purchase token

pragma solidity ^0.4.18;

import "zeppelin-solidity/contracts/crowdsale/Crowdsale.sol";
import "zeppelin-solidity/contracts/ownership/Ownable.sol";


contract LoomSale is Crowdsale, Ownable {
    using SafeMath for uint256;

    function LoomSale(uint256 _rate, address _wallet, ERC20 _loomTokenAddr) public
        Crowdsale(_rate, _wallet, _loomTokenAddr) {}

    // Owner Withdraw, Loom take out their ether
    function ownerWithdraw() public onlyOwner {
        uint256 amount = address(this).balance;
        require(amount > 0);
        wallet.transfer(amount);
    }

    function _getTokenAmount(uint256 _weiAmount) internal view returns (uint256) {
        return _weiAmount.div(rate).mul(1000);
    }

    event PreValidate(uint256 loomTokenLeft, uint256 weiAmount);

    function _preValidatePurchase(address _beneficiary, uint256 _weiAmount) internal {
        require(_beneficiary != address(0));
        require(_weiAmount != 0);
        require(token.balanceOf(this) >= _getTokenAmount(_weiAmount));
        PreValidate(token.balanceOf(this), _getTokenAmount(_weiAmount));
    }

    // Don't forward on buy wait for owner withdraw
    function _forwardFunds() internal {}

}