Contract Address Details

// SPDX-License-Identifier: MIT
pragma solidity 0.8.13;

interface IBribeFactory {
    function createExternalBribe(address[] memory) external returns (address);
}

// OpenZeppelin Contracts (last updated v4.9.0) (utils/math/Math.sol)

/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    enum Rounding {
        Down, // Toward negative infinity
        Up, // Toward infinity
        Zero // Toward zero
    }

    /**
     * @dev Returns the largest of two numbers.
     */
    function max(uint256 a, uint256 b) internal pure returns (uint256) {
        return a > b ? a : b;
    }

    /**
     * @dev Returns the smallest of two numbers.
     */
    function min(uint256 a, uint256 b) internal pure returns (uint256) {
        return a < b ? a : b;
    }

    /**
     * @dev Returns the average of two numbers. The result is rounded towards
     * zero.
     */
    function average(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b) / 2 can overflow.
        return (a & b) + (a ^ b) / 2;
    }

    /**
     * @dev Returns the ceiling of the division of two numbers.
     *
     * This differs from standard division with `/` in that it rounds up instead
     * of rounding down.
     */
    function ceilDiv(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b - 1) / b can overflow on addition, so we distribute.
        return a == 0 ? 0 : (a - 1) / b + 1;
    }

    /**
     * @notice Calculates floor(x * y / denominator) with full precision. Throws if result overflows a uint256 or denominator == 0
     * @dev Original credit to Remco Bloemen under MIT license (https://xn--2-umb.com/21/muldiv)
     * with further edits by Uniswap Labs also under MIT license.
     */
    function mulDiv(uint256 x, uint256 y, uint256 denominator) internal pure returns (uint256 result) {
        unchecked {
            // 512-bit multiply [prod1 prod0] = x * y. Compute the product mod 2^256 and mod 2^256 - 1, then use
            // use the Chinese Remainder Theorem to reconstruct the 512 bit result. The result is stored in two 256
            // variables such that product = prod1 * 2^256 + prod0.
            uint256 prod0; // Least significant 256 bits of the product
            uint256 prod1; // Most significant 256 bits of the product
            assembly {
                let mm := mulmod(x, y, not(0))
                prod0 := mul(x, y)
                prod1 := sub(sub(mm, prod0), lt(mm, prod0))
            }

            // Handle non-overflow cases, 256 by 256 division.
            if (prod1 == 0) {
                // Solidity will revert if denominator == 0, unlike the div opcode on its own.
                // The surrounding unchecked block does not change this fact.
                // See https://docs.soliditylang.org/en/latest/control-structures.html#checked-or-unchecked-arithmetic.
                return prod0 / denominator;
            }

            // Make sure the result is less than 2^256. Also prevents denominator == 0.
            require(denominator > prod1, "Math: mulDiv overflow");

            ///////////////////////////////////////////////
            // 512 by 256 division.
            ///////////////////////////////////////////////

            // Make division exact by subtracting the remainder from [prod1 prod0].
            uint256 remainder;
            assembly {
                // Compute remainder using mulmod.
                remainder := mulmod(x, y, denominator)

                // Subtract 256 bit number from 512 bit number.
                prod1 := sub(prod1, gt(remainder, prod0))
                prod0 := sub(prod0, remainder)
            }

            // Factor powers of two out of denominator and compute largest power of two divisor of denominator. Always >= 1.
            // See https://cs.stackexchange.com/q/138556/92363.

            // Does not overflow because the denominator cannot be zero at this stage in the function.
            uint256 twos = denominator & (~denominator + 1);
            assembly {
                // Divide denominator by twos.
                denominator := div(denominator, twos)

                // Divide [prod1 prod0] by twos.
                prod0 := div(prod0, twos)

                // Flip twos such that it is 2^256 / twos. If twos is zero, then it becomes one.
                twos := add(div(sub(0, twos), twos), 1)
            }

            // Shift in bits from prod1 into prod0.
            prod0 |= prod1 * twos;

            // Invert denominator mod 2^256. Now that denominator is an odd number, it has an inverse modulo 2^256 such
            // that denominator * inv = 1 mod 2^256. Compute the inverse by starting with a seed that is correct for
            // four bits. That is, denominator * inv = 1 mod 2^4.
            uint256 inverse = (3 * denominator) ^ 2;

            // Use the Newton-Raphson iteration to improve the precision. Thanks to Hensel's lifting lemma, this also works
            // in modular arithmetic, doubling the correct bits in each step.
            inverse *= 2 - denominator * inverse; // inverse mod 2^8
            inverse *= 2 - denominator * inverse; // inverse mod 2^16
            inverse *= 2 - denominator * inverse; // inverse mod 2^32
            inverse *= 2 - denominator * inverse; // inverse mod 2^64
            inverse *= 2 - denominator * inverse; // inverse mod 2^128
            inverse *= 2 - denominator * inverse; // inverse mod 2^256

            // Because the division is now exact we can divide by multiplying with the modular inverse of denominator.
            // This will give us the correct result modulo 2^256. Since the preconditions guarantee that the outcome is
            // less than 2^256, this is the final result. We don't need to compute the high bits of the result and prod1
            // is no longer required.
            result = prod0 * inverse;
            return result;
        }
    }

    /**
     * @notice Calculates x * y / denominator with full precision, following the selected rounding direction.
     */
    function mulDiv(uint256 x, uint256 y, uint256 denominator, Rounding rounding) internal pure returns (uint256) {
        uint256 result = mulDiv(x, y, denominator);
        if (rounding == Rounding.Up && mulmod(x, y, denominator) > 0) {
            result += 1;
        }
        return result;
    }

    /**
     * @dev Returns the square root of a number. If the number is not a perfect square, the value is rounded down.
     *
     * Inspired by Henry S. Warren, Jr.'s "Hacker's Delight" (Chapter 11).
     */
    function sqrt(uint256 a) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        // For our first guess, we get the biggest power of 2 which is smaller than the square root of the target.
        //
        // We know that the "msb" (most significant bit) of our target number `a` is a power of 2 such that we have
        // `msb(a) <= a < 2*msb(a)`. This value can be written `msb(a)=2**k` with `k=log2(a)`.
        //
        // This can be rewritten `2**log2(a) <= a < 2**(log2(a) + 1)`
        // → `sqrt(2**k) <= sqrt(a) < sqrt(2**(k+1))`
        // → `2**(k/2) <= sqrt(a) < 2**((k+1)/2) <= 2**(k/2 + 1)`
        //
        // Consequently, `2**(log2(a) / 2)` is a good first approximation of `sqrt(a)` with at least 1 correct bit.
        uint256 result = 1 << (log2(a) >> 1);

        // At this point `result` is an estimation with one bit of precision. We know the true value is a uint128,
        // since it is the square root of a uint256. Newton's method converges quadratically (precision doubles at
        // every iteration). We thus need at most 7 iteration to turn our partial result with one bit of precision
        // into the expected uint128 result.
        unchecked {
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            return min(result, a / result);
        }
    }

    /**
     * @notice Calculates sqrt(a), following the selected rounding direction.
     */
    function sqrt(uint256 a, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = sqrt(a);
            return result + (rounding == Rounding.Up && result * result < a ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 2, rounded down, of a positive value.
     * Returns 0 if given 0.
     */
    function log2(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >> 128 > 0) {
                value >>= 128;
                result += 128;
            }
            if (value >> 64 > 0) {
                value >>= 64;
                result += 64;
            }
            if (value >> 32 > 0) {
                value >>= 32;
                result += 32;
            }
            if (value >> 16 > 0) {
                value >>= 16;
                result += 16;
            }
            if (value >> 8 > 0) {
                value >>= 8;
                result += 8;
            }
            if (value >> 4 > 0) {
                value >>= 4;
                result += 4;
            }
            if (value >> 2 > 0) {
                value >>= 2;
                result += 2;
            }
            if (value >> 1 > 0) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 2, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log2(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log2(value);
            return result + (rounding == Rounding.Up && 1 << result < value ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 10, rounded down, of a positive value.
     * Returns 0 if given 0.
     */
    function log10(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >= 10 ** 64) {
                value /= 10 ** 64;
                result += 64;
            }
            if (value >= 10 ** 32) {
                value /= 10 ** 32;
                result += 32;
            }
            if (value >= 10 ** 16) {
                value /= 10 ** 16;
                result += 16;
            }
            if (value >= 10 ** 8) {
                value /= 10 ** 8;
                result += 8;
            }
            if (value >= 10 ** 4) {
                value /= 10 ** 4;
                result += 4;
            }
            if (value >= 10 ** 2) {
                value /= 10 ** 2;
                result += 2;
            }
            if (value >= 10 ** 1) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 10, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log10(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log10(value);
            return result + (rounding == Rounding.Up && 10 ** result < value ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 256, rounded down, of a positive value.
     * Returns 0 if given 0.
     *
     * Adding one to the result gives the number of pairs of hex symbols needed to represent `value` as a hex string.
     */
    function log256(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >> 128 > 0) {
                value >>= 128;
                result += 16;
            }
            if (value >> 64 > 0) {
                value >>= 64;
                result += 8;
            }
            if (value >> 32 > 0) {
                value >>= 32;
                result += 4;
            }
            if (value >> 16 > 0) {
                value >>= 16;
                result += 2;
            }
            if (value >> 8 > 0) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 256, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log256(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log256(value);
            return result + (rounding == Rounding.Up && 1 << (result << 3) < value ? 1 : 0);
        }
    }
}

interface IBribe {
    function _deposit(uint amount, uint tokenId) external;
    function _withdraw(uint amount, uint tokenId) external;
    function getRewardForOwner(uint tokenId, address[] memory tokens) external;
    function notifyRewardAmount(address token, uint amount) external;
    function left(address token) external view returns (uint);
}

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function transfer(address recipient, uint amount) external returns (bool);
    function decimals() external view returns (uint8);
    function symbol() external view returns (string memory);
    function balanceOf(address) external view returns (uint);
    function transferFrom(address sender, address recipient, uint amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint);
    function approve(address spender, uint value) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint value);
    event Approval(address indexed owner, address indexed spender, uint value);
}

interface IGauge {
    function notifyRewardAmount(address token, uint amount) external;
    function getReward(address account, address[] memory tokens) external;
    function left(address token) external view returns (uint);
    function stake() external view returns (address);
}

interface IVoter {
    function _ve() external view returns (address);
    function governor() external view returns (address);
    function emergencyCouncil() external view returns (address);
    function attachTokenToGauge(uint _tokenId, address account) external;
    function detachTokenFromGauge(uint _tokenId, address account) external;
    function emitDeposit(uint _tokenId, address account, uint amount) external;
    function emitWithdraw(uint _tokenId, address account, uint amount) external;
    function isWhitelisted(address token) external view returns (bool);
    function notifyRewardAmount(uint amount) external;
    function distribute(address _gauge) external;
    function gauges(address) external view returns (address);
}

interface IVotingEscrow {

    struct Point {
        int128 bias;
        int128 slope; // # -dweight / dt
        uint256 ts;
        uint256 blk; // block
    }

    function token() external view returns (address);
    function team() external returns (address);
    function epoch() external view returns (uint);
    function point_history(uint loc) external view returns (Point memory);
    function user_point_history(uint tokenId, uint loc) external view returns (Point memory);
    function user_point_epoch(uint tokenId) external view returns (uint);

    function ownerOf(uint) external view returns (address);
    function isApprovedOrOwner(address, uint) external view returns (bool);
    function transferFrom(address, address, uint) external;

    function voting(uint tokenId) external;
    function abstain(uint tokenId) external;
    function attach(uint tokenId) external;
    function detach(uint tokenId) external;

    function checkpoint() external;
    function deposit_for(uint tokenId, uint value) external;
    function create_lock_for(uint, uint, address) external returns (uint);

    function balanceOfNFT(uint) external view returns (uint);
    function totalSupply() external view returns (uint);
}

// Bribes pay out rewards for a given pool based on the votes that were received from the user (goes hand in hand with Voter.vote())
contract ExternalBribe is IBribe {
    address public immutable voter; // only voter can modify balances (since it only happens on vote())
    address public immutable _ve; // 天使のたまご

    uint internal constant DURATION = 7 days; // rewards are released over the voting period
    uint internal constant MAX_REWARD_TOKENS = 16;

    uint public totalSupply;
    mapping(uint => uint) public balanceOf;
    mapping(address => mapping(uint => uint)) public tokenRewardsPerEpoch;
    mapping(address => uint) public periodFinish;
    mapping(address => mapping(uint => uint)) public lastEarn;

    address[] public rewards;
    mapping(address => bool) public isReward;

    /// @notice A checkpoint for marking balance
    struct Checkpoint {
        uint timestamp;
        uint balanceOf;
    }

    /// @notice A checkpoint for marking supply
    struct SupplyCheckpoint {
        uint timestamp;
        uint supply;
    }

    /// @notice A record of balance checkpoints for each account, by index
    mapping (uint => mapping (uint => Checkpoint)) public checkpoints;
    /// @notice The number of checkpoints for each account
    mapping (uint => uint) public numCheckpoints;
    /// @notice A record of balance checkpoints for each token, by index
    mapping (uint => SupplyCheckpoint) public supplyCheckpoints;
    /// @notice The number of checkpoints
    uint public supplyNumCheckpoints;

    event Deposit(address indexed from, uint tokenId, uint amount);
    event Withdraw(address indexed from, uint tokenId, uint amount);
    event NotifyReward(address indexed from, address indexed reward, uint epoch, uint amount);
    event ClaimRewards(address indexed from, address indexed reward, uint amount);
    event HandleLeftOverRewards(address indexed reward, uint originalEpoch, uint updatedEpoch, uint amount);

    constructor(address _voter, address[] memory _allowedRewardTokens) {
        voter = _voter;
        _ve = IVoter(_voter)._ve();

        for (uint i; i < _allowedRewardTokens.length; i++) {
            if (_allowedRewardTokens[i] != address(0)) {
                isReward[_allowedRewardTokens[i]] = true;
                rewards.push(_allowedRewardTokens[i]);
            }
        }
    }

    // simple re-entrancy check
    uint internal _unlocked = 1;
    modifier lock() {
        require(_unlocked == 1);
        _unlocked = 2;
        _;
        _unlocked = 1;
    }

    function _bribeStart(uint timestamp) internal pure returns (uint) {
        return timestamp - (timestamp % (7 days));
    }

    function getEpochStart(uint timestamp) public pure returns (uint) {
        uint bribeStart = _bribeStart(timestamp);
        uint bribeEnd = bribeStart + DURATION;
        return timestamp < bribeEnd ? bribeStart : bribeStart + 7 days;
    }

    /**
    * @notice Determine the prior balance for an account as of a block number
    * @dev Block number must be a finalized block or else this function will revert to prevent misinformation.
    * @param tokenId The token of the NFT to check
    * @param timestamp The timestamp to get the balance at
    * @return The balance the account had as of the given block
    */
    function getPriorBalanceIndex(uint tokenId, uint timestamp) public view returns (uint) {
        uint nCheckpoints = numCheckpoints[tokenId];
        if (nCheckpoints == 0) {
            return 0;
        }
        // First check most recent balance
        if (checkpoints[tokenId][nCheckpoints - 1].timestamp <= timestamp) {
            return (nCheckpoints - 1);
        }
        // Next check implicit zero balance
        if (checkpoints[tokenId][0].timestamp > timestamp) {
            return 0;
        }

        uint lower = 0;
        uint upper = nCheckpoints - 1;
        while (upper > lower) {
            uint center = upper - (upper - lower) / 2; // ceil, avoiding overflow
            Checkpoint memory cp = checkpoints[tokenId][center];
            if (cp.timestamp == timestamp) {
                return center;
            } else if (cp.timestamp < timestamp) {
                lower = center;
            } else {
                upper = center - 1;
            }
        }
        return lower;
    }

    function getPriorSupplyIndex(uint timestamp) public view returns (uint) {
        uint nCheckpoints = supplyNumCheckpoints;
        if (nCheckpoints == 0) {
            return 0;
        }

        // First check most recent balance
        if (supplyCheckpoints[nCheckpoints - 1].timestamp <= timestamp) {
            return (nCheckpoints - 1);
        }

        // Next check implicit zero balance
        if (supplyCheckpoints[0].timestamp > timestamp) {
            return 0;
        }

        uint lower = 0;
        uint upper = nCheckpoints - 1;
        while (upper > lower) {
            uint center = upper - (upper - lower) / 2; // ceil, avoiding overflow
            SupplyCheckpoint memory cp = supplyCheckpoints[center];
            if (cp.timestamp == timestamp) {
                return center;
            } else if (cp.timestamp < timestamp) {
                lower = center;
            } else {
                upper = center - 1;
            }
        }
        return lower;
    }

    function _writeCheckpoint(uint tokenId, uint balance) internal {
        uint _timestamp = block.timestamp;
        uint _nCheckPoints = numCheckpoints[tokenId];
        if (_nCheckPoints > 0 && checkpoints[tokenId][_nCheckPoints - 1].timestamp == _timestamp) {
            checkpoints[tokenId][_nCheckPoints - 1].balanceOf = balance;
        } else {
            checkpoints[tokenId][_nCheckPoints] = Checkpoint(_timestamp, balance);
            numCheckpoints[tokenId] = _nCheckPoints + 1;
        }
    }

    function _writeSupplyCheckpoint() internal {
        uint _nCheckPoints = supplyNumCheckpoints;
        uint _timestamp = block.timestamp;

        if (_nCheckPoints > 0 && supplyCheckpoints[_nCheckPoints - 1].timestamp == _timestamp) {
            supplyCheckpoints[_nCheckPoints - 1].supply = totalSupply;
        } else {
            supplyCheckpoints[_nCheckPoints] = SupplyCheckpoint(_timestamp, totalSupply);
            supplyNumCheckpoints = _nCheckPoints + 1;
        }
    }

    function rewardsListLength() external view returns (uint) {
        return rewards.length;
    }

    // returns the last time the reward was modified or periodFinish if the reward has ended
    function lastTimeRewardApplicable(address token) public view returns (uint) {
        return Math.min(block.timestamp, periodFinish[token]);
    }

    // allows a user to claim rewards for a given token
    function getReward(uint tokenId, address[] memory tokens) external lock  {
        require(IVotingEscrow(_ve).isApprovedOrOwner(msg.sender, tokenId));
        for (uint i = 0; i < tokens.length; i++) {
            uint _reward = earned(tokens[i], tokenId);
            lastEarn[tokens[i]][tokenId] = block.timestamp;
            if (_reward > 0) _safeTransfer(tokens[i], msg.sender, _reward);

            emit ClaimRewards(msg.sender, tokens[i], _reward);
        }
    }

    // used by Voter to allow batched reward claims
    function getRewardForOwner(uint tokenId, address[] memory tokens) external lock  {
        require(msg.sender == voter);
        address _owner = IVotingEscrow(_ve).ownerOf(tokenId);
        for (uint i = 0; i < tokens.length; i++) {
            uint _reward = earned(tokens[i], tokenId);
            lastEarn[tokens[i]][tokenId] = block.timestamp;
            if (_reward > 0) _safeTransfer(tokens[i], _owner, _reward);

            emit ClaimRewards(_owner, tokens[i], _reward);
        }
    }

    function earned(address token, uint tokenId) public view returns (uint) {
        if (numCheckpoints[tokenId] == 0) {
            return 0;
        }

        uint reward = 0;
        uint _bal = 0;
        uint _supply = 1;
        uint _index = 0;
        uint _currTs = _bribeStart(lastEarn[token][tokenId]); // take epoch last claimed in as starting point

        _index = getPriorBalanceIndex(tokenId, _currTs);

        // accounts for case where lastEarn is before first checkpoint
        _currTs = Math.max(_currTs, _bribeStart(checkpoints[tokenId][_index].timestamp)); 

        // get epochs between current epoch and first checkpoint in same epoch as last claim
        uint numEpochs = (_bribeStart(block.timestamp) - _currTs) / DURATION;

        if (numEpochs > 0) {
            for (uint256 i = 0; i < numEpochs; i++) {
                // get index of last checkpoint in this epoch
                _index = getPriorBalanceIndex(tokenId, _currTs + DURATION); 
                // get checkpoint in this epoch
                _bal = checkpoints[tokenId][_index].balanceOf;
                // get supply of last checkpoint in this epoch
                _supply = supplyCheckpoints[getPriorSupplyIndex(_currTs + DURATION)].supply;
                if (_supply != 0) {
                    reward += _bal * tokenRewardsPerEpoch[token][_currTs] / _supply;
                }
                _currTs += DURATION;
            }
        }

        return reward;
    }

    // This is an external function, but internal notation is used since it can only be called "internally" from Gauges
    function _deposit(uint amount, uint tokenId) external {
        require(msg.sender == voter);

        totalSupply += amount;
        balanceOf[tokenId] += amount;

        _writeCheckpoint(tokenId, balanceOf[tokenId]);
        _writeSupplyCheckpoint();

        emit Deposit(msg.sender, tokenId, amount);
    }

    function _withdraw(uint amount, uint tokenId) external {
        require(msg.sender == voter);

        totalSupply -= amount;
        balanceOf[tokenId] -= amount;

        _writeCheckpoint(tokenId, balanceOf[tokenId]);
        _writeSupplyCheckpoint();

        emit Withdraw(msg.sender, tokenId, amount);
    }

    function left(address token) external view returns (uint) {
        uint adjustedTstamp = getEpochStart(block.timestamp);
        return tokenRewardsPerEpoch[token][adjustedTstamp];
    }

    function notifyRewardAmount(address token, uint amount) external lock {
        require(amount > 0);
        if (!isReward[token]) {
          require(IVoter(voter).isWhitelisted(token), "bribe tokens must be whitelisted");
          require(rewards.length < MAX_REWARD_TOKENS, "too many rewards tokens");
        }
        // bribes kick in at the start of next bribe period
        uint adjustedTstamp = getEpochStart(block.timestamp);
        uint epochRewards = tokenRewardsPerEpoch[token][adjustedTstamp];

        uint256 balanceBefore = IERC20(token).balanceOf(address(this));
        _safeTransferFrom(token, msg.sender, address(this), amount);
        uint256 balanceAfter = IERC20(token).balanceOf(address(this));

        amount = balanceAfter - balanceBefore;

        tokenRewardsPerEpoch[token][adjustedTstamp] = epochRewards + amount;

        periodFinish[token] = adjustedTstamp + DURATION;

        if (!isReward[token]) {
            isReward[token] = true;
            rewards.push(token);
        }

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

    // This is an external function that can only be called by teams to handle unclaimed rewards due to zero vote
    function handleLeftOverRewards(uint epochTimestamp, address[] memory tokens) external {
        require(msg.sender == IVotingEscrow(_ve).team(), "only team");

        // require that supply of that epoch to be ZERO
        uint epochStart = getEpochStart(epochTimestamp);
        SupplyCheckpoint memory sp0 = supplyCheckpoints[getPriorSupplyIndex(epochStart + DURATION)];
        if (epochStart + DURATION > _bribeStart(sp0.timestamp)) {
            require(sp0.supply == 0, "this epoch has votes");
        }

        // do sth like notifyRewardAmount
        uint length = tokens.length;
        for (uint i = 0; i < length;) {
            // check bribe amount 
            uint previousEpochRewards = tokenRewardsPerEpoch[tokens[i]][epochStart];
            require(previousEpochRewards != 0, "no bribes for this epoch");

            // get timestamp of current epoch
            uint adjustedTstamp = getEpochStart(block.timestamp);

            // get notified reward of current epoch
            uint currentEpochRewards = tokenRewardsPerEpoch[tokens[i]][adjustedTstamp];

            // add previous unclaimed rewards to current epoch
            tokenRewardsPerEpoch[tokens[i]][adjustedTstamp] = currentEpochRewards + previousEpochRewards;

            // remove token rewards from previous epoch
            tokenRewardsPerEpoch[tokens[i]][epochStart] = 0;

            // amend period finish
            periodFinish[tokens[i]] = adjustedTstamp + DURATION;

            emit HandleLeftOverRewards(tokens[i], epochStart, adjustedTstamp, previousEpochRewards);

            unchecked {
                ++i;
            }
        }
    }

    function swapOutRewardToken(uint i, address oldToken, address newToken) external {
        require(msg.sender == IVotingEscrow(_ve).team(), 'only team');
        require(rewards[i] == oldToken);
        isReward[oldToken] = false;
        isReward[newToken] = true;
        rewards[i] = newToken;
    }

    function _safeTransfer(address token, address to, uint256 value) internal {
        require(token.code.length > 0);
        (bool success, bytes memory data) =
        token.call(abi.encodeWithSelector(IERC20.transfer.selector, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))));
    }

    function _safeTransferFrom(address token, address from, address to, uint256 value) internal {
        require(token.code.length > 0);
        (bool success, bytes memory data) =
        token.call(abi.encodeWithSelector(IERC20.transferFrom.selector, from, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))));
    }
}

contract BribeFactory is IBribeFactory {
    address public last_external_bribe;

    function createExternalBribe(address[] memory allowedRewards) external returns (address) {
        last_external_bribe = address(new ExternalBribe(msg.sender, allowedRewards));
        return last_external_bribe;
    }
}