feat: implement event bus

include/engine/core/engine_bus.hpp

@@ -0,0 +1,73 @@
+#ifndef __MSC_ENGINE_BUS_HPP__
+#define __MSC_ENGINE_BUS_HPP__
+
+#include <string>
+#include <vector>
+#include <mutex>
+#include <unordered_map>
+#include <functional>
+#include <cstdint>
+
+/// @brief Event base class
+class MscEvent
+{
+public:
+    virtual ~MscEvent() = default;
+
+    /// @brief Get event name
+    virtual std::string getName() const = 0;
+
+    /// @brief Is current event is canceled
+    virtual bool isCanceled() const = 0;
+
+    /// @brief Cancel current event
+    virtual void cancel() = 0;
+};
+
+/// @brief Engine event bus
+class MscEventBus
+{
+public:
+    /// @brief Event handler alias
+    using Listener = std::function<void(MscEvent &)>;
+
+    /// @brief Subscription identifier alias
+    using SubscriptionId = std::uint64_t;
+
+    /// @brief Emit event
+    /// @param event event context
+    void publish(MscEvent &event);
+
+    /// @brief Subscribe to specified event
+    /// @param name event name
+    /// @param listener event handler
+    /// @returns subscription identifier to make it possitble to remove listener
+    SubscriptionId subscribe(const std::string &name, Listener listener);
+
+    /// @brief Subscribe to specified event and execute once on publish
+    /// @param name event name
+    /// @param listener event handler
+    void subscribeOnce(const std::string &name, Listener listener);
+
+    /// @brief Unsubscribe listener by its own id
+    /// @param id subscription id
+    /// @return `true` if listener has been deleted, otherwise `false`
+    bool unsubscribe(SubscriptionId id);
+
+private:
+    using ListenerWithId = struct
+    {
+        SubscriptionId id;
+        Listener listener;
+        bool once;
+    };
+
+    std::unordered_map<std::string, std::vector<ListenerWithId>> _listeners;
+    std::unordered_map<SubscriptionId, std::string> _listenersPaths;
+    std::uint64_t _lastId = 0;
+    std::mutex _listenersMutex;
+
+    SubscriptionId _subscribe(const std::string &name, Listener listener, bool once);
+};
+
+#endif // __MSC_ENGINE_BUS_HPP__