id 1763281728

CMakeLists.txt

@@ -96,6 +96,7 @@ set(APP_SOURCES
     "src/patterns/structural/Proxy.cpp"
     "src/patterns/structural/Composite.cpp"
     "src/patterns/structural/Flyweight.cpp"
+    "src/patterns/structural/Facade.cpp"
 )
 
 # Test files

src/patterns/structural/Composite.cpp

@@ -4,7 +4,7 @@
 // Appicability:
 // (*)   when you have to implement a tree-like object structure.
 // (**)  when you want the client code to treat both simple and complex elements uniformly.
-// UML: docs/uml/patterns_structural_Composite.drawio.svg
+// UML: docs/uml/patterns_structural_facade.drawio.svg
 
 #include <iostream>
 #include <string>

src/patterns/structural/Facade.cpp

@@ -0,0 +1,274 @@
+// cppcheck-suppress-file [functionStatic]
+
+// Facade is a structural design pattern that provides a simplified interface 
+// to a library, a framework, or any other complex set of classes.
+// Appicability:
+// (*)   when you need to have a limited but straightforward interface to a complex subsystem.
+// (**)  when you want to structure a subsystem into layers.
+// UML: none
+
+#include <iostream>
+namespace
+{
+    namespace Problem
+    {
+
+        class AuthSubSystem
+        {
+        public:
+            virtual ~AuthSubSystem() = default;
+            void login() const
+            {
+                std::cout << "AuthSubSystem: login\n";
+            }
+        };
+
+        class ValidatorSubSystem
+        {
+        public:
+            virtual ~ValidatorSubSystem() = default;
+            virtual void check() const
+            {
+                std::cout << "ValidatorSubSystem: check input\n";
+            }
+        };
+
+        class LoggerSubSystem
+        {
+        public:
+            virtual ~LoggerSubSystem() = default;
+            void write() const
+            {
+                std::cout << "LoggerSubSystem: write log\n";
+            }
+        };
+
+        class BackendSubSystem
+        {
+        public:
+            virtual ~BackendSubSystem() = default;
+            void send() const
+            {
+                std::cout << "BackendSubSystem: send request\n";
+            }
+        };
+
+        namespace Client1
+        {
+            // The client must manually interact with each subsystem.
+            // This creates unnecessary complexity.
+            void clientCode(const ValidatorSubSystem &s1, const AuthSubSystem &s2, const LoggerSubSystem &s3, const BackendSubSystem &s4)
+            {
+                s1.check();
+                s2.login();
+                s3.write();
+                s4.send();
+
+                // In real code, the client must also
+                //   - know call ordering
+                //   - combine subsystem operations
+                //   - manage lifecycle and error handling
+            }
+        }
+
+        namespace Client2
+        {
+            // The client must manually interact with each subsystem.
+            // This creates unnecessary complexity.
+            void clientCode(const ValidatorSubSystem &s1)
+            {
+                s1.check();
+            }
+        }
+
+        void run()
+        {
+            std::cout << "\n\nProblem\n";
+
+            ValidatorSubSystem v;
+            AuthSubSystem a;
+            LoggerSubSystem l;
+            BackendSubSystem b;
+
+            Client1::clientCode(v, a, l, b);
+            Client2::clientCode(v);
+        }
+    }
+
+    namespace Facade
+    {
+
+        class AuthSubSystem
+        {
+        public:
+            virtual ~AuthSubSystem() = default;
+            void login() const
+            {
+                std::cout << "AuthSubSystem: login\n";
+            }
+        };
+
+        class ValidatorSubSystem
+        {
+        public:
+            virtual ~ValidatorSubSystem() = default;
+            void check() const
+            {
+                std::cout << "ValidatorSubSystem: check input\n";
+            }
+        };
+
+        class LoggerSubSystem
+        {
+        public:
+            virtual ~LoggerSubSystem() = default;
+            void write() const
+            {
+                std::cout << "LoggerSubSystem: write log\n";
+            }
+        };
+
+        class BackendSubSystem
+        {
+        public:
+            virtual ~BackendSubSystem() = default;
+            virtual void send() const
+            {
+                std::cout << "BackendSubSystem: send request\n";
+            }
+        };
+
+        // =======================
+        // Mock subclasses (for testing)
+        // =======================
+        class MockBackendSubSystem : public BackendSubSystem
+        {
+        public:
+            void send() const override
+            {
+                std::cout << "[MockBackend] fake-send\n";
+            }
+        };
+
+        /**
+         * The Facade class provides a simple interface to the complex logic of one or
+         * several subsystems. The Facade delegates the client requests to the
+         * appropriate objects within the subsystem. The Facade is also responsible for
+         * managing their lifecycle. All of this shields the client from the undesired
+         * complexity of the subsystem.
+         */
+        class RequestFacade
+        {
+        protected:
+            const AuthSubSystem *auth_;
+            const ValidatorSubSystem *validator_;
+            const LoggerSubSystem *logger_;
+            const BackendSubSystem *backend_;
+
+            /**
+             * Depending on your application's needs, you can provide the Facade with
+             * existing subsystem objects or force the Facade to create them on its own.
+             */
+        public:
+            /**
+             * In this case we will delegate the memory ownership to Facade Class
+             */
+            explicit RequestFacade(const AuthSubSystem *s1 = nullptr,
+                                   const ValidatorSubSystem *s2 = nullptr,
+                                   const LoggerSubSystem *s3 = nullptr,
+                                   const BackendSubSystem *s4 = nullptr)
+            {
+                this->auth_ = s1 ?: new AuthSubSystem;
+                this->validator_ = s2 ?: new ValidatorSubSystem;
+                this->logger_ = s3 ?: new LoggerSubSystem;
+                this->backend_ = s4 ?: new BackendSubSystem;
+            }
+
+            ~RequestFacade()
+            {
+                delete auth_;
+                delete validator_;
+                delete logger_;
+                delete backend_;
+            }
+
+            /**
+             * The Facade's methods are convenient shortcuts to the sophisticated
+             * functionality of the subsystems. However, clients get only to a fraction of
+             * a subsystem's capabilities.
+             */
+            void sendRequest() const
+            {
+                validator_->check();
+                auth_->login();
+                logger_->write();
+                backend_->send();
+            }
+
+            void validate() const
+            {
+                validator_->check();
+            }
+        };
+
+        namespace Client1
+        {
+            /**
+             * The client code works with complex subsystems through a simple interface
+             * provided by the Facade. When a facade manages the lifecycle of the subsystem,
+             * the client might not even know about the existence of the subsystem. This
+             * approach lets you keep the complexity under control.
+             */
+            void clientCode(const RequestFacade &facade)
+            {
+                facade.sendRequest();
+            }
+        }
+
+        namespace Client2
+        {
+            /**
+             * The client code works with complex subsystems through a simple interface
+             * provided by the Facade. When a facade manages the lifecycle of the subsystem,
+             * the client might not even know about the existence of the subsystem. This
+             * approach lets you keep the complexity under control.
+             */
+            void clientCode(const RequestFacade &facade)
+            {
+                facade.validate();
+            }
+        }
+
+        void run()
+        {
+            std::cout << "\n\nFacade\n";
+            {
+                RequestFacade *facade = new RequestFacade();
+                Client1::clientCode(*facade);
+                Client2::clientCode(*facade);
+                delete facade;
+            }
+
+            {
+                // injected subsystems for mocktest
+                std::cout << "\n";
+                const MockBackendSubSystem *b = new MockBackendSubSystem();
+                RequestFacade *facade = new RequestFacade(nullptr, nullptr, nullptr, b);
+                Client1::clientCode(*facade);
+                delete facade;
+            }
+        }
+    }
+}
+
+struct FacadeAutoRuner
+{
+    FacadeAutoRuner()
+    {
+        std::cout << "\n--- Facade Pattern Example ---\n";
+        Problem::run();
+        Facade::run();
+    }
+};
+
+static FacadeAutoRuner instance;