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**
** Copyright (C) 2016 The Qt Company Ltd.
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**
** This file is part of Qt Creator.
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** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3 as published by the Free Software
** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
** included in the packaging of this file. Please review the following
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#pragma once

#include "functiontraits.h"
#include "optional.h"
#include "utils_global.h"

#include <QCoreApplication>
#include <QFuture>
#include <QFutureInterface>
#include <QFutureWatcher>
#include <QRunnable>
#include <QThread>
#include <QThreadPool>

#include <functional>

// hasCallOperator & Co must be outside of any namespace
// because of internal compiler error with MSVC2015 Update 2

using testCallOperatorYes = char;
using testCallOperatorNo = struct { char foo[2]; };

template<typename C>
static testCallOperatorYes testCallOperator(decltype(&C::operator()));

template<typename>
static testCallOperatorNo testCallOperator(...);

template<typename T>
struct hasCallOperator
{
    static const bool value = (sizeof(testCallOperator<T>(nullptr)) == sizeof(testCallOperatorYes));
};

namespace Utils {

using StackSizeInBytes = optional<uint>;

namespace Internal {

/*
   resultType<F>::type

   Returns the type of results that would be reported by a callable of type F
   when called through the runAsync methods. I.e. the ResultType in

   void f(QFutureInterface<Result> &fi, ...)
   ResultType f(...)

   Returns void if F is not callable, and if F is a callable that does not take
   a QFutureInterface& as its first parameter and returns void.
*/

template <typename Function>
struct resultType;

template <typename Function, typename Arg>
struct resultTypeWithArgument;

template <typename Function, int index, bool>
struct resultTypeTakesArguments;

template <typename Function, bool>
struct resultTypeIsMemberFunction;

template <typename Function, bool>
struct resultTypeIsFunctionLike;

template <typename Function, bool>
struct resultTypeHasCallOperator;

template <typename Function, typename ResultType>
struct resultTypeWithArgument<Function, QFutureInterface<ResultType>&>
{
    using type = ResultType;
};

template <typename Function, typename Arg>
struct resultTypeWithArgument
{
    using type = functionResult_t<Function>;
};

template <typename Function, int index>
struct resultTypeTakesArguments<Function, index, true>
        : public resultTypeWithArgument<Function, typename functionTraits<Function>::template argument<index>::type>
{
};

template <typename Function, int index>
struct resultTypeTakesArguments<Function, index, false>
{
    using type = functionResult_t<Function>;
};

template <typename Function>
struct resultTypeIsFunctionLike<Function, true>
        : public resultTypeTakesArguments<Function, 0, (functionTraits<Function>::arity > 0)>
{
};

template <typename Function>
struct resultTypeIsMemberFunction<Function, true>
        : public resultTypeTakesArguments<Function, 1, (functionTraits<Function>::arity > 1)>
{
};

template <typename Function>
struct resultTypeIsMemberFunction<Function, false>
{
    using type = void;
};

template <typename Function>
struct resultTypeIsFunctionLike<Function, false>
        : public resultTypeIsMemberFunction<Function, std::is_member_function_pointer<Function>::value>
{
};

template <typename Function>
struct resultTypeHasCallOperator<Function, false>
        : public resultTypeIsFunctionLike<Function, std::is_function<std::remove_pointer_t<std::decay_t<Function>>>::value>
{
};

template <typename Callable>
struct resultTypeHasCallOperator<Callable, true>
        : public resultTypeTakesArguments<Callable, 0, (functionTraits<Callable>::arity > 0)>
{
};

template <typename Function>
struct resultType
        : public resultTypeHasCallOperator<Function, hasCallOperator<Function>::value>
{
};

template <typename Function>
struct resultType<Function&> : public resultType<Function>
{
};

template <typename Function>
struct resultType<const Function&> : public resultType<Function>
{
};

template <typename Function>
struct resultType<Function &&> : public resultType<Function>
{
};

template <typename Function>
struct resultType<std::reference_wrapper<Function>> : public resultType<Function>
{
};
template <typename Function>
struct resultType<std::reference_wrapper<const Function>> : public resultType<Function>
{
};

/*
   Callable object that wraps a member function pointer with the object it
   will be called on.
*/

template <typename Function>
class MemberCallable;

template <typename Result, typename Obj, typename... Args>
class MemberCallable<Result(Obj::*)(Args...) const>
{
public:
    MemberCallable(Result(Obj::* function)(Args...) const, const Obj *obj)
        : m_function(function),
          m_obj(obj)
    {
    }

    Result operator()(Args&&... args) const
    {
        return ((*m_obj).*m_function)(std::forward<Args>(args)...);
    }

private:
    Result(Obj::* m_function)(Args...) const;
    const Obj *m_obj;
};

template <typename Result, typename Obj, typename... Args>
class MemberCallable<Result(Obj::*)(Args...)>
{
public:
    MemberCallable(Result(Obj::* function)(Args...), Obj *obj)
        : m_function(function),
          m_obj(obj)
    {
    }

    Result operator()(Args&&... args) const
    {
        return ((*m_obj).*m_function)(std::forward<Args>(args)...);
    }

private:
    Result(Obj::* m_function)(Args...);
    Obj *m_obj;
};

/*
   Helper functions for runAsync that run in the started thread.
*/

// void function that does not take QFutureInterface
template <typename ResultType, typename Function, typename... Args>
void runAsyncReturnVoidDispatch(std::true_type, QFutureInterface<ResultType> &, Function &&function, Args&&... args)
{
    function(std::forward<Args>(args)...);
}

// non-void function that does not take QFutureInterface
template <typename ResultType, typename Function, typename... Args>
void runAsyncReturnVoidDispatch(std::false_type, QFutureInterface<ResultType> &futureInterface, Function &&function, Args&&... args)
{
    futureInterface.reportResult(function(std::forward<Args>(args)...));
}

// function that takes QFutureInterface
template <typename ResultType, typename Function, typename... Args>
void runAsyncQFutureInterfaceDispatch(std::true_type, QFutureInterface<ResultType> &futureInterface, Function &&function, Args&&... args)
{
    function(futureInterface, std::forward<Args>(args)...);
}

// function that does not take QFutureInterface
template <typename ResultType, typename Function, typename... Args>
void runAsyncQFutureInterfaceDispatch(std::false_type, QFutureInterface<ResultType> &futureInterface, Function &&function, Args&&... args)
{
    runAsyncReturnVoidDispatch(std::is_void<std::invoke_result_t<Function, Args...>>(),
                               futureInterface, std::forward<Function>(function), std::forward<Args>(args)...);
}

// function, function pointer, or other callable object that is no member pointer
template <typename ResultType, typename Function, typename... Args,
          typename = std::enable_if_t<!std::is_member_pointer<std::decay_t<Function>>::value>
         >
void runAsyncMemberDispatch(QFutureInterface<ResultType> &futureInterface, Function &&function, Args&&... args)
{
    runAsyncQFutureInterfaceDispatch(functionTakesArgument<Function, 0, QFutureInterface<ResultType>&>(),
                                     futureInterface, std::forward<Function>(function), std::forward<Args>(args)...);
}

// Function = member function
template <typename ResultType, typename Function, typename Obj, typename... Args,
          typename = std::enable_if_t<std::is_member_pointer<std::decay_t<Function>>::value>
         >
void runAsyncMemberDispatch(QFutureInterface<ResultType> &futureInterface, Function &&function, Obj &&obj, Args&&... args)
{
    // Wrap member function with object into callable
    runAsyncImpl(futureInterface,
                 MemberCallable<std::decay_t<Function>>(std::forward<Function>(function), std::forward<Obj>(obj)),
                 std::forward<Args>(args)...);
}

// cref to function/callable
template <typename ResultType, typename Function, typename... Args>
void runAsyncImpl(QFutureInterface<ResultType> &futureInterface,
                  std::reference_wrapper<Function> functionWrapper, Args&&... args)
{
    runAsyncMemberDispatch(futureInterface, functionWrapper.get(), std::forward<Args>(args)...);
}

// function/callable, no cref
template <typename ResultType, typename Function, typename... Args>
void runAsyncImpl(QFutureInterface<ResultType> &futureInterface,
                  Function &&function, Args&&... args)
{
    runAsyncMemberDispatch(futureInterface, std::forward<Function>(function),
                           std::forward<Args>(args)...);
}
/*
   AsyncJob is a QRunnable that wraps a function with the
   arguments that are passed to it when it is run in a thread.
*/

template <class T>
std::decay_t<T>
decayCopy(T&& v)
{
    return std::forward<T>(v);
}

template <typename ResultType, typename Function, typename... Args>
class AsyncJob : public QRunnable
{
public:
    AsyncJob(Function &&function, Args&&... args)
          // decay copy like std::thread
        : data(decayCopy(std::forward<Function>(function)), decayCopy(std::forward<Args>(args))...)
    {
        // we need to report it as started even though it isn't yet, because someone might
        // call waitForFinished on the future, which does _not_ block if the future is not started
        futureInterface.setRunnable(this);
        futureInterface.reportStarted();
    }

    ~AsyncJob() override
    {
        // QThreadPool can delete runnables even if they were never run (e.g. QThreadPool::clear).
        // Since we reported them as started, we make sure that we always report them as finished.
        // reportFinished only actually sends the signal if it wasn't already finished.
        futureInterface.reportFinished();
    }

    QFuture<ResultType> future() { return futureInterface.future(); }

    void run() override
    {
        if (priority != QThread::InheritPriority)
            if (QThread *thread = QThread::currentThread())
                if (thread != qApp->thread())
                    thread->setPriority(priority);
        if (futureInterface.isCanceled()) {
            futureInterface.reportFinished();
            return;
        }
        runHelper(std::make_index_sequence<std::tuple_size<Data>::value>());
    }

    void setThreadPool(QThreadPool *pool)
    {
        futureInterface.setThreadPool(pool);
    }

    void setThreadPriority(QThread::Priority p)
    {
        priority = p;
    }

private:
    using Data = std::tuple<std::decay_t<Function>, std::decay_t<Args>...>;

    template <std::size_t... index>
    void runHelper(std::index_sequence<index...>)
    {
        // invalidates data, which is moved into the call
        runAsyncImpl(futureInterface, std::move(std::get<index>(data))...);
        if (futureInterface.isPaused())
            futureInterface.waitForResume();
        futureInterface.reportFinished();
    }

    Data data;
    QFutureInterface<ResultType> futureInterface;
    QThread::Priority priority = QThread::InheritPriority;
};

class QTCREATOR_UTILS_EXPORT RunnableThread : public QThread
{
public:
    explicit RunnableThread(QRunnable *runnable, QObject *parent = nullptr);

protected:
    void run() override;

private:
    QRunnable *m_runnable;
};

template<typename Function,
         typename... Args,
         typename ResultType = typename Internal::resultType<Function>::type>
QFuture<ResultType> runAsync_internal(QThreadPool *pool,
                                      StackSizeInBytes stackSize,
                                      QThread::Priority priority,
                                      Function &&function,
                                      Args &&... args)
{
    Q_ASSERT(!(pool && stackSize)); // stack size cannot be changed once a thread is started
    auto job = new Internal::AsyncJob<ResultType,Function,Args...>
            (std::forward<Function>(function), std::forward<Args>(args)...);
    job->setThreadPriority(priority);
    QFuture<ResultType> future = job->future();
    if (pool) {
        job->setThreadPool(pool);
        pool->start(job);
    } else {
        auto thread = new Internal::RunnableThread(job);
        if (stackSize)
            thread->setStackSize(stackSize.value());
        thread->moveToThread(qApp->thread()); // make sure thread gets deleteLater on main thread
        QObject::connect(thread, &QThread::finished, thread, &QObject::deleteLater);
        thread->start(priority);
    }
    return future;
}

} // Internal

/*!
    The interface of \c {runAsync} is similar to the std::thread constructor and \c {std::invoke}.

    The \a function argument can be a member function,
    an object with \c {operator()} (with no overloads),
    a \c {std::function}, lambda, function pointer or function reference.
    The \a args are passed to the function call after they are copied/moved to the thread.

    The \a function can take a \c {QFutureInterface<ResultType>&} as its first argument, followed by
    other custom arguments which need to be passed to this function.
    If it does not take a \c {QFutureInterface<ResultType>&} as its first argument
    and its return type is not void, the function call's result is reported to the QFuture.
    If \a function is a (non-static) member function, the first argument in \a args is expected
    to be the object that the function is called on.

    If a thread \a pool is given, the function is run there. Otherwise a new, independent thread
    is started.

    \sa std::thread
    \sa std::invoke
    \sa QThreadPool
    \sa QThread::Priority
 */
template <typename Function, typename... Args,
          typename ResultType = typename Internal::resultType<Function>::type>
QFuture<ResultType>
runAsync(QThreadPool *pool, QThread::Priority priority, Function &&function, Args&&... args)
{
    return Internal::runAsync_internal(pool,
                                       StackSizeInBytes(),
                                       priority,
                                       std::forward<Function>(function),
                                       std::forward<Args>(args)...);
}

/*!
    Runs \a function with \a args in a new thread with given thread \a priority.
    \sa runAsync(QThreadPool*,QThread::Priority,Function&&,Args&&...)
    \sa QThread::Priority
 */
template <typename Function, typename... Args,
          typename ResultType = typename Internal::resultType<Function>::type>
QFuture<ResultType>
runAsync(QThread::Priority priority, Function &&function, Args&&... args)
{
    return runAsync(static_cast<QThreadPool *>(nullptr), priority,
                    std::forward<Function>(function), std::forward<Args>(args)...);
}

/*!
    Runs \a function with \a args in a new thread with given thread \a stackSize and
    thread priority QThread::InheritPriority .
    \sa runAsync(QThreadPool*,QThread::Priority,Function&&,Args&&...)
    \sa QThread::Priority
    \sa QThread::setStackSize
*/
template<typename Function,
         typename... Args,
         typename ResultType = typename Internal::resultType<Function>::type>
QFuture<ResultType> runAsync(Utils::StackSizeInBytes stackSize, Function &&function, Args &&... args)
{
    return Internal::runAsync_internal(static_cast<QThreadPool *>(nullptr),
                                       stackSize,
                                       QThread::InheritPriority,
                                       std::forward<Function>(function),
                                       std::forward<Args>(args)...);
}

/*!
    Runs \a function with \a args in a new thread with given thread \a stackSize and
    given thread \a priority.
    \sa runAsync(QThreadPool*,QThread::Priority,Function&&,Args&&...)
    \sa QThread::Priority
    \sa QThread::setStackSize
*/
template<typename Function,
         typename... Args,
         typename ResultType = typename Internal::resultType<Function>::type>
QFuture<ResultType> runAsync(Utils::StackSizeInBytes stackSize,
                             QThread::Priority priority,
                             Function &&function,
                             Args &&... args)
{
    return Internal::runAsync_internal(static_cast<QThreadPool *>(nullptr),
                                       stackSize,
                                       priority,
                                       std::forward<Function>(function),
                                       std::forward<Args>(args)...);
}

/*!
    Runs \a function with \a args in a new thread with thread priority QThread::InheritPriority.
    \sa runAsync(QThreadPool*,QThread::Priority,Function&&,Args&&...)
    \sa QThread::Priority
 */
template <typename Function, typename... Args,
          typename = std::enable_if_t<
                !std::is_same<std::decay_t<Function>, QThreadPool>::value
                && !std::is_same<std::decay_t<Function>, QThread::Priority>::value
              >,
          typename ResultType = typename Internal::resultType<Function>::type>
QFuture<ResultType>
runAsync(Function &&function, Args&&... args)
{
    return runAsync(static_cast<QThreadPool *>(nullptr),
                    QThread::InheritPriority, std::forward<Function>(function),
                    std::forward<Args>(args)...);
}

/*!
    Runs \a function with \a args in a thread \a pool with thread priority QThread::InheritPriority.
    \sa runAsync(QThreadPool*,QThread::Priority,Function&&,Args&&...)
    \sa QThread::Priority
 */
template <typename Function, typename... Args,
          typename = std::enable_if_t<!std::is_same<std::decay_t<Function>, QThread::Priority>::value>,
          typename ResultType = typename Internal::resultType<Function>::type>
QFuture<ResultType>
runAsync(QThreadPool *pool, Function &&function, Args&&... args)
{
    return runAsync(pool, QThread::InheritPriority, std::forward<Function>(function),
                    std::forward<Args>(args)...);
}


/*!
    Adds a handler for when a result is ready.
    This creates a new QFutureWatcher. Do not use if you intend to react on multiple conditions
    or create a QFutureWatcher already for other reasons.
*/
template <typename R, typename T>
const QFuture<T> &onResultReady(const QFuture<T> &future, R *receiver, void(R::*member)(const T &))
{
    auto watcher = new QFutureWatcher<T>();
    QObject::connect(watcher, &QFutureWatcherBase::finished, watcher, &QObject::deleteLater);
    QObject::connect(watcher, &QFutureWatcherBase::resultReadyAt, receiver,
                     [receiver, member, watcher](int index) {
                         (receiver->*member)(watcher->future().resultAt(index));
                     });
    watcher->setFuture(future);
    return future;
}

/*!
    Adds a handler for when a result is ready. The guard object determines the lifetime of
    the connection.
    This creates a new QFutureWatcher. Do not use if you intend to react on multiple conditions
    or create a QFutureWatcher already for other reasons.
*/
template <typename T, typename Function>
const QFuture<T> &onResultReady(const QFuture<T> &future, QObject *guard, Function f)
{
    auto watcher = new QFutureWatcher<T>();
    QObject::connect(watcher, &QFutureWatcherBase::finished, watcher, &QObject::deleteLater);
    QObject::connect(watcher, &QFutureWatcherBase::resultReadyAt, guard, [f, watcher](int index) {
        f(watcher->future().resultAt(index));
    });
    watcher->setFuture(future);
    return future;
}

/*!
    Adds a handler for when a result is ready.
    This creates a new QFutureWatcher. Do not use if you intend to react on multiple conditions
    or create a QFutureWatcher already for other reasons.
*/
template <typename T, typename Function>
const QFuture<T> &onResultReady(const QFuture<T> &future, Function f)
{
    auto watcher = new QFutureWatcher<T>();
    QObject::connect(watcher, &QFutureWatcherBase::finished, watcher, &QObject::deleteLater);
    QObject::connect(watcher, &QFutureWatcherBase::resultReadyAt, [f, watcher](int index) {
        f(watcher->future().resultAt(index));
    });
    watcher->setFuture(future);
    return future;
}

/*!
    Adds a handler for when the future is finished.
    This creates a new QFutureWatcher. Do not use if you intend to react on multiple conditions
    or create a QFutureWatcher already for other reasons.
*/
template<typename R, typename T>
const QFuture<T> &onFinished(const QFuture<T> &future,
                             R *receiver,
                             void (R::*member)(const QFuture<T> &))
{
    auto watcher = new QFutureWatcher<T>();
    QObject::connect(watcher, &QFutureWatcherBase::finished, watcher, &QObject::deleteLater);
    QObject::connect(watcher,
                     &QFutureWatcherBase::finished,
                     receiver,
                     [receiver, member, watcher]() { (receiver->*member)(watcher->future()); });
    watcher->setFuture(future);
    return future;
}

/*!
    Adds a handler for when the future is finished. The guard object determines the lifetime of
    the connection.
    This creates a new QFutureWatcher. Do not use if you intend to react on multiple conditions
    or create a QFutureWatcher already for other reasons.
*/
template<typename T, typename Function>
const QFuture<T> &onFinished(const QFuture<T> &future, QObject *guard, Function f)
{
    auto watcher = new QFutureWatcher<T>();
    QObject::connect(watcher, &QFutureWatcherBase::finished, watcher, &QObject::deleteLater);
    QObject::connect(watcher, &QFutureWatcherBase::finished, guard, [f, watcher]() {
        f(watcher->future());
    });
    watcher->setFuture(future);
    return future;
}

/*!
    Adds a handler for when the future is finished.
    This creates a new QFutureWatcher. Do not use if you intend to react on multiple conditions
    or create a QFutureWatcher already for other reasons.
*/
template<typename T, typename Function>
const QFuture<T> &onFinished(const QFuture<T> &future, Function f)
{
    auto watcher = new QFutureWatcher<T>();
    QObject::connect(watcher, &QFutureWatcherBase::finished, watcher, &QObject::deleteLater);
    QObject::connect(watcher, &QFutureWatcherBase::finished, [f, watcher]() {
        f(watcher->future());
    });
    watcher->setFuture(future);
    return future;
}

} // namespace Utils
