contract TokenSale is Owned{
    IERC20Token public tokenContract;  // the token being sold
    uint256 public price = 625;              // 1eth = 62.5 tokens
    uint256 public decimals = 18;
    
    uint256 public tokensSold;
    uint256 public ethRaised;
    uint256 public MaxETHAmount;
    
    bool public PresaleStarted = false;
    
    address[] internal buyers;
    mapping (address => uint256) public _balances;

    event Sold(address buyer, uint256 amount);
    event DistributedTokens(uint256 tokensSold);

    constructor(IERC20Token _tokenContract, uint256 _maxEthAmount) {
        owner = msg.sender;
        tokenContract = _tokenContract;
        MaxETHAmount = _maxEthAmount;
    }
    
    fallback() external payable {
        buyTokensWithETH(msg.sender);
    }
    
    receive() external payable{ buyTokensWithETH(msg.sender); }

    // Guards against integer overflows
    function safeMultiply(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        } else {
            uint256 c = a * b;
            assert(c / a == b);
            return c;
        }
    }
    
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

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

    
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }
    
    function multiply(uint x, uint y) internal pure returns (uint z) {
        require(y == 0 || (z = x * y) / y == x);
    }
    
    function setPrice(uint256 price_) external onlyOwner{
        price = price_;
    }
    
    function isBuyer(address _address)
        public
        view
        returns (bool)
    {
        for (uint256 s = 0; s < buyers.length; s += 1) {
            if (_address == buyers[s]) return (true);
        }
        return (false);
    }

    function addbuyer(address _buyer, uint256 _amount) internal {
        bool _isbuyer = isBuyer(_buyer);
        if (!_isbuyer) buyers.push(_buyer);
        
        _balances[_buyer] = add(_balances[_buyer], _amount);
    }
    
    function togglePresale() public onlyOwner{
        PresaleStarted = !PresaleStarted;
    }
    
    function changeToken(IERC20Token newToken) external onlyOwner{
        tokenContract = newToken;
    }


    function buyTokensWithETH(address _receiver) public payable {
        require(PresaleStarted, "Presale not started yet!");
        require(ethRaised < MaxETHAmount, "Presale finished");
        uint _amount = msg.value;
        require(ethRaised+_amount <= MaxETHAmount, "Remaining Limit not Enough");
        require(_receiver != address(0), "Can't send to 0x00 address"); 
        require(_amount > 0, "Can't buy with 0 eth"); 
        
        require(owner.send(_amount), "Unable to transfer eth to owner");
        ethRaised += _amount;
        
        addbuyer(msg.sender, _amount);
        
    }
    
    function airDrop() public onlyOwner{
        require(multiply(ethRaised, div(price, 10)) <= tokenContract.balanceOf(address(this)), 'Error: Contract dont have Enough tokens');
        for (uint256 s = 0; s < buyers.length; s += 1) {
            uint256 gBalance = _balances[buyers[s]];
            
            if(gBalance > 0) {
                _balances[buyers[s]] = 0;
                
                uint tokensToBuy = multiply(div(gBalance, 10), (price));
                require(tokenContract.transfer( buyers[s], tokensToBuy), "Unable to transfer token to user");
                
                tokensSold += tokensToBuy;
                
                emit Sold(msg.sender, tokensToBuy);
            }
        }
        
        ethRaised = 0;
        emit DistributedTokens(tokensSold);
    }
    

    function endSale() public {
        require(msg.sender == owner);

        // Send unsold tokens to the owner.
        require(tokenContract.transfer(owner, tokenContract.balanceOf(address(this))));

        msg.sender.transfer(address(this).balance);
    }
}
function safeMultiply(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        } else {
            uint256 c = a * b;
            assert(c / a == b);
            return c;
        }
    }
// Guards against integer overflows