export type Debounced<Args extends unknown[]> = ((...args: Args) => void) & {
  flush: () => void;
  cancel: () => void;
};

export function debounce<Args extends unknown[]>(
  fn: (...args: Args) => void,
  waitMs: number
): Debounced<Args> {
  let timer: ReturnType<typeof setTimeout> | null = null;
  let pendingArgs: Args | null = null;

  const debounced = (...args: Args): void => {
    pendingArgs = args;
    if (timer !== null) clearTimeout(timer);
    timer = setTimeout(() => {
      timer = null;
      const a = pendingArgs!;
      pendingArgs = null;
      fn(...a);
    }, waitMs);
  };

  debounced.flush = (): void => {
    if (timer === null) return;
    clearTimeout(timer);
    timer = null;
    const a = pendingArgs!;
    pendingArgs = null;
    fn(...a);
  };

  debounced.cancel = (): void => {
    if (timer !== null) clearTimeout(timer);
    timer = null;
    pendingArgs = null;
  };

  return debounced;
}