function _fetchAndValidate(address token) internal view returns (bool isValid, uint256 price) {
  Oracle memory oracle = oracles[token];
  try AggregatorV3Interface(oracle.aggregator).latestRoundData() returns (
    uint80, /*roundId*/
    int256 answer,
    uint256, /*startedAt*/
    uint256 updatedAt,
    uint80 /*answeredInRound*/
  ) {
    isValid = (answer > 0 && block.timestamp - updatedAt <= oracle.stalePeriod);
    return (isValid, wdiv(uint256(answer), oracle.aggregatorScale));
  } catch {
    // return the default values (false, 0) on failure
  }
}
