pragma solidity ^0.6.0;
// SPDX-License-Identifier: UNLICENSED

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 *
*/

library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    assert(c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }

  function ceil(uint a, uint m) internal pure returns (uint r) {
    return (a + m - 1) / m * m;
  }
}

// ----------------------------------------------------------------------------
// Owned contract
// ----------------------------------------------------------------------------
contract Owned {
    address payable public owner;

    event OwnershipTransferred(address indexed _from, address indexed _to);

    constructor() public {
        owner = msg.sender;
    }

    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address payable _newOwner) public onlyOwner {
        owner = _newOwner;
        emit OwnershipTransferred(msg.sender, _newOwner);
    }
}


// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// ----------------------------------------------------------------------------
interface IToken {
    function transfer(address to, uint256 tokens) external returns (bool success);
    function balanceOf(address tokenOwner) external view returns (uint256 balance);
}

contract PreSale is Owned {
    using SafeMath for uint256;
    address public tokenAddress = 0x7a0F27B4ECDF145d22719aeC06bD2c18A0cDfAA5;
    uint256 tokenRatePerEth = 100;
    address payable fundsReceiver;
    
    constructor() public {
        owner = 0xed82261bCE9F9F730a91897B92e9E27F8FD1a181;
        fundsReceiver = 0xed82261bCE9F9F730a91897B92e9E27F8FD1a181;
    }

    receive() external payable {
        
        uint256 tokens = getTokenAmount(msg.value);
        
        require(IToken(tokenAddress).transfer(msg.sender, tokens), "Insufficient balance of sale contract!");
        
        // send received funds to the owner
        fundsReceiver.transfer(msg.value);
    }
    
    function getTokenAmount(uint256 amount) internal view returns(uint256){
        return (amount.mul(tokenRatePerEth));
    }
    
    function getUnSoldTokens() external onlyOwner{
        uint256 tokens = IToken(tokenAddress).balanceOf(address(this));
        require(IToken(tokenAddress).transfer(owner, tokens), "No tokens in contract");
    }
}