, &Barrier::stopWithResult);
            return TaskAction::Continue;
        }) {}
};

} // namespace Tasking
