// The canonical per-workstream tab order (persisted in papyrus KV) is the source of truth for
// how a workstream's tabs are arranged. `reconcileTabOrder` keeps it complete and current: the
// user's stored arrangement is preserved (minus ids of sessions that no longer exist), and every
// session missing from it — a just-created tab, or one made outside papyrus — is appended in
// CREATION order (oldest first; session id as a stable tiebreak). So a new session always lands
// at the end rather than at silverwood's arbitrary `session ls` map position. The result is
// deterministic, so callers persist it lazily (only when it differs from what's stored).

export interface OrderedSession {
  sessionId: string;
  createdAt: string;
}

export function reconcileTabOrder(
  stored: string[] | undefined,
  sessions: OrderedSession[],
): string[] {
  const live = new Set(sessions.map((s) => s.sessionId));
  const kept = (stored ?? []).filter((id) => live.has(id));
  const have = new Set(kept);
  const appended = sessions
    .filter((s) => !have.has(s.sessionId))
    .sort(
      (a, b) => a.createdAt.localeCompare(b.createdAt) || a.sessionId.localeCompare(b.sessionId),
    )
    .map((s) => s.sessionId);
  return [...kept, ...appended];
}

// Positional equality — lets a caller skip the KV write when `stored` is already canonical.
// A `undefined` stored order is never equal (an unset workstream must be initialized).
export function sameIds(a: string[] | undefined, b: string[]): boolean {
  return !!a && a.length === b.length && a.every((x, i) => x === b[i]);
}