import { headers } from 'next/headers';
import { NextRequest, NextResponse } from 'next/server';
import { stripe } from '@/lib/stripe';
import {
  syncSubscriptionFromStripe,
  handleSubscriptionDeleted,
  resolveUserIdFromStripeEvent,
} from '@/lib/billing/sync-subscription-from-stripe';
import { addPurchasedCredits } from '@/lib/credits';
import {
  getCreditPack,
  isCreditPackId,
  resolvePackFromPriceId,
} from '@/lib/billing/credit-packs';
import type Stripe from 'stripe';

export const runtime = 'nodejs';

async function fulfillCreditPackPurchase(session: Stripe.Checkout.Session) {
  if (session.mode !== 'payment') return;
  if (session.payment_status && session.payment_status !== 'paid' && session.payment_status !== 'no_payment_required') {
    console.warn('[billing/webhook] pack checkout not paid yet', session.id, session.payment_status);
    return;
  }

  const userId = session.metadata?.userId as string | undefined;
  if (!userId) {
    console.warn('[billing/webhook] credit pack: no userId', session.id);
    return;
  }

  let packId = session.metadata?.packId as string | undefined;
  let credits = Number(session.metadata?.credits ?? 0);

  if ((!packId || !Number.isFinite(credits) || credits <= 0) && session.line_items == null) {
    try {
      const full = await stripe.checkout.sessions.retrieve(session.id, {
        expand: ['line_items.data.price'],
      });
      const priceId = full.line_items?.data?.[0]?.price?.id;
      if (priceId) {
        const resolved = await resolvePackFromPriceId(priceId);
        if (resolved) {
          packId = resolved.packId;
          credits = resolved.credits;
        }
      }
    } catch (err) {
      console.error('[billing/webhook] expand line_items failed', err);
    }
  }

  if (packId && isCreditPackId(packId) && (!Number.isFinite(credits) || credits <= 0)) {
    credits = getCreditPack(packId).credits;
  }

  if (!Number.isFinite(credits) || credits <= 0) {
    console.warn('[billing/webhook] credit pack: invalid credits', session.id, { packId, credits });
    return;
  }

  const result = await addPurchasedCredits(userId, credits, {
    stripeSessionId: session.id,
    packId: packId ?? null,
    type: 'credit_pack',
    paymentIntent:
      typeof session.payment_intent === 'string'
        ? session.payment_intent
        : session.payment_intent?.id ?? null,
  });

  if (result.applied) {
    console.info('[billing/webhook] credited pack', {
      userId,
      credits: result.units,
      packId,
      sessionId: session.id,
    });
  }
}

export async function POST(req: NextRequest) {
  const body = await req.text();
  const headersList = await headers();
  const sig = headersList.get('stripe-signature');

  if (!sig) {
    return NextResponse.json({ error: 'Missing stripe-signature header' }, { status: 400 });
  }

  if (!process.env.STRIPE_WEBHOOK_SECRET) {
    console.error('[billing/webhook] STRIPE_WEBHOOK_SECRET not configured');
    return NextResponse.json({ error: 'Webhook not configured' }, { status: 500 });
  }

  let event: Stripe.Event;
  try {
    event = stripe.webhooks.constructEvent(body, sig, process.env.STRIPE_WEBHOOK_SECRET);
  } catch (err) {
    console.error('[billing/webhook] Signature verification failed:', err);
    return NextResponse.json({ error: 'Invalid signature' }, { status: 400 });
  }

  try {
    switch (event.type) {
      case 'checkout.session.completed': {
        const session = event.data.object as Stripe.Checkout.Session;
        if (session.mode === 'subscription' && session.subscription) {
          const subscriptionId = typeof session.subscription === 'string'
            ? session.subscription
            : session.subscription.id;
          const subscription = await stripe.subscriptions.retrieve(subscriptionId);
          const userId = (session.metadata?.userId as string | undefined)
            ?? (subscription.metadata?.userId as string | undefined);
          if (userId) {
            await syncSubscriptionFromStripe(subscription, userId);
          } else {
            console.warn('[billing/webhook] checkout.session.completed: no userId in metadata', session.id);
          }
        } else if (
          session.mode === 'payment' &&
          (session.metadata?.type === 'credit_pack' || session.metadata?.packId)
        ) {
          await fulfillCreditPackPurchase(session);
        }
        break;
      }

      case 'customer.subscription.created':
      case 'customer.subscription.updated': {
        const subscription = event.data.object as Stripe.Subscription;
        const userId = await resolveUserIdFromStripeEvent(subscription);
        if (userId) {
          await syncSubscriptionFromStripe(subscription, userId);
        } else {
          console.warn('[billing/webhook] subscription event: no userId found', subscription.id);
        }
        break;
      }

      case 'customer.subscription.deleted': {
        const subscription = event.data.object as Stripe.Subscription;
        await handleSubscriptionDeleted(subscription);
        break;
      }

      case 'invoice.payment_failed': {
        const invoice = event.data.object as Stripe.Invoice & { subscription?: string | { id: string } };
        if (invoice.subscription) {
          const subscriptionId = typeof invoice.subscription === 'string'
            ? invoice.subscription
            : invoice.subscription.id;
          const subscription = await stripe.subscriptions.retrieve(subscriptionId);
          const userId = await resolveUserIdFromStripeEvent(subscription);
          if (userId) {
            await syncSubscriptionFromStripe(subscription, userId);
          }
        }
        break;
      }

      default:
        break;
    }

    return NextResponse.json({ received: true });
  } catch (error) {
    console.error('[billing/webhook] Handler error:', error);
    return NextResponse.json({ error: 'Webhook handler failed' }, { status: 500 });
  }
}