event_bus.h

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#pragma once
 
#include <functional>
#include <mutex>
#include <typeindex>
#include <typeinfo>
#include <unordered_map>
#include <utility>
#include <vector>
 
namespace librats {
 
class EventBus {
public:
    template <class E>
    void on(std::function<void(const E&)> handler) {
        std::lock_guard<std::mutex> lock(mutex_);
        handlers_[std::type_index(typeid(E))].push_back(
            [h = std::move(handler)](const void* e) { h(*static_cast<const E*>(e)); });
    }
 
    template <class E>
    void emit(const E& event) {
        std::vector<ErasedHandler> snapshot;
        {
            std::lock_guard<std::mutex> lock(mutex_);
            auto it = handlers_.find(std::type_index(typeid(E)));
            if (it == handlers_.end()) return;
            snapshot = it->second;  // copy under lock, then invoke unlocked
        }
        for (auto& h : snapshot) h(&event);
    }
 
private:
    using ErasedHandler = std::function<void(const void*)>;
    std::mutex mutex_;
    std::unordered_map<std::type_index, std::vector<ErasedHandler>> handlers_;
};
 
} // namespace librats