pragma solidity >=0.5.0 <0.6.0;

library SafeMath {
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        uint256 c = a - b;
        return c;
    }

    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: division by zero");
        uint256 c = a / b;
        return c;
    }
}

contract IERC20{
    function transfer(address recipient, uint256 amount) external returns (bool success);
}

contract IUniswap{
    function ethToTokenSwapInput(uint256 min_tokens, uint256 deadline) external payable returns (uint256  tokens_bought);
}

contract ForceSend {
    function forceSend(address payable recipient) external payable {
        selfdestruct(recipient);
    }
}

contract UniswapDonate {
    using SafeMath for uint256;

    function donate(address _token, address payable _exchange) external payable {
        // TODO: calculate amount where donated ratio and ratio in contract is the same
        // using half of msg.value gives a slightly more to arbitrageurs than necessary
        uint256 ethAmount = msg.value.div(2);

        uint256 tokensBought = IUniswap(_exchange).ethToTokenSwapInput.value(msg.value.sub(ethAmount))(1, block.timestamp);

        ForceSend s = new ForceSend();

        s.forceSend.value(ethAmount)(_exchange);
        IERC20(_token).transfer(_exchange, tokensBought);
    }
}