Finance Expert

Expert guidance for financial systems, FinTech applications, banking platforms, payment processing, and financial technology development.

Core Concepts

Financial Systems

• Core banking systems
• Payment processing
• Trading platforms
• Risk management
• Regulatory compliance (PCI-DSS, SOX, Basel III)
• Financial reporting

FinTech Stack

• Payment gateways (Stripe, PayPal, Square)
• Banking APIs (Plaid, Yodlee)
• Blockchain/crypto
• Open Banking APIs
• Mobile banking
• Digital wallets

Key Challenges

• Security and fraud prevention
• Real-time processing
• High availability (99.999%)
• Regulatory compliance
• Data privacy
• Transaction accuracy

Payment Processing

# Payment gateway integration (Stripe)
import stripe
from decimal import Decimal

stripe.api_key = "sk_test_..."

class PaymentService:
    def create_payment_intent(self, amount: Decimal, currency: str = "usd"):
        """Create payment intent with idempotency"""
        return stripe.PaymentIntent.create(
            amount=int(amount * 100),  # Convert to cents
            currency=currency,
            payment_method_types=["card"],
            metadata={"order_id": "12345"}
        )

    def process_refund(self, payment_intent_id: str, amount: Decimal = None):
        """Process full or partial refund"""
        return stripe.Refund.create(
            payment_intent=payment_intent_id,
            amount=int(amount * 100) if amount else None
        )

    def handle_webhook(self, payload: str, signature: str):
        """Handle Stripe webhook events"""
        try:
            event = stripe.Webhook.construct_event(
                payload, signature, webhook_secret
            )

            if event.type == "payment_intent.succeeded":
                payment_intent = event.data.object
                self.handle_successful_payment(payment_intent)
            elif event.type == "payment_intent.payment_failed":
                payment_intent = event.data.object
                self.handle_failed_payment(payment_intent)

            return {"status": "success"}
        except ValueError:
            return {"status": "invalid_payload"}

Banking Integration

# Open Banking API integration (Plaid)
from plaid import Client
from plaid.errors import PlaidError

class BankingService:
    def __init__(self):
        self.client = Client(
            client_id="...",
            secret="...",
            environment="sandbox"
        )

    def create_link_token(self, user_id: str):
        """Create link token for Plaid Link"""
        response = self.client.LinkToken.create({
            "user": {"client_user_id": user_id},
            "client_name": "My App",
            "products": ["auth", "transactions"],
            "country_codes": ["US"],
            "language": "en"
        })
        return response["link_token"]

    def exchange_public_token(self, public_token: str):
        """Exchange public token for access token"""
        response = self.client.Item.public_token.exchange(public_token)
        return {
            "access_token": response["access_token"],
            "item_id": response["item_id"]
        }

    def get_accounts(self, access_token: str):
        """Get user's bank accounts"""
        response = self.client.Accounts.get(access_token)
        return response["accounts"]

    def get_transactions(self, access_token: str, start_date: str, end_date: str):
        """Get transactions for date range"""
        response = self.client.Transactions.get(
            access_token,
            start_date,
            end_date
        )
        return response["transactions"]

Financial Calculations

from decimal import Decimal, ROUND_HALF_UP
from datetime import datetime, timedelta

class FinancialCalculator:
    @staticmethod
    def calculate_interest(principal: Decimal, rate: Decimal, periods: int) -> Decimal:
        """Calculate compound interest"""
        return principal * ((1 + rate) ** periods - 1)

    @staticmethod
    def calculate_loan_payment(principal: Decimal, annual_rate: Decimal, months: int) -> Decimal:
        """Calculate monthly loan payment (amortization)"""
        monthly_rate = annual_rate / 12
        payment = principal * (monthly_rate * (1 + monthly_rate) ** months) / \
                  ((1 + monthly_rate) ** months - 1)
        return payment.quantize(Decimal('0.01'), rounding=ROUND_HALF_UP)

    @staticmethod
    def calculate_npv(cash_flows: list[Decimal], discount_rate: Decimal) -> Decimal:
        """Calculate Net Present Value"""
        npv = Decimal('0')
        for i, cf in enumerate(cash_flows):
            npv += cf / ((1 + discount_rate) ** i)
        return npv.