function withdraw(uint256 _amount) external override nonReentrant {
  uint256 _baseTokenAmount = (_amount * baseTokenDenominator) / 1e18;
  uint256 _fee = (_baseTokenAmount * withdrawFee) / FEE_DENOMINATOR;
  if (withdrawFee > 0) { require(_fee > 0, "fee = 0"); }
  else { require(_baseTokenAmount > 0, "amount = 0"); }
  _burn(msg.sender, _amount);
  uint256 _baseTokenAmountAfterFee = _baseTokenAmount - _fee;
  if (address(withdrawHook) != address(0)) {
    baseToken.approve(address(withdrawHook), _fee);
    withdrawHook.hook(msg.sender, _baseTokenAmount, _baseTokenAmountAfterFee);
    baseToken.approve(address(withdrawHook), 0);
  }
  baseToken.transfer(msg.sender, _baseTokenAmountAfterFee);
  emit Withdraw(msg.sender, _baseTokenAmountAfterFee, _fee);
}
if (lastGlobalPeriodReset + globalPeriodLength < block.timestamp) {
  lastGlobalPeriodReset = block.timestamp;
  globalAmountWithdrawnThisPeriod = _amountBeforeFee;
} else {
  require(globalAmountWithdrawnThisPeriod + _amountBeforeFee <= globalWithdrawLimitPerPeriod, "global withdraw limit exceeded");
  globalAmountWithdrawnThisPeriod += _amountBeforeFee;
}
if (lastUserPeriodReset + userPeriodLength < block.timestamp) {
  lastUserPeriodReset = block.timestamp;
  userToAmountWithdrawnThisPeriod[_sender] = _amountBeforeFee;
} else {
  require(userToAmountWithdrawnThisPeriod[_sender] + _amountBeforeFee <= userWithdrawLimitPerPeriod, "user withdraw limit exceeded");
  userToAmountWithdrawnThisPeriod[_sender] += _amountBeforeFee;
}
