1. Auth (API keys, secrets)
2. Create Products/Prices
3. Implement Checkout
4. Handle Webhooks
5. Manage Subscriptions
6. Monitor & Reconcile

// Server: Create checkout session
import Stripe from 'stripe'
const stripe = new Stripe(process.env.STRIPE_SECRET_KEY!)

const session = await stripe.checkout.sessions.create({
  line_items: [{
    price: 'price_xxx',
    quantity: 1
  }],
  mode: 'subscription',
  success_url: 'https://myapp.com/success?session_id={CHECKOUT_SESSION_ID}',
  cancel_url: 'https://myapp.com/cancel'
})

// Redirect to session.url

// Webhook handler
import { buffer } from 'micro'

export async function POST(req: Request) {
  const body = await req.text()
  const sig = req.headers.get('stripe-signature')!
  
  const event = stripe.webhooks.constructEvent(body, sig, process.env.STRIPE_WEBHOOK_SECRET!)
  
  switch (event.type) {
    case 'checkout.session.completed':
      await handleCheckoutComplete(event.data.object)
      break
    case 'invoice.payment_succeeded':
      await handlePaymentSuccess(event.data.object)
      break
    case 'customer.subscription.deleted':
      await handleSubscriptionCancelled(event.data.object)
      break
  }
  
  return new Response('ok')
}