// Create or retrieve the Stripe customer
const customer = await stripe.customers.create({
  email: customerEmail,
  payment_method: paymentMethodId,
  invoice_settings: { default_payment_method: paymentMethodId },
});

// Create the subscription
const subscription = await stripe.subscriptions.create({
  customer: customer.id,
  items: [{ price: 'price_monthly_pro_29' }], // Price ID from Stripe Dashboard
  payment_behavior: 'default_incomplete', // Create subscription, then confirm payment
  payment_settings: { save_default_payment_method: 'on_subscription' },
  expand: ['latest_invoice.payment_intent'],
  trial_period_days: 14, // Optional trial
  metadata: { customer_id: customerId },
});

// Return client_secret for 3DS confirmation if needed
const clientSecret = subscription.latest_invoice?.payment_intent?.client_secret;
res.json({ subscriptionId: subscription.id, clientSecret });

// Webhook handler for subscription events
async function handleSubscriptionWebhook(event) {
  switch (event.type) {
    case 'customer.subscription.updated':
      await syncSubscriptionStatus(event.data.object);
      break;

    case 'customer.subscription.deleted':
      // Subscription cancelled — revoke access
      await db.subscriptions.update({
        where: { stripeSubscriptionId: event.data.object.id },
        data: { status: 'cancelled', cancelledAt: new Date() },
      });
      break;

    case 'invoice.payment_succeeded':
      await recordSuccessfulBillingCycle(event.data.object);
      break;

    case 'invoice.payment_failed':
      // Send dunning email — Stripe retries automatically per your settings
      await sendDunningEmail(event.data.object);
      break;

    case 'customer.subscription.trial_will_end':
      // Send trial ending email 3 days before trial ends
      await sendTrialEndingEmail(event.data.object);
      break;
  }
}

// Upgrade or downgrade a subscription
const subscription = await stripe.subscriptions.retrieve(stripeSubscriptionId);

await stripe.subscriptions.update(stripeSubscriptionId, {
  items: [{ id: subscription.items.data[0].id, price: newPriceId }],
  proration_behavior: 'create_prorations', // Charge/credit the difference immediately
});
// Stripe creates a prorated invoice automatically

// Cancel at period end — customer retains access until the next billing date
await stripe.subscriptions.update(stripeSubscriptionId, {
  cancel_at_period_end: true,
});

// Immediate cancellation
await stripe.subscriptions.cancel(stripeSubscriptionId);