export const DEADLINE_EXPIRED_CODE = "ETIMEOUT";

export function createDeadline(budgetMs: number, now = Date.now()) {
  return now + Math.max(0, budgetMs);
}

export function remainingMs(deadline: number, now = Date.now()) {
  return Math.max(0, deadline - now);
}

export function timeoutError(message: string) {
  const error = new Error(message) as Error & { code: string };
  error.code = DEADLINE_EXPIRED_CODE;
  return error;
}

export async function withDeadline<T>(
  operation: Promise<T>,
  deadline: number,
  onTimeout: () => void,
  message: string,
): Promise<T> {
  const remaining = remainingMs(deadline);
  if (!remaining) {
    onTimeout();
    throw timeoutError(message);
  }

  let timer: ReturnType<typeof setTimeout> | undefined;
  const timeout = new Promise<T>((_, reject) => {
    timer = setTimeout(() => {
      onTimeout();
      reject(timeoutError(message));
    }, remaining);
  });

  try {
    return await Promise.race([operation, timeout]);
  } finally {
    if (timer) clearTimeout(timer);
  }
}