export function canBeCastAsIntegerOrNull(
  probableNumberOrNull: string | undefined | number | null,
): probableNumberOrNull is number | null {
  if (probableNumberOrNull === undefined) {
    return false;
  }

  if (typeof probableNumberOrNull === 'number') {
    return Number.isInteger(probableNumberOrNull);
  }

  if (probableNumberOrNull === null) {
    return true;
  }

  if (probableNumberOrNull === '') {
    return true;
  }

  if (typeof probableNumberOrNull === 'string') {
    const stringAsNumber = +probableNumberOrNull;

    if (isNaN(stringAsNumber)) {
      return false;
    }
    if (Number.isInteger(stringAsNumber)) {
      return true;
    }
  }

  return false;
}

export function castAsIntegerOrNull(
  probableNumberOrNull: string | undefined | number | null,
): number | null {
  if (canBeCastAsIntegerOrNull(probableNumberOrNull) === false) {
    throw new Error('Cannot cast to number or null');
  }

  if (probableNumberOrNull === null) {
    return null;
  }

  if (probableNumberOrNull === '') {
    return null;
  }

  if (typeof probableNumberOrNull === 'number') {
    return probableNumberOrNull;
  }

  if (typeof probableNumberOrNull === 'string') {
    return +probableNumberOrNull;
  }

  return null;
}