Paypal Integration

# paypal-integration — detailed patterns and worked examples

## Express Checkout Implementation

### Server-Side Order Creation

```python
import requests
import json

class PayPalClient:
    def __init__(self, client_id, client_secret, mode='sandbox'):
        self.client_id = client_id
        self.client_secret = client_secret
        self.base_url = 'https://api-m.sandbox.paypal.com' if mode == 'sandbox' else 'https://api-m.paypal.com'
        self.access_token = self.get_access_token()

    def get_access_token(self):
        """Get OAuth access token."""
        url = f"{self.base_url}/v1/oauth2/token"
        headers = {"Accept": "application/json", "Accept-Language": "en_US"}

        response = requests.post(
            url,
            headers=headers,
            data={"grant_type": "client_credentials"},
            auth=(self.client_id, self.client_secret)
        )

        return response.json()['access_token']

    def create_order(self, amount, currency='USD'):
        """Create a PayPal order."""
        url = f"{self.base_url}/v2/checkout/orders"
        headers = {
            "Content-Type": "application/json",
            "Authorization": f"Bearer {self.access_token}"
        }

        payload = {
            "intent": "CAPTURE",
            "purchase_units": [{
                "amount": {
                    "currency_code": currency,
                    "value": str(amount)
                }
            }]
        }

        response = requests.post(url, headers=headers, json=payload)
        return response.json()

    def capture_order(self, order_id):
        """Capture payment for an order."""
        url = f"{self.base_url}/v2/checkout/orders/{order_id}/capture"
        headers = {
            "Content-Type": "application/json",
            "Authorization": f"Bearer {self.access_token}"
        }

        response = requests.post(url, headers=headers)
        return response.json()

    def get_order_details(self, order_id):
        """Get order details."""
        url = f"{self.base_url}/v2/checkout/orders/{order_id}"
        headers = {
            "Authorization": f"Bearer {self.access_token}"
        }

        response = requests.get(url, headers=headers)
        return response.json()
```

## IPN (Instant Payment Notification) Handling

### IPN Verification and Processing

```python
from flask import Flask, request
import requests
from urllib.parse import parse_qs

app = Flask(__name__)

@app.route('/ipn', methods=['POST'])
def handle_ipn():
    """Handle PayPal IPN notifications."""
    # Get IPN message
    ipn_data = request.form.to_dict()

    # Verify IPN with PayPal
    if not verify_ipn(ipn_data):
        return 'IPN verification failed', 400

    # Process IPN based on transaction type
    payment_status = ipn_data.get('payment_status')
    txn_type = ipn_data.get('txn_type')

    if payment_status == 'Completed':
        handle_payment_completed(ipn_data)
    elif payment_status == 'Refunded':
        handle_refund(ipn_data)
    elif payment_status == 'Reversed':
        handle_chargeback(ipn_data)

    return 'IPN processed', 200

def verify_ipn(ipn_data):
    """Verify IPN message authenticity."""
    # Add 'cmd' parameter
    verify_data = ipn_data.copy()
    verify_data['cmd'] = '_notify-validate'

    # Send back to PayPal for verification
    paypal_url = 'https://ipnpb.sandbox.paypal.com/cgi-bin/webscr'  # or production URL

    response = requests.post(paypal_url, data=verify_data)

    return response.text == 'VERIFIED'

def handle_payment_completed(ipn_data):
    """Process completed payment."""
    txn_id = ipn_data.get('txn_id')
    payer_email = ipn_data.get('payer_email')
    mc_gross = ipn_data.get('mc_gross')
    item_name = ipn_data.get('item_name')

    # Check if already processed (prevent duplicates)
    if is_transaction_processed(txn_id):
        return

    # Update database
    # Send confirmation email
    # Fulfill order
    print(f"Payment completed: {tx