/**
 * [Gitea #128] "While you were deafened: Alice, Bob joined · Cole left".
 * Pure diff + wording; the hook snapshots the participant set on deafen and
 * calls this on undeafen.
 */
export const DEAFEN_CATCHUP_MIN_MS = 10_000;
const MAX_NAMES = 3;

const list = (names: string[]): string => {
  const shown = names.slice(0, MAX_NAMES);
  const more = names.length - shown.length;
  return more > 0 ? `${shown.join(', ')} and ${more} more` : shown.join(', ');
};

export const deafenCatchUpText = (
  before: Set<string>,
  after: Set<string>,
  nameOf: (userId: string) => string,
): string | null => {
  const joined = Array.from(after).filter((u) => !before.has(u));
  const left = Array.from(before).filter((u) => !after.has(u));
  if (joined.length === 0 && left.length === 0) return null;
  const parts: string[] = [];
  if (joined.length) parts.push(`${list(joined.map(nameOf))} joined`);
  if (left.length) parts.push(`${list(left.map(nameOf))} left`);
  return `While you were deafened: ${parts.join(' · ')}`;
};