import { NextRequest, NextResponse } from 'next/server';
import { auth } from '@/auth';
import { stripe } from '@/lib/stripe';
import { resolvePriceId } from '@/lib/billing/stripe-prices';
import { prisma } from '@/lib/prisma';
import { z } from 'zod';

const bodySchema = z.object({
  tier: z.enum(['PRO', 'BUSINESS']),
  interval: z.enum(['month', 'year']),
});

export async function POST(req: NextRequest) {
  const session = await auth();
  if (!session?.user?.id || !session.user.email) {
    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
  }

  const parsed = bodySchema.safeParse(await req.json());
  if (!parsed.success) {
    return NextResponse.json({ error: 'Invalid request body' }, { status: 400 });
  }

  const { tier, interval } = parsed.data;
  const userId = session.user.id;
  const userEmail = session.user.email;

  try {
    const priceId = resolvePriceId(tier, interval);

    const subscription = await prisma.subscription.findUnique({ where: { userId } });
    let customerId = subscription?.stripeCustomerId ?? undefined;

    if (customerId && customerId.startsWith('cus_mock')) {
      customerId = undefined;
    }

    if (!customerId) {
      const customer = await stripe.customers.create({
        email: userEmail,
        metadata: { userId },
      });
      customerId = customer.id;
      
      // Update DB to save the real Stripe customer ID
      await prisma.subscription.upsert({
        where: { userId },
        update: { stripeCustomerId: customerId },
        create: {
          userId,
          stripeCustomerId: customerId,
          tier: 'BASIC',
          status: 'ACTIVE',
          currentPeriodStart: new Date(),
          currentPeriodEnd: new Date(Date.now() + 30 * 24 * 3600 * 1000), // temp basic dates
        }
      });
    }

    const host = req.headers.get('x-forwarded-host') ?? req.headers.get('host') ?? 'localhost:3000';
    const proto = req.headers.get('x-forwarded-proto') ?? 'http';
    const origin = `${proto}://${host}`;

    const sessionParams = {
      customer: customerId,
      mode: 'subscription' as const,
      line_items: [{ price: priceId, quantity: 1 }],
      ui_mode: 'embedded_page',
      return_url: `${origin}/settings/billing?session_id={CHECKOUT_SESSION_ID}`,
      metadata: { userId, tier },
      subscription_data: { metadata: { userId, tier } },
      customer_update: { address: 'auto' },
    };
    const checkoutSession = await stripe.checkout.sessions.create(sessionParams as any);

    if (checkoutSession.client_secret) {
      return NextResponse.json({
        clientSecret: checkoutSession.client_secret,
        sessionId: checkoutSession.id,
      });
    }

    return NextResponse.json({ url: checkoutSession.url });
  } catch (error) {
    console.error('[billing/create-checkout]', error);
    return NextResponse.json({ error: 'Failed to create checkout session' }, { status: 500 });
  }
}