import { NextRequest, NextResponse } from 'next/server';
import { auth } from '@/auth';
import { stripe } from '@/lib/stripe';
import { isBillingEnabled, 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']),
  /** Prefer hosted redirect when embedded checkout is unavailable */
  mode: z.enum(['hosted', 'embedded']).optional(),
});

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

  if (!(await isBillingEnabled())) {
    return NextResponse.json({ error: 'Billing is not enabled' }, { status: 403 });
  }

  const secret = process.env.STRIPE_SECRET_KEY;
  if (!secret || secret === 'sk_test_placeholder') {
    return NextResponse.json(
      { error: 'Stripe is not configured (STRIPE_SECRET_KEY missing)' },
      { status: 503 },
    );
  }

  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 preferredMode = parsed.data.mode ?? 'hosted';
  const userId = session.user.id;
  const userEmail = session.user.email;

  try {
    let priceId: string;
    try {
      priceId = await resolvePriceId(tier, interval);
    } catch (e) {
      console.error('[billing/create-checkout] price resolve failed:', e);
      return NextResponse.json(
        { error: 'Stripe price IDs not configured. Set them in Admin > Billing.' },
        { status: 503 },
      );
    }

    if (priceId.startsWith('price_mock_')) {
      return NextResponse.json(
        { error: 'Stripe price IDs not configured. Set them in Admin > Billing.' },
        { status: 503 },
      );
    }

    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;

      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),
        },
      });
    }

    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}`;

    // Hosted Checkout is the most reliable path (redirect). Embedded is optional.
    if (preferredMode === 'embedded') {
      try {
        const embedded = await stripe.checkout.sessions.create({
          customer: customerId,
          mode: 'subscription',
          line_items: [{ price: priceId, quantity: 1 }],
          ui_mode: 'embedded' as any,
          return_url: `${origin}/settings/billing?session_id={CHECKOUT_SESSION_ID}`,
          metadata: { userId, tier },
          subscription_data: { metadata: { userId, tier } },
          customer_update: { address: 'auto' },
          allow_promotion_codes: true,
        } as any);
        if (embedded.client_secret) {
          return NextResponse.json({
            clientSecret: embedded.client_secret,
            sessionId: embedded.id,
          });
        }
      } catch (embeddedErr) {
        console.warn('[billing/create-checkout] embedded failed, falling back to hosted:', embeddedErr);
      }
    }

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

    if (!checkoutSession.url) {
      return NextResponse.json({ error: 'Checkout session has no URL' }, { status: 500 });
    }

    return NextResponse.json({ url: checkoutSession.url, sessionId: checkoutSession.id });
  } catch (error) {
    console.error('[billing/create-checkout]', error);
    const msg = error instanceof Error ? error.message : 'Failed to create checkout session';
    return NextResponse.json({ error: msg }, { status: 500 });
  }
}