#pragma once

#if __cplusplus < 201103L
#error "C++ version lower than C++11"
#endif

#include <mutex>
#include <condition_variable>
#include <memory>
#include <chrono>
#include <cassert>

namespace std {

enum class future_status {
    ready,
    timeout,
    deferred
};

namespace detail {

class shared_state_base {
protected:
    typedef void (*deleter_fn)(void *v);

    using scoped_lock = std::lock_guard<std::mutex>;
    using unique_lock = std::unique_lock<std::mutex>;
public:
    explicit shared_state_base(deleter_fn d) : v_(nullptr), d_(d), valid_(true) {}

    ~shared_state_base() { d_(v_); }

    shared_state_base(shared_state_base &&other) = delete;

    shared_state_base(const shared_state_base &other) = delete;

    shared_state_base &operator=(shared_state_base &&other) = delete;

    shared_state_base &operator=(const shared_state_base &other) = delete;

    void wait() {
        unique_lock lock(m_);
        c_.wait(lock, [this] { return has_value(); });
    }

    template <class Rep, class Period>
    std::future_status
    wait_for(const std::chrono::duration<Rep, Period> &rel_time) {
        unique_lock lock(m_);
        if (c_.wait_for(lock, rel_time, [this] { return has_value(); })) {
            return std::future_status::ready;
        }
        return std::future_status::timeout;
    }

    template <class Clock, class Duration>
    std::future_status
    wait_until(const std::chrono::time_point<Clock, Duration> &abs_time) {
        unique_lock lock(m_);
        if (c_.wait_until(lock, abs_time, [this] { return has_value(); })) {
            return std::future_status::ready;
        }
        return std::future_status::timeout;
    }

protected:
    bool has_value() { return v_ != nullptr; }

protected:
    std::mutex m_;
    std::condition_variable c_;
    void *v_;
    deleter_fn d_;
    bool valid_;
};


template <typename R>
class shared_state: public shared_state_base {
public:
    shared_state() :shared_state_base(default_deleter_) {}

    ~shared_state() {}

    R &get() {
        wait();
        scoped_lock lock(m_);
        assert(valid_);
        valid_ = false;
        return *(static_cast<R *>(v_));
    }

    void set(const R &v) {
        scoped_lock lock(m_);
        assert(!has_value());
        v_ = new R(v);
        valid_ = true;
        c_.notify_one();
    }

    void set(R &&v) {
        scoped_lock lock(m_);
        assert(!has_value());
        v_ = new R(std::move(v));
        valid_ = true;
        c_.notify_one();
    }

    bool valid() {
        scoped_lock lock(m_);
        return valid_;
    }

private:
    static void default_deleter_(void *v) { delete static_cast<R *>(v); }
};

} // namespace detail

template <typename R>
class shared_future {
};


template <typename R>
class future {
    using state_type = std::shared_ptr<detail::shared_state<R>>;
public:
    future() {}

    explicit future(const state_type &state) : state_(state) {}

    future(future &&other) noexcept: state_(std::move(other.state_)) {
        other.state_.reset();
    }

    future(const future &other) = delete;

    ~future() {}

    future &operator=(future &&other) noexcept {
        if (&other != this) {
            state_ = std::move(other.state_);
            other.state_.reset();
        }
        return *this;
    }

    future &operator=(const future &other) = delete;

    void swap(future &other) noexcept {
        std::swap(state_, other.state_);
    }

    std::shared_future<R> share() noexcept { return std::shared_future<R>(); }

    R get() { return state_->get(); }

    bool valid() const noexcept { return state_->valid(); }

    void wait() const { state_->wait(); }

    template <class Rep, class Period>
    std::future_status
    wait_for(const std::chrono::duration<Rep, Period> &rel_time) const {
        return state_->wait_for(rel_time);
    }

    template <class Clock, class Duration>
    std::future_status
    wait_until(const std::chrono::time_point<Clock, Duration> &abs_time) const {
        return state_->wait_until(abs_time);
    }

private:
    state_type state_;
};


template <>
class future<void> {
    using state_type = std::shared_ptr<detail::shared_state<int>>;
public:
    future() {}

    explicit future(const state_type &state) : state_(state) {}

    future(future &&other) noexcept: state_(std::move(other.state_)) {
        other.state_.reset();
    }

    future(const future &other) = delete;

    ~future() {}

    future &operator=(future &&other) noexcept {
        if (&other != this) {
            state_ = std::move(other.state_);
            other.state_.reset();
        }
        return *this;
    }

    future &operator=(const future &other) = delete;

    void swap(future &other) noexcept {
        std::swap(state_, other.state_);
    }

    std::shared_future<void> share() noexcept { return std::shared_future<void>(); }

    void get() { state_->get(); }

    bool valid() const noexcept { return state_->valid(); }

    void wait() const { state_->wait(); }

    template <class Rep, class Period>
    std::future_status
    wait_for(const std::chrono::duration<Rep, Period> &rel_time) const {
        return state_->wait_for(rel_time);
    }

    template <class Clock, class Duration>
    std::future_status
    wait_until(const std::chrono::time_point<Clock, Duration> &abs_time) const {
        return state_->wait_until(abs_time);
    }

private:
    state_type state_;
};


template <typename R>
class promise {
    using state_type = std::shared_ptr<detail::shared_state<R>>;
public:
    promise() : state_(new detail::shared_state<R>()) {}

    promise(promise &&other) noexcept: state_(std::move(other.state_)) {
        other.state_.reset();
    }

    promise(const promise &other) = delete;

    ~promise() {}

    promise &operator=(promise &&other) noexcept {
        if (&other != this) {
            state_ = std::move(other.state_);
            other.state_.reset();
        }
        return *this;
    }

    promise &operator=(const promise &other) = delete;

    void swap(promise &other) noexcept {
        std::swap(state_, other.state_);
    }

    std::future<R> get_future() { return std::future<R>(state_); }

    void set_value(const R &value) { state_->set(value); }

    void set_value(R &&value) { state_->set(std::move(value)); }

    void set_value_at_thread_exit(const R &value);

    void set_value_at_thread_exit(R &&value);

    void set_exception(std::exception_ptr p);

    void set_exception_at_thread_exit(std::exception_ptr p);

private:
    state_type state_;
};


template <>
class promise<void> {
    using state_type = std::shared_ptr<detail::shared_state<int>>;
public:
    promise() : state_(new detail::shared_state<int>()) {}

    promise(promise &&other) noexcept: state_(std::move(other.state_)) {
        other.state_.reset();
    }

    promise(const promise &other) = delete;

    ~promise() {}

    promise &operator=(promise &&other) noexcept {
        if (&other != this) {
            state_ = std::move(other.state_);
            other.state_.reset();
        }
        return *this;
    }

    promise &operator=(const promise &other) = delete;

    void swap(promise &other) noexcept {
        std::swap(state_, other.state_);
    }

    std::future<void> get_future() { return std::future<void>(state_); }

    void set_value() { state_->set(0); }

    void set_value_at_thread_exit();

    void set_exception(std::exception_ptr p);

    void set_exception_at_thread_exit(std::exception_ptr p);

private:
    state_type state_;
};


template <class R>
void swap(std::future<R> &lhs, std::future<R> &rhs) noexcept {
    lhs.swap(rhs);
}

template <class R>
void swap(std::promise<R> &lhs, std::promise<R> &rhs) noexcept {
    lhs.swap(rhs);
}

} // namespace std