// A single monotonic counter of JMAP TRANSPORT failures.
//
// WHY THIS EXISTS. The offline replica is a read-path FALLBACK, and to be one it
// has to know that a read genuinely failed. `lib/jmap/client.ts` makes that
// impossible to see from the outside: its read methods swallow their own errors
// and return plausible-looking success. `getEmails()` returns
// `{ emails: [], hasMore: false, total: 0 }`, so a dead network is
// indistinguishable from an empty folder. `getEmail()` returns `null`.
// `getMailboxes()` returns a SYNTHETIC single Inbox. Falling back on those shapes
// alone would mean serving stale replica rows for a folder the user had genuinely
// just emptied.
//
// So `authenticatedFetch` bumps this counter when, and only when, `fetch` itself
// rejects - not on a 4xx, not on a 429 (that is a rate limit, and the server is
// plainly reachable), not on a JMAP method error. The fallback layer samples the
// counter before and after a call: a suspicious result PLUS an increment during
// that exact call is a transport failure. Either signal alone is not enough.
//
// Module-level rather than per-client on purpose: it answers "is the network
// working right now", which is a property of the machine, not of one account's
// client instance.

let failures = 0;
let lastFailureAt = 0;
let lastSuccessAt = 0;

/** Called only when `fetch` itself rejects. Never for an HTTP status. */
export function noteTransportFailure(): void {
  failures++;
  lastFailureAt = Date.now();
}

export function noteTransportSuccess(): void {
  lastSuccessAt = Date.now();
}

/** Monotonic. Sample before and after a call to attribute a failure to it. */
export function transportFailureCount(): number {
  return failures;
}

export function transportHealth(): {
  failures: number;
  lastFailureAt: number;
  lastSuccessAt: number;
  /** Best-effort "probably offline": a failure more recent than any success. */
  likelyOffline: boolean;
} {
  return {
    failures,
    lastFailureAt,
    lastSuccessAt,
    likelyOffline: lastFailureAt > lastSuccessAt,
  };
}

/** Test-only reset. */
export function resetTransportHealth(): void {
  failures = 0;
  lastFailureAt = 0;
  lastSuccessAt = 0;
}