import {
  generateRegistrationOptions,
  verifyRegistrationResponse,
  generateAuthenticationOptions,
  verifyAuthenticationResponse,
} from "@simplewebauthn/server";
import type {
  RegistrationResponseJSON,
  AuthenticationResponseJSON,
  AuthenticatorTransportFuture,
} from "@simplewebauthn/types";
import { BRAND } from "@/lib/brand";

/**
 * SEC3-b: WebAuthn/Passkey-Basis. Kapselt die RP-/Origin-Konfiguration (aus AUTH_URL bzw.
 * WEBAUTHN_*-Overrides) und die vier @simplewebauthn/server-Zeremonien mit unserer
 * base64url-Kodierung. Höhere Schichten (Actions/Route) kümmern sich um Challenge-Store
 * (Cookie) und Persistenz.
 */

export const RP_NAME = BRAND.name;
/** Cookie-Name der kurzlebigen Login-Challenge (pre-session Passkey-Login). */
export const LOGIN_CHALLENGE_COOKIE = "wa_login_challenge";

function authUrl(): URL {
  return new URL(process.env.WEBAUTHN_ORIGIN || process.env.AUTH_URL || "http://localhost:3000");
}
/** Relying-Party-ID = registrierbare Domain (ohne Protokoll/Port). */
export function rpID(): string {
  return process.env.WEBAUTHN_RP_ID || authUrl().hostname;
}
/** Erwarteter Origin der Zeremonie (Protokoll + Host + Port). */
export function rpOrigin(): string {
  return authUrl().origin;
}

export function toB64Url(bytes: Uint8Array): string {
  return Buffer.from(bytes).toString("base64url");
}
export function fromB64Url(s: string): Uint8Array {
  return new Uint8Array(Buffer.from(s, "base64url"));
}

type StoredCred = { credentialId: string; transports: string[] };

/** Registrierungs-Optionen (Challenge) für einen angemeldeten Nutzer erzeugen. */
export function buildRegistrationOptions(params: {
  userId: string;
  userName: string;
  userDisplayName: string;
  existing: StoredCred[];
}) {
  return generateRegistrationOptions({
    rpName: RP_NAME,
    rpID: rpID(),
    userID: params.userId,
    userName: params.userName,
    userDisplayName: params.userDisplayName,
    attestationType: "none",
    excludeCredentials: params.existing.map((c) => ({
      id: fromB64Url(c.credentialId),
      type: "public-key",
      transports: c.transports as AuthenticatorTransportFuture[],
    })),
    authenticatorSelection: { residentKey: "preferred", userVerification: "preferred" },
  });
}

export function verifyReg(response: RegistrationResponseJSON, expectedChallenge: string) {
  return verifyRegistrationResponse({
    response,
    expectedChallenge,
    expectedOrigin: rpOrigin(),
    expectedRPID: rpID(),
    requireUserVerification: false,
  });
}

/** Authentifizierungs-Optionen (Challenge) — allowCredentials optional (Discoverable/Resident). */
export function buildAuthenticationOptions(allow: StoredCred[]) {
  return generateAuthenticationOptions({
    rpID: rpID(),
    allowCredentials: allow.map((c) => ({
      id: fromB64Url(c.credentialId),
      type: "public-key",
      transports: c.transports as AuthenticatorTransportFuture[],
    })),
    userVerification: "preferred",
  });
}

export function verifyAuth(params: {
  response: AuthenticationResponseJSON;
  expectedChallenge: string;
  credential: { credentialId: string; publicKey: string; counter: bigint };
}) {
  return verifyAuthenticationResponse({
    response: params.response,
    expectedChallenge: params.expectedChallenge,
    expectedOrigin: rpOrigin(),
    expectedRPID: rpID(),
    authenticator: {
      credentialID: fromB64Url(params.credential.credentialId),
      credentialPublicKey: fromB64Url(params.credential.publicKey),
      counter: Number(params.credential.counter),
    },
    requireUserVerification: false,
  });
}