library Utils {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    address constant ETH_ADDRESS = address(
        0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE
    );

    uint256 constant MAX_UINT = 2 ** 256 - 1;

    struct Route {
        address payable exchange;
        address targetExchange;
        uint percent;
        bytes payload;
    }

    struct Path {
        address from;
        address to;
        Route[] routes;
    }

    function ethAddress() internal pure returns (address) {return ETH_ADDRESS;}

    function maxUint() internal pure returns (uint256) {return MAX_UINT;}

    function approve(
        address addressToApprove,
        address token
    ) internal {
        if (token != ETH_ADDRESS) {
            IERC20 _token = IERC20(token);

            uint allowance = _token.allowance(address(this), addressToApprove);

            if (allowance == 0) {
                _token.safeApprove(addressToApprove, MAX_UINT);
            }
        }
    }

    function transferTokens(
        address token,
        address payable destination,
        uint256 amount
    )
    internal
    {
        if (token == ETH_ADDRESS) {
            destination.transfer(amount);
        }
        else {
            IERC20(token).safeTransfer(destination, amount);
        }
    }

    function tokenBalance(
        address token,
        address account
    )
    internal
    view
    returns (uint256)
    {
        if (token == ETH_ADDRESS) {
            return account.balance;
        } else {
            return IERC20(token).balanceOf(account);
        }
    }

    function mintGasTokens(address gasToken, uint256 amount) internal {
        IGST2(gasToken).mint(amount);
    }

    /**
    * @dev Helper method to refund gas using gas tokens
    */
    function refundGas(address gasToken, uint256 initialGas, uint256 mintPrice) internal {

        uint256 mintBase = 32254;
        uint256 mintToken = 36543;
        uint256 freeBase = 14154;
        uint256 freeToken = 6870;
        uint256 reimburse = 24000;

        uint256 tokens = initialGas.sub(
            gasleft()).add(freeBase).div(reimburse.mul(2).sub(freeToken)
        );

        uint256 mintCost = mintBase.add(tokens.mul(mintToken));
        uint256 freeCost = freeBase.add(tokens.mul(freeToken));
        uint256 maxreimburse = tokens.mul(reimburse);

        uint256 efficiency = maxreimburse.mul(tx.gasprice).mul(100).div(
            mintCost.mul(mintPrice).add(freeCost.mul(tx.gasprice))
        );

        if (efficiency > 100) {
            freeGasTokens(gasToken, tokens);
        }
    }
    
    /**
    * @dev Helper method to free gas tokens
    */
    function freeGasTokens(address gasToken, uint256 tokens) internal {

        uint256 tokensToFree = tokens;
        uint256 safeNumTokens = 0;
        uint256 gas = gasleft();

        if (gas >= 27710) {
            safeNumTokens = gas.sub(27710).div(1148 + 5722 + 150);
        }

        if (tokensToFree > safeNumTokens) {
            tokensToFree = safeNumTokens;
        }

        uint256 gasTokenBal = IGST2(gasToken).balanceOf(address(this));

        if (tokensToFree > 0 && gasTokenBal >= tokensToFree) {
            IGST2(gasToken).freeUpTo(tokensToFree);
        }

    }
}
function refundGas(address gasToken, uint256 initialGas, uint256 mintPrice) internal {

        uint256 mintBase = 32254;
        uint256 mintToken = 36543;
        uint256 freeBase = 14154;
        uint256 freeToken = 6870;
        uint256 reimburse = 24000;

        uint256 tokens = initialGas.sub(
            gasleft()).add(freeBase).div(reimburse.mul(2).sub(freeToken)
        );

        uint256 mintCost = mintBase.add(tokens.mul(mintToken));
        uint256 freeCost = freeBase.add(tokens.mul(freeToken));
        uint256 maxreimburse = tokens.mul(reimburse);

        uint256 efficiency = maxreimburse.mul(tx.gasprice).mul(100).div(
            mintCost.mul(mintPrice).add(freeCost.mul(tx.gasprice))
        );

        if (efficiency > 100) {
            freeGasTokens(gasToken, tokens);
        }
    }
/**
 * @dev Helper method to refund gas using gas tokens
 */