function lockTokens(
    address user,
    address asset,
    uint256 amount
) external payable override onlySavingsAccount nonReentrant returns (uint256 sharesReceived) {
    require(amount != 0, 'Invest: amount');
    if (asset != address(0)) {
        IERC20(asset).safeTransferFrom(user, address(this), amount);
    } else {
        require(msg.value == amount, 'Invest: ETH amount');
    }
    sharesReceived = amount;
    emit LockedTokens(user, asset, sharesReceived);
}
function _unlockTokens(address asset, uint256 amount) internal returns (uint256 received) {
    require(amount != 0, 'Invest: amount');
    received = amount;
    if (asset == address(0)) {
        (bool success, ) = savingsAccount.call{value: received}('');
        require(success, 'Transfer failed');
    } else {
        IERC20(asset).safeTransfer(savingsAccount, received);
    }
    emit UnlockedTokens(asset, received);
}
