Kylin/Universal/Private/PromiseData.h

#ifndef __PROMISEDATA_H__
#define __PROMISEDATA_H__

#include <cassert>
#include <list>
#include <memory>
#include <mutex>

template <typename T>
class PromiseValue {
public:
    PromiseValue() {
    }
    PromiseValue(const T &data) : m_data(std::make_shared<T>(data)) {
    }
    PromiseValue(T &&data) : m_data(std::make_shared<T>(std::forward<T>(data))) {
    }
    bool isNull() const {
        return m_data == nullptr;
    }
    const T &data() const {
        return *m_data;
    }

private:
    std::shared_ptr<T> m_data;
};

class PromiseError {
public:
    template <typename T>
    PromiseError(const T &value) {
        try {
            throw value;
        } catch (...) {
            m_data = std::current_exception();
        }
    }

    PromiseError() {
    }
    PromiseError(const std::exception_ptr &exception) : m_data{exception} {
    }
    void rethrow() const {
        std::rethrow_exception(m_data);
    }
    bool isNull() const {
        return m_data == nullptr;
    }

private:
    std::exception_ptr m_data; // std::exception_ptr is already a shared pointer
};

template <typename T, typename F>
class PromiseDataBase {
public:
    using Handler = std::function<F>;
    using Catcher = std::function<void(const PromiseError &)>;

    bool isFulfilled() const {
        return !isPending() && m_error.isNull();
    }
    bool isRejected() const {
        return !isPending() && !m_error.isNull();
    }

    bool isPending() const {
        std::lock_guard locker{m_mutex};
        return !m_settled;
    }

    void addHandler(std::function<F> handler) {
        std::lock_guard locker{m_mutex};
        m_handlers.push_back(std::move(handler));
    }

    void addCatcher(std::function<void(const PromiseError &)> catcher) {
        std::lock_guard locker{m_mutex};
        m_catchers.push_back(std::move(catcher));
    }

    template <typename E>
    void reject(E &&error) {
        assert(isPending());
        assert(m_error.isNull());
        m_error = PromiseError{std::forward<E>(error)};
        setSettled();
    }

    const PromiseError &error() const {
        assert(isRejected());
        return m_error;
    }

    void dispatch() {
        if (isPending()) {
            return;
        }

        m_mutex.lock();
        auto handlers = std::move(m_handlers);
        auto catchers = std::move(m_catchers);
        m_mutex.unlock();

        if (m_error.isNull()) {
            notify(handlers);
            return;
        }

        PromiseError error = m_error;
        assert(!error.isNull());

        for (auto &catcher : catchers) {
            catcher(error);
        }
    }

protected:
    virtual void notify(const std::list<Handler> &handlers) = 0;
    void setSettled() {
        std::lock_guard locker{m_mutex};
        assert(!m_settled);
        m_settled = true;
    }
    mutable std::mutex m_mutex;

private:
    bool m_settled = false;
    std::list<Handler> m_handlers;
    std::list<Catcher> m_catchers;
    PromiseError m_error;
};

template <typename T>
class PromiseData : public PromiseDataBase<T, void(const T &)> {
    using Handler = typename PromiseDataBase<T, void(const T &)>::Handler;

public:
    template <typename V>
    void resolve(V &&value) {
        assert(this->isPending());
        assert(m_value.isNull());
        m_value = PromiseValue<T>{std::forward<V>(value)};
        this->setSettled();
    }

    const PromiseValue<T> &value() const {
        assert(this->isFulfilled());
        return m_value;
    }

protected:
    void notify(const std::list<Handler> &handlers) final {
        PromiseValue<T> value = m_value;
        assert(!value.isNull());
        for (auto &handler : handlers) {
            handler(value.data());
        }
    }

private:
    PromiseValue<T> m_value;
};

template <>
class PromiseData<void> : public PromiseDataBase<void, void()> {
    using Handler = PromiseDataBase<void, void()>::Handler;

public:
    void resolve() {
        setSettled();
    }

protected:
    void notify(const std::list<Handler> &handlers) {
        for (const auto &handler : handlers) {
            handler();
        }
    }
};

#endif // __PROMISEDATA_H__