    function notifyRewardAmount(uint256 reward) internal updateReward(address(0)) {
        historicalRewards = historicalRewards.add(reward);
        if (block.timestamp >= periodFinish) {
            rewardRate = reward.div(duration);
        } else {
            uint256 remaining = periodFinish.sub(block.timestamp);
            uint256 leftover = remaining.mul(rewardRate);
            reward = reward.add(leftover);
            rewardRate = reward.div(duration);
        }
        currentRewards = reward;
        lastUpdateTime = block.timestamp;
        periodFinish = block.timestamp.add(duration);
        emit RewardAdded(reward);
    }
    function queueNewRewards(uint256 _rewards) external returns (bool) {
        require(msg.sender == operator, "!authorized");

        _rewards = _rewards.add(queuedRewards);

        if (block.timestamp >= periodFinish) {
            notifyRewardAmount(_rewards);
            queuedRewards = 0;
            return true;
        }

        //et = now - (finish-duration)
        uint256 elapsedTime = block.timestamp.sub(periodFinish.sub(duration));
        //current at now: rewardRate * elapsedTime
        uint256 currentAtNow = rewardRate * elapsedTime;
        uint256 queuedRatio = currentAtNow.mul(1000).div(_rewards);

        //uint256 queuedRatio = currentRewards.mul(1000).div(_rewards);
        if (queuedRatio < newRewardRatio) {
            notifyRewardAmount(_rewards);
            queuedRewards = 0;
        } else {
            queuedRewards = _rewards;
        }
        return true;
    }
