id 1763705535

CMakeLists.txt

@@ -101,6 +101,7 @@ set(APP_SOURCES
     "src/patterns/behavioral/ChainOfCommand.cpp"
     "src/patterns/behavioral/Command.cpp"
     "src/patterns/behavioral/Iterator.cpp"
+    "src/patterns/behavioral/Mediator.cpp"
 )
 
 # Test files

src/patterns/behavioral/Mediator.cpp

@@ -0,0 +1,179 @@
+// Mediator is a behavioral design pattern that lets you reduce chaotic dependencies between objects.
+// The pattern restricts direct communications between the objects and forces them to collaborate only via a mediator object.
+// Usage examples: The most popular usage of the Mediator pattern in C++ code is facilitating communications between GUI components of an app.
+// The synonym of the Mediator is the `Controller` part of MVC pattern.
+// Appicability:
+// (*)   when your collection has a complex data structure under the hood, but you want to hide its complexity from clients (either for convenience or security reasons).
+// (**)  when you can’t reuse a component in a different program because it’s too dependent on other components.
+// (***) when you find yourself creating tons of component subclasses just to reuse some basic behavior in various contexts.
+
+// UML: docs/uml/patterns_behavioral_mediator.drawio.svg
+
+#include <iostream>
+#include <string>
+#include <vector>
+namespace
+{
+    namespace Mediator
+    {
+
+        enum class Event
+        {
+            CREATE = 0,
+            READ,
+            UPDATE,
+            DELETE,
+        };
+
+        static inline const char *getEventName(const Event &e)
+        {
+            switch (e)
+            {
+            case Event::CREATE:
+                return "CREATE";
+            case Event::READ:
+                return "READ";
+            case Event::UPDATE:
+                return "UPDATE";
+            case Event::DELETE:
+                return "DELETE";
+            }
+            return "invalid_event";
+        }
+
+        class IComponent
+        {
+        public:
+            virtual ~IComponent() = default;
+
+            virtual void send(const Event e) = 0;
+            virtual void receive(const Event e) = 0;
+        };
+
+        /**
+         * The Mediator interface declares methods of communication with components, which usually include just a single notification method.
+         * Components may pass any context as arguments of this method, including their own objects,
+         * but only in such a way that no coupling occurs between a receiving component and the sender’s class.
+         */
+        class IMediator
+        {
+        public:
+            virtual ~IMediator() = default;
+            virtual void registerComponent(IComponent *const c) = 0;
+            virtual void notify(IComponent *sender, const Event &e) = 0;
+        };
+
+        /**
+         * Concrete Mediators implement cooperative behavior by coordinating several components.
+         * Concrete mediators often keep references to all components they manage and sometimes even manage their lifecycle.
+         */
+        class ComponentMediator : public IMediator
+        {
+        private:
+            std::vector<IComponent *> m_components;
+
+        public:
+            void registerComponent(IComponent *const c) override
+            {
+                m_components.push_back(c);
+            }
+
+            void notify(IComponent *const sender, const Event &e) override
+            {
+                for (auto c : m_components)
+                {
+                    if (c != sender)
+                    {
+                        c->receive(e);
+                    }
+                }
+            }
+        };
+
+        /**
+         * Components are various classes that contain some business logic.
+         * Each component has a reference to a mediator, declared with the type of the mediator interface.
+         * The component isn’t aware of the actual class of the mediator, so you can reuse the component in other programs by linking it to a different mediator.
+         */
+        class AbstractComponent : public IComponent
+        {
+        private:
+            const std::string m_id;
+
+        protected:
+            IMediator *m_mediator;
+            void log(const Event &e, const std::string &msg) const
+            {
+                std::cout << "\t" + msg + "-id:" + m_id + "-event:" + getEventName(e) + "\n";
+            }
+
+        public:
+            explicit AbstractComponent(const std::string &id, IMediator *const m = nullptr) : m_id{id}, m_mediator{m} {};
+        };
+
+        /**
+         * Concrete Components implement various functionality. They don't depend on
+         * other components. They also don't depend on any concrete mediator classes.
+         */
+        class ConreteComponent : public AbstractComponent
+        {
+        public:
+            explicit ConreteComponent(const std::string &id, IMediator *const m = nullptr) : AbstractComponent{id, m} {}
+
+            void send(const Event e) override
+            {
+                log(e, "[SEND]");
+                if (m_mediator != nullptr)
+                    m_mediator->notify(this, e);
+            }
+
+            void receive(const Event e) override
+            {
+                log(e, "[RECV]");
+                // Additional handling logic can go here
+            }
+        };
+
+        namespace Client
+        {
+            void clientCode(IComponent *comp)
+            {
+                comp->send(Event::READ);
+            }
+        }
+
+        void run()
+        {
+            IMediator *mediator = new ComponentMediator();
+            IComponent *c1 = new ConreteComponent("1763700876", mediator);
+            IComponent *c2 = new ConreteComponent("1763700882", mediator);
+            IComponent *c3 = new ConreteComponent("1763700899", mediator);
+            IComponent *c4 = new ConreteComponent("1763700900", mediator);
+
+            // Only c1, c3, c4 receive notifications.
+            mediator->registerComponent(c1);
+            mediator->registerComponent(c3);
+            mediator->registerComponent(c4);
+
+            // c2 triggers event => observed by others
+            Client::clientCode(c2);
+
+            delete mediator;
+            delete c1;
+            delete c2;
+            delete c3;
+            delete c4;
+        }
+    }
+}
+
+struct MediatorAutoRunner
+{
+    MediatorAutoRunner()
+    {
+        std::cout << "\n--- Mediator Pattern Example ---\n";
+        Mediator::run();
+    }
+};
+
+static MediatorAutoRunner instance;