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__

src/engine/core/event_bus.cpp

@@ -0,0 +1,80 @@
+#include <engine/core/engine_bus.hpp>
+#include <utility>
+#include <cstddef>
+
+void MscEventBus::publish(MscEvent &event)
+{
+    std::vector<ListenerWithId> listeners;
+
+    {
+        std::lock_guard<std::mutex> lock(_listenersMutex);
+        auto it = _listeners.find(event.getName());
+        if (it == _listeners.end())
+            return;
+
+        for (const auto &entry : it->second)
+            listeners.push_back(entry);
+    }
+
+    for (const auto &entry : listeners)
+    {
+        if (event.isCanceled())
+            break;
+
+        entry.listener(event);
+        if (entry.once)
+            unsubscribe(entry.id);
+    }
+}
+
+MscEventBus::SubscriptionId MscEventBus::_subscribe(const std::string &name, MscEventBus::Listener listener, bool once)
+{
+    std::lock_guard<std::mutex> lock(_listenersMutex);
+
+    const SubscriptionId id = ++_lastId;
+    auto listenerWithId = ListenerWithId{
+        .id = id,
+        .listener = std::move(listener),
+        .once = once};
+
+    _listeners[name].push_back(std::move(listenerWithId));
+    _listenersPaths[id] = name;
+
+    return id;
+}
+
+MscEventBus::SubscriptionId MscEventBus::subscribe(const std::string &name, Listener listener)
+{
+    return _subscribe(name, std::move(listener), false);
+}
+
+void MscEventBus::subscribeOnce(const std::string &name, Listener listener)
+{
+    _subscribe(name, std::move(listener), true);
+}
+
+bool MscEventBus::unsubscribe(SubscriptionId id)
+{
+    std::lock_guard<std::mutex> lock(_listenersMutex);
+
+    auto it = _listenersPaths.find(id);
+    if (it == _listenersPaths.end())
+        return false;
+
+    auto &listeners = _listeners.at(it->second);
+    for (std::size_t i = 0; i < listeners.size(); i++)
+    {
+        if (listeners.at(i).id != id)
+            continue;
+
+        listeners.erase(listeners.begin() + i);
+        _listenersPaths.erase(id);
+
+        if (listeners.empty())
+            _listeners.erase(it->second);
+
+        return true;
+    }
+
+    return false;
+}