process.hpp

#ifndef ENTT_PROCESS_PROCESS_HPP
#define ENTT_PROCESS_PROCESS_HPP
 
 
#include <utility>
#include <type_traits>
#include "../config/config.h"
 
 
namespace entt {
 
 
template<typename Derived, typename Delta>
class process {
    enum class state: unsigned int {
        UNINITIALIZED = 0,
        RUNNING,
        PAUSED,
        SUCCEEDED,
        FAILED,
        ABORTED,
        FINISHED,
        REJECTED
    };
 
    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::UNINITIALIZED>)
    -> decltype(std::declval<Target>().init(), void()) {
        static_cast<Target *>(this)->init();
    }
 
    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::RUNNING>, Delta delta, void *data)
    -> decltype(std::declval<Target>().update(delta, data), void()) {
        static_cast<Target *>(this)->update(delta, data);
    }
 
    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::SUCCEEDED>)
    -> decltype(std::declval<Target>().succeeded(), void()) {
        static_cast<Target *>(this)->succeeded();
    }
 
    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::FAILED>)
    -> decltype(std::declval<Target>().failed(), void()) {
        static_cast<Target *>(this)->failed();
    }
 
    template<typename Target = Derived>
    auto next(std::integral_constant<state, state::ABORTED>)
    -> decltype(std::declval<Target>().aborted(), void()) {
        static_cast<Target *>(this)->aborted();
    }
 
    void next(...) const ENTT_NOEXCEPT {}
 
protected:
    void succeed() ENTT_NOEXCEPT {
        if(alive()) {
            current = state::SUCCEEDED;
        }
    }
 
    void fail() ENTT_NOEXCEPT {
        if(alive()) {
            current = state::FAILED;
        }
    }
 
    void pause() ENTT_NOEXCEPT {
        if(current == state::RUNNING) {
            current = state::PAUSED;
        }
    }
 
    void unpause() ENTT_NOEXCEPT {
        if(current  == state::PAUSED) {
            current  = state::RUNNING;
        }
    }
 
public:
    using delta_type = Delta;
 
    virtual ~process() {
        static_assert(std::is_base_of_v<process, Derived>, "Incorrect use of the class template");
    }
 
    void abort(const bool immediately = false) {
        if(alive()) {
            current = state::ABORTED;
 
            if(immediately) {
                tick({});
            }
        }
    }
 
    [[nodiscard]] bool alive() const ENTT_NOEXCEPT {
        return current == state::RUNNING || current == state::PAUSED;
    }
 
    [[nodiscard]] bool finished() const ENTT_NOEXCEPT {
        return current == state::FINISHED;
    }
 
    [[nodiscard]] bool paused() const ENTT_NOEXCEPT {
        return current == state::PAUSED;
    }
 
    [[nodiscard]] bool rejected() const ENTT_NOEXCEPT {
        return current == state::REJECTED;
    }
 
    void tick(const Delta delta, void *data = nullptr) {
        switch (current) {
        case state::UNINITIALIZED:
            next(std::integral_constant<state, state::UNINITIALIZED>{});
            current = state::RUNNING;
            break;
        case state::RUNNING:
            next(std::integral_constant<state, state::RUNNING>{}, delta, data);
            break;
        default:
            // suppress warnings
            break;
        }
 
        // if it's dead, it must be notified and removed immediately
        switch(current) {
        case state::SUCCEEDED:
            next(std::integral_constant<state, state::SUCCEEDED>{});
            current = state::FINISHED;
            break;
        case state::FAILED:
            next(std::integral_constant<state, state::FAILED>{});
            current = state::REJECTED;
            break;
        case state::ABORTED:
            next(std::integral_constant<state, state::ABORTED>{});
            current = state::REJECTED;
            break;
        default:
            // suppress warnings
            break;
        }
    }
 
private:
    state current{state::UNINITIALIZED};
};
 
 
template<typename Func, typename Delta>
struct process_adaptor: process<process_adaptor<Func, Delta>, Delta>, private Func {
    template<typename... Args>
    process_adaptor(Args &&... args)
        : Func{std::forward<Args>(args)...}
    {}
 
    void update(const Delta delta, void *data) {
        Func::operator()(delta, data, [this]() { this->succeed(); }, [this]() { this->fail(); });
    }
};
 
 
}
 
 
#endif