// ---------------------------------------------------------------------------
// shell/session.ts — the CLIENT half of X2's auth contract (EXIT wave 1, X5).
//
// WHAT THIS REPLACES. The shell's door was HTTP Basic on a shared APP_PASSWORD
// (`api/main.py`'s BasicAuth middleware): no per-user identity, no BU isolation,
// no `may_open` gate — which is why SHELL.md says this frame must not be
// reachable by a real user until EXIT-3 lands. This module is the per-user door:
// the SAME `core/users` accounts the Streamlit `gate()` verifies, reached over
// `POST /api/v1/auth/login` and carried by the X3 signed cookie.
//
// ⚠ THE COOKIE IS HttpOnly (X3), SO THIS CODE CANNOT SEE IT — and that is the
// point. There is no client-side "am I logged in?" bit to cache, mirror into
// localStorage, or trust: the only way to know is to ASK the server, which is
// also the only party that can tell whether the user's `epoch` was bumped out
// from under an outstanding cookie. So `me()` runs on every boot, and its
// answer is never persisted. A cached session flag would keep painting the
// frame for a revoked user, which is the whole reason X3 has an epoch.
//
// WHY THIS FILE HOLDS NO import.meta. It is compiled to CommonJS and run under
// node by `verify_login.py`; `import.meta` is a hard error there. Anything
// environment-shaped (the current app's base URL) is a PARAMETER, never a
// module-level read — see nav.ts for the same rule.
// ---------------------------------------------------------------------------

// The prefix and the credentials word live in `apiContract.ts` — ONE copy, read
// by this module, by nav.ts and by the grid's apiBridge. `verify_login.py`
// mutates them there to prove the gate can see them.
import { API_V1, CREDENTIALS as CREDS, checkTenant } from "../apiContract";

export { API_V1 };

/**
 * The session's user, per X2's login/me payload. Deliberately narrow: the shell
 * needs identity for the account row and nothing else. **Scope is NOT decided
 * here** — the row pool is BU-scoped server-side (EXIT-3b) and the nav is
 * `may_open`-filtered server-side (X6), so `bus`/`modules` are for DISPLAY, and
 * a client that re-derived permission from them would be the permission system
 * trusting its own subject (the `Field.createdBy` precedent in types.ts).
 */
export interface SessionUser {
  username: string;
  name: string;
  role: string;
  /** BU labels this user may view — `core.users.allowed_bus_labels` semantics. */
  bus: string[];
  /** Granted registry keys, or the literal `'all'` — `core/users`' own encoding. */
  modules: string[] | "all";
  /** Wave 14 C-AVATAR — the user's OWN profile photo as a data URL, or absent. Everyone
   *  else's photos ride `workspace.userAvatars`, keyed by display name. */
  avatar?: string | null;
}

export function isAdmin(user: SessionUser | null): boolean {
  return user?.role === "admin";
}

/**
 * Normalise the server's user object.
 *
 * DEFENSIVE ON THE DISPLAY FIELDS, STRICT ON IDENTITY. A missing `name` falls
 * back to the username (a person with no display name still gets a door); a
 * missing `username` returns null, because an authenticated session with no
 * subject is not a session. The distinction matters: hard-failing on a cosmetic
 * field would turn a harmless server change into every user locked out, while
 * inventing a subject would be worse than the 401 it papers over.
 */
export function parseUser(raw: unknown): SessionUser | null {
  if (!raw || typeof raw !== "object" || Array.isArray(raw)) return null;
  const r = raw as Record<string, unknown>;
  const username = typeof r.username === "string" ? r.username.trim() : "";
  if (!username) return null;
  const name = typeof r.name === "string" && r.name.trim() !== "" ? r.name.trim() : username;
  const role = typeof r.role === "string" ? r.role : "";
  const bus = Array.isArray(r.bus) ? r.bus.filter((b): b is string => typeof b === "string") : [];
  const modules =
    r.modules === "all"
      ? "all"
      : Array.isArray(r.modules)
        ? r.modules.filter((m): m is string => typeof m === "string")
        : [];
  // Defensive like the display fields: only a data: image URL is carried; anything
  // else renders the initials disc rather than a broken <img>.
  const avatar =
    typeof r.avatar === "string" && r.avatar.startsWith("data:image/") ? r.avatar : null;
  return { username, name, role, bus, modules, avatar };
}

/** The `{user: {...}}` envelope both `/auth/login` and `/auth/me` return. */
export function parseUserEnvelope(body: unknown): SessionUser | null {
  if (!body || typeof body !== "object") return null;
  return parseUser((body as { user?: unknown }).user);
}

// --- error copy ------------------------------------------------------------

/** Shown when the server gives us nothing better on a rejected credential. Same
 *  words as the Streamlit `gate()` — one product, one wrong-password sentence. */
export const BAD_CREDENTIALS = "Incorrect username or password.";
export const SERVER_UNAVAILABLE = "Sign-in is unavailable right now. Try again in a moment.";
export const NETWORK_UNAVAILABLE = "Cannot reach the server. Check your connection and try again.";

/**
 * X2's error envelope is `{"error": {"code", "message"}}`. Which message the
 * user sees is a policy question, so the rule is explicit rather than "show
 * whatever came back":
 *
 *   - **4xx → prefer the SERVER's message.** A 4xx message is policy the client
 *     cannot know — "too many attempts, try again in 30 seconds" is the server's
 *     backoff talking (X5: *the server owns backoff*), and replacing it with our
 *     generic line would hide the only actionable thing on the screen.
 *   - **5xx → OUR generic line.** A 500's message describes the server's
 *     internals to someone who is, by definition, not authenticated yet.
 *   - **status 0 → a transport failure**, which never reached a server at all.
 *
 * `status` 0 is our own encoding for "fetch threw" — there is no HTTP 0.
 */
export function errorMessage(status: number, body: unknown): string {
  if (status === 0) return NETWORK_UNAVAILABLE;
  if (status >= 500) return SERVER_UNAVAILABLE;
  const err = (body as { error?: { message?: unknown } } | null)?.error;
  const msg = typeof err?.message === "string" ? err.message.trim() : "";
  if (msg) return msg;
  return status === 401 ? BAD_CREDENTIALS : SERVER_UNAVAILABLE;
}

// --- the three calls -------------------------------------------------------

export type LoginResult =
  | { ok: true; user: SessionUser }
  | { ok: false; message: string };

async function readJson(res: Response): Promise<unknown> {
  try {
    return await res.json();
  } catch {
    return null;
  }
}

/**
 * X2 `POST /api/v1/auth/login`. NO client-side backoff, deliberately: X5 gives
 * the delay to the server, because a delay a browser imposes on itself is a
 * delay an attacker's script simply does not import.
 *
 * `tenant` is omitted rather than defaulted — X2 types it optional with the
 * server's own default, and a client that pins `'royal-imports'` into every
 * login is a client that has to be re-shipped for tenant #2.
 */
export async function login(username: string, password: string): Promise<LoginResult> {
  let res: Response;
  try {
    res = await fetch(`${API_V1}/auth/login`, {
      method: "POST",
      credentials: CREDS,
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({ username, password }),
    });
  } catch {
    return { ok: false, message: errorMessage(0, null) };
  }
  const body = await readJson(res);
  if (!res.ok) return { ok: false, message: errorMessage(res.status, body) };
  const user = parseUserEnvelope(body);
  // A 200 whose body we cannot read as a user is NOT a session. Treating it as
  // one would paint the frame for a subject nobody can name.
  if (!user) return { ok: false, message: SERVER_UNAVAILABLE };
  return { ok: true, user };
}

/**
 * X2 `GET /api/v1/auth/me`. FAIL-CLOSED: anything that is not a 200 carrying a
 * readable user — 401, 404 (the route not built yet), a proxy's HTML error
 * page, a dropped connection — reads as NO SESSION. There is no state in which
 * a failure to confirm the session is treated as having one.
 */
export async function me(): Promise<SessionUser | null> {
  try {
    const res = await fetch(`${API_V1}/auth/me`, { credentials: CREDS });
    // ⭐ THE BOOT SIDE OF THE TENANT GUARD. `me()` runs on every boot, so this is what ARMS
    // the comparator with the tenant this frame belongs to — every later call then only has to
    // notice a change. It also catches the swap directly on a re-check.
    // ⚠ Deliberately BEFORE the `!res.ok` return: a repointed tab still gets a 200 here, and
    // the guard must see the header on exactly the request that establishes identity.
    if (checkTenant(res)) return null;
    if (!res.ok) return null;
    return parseUserEnvelope(await readJson(res));
  } catch {
    return null;
  }
}

/**
 * X2 `POST /api/v1/auth/logout` → 204, cookie cleared.
 *
 * Returns nothing and swallows failures ON PURPOSE: the caller drops to the
 * login screen either way. A logout button that reports failure and leaves the
 * user sitting in the app is worse than one that always closes the door on this
 * browser — and the cookie is the server's to invalidate, so the honest local
 * action is "stop showing the frame".
 */
export async function logout(): Promise<void> {
  try {
    await fetch(`${API_V1}/auth/logout`, { method: "POST", credentials: CREDS });
  } catch {
    // deliberate: see above
  }
}