Add CoR pattern

Author: urbytes21

CMakeLists.txt

@@ -98,6 +98,7 @@ set(APP_SOURCES
     "src/patterns/structural/Flyweight.cpp"
     "src/patterns/structural/Facade.cpp"
     "src/patterns/structural/Decorator.cpp"
+    "src/patterns/behavioral/ChainOfCommand.cpp"
 )
 
 # Test files

docs/uml/patterns_behavioral_CoR.drawio.svg

@@ -0,0 +1,162 @@
+// CoR is a behavioral design pattern that lets you pass requests along a chain of handlers.
+// Upon receiving a request, each handler decides either to process the request
+// or to pass it to the next handler in the chain.
+// Allows an object to send a command without knowing what object will receive and handle it.
+// Appicability:
+// (*) when it’s essential to execute several handlers in a particular order.
+// (**)when the set of handlers and their order are supposed to change at runtime.
+
+// UML: docs/uml/patterns_behavioral_CoR.drawio.svg
+
+#include <iostream>
+#include <string>
+#include <vector>
+
+namespace
+{
+    namespace CoR
+    {
+        class IHandler
+        {
+        public:
+            virtual void setNextHandler(IHandler *handler) = 0;
+            virtual IHandler *setNext(IHandler *handler) = 0;
+            virtual void handle(const std::string &request) = 0;
+        };
+
+        class AbstractHandler : public IHandler
+        {
+        private:
+            IHandler *m_setNext;
+
+        public:
+            AbstractHandler() : m_setNext{nullptr} {};
+
+            void setNextHandler(IHandler *handler) override
+            {
+                this->m_setNext = handler;
+            }
+
+            // handler1->setNext(handler2)->setNext(handler3)
+            IHandler *setNext(IHandler *handler) override
+            {
+                this->m_setNext = handler;
+                return handler;
+            }
+
+            void handle(const std::string &request) override
+            {
+                if (this->m_setNext != nullptr)
+                {
+                    this->m_setNext->handle(request);
+                }
+                else
+                {
+                    std::cout << "\tNo handler processed request: " << request << "\n";
+                }
+            }
+        };
+
+        class ConcreteHandlerGET : public AbstractHandler
+        {
+        private:
+            static constexpr const char *header = "GET";
+
+        public:
+            void handle(const std::string &request) override
+            {
+                if (request.rfind(header, 0) == 0)
+                {
+                    // If request is eligible, handle it
+                    std::cout << "\tHandle GET request: " << request << "\n";
+                    // In realworld, it should be other logics here
+                }
+                else
+                {
+                    AbstractHandler::handle(request);
+                }
+            }
+        };
+
+        class ConcreteHandlerPUT : public AbstractHandler
+        {
+        private:
+            static constexpr const char *header = "PUT";
+
+        public:
+            void handle(const std::string &request) override
+            {
+                if (request.rfind(header, 0) == 0)
+                {
+                    std::cout << "\tHandle PUT request: " << request << "\n";
+                }
+                else
+                {
+                    AbstractHandler::handle(request);
+                }
+            }
+        };
+
+        class ConcreteHandlerPOST : public AbstractHandler
+        {
+        private:
+            static constexpr const char *header = "POST";
+
+        public:
+            void handle(const std::string &request) override
+            {
+                if (request.rfind(header, 0) == 0)
+                {
+                    std::cout << "\tHandle POST request: " << request << "\n";
+                }
+                else
+                {
+                    AbstractHandler::handle(request);
+                }
+            }
+        };
+
+        namespace Client
+        {
+            void clientCode(IHandler &handler, const std::string &request)
+            {
+                handler.handle(request);
+            }
+        }
+
+        void run()
+        {
+            // Setup Chain of Responsibility
+            IHandler *postHandler = new ConcreteHandlerPOST();
+            IHandler *gettHandler = new ConcreteHandlerGET();
+            IHandler *puttHandler = new ConcreteHandlerPUT();
+            postHandler->setNext(gettHandler)->setNext(puttHandler);
+
+            // Send requests to the chain
+            std::string dummy = "DUMMY ..";
+            std::string postRequest = "POST /test/demo_form.php HTTP/1.1 ..";
+            std::string getRequest = "GET /users/123 ..";
+            std::cout << "Send dummy request\n";
+            Client::clientCode(*postHandler, dummy);
+            std::cout << "Send POST request\n";
+            Client::clientCode(*postHandler, postRequest);
+            std::cout << "Send GET request\n";
+            Client::clientCode(*postHandler, getRequest);
+
+            delete postHandler;
+            delete gettHandler;
+            delete puttHandler;
+        }
+    }
+
+}
+
+struct CoRAutoRunner
+{
+    CoRAutoRunner()
+    {
+        CoR::run();
+    }
+};
+
+static CoRAutoRunner instance;