v1 using observer pattern

subscriber-notifs/CMakeLists.txt

@@ -4,11 +4,11 @@ project(subscriber-notifs VERSION 1.0)
 set(CMAKE_CXX_STANDARD 20)
 
 file(GLOB_RECURSE SRC_FILES "src/*.cpp")
-file(GLOB_RECURSE HEADER_FILES "src/*.h" "src/*.hpp")
+file(GLOB_RECURSE HEADER_FILES "include/*.hpp")
 
 add_executable(sub_notifs ${SRC_FILES} ${HEADER_FILES})
 
-target_include_directories(sub_notifs PRIVATE ${HEADER_FILES})
+target_include_directories(sub_notifs PRIVATE include )
 
 # from: https://cmake.org/cmake/help/latest/module/FindThreads.html
 find_package(Threads REQUIRED)

subscriber-notifs/include/app/inventory_manager.hpp

@@ -0,0 +1,20 @@
+
+#pragma once
+
+#include <string>
+#include <unordered_map>
+
+#include "core/subscribable.hpp"
+
+using ProductCount = int;
+using ProductId = std::string;
+
+// inventory manager is not generic ( works with the specific types ProductId
+// and ProductCount ) but the subscribable is generic
+class InventoryManager : public Subscribable<ProductId, ProductCount> {
+   private:
+    std::unordered_map<ProductId, int> inventory_;
+
+   public:
+    void setInventory(const ProductId& productId, ProductCount quantity);
+};

subscriber-notifs/include/app/services.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "app/inventory_manager.hpp"
+#include "core/subscriber.hpp"
+
+class SmsService : public Subscriber<ProductId, ProductCount> {
+   public:
+    void onNotification(const ProductId& productId,
+                        const ProductCount& quantity) override;
+};
+
+class EmailService : public Subscriber<ProductId, ProductCount> {
+   public:
+    void onNotification(const ProductId& productId,
+                        const ProductCount& quantity) override;
+};
+
+class LogService : public Subscriber<ProductId, ProductCount> {
+   public:
+    void onNotification(const ProductId& productId,
+                        const ProductCount& quantity) override;
+};

subscriber-notifs/include/core/subscribable.hpp

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <unordered_map>
+#include <vector>
+
+#include "subscriber.hpp"
+
+template <typename TEventId, typename TEventInfo>
+class Subscribable {
+    using TSubscriber = Subscriber<TEventId, TEventInfo>;
+
+   private:
+    std::unordered_map<TEventId, std::vector<TSubscriber*>> subscribersMap_;
+
+   public:
+    void subscribe(const TEventId& eventId, TSubscriber* subscriber) {
+        subscribersMap_[eventId].push_back(subscriber);
+    }
+
+    void unsubscribe(const TEventId& eventId, TSubscriber* subscriber) {
+        auto entry = subscribersMap_.find(eventId);
+        if (entry == subscribersMap_.end()) {
+            return;
+        }
+
+        std::erase(entry->second, subscriber);
+        if (entry->second.empty()) {
+            subscribersMap_.erase(entry);
+        }
+    }
+
+    void notify(const TEventId& eventId, const TEventInfo& eventInfo) {
+        auto entry = subscribersMap_.find(eventId);
+        if (entry == subscribersMap_.end()) {
+            return;
+        }
+
+        for (TSubscriber* subscriber : entry->second) {
+            subscriber->onNotification(eventId, eventInfo);
+        }
+    }
+};

subscriber-notifs/include/core/subscriber.hpp

@@ -0,0 +1,10 @@
+#pragma once
+
+template <typename TEventId, typename TEventInfo>
+class Subscriber {
+   public:
+    virtual void onNotification(const TEventId& eventId,
+                                const TEventInfo& eventInfo) = 0;
+
+    virtual ~Subscriber() = default;
+};

subscriber-notifs/src/app/inventory_manager.cpp

@@ -0,0 +1,7 @@
+#include "app/inventory_manager.hpp"
+
+void InventoryManager::setInventory(const ProductId& productId,
+                                    ProductCount quantity) {
+    inventory_[productId] = quantity;
+    this->notify(productId, quantity);
+}

subscriber-notifs/src/app/services.cpp

@@ -0,0 +1,21 @@
+#include "app/services.hpp"
+
+#include <iostream>
+
+void SmsService::onNotification(const ProductId& productId,
+                                const ProductCount& quantity) {
+    std::cout << "SMS Notification - Product: " << productId
+              << ", Quantity: " << quantity << std::endl;
+}
+
+void EmailService::onNotification(const ProductId& productId,
+                                  const ProductCount& quantity) {
+    std::cout << "Email Notification - Product: " << productId
+              << ", Quantity: " << quantity << std::endl;
+}
+
+void LogService::onNotification(const ProductId& productId,
+                                const ProductCount& quantity) {
+    std::cout << "Log Entry - Product: " << productId
+              << ", Quantity: " << quantity << std::endl;
+}

subscriber-notifs/src/main.cpp

@@ -0,0 +1,19 @@
+#include "app/inventory_manager.hpp"
+#include "app/services.hpp"
+
+int main() {
+    InventoryManager inventoryManager;
+
+    SmsService smsService;
+    EmailService emailService;
+    LogService logService;
+
+    inventoryManager.subscribe("ProductA", &smsService);
+    inventoryManager.subscribe("ProductB", &emailService);
+    inventoryManager.subscribe("ProductA", &logService);
+
+    inventoryManager.setInventory("ProductA", 100);
+    inventoryManager.setInventory("ProductB", 200);
+
+    return 0;
+}