Provide ChainOfResponsibility example

Author: moritztim

src/ChainOfResponsibility/RealWorld/index.ts

@@ -0,0 +1,113 @@
+/**
+ * EN: Real World Example for the Chain of Responsibility Design Pattern
+ *
+ * Need: Handle different types of authentication in an HTTP request
+ *
+ * Solution: Create a chain of authentication handlers, where each handler
+ * checks a specific authentication type. If a handler can't authenticate the
+ * request, it passes the request to the next handler in the chain.
+ */
+
+/**
+ * EN: The Handler interface declares a method for building the chain of
+ * handlers. It also declares a method for executing a request.
+ *
+ * RU: Интерфейс Обработчика объявляет метод построения цепочки обработчиков. Он
+ * также объявляет метод для выполнения запроса.
+ */
+interface Handler<Request = string, Result = string> {
+    setNext(handler: Handler<Request, Result>): Handler<Request, Result>;
+
+    handle(request: Request): Result;
+}
+/**
+ * EN: The AuthenticationHandler interface declares a method for authenticating
+ * an HTTP request.
+ */
+interface AuthenticationHandler
+    extends Handler<AuthenticationRequest, AuthenticationResult> { }
+
+/**
+ * EN: The AuthenticationRequest represents an HTTP request that needs to be
+ * authenticated
+ */
+type AuthenticationRequest = {
+    user?: {
+        name: string;
+        password: string;
+    };
+    apiKey?: string;
+    jwtToken?: string;
+};
+
+/**
+ * EN: The AuthenticationResult represents the result of an authentication
+ * attempt
+ */
+type AuthenticationResult = {
+    success: boolean,
+    message: string
+}
+
+/**
+ * EN: The base AbstractAuthenticationHandler implements the default chaining
+ * behavior
+ */
+abstract class AbstractAuthenticationHandler implements AuthenticationHandler {
+    private nextHandler: AuthenticationHandler;
+
+    public setNext(handler: AuthenticationHandler): AuthenticationHandler {
+        this.nextHandler = handler;
+        return handler;
+    }
+
+    public handle(request: AuthenticationRequest): AuthenticationResult {
+        if (this.nextHandler) {
+            return this.nextHandler.handle(request);
+        }
+
+        return { success: false, message: 'Unable to authenticate user.' };
+    }
+}
+
+/**
+ * EN: All Concrete Handlers either handle a request or pass it to the next
+ * handler in the chain.
+ *
+ * RU: Все Конкретные Обработчики либо обрабатывают запрос, либо передают его
+ * следующему обработчику в цепочке.
+ */
+class BasicAuthenticationHandler extends AbstractAuthenticationHandler {
+    public handle(request: AuthenticationRequest): AuthenticationResult {
+        const user = request.user;
+        if (user.name === 'admin' && user.password === 'password') {
+            return {
+                success: true,
+                message: 'User authenticated with basic authentication.'
+            };
+        }
+        return super.handle(request);
+    }
+}
+
+class ApiKeyAuthenticationHandler extends AbstractAuthenticationHandler {
+    public handle(request: AuthenticationRequest): AuthenticationResult {
+        if (request.apiKey === 'my-api-key') {
+            return {
+                success: true, message: 'User authenticated with API key.'
+            };
+        }
+        return super.handle(request);
+    }
+}
+
+class JwtAuthenticationHandler extends AbstractAuthenticationHandler {
+    public handle(request: AuthenticationRequest): AuthenticationResult {
+        if (request.jwtToken === 'my-jwt-token') {
+            return {
+                success: true, message: 'User authenticated with JWT token.'
+            };
+        }
+        return super.handle(request);
+    }
+}