const FIBONACCI_FACTOR = 5;
const FIBONACCI_OFFSET = 4;

function isPerfetSquare(x: number): boolean {
  const s = Math.sqrt(x);
  return Number.isInteger(s);
}

function isFibonacci(n: number): boolean {
  if (n < 0) return false;

  const nSquared = n ** 2; 
  const plushCheck = FIBONACCI_FACTOR * nSquared + FIBONACCI_OFFSET;
  const minusCheck = FIBONACCI_FACTOR * nSquared - FIBONACCI_OFFSET;

  return isPerfetSquare(plushCheck) || isPerfetSquare(minusCheck);
}

// No modificar: necesario para evaluar el resultado.
export { isFibonacci };