/**
 * [Gitea #201 KE-1] Notice when this device's encryption store has diverged
 * from the server: every POST /keys/upload answers 400 "One time key ...
 * already exists", and the SDK retries forever (matrix-rust-sdk#5200, open),
 * so new encrypted messages and calls quietly degrade. The server saw 474k of
 * these between May 30 and Jul 8 2026. The only fix is a fresh login on that
 * device, so we tell the user (KeyUploadBanner) instead of looping silently.
 *
 * Watched at the fetch layer (MatrixClient `fetchFn`), so it doesn't depend on
 * SDK log wording. Pure state + a tiny subscribe API; no network I/O of its own.
 */

/** Conflicts needed before we call the device stuck. The SDK retries within
 * seconds, so a real divergence crosses this quickly; a one-off race doesn't. */
export const STUCK_AFTER = 3;
/** Conflicts older than this don't count (a long-ago blip isn't "now"). */
export const WINDOW_MS = 15 * 60 * 1000;

export type KeyUploadWatchState = { stuck: boolean; conflicts: number; lastError?: string };

let conflictTimes: number[] = [];
let lastError: string | undefined;
let state: KeyUploadWatchState = { stuck: false, conflicts: 0 };
const listeners = new Set<() => void>();

const publish = (next: KeyUploadWatchState) => {
  if (next.stuck === state.stuck && next.conflicts === state.conflicts) return;
  state = next;
  listeners.forEach((l) => l());
};

export const isKeyUploadUrl = (url: string): boolean => {
  try {
    return /\/_matrix\/client\/[^/]+\/keys\/upload\/?$/.test(new URL(url, 'http://x').pathname);
  } catch {
    return false;
  }
};

/** The 400 body that marks a diverged one-time-key store. */
export const isOtkConflict = (status: number, body: string): boolean =>
  status === 400 && /one time key .*already exists/i.test(body);

/** Feed one /keys/upload response. `now` is injectable for tests. */
export const recordKeyUpload = (status: number, body: string, now = Date.now()): void => {
  if (status >= 200 && status < 300) {
    // A successful upload means the stores agree again.
    conflictTimes = [];
    lastError = undefined;
    publish({ stuck: false, conflicts: 0 });
    return;
  }
  if (!isOtkConflict(status, body)) return;
  conflictTimes = [...conflictTimes, now].filter((t) => now - t <= WINDOW_MS);
  lastError = body.slice(0, 300);
  publish({
    stuck: conflictTimes.length >= STUCK_AFTER,
    conflicts: conflictTimes.length,
    lastError,
  });
};

export const getKeyUploadWatch = (): KeyUploadWatchState => state;

export const subscribeKeyUploadWatch = (cb: () => void): (() => void) => {
  listeners.add(cb);
  return () => listeners.delete(cb);
};

/** Test/logout helper: forget everything (a new session starts clean). */
export const resetKeyUploadWatch = (): void => {
  conflictTimes = [];
  lastError = undefined;
  publish({ stuck: false, conflicts: 0 });
};

const urlOf = (input: RequestInfo | URL): string =>
  typeof input === 'string' ? input : input instanceof URL ? input.href : input.url;

/**
 * Wrap a fetch so /keys/upload responses are observed. The response the SDK
 * gets is untouched; a clone is read in the background, never awaited.
 */
export const watchKeyUploads =
  (inner: typeof fetch): typeof fetch =>
  async (input, init) => {
    const res = await inner(input, init);
    try {
      if (isKeyUploadUrl(urlOf(input))) {
        if (res.ok) recordKeyUpload(res.status, '');
        else if (res.status === 400)
          res
            .clone()
            .text()
            .then((body) => recordKeyUpload(res.status, body))
            .catch(() => undefined);
      }
    } catch {
      // observation must never break the request
    }
    return res;
  };