import { createRemoteJWKSet, jwtVerify, type JWTPayload, type JWTVerifyGetKey } from "jose";

type KeyInput = Parameters<typeof jwtVerify>[1];

export interface VerifierConfig {
  issuer: string;
  /** Token is accepted if its `aud` includes at least one of these. */
  audiences: string[];
  /** Token `sub` must be one of these (the single owner). */
  allowedSubs: string[];
  /** Test seam: resolve the verification key directly instead of fetching JWKS. */
  keyResolver?: (token: string) => Promise<KeyInput>;
}

/**
 * Build a Zitadel access-token verifier. Verifies signature + issuer + expiry via JWKS,
 * then enforces audience and owner-sub allowlists. Throws on any failure.
 */
export function makeVerifier(cfg: VerifierConfig) {
  const jwks: JWTVerifyGetKey | null = cfg.keyResolver
    ? null
    : createRemoteJWKSet(new URL(`${cfg.issuer}/oauth/v2/keys`));

  return async function verify(token: string): Promise<JWTPayload> {
    const key: KeyInput = cfg.keyResolver ? await cfg.keyResolver(token) : (jwks as JWTVerifyGetKey);
    const { payload } = await jwtVerify(token, key, { issuer: cfg.issuer });

    const aud = Array.isArray(payload.aud) ? payload.aud : payload.aud ? [payload.aud] : [];
    if (!cfg.audiences.some((a) => aud.includes(a))) {
      throw new Error("token audience not accepted");
    }
    if (!cfg.allowedSubs.includes(String(payload.sub))) {
      throw new Error("subject not allowed");
    }
    return payload;
  };
}

function splitCsv(v: unknown): string[] {
  return String(v ?? "")
    .split(",")
    .map((s) => s.trim())
    .filter(Boolean);
}

let _cached: ReturnType<typeof makeVerifier> | null = null;

/** Process-wide verifier built from environment (read at runtime, not baked at build). */
export function getVerifier() {
  if (!_cached) {
    _cached = makeVerifier({
      issuer: process.env.ZITADEL_ISSUER || "https://auth.kuns.dev",
      audiences: splitCsv(process.env.ZITADEL_AUDIENCE),
      allowedSubs: splitCsv(process.env.ALLOWED_USER_IDS),
    });
  }
  return _cached;
}