From 2e582ba3e459dc8f4e0fc98ccc97f8e1a54a3abd Mon Sep 17 00:00:00 2001
From: Jovan Cvetkov <jcvetkov@griddynamics.com>
Date: Tue, 2 Jun 2026 00:49:26 +0200
Subject: [PATCH] Type annotated index.js

---
 index.ts | 184 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 184 insertions(+)
 create mode 100644 index.ts

diff --git a/index.ts b/index.ts
new file mode 100644
index 0000000..6af96c2
--- /dev/null
+++ b/index.ts
@@ -0,0 +1,184 @@
+enum HttpStatus {
+  OK = 200,
+  INTERNAL_SERVER_ERROR = 500,
+  BAD_REQUEST = 400,
+  NOT_FOUND = 404,
+  UNAUTHORIZED = 401,
+  FORBIDDEN = 403,
+}
+
+type HttpMethod = "GET" | "POST" | "PUT" | "PATCH" | "DELETE";
+
+type Role = "user" | "admin";
+
+interface User {
+  name: string;
+  age: number;
+  roles: Role[];
+  createdAt: Date;
+  isDeleted: boolean;
+}
+
+namespace App {
+  export interface Request<T extends object, U extends object> {
+    method: HttpMethod;
+    path: string;
+    body?: T;
+    host: string;
+    params: U;
+  }
+
+  export interface Response {
+    status: HttpStatus;
+  }
+
+  export interface Error {
+    message: string;
+    code: number;
+    details?: string;
+  }
+}
+
+type TeardownFn = () => void;
+
+interface ObserverHandlers<T> {
+  next?: (value: T) => void;
+  error?: (error: App.Error) => void;
+  complete?: () => void;
+}
+
+class Observer<T> {
+  private isUnsubscribed: boolean = false;
+
+  constructor(
+    private handlers: ObserverHandlers<T>,
+    public _unsubscribe?: TeardownFn,
+  ) {}
+
+  public next(value: T): void {
+    if (this.handlers.next && !this.isUnsubscribed) {
+      this.handlers.next(value);
+    }
+  }
+
+  public error(error: App.Error): void {
+    if (!this.isUnsubscribed) {
+      if (this.handlers.error) {
+        this.handlers.error(error);
+      }
+
+      this.unsubscribe();
+    }
+  }
+
+  public complete(): void {
+    if (!this.isUnsubscribed) {
+      if (this.handlers.complete) {
+        this.handlers.complete();
+      }
+
+      this.unsubscribe();
+    }
+  }
+
+  public unsubscribe(): void {
+    this.isUnsubscribed = true;
+
+    if (this._unsubscribe) {
+      this._unsubscribe();
+    }
+  }
+}
+
+type SubscribeFn<T> = (observer: Observer<T>) => TeardownFn;
+
+interface Subscription {
+  unsubscribe: () => void;
+}
+
+class Observable<T> {
+  constructor(private _subscribe: SubscribeFn<T>) {}
+
+  public static from<U>(values: U[]): Observable<U> {
+    return new Observable<U>((observer: Observer<U>) => {
+      values.forEach((value) => observer.next(value));
+
+      observer.complete();
+
+      return () => {
+        console.log("unsubscribed");
+      };
+    });
+  }
+
+  public subscribe(obs: ObserverHandlers<T>): Subscription {
+    const observer = new Observer<T>(obs);
+
+    observer._unsubscribe = this._subscribe(observer);
+
+    return {
+      unsubscribe() {
+        observer.unsubscribe();
+      },
+    };
+  }
+}
+
+const userMock: User = {
+  name: "User Name",
+  age: 26,
+  roles: ["user", "admin"],
+  createdAt: new Date(),
+  isDeleted: false,
+};
+
+type Params = {
+  id: string;
+};
+
+type MockRequest = App.Request<User, Partial<Params>>;
+
+const requestMock: MockRequest[] = [
+  {
+    method: "POST",
+    host: "service.example",
+    path: "user",
+    body: userMock,
+    params: {},
+  },
+  {
+    method: "GET",
+    host: "service.example",
+    path: "user",
+    params: {
+      id: "3f5h67s4s",
+    },
+  },
+];
+
+const handleRequest = (request: MockRequest): App.Response => {
+  return {
+    status: HttpStatus.OK,
+  };
+};
+
+const handleError = (error: App.Error): App.Response => {
+  console.error(`Error [${error.code}]: ${error.message}`);
+  if (error.details) {
+    console.error(`Details: ${error.details}`);
+  }
+
+  return { status: HttpStatus.INTERNAL_SERVER_ERROR };
+};
+
+const handleComplete = (): void => console.log("complete");
+
+const requests$ = Observable.from<MockRequest>(requestMock);
+
+const subscription = requests$.subscribe({
+  next: handleRequest,
+  error: handleError,
+  complete: handleComplete,
+});
+
+subscription.unsubscribe();