btcpaymailer/app.py

import os
import requests
from flask import Flask, request, jsonify

app = Flask(__name__)

# --- Configuration ---
# Ensure these are passed as environment variables
WEBHOOK_SECRET = os.getenv("WEBHOOK_SECRET", "your_secret_token_here")
BTCPAY_URL = os.getenv("BTCPAY_URL", "https://payment.nxtgroup.org")
BTCPAY_API_KEY = os.getenv("BTCPAY_API_KEY") # Needs 'btcpay.store.canviewinvoices' permission
POSTMARK_API_KEY = os.getenv("POSTMARK_API_KEY")
FROM_EMAIL = os.getenv("FROM_EMAIL", "billing@nxtgroup.org")
BCC_EMAIL = os.getenv("BCC_EMAIL", "admin@nxtgroup.org")

def get_html_template(order_id, invoice_id, amount, currency, amount_paid, remaining):
    return f"""
    <div style="font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif; background-color: #f4f5f7; padding: 40px 20px; color: #333333; line-height: 1.6;">
        <div style="max-width: 600px; margin: 0 auto; background-color: #ffffff; border: 1px solid #e5e7eb; border-radius: 8px; overflow: hidden; box-shadow: 0 4px 6px rgba(0,0,0,0.05);">
            
            <div style="background-color: #f59e0b; padding: 25px 30px; text-align: center;">
                <h1 style="margin: 0; color: #ffffff; font-size: 24px; font-weight: 600;">Incomplete Payment Detected</h1>
            </div>

            <div style="padding: 30px;">
                <p style="margin-top: 0; font-size: 16px;">Hi,</p>
                <p style="font-size: 16px;">We received a payment for your order <strong>#{order_id}</strong>, but it does not cover the full amount required to complete the purchase.</p>

                <div style="background-color: #fffbeb; border-left: 4px solid #f59e0b; padding: 15px 20px; margin: 25px 0;">
                    <p style="margin: 0 0 8px 0; font-size: 16px;"><strong>Total Amount:</strong> {amount} {currency}</p>
                    <p style="margin: 0 0 8px 0; font-size: 16px;"><strong>Amount Paid:</strong> {amount_paid} {currency}</p>
                    <p style="margin: 0; font-size: 18px; color: #b45309;"><strong>Remaining Balance:</strong> {remaining} {currency}</p>
                </div>

                <p style="font-size: 16px;">To ensure your order is processed, please return to the invoice and pay the remaining balance before the timer expires.</p>

                <div style="text-align: center; margin: 30px 0;">
                    <a href="{BTCPAY_URL}/i/{invoice_id}" target="_blank" style="background-color: #2563eb; color: #ffffff; text-decoration: none; padding: 14px 28px; border-radius: 6px; font-weight: bold; font-size: 16px; display: inline-block;">Pay Remaining Balance</a>
                </div>

                <p style="font-size: 14px; color: #6b7280; word-break: break-all; text-align: center;">
                    Or copy and paste this link into your browser:<br>
                    <a href="{BTCPAY_URL}/i/{invoice_id}" style="color: #2563eb; text-decoration: underline;">{BTCPAY_URL}/i/{invoice_id}</a>
                </p>

                <div style="background-color: #fef2f2; border: 1px solid #fee2e2; border-left: 4px solid #ef4444; padding: 15px; border-radius: 4px; margin-top: 30px;">
                    <p style="margin: 0; font-size: 14px; color: #991b1b;">
                        <strong>Important:</strong> If the full balance is not received before the invoice expires, the order will be cancelled and you will need to contact support for a refund of the partial amount.
                    </p>
                </div>
            </div>

            <div style="background-color: #f9fafb; padding: 20px 30px; border-top: 1px solid #e5e7eb; text-align: center;">
                <p style="margin: 0; font-size: 14px; color: #6b7280;">Best regards,<br><strong style="color: #374151;">NXT Group</strong></p>
            </div>
        </div>
    </div>
    """

def send_postmark_email(to_email, subject, html_body):
    headers = {
        "Accept": "application/json",
        "Content-Type": "application/json",
        "X-Postmark-Server-Token": POSTMARK_API_KEY
    }
    payload = {
        "From": FROM_EMAIL,
        "To": to_email,
        "Bcc": BCC_EMAIL,
        "Subject": subject,
        "HtmlBody": html_body,
        "MessageStream": "outbound"
    }
    
    response = requests.post("https://api.postmarkapp.com/email", json=payload, headers=headers)
    return response.status_code == 200

@app.route('/btcpay-webhook', methods=['POST'])
def btcpay_webhook():
    # 1. Verify Secret Token
    token = request.args.get('token')
    if token != WEBHOOK_SECRET:
        return jsonify({"error": "Unauthorized"}), 401

    data = request.json
    
    # 2. Only process 'InvoiceReceivedPayment' events
    if data.get('type') != 'InvoiceReceivedPayment':
        return jsonify({"status": "ignored", "reason": "Not a payment event"}), 200

    store_id = data.get('storeId')
    invoice_id = data.get('invoiceId')

    # 3. Fetch full invoice details from BTCPay API
    headers = {"Authorization": f"token {BTCPAY_API_KEY}"}
    invoice_resp = requests.get(f"{BTCPAY_URL}/api/v1/stores/{store_id}/invoices/{invoice_id}", headers=headers)
    
    if invoice_resp.status_code != 200:
        return jsonify({"error": "Failed to fetch invoice"}), 500
        
    invoice_data = invoice_resp.json()
    
    amount = float(invoice_data.get('amount', 0))
    amount_paid = float(invoice_data.get('amountPaid', 0))
    currency = invoice_data.get('currency', '')
    status = invoice_data.get('status', '')
    metadata = invoice_data.get('metadata', {})
    
    buyer_email = metadata.get('buyerEmail')
    order_id = metadata.get('orderId', invoice_id)

    # 4. Check if it's a partial payment on an active invoice
    if status == 'New' and 0 < amount_paid < amount:
        if not buyer_email:
            return jsonify({"error": "No buyer email associated with invoice"}), 400
            
        remaining = round(amount - amount_paid, 8)
        
        # Generate HTML and Send Email
        html_body = get_html_template(order_id, invoice_id, amount, currency, amount_paid, remaining)
        subject = f"Action Required: Partial payment received for Order #{order_id}"
        
        email_sent = send_postmark_email(buyer_email, subject, html_body)
        
        if email_sent:
            return jsonify({"status": "success", "message": "Partial payment email sent"}), 200
        else:
            return jsonify({"error": "Failed to send email via Postmark"}), 500

    return jsonify({"status": "ignored", "reason": "Payment meets total or invoice not in New state"}), 200

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)