Crowdsale.sol

pragma solidity 0.4.24;

import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
import "openzeppelin-solidity/contracts/math/SafeMath.sol";

contract Crowdsale {
  using SafeMath for uint256;

  ERC20 public token;
  address public wallet;
  uint256 public rate;
  uint256 public weiRaised;

  constructor(uint256 _rate, address _wallet, ERC20 _token) public {
    require(_rate > 0);
    require(_wallet != address(0));
    require(_token != address(0));

    rate = _rate;
    wallet = _wallet;
    token = _token;
  }

  function () external payable {
    buyTokens(msg.sender);
  }

  function buyTokens(address _beneficiary) public payable {
    require(_beneficiary != address(0));
    require(msg.value != 0);

    uint256 tokens = msg.value.mul(rate);
    weiRaised = weiRaised.add(msg.value);

    token.transfer(_beneficiary, tokens);
    wallet.transfer(msg.value);
  }
}