import type { FastifyInstance } from 'fastify';
import type Stripe from 'stripe';
import { and, eq } from 'drizzle-orm';
import { getDb, firms, users, stripeEvents } from '@lawdesk/db';
import { env } from '../env';
import { getStripe } from '../lib/stripe';
import {
  sendEmail,
  planUpgradedEmail,
  paymentFailedEmail,
  subscriptionEndedEmail,
} from '../lib/email';
import { logAudit } from '../lib/audit';

// Registered as a sub-app so its own buffer-only content-type parser doesn't affect the rest of
// the API. Stripe webhooks need the raw request body to verify the signature.
export async function stripeWebhookRoute(app: FastifyInstance) {
  app.removeContentTypeParser(['application/json']);
  app.addContentTypeParser('*', { parseAs: 'buffer' }, (_req, body, done) => done(null, body));

  app.post('/api/webhooks/stripe', async (req, reply) => {
    if (!env.STRIPE_WEBHOOK_SECRET) {
      return reply.code(503).send({ error: 'webhook_not_configured' });
    }

    const sig = req.headers['stripe-signature'];
    if (!sig || typeof sig !== 'string') {
      return reply.code(400).send({ error: 'missing_signature' });
    }

    const stripe = getStripe();
    let event: Stripe.Event;
    try {
      event = stripe.webhooks.constructEvent(req.body as Buffer, sig, env.STRIPE_WEBHOOK_SECRET);
    } catch (err) {
      app.log.warn({ err }, 'stripe webhook signature verification failed');
      return reply.code(400).send({ error: 'invalid_signature' });
    }

    try {
      // Idempotency for Stripe's at-least-once delivery. Skip events we've already fully
      // processed so retries don't re-send emails or re-write audit rows.
      const [seen] = await getDb()
        .select({ id: stripeEvents.id })
        .from(stripeEvents)
        .where(eq(stripeEvents.id, event.id))
        .limit(1);
      if (seen) {
        app.log.info({ id: event.id, type: event.type }, 'stripe webhook duplicate event ignored');
        return { received: true, duplicate: true };
      }

      await handleEvent(event, app);

      // Record only AFTER successful processing: a transient handler failure (→ 500 → Stripe
      // retry) then re-processes instead of being skipped forever. applyPlan is idempotent, so
      // the narrow check-then-insert race on truly concurrent redeliveries is harmless.
      await getDb()
        .insert(stripeEvents)
        .values({ id: event.id, type: event.type })
        .onConflictDoNothing();
    } catch (err) {
      app.log.error({ err, type: event.type }, 'stripe webhook handler failed');
      // Return 200 anyway for some failures? No — let Stripe retry on transient failures.
      return reply.code(500).send({ error: 'handler_failed' });
    }

    return { received: true };
  });
}

async function handleEvent(event: Stripe.Event, app: FastifyInstance) {
  switch (event.type) {
    case 'checkout.session.completed': {
      const session = event.data.object as Stripe.Checkout.Session;
      const firmId = session.client_reference_id ?? (session.metadata?.firmId as string | undefined);
      const planFromMeta = (session.metadata?.plan ?? '') as 'pro' | 'lifetime' | '';
      if (!firmId) return app.log.warn({ session: session.id }, 'checkout.session.completed without firmId');

      // Determine plan from session.mode if metadata didn't pin it.
      const plan: 'pro' | 'lifetime' = planFromMeta || (session.mode === 'subscription' ? 'pro' : 'lifetime');

      const customerId = typeof session.customer === 'string' ? session.customer : session.customer?.id ?? null;
      const subscriptionId =
        typeof session.subscription === 'string' ? session.subscription : session.subscription?.id ?? null;

      await applyPlan(firmId, plan, { customerId, subscriptionId });
      // Fire-and-forget: an email failure must not throw out of the handler (→ 500 → Stripe
      // redelivery → duplicate processing). The plan (DB writes above) is already applied.
      sendPlanUpgradedNotice(firmId, plan).catch((err) =>
        app.log.warn({ err, firmId }, 'plan upgraded email failed'),
      );
      break;
    }

    case 'customer.subscription.updated':
    case 'customer.subscription.created': {
      const sub = event.data.object as Stripe.Subscription;
      const firmId = (sub.metadata?.firmId as string | undefined) ?? null;
      if (!firmId) return;
      // Only flip to 'pro' while the subscription is paying.
      const active = ['active', 'trialing', 'past_due'].includes(sub.status);
      if (active) await applyPlan(firmId, 'pro', { subscriptionId: sub.id });
      break;
    }

    case 'customer.subscription.deleted': {
      const sub = event.data.object as Stripe.Subscription;
      const firmId = (sub.metadata?.firmId as string | undefined) ?? null;
      if (!firmId) return;
      await applyPlan(firmId, 'starter', { subscriptionId: null });
      for (const u of await firmOwners(firmId)) {
        const tpl = subscriptionEndedEmail(u.fullName);
        sendEmail({ to: u.email, ...tpl }).catch((err) =>
          app.log.warn({ err, firmId }, 'subscription ended email failed'),
        );
      }
      break;
    }

    case 'invoice.payment_failed': {
      const invoice = event.data.object as Stripe.Invoice;
      app.log.warn({ invoice: invoice.id, customer: invoice.customer }, 'stripe invoice payment failed');

      const customerId = typeof invoice.customer === 'string' ? invoice.customer : invoice.customer?.id;
      if (!customerId) break;
      const [firm] = await getDb()
        .select({ id: firms.id })
        .from(firms)
        .where(eq(firms.stripeCustomerId, customerId))
        .limit(1);
      if (!firm) break;

      const amount = invoice.amount_due
        ? new Intl.NumberFormat('en-US', {
            style: 'currency',
            currency: (invoice.currency ?? 'usd').toUpperCase(),
          }).format(invoice.amount_due / 100)
        : null;
      for (const u of await firmOwners(firm.id)) {
        const tpl = paymentFailedEmail(u.fullName, amount);
        sendEmail({ to: u.email, ...tpl }).catch((err) =>
          app.log.warn({ err, firmId: firm.id }, 'payment failed email failed'),
        );
      }
      break;
    }

    default:
      // Ignore — Stripe sends many event types we don't care about.
      break;
  }
}

async function applyPlan(
  firmId: string,
  plan: 'starter' | 'pro' | 'lifetime',
  ids: { customerId?: string | null; subscriptionId?: string | null } = {},
) {
  const patch: Record<string, unknown> = {
    plan,
    watermarkEnabled: plan === 'starter',
    updatedAt: new Date(),
  };
  if (ids.customerId !== undefined) patch.stripeCustomerId = ids.customerId;
  if (ids.subscriptionId !== undefined) patch.stripeSubscriptionId = ids.subscriptionId;

  await getDb().update(firms).set(patch).where(eq(firms.id, firmId));
  await logAudit({
    firmId,
    action: `billing.plan.${plan}`,
    meta: { stripeCustomerId: ids.customerId, stripeSubscriptionId: ids.subscriptionId },
  });
}

// Billing emails go to owners only — staff shouldn't get payment notices.
async function firmOwners(firmId: string) {
  return getDb()
    .select({ email: users.email, fullName: users.fullName })
    .from(users)
    .where(and(eq(users.firmId, firmId), eq(users.role, 'owner')));
}

async function sendPlanUpgradedNotice(firmId: string, plan: 'pro' | 'lifetime') {
  const label = plan === 'pro' ? 'Professional' : 'Lifetime';
  for (const u of await firmOwners(firmId)) {
    const tpl = planUpgradedEmail(u.fullName, label);
    await sendEmail({ to: u.email, ...tpl });
  }
}