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Estimate the scale of the system you are going to design...
Define what APIs are expected from the system...
/api/users/register: Create a new user account./api/users/login: Authenticate a user./api/users/profile: Fetch user profile and linked accounts./api/wallet/add_money: Add money to the wallet./api/wallet/balance: Check wallet balance./api/wallet/history: Retrieve transaction history./api/payments/online: Make an online payment to a merchant./api/payments/offline: Make a QR code payment for offline transactions./api/payments/recurring: Set up recurring payments./api/transfer/send: Transfer money to another user./api/transfer/receive: Fetch incoming transfer requests./api/bank/link_account: Link a bank account to the wallet./api/bank/details: Fetch linked bank account details./api/bank/withdraw: Withdraw wallet balance to a bank account./api/merchants/register: Register a merchant account./api/merchants/transactions: Fetch merchant transaction history./api/merchants/qrcode: Generate a dynamic QR code for payments./api/notifications/send: Send transaction notifications./api/notifications: Retrieve past notifications.Defining the system data model early on will clarify how data will flow among different components of the system. Also you could draw an ER diagram using the diagramming tool to enhance your design...
Usersuser_id (Primary Key): Unique identifier for each user.name: Full name of the user.email: Email address.phone_number: Phone number.password_hash: Hashed password.created_at: Account creation timestamp.Walletswallet_id (Primary Key): Unique identifier for each wallet.user_id (Foreign Key): Associated user ID.balance: Current wallet balance.last_updated: Timestamp of the last balance update.Transactionstransaction_id (Primary Key): Unique identifier for each transaction.user_id (Foreign Key): Associated user ID.amount: Transaction amount.transaction_type: Type (e.g., credit, debit).status: Transaction status (e.g., success, failed).timestamp: Time of the transaction.Merchantsmerchant_id (Primary Key): Unique identifier for each merchant.name: Merchant name.email: Merchant email.phone_number: Merchant phone number.qrcode: Static or dynamic QR code for payments.Notificationsnotification_id (Primary Key): Unique identifier for each notification.user_id (Foreign Key): Associated user ID.message: Notification content.timestamp: Time of notification delivery.You should identify enough components that are needed to solve the actual problem from end to end. Also remember to draw a block diagram using the diagramming tool to augment your design. If you are unfamiliar with the tool, you can simply describe your design to the chat bot and ask it to generate a starter diagram for you to modify...
Handles user registration, authentication, and profile management. Ensures secure access to the wallet and related features.
Manages the wallet’s balance, transactions, and fund transfers. Ensures accurate updates during concurrent transactions.
Handles secure payment processing for adding funds, making payments, and settling with merchants.
Facilitates money transfers between wallet users. Ensures real-time updates and secure transactions.
Allows merchants to register, generate QR codes, and accept payments. Provides detailed transaction records for reconciliation.
Manages alerts and notifications for transactions, refunds, and promotional messages.
Tracks and analyzes wallet activities, such as transaction volume, user engagement, and merchant performance.
Explain how the request flows from end to end in your high level design. Also you could draw a sequence diagram using the diagramming tool to enhance your explanation...
Steps:
POST /api/users/register request with user details.Steps:
POST /api/wallet/add_money request with the amount and payment method.Steps:
POST /api/transfer/send request with the recipient’s details and amount.Steps:
POST /api/payments/online request with the merchant ID and amount.Steps:
GET /api/wallet/history request.Steps:
Dig deeper into 2-3 components and explain in detail how they work. For example, how well does each component scale? Any relevant algorithm or data structure you like to use for a component? Also you could draw a diagram using the diagramming tool to enhance your design...
The User Management Service is responsible for user registration, authentication, and profile management. It handles user onboarding, validates credentials during login, and manages user sessions. When a new user registers, the service validates the data (e.g., email, phone number) for uniqueness, hashes passwords for secure storage, and creates an account. Upon login, it verifies credentials, generates a session token, and updates login activity.
Implementation Detail (Password Hashing):
python
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from bcrypt import hashpw, gensalt, checkpw
def hash_password(password):
return hashpw(password.encode('utf-8'), gensalt())
def verify_password(password, hashed):
return checkpw(password.encode('utf-8'), hashed)
The Wallet Service manages user balances, processes fund transfers, and logs transactions. When a user adds money, the service deducts the amount from the linked bank/card via the Payment Gateway Integration and credits the wallet. It also verifies balance sufficiency before transfers and ensures atomic updates to prevent data inconsistency.
Implementation Detail (Ledger Model):
python
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class Ledger:
def init(self):
self.entries = []
def add_entry(self, transaction_id, user_id, amount, transaction_type):
self.entries.append({
"transaction_id": transaction_id,
"user_id": user_id,
"amount": amount,
"transaction_type": transaction_type
})
This service acts as a bridge between the Wallet Service and external payment gateways. It handles payments for adding funds, processing refunds, and making payments to merchants. It ensures secure communication with third-party gateways, validates transactions, and updates payment statuses.
Implementation Detail (Tokenization):
python
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import hashlib
def tokenize(data):
return hashlib.sha256(data.encode()).hexdigest()
The P2P Transfer Service allows users to send and receive money. It validates sender and recipient accounts, ensures sufficient balance, and updates both wallets atomically. It also logs transactions and notifies users of transfer details.
Implementation Detail (P2P Transfer):
python
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def transfer_funds(sender_id, recipient_id, amount):
sender_wallet = get_wallet(sender_id)
recipient_wallet = get_wallet(recipient_id)
if sender_wallet.balance >= amount:
sender_wallet.balance -= amount
recipient_wallet.balance += amount
log_transaction(sender_id, recipient_id, amount)
else:
raise ValueError("Insufficient Balance")
Explain any trade offs you have made and why you made certain tech choices...
Microservices Architecture:
NoSQL for Transactions:
Distributed Locks for Wallet Updates:
Tokenization for Sensitive Data:
Try to discuss as many failure scenarios/bottlenecks as possible.
Concurrent Wallet Updates:
Payment Gateway Downtime:
High Transaction Volume:
Fraudulent Transactions:
Data Loss in Message Queues:
What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?
AI-Powered Fraud Detection:
Predictive Autoscaling:
Blockchain for Ledger Management:
Enhanced Monitoring and Alerting:
Cross-Border Payment Support: