feat(behavioral): add chain-of-responsibility pattern

Author: hra4h03

behavioral/chain-of-responsibilities.ts

@@ -0,0 +1,86 @@
+import http from "http";
+
+type HandlerClass = { new (handler?: Handler): Handler };
+
+abstract class Handler {
+ constructor(private readonly handler?: Handler) {}
+
+ process(req: http.IncomingMessage, res: http.ServerResponse) {
+ console.log("BaseHandler: processing");
+
+ if (!this.handler) {
+ res.writeHead(404, { "Content-Type": "application/json" });
+ res.write(JSON.stringify({ error: 404, message: "Not found" }));
+ return res.end();
+ }
+
+ this.handler.process(req, res);
+ }
+}
+
+class AuthorizationHandler extends Handler {
+ constructor(nextHandler?: Handler) {
+ super(nextHandler);
+ }
+
+ process(req: http.IncomingMessage, res: http.ServerResponse) {
+ console.log("AuthorizationHandler: processing");
+
+ const authorization = req.headers.authorization;
+ const token = authorization?.split(" ")?.[1];
+
+ // implementation of authorization process
+ if (token) return super.process(req, res);
+
+ res.writeHead(401, { "Content-Type": "application/json" });
+ res.write(JSON.stringify({ error: 401, message: "Not Authorized" }));
+ return res.end();
+ }
+}
+
+class UsersHandler extends Handler {
+ static users = [{ name: "Aram" }, { name: "Anri" }];
+
+ async process(req: http.IncomingMessage, res: http.ServerResponse) {
+ console.log("UsersHandler: processing");
+
+ res.writeHead(200, { "Content-Type": "application/json" });
+ res.write(JSON.stringify({ users: UsersHandler.users }));
+ res.end();
+ }
+}
+class HttpServer {
+ constructor(private readonly handlers: Record<string, Handler> = {}) {}
+
+ get(route: string, ...Handlers: HandlerClass[]) {
+ const requestHandler = this.buildChain(Handlers);
+ this.handlers[route] = requestHandler;
+ }
+
+ listen(port: number) {
+ const server = http.createServer(this.baseHandler.bind(this));
+ server.listen(port);
+ }
+
+ // utility functions
+ private buildChain(Handlers: HandlerClass[]): Handler {
+ return Handlers.reduceRight(
+ (previousHandler: Handler | undefined, CurrentHandler: HandlerClass) => {
+ return new CurrentHandler(previousHandler);
+ },
+ undefined
+ )!;
+ }
+
+ private baseHandler(req: http.IncomingMessage, res: http.ServerResponse) {
+ for (const [route, handler] of Object.entries(this.handlers)) {
+ if (req.url === route) return handler.process(req, res);
+ }
+ }
+}
+
+const app = new HttpServer();
+
+app.get("/users", AuthorizationHandler, UsersHandler);
+
+app.listen(3000);