Your Stripe checkout works.
Your billing probably doesn't. Not yet.

/**
 * Accept-fast Stripe webhook. Workers drain the ledger after the response.
 */
import { after, NextResponse } from 'next/server';
import { billingPolicy } from '@/lib/stripe/config';
import { acceptWebhook } from '@/lib/stripe/webhook-handler';
import { drainPendingEvents } from '@/lib/stripe/webhook-worker';

// Runs on the Node.js runtime (the default): raw body, Node crypto and the postgres driver.
// Don't add `export const runtime`: Next 16 rejects route segment config under
// `cacheComponents` (next.config.ts), and the Edge runtime can't run this route.

/**
 * Chunked bodies carry no Content-Length: stop reading once the cap is passed, so memory
 * stays bounded at the cap plus one chunk. Returns null when the body is too large.
 */
async function readBodyWithCap(req: Request, maxBytes: number): Promise<string | null> {
  if (!req.body) {
    return '';
  }
  const reader = req.body.getReader();
  const chunks: Uint8Array[] = [];
  let received = 0;
  for (;;) {
    const { done, value } = await reader.read();
    if (done) break;
    received += value.byteLength;
    if (received > maxBytes) {
      await reader.cancel();
      return null;
    }
    chunks.push(value);
  }
  return Buffer.concat(chunks).toString('utf8');
}

export async function POST(req: Request) {
  const contentLengthHeader = req.headers.get('content-length');
  if (
    contentLengthHeader &&
    Number(contentLengthHeader) > billingPolicy.maxWebhookBodyBytes
  ) {
    return NextResponse.json({ error: 'payload_too_large' }, { status: 413 });
  }

  const body = await readBodyWithCap(req, billingPolicy.maxWebhookBodyBytes);
  if (body === null) {
    return NextResponse.json({ error: 'payload_too_large' }, { status: 413 });
  }
  const signature = req.headers.get('stripe-signature');
  const accepted = await acceptWebhook(body, signature, billingPolicy.maxWebhookBodyBytes);

  if (accepted.status === 200 && accepted.body.queued === true && process.env.VITEST !== 'true') {
    after(() => {
      void drainPendingEvents(billingPolicy.drainBatchSize);
    });
  }

  return NextResponse.json(accepted.body, { status: accepted.status });
}