/**
 * Where the session token is kept, and how the HTTP client reaches it.
 *
 * A module of its own, holding nothing but the storage key and a reader,
 * because the two files that need it cannot import each other: `session.ts`
 * calls the API to sign in, and `client.ts` needs the token to make that same
 * API call authorised. Anything shared between them has to sit underneath both.
 *
 * It imports nothing, on purpose — that is what keeps it free of the cycle.
 */

/**
 * The single owner of this key.
 *
 * `session.ts` writes the blob and `client.ts` reads one field out of it, and a
 * second copy of the string is how those two quietly stop agreeing after a
 * rename.
 */
export const SESSION_STORAGE_KEY = 'nearle.session.v1';

/**
 * The signed session on this tab, if there is one.
 *
 * Reads storage on every call rather than caching. Sign-in and sign-out both
 * happen while the app is running, and a cached token would keep authorising
 * requests for a user who has just left — or send nothing for one who has just
 * arrived, until a reload.
 *
 * Returns undefined for every failure, including a throw. `sessionStorage`
 * raises rather than returning null in a browser with site data blocked, and a
 * console that cannot read a token should make an unauthenticated request and
 * be refused by the server, not fail to render.
 */
export function readSessionToken(): string | undefined {
  try {
    const raw = sessionStorage.getItem(SESSION_STORAGE_KEY);
    if (!raw) return undefined;
    const parsed: unknown = JSON.parse(raw);
    if (typeof parsed !== 'object' || parsed === null) return undefined;
    const token = (parsed as { token?: unknown }).token;
    return typeof token === 'string' && token !== '' ? token : undefined;
  } catch {
    return undefined;
  }
}

/**
 * The `Authorization` header for a request, or nothing at all.
 *
 * Nothing, rather than an empty or `Bearer null` header, when there is no
 * session. A header that is present but meaningless is worse than an absent
 * one: `middleware.WebAuth` refuses a token that does not verify whatever the
 * enforcement flag says, so sending rubbish would turn every anonymous call
 * into a 401 — including the ones that are still meant to work while the
 * rollout is in progress.
 */
export function authHeader(): Record<string, string> {
  const token = readSessionToken();
  return token ? { Authorization: `Bearer ${token}` } : {};
}