id 1763735936

CMakeLists.txt

@@ -102,6 +102,7 @@ set(APP_SOURCES
     "src/patterns/behavioral/Command.cpp"
     "src/patterns/behavioral/Iterator.cpp"
     "src/patterns/behavioral/Mediator.cpp"
+    "src/patterns/behavioral/Memento.cpp"
 )
 
 # Test files

src/patterns/behavioral/Memento.cpp

@@ -0,0 +1,235 @@
+// Memento is a behavioral design pattern that lets you save and restore the previous state of an object
+// without violating encapsulation, captures and externalizes an object's internal state
+// Appicability:
+// (*)    when you want to produce snapshots of the object’s state to be able to restore a previous state of the object.
+// (**)   when direct access to the object’s fields/getters/setters violates its encapsulation.
+// UML: docs/uml/patterns_behavioral_memento.drawio.svg
+
+#include <iostream>
+#include <string>
+#include <ctime>   // for std::time
+#include <cstdlib> // for std::rand, std::srand
+#include <vector>
+#include <iomanip>
+#include <sstream>
+namespace
+{
+    namespace Memento
+    {
+        /**
+         * Memento interface provides a way to retrieve the memento's metadata, such as creation date or name.
+         * However, it doesn't expose the Originator's state.
+         */
+        class IMemento
+        {
+        public:
+            virtual ~IMemento() = default;
+
+            virtual std::string getName() const = 0;
+            virtual std::string getDate() const = 0;
+            virtual std::string getState() const = 0;
+        };
+
+        /**
+         * Concrete Memento contains the infrastructure for storing the Originator's state.
+         */
+        class ConcreteMemento : public IMemento
+        {
+        private:
+            std::string m_state;
+            std::string m_date;
+            std::string m_name;
+
+        public:
+            explicit ConcreteMemento(const std::string &state) : m_state{state}
+            {
+                // Get current time
+                std::time_t now = std::time(nullptr);
+                std::tm *t = std::localtime(&now);
+
+                // Format date as YYYYMMDD_HHMMSS
+                std::stringstream date_ss;
+                date_ss << std::put_time(t, "%Y%m%d_%H%M%S");
+                m_date = date_ss.str();
+
+                // Append a random number for uniqueness
+                int rand_num = std::rand() % 10000; // optional: limit size
+                std::stringstream name_ss;
+                name_ss << "mem_" << m_date << "_" << rand_num;
+                m_name = name_ss.str();
+            }
+
+            std::string getName() const override
+            {
+                return m_name;
+            };
+
+            std::string getDate() const override
+            {
+                return this->m_date;
+            };
+
+            std::string getState() const override
+            {
+                return this->m_state;
+            }
+        };
+
+        /**
+         * Originator holds some important state that may change over time.
+         * It also defines a method for saving the state inside a memento and another method for
+         * restoring the state from it.
+         */
+        class Originator
+        {
+        private:
+            std::string m_state;
+
+            // Simulate new state using rand
+            static std::string generateRandomString(int len = 10)
+            {
+                // String literal concatenation
+                const char alphaNum[] =
+                    "0123456789"
+                    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+                    "abcdefghijklmnopqrstuvwxyz";
+
+                int strLen = sizeof(alphaNum) - 1;
+                std::string ranStr;
+                for (int i = 0; i < len; ++i)
+                {
+                    ranStr += alphaNum[std::rand() % strLen];
+                }
+                return ranStr;
+            }
+
+        public:
+            explicit Originator(const std::string &state) : m_state{state}
+            {
+                std::cout << "[O]Initial state is: " << this->m_state << "\n";
+            }
+
+            void operation()
+            {
+                std::cout << "[O]Doing something important.\n";
+                this->m_state = this->generateRandomString(30);
+                std::cout << "[O]The state has changed to: " << this->m_state << "\n";
+            }
+
+            //  Save the current state inside a memento.
+            IMemento *save()
+            {
+                return new ConcreteMemento(this->m_state);
+            }
+
+            // Restores the Originator's state from a memento object.
+            void restore(IMemento *mem)
+            {
+                this->m_state = mem->getState();
+                std::cout << "[O]The state has restored to: " << this->m_state << "\n";
+
+                delete mem;
+            }
+        };
+
+        /**
+         * The Caretaker doesn't depend on the Concrete Memento class. Therefore, it
+         * doesn't have access to the originator's state, stored inside the memento. It
+         * works with all mementos via the base Memento interface.
+         */
+        class CareTaker
+        {
+        private:
+            std::vector<IMemento *> m_mementos;
+            Originator *m_originator;
+
+        public:
+            explicit CareTaker(Originator *const org) : m_originator{org} {}
+            ~CareTaker()
+            {
+                for (IMemento *m : m_mementos)
+                {
+                    delete m;
+                }
+            }
+
+            void backup()
+            {
+                std::cout << "[C]Saving Originator's state...\n";
+                this->m_mementos.push_back(this->m_originator->save());
+            }
+
+            void undo()
+            {
+                if (this->m_mementos.size() != 0)
+                {
+                    IMemento *mem = m_mementos.back();
+                    this->m_mementos.pop_back();
+
+                    std::cout << "[C]Restoring state to: " << mem->getName() << "\n";
+                    this->m_originator->restore(mem);
+                }
+            }
+
+            void history() const
+            {
+                std::cout << "[C]The list of mementos:\n";
+                for (const IMemento *m : m_mementos)
+                {
+                    std::cout << "\t" << m->getName() << "\n";
+                }
+            }
+        };
+
+        namespace Client
+        {
+            void clientCode(Originator *const org)
+            {
+                CareTaker *careTaker = new CareTaker(org);
+
+                // 1
+                careTaker->backup();
+                org->operation();
+
+                // 2
+                careTaker->backup();
+                org->operation();
+
+                // 3
+                careTaker->backup();
+                org->operation();
+
+                careTaker->history();
+                careTaker->undo();
+                careTaker->undo();
+                careTaker->history();
+                careTaker->undo();
+
+                // [P] The previous state can’t be restored directly because m_state is private.
+                // We need a Memento to save and recover internal state safely.
+            }
+        }
+
+        void run()
+        {
+            // Gen seed
+            std::srand(static_cast<unsigned int>(std::time(NULL)));
+
+            Originator *origin = new Originator("Hello World");
+            Client::clientCode(origin);
+
+            delete origin;
+        }
+    }
+}
+
+struct MementoAutoRunner
+{
+    MementoAutoRunner()
+    {
+        std::cout << "\n--- Memento Pattern Example ---\n";
+        Memento::run();
+    }
+};
+
+static MementoAutoRunner instance;