qt-promise-handler.hpp
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qt-promise-handler.hpp
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	/*
	* This file is part of kazv.
	* SPDX-FileCopyrightText: 2020-2023 tusooa <tusooa@kazv.moe>
	* SPDX-License-Identifier: AGPL-3.0-or-later
	*/

	#pragma once
	#include <kazv-defs.hpp>

	#include <future>

	#include <QObject>
	#include <QMetaObject>
	#include <QPointer>
	#include <QTimer>

	#include <promise-interface.hpp>

	template<class T>
	class QtPromise;

	namespace QtPromiseDetail
	{
	struct QtPromiseHelper
	{
	template<class T>
	using PromiseType = QtPromise<T>;
	};

	struct IdentityFunc
	{
	template<class T>
	constexpr T &&operator()(T &&t) const {
	return std::forward<T>(t);
	}
	};

	template<class Func>
	void post(QObject *obj, Func &&func)
	{
	QMetaObject::invokeMethod(obj, std::forward<Func>(func), Qt::QueuedConnection);
	}
	}

	class QtPromiseSignalTrigger : public QObject
	{
	Q_OBJECT
	public:
	QtPromiseSignalTrigger(QObject *parent = 0);

	~QtPromiseSignalTrigger();

	Q_SIGNALS:
	void finished();
	};

	template<class T>
	class QtPromise : public Kazv::AbstractPromise<QtPromiseDetail::QtPromiseHelper::PromiseType, T>
	{
	using BaseT = Kazv::AbstractPromise<QtPromiseDetail::QtPromiseHelper::PromiseType, T>;

	template<class FuncT, class PromiseT, class ResolveT>
	struct WaitHelper
	{
	void resolveOrWait()
	{
	auto res = func(p.get());
	using ResT = decltype(res);
	if constexpr (Kazv::isPromise<ResT>) {
	res.then([resolve=resolve](auto val) {
	resolve(std::move(val));
	return std::decay_t<decltype(val)>(); // we don't care about this value
	});
	} else {
	resolve(res);
	}
	}

	void wait()
	{
	if (p.ready()) {
	QtPromiseDetail::post(
	executor,
	[*this]() mutable { resolveOrWait(); }
	);
	} else {
	QObject::connect(
	p.m_signalTrigger, &QtPromiseSignalTrigger::finished,
	executor, [*this]() mutable {
	resolveOrWait();
	}
	);
	}
	}

	QPointer<QObject> executor;
	PromiseT p;
	FuncT func;
	ResolveT resolve;
	};

	struct ResolveHelper
	{
	template<class ValT>
	void operator()(ValT val) const
	{
	using ResT = std::decay_t<decltype(val)>;
	if constexpr (Kazv::isPromise<ResT>) {
	QtPromiseDetail::post(
	executor,
	[qtPromise=std::move(val), *this]() mutable {
	if (qtPromise.ready()) {
	setValue(qtPromise.get());
	} else {
	qtPromise.then([*this](auto val) mutable {
	setValue(std::move(val));
	return std::decay_t<decltype(val)>(); // we don't care about this value
	});
	}
	});
	} else {
	QtPromiseDetail::post(
	executor,
	[*this, val=std::move(val)]() mutable {
	setValue(std::move(val));
	});
	}
	}

	void setValue(T resolvedValue) const
	{
	p->set_value(std::move(resolvedValue));
	if (signalTrigger) {
	Q_EMIT signalTrigger->finished();
	signalTrigger->deleteLater();
	}
	}

	QPointer<QObject> executor;
	QPointer<QtPromiseSignalTrigger> signalTrigger;
	std::shared_ptr<std::promise<T>> p;
	};
	public:
	QtPromise(QObject *executor, T value)
	: BaseT(this)
	, m_executor(executor)
	, m_signalTrigger()
	{
	std::promise<T> p;
	m_val = p.get_future().share();
	p.set_value(std::move(value));
	}

	template<class Func>
	QtPromise(QObject *executor, Func &&callback)
	: BaseT(this)
	, m_executor(executor)
	, m_signalTrigger(new QtPromiseSignalTrigger())
	{
	auto p = std::make_shared<std::promise<T>>();
	m_val = p->get_future().share();

	m_signalTrigger->moveToThread(m_executor->thread());
	auto resolve = ResolveHelper{m_executor, m_signalTrigger, p};

	QtPromiseDetail::post(
	m_executor,
	[=, callback=std::forward<Func>(callback),
	resolve=std::move(resolve)]() {
	callback(resolve);
	});
	}

	// FuncT: (DataT) -> AnotherDataT
	// where AnotherDataT = PromiseThenResult<FuncT, typename BaseT::DataT>
	template<class FuncT>
	auto then(FuncT &&func)
	-> QtPromise<Kazv::PromiseThenResult<FuncT, typename BaseT::DataT>> {
	return QtPromise<Kazv::PromiseThenResult<FuncT, typename BaseT::DataT>>(
	m_executor,
	[=, func=std::forward<FuncT>(func), *this](auto resolve) {
	auto waitHelper = WaitHelper<std::decay_t<FuncT>,
	QtPromise,
	std::decay_t<decltype(resolve)>>{
	m_executor,
	*this,
	func,
	resolve
	};
	waitHelper.wait();
	});
	}

	bool ready() const {
	return m_val.wait_for(std::chrono::seconds(0)) == std::future_status::ready;
	}

	T get() const {
	return m_val.get();
	}
	private:
	QPointer<QObject> m_executor;
	QPointer<QtPromiseSignalTrigger> m_signalTrigger;
	std::shared_future<T> m_val;
	};

	class QtPromiseHandler : public Kazv::PromiseInterface<QtPromiseHandler,
	QtPromiseDetail::QtPromiseHelper::PromiseType>
	{
	using BaseT = Kazv::PromiseInterface<QtPromiseHandler,
	QtPromiseDetail::QtPromiseHelper::PromiseType>;
	public:
	template<class T>
	using PromiseT = QtPromise<T>;

	QtPromiseHandler(std::reference_wrapper<QObject> executor)
	: BaseT(this)
	, m_executor(&executor.get())
	{}

	QtPromiseHandler(const QtPromiseHandler &that)
	: BaseT(this)
	, m_executor(that.m_executor)
	{}

	QtPromiseHandler(QtPromiseHandler &&that)
	: BaseT(this)
	, m_executor(std::move(that.m_executor))
	{}

	QtPromiseHandler &operator=(const QtPromiseHandler &that) {
	m_executor = that.m_executor;
	return *this;
	}

	QtPromiseHandler &operator=(QtPromiseHandler &&that) {
	m_executor = std::move(that.m_executor);
	return *this;
	}

	template<class T, class FuncT>
	PromiseT<T> create(FuncT &&func) {
	return PromiseT<T>(m_executor, std::forward<FuncT>(func));
	}

	template<class T>
	PromiseT<T> createResolved(T val) {
	return PromiseT<T>(m_executor, std::move(val));
	}

	private:
	QPointer<QObject> m_executor;
	};

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