pragma solidity ^0.5.0;


import "./DappToken.sol";


contract DappTokenSale {

    address admin;
    DappToken public tokenContract;
    uint256 public tokenPrice;
    uint256 public tokensSold;

    event Sell(address _buyer, uint256 _amount);

    constructor (DappToken _tokenContract, uint256 _tokenPrice) public {
        admin = msg.sender;
        tokenContract = _tokenContract;
        tokenPrice = _tokenPrice;
    }
    function multiply (uint x, uint y) internal pure returns (uint z) {
        require(y == 0 || (z = x * y) / y == x);
    }

    function buyTokens (uint256 _numberOfTokens) public payable {

        require (msg.value == multiply(_numberOfTokens, tokenPrice));
        require (tokenContract.balanceOf(address(this)) >= _numberOfTokens);
        require (tokenContract.transfer(msg.sender, _numberOfTokens));


        tokensSold += _numberOfTokens;
        emit Sell(msg.sender, _numberOfTokens);
    }
        function endSale () public {

            require (msg.value == admin);
            require (tokenContract.transfer(admin, tokenContract.balanceOf(address(this))));
            selfdestruct(admin);
        }

    }