signals.hpp

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#ifndef FOOLSENGINE_SIGNALS_H
#define FOOLSENGINE_SIGNALS_H
 
#include <memory>
#include <cassert>
#include <functional>
#include <string>
#include <map>
#include <set>
 
namespace ToyMaker {
    class SignalTracker;
    class ISignalObserver;
    class ISignal;
    template <typename ...TArgs>
    class SignalObserver_;
    template <typename ...TArgs>
    class Signal_;
    template <typename ...TArgs>
    class SignalObserver;
    template <typename ...TArgs>
    class Signal;
 
    class ISignalObserver {};

    class ISignal {
    public:
        virtual void registerObserver(std::weak_ptr<ISignalObserver> observer)=0;
    };

    template <typename ...TArgs>
    class Signal_: public ISignal {
    public:
        void emit (TArgs... args);

        void registerObserver(std::weak_ptr<ISignalObserver> observer) override;
 
    private:
        Signal_() = default;

        std::set<
            std::weak_ptr<SignalObserver_<TArgs...>>,
            std::owner_less<std::weak_ptr<SignalObserver_<TArgs...>>>
        > mObservers {};
 
    friend class SignalTracker;
    friend class Signal<TArgs...>;
    };

    template <typename ...TArgs>
    class SignalObserver_: public ISignalObserver {
    public:
        void operator() (TArgs... args);
    private:
        SignalObserver_(std::function<void(TArgs...)> callback);

        std::function<void(TArgs...)> mStoredFunction {};
    friend class SignalTracker;
    friend class SignalObserver<TArgs...>;
    };

    class SignalTracker {
    public:
        SignalTracker();

        SignalTracker(const SignalTracker& other);
    
        SignalTracker& operator=(const SignalTracker& other);

        SignalTracker(SignalTracker&& other);

        SignalTracker& operator=(SignalTracker&& other);

        void connect(const std::string& theirSignal, const std::string& ourObserver, SignalTracker& other);
 
    private:

        template <typename ...TArgs>
        std::shared_ptr<Signal_<TArgs...>> declareSignal(
            const std::string& signalName
        );

        template <typename ...TArgs>
        std::shared_ptr<SignalObserver_<TArgs...>> declareSignalObserver(
            const std::string& observerName,
            std::function<void(TArgs...)> callbackFunction 
        );

        void garbageCollection();

        std::unordered_map<std::string, std::weak_ptr<ISignalObserver>> mObservers {};

        std::unordered_map<std::string, std::weak_ptr<ISignal>> mSignals {};
    friend class ISignal;
    friend class IObserver;
 
    template <typename ...TArgs>
    friend class SignalObserver;
 
    template <typename ...TArgs>
    friend class Signal;
    };

    template <typename ...TArgs>
    class Signal {
    public:
        Signal(SignalTracker& owningTracker, const std::string& name); 
 
        Signal(const Signal& other) = delete;
        Signal(Signal&& other) = delete;
        Signal& operator=(const Signal& other) = delete;
        Signal& operator=(Signal&& other) = delete;

        void emit(TArgs...args);

        void resetSignal(SignalTracker& owningTracker, const std::string& name);
 
    private:
        void registerObserver(SignalObserver<TArgs...>& observer);

        std::shared_ptr<Signal_<TArgs...>> mSignal_;
 
    friend class SignalObserver<TArgs...>;
    };
 

    template <typename ...TArgs>
    class SignalObserver {
    public:
        SignalObserver(SignalTracker& owningTracker, const std::string& name, std::function<void(TArgs...)> callback);
 
        SignalObserver(const SignalObserver& other)=delete;
        SignalObserver(SignalObserver&& other)=delete;
        SignalObserver& operator=(const SignalObserver& other) = delete;
        SignalObserver& operator=(SignalObserver&& other) = delete;

        void resetObserver(SignalTracker& owningTracker, const std::string& name, std::function<void(TArgs...)> callback);

        void connectTo(Signal<TArgs...>& signal);
    
    private:

        std::shared_ptr<SignalObserver_<TArgs...>> mSignalObserver_;
    
    friend class Signal<TArgs...>;
    };
 
    template <typename ...TArgs>
    inline void Signal_<TArgs...>::registerObserver(std::weak_ptr<ISignalObserver> observer) {
        assert(!observer.expired() && "Cannot register a null pointer as an observer");
        mObservers.insert(std::static_pointer_cast<SignalObserver_<TArgs...>>(observer.lock()));
    }
    template <typename ...TArgs>
    void Signal_<TArgs...>::emit (TArgs ... args) {
        //observers that will be removed from the list after this signal has been emitted
        std::vector<std::weak_ptr<SignalObserver_<TArgs...>>> expiredObservers {};
 
        for(auto observer: mObservers) {
            // lock means that this observer is still active
            if(std::shared_ptr<SignalObserver_<TArgs...>> activeObserver = observer.lock()) {
                (*activeObserver)(args...);
 
            // go to the purge list
            } else {
                expiredObservers.push_back(observer);
            }
        }
 
        // remove dead observers
        for(auto expiredObserver: expiredObservers) {
            mObservers.erase(expiredObserver);
        }
    }
 
    template <typename ...TArgs>
    inline SignalObserver_<TArgs...>::SignalObserver_(std::function<void(TArgs...)> callback):
    mStoredFunction{ callback }
    {}
    template <typename ...TArgs>
    inline void SignalObserver_<TArgs...>::operator() (TArgs ... args) { 
        mStoredFunction(args...);
    }
 
    template <typename ...TArgs>
    inline std::shared_ptr<Signal_<TArgs...>> SignalTracker::declareSignal(const std::string& name) {
        std::shared_ptr<ISignal> newSignal { new Signal_<TArgs...>{} };
        mSignals.insert({name, newSignal});
        garbageCollection();
        return std::static_pointer_cast<Signal_<TArgs...>>(newSignal);
    }
    template <typename ...TArgs>
    inline std::shared_ptr<SignalObserver_<TArgs...>> SignalTracker::declareSignalObserver(const std::string& name, std::function<void(TArgs...)> callback) {
        std::shared_ptr<ISignalObserver> newObserver { new SignalObserver_<TArgs...>{callback} };
        mObservers.insert({name, newObserver});
        garbageCollection();
        return std::static_pointer_cast<SignalObserver_<TArgs...>>(newObserver);
    }
    template <typename ...TArgs>
    Signal<TArgs...>::Signal(SignalTracker& owningTracker, const std::string& name) {
        resetSignal(owningTracker, name);
    }
    template <typename ...TArgs>
    void Signal<TArgs...>::emit(TArgs...args) {
        mSignal_->emit(args...);
    }
    template <typename ...TArgs>
    void Signal<TArgs...>::resetSignal(SignalTracker& owningTracker, const std::string& name) {
        mSignal_ = owningTracker.declareSignal<TArgs...>(name);
    }
    template <typename ...TArgs>
    void Signal<TArgs...>::registerObserver(SignalObserver<TArgs...>& observer) {
        mSignal_->registerObserver(observer.mSignalObserver_);
    }
 
    template <typename ...TArgs>
    SignalObserver<TArgs...>::SignalObserver(SignalTracker& owningTracker, const std::string& name, std::function<void(TArgs...)> callback) {
        resetObserver(owningTracker, name, callback);
    };
    template <typename ...TArgs>
    void SignalObserver<TArgs...>::resetObserver(SignalTracker& owningTracker, const std::string& name, std::function<void(TArgs...)> callback) {
        assert(callback && "Empty callback is not allowed");
        mSignalObserver_ = owningTracker.declareSignalObserver<TArgs...>(name, callback);
    }
    template <typename ...TArgs>
    void SignalObserver<TArgs...>::connectTo(Signal<TArgs...>& signal) {
        signal.registerObserver(*this);
    }
}
 
#endif