function notifyRewardAmount(address token, uint amount) external lock {
    require(token != stake);
    require(amount > 0);
    if (!isReward[token]) {
        require(rewards.length < MAX_REWARD_TOKENS, "too many rewards tokens");
    }
    // rewards accrue only during the bribe period
    uint bribeStart = block.timestamp - (block.timestamp % (7 days)) + BRIBE_LAG;
    uint adjustedTstamp = block.timestamp < bribeStart ? bribeStart : bribeStart + 7 days;
    if (rewardRate[token] == 0) _writeRewardPerTokenCheckpoint(token, 0, adjustedTstamp);
    (rewardPerTokenStored[token], lastUpdateTime[token]) = _updateRewardPerToken(token);
    _claimFees();

    if (block.timestamp >= periodFinish[token]) {
        _safeTransferFrom(token, msg.sender, address(this), amount);
        rewardRate[token] = amount / DURATION;
    } else {
        uint _remaining = periodFinish[token] - block.timestamp;
        uint _left = _remaining * rewardRate[token];
        require(amount > _left);
        _safeTransferFrom(token, msg.sender, address(this), amount);
        rewardRate[token] = (amount + _left) / DURATION;
    }
    require(rewardRate[token] > 0);
    uint balance = IERC20(token).balanceOf(address(this));
    require(rewardRate[token] <= balance / DURATION, "Provided reward too high");
    periodFinish[token] = adjustedTstamp + DURATION;
    if (!isReward[token]) {
        isReward[token] = true;
        rewards.push(token);
        IBribe(bribe).addRewardToken(token);
    }

    emit NotifyReward(msg.sender, token, amount);
}
