EventEmitter.hpp

#include <map>
#include <functional>

typedef unsigned long ListenerID;

template <class EventData>
using Listener = std::function<void(EventData)>;

template <class EventData>
using ListenersMap = std::map<ListenerID, Listener<EventData>>;

template <class Event, class EventData>
using EventListenerMap = std::map<Event, ListenersMap<EventData>>;

template<class Event, class EventData>
class EventEmitter {
private:
    ListenerID next_id = 0;
    EventListenerMap<Event, EventData> event_listener_map;
public:

    ListenerID on(Event event, Listener<EventData> listener) {
        auto it = this->event_listener_map.find(event);
        if (it == this->event_listener_map.end()) {
            this->event_listener_map.insert(std::pair<Event, ListenersMap<EventData>>(event, std::map<ListenerID, Listener<EventData>>()));
            it = this->event_listener_map.find(event);
        }
        auto listener_id = ++this->next_id;
        it->second.insert(std::pair<ListenerID , Listener<EventData>>(listener_id, listener));
        return listener_id;
    };

    ListenerID once(Event event, Listener<EventData> listener) {
        ListenerID listener_id = this->next_id + 1;
        this->on(event, [this, listener_id, &listener, &event](EventData data){
            this->off(event, listener_id);
            listener(data);
        });
        return listener_id;
    };

    void off(Event event, ListenerID listener_id) {
        auto it = this->event_listener_map.find(event);
        if (it == this->event_listener_map.end()){ return; }
        it->second.erase(listener_id);
    };

    void off(Event event) {
        this->event_listener_map.erase(event);
    };

    void off(){
        this->event_listener_map.clear();
    };

    bool emit(Event event, EventData data){
        auto event_listeners = this->event_listener_map.find(event);
        if (event_listeners == this->event_listener_map.end()) { return false; }
        auto listeners =  event_listeners->second;
        bool sign = false;
        for (auto& listener: listeners) {
            sign = true;
            listener.second(data);
        }
        return sign;
    };
};