function drawRandomWinner() public {
        require(msg.sender == owner);
        require(raffleEndTime < block.timestamp);
        require(!raffleWinningTicketSelected);
        
        uint256 seed = raffleTicketsBought + block.timestamp;
        raffleTicketThatWon = addmod(uint256(block.blockhash(block.number-1)), seed, (raffleTicketsBought + 1));
        raffleWinningTicketSelected = true;
    }