/**
 * Server-side Stripe client + helpers for Phase 4 (card payments).
 *
 * Architecture (see Phase 4 notes):
 *   1. Customer clicks "Pay with card" on /billing/<number>.
 *   2. Server creates Stripe Checkout Session (mode='payment') with
 *      the invoice total as a single line item. We pass `customer`
 *      to reuse an existing Stripe Customer if the org already has
 *      one, otherwise we create one and persist its id in
 *      org_billing_config.stripe_customer_id.
 *   3. Returns session.url; the browser redirects there.
 *   4. Customer pays; Stripe redirects to success_url with the
 *      session id appended.
 *   5. /api/stripe/webhook receives `checkout.session.completed`,
 *      verifies signature, looks up the invoice id from metadata,
 *      flips the invoice to 'paid'.
 *
 * Env vars:
 *   STRIPE_SECRET_KEY          (required) - sk_test_... in sandbox, sk_live_... in prod
 *   STRIPE_WEBHOOK_SECRET      (required for webhook) - whsec_...
 *   APP_BASE_URL               (required) - e.g. https://app.pieced.ch
 *
 * SDK: stripe@22.x (Node SDK v22), pinned API version 2026-03-25.dahlia.
 * Pinning the API version means a `npm update` of the SDK won't
 * silently change request/response shapes; we explicitly bump when
 * we want a new API version.
 */

import Stripe from "stripe";
import type { Invoice } from "@/types";

// Pinned API version. `as const` narrows this to a string-literal
// type that the Stripe constructor's `apiVersion` field accepts
// exactly. When the installed SDK bumps to a new pinned version,
// TypeScript will surface the mismatch at the `new Stripe(...)` call
// below — bump this string deliberately alongside the SDK upgrade
// and review the API changelog before doing so.
const STRIPE_API_VERSION = "2026-04-22.dahlia" as const;

// Cache the client across hot reloads / serverless invocations.
// We don't instantiate at module load because some build steps run
// without runtime env vars set — only fail when actually used.
let cachedClient: Stripe | null = null;

export function getStripeClient(): Stripe {
  if (cachedClient) return cachedClient;
  const key = process.env.STRIPE_SECRET_KEY;
  if (!key) {
    throw new Error(
      "STRIPE_SECRET_KEY is not set. Configure it in your environment."
    );
  }
  cachedClient = new Stripe(key, {
    apiVersion: STRIPE_API_VERSION,
    // Identify ourselves in Stripe's request logs so support can
    // distinguish PieCed traffic from other integrations on the
    // same account.
    appInfo: {
      name: "PieCed Portal",
      version: "1.0.0",
      url: "https://app.pieced.ch",
    },
  });
  return cachedClient;
}

/**
 * Return the configured webhook secret. Separated so the webhook
 * handler can fail fast with a clear error message rather than the
 * generic "STRIPE_SECRET_KEY missing" path above.
 */
export function getWebhookSecret(): string {
  const secret = process.env.STRIPE_WEBHOOK_SECRET;
  if (!secret) {
    throw new Error(
      "STRIPE_WEBHOOK_SECRET is not set. Get it from the webhook endpoint in your Stripe dashboard."
    );
  }
  return secret;
}

/**
 * Convert a CHF decimal amount (e.g. 123.45) to integer rappen
 * (e.g. 12345). Stripe API requires integer amounts in the
 * currency's smallest unit. Centralised so we don't have rounding
 * drift between callers.
 */
export function chfToRappen(amountChf: number): number {
  // toFixed(2) avoids floating-point ugliness (0.1 + 0.2 = 0.30000000000000004).
  return Math.round(parseFloat(amountChf.toFixed(2)) * 100);
}

/**
 * Look up or create the Stripe Customer for a PieCed org.
 *
 * Lazy creation: orgs that only pay by invoice never get a Stripe
 * Customer. The first "Pay with card" click triggers creation; the
 * id is persisted in org_billing_config so subsequent invoices
 * reuse it.
 *
 * Returns the Stripe customer id (`cus_...`).
 */
export async function ensureStripeCustomerForOrg(params: {
  zitadelOrgId: string;
  // Snapshot taken at click-time, NOT at invoice issuance — the
  // org's current address goes on the Stripe customer object.
  // Stripe's address on file is independent of any one invoice.
  companyName: string;
  billingEmail: string;
  address: {
    line1: string;
    postalCode: string;
    city: string;
    country: string; // ISO 3166-1 alpha-2 (e.g. "CH")
  };
}): Promise<string> {
  // Lazy import to avoid pulling pg into edge-runtime modules that
  // might import this file. Same pattern used elsewhere in lib/.
  const { getOrgBillingConfig, updateOrgBillingConfig } = await import("./db");
  const existing = await getOrgBillingConfig(params.zitadelOrgId);
  if (existing.stripeCustomerId) {
    return existing.stripeCustomerId;
  }
  const stripe = getStripeClient();
  const customer = await stripe.customers.create({
    email: params.billingEmail,
    name: params.companyName,
    address: {
      line1: params.address.line1,
      postal_code: params.address.postalCode,
      city: params.address.city,
      country: params.address.country,
    },
    metadata: {
      zitadel_org_id: params.zitadelOrgId,
    },
  });
  await updateOrgBillingConfig(params.zitadelOrgId, {
    stripeCustomerId: customer.id,
  });
  return customer.id;
}

/**
 * Create a Checkout Session for paying a single invoice by card.
 *
 * Design notes:
 *
 * - Single line item with the invoice total (gross, VAT included).
 *   Our own invoice PDF already breaks down lines + VAT; the Stripe
 *   page is the checkout, not a duplicate of the invoice.
 *
 * - `automatic_tax` is disabled because the invoice already has
 *   VAT computed by our pipeline. Letting Stripe re-calculate
 *   would double-charge or contradict our PDF.
 *
 * - `payment_method_types` is NOT set, so Stripe surfaces dynamic
 *   payment methods configured on the account (cards, TWINT for
 *   Swiss customers, Apple Pay, Google Pay, etc.) automatically.
 *
 * - `metadata` and `payment_intent_data.metadata` BOTH carry the
 *   invoice id. The session-level copy is enough for the
 *   `checkout.session.completed` webhook; the intent-level copy
 *   lets us correlate refunds and disputes which fire on the
 *   PaymentIntent and don't include session metadata.
 *
 * - `client_reference_id` is set to our invoice id as a stable
 *   reference. Visible in the Stripe dashboard, useful for support.
 *
 * - `locale` follows the invoice's locale so the customer sees
 *   the Stripe page in their language (frozen at invoice issue
 *   time; consistent with PDF + email).
 */
export async function createCheckoutSessionForInvoice(params: {
  invoice: Invoice;
  customerId: string;
  baseUrl: string;
}): Promise<{ url: string; sessionId: string }> {
  const stripe = getStripeClient();
  const { invoice, customerId, baseUrl } = params;

  // Stripe Checkout supports a limited set of locales; map our
  // four to Stripe's codes and fall back to 'auto' if anything
  // outside the set ever appears.
  //
  // We deliberately don't annotate this with
  // `Stripe.Checkout.SessionCreateParams.Locale` — stripe-node v22
  // ships with a known type-export regression
  // (stripe/stripe-node#2662) where params types under namespaced
  // resources aren't re-exported from the resource barrel. The
  // `as const` literal narrowing gives the variable the union type
  // `"de" | "fr" | "it" | "en" | "auto"`, which `sessions.create`
  // accepts at the call site via its own inline parameter typing.
  // When the SDK fixes the re-export, we can put the annotation
  // back without touching the call site.
  const stripeLocale =
    invoice.locale === "de"
      ? ("de" as const)
      : invoice.locale === "fr"
      ? ("fr" as const)
      : invoice.locale === "it"
      ? ("it" as const)
      : invoice.locale === "en"
      ? ("en" as const)
      : ("auto" as const);

  const successUrl = `${baseUrl}/billing/${encodeURIComponent(invoice.invoiceNumber)}?paid=1&session_id={CHECKOUT_SESSION_ID}`;
  const cancelUrl = `${baseUrl}/billing/${encodeURIComponent(invoice.invoiceNumber)}?cancelled=1`;

  const session = await stripe.checkout.sessions.create({
    mode: "payment",
    customer: customerId,
    client_reference_id: invoice.id,
    locale: stripeLocale,
    line_items: [
      {
        quantity: 1,
        price_data: {
          currency: "chf",
          unit_amount: chfToRappen(invoice.totalChf),
          product_data: {
            name: `Invoice ${invoice.invoiceNumber}`,
            description: `PieCed IT — ${invoice.periodStart.slice(0, 10)} → ${invoice.periodEnd.slice(0, 10)}`,
          },
        },
      },
    ],
    metadata: {
      invoice_id: invoice.id,
      invoice_number: invoice.invoiceNumber,
      zitadel_org_id: invoice.zitadelOrgId,
    },
    payment_intent_data: {
      // Mirror invoice id at the PaymentIntent level so refunds &
      // disputes (which fire on the PI, not the session) can be
      // correlated to our invoice without an extra lookup.
      metadata: {
        invoice_id: invoice.id,
        invoice_number: invoice.invoiceNumber,
        zitadel_org_id: invoice.zitadelOrgId,
      },
      // Statement descriptor shown on the customer's card
      // statement. Limited to 22 chars total; we use the prefix
      // since Stripe will prepend the merchant name from the
      // account anyway. Keep it short and recognisable.
      description: `Invoice ${invoice.invoiceNumber}`,
    },
    success_url: successUrl,
    cancel_url: cancelUrl,
    // VAT is already in invoice.totalChf — don't let Stripe touch tax.
    automatic_tax: { enabled: false },
  });

  if (!session.url) {
    throw new Error(
      `Stripe returned a session without a redirect URL (id=${session.id})`
    );
  }
  return { url: session.url, sessionId: session.id };
}

// ---------------------------------------------------------------------------
// Phase 7 — refunds
// ---------------------------------------------------------------------------

/**
 * Create a Stripe Refund against an invoice's PaymentIntent.
 *
 * The amount is in CHF; we convert to rappen for Stripe's smallest-
 * currency-unit API. Pass 0 or undefined for `amountChf` to refund
 * the full charge.
 *
 * Returns the Stripe refund object so the caller can record the
 * refund id and final status. Stripe processes refunds asynchronously
 * for some payment methods, so the initial status may be 'pending'
 * — the charge.refunded webhook delivers the eventual succeeded /
 * failed transition.
 *
 * Throws on Stripe API errors (no charge, insufficient balance,
 * etc.). The caller surfaces these to the admin via the API
 * response — we don't swallow them because partial-refund logic
 * shouldn't be guessing about server state.
 */
export async function createInvoiceRefund(params: {
  paymentIntentId: string;
  amountChf?: number;
  reason?: "duplicate" | "fraudulent" | "requested_by_customer";
  metadata?: Record<string, string>;
}): Promise<{
  id: string;
  amountChf: number;
  status: string;
}> {
  const stripe = getStripeClient();
  const refundParams: Parameters<typeof stripe.refunds.create>[0] = {
    payment_intent: params.paymentIntentId,
    metadata: params.metadata,
  };
  if (params.amountChf && params.amountChf > 0) {
    refundParams.amount = chfToRappen(params.amountChf);
  }
  if (params.reason) {
    refundParams.reason = params.reason;
  }
  const refund = await stripe.refunds.create(refundParams);
  // The amount on the response is in rappen; convert back. If no
  // amount was passed, Stripe defaults to the full remaining
  // charge, which is what we read back.
  return {
    id: refund.id,
    amountChf: refund.amount != null ? refund.amount / 100 : 0,
    status: refund.status ?? "unknown",
  };
}