import "server-only";
import { createHash, randomBytes } from "node:crypto";
import { createRemoteJWKSet, jwtVerify } from "jose";
import { env } from "./env";

/**
 * Schlanke OIDC-Anbindung (Authorization Code + PKCE) für Authelia, Keycloak,
 * Authentik und Verwandte.
 *
 * Bewusst ohne Client-Bibliothek: Flimmer braucht genau einen Ablauf, und der
 * passt in wenige Dutzend Zeilen — dafür lohnt keine weitere Abhängigkeit mit
 * eigenem Versionsrhythmus.
 */

type Discovery = {
  issuer: string;
  authorization_endpoint: string;
  token_endpoint: string;
  jwks_uri: string;
  userinfo_endpoint?: string;
  end_session_endpoint?: string;
};

let cached: { at: number; doc: Discovery } | null = null;
const DISCOVERY_TTL_MS = 60 * 60 * 1000;

export async function discover(): Promise<Discovery> {
  if (cached && Date.now() - cached.at < DISCOVERY_TTL_MS) return cached.doc;

  const url = `${env.oidc.issuer.replace(/\/+$/, "")}/.well-known/openid-configuration`;
  const response = await fetch(url, { cache: "no-store" });
  if (!response.ok) {
    throw new Error(`OIDC-Discovery fehlgeschlagen (${response.status}) für ${url}`);
  }
  const doc = (await response.json()) as Discovery;
  cached = { at: Date.now(), doc };
  return doc;
}

let jwks: ReturnType<typeof createRemoteJWKSet> | null = null;
async function getJwks() {
  if (!jwks) {
    const doc = await discover();
    jwks = createRemoteJWKSet(new URL(doc.jwks_uri));
  }
  return jwks;
}

export const redirectUri = () => `${env.appUrl}/api/auth/oidc/callback`;

/** Erzeugt state und PKCE-Verifier für einen neuen Anmeldeversuch. */
export function createChallenge() {
  const state = randomBytes(16).toString("base64url");
  const verifier = randomBytes(32).toString("base64url");
  const challenge = createHash("sha256").update(verifier).digest("base64url");
  return { state, verifier, challenge };
}

export async function authorizationUrl(state: string, challenge: string): Promise<string> {
  const doc = await discover();
  const url = new URL(doc.authorization_endpoint);
  url.searchParams.set("response_type", "code");
  url.searchParams.set("client_id", env.oidc.clientId);
  url.searchParams.set("redirect_uri", redirectUri());
  url.searchParams.set("scope", env.oidc.scopes);
  url.searchParams.set("state", state);
  url.searchParams.set("code_challenge", challenge);
  url.searchParams.set("code_challenge_method", "S256");
  return url.toString();
}

export type OidcIdentity = {
  issuer: string;
  subject: string;
  email: string | null;
  name: string | null;
};

/** Tauscht den Code gegen Tokens und prüft das ID-Token. */
export async function exchangeCode(code: string, verifier: string): Promise<OidcIdentity> {
  const doc = await discover();

  const response = await fetch(doc.token_endpoint, {
    method: "POST",
    headers: {
      "content-type": "application/x-www-form-urlencoded",
      accept: "application/json",
    },
    body: new URLSearchParams({
      grant_type: "authorization_code",
      code,
      redirect_uri: redirectUri(),
      client_id: env.oidc.clientId,
      client_secret: env.oidc.clientSecret,
      code_verifier: verifier,
    }),
    cache: "no-store",
  });

  if (!response.ok) {
    throw new Error(`Token-Tausch fehlgeschlagen (${response.status}).`);
  }

  const tokens = (await response.json()) as { id_token?: string; access_token?: string };
  if (!tokens.id_token) {
    throw new Error("Der Anbieter hat kein ID-Token geliefert.");
  }

  const { payload } = await jwtVerify(tokens.id_token, await getJwks(), {
    issuer: doc.issuer,
    audience: env.oidc.clientId,
  });

  const subject = typeof payload.sub === "string" ? payload.sub : null;
  if (!subject) throw new Error("Das ID-Token enthält keine Subjekt-Kennung.");

  let email = typeof payload.email === "string" ? payload.email.toLowerCase() : null;
  let name =
    typeof payload.name === "string"
      ? payload.name
      : typeof payload.preferred_username === "string"
        ? payload.preferred_username
        : null;

  // Manche Anbieter liefern Profilangaben erst am userinfo-Endpunkt.
  if ((!email || !name) && doc.userinfo_endpoint && tokens.access_token) {
    try {
      const info = await fetch(doc.userinfo_endpoint, {
        headers: { authorization: `Bearer ${tokens.access_token}` },
        cache: "no-store",
      });
      if (info.ok) {
        const profile = (await info.json()) as Record<string, unknown>;
        if (!email && typeof profile.email === "string") email = profile.email.toLowerCase();
        if (!name && typeof profile.name === "string") name = profile.name;
      }
    } catch {
      // Profilangaben sind nur schmückendes Beiwerk — der Login klappt auch ohne.
    }
  }

  return { issuer: doc.issuer, subject, email, name };
}