import Stripe from 'stripe';
import { NextResponse } from 'next/server';
import { Timestamp } from 'firebase/firestore';
import {
  createCreditTransaction,
  createPurchase,
  getUser,
  updateUserCredits,
} from '@/lib/firestore';

const stripeSecretKey = process.env.STRIPE_SECRET_KEY;
const webhookSecret = process.env.STRIPE_WEBHOOK_SECRET;

const stripe = stripeSecretKey
  ? new Stripe(stripeSecretKey, { apiVersion: '2024-06-20' })
  : null;

export async function POST(request: Request) {
  if (!stripe || !webhookSecret) {
    return NextResponse.json({ error: 'Stripe webhook not configured.' }, { status: 500 });
  }

  const signature = request.headers.get('stripe-signature');
  if (!signature) {
    return NextResponse.json({ error: 'Missing Stripe signature.' }, { status: 400 });
  }

  const payload = await request.text();

  let event: Stripe.Event;
  try {
    event = stripe.webhooks.constructEvent(payload, signature, webhookSecret);
  } catch (error) {
    console.error('Stripe webhook signature error:', error);
    return NextResponse.json({ error: 'Invalid signature.' }, { status: 400 });
  }

  if (event.type === 'checkout.session.completed') {
    const session = event.data.object as Stripe.Checkout.Session;
    const metadata = session.metadata ?? {};
    const userId = metadata.userId;
    const credits = Number(metadata.credits);
    const amount = Number(metadata.amount);

    if (!userId || !Number.isFinite(credits) || credits <= 0) {
      return NextResponse.json({ error: 'Invalid checkout metadata.' }, { status: 400 });
    }

    const user = await getUser(userId);
    if (!user) {
      return NextResponse.json({ error: 'User not found.' }, { status: 404 });
    }

    const newBalance = user.creditBalance + credits;
    await updateUserCredits(userId, newBalance);

    await createCreditTransaction({
      userId,
      amount: credits,
      type: 'purchase',
      balanceAfter: newBalance,
      createdAt: Timestamp.now(),
    });

    await createPurchase({
      userId,
      credits,
      amount: Number.isFinite(amount) ? amount : credits,
      currency: session.currency ?? 'eur',
      stripeSessionId: session.id,
      createdAt: Timestamp.now(),
    });
  }

  return NextResponse.json({ received: true });
}