Build a Parking Payment App

A parking payment app manages sessions between vehicle entry and exit. The core data is simple: when did the vehicle enter, when did it exit, how much does it owe, and has it paid?

The flow:

1. Driver scans QR code (or attendant enters plate number) at entry
2. System creates a parking session with entry timestamp and vehicle identifier
3. At exit, driver requests payment — system calculates fee based on duration
4. Driver pays via Paystack on their phone or a kiosk
5. Webhook confirms payment — system updates session to paid and signals barrier open
6. Vehicle exits within a grace period (say 5 minutes after payment)

Database tables: parking_lots (location, rate per hour, max daily rate), sessions (plate, lot_id, entry_at, exit_at, fee_amount, status, paystack_reference), rates (lot_id, period, rate — for peak/off-peak pricing).

function calculateParkingFee(entryAt, exitAt, ratePerHour, maxDailyRate) {
  var minutes = Math.ceil((exitAt - entryAt) / 60000); // ms to minutes
  var hours = Math.ceil(minutes / 60); // round up to nearest hour
  var fee = hours * ratePerHour;
  return Math.min(fee, maxDailyRate); // cap at daily max
}

async function initiateExitPayment(sessionId, driverEmail) {
  var session = await db.sessions.findById(sessionId);
  var lot = await db.parkingLots.findById(session.lot_id);
  var now = Date.now();
  var fee = calculateParkingFee(session.entry_at, now, lot.rate_per_hour, lot.max_daily_rate);

  var reference = 'PARK-' + sessionId + '-' + Date.now();
  await db.sessions.update(sessionId, { fee_amount: fee, paystack_reference: reference });

  var response = await fetch('https://api.paystack.co/transaction/initialize', {
    method: 'POST',
    headers: { Authorization: 'Bearer ' + process.env.PAYSTACK_SECRET_KEY, 'Content-Type': 'application/json' },
    body: JSON.stringify({
      email: driverEmail,
      amount: fee, // in kobo/cents
      currency: 'KES',
      reference: reference,
      metadata: { session_id: sessionId, plate: session.plate, lot_name: lot.name },
    }),
  });

  var data = await response.json();
  return data.data.authorization_url; // send to driver's phone
}

The webhook handler verifies the signature, finds the session by reference, marks it paid, and signals the barrier controller (via GPIO, serial port, or REST API depending on your hardware).

if (event.event === 'charge.success') {
  var sessionId = event.data.metadata.session_id;
  await db.sessions.update(sessionId, { status: 'paid', exit_at: new Date(), paystack_txn: event.data.id });
  await barrierController.open(sessionId); // trigger exit barrier
}

See build a vehicle inspection booking and payment app for another government/transport sector Paystack integration.

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