use safe erc20 & new logGas

contracts/lib/SafeERC20.sol

@@ -45,6 +45,22 @@ library SafeERC20 {
         );
     }
 
+    function safeApprove(
+        IERC20 token,
+        address spender,
+        uint256 value
+    ) internal {
+        // safeApprove should only be called when setting an initial allowance,
+        // or when resetting it to zero. To increase and decrease it, use
+        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
+        // solhint-disable-next-line max-line-length
+        require(
+            (value == 0) || (token.allowance(address(this), spender) == 0),
+            "SafeERC20: approve from non-zero to non-zero allowance"
+        );
+        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
+    }
+
     /**
      * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
      * on the return value: the return value is optional (but if data is returned, it must not be false).