path: root/promise.hpp

#ifndef _CPPROMISE_HPP
#define _CPPROMISE_HPP

/**
 * MIT License
 * Copyright (c) 2018 Ted Yin <[email protected]>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <vector>
#include <memory>
#include <functional>
#include <type_traits>

#if __cplusplus >= 201703L
#ifdef __has_include
#   if __has_include(<any>)
#       include <any>
#       ifdef __cpp_lib_any
#           define _CPPROMISE_STD_ANY
#       endif
#   endif
#endif
#endif

#ifndef _CPPROMISE_STD_ANY
#include <boost/any.hpp>
#endif

/**
 * Implement type-safe Promise primitives similar to the ones specified by
 * Javascript Promise/A+.
 */
namespace promise {
#ifdef _CPPROMISE_STD_ANY
    using pm_any_t = std::any;
    template<typename T>
    constexpr auto any_cast = static_cast<T(*)(const std::any&)>(std::any_cast<T>);
    using bad_any_cast = std::bad_any_cast;
#else
#   warning "using boost::any"
#   pragma message "using boost::any"
    using pm_any_t = boost::any;
    template<typename T>
    constexpr auto any_cast = static_cast<T(*)(const boost::any&)>(boost::any_cast<T>);
    using bad_any_cast = boost::bad_any_cast;
#endif
    using callback_t = std::function<void()>;
    using values_t = std::vector<pm_any_t>;

    /* match lambdas */
    template<typename T>
    struct function_traits:
        public function_traits<decltype(&T::operator())> {};
 
    template<typename ReturnType>
    struct function_traits<ReturnType()> {
        using ret_type = ReturnType;
        using arg_type = void;
        using empty_arg = void;
    };
   
    /* match plain functions */
    template<typename ReturnType, typename ArgType>
    struct function_traits<ReturnType(ArgType)> {
        using ret_type = ReturnType;
        using arg_type = ArgType;
        using non_empty_arg = void;
    };
 
    /* match function pointers */
    template<typename ReturnType, typename... ArgType>
    struct function_traits<ReturnType(*)(ArgType...)>:
        public function_traits<ReturnType(ArgType...)> {};

    /* match const member functions */
    template<typename ClassType, typename ReturnType, typename... ArgType>
    struct function_traits<ReturnType(ClassType::*)(ArgType...) const>:
        public function_traits<ReturnType(ArgType...)> {};

    /* match member functions */
    template<typename ClassType, typename ReturnType, typename... ArgType>
    struct function_traits<ReturnType(ClassType::*)(ArgType...)>:
        public function_traits<ReturnType(ArgType...)> {};

    template<typename Func, typename ReturnType>
    using enable_if_return = typename std::enable_if<
            std::is_same<typename function_traits<Func>::ret_type,
                         ReturnType>::value>;

    template<typename Func, typename ReturnType>
    using disable_if_return = typename std::enable_if<
            !std::is_same<typename function_traits<Func>::ret_type,
                         ReturnType>::value>;

    class Promise;
    class promise_t: std::shared_ptr<Promise> {
        public:
        friend Promise;
        template<typename PList> friend promise_t all(PList promise_list);
        template<typename Func>
        promise_t(Func callback):
            std::shared_ptr<Promise>(std::make_shared<Promise>()) {
            callback(*this);
        }

        template<typename T> inline void resolve(T result) const;
        template<typename T> inline void reject(T reason) const;
        inline void resolve() const;
        inline void reject() const;

        template<typename FuncFulfilled>
        inline promise_t then(FuncFulfilled on_fulfilled) const;

        template<typename FuncFulfilled, typename FuncRejected>
        inline promise_t then(FuncFulfilled on_fulfilled,
                            FuncRejected on_rejected) const;

        template<typename FuncRejected>
        inline promise_t fail(FuncRejected on_rejected) const;
    };

#define PROMISE_ERR_INVALID_STATE do {throw std::runtime_error("invalid promise state");} while (0)
#define PROMISE_ERR_MISMATCH_TYPE do {throw std::runtime_error("mismatching promise value types");} while (0)
    
    class Promise {
        std::vector<callback_t> fulfilled_callbacks;
        std::vector<callback_t> rejected_callbacks;
        enum class State {
            Pending,
            Fulfilled,
            Rejected,
        } state;
        pm_any_t result;
        pm_any_t reason;

        void add_on_fulfilled(callback_t cb) {
            fulfilled_callbacks.push_back(cb);
        }

        void add_on_rejected(callback_t cb) {
            rejected_callbacks.push_back(cb);
        }

        template<typename Func, typename function_traits<Func>::non_empty_arg * = nullptr>
        static constexpr auto cps_transform(Func f, const pm_any_t &result, const promise_t &npm) {
            return [&result, f, npm]() mutable {
                f(result)->then(
                    [npm] (pm_any_t result_) {
                        npm->resolve(result_);
                    },
                    [npm] (pm_any_t reason_) {
                        npm->reject(reason_);
                    });
            };
        }

        template<typename Func, typename function_traits<Func>::empty_arg * = nullptr>
        static constexpr auto cps_transform(Func f, const pm_any_t &, const promise_t &npm) {
            return [f, npm]() mutable {
                f()->then(
                    [npm] (pm_any_t result_) {
                        npm->resolve(result_);
                    },
                    [npm] (pm_any_t reason_) {
                        npm->reject(reason_);
                    });
            };
        }

        template<typename Func,
            typename enable_if_return<Func, promise_t>::type * = nullptr>
        constexpr auto gen_on_fulfilled(Func on_fulfilled, const promise_t &npm) {
            return cps_transform(on_fulfilled, this->result, npm);
        }

        template<typename Func,
            typename enable_if_return<Func, promise_t>::type * = nullptr>
        constexpr auto gen_on_rejected(Func on_rejected, const promise_t &npm) {
            return cps_transform(on_rejected, this->reason, npm);
        }


        template<typename Func,
            typename enable_if_return<Func, void>::type * = nullptr,
            typename function_traits<Func>::non_empty_arg * = nullptr>
        constexpr auto gen_on_fulfilled(Func on_fulfilled, const promise_t &npm) {
            return [this, on_fulfilled, npm]() mutable {
                on_fulfilled(result);
                npm->resolve();
            };
        }

        template<typename Func,
            typename enable_if_return<Func, void>::type * = nullptr,
            typename function_traits<Func>::empty_arg * = nullptr>
        constexpr auto gen_on_fulfilled(Func on_fulfilled, const promise_t &npm) {
            return [on_fulfilled, npm]() mutable {
                on_fulfilled();
                npm->resolve();
            };
        }

        template<typename Func,
            typename enable_if_return<Func, void>::type * = nullptr,
            typename function_traits<Func>::non_empty_arg * = nullptr>
        constexpr auto gen_on_rejected(Func on_rejected, const promise_t &npm) {
            return [this, on_rejected, npm]() mutable {
                on_rejected(reason);
                npm->reject();
            };
        }

        template<typename Func,
            typename enable_if_return<Func, void>::type * = nullptr,
            typename function_traits<Func>::empty_arg * = nullptr>
        constexpr auto gen_on_rejected(Func on_rejected, const promise_t &npm) {
            return [on_rejected, npm]() mutable {
                on_rejected();
                npm->reject();
            };
        }

        template<typename Func,
            typename enable_if_return<Func, pm_any_t>::type * = nullptr,
            typename function_traits<Func>::non_empty_arg * = nullptr>
        constexpr auto gen_on_fulfilled(Func on_fulfilled, const promise_t &npm) {
            return [this, on_fulfilled, npm]() mutable {
                npm->resolve(on_fulfilled(result));
            };
        }

        template<typename Func,
            typename enable_if_return<Func, pm_any_t>::type * = nullptr,
            typename function_traits<Func>::empty_arg * = nullptr>
        constexpr auto gen_on_fulfilled(Func on_fulfilled, const promise_t &npm) {
            return [on_fulfilled, npm]() mutable {
                npm->resolve(on_fulfilled());
            };
        }

        template<typename Func,
            typename enable_if_return<Func, pm_any_t>::type * = nullptr,
            typename function_traits<Func>::non_empty_arg * = nullptr>
        constexpr auto gen_on_rejected(Func on_rejected, const promise_t &npm) {
            return [this, on_rejected, npm]() mutable {
                npm->reject(on_rejected(reason));
            };
        }

        template<typename Func,
            typename enable_if_return<Func, pm_any_t>::type * = nullptr,
            typename function_traits<Func>::empty_arg * = nullptr>
        constexpr auto gen_on_rejected(Func on_rejected, const promise_t &npm) {
            return [on_rejected, npm]() mutable {
                npm->reject(on_rejected());
            };
        }

        void trigger_fulfill() {
            state = State::Fulfilled;
            for (const auto &cb: fulfilled_callbacks) cb();
            fulfilled_callbacks.clear();
        }

        void trigger_reject() {
            state = State::Rejected;
            for (const auto &cb: rejected_callbacks) cb();
            rejected_callbacks.clear();
        }

        public:

        Promise(): state(State::Pending) {}
        ~Promise() {}

        template<typename FuncFulfilled, typename FuncRejected>
        promise_t then(FuncFulfilled on_fulfilled,
                      FuncRejected on_rejected) {
            switch (state)
            {
                case State::Pending:
                    return promise_t([this, on_fulfilled, on_rejected](promise_t npm) {
                        add_on_fulfilled(gen_on_fulfilled(on_fulfilled, npm));
                        add_on_rejected(gen_on_rejected(on_rejected, npm));
                    });
                case State::Fulfilled:
                    return promise_t([this, on_fulfilled](promise_t npm) {
                        gen_on_fulfilled(on_fulfilled, npm)();
                    });
                case State::Rejected:
                    return promise_t([this, on_rejected](promise_t npm) {
                        gen_on_rejected(on_rejected, npm)();
                    });
                default: PROMISE_ERR_INVALID_STATE;
            }
        }

        template<typename FuncFulfilled>
        promise_t then(FuncFulfilled on_fulfilled) {
            switch (state)
            {
                case State::Pending:
                    return promise_t([this, on_fulfilled](promise_t npm) {
                        add_on_fulfilled(gen_on_fulfilled(on_fulfilled, npm));
                        add_on_rejected([this, npm]() {npm->reject(reason);});
                    });
                case State::Fulfilled:
                    return promise_t([this, on_fulfilled](promise_t npm) {
                        gen_on_fulfilled(on_fulfilled, npm)();
                    });
                case State::Rejected:
                    return promise_t([this](promise_t npm) {npm->reject(reason);});
                default: PROMISE_ERR_INVALID_STATE;
            }
        }
 
        template<typename FuncRejected>
        promise_t fail(FuncRejected on_rejected) {
            switch (state)
            {
                case State::Pending:
                    return promise_t([this, on_rejected](promise_t npm) {
                        callback_t ret;
                        add_on_rejected(gen_on_rejected(on_rejected, npm));
                        add_on_fulfilled([this, npm]() {npm->resolve(result);});
                    });
                case State::Fulfilled:
                    return promise_t([this](promise_t npm) {npm->resolve(result);});
                case State::Rejected:
                    return promise_t([this, on_rejected](promise_t npm) {
                        gen_on_rejected(on_rejected, npm)();
                    });
                default: PROMISE_ERR_INVALID_STATE;
            }
        }
  
        void resolve() {
            if (state == State::Pending) trigger_fulfill();
        }

        void reject() {
            if (state == State::Pending) trigger_reject();
        }

        void resolve(pm_any_t _result) {
            if (state == State::Pending)
            {
                result = _result;
                trigger_fulfill();
            }
        }

        void reject(pm_any_t _reason) {
            if (state == State::Pending)
            {
                reason = _reason;
                trigger_reject();
            }
        }
    };
        
    template<typename PList> promise_t all(PList promise_list) {
        return promise_t([promise_list] (promise_t npm) {
            auto size = std::make_shared<size_t>(promise_list.size());
            auto results = std::make_shared<values_t>();
            if (!size) PROMISE_ERR_MISMATCH_TYPE;
            results->resize(*size);
            size_t idx = 0;
            for (const auto &pm: promise_list) {
                pm->then(
                    [results, size, idx, npm](pm_any_t result) {
                        (*results)[idx] = result;
                        if (!--(*size))
                            npm->resolve(*results);
                    },
                    [npm, size](pm_any_t reason) {
                        npm->reject(reason);
                    });
                idx++;
            }
        });
    }

    template<typename T>
    inline void promise_t::resolve(T result) const { (*this)->resolve(result); }

    template<typename T>
    inline void promise_t::reject(T reason) const { (*this)->reject(reason); }

    inline void promise_t::resolve() const { (*this)->resolve(); }
    inline void promise_t::reject() const { (*this)->reject(); }

    template<typename T>
    struct callback_types {
        using arg_type = typename function_traits<T>::arg_type;
        using ret_type = typename std::conditional<
            std::is_same<typename function_traits<T>::ret_type, promise_t>::value,
            promise_t, pm_any_t>::type;
    };

    template<typename Func,
        typename enable_if_return<Func, void>::type * = nullptr,
        typename function_traits<Func>::non_empty_arg * = nullptr>
    constexpr auto gen_any_callback(Func f) {
        using func_t = callback_types<Func>;
        return [f](pm_any_t v) mutable {
            try {
                f(any_cast<typename func_t::arg_type>(v));
            } catch (bad_any_cast e) { PROMISE_ERR_MISMATCH_TYPE; }
        };
    }

    template<typename Func,
        typename enable_if_return<Func, void>::type * = nullptr,
        typename function_traits<Func>::empty_arg * = nullptr>
    constexpr auto gen_any_callback(Func f) { return f; }

    template<typename Func,
        typename disable_if_return<Func, void>::type * = nullptr,
        typename function_traits<Func>::non_empty_arg * = nullptr>
    constexpr auto gen_any_callback(Func f) {
        using func_t = callback_types<Func>;
        return [f](pm_any_t v) mutable {
            try {
                return typename func_t::ret_type(
                    f(any_cast<typename func_t::arg_type>(v)));
            } catch (bad_any_cast e) { PROMISE_ERR_MISMATCH_TYPE; }
        };
    }

    template<typename Func,
        typename disable_if_return<Func, void>::type * = nullptr,
        typename function_traits<Func>::empty_arg * = nullptr>
    constexpr auto gen_any_callback(Func f) {
        using func_t = callback_types<Func>;
        return [f]() mutable {
            return typename func_t::ret_type(f());
        };
    }

    template<typename FuncFulfilled>
    inline promise_t promise_t::then(FuncFulfilled on_fulfilled) const {
        return (*this)->then(gen_any_callback(on_fulfilled));
    }

    template<typename FuncFulfilled, typename FuncRejected>
    inline promise_t promise_t::then(FuncFulfilled on_fulfilled,
                                    FuncRejected on_rejected) const {
        return (*this)->then(gen_any_callback(on_fulfilled),
                            gen_any_callback(on_rejected));
    }

    template<typename FuncRejected>
    inline promise_t promise_t::fail(FuncRejected on_rejected) const {
        return (*this)->fail(gen_any_callback(on_rejected));
    }
}

#endif