import { NextResponse } from "next/server";
import type Stripe from "stripe";
import { getStripeClient, getWebhookSecret } from "@/lib/stripe";
import {
  markInvoicePaid,
  markStripeEventProcessed,
  setInvoiceStripePaymentIntent,
  tryRecordStripeEvent,
} from "@/lib/db";

/**
 * POST /api/stripe/webhook
 *
 * Receives signed events from Stripe. The lifecycle:
 *
 *   1. Read RAW body (request.text(), NOT request.json() — Stripe's
 *      HMAC is computed over the raw bytes and any JSON re-parse
 *      will subtly mangle whitespace or property ordering and the
 *      signature will fail).
 *   2. Verify signature against the configured webhook secret. If
 *      verification fails → 400. An attacker forging webhook calls
 *      could otherwise mark our invoices paid.
 *   3. Idempotency: INSERT the event id into stripe_events. If the
 *      INSERT conflicts (duplicate delivery, which is normal — Stripe
 *      retries failed deliveries for up to 72h), return 200 immediately
 *      so Stripe doesn't keep retrying.
 *   4. Process the event based on type. Currently we care about:
 *        - checkout.session.completed   → flip invoice to paid
 *        - charge.refunded              → log; void/credit handling is Phase 7
 *        - payment_intent.payment_failed → log only; the failure is
 *                                          already shown to the user on
 *                                          the Stripe page, no action.
 *      Unknown event types are ack'd with 200 (we may have other
 *      events enabled at the Stripe end that we don't yet care about,
 *      and 200 + log is cheaper than 404 + Stripe retries).
 *   5. Stamp processed_at on success.
 *
 * Return contract: 2xx ack → Stripe stops retrying. Any non-2xx →
 * Stripe retries with exponential backoff up to 72h. We aim for
 * 200 on every reachable path (verified, deduplicated, or processed),
 * and only 400 for signature failures (those would never succeed
 * on retry anyway, so retrying is wasted effort).
 *
 * Performance: handlers run synchronously here because PieCed's
 * event volume is tiny. If/when that changes, the obvious refactor
 * is to enqueue (Phase 7) and ack first — but at v1 the inline
 * model is simpler to reason about and harder to lose events with.
 */

// Next.js: explicitly disable static optimization; this route MUST
// run on every request and must not be cached.
export const dynamic = "force-dynamic";

export async function POST(request: Request) {
  // 1. Raw body — Stripe verifies the signature over these exact bytes.
  const rawBody = await request.text();
  const signature = request.headers.get("stripe-signature");
  if (!signature) {
    return new NextResponse("Missing stripe-signature header", {
      status: 400,
    });
  }

  // 2. Verify signature.
  let event: Stripe.Event;
  try {
    const stripe = getStripeClient();
    const secret = getWebhookSecret();
    event = stripe.webhooks.constructEvent(rawBody, signature, secret);
  } catch (err) {
    console.error("Stripe webhook signature verification failed:", err);
    // 400 — never retry. The webhook configuration is wrong on
    // either end (rotated secret, wrong endpoint, etc.); retries
    // won't fix it.
    return new NextResponse("Invalid signature", { status: 400 });
  }

  // 3. Idempotency. INSERT event.id → fail-fast on duplicate.
  let firstDelivery: boolean;
  try {
    firstDelivery = await tryRecordStripeEvent(
      event.id,
      event.type,
      event
    );
  } catch (err) {
    console.error(
      `Failed to record stripe event ${event.id} (${event.type}):`,
      err
    );
    // 5xx so Stripe retries — this is a DB hiccup, not a logic error.
    return new NextResponse("DB error", { status: 500 });
  }
  if (!firstDelivery) {
    // Already processed; ack happily.
    return new NextResponse("Duplicate delivery; acknowledged.", {
      status: 200,
    });
  }

  // 4. Process. Each handler is responsible for being safe to run
  //    exactly once (we already deduplicated by event.id above).
  try {
    switch (event.type) {
      case "checkout.session.completed":
        await handleCheckoutCompleted(
          event.data.object as Stripe.Checkout.Session
        );
        break;
      case "charge.refunded":
        await handleChargeRefunded(event.data.object as Stripe.Charge);
        break;
      case "payment_intent.payment_failed":
        await handlePaymentFailed(
          event.data.object as Stripe.PaymentIntent
        );
        break;
      default:
        // Unknown event — log so we notice if Stripe starts sending
        // something we should handle, but ack so we don't accumulate
        // retries forever.
        console.log(
          `Stripe webhook: ignoring event type ${event.type} (id ${event.id})`
        );
    }
  } catch (err) {
    console.error(
      `Stripe webhook handler failed for ${event.type} (id ${event.id}):`,
      err
    );
    // 5xx → Stripe retries. The handler is idempotent because the
    // stripe_events row already exists, so on the next attempt we'd
    // short-circuit at step 3. To actually retry the work we'd need
    // to DELETE the stripe_events row first; for v1 we don't bother
    // and let a human investigate the logs.
    return new NextResponse("Handler error", { status: 500 });
  }

  // 5. Mark processed.
  try {
    await markStripeEventProcessed(event.id);
  } catch (err) {
    // Non-fatal — the event was already processed, this is just the
    // bookkeeping flag. Log and move on.
    console.error(
      `Failed to mark stripe event ${event.id} processed:`,
      err
    );
  }

  return new NextResponse("OK", { status: 200 });
}

// ---------------------------------------------------------------------------
// Handlers
// ---------------------------------------------------------------------------

async function handleCheckoutCompleted(
  session: Stripe.Checkout.Session
): Promise<void> {
  // Defensive: paid sessions are what we want; sessions can also
  // complete in "unpaid" state (rare for mode=payment, more common
  // for async/delayed methods like SEPA). Only flip the invoice
  // when payment actually cleared.
  if (session.payment_status !== "paid") {
    console.log(
      `Checkout session ${session.id} completed but payment_status=${session.payment_status}; waiting for downstream events.`
    );
    return;
  }
  const invoiceId =
    session.metadata?.invoice_id ?? session.client_reference_id ?? null;
  if (!invoiceId) {
    console.error(
      `Checkout session ${session.id} completed without invoice_id metadata; cannot link to invoice.`
    );
    return;
  }
  const paymentIntentId =
    typeof session.payment_intent === "string"
      ? session.payment_intent
      : session.payment_intent?.id;

  // Persist the PaymentIntent id on the invoice for traceability +
  // future refund correlation.
  if (paymentIntentId) {
    await setInvoiceStripePaymentIntent(invoiceId, paymentIntentId);
  }

  // Flip status. markInvoicePaid is idempotent — re-running on an
  // already-paid invoice returns null and we log + skip.
  const updated = await markInvoicePaid(invoiceId, {
    paidBy: "stripe",
    paidMethodDetail: paymentIntentId
      ? `Stripe Checkout (${paymentIntentId})`
      : "Stripe Checkout",
    paidAt: session.created ? new Date(session.created * 1000) : undefined,
  });
  if (!updated) {
    // Already paid or void/draft — fine, nothing to do.
    console.log(
      `Invoice ${invoiceId} was not in a payable state when Stripe webhook arrived (likely already paid).`
    );
    return;
  }
  console.log(
    `Invoice ${invoiceId} marked paid via Stripe (session ${session.id}, intent ${paymentIntentId}).`
  );
}

async function handleChargeRefunded(charge: Stripe.Charge): Promise<void> {
  // v1 scope: log only. Refunds always go through Stripe → admin
  // initiates them in the dashboard. Updating our invoice status
  // to 'void' or partial-credit needs more product thinking
  // (partial refunds? credit notes? VAT corrections?). Phase 7.
  console.log(
    `Charge ${charge.id} refunded (amount ${charge.amount_refunded} ${charge.currency}); no portal-side state change.`
  );
}

async function handlePaymentFailed(
  intent: Stripe.PaymentIntent
): Promise<void> {
  // The Stripe-hosted page already shows the failure to the user.
  // We log here for support visibility and to surface in Workbench.
  // No invoice state change — it stays 'open' until paid.
  console.log(
    `PaymentIntent ${intent.id} failed: ${
      intent.last_payment_error?.message ?? "(no message)"
    }`
  );
}