Transfer X% of Eth. sent to smart contract, to contract owner on buy function call

Question

I use this "buy" function in a smart contract, to receive Eth. for a token. I would like to extend the function, so if the Eth amount in a transaction is higher than X Eth. then send Y% to smart contract owner.

I'm not sure about what would be the best way to do this, so I'm looking for any suggestions.

Thanks in advance :-)

/**
 @dev Buy tokens with ether. 
 @param minPurchaseReturn The minimum number of tokens you will accept.
 */
function buy(uint minPurchaseReturn) public payable {
    uint amount = formulaContract.calculatePurchaseReturn(
        (tokenContract.totalSupply() - uncirculatedSupplyCount) - tokenContract.balanceOf(this),
        (address(this).balance + virtualReserveBalance) - msg.value,
        weight,
        msg.value);
    amount = (amount - ((amount * fee) / 1000000));

    //Now do the trade if conditions are met
    require (enabled);
    require (amount >= minPurchaseReturn);
    require (tokenContract.balanceOf(this) >= amount);

    //Accounting - so we can pull the fees out without changing the balance
    collectedFees += (msg.value * fee) / 1000000;

    emit Buy(msg.sender, msg.value, amount);
    tokenContract.transfer(msg.sender, amount);
}

Answer 1

You can see the amount of Eth coming in msg.value, so use it in your calculations. Add something like this:

uint threshold = 1 ether;
uint percentage = 5;

function buy(uint minPurchaseReturn) public payable {
    ...
    if(msg.value > threshold){
        //the following line introduces no overflow risk
        //since there's not enough Ether to overflow uint256 
        //by multiplying msg.value by 100
        uint myPrecious = msg.value * percentage / 100; 
        _owner.transfer(myPrecious);
    }
    ...

You can inherit Ownable.sol to get _owner value.