diff --git a/README.md b/README.md
index e54cdbd..3794e86 100644
--- a/README.md
+++ b/README.md
@@ -1,65 +1,18 @@
 # Hands On OOP
+# Merchant Service Simulation
 
-## Deskripsi Tugas
-Buatlah suatu program yang *perlu* mengimplementasikan konsep-konsep OOP, seminimalnya
-- Inheritance
-- Interface dan/atau abstract class
-- Polimorfisme
-- Mengimplementasikan (minimal 1) design pattern
-- Mengimplementasikan (minimal 1) prinsip SOLID
+# Deskripsi Program
+Program ini berbasis CLI yang mensimulasikan bagaimana user sebagai customer dari sebuah merchant dapat berinteraksi seperti membeli barang, top up balance, dan menu-menu lain.
 
-Tugas ini sangat membebaskan kalian untuk berkreasi. Konsep-konsep lain yang kalian gunakan dan keunikan program akan sangat dihargai dan dihitung sebagai bonus nilai (jangan lupa tulis di penjelasan program). Silakan berkreasi! :D
+# Design Pattern
+Creational Pattern (Prototype): pada program ini, terdapat abstract class (pada class `baseUser`) yang digunakan untuk membangun class-class yang lain.
 
-### Beberapa Bonus yang Direkomendasikan
-- Stream API dan/atau functional programming
-- Multilevel inheritance
-- Interactive program (Menerima input dan mengeluarkan output sesuai input)
-
-## Penjelasan Program
-Selain membuat program, kalian perlu menuliskan penjelasan program kalian, dengan seminimalnya berisikan
-- Deskripsi program
-- Penjelasan design pattern yang dipilih
-- Letak implementasi design pattern tersebut
-- Alasan pemilihan design pattern tersebut
-- Cara menjalankan program
-- Versi bahasa dan dependency (jika ada) yang digunakan
-- Konsep-konsep lain yang kalian gunakan dan keunikan program (jika ada)
-
-## Pengumpulan
-- Pengumpulan tugas ini mirip dengan tugas sebelumnya. 
-- Fork ke repository github kalian masing - masing
-- Buka repository pada repo yang telah di fork sebelumnya
-- Clone repository tersebut
-- Buat program sesuai deskripsi di atas di dalam folder dengan format `Nama_Univ`
-- Tulis penjelasan program kalian pada file `README.md` di dalam folder tersebut
-- Add folder tersebut ke dalam staging
-- Letakkan folder tersebut sejajar dengan file README.md
-- Setelah itu push kembali ke repository kalian
-- Pull request kedalam repository GDSC yang sudah anda fork tadi
-- Isi judul pull request dengan "Hands on OOP submission by < Nama kalian >"
-
-## Bahasa Pemrograman
-Tidak semua bahasa pemrograman dapat mengimplementasikan OOP. Untuk tugas ini, ada bahasa yang dapat digunakan dan tidak dapat digunakan.
-
-### Bahasa yang dapat digunakan
-Selain bahasa di bawah ini, kalian dapat me-request bahasa lain, dengan persetujuan tim kurikulum GDSC ITB
-
-- C++
-- Java
-- Kotlin
-- Typescript
-- Go (Golang)
-- C#
-
-### Bahasa yang tidak dapat digunakan
-Karena keterbatasan di bahasa-bahasa berikut, bahasa di bawah ini tidak digunakan di tugas ini
-- Python
-- PHP
-- C
-
-## Deliverable
-- Kumpulkan link github fork repository dan link pull request kalian ke gform yang dibagikan
-
-## Deadline
-- Jumat, 27 Januari 2023, pukul 23.59
+# Cara menjalankan program
+```shell
+cd src
+tsc index.ts
+node index.js
+```
 
+# Versi Bahasa 
+- Typescript 4.8.4 (compatible untuk versi ^3.0.0)
diff --git a/package-lock.json b/package-lock.json
new file mode 100644
index 0000000..2ab6666
--- /dev/null
+++ b/package-lock.json
@@ -0,0 +1,24 @@
+{
+  "name": "OOP",
+  "lockfileVersion": 2,
+  "requires": true,
+  "packages": {
+    "": {
+      "dependencies": {
+        "@types/node": "^18.11.18"
+      }
+    },
+    "node_modules/@types/node": {
+      "version": "18.11.18",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-18.11.18.tgz",
+      "integrity": "sha512-DHQpWGjyQKSHj3ebjFI/wRKcqQcdR+MoFBygntYOZytCqNfkd2ZC4ARDJ2DQqhjH5p85Nnd3jhUJIXrszFX/JA=="
+    }
+  },
+  "dependencies": {
+    "@types/node": {
+      "version": "18.11.18",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-18.11.18.tgz",
+      "integrity": "sha512-DHQpWGjyQKSHj3ebjFI/wRKcqQcdR+MoFBygntYOZytCqNfkd2ZC4ARDJ2DQqhjH5p85Nnd3jhUJIXrszFX/JA=="
+    }
+  }
+}
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..1dac93d
--- /dev/null
+++ b/package.json
@@ -0,0 +1,5 @@
+{
+  "dependencies": {
+    "@types/node": "^18.11.18"
+  }
+}
diff --git a/src/index.ts b/src/index.ts
new file mode 100644
index 0000000..3a54a20
--- /dev/null
+++ b/src/index.ts
@@ -0,0 +1,144 @@
+import { sleep } from "./lib/time_sleep";
+import { inputData } from "./lib/readline";
+import { storeItem, adminCredentials  } from "./lib/constant/store";
+import {
+    User,
+    Merchant,
+    Auth,
+} from "./lib/user";
+import * as console from "console";
+
+const main = async () => {
+    let running = true;
+    console.log("Welcome~!");
+
+    let auth = new Auth();
+    let merchant = new Merchant(
+        adminCredentials.username,
+        adminCredentials.password,
+    );
+
+    while (running) {
+        console.log("1. Login");
+        console.log("2. Sign up");
+        console.log("3. Exit")
+
+        let userChoice: any = await inputData("choice");
+        let validInput = false;
+
+        switch (userChoice){
+            case "1":
+                // login
+                await auth.login();
+                if (auth.currentUserIndex !== -1) {
+                    let data = auth.getData();
+                    let currentUserIndex = auth.currentUserIndex;
+                    // found login credentials
+                    console.log(`\nHi ${data[auth.currentUserIndex].username}!`);
+
+                    let currentUser = new User(
+                        data[currentUserIndex].username,
+                        data[currentUserIndex].password,
+                        data.length + 1
+                    );
+
+                    let quitMenu = false;
+                    do {
+                        // Menu
+                        do {
+                            console.log("\nMenu")
+                            console.log("1. Check Basket");
+                            console.log("2. Check Store");
+                            console.log("3. Top Up Balance");
+                            console.log("4. Exit");
+                            userChoice = await inputData("choice");
+
+                            if (userChoice === "1" || userChoice === "2" || userChoice === "3" || userChoice === "4") {
+                                validInput = true;
+                            }
+
+                        } while (!validInput)
+                        validInput = false;
+
+                        switch (userChoice) {
+                            case "1":
+                                currentUser.getBasketItem();
+                                console.log("\nWant to checkout things?");
+                                console.log("1. Yes");
+                                console.log("2. No");
+                                userChoice = await inputData("choice");
+
+                                switch (userChoice){
+                                    case "1":
+                                        let chosenItem = await currentUser.checkoutPayment();
+                                        if (chosenItem !== -1) {
+                                            merchant.markPayment(currentUser.getUsername(), chosenItem);
+                                        }
+                                        break;
+                                    default:
+                                }
+
+                                break;
+                            case "2":
+                                console.log("\nSelect item to buy:");
+                                storeItem.forEach((item) => {
+                                    console.log(`\t${item.item_id}. cost: ${item.cost}`);
+                                })
+                                userChoice = parseInt(await inputData("choice")) - 1;
+                                if (userChoice > 5) {
+                                    console.log("Invalid input!");
+                                }
+                                else {
+                                    currentUser.makePayment(
+                                        storeItem[userChoice].cost,
+                                        storeItem[userChoice].item_id
+                                    )
+                                    merchant.addCustomer(
+                                        {
+                                            username: currentUser.getUsername(),
+                                            item_id: storeItem[userChoice].item_id,
+                                            total_cost: storeItem[userChoice].cost,
+                                            status: "unpaid",
+                                        }
+                                    )
+                                    console.log(`Successfully bought item with id ${storeItem[userChoice].item_id}\n`);
+                                }
+                                break;
+                            case "3":
+                                currentUser.topUpBalance();
+                                break;
+                            case "4":
+                                quitMenu = true;
+                                running = false;
+                                break;
+                            default:
+                        }
+
+                    } while (!quitMenu)
+
+                }
+                else {
+                    console.log("Account not found!");
+                }
+                break;
+            case "2":
+                await auth.signUp();
+                break;
+            case "3":
+                running = false;
+                break;
+            default:
+        }
+
+    }
+}
+
+main().then(() => {
+    sleep(1000).then(() => {
+        console.log("See you next time!");
+
+    })
+});
+
+// solved TS2451
+export {};
\ No newline at end of file
diff --git a/src/lib/constant/store.ts b/src/lib/constant/store.ts
new file mode 100644
index 0000000..d3957a3
--- /dev/null
+++ b/src/lib/constant/store.ts
@@ -0,0 +1,13 @@
+export const storeItem = [
+    {item_id: 1, cost: 20000},
+    {item_id: 2, cost: 30000},
+    {item_id: 3, cost: 50000},
+    {item_id: 4, cost: 100000},
+    {item_id: 5, cost: 200000},
+];
+
+export const adminCredentials = {
+    username: "admin",
+    password: "test12345",
+}
+
diff --git a/src/lib/readline.ts b/src/lib/readline.ts
new file mode 100644
index 0000000..6cf0d97
--- /dev/null
+++ b/src/lib/readline.ts
@@ -0,0 +1,21 @@
+import * as readline from "readline"
+import { toCapitallize } from "./string_modifier";
+
+/**
+ * Readline module built in Node
+ */
+export const stdin =  readline.createInterface({
+    input: process.stdin,
+    output: process.stdout
+});
+
+/**
+ * input from console
+ * @async true
+ * @param user_data captured string from console
+ * @returns full string of user input
+ */
+export const inputData = async (user_data: string) => {
+    let userInput: string = await new Promise(resolve => stdin.question(`Enter ${user_data.toLowerCase()}: `, resolve));
+    return toCapitallize(userInput);
+}
\ No newline at end of file
diff --git a/src/lib/string_modifier.ts b/src/lib/string_modifier.ts
new file mode 100644
index 0000000..c74be67
--- /dev/null
+++ b/src/lib/string_modifier.ts
@@ -0,0 +1,17 @@
+/**
+ * Takes in full string and return the capitalized version
+ * @param str input string
+ * @returns capitalized string
+ * */
+export const toCapitallize = (str: string) => {
+    let tempStr: string;
+    let rawStrArr = str.split(" ");
+    rawStrArr.forEach((ele, index) => {
+        tempStr = ele.toLowerCase();
+        let strArr = tempStr.split("");
+        strArr[0] = strArr[0].toUpperCase();
+        rawStrArr[index] = strArr.join("");
+    })
+    tempStr = rawStrArr.join(" ");
+    return tempStr;
+}
\ No newline at end of file
diff --git a/src/lib/time_sleep.ts b/src/lib/time_sleep.ts
new file mode 100644
index 0000000..5434e77
--- /dev/null
+++ b/src/lib/time_sleep.ts
@@ -0,0 +1,10 @@
+/**
+ * Set time sleep for given milliseconds
+ * @param ms millis
+ * @returns timeout Promise
+ */
+export const sleep = async (ms: number) => {
+    return new Promise (resolve => setTimeout(resolve, ms));
+}
+
+
diff --git a/src/lib/user.ts b/src/lib/user.ts
new file mode 100644
index 0000000..41df393
--- /dev/null
+++ b/src/lib/user.ts
@@ -0,0 +1,337 @@
+import { stdin, inputData } from "./readline";
+import { sleep } from "./time_sleep";
+import { toCapitallize } from "./string_modifier";
+import {
+    account,
+    customer,
+    paymentObject,
+    authentication,
+    credential,
+} from "../typings";
+
+
+// solved TS2420:
+// @ts-ignore
+abstract class baseUser implements account{
+    // Class props
+    protected _username: string = undefined;
+    protected _password: string | number = undefined;
+    protected _id: number = undefined;
+    protected balance: number = 0;
+    // Status set to paid
+    protected isMerchant: boolean = false;
+    protected status: string = "paid";
+
+    /**
+     * @param user_data changed user field
+     * @returns error message for set / unset value
+     * */
+    protected _errChangesMsg (
+        user_data: string,
+    ) {
+        return `${toCapitallize(user_data)} cannot be same as previous!`;
+    }
+    /**
+     * @param user_data changed user field
+     * @returns success message for changes on value
+     * */
+    protected _succChangesMsg (
+        user_data: string
+    ) {
+        return `Successfully changes ${user_data.toLowerCase()}!`;
+    }
+
+    // Getters
+    public getUsername () {
+        return this._username;
+    }
+
+    public changeUsername (newUsername: string) {
+        if (this._username === newUsername) {
+            console.log(this._errChangesMsg("username"));
+        }
+        else {
+            this._username = newUsername;
+            console.log(this._succChangesMsg("username"));
+        }
+    }
+
+    protected getPassword () {
+        return this._password;
+    }
+
+    public changePassword (newPassword: number | string) {
+        if (this.getPassword() === newPassword) {
+            console.log(this._errChangesMsg("new password"));
+        } else {
+            stdin.question(
+                "Confirm Password: ",
+                async (input: string | number) => {
+                    // TODO : Refactor this code using the new input function
+                    console.log("Processing");
+                    await sleep(1000);
+                    if (newPassword === input) {
+                        this._password = newPassword;
+                        console.log(this._succChangesMsg("password"))
+                    } else {
+                        console.log("Confirmed password is not same!");
+                    }
+                }
+            )
+        }
+    }
+
+    /**
+     * Increase the current user balance
+     * @param topUpValue top up amount, defaults to 50000
+     * */
+    public topUpBalance (topUpValue: number = 50000) {
+        this.balance = this.balance + topUpValue;
+        console.log(`Top up ${topUpValue}. Current balance: ${this.balance}`);
+    }
+
+
+}
+
+export class User extends baseUser{
+    private paymentBasket: paymentObject[] = [];
+    // Constructor
+    constructor(username: string, password: number | string, id: number) {
+        super();
+        this._username = username;
+        this._password = password;
+        this._id = id;
+    }
+
+    // Getters
+    public getBalance () {
+        return this.balance;
+    }
+
+    public getBasket () {
+        return this.paymentBasket;
+    }
+
+    /**
+     * Show all list of item inside current user basket
+     * */
+    public getBasketItem () {
+        console.log(`${toCapitallize(this._username)}'s basket:`);
+        console.log("No.----Item Id----Cost");
+        for (let i = 0; i < this.paymentBasket.length; i++) {
+            console.log(`|${i + 1}|\t|${this.paymentBasket[i].item_id}|\t|${this.paymentBasket[i].cost}|`);
+        }
+        if (this.paymentBasket.length === 0) {
+            console.log("Empty here..");
+        }
+    }
+
+    /**
+     * Takes in item cost & id and push it to basket
+     * @param cost item cost
+     * @param id item id
+     * */
+    public makePayment (cost: number, id: number) {
+        // per unique item have different object
+        let item: paymentObject = {
+            username: this._username,
+            // unique item id to mark transaction
+            item_id: id,
+            cost: cost,
+            // false status === uncheckPayment, status set to true when the item is checked out
+            status: "unpaid",
+        };
+        this.paymentBasket.push(item);
+        console.log("Item is stored on your basket. Please check it!");
+    }
+
+    /**
+     * Prompt input to removed selected items inside basket if sufficient
+     * */
+    public async checkoutPayment() {
+        console.log(`Balance: ${this.balance}`);
+        let choosenItem: number;
+        let success: boolean = false;
+        if (this.paymentBasket.length !== 0) {
+            const maxChoice: number = this.paymentBasket.length;
+            let userChoice: number =  parseInt(await inputData("choice"), 10);
+            let endChoice: boolean = false;
+            while (!endChoice) {
+                if (userChoice > maxChoice) {
+                    console.log("Invalid input!");
+                    userChoice = parseInt(await inputData("choice"), 10);
+                } else {
+                    endChoice = true;
+                    // Filter out the chosen index
+                    this.paymentBasket = this.paymentBasket.filter((ele, index) => {
+                        if (index === userChoice - 1) {
+                            if (ele.cost > this.balance) {
+                                console.log("Not enough balance!");
+                                choosenItem = -1;
+                            }
+                            else {
+                                success = true;
+                                choosenItem === ele.item_id;
+                                this.balance = this.balance - ele.cost;
+                                return index !== userChoice - 1;
+
+                            }
+                        } else {
+                            return index !== userChoice - 1;
+                        }
+                    })
+                    if (success) {
+                        console.log("Successfully checked out an item! Current Basket: ");
+                        this.getBasketItem();
+                    }
+                }
+            }
+        }
+        else {
+            console.log("Nothing in basket");
+            choosenItem = -1;
+        }
+        return choosenItem;
+    }
+}
+
+export class Merchant extends baseUser {
+
+    // List of this merchant customer
+    customers: customer[] = [];
+    constructor(username: string, password: string | number) {
+        super();
+        this._username = username;
+        this._password = password;
+    }
+
+    /**
+     * @param customerData customer data
+     * */
+    public addCustomer(customerData: customer) {
+        this.customers.push(customerData);
+    }
+
+    /**
+     * @param username customer username
+     * @param item_id item id
+     * @returns removed given customer username from merchant basket
+     * */
+    private removeCustomer(username: string, item_id: string) {
+        this.customers = this.customers.filter(
+            (ele) => {
+                return ele.item_id !== item_id && ele.username !== username;
+            }
+        )
+    }
+
+    /**
+     * Mark item status on customers list based on users checked out items
+     * @param username customer username
+     * @param item_id item id
+     * */
+    public markPayment (username: string, item_id: string | number) {
+        // console.log("----------->" + this.customers.length);
+        this.customers.forEach((customer) => {
+            if (customer.username === username && customer.item_id === item_id) {
+                customer.status = "paid";
+            }
+        })
+    }
+
+    /**
+     * Prompt input for username & item id to match the customers data
+     * @returns confirmed boolean value
+     * */
+    public async confirmPayment() {
+        const username: string = await inputData("username");
+        const item_id: string = await inputData("item id")
+        const length: number = this.customers.length;
+        let confirmed: boolean = false;
+        this.removeCustomer(username, item_id);
+        if (this.customers.length === length) {
+            console.log(`Unable to find ${username} (does not exist).`);
+        }
+        else {
+            confirmed = true;
+            console.log(`Successfully confirmed ${username}!`);
+        }
+        return confirmed;
+    }
+
+    /**
+     * Shows the content of customers list
+     * */
+    public getCustomerList () {
+        console.log(`${toCapitallize(this._username)}'s customers:`);
+        if (this.customers.length > 0){
+            this.customers.forEach((ele) => {
+                console.log(`Username: ${ele.username}`);
+                console.log(`\tTotal: ${ele.total_cost}`);
+                console.log(`\tStatus: ${ele.status}`);
+            })
+        }
+        else {
+            console.log("No customer.");
+        }
+    }
+
+}
+
+// solved TS2420:
+// @ts-ignore
+export class Auth implements authentication {
+    private database: credential[] = [
+        {
+            username: "admin",
+            password: "test12345",
+            balance: 0,
+            loggedIn: true,
+            isMerchant: true,
+        }
+    ];
+    public currentUserIndex: number = -1;
+    private username: string;
+    private password: number | string;
+
+    // Getters
+    public getData () {
+        return this.database;
+    }
+
+    /**
+     * Prompt an login form
+     * @param asMerchant (not available)
+     * */
+    public async login (asMerchant: boolean = false) {
+        const username = await inputData("username");
+        const password = await inputData("password");
+        console.log("Authenticating...");
+        let foundCredential = false;
+        let isMerchant = asMerchant;
+        this.database.forEach((credential, index) => {
+            if (credential.username === username && credential.password === password) {
+                foundCredential = true;
+                this.currentUserIndex = index;
+            }
+        })
+        if (foundCredential) {
+            this.database[this.currentUserIndex].loggedIn = true;
+        }
+    }
+
+    /**
+     * Prompt a sign-up  form
+     * */
+    public async signUp () {
+        let currentUser: credential = {
+            username: await inputData("username"),
+            password: await inputData("password"),
+            balance: 0,
+            loggedIn: false,
+            isMerchant: false
+        }
+        this.database.push(currentUser);
+        console.log(`Account created! Please login!`);
+    }
+}
diff --git a/src/typings/index.d.ts b/src/typings/index.d.ts
new file mode 100644
index 0000000..7850f2c
--- /dev/null
+++ b/src/typings/index.d.ts
@@ -0,0 +1,62 @@
+
+export declare interface account {
+    _username: string;
+    _password: string | number;
+    _id: number;
+    balance: number;
+    isMerchant: boolean;
+    status: string;
+    /**
+     * @returns current username user object
+     * */
+    getUsername(): string;
+
+    /**
+     * @description change current username of user object
+     * @param newUsername new username
+     * */
+    changeUsername(newUsername: string): void;
+
+    /**
+     * @returns current user password
+     * */
+    getPassword(): string | number;
+
+    /**
+     * @description change current password of user object
+     * @param newPassword new password
+     * */
+    changePassword(newPassword: number | string): void;
+
+    /**
+     * @returns top up user balance
+     * */
+    topUpBalance(): void;
+}
+
+export declare interface paymentObject {
+    username: string;
+    item_id: string | number;
+    cost: number;
+    status?: string;
+}
+
+export declare interface customer {
+    username: string;
+    item_id: string | number;
+    total_cost: number;
+    status: string; // paid or unpaid
+    appeal?: boolean;
+}
+
+export declare interface authentication {
+    database: credential[];
+}
+
+export declare interface credential {
+    username: string;
+    password: string | number;
+    balance: number;
+    loggedIn?: boolean;
+    isMerchant: boolean;
+}
\ No newline at end of file
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..72964aa
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,32 @@
+{
+    "compilerOptions": {
+        "lib": ["es6"],
+        "module": "CommonJS",
+        "types": ["node"],
+        "removeComments": false,
+        "experimentalDecorators": true,
+        "noImplicitOverride": true,
+        "sourceMap": true,
+        "moduleDetection": "force",
+        "moduleResolution": "node",
+        "outDir": "./dist",
+        "baseUrl": "."
+//        "paths": {
+//            "@/*": ["src/*"],
+//            "@/lib/*": ["src/lib/*"],
+//        },
+    },
+    "include": [
+        "src",
+        "src/**/*.ts",
+        "src/typings"
+    ],
+    "exclude": [
+        "node_modules",
+        "dist",
+    ],
+    "typeRoots": [
+        "src/typings",
+        "node_modules/@types",
+    ]
+}
\ No newline at end of file