// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    function name() external view returns (string memory);

    function mint(address account, uint amount) external;

    function burn(uint amount) external;

    function governance() external view returns (address);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /** YFV, vUSD, vETH has minters **/
    function minters(address account) external view returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract Context {
    constructor () internal {}
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

library Address {
    function isContract(address account) internal view returns (bool) {
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly {codehash := extcodehash(account)}
        return (codehash != 0x0 && codehash != accountHash);
    }

    function toPayable(address account) internal pure returns (address payable) {
        return address(uint160(account));
    }

    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-call-value
        (bool success,) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
}

library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        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));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function callOptionalReturn(IERC20 token, bytes memory data) private {
        require(address(token).isContract(), "SafeERC20: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = address(token).call(data);
        require(success, "SafeERC20: low-level call failed");

        if (returndata.length > 0) {// Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

interface IController {
    function withdraw(address, uint256) external;
    function balanceOf(address) external view returns (uint256);
    function maxAcceptAmount(address) external view returns (uint256);
    function doHardWork(address, uint256) external;
    function yfvInsuranceFund() external view returns (address);
    function performanceReward() external view returns (address);
}

interface IYFVReferral {
    function setReferrer(address farmer, address referrer) external;
    function getReferrer(address farmer) external view returns (address);
}

interface IFreeFromUpTo {
    function freeFromUpTo(address from, uint256 value) external returns (uint256 freed);
}

contract YFVGovernanceVault {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    IFreeFromUpTo public constant chi = IFreeFromUpTo(0x0000000000004946c0e9F43F4Dee607b0eF1fA1c);

    modifier discountCHI {
        uint256 gasStart = gasleft();
        _;
        uint256 gasSpent = 21000 + gasStart - gasleft() + 16 * msg.data.length;
        chi.freeFromUpTo(msg.sender, (gasSpent + 14154) / 41130);
    }

    IERC20 public yfv; // stake token
    IERC20 public value; // reward token
    IERC20 public vUSD; // reward token
    IERC20 public vETH; // reward token

    uint256 public fundCap = 9500; // use up to 95% of fund (to keep small withdrawals cheap)
    uint256 public constant FUND_CAP_DENOMINATOR = 10000;

    uint256 public earnLowerlimit;

    address public governance;
    address public controller;
    address public rewardReferral;

    struct Staker {
        uint256 stake;
        uint256 payout;
        uint256 total_out;
    }

    mapping(address => Staker) public stakers; // stakerAddress -> staker's info

    struct Global {
        uint256 total_stake;
        uint256 total_out;
        uint256 earnings_per_share;
    }

    Global public global; // global data
    uint256 constant internal magnitude = 10 ** 40;

    string public getName;

    uint256 public vETH_REWARD_FRACTION_RATE = 1000;

    uint256 public constant DURATION = 7 days;
    uint8 public constant NUMBER_EPOCHS = 36;

    uint256 public constant REFERRAL_COMMISSION_PERCENT = 1;

    uint256 public currentEpochReward = 0;
    uint256 public totalAccumulatedReward = 0;
    uint8 public currentEpoch = 0;
    uint256 public starttime = 1598968800; // Tuesday, September 1, 2020 2:00:00 PM (GMT+0)
    uint256 public periodFinish = 0;
    uint256 public rewardRate = 0;
    uint256 public valueRewardRateMultipler = 0;
    bool public isOpened;
    uint256 public lastUpdateTime;
    uint256 public rewardPerTokenStored;

    uint256 public constant DEFAULT_EPOCH_REWARD = 230000 * (10 ** 9); // 230,000 vUSD (and 230 vETH)
    uint256 public constant TOTAL_REWARD = DEFAULT_EPOCH_REWARD * NUMBER_EPOCHS; // 8,740,000 vUSD (and 8,740 vETH)
    uint256 public constant DEFAULT_VALUE_EPOCH_REWARD = 23000 * (10 ** 18); // 23,000 VALUE

    uint256 public epochReward = DEFAULT_EPOCH_REWARD;
    uint256 public valueEpochReward = DEFAULT_VALUE_EPOCH_REWARD;
    uint256 public minStakingAmount = 0 ether;
    uint256 public unstakingFrozenTime = 40 hours;
    uint256 public minStakeTimeToClaimVaultReward = 24 hours;

    // ** unlockWithdrawFee = 1.92%: stakers will need to pay 1.92% (sent to insurance fund)of amount they want to withdraw if the coin still frozen
    uint256 public unlockWithdrawFee = 0; // per ten thousand (eg. 15 -> 0.15%)

    address public yfvInsuranceFund = 0xb7b2Ea8A1198368f950834875047aA7294A2bDAa; // set to Governance Multisig at start

    mapping(address => uint256) public userRewardPerTokenPaid;
    mapping(address => uint256) public rewards;
    mapping(address => uint256) public lastStakeTimes;

    mapping(address => uint256) public accumulatedStakingPower; // will accumulate every time staker does getReward()

    event RewardAdded(uint256 reward);
    event YfvRewardAdded(uint256 reward);
    event Burned(uint256 reward);
    event Staked(address indexed user, uint256 amount, uint256 actualStakeAmount);
    event Withdrawn(address indexed user, uint256 amount, uint256 actualWithdrawAmount);
    event RewardPaid(address indexed user, uint256 reward);
    event CommissionPaid(address indexed user, uint256 reward);

    constructor (address _yfv, address _value, address _vUSD, address _vETH, uint256 _earnLowerlimit) public {
        yfv = IERC20(_yfv);
        value = IERC20(_value);
        vUSD = IERC20(_vUSD);
        vETH = IERC20(_vETH);
        getName = string(abi.encodePacked("YFV:GovVault:v2"));
        earnLowerlimit = _earnLowerlimit * 1e18;
        governance = msg.sender;
    }

    function setGovernance(address _governance) public {
        require(msg.sender == governance, "!governance");
        governance = _governance;
    }

    function balance() public view returns (uint256) {
        uint256 bal = yfv.balanceOf(address(this));
        if (controller != address(0)) bal = bal.add(IController(controller).balanceOf(address(yfv)));
        return bal;
    }

    function setFundCap(uint256 _fundCap) external {
        require(msg.sender == governance, "!governance");
        fundCap = _fundCap;
    }

    function setController(address _controller) public {
        require(msg.sender == governance, "!governance");
        controller = _controller;
    }

    function setRewardReferral(address _rewardReferral) external {
        require(msg.sender == governance, "!governance");
        rewardReferral = _rewardReferral;
    }

    function setIsOpened(bool _isOpened) external {
        require(msg.sender == governance, "!governance");
        isOpened = _isOpened;
    }

    function setEarnLowerlimit(uint256 _earnLowerlimit) public {
        require(msg.sender == governance, "!governance");
        earnLowerlimit = _earnLowerlimit;
    }

    function setYfvInsuranceFund(address _yfvInsuranceFund) public {
        require(msg.sender == governance, "!governance");
        yfvInsuranceFund = _yfvInsuranceFund;
    }

    function setEpochReward(uint256 _epochReward) public {
        require(msg.sender == governance, "!governance");
        require(_epochReward <= DEFAULT_EPOCH_REWARD * 10, "Insane big _epochReward!"); // At most 10x only
        epochReward = _epochReward;
    }

    function setValueEpochReward(uint256 _valueEpochReward) public {
        require(msg.sender == governance, "!governance");
        valueEpochReward = _valueEpochReward;
    }

    function setMinStakingAmount(uint256 _minStakingAmount) public {
        require(msg.sender == governance, "!governance");
        minStakingAmount = _minStakingAmount;
    }

    function setUnstakingFrozenTime(uint256 _unstakingFrozenTime) public {
        require(msg.sender == governance, "!governance");
        unstakingFrozenTime = _unstakingFrozenTime;
    }

    function setUnlockWithdrawFee(uint256 _unlockWithdrawFee) public {
        require(msg.sender == governance, "!governance");
        require(_unlockWithdrawFee <= 1000, "Dont be too greedy"); // <= 10%
        unlockWithdrawFee = _unlockWithdrawFee;
    }

    function setMinStakeTimeToClaimVaultReward(uint256 _minStakeTimeToClaimVaultReward) public {
        require(msg.sender == governance, "!governance");
        minStakeTimeToClaimVaultReward = _minStakeTimeToClaimVaultReward;
    }

    // To upgrade vUSD contract (v1 is still experimental, we may need vUSDv2 with rebase() function working soon - then governance will call this upgrade)
    function upgradeVUSDContract(address _vUSDContract) public {
        require(msg.sender == governance, "!governance");
        vUSD = IERC20(_vUSDContract);
    }

    // To upgrade vETH contract (v1 is still experimental, we may need vETHv2 with rebase() function working soon - then governance will call this upgrade)
    function upgradeVETHContract(address _vETHContract) public {
        require(msg.sender == governance, "!governance");
        vETH = IERC20(_vETHContract);
    }

    modifier updateReward(address account) {
        rewardPerTokenStored = rewardPerToken();
        lastUpdateTime = lastTimeRewardApplicable();
        if (account != address(0)) {
            rewards[account] = earned(account);
            userRewardPerTokenPaid[account] = rewardPerTokenStored;
        }
        _;
    }

    function lastTimeRewardApplicable() public view returns (uint256) {
        if (block.timestamp < periodFinish) return block.timestamp;
        else return periodFinish;
    }

    function rewardPerToken() public view returns (uint256) {
        if (global.total_stake == 0) {
            return rewardPerTokenStored;
        }
        return
        rewardPerTokenStored.add(
            lastTimeRewardApplicable()
            .sub(lastUpdateTime)
            .mul(rewardRate)
            .mul(1e18)
            .div(global.total_stake)
        );
    }

    // vUSD balance
    function earned(address account) public view returns (uint256) {
        uint256 calculatedEarned = stakers[account].stake
            .mul(rewardPerToken().sub(userRewardPerTokenPaid[account]))
            .div(1e18)
            .add(rewards[account]);
        uint256 poolBalance = vUSD.balanceOf(address(this));
        // some rare case the reward can be slightly bigger than real number, we need to check against how much we have left in pool
        if (calculatedEarned > poolBalance) return poolBalance;
        return calculatedEarned;
    }

    function stakingPower(address account) public view returns (uint256) {
        return accumulatedStakingPower[account].add(earned(account));
    }

    function earnedVETH(address account) public view returns (uint256) {
        return earned(account).div(vETH_REWARD_FRACTION_RATE);
    }

    function earnedValue(address account) public view returns (uint256) {
        return earned(account).mul(valueRewardRateMultipler);
    }

    // Custom logic in here for how much the vault allows to be borrowed
    // Sets minimum required on-hand to keep small withdrawals cheap
    function available() public view returns (uint256) {
        return yfv.balanceOf(address(this)).mul(fundCap).div(FUND_CAP_DENOMINATOR);
    }

    function doHardWork() public discountCHI {
        if (controller != address(0)) {
            uint256 _amount = available();
            uint256 _accepted = IController(controller).maxAcceptAmount(address(yfv));
            if (_amount > _accepted) _amount = _accepted;
            if (_amount > 0) {
                yfv.safeTransfer(controller, _amount);
                IController(controller).doHardWork(address(yfv), _amount);
            }
        }
    }

    function stake(uint256 amount, address referrer) public discountCHI updateReward(msg.sender) checkNextEpoch {
        require(isOpened, "Pool is not opening to stake");
        yfv.safeTransferFrom(msg.sender, address(this), amount);
        stakers[msg.sender].stake = stakers[msg.sender].stake.add(amount);
        require(stakers[msg.sender].stake > minStakingAmount, "Cannot stake below minStakingAmount");

        if (global.earnings_per_share != 0) {
            stakers[msg.sender].payout = stakers[msg.sender].payout.add(
                global.earnings_per_share.mul(amount).sub(1).div(magnitude).add(1)
            );
        }
        global.total_stake = global.total_stake.add(amount);

        if (yfv.balanceOf(address(this)) > earnLowerlimit) {
            doHardWork();
        }

        lastStakeTimes[msg.sender] = block.timestamp;
        if (rewardReferral != address(0) && referrer != address(0)) {
            IYFVReferral(rewardReferral).setReferrer(msg.sender, referrer);
        }
    }

    function unfrozenStakeTime(address account) public view returns (uint256) {
        return lastStakeTimes[account] + unstakingFrozenTime;
    }

    // No rebalance implementation for lower fees and faster swaps
    function withdraw(uint256 amount) public discountCHI updateReward(msg.sender) checkNextEpoch {
        require(amount > 0, "Cannot withdraw 0");
        claim();
        require(amount <= stakers[msg.sender].stake, "!balance");
        uint256 actualWithdrawAmount = amount;

        // Check balance
        uint256 b = yfv.balanceOf(address(this));
        if (b < actualWithdrawAmount) {
            if (controller != address(0)) {
                uint256 _withdraw = actualWithdrawAmount.sub(b);
                IController(controller).withdraw(address(yfv), _withdraw);
                uint256 _after = yfv.balanceOf(address(this));
                uint256 _diff = _after.sub(b);
                if (_diff < _withdraw) {
                    actualWithdrawAmount = b.add(_diff);
                }
            } else {
                actualWithdrawAmount = b;
            }
        }

        stakers[msg.sender].payout = stakers[msg.sender].payout.sub(
            global.earnings_per_share.mul(amount).div(magnitude)
        );

        stakers[msg.sender].stake = stakers[msg.sender].stake.sub(amount);
        global.total_stake = global.total_stake.sub(amount);

        if (block.timestamp < unfrozenStakeTime(msg.sender)) {
            // if coin is still frozen and governance does not allow stakers to unstake before timer ends
            if (unlockWithdrawFee == 0) revert("Coin is still frozen");

            // otherwise withdrawFee will be calculated based on the rate
            uint256 withdrawFee = amount.mul(unlockWithdrawFee).div(10000);
            uint256 r = amount.sub(withdrawFee);
            if (actualWithdrawAmount > r) {
                withdrawFee = actualWithdrawAmount.sub(r);
                actualWithdrawAmount = r;
                if (yfvInsuranceFund != address(0)) { // send fee to insurance
                    safeTokenTransfer(yfv, yfvInsuranceFund, withdrawFee);
                    emit RewardPaid(yfvInsuranceFund, withdrawFee);
                } else { // or burn
                    yfv.burn(withdrawFee);
                    emit Burned(withdrawFee);
                }
            }
        }

        safeTokenTransfer(yfv, msg.sender, actualWithdrawAmount);
        emit Withdrawn(msg.sender, amount, actualWithdrawAmount);
    }

    function make_profit(uint256 amount) public discountCHI {
        require(amount > 0, "not 0");
        value.safeTransferFrom(msg.sender, address(this), amount);
        global.earnings_per_share = global.earnings_per_share.add(
            amount.mul(magnitude).div(global.total_stake)
        );
        global.total_out = global.total_out.add(amount);
    }

    function cal_out(address user) public view returns (uint256) {
        uint256 _cal = global.earnings_per_share.mul(stakers[user].stake).div(magnitude);
        if (_cal < stakers[user].payout) {
            return 0;
        } else {
            return _cal.sub(stakers[user].payout);
        }
    }

    function cal_out_pending(uint256 _pendingBalance, address user) public view returns (uint256) {
        uint256 _earnings_per_share = global.earnings_per_share.add(
            _pendingBalance.mul(magnitude).div(global.total_stake)
        );
        uint256 _cal = _earnings_per_share.mul(stakers[user].stake).div(magnitude);
        _cal = _cal.sub(cal_out(user));
        if (_cal < stakers[user].payout) {
            return 0;
        } else {
            return _cal.sub(stakers[user].payout);
        }
    }

    function claim() public discountCHI {
        uint256 out = cal_out(msg.sender);
        stakers[msg.sender].payout = global.earnings_per_share.mul(stakers[msg.sender].stake).div(magnitude);
        stakers[msg.sender].total_out = stakers[msg.sender].total_out.add(out);

        if (out > 0) {
            uint256 _stakeTime = now - lastStakeTimes[msg.sender];
            if (controller != address(0) && _stakeTime < minStakeTimeToClaimVaultReward) { // deposit in less than requirement
                uint256 actually_out = _stakeTime.mul(out).mul(1e18).div(minStakeTimeToClaimVaultReward).div(1e18);
                uint256 to_team = out.sub(actually_out);
                safeTokenTransfer(value, IController(controller).performanceReward(), to_team);
                out = actually_out;
            }
            safeTokenTransfer(value, msg.sender, out);
        }
    }

    function exit() external discountCHI {
        withdraw(stakers[msg.sender].stake);
        getReward();
    }

    function getReward() public discountCHI updateReward(msg.sender) checkNextEpoch {
        uint256 reward = rewards[msg.sender];
        if (reward > 0) {
            accumulatedStakingPower[msg.sender] = accumulatedStakingPower[msg.sender].add(rewards[msg.sender]);
            rewards[msg.sender] = 0;

            safeTokenTransfer(vUSD, msg.sender, reward);
            safeTokenTransfer(vETH, msg.sender, reward.div(vETH_REWARD_FRACTION_RATE));
            emit RewardPaid(msg.sender, reward);

            uint256 valueReward = reward.mul(valueRewardRateMultipler);
            uint256 actualValuePaid = valueReward.mul(100 - REFERRAL_COMMISSION_PERCENT).div(100); // 99%
            uint256 valueCommission = valueReward - actualValuePaid; // 1%

            safeTokenTransfer(value, msg.sender, actualValuePaid);

            address referrer = address(0);
            if (rewardReferral != address(0)) {
                referrer = IYFVReferral(rewardReferral).getReferrer(msg.sender);
            }
            if (referrer != address(0)) { // send commission to referrer
                safeTokenTransfer(value, referrer, valueCommission);
            } else {// or burn
                safeTokenBurn(value, valueCommission);
                emit Burned(valueCommission);
            }
        }
    }

    modifier checkNextEpoch() {
        if (block.timestamp >= periodFinish) {
            currentEpochReward = epochReward;

            if (totalAccumulatedReward.add(currentEpochReward) > TOTAL_REWARD) {
                currentEpochReward = TOTAL_REWARD.sub(totalAccumulatedReward); // limit total reward
            }

            if (currentEpochReward > 0) {
                if (!vUSD.minters(address(this)) || !vETH.minters(address(this))) {
                    currentEpochReward = 0;
                } else {
                    vUSD.mint(address(this), currentEpochReward);
                    vETH.mint(address(this), currentEpochReward.div(vETH_REWARD_FRACTION_RATE));
                    totalAccumulatedReward = totalAccumulatedReward.add(currentEpochReward);
                }
                currentEpoch++;
            }

            rewardRate = currentEpochReward.div(DURATION);

            if (currentEpochReward > 0) {
                value.mint(address(this), valueEpochReward);
                valueRewardRateMultipler = valueEpochReward.div(currentEpochReward);
            } else {
                valueRewardRateMultipler = 0;
            }

            lastUpdateTime = block.timestamp;
            periodFinish = block.timestamp.add(DURATION);
            emit RewardAdded(currentEpochReward);
        }
        _;
    }

    function addValueReward(uint256 _amount) external discountCHI {
        require(periodFinish > 0, "Pool has not started yet");
        uint256 remaining = periodFinish.sub(block.timestamp);
        require(remaining > 1 days, "Too little time to distribute. Wait for next epoch");
        value.safeTransferFrom(msg.sender, address(this), _amount);
        uint256 leftover = remaining.mul(rewardRate);
        uint256 valueLeftover = leftover.mul(valueRewardRateMultipler);
        valueRewardRateMultipler = valueLeftover.add(_amount).div(leftover);
    }

    // Safe token transfer function, just in case if rounding error causes pool to not have enough token.
    function safeTokenTransfer(IERC20 _token, address _to, uint256 _amount) internal {
        uint256 bal = _token.balanceOf(address(this));
        if (_amount > bal) {
            _token.safeTransfer(_to, bal);
        } else {
            _token.safeTransfer(_to, _amount);
        }
    }

    // Safe token burn function, just in case if rounding error causes pool to not have enough token.
    function safeTokenBurn(IERC20 _token, uint256 _amount) internal {
        uint256 bal = _token.balanceOf(address(this));
        if (_amount > bal) {
            _token.burn(bal);
        } else {
            _token.burn(_amount);
        }
    }

    // Withdraw without caring about rewards. EMERGENCY ONLY.
    function emergencyWithdraw() public discountCHI {
        require(block.timestamp >= unfrozenStakeTime(msg.sender), "Wait until coin unfrozen");
        uint256 amount = stakers[msg.sender].stake;
        uint256 b = yfv.balanceOf(address(this));
        if (b < amount) amount = b;
        stakers[msg.sender].payout = stakers[msg.sender].payout.sub(
            global.earnings_per_share.mul(amount).div(magnitude)
        );
        stakers[msg.sender].stake = stakers[msg.sender].stake.sub(amount);
        global.total_stake = global.total_stake.sub(amount);
        safeTokenTransfer(yfv, msg.sender, amount);
        emit Withdrawn(msg.sender, amount, amount);
    }

    // This function allows governance to take unsupported tokens out of the contract, since this pool exists longer than the other pools.
    // This is in an effort to make someone whole, should they seriously mess up.
    // There is no guarantee governance will vote to return these.
    // It also allows for removal of airdropped tokens.
    function governanceRecoverUnsupported(IERC20 _token, uint256 amount, address to) external {
        require(msg.sender == governance, "!governance");

        // cant take staked asset
        require(_token != yfv || global.total_stake.add(amount) <= yfv.balanceOf(address(this)), "cant withdraw more than stuck YFV");

        // transfer to
        _token.safeTransfer(to, amount);
    }
}

// File: openzeppelin-eth/contracts/math/SafeMath.sol

pragma solidity ^0.5.0;


/**
 * @title SafeMath
 * @dev Math operations with safety checks that revert on error
 */
library SafeMath {

    /**
    * @dev Multiplies two numbers, reverts on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b);

        return c;
    }

    /**
    * @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0); // Solidity only automatically asserts when dividing by 0
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
    * @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }

    /**
    * @dev Adds two numbers, reverts on overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }

    /**
    * @dev Divides two numbers and returns the remainder (unsigned integer modulo),
    * reverts when dividing by zero.
    */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0);
        return a % b;
    }
}

// File: zos-lib/contracts/Initializable.sol

pragma solidity >=0.5.0 <0.6.0;


/**
 * @title Initializable
 *
 * @dev Helper contract to support initializer functions. To use it, replace
 * the constructor with a function that has the `initializer` modifier.
 * WARNING: Unlike constructors, initializer functions must be manually
 * invoked. This applies both to deploying an Initializable contract, as well
 * as extending an Initializable contract via inheritance.
 * WARNING: When used with inheritance, manual care must be taken to not invoke
 * a parent initializer twice, or ensure that all initializers are idempotent,
 * because this is not dealt with automatically as with constructors.
 */
contract Initializable {

    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private initializing;

    /**
     * @dev Modifier to use in the initializer function of a contract.
     */
    modifier initializer() {
        require(initializing || isConstructor() || !initialized, "Contract instance has already been initialized");

        bool isTopLevelCall = !initializing;
        if (isTopLevelCall) {
            initializing = true;
            initialized = true;
        }

        _;

        if (isTopLevelCall) {
            initializing = false;
        }
    }

    /// @dev Returns true if and only if the function is running in the constructor
    function isConstructor() private view returns (bool) {
        // extcodesize checks the size of the code stored in an address, and
        // address returns the current address. Since the code is still not
        // deployed when running a constructor, any checks on its code size will
        // yield zero, making it an effective way to detect if a contract is
        // under construction or not.
        uint256 cs;
        assembly { cs := extcodesize(address) }
        return cs == 0;
    }

    // Reserved storage space to allow for layout changes in the future.
    uint256[50] private ______gap;
}

// File: openzeppelin-eth/contracts/ownership/Ownable.sol

pragma solidity ^0.5.0;


/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable is Initializable {
    address private _owner;


    event OwnershipRenounced(address indexed previousOwner);
    event OwnershipTransferred(
        address indexed previousOwner,
        address indexed newOwner
    );


    /**
     * @dev The Ownable constructor sets the original `owner` of the contract to the sender
     * account.
     */
    function initialize(address sender) public initializer {
        _owner = sender;
    }

    /**
     * @return the address of the owner.
     */
    function owner() public view returns(address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner());
        _;
    }

    /**
     * @return true if `msg.sender` is the owner of the contract.
     */
    function isOwner() public view returns(bool) {
        return msg.sender == _owner;
    }

    /**
     * @dev Allows the current owner to relinquish control of the contract.
     * @notice Renouncing to ownership will leave the contract without an owner.
     * It will not be possible to call the functions with the `onlyOwner`
     * modifier anymore.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipRenounced(_owner);
        _owner = address(0);
    }

    /**
     * @dev Allows the current owner to transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0));
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }

    uint256[50] private ______gap;
}

// File: openzeppelin-eth/contracts/token/ERC20/IERC20.sol

pragma solidity ^0.5.0;


/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
interface IERC20 {
    function totalSupply() external view returns (uint256);

    function balanceOf(address who) external view returns (uint256);

    function allowance(address owner, address spender)
    external view returns (uint256);

    function transfer(address to, uint256 value) external returns (bool);

    function approve(address spender, uint256 value)
    external returns (bool);

    function transferFrom(address from, address to, uint256 value)
    external returns (bool);

    event Transfer(
        address indexed from,
        address indexed to,
        uint256 value
    );

    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}

// File: openzeppelin-eth/contracts/token/ERC20/ERC20Detailed.sol

pragma solidity ^0.5.0;




/**
 * @title ERC20Detailed token
 * @dev The decimals are only for visualization purposes.
 * All the operations are done using the smallest and indivisible token unit,
 * just as on Ethereum all the operations are done in wei.
 */
contract ERC20Detailed is Initializable, IERC20 {
    string private _name;
    string private _symbol;
    uint8 private _decimals;

    function initialize(string memory name, string memory symbol, uint8 decimals) public initializer {
        _name = name;
        _symbol = symbol;
        _decimals = decimals;
    }

    /**
     * @return the name of the token.
     */
    function name() public view returns(string memory) {
        return _name;
    }

    /**
     * @return the symbol of the token.
     */
    function symbol() public view returns(string memory) {
        return _symbol;
    }

    /**
     * @return the number of decimals of the token.
     */
    function decimals() public view returns(uint8) {
        return _decimals;
    }

    uint256[50] private ______gap;
}

// File: uFragments/contracts/lib/SafeMathInt.sol

/*
MIT License

Copyright (c) 2018 requestnetwork
Copyright (c) 2018 Fragments, Inc.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

pragma solidity ^0.5.0;


/**
 * @title SafeMathInt
 * @dev Math operations for int256 with overflow safety checks.
 */
library SafeMathInt {
    int256 private constant MIN_INT256 = int256(1) << 255;
    int256 private constant MAX_INT256 = ~(int256(1) << 255);

    /**
     * @dev Multiplies two int256 variables and fails on overflow.
     */
    function mul(int256 a, int256 b)
    internal
    pure
    returns (int256)
    {
        int256 c = a * b;

        // Detect overflow when multiplying MIN_INT256 with -1
        require(c != MIN_INT256 || (a & MIN_INT256) != (b & MIN_INT256));
        require((b == 0) || (c / b == a));
        return c;
    }

    /**
     * @dev Division of two int256 variables and fails on overflow.
     */
    function div(int256 a, int256 b)
    internal
    pure
    returns (int256)
    {
        // Prevent overflow when dividing MIN_INT256 by -1
        require(b != -1 || a != MIN_INT256);

        // Solidity already throws when dividing by 0.
        return a / b;
    }

    /**
     * @dev Subtracts two int256 variables and fails on overflow.
     */
    function sub(int256 a, int256 b)
    internal
    pure
    returns (int256)
    {
        int256 c = a - b;
        require((b >= 0 && c <= a) || (b < 0 && c > a));
        return c;
    }

    /**
     * @dev Adds two int256 variables and fails on overflow.
     */
    function add(int256 a, int256 b)
    internal
    pure
    returns (int256)
    {
        int256 c = a + b;
        require((b >= 0 && c >= a) || (b < 0 && c < a));
        return c;
    }

    /**
     * @dev Converts to absolute value, and fails on overflow.
     */
    function abs(int256 a)
    internal
    pure
    returns (int256)
    {
        require(a != MIN_INT256);
        return a < 0 ? -a : a;
    }
}

// File: uFragments/contracts/UFragments.sol

pragma solidity ^0.5.0;






/**
 * @title uFragments ERC20 token
 * @dev This is part of an implementation of the uFragments Ideal Money protocol.
 *      uFragments is a normal ERC20 token, but its supply can be adjusted by splitting and
 *      combining tokens proportionally across all wallets.
 *
 *      uFragment balances are internally represented with a hidden denomination, 'gons'.
 *      We support splitting the currency in expansion and combining the currency on contraction by
 *      changing the exchange rate between the hidden 'gons' and the public 'fragments'.
 */
contract vUSD is ERC20Detailed, Ownable {
    // PLEASE READ BEFORE CHANGING ANY ACCOUNTING OR MATH
    // Anytime there is division, there is a risk of numerical instability from rounding errors. In
    // order to minimize this risk, we adhere to the following guidelines:
    // 1) The conversion rate adopted is the number of gons that equals 1 fragment.
    //    The inverse rate must not be used--TOTAL_GONS is always the numerator and _totalSupply is
    //    always the denominator. (i.e. If you want to convert gons to fragments instead of
    //    multiplying by the inverse rate, you should divide by the normal rate)
    // 2) Gon balances converted into Fragments are always rounded down (truncated).
    //
    // We make the following guarantees:
    // - If address 'A' transfers x Fragments to address 'B'. A's resulting external balance will
    //   be decreased by precisely x Fragments, and B's external balance will be precisely
    //   increased by x Fragments.
    //
    // We do not guarantee that the sum of all balances equals the result of calling totalSupply().
    // This is because, for any conversion function 'f()' that has non-zero rounding error,
    // f(x0) + f(x1) + ... + f(xn) is not always equal to f(x0 + x1 + ... xn).
    using SafeMath for uint256;
    using SafeMathInt for int256;

    event LogRebase(uint256 indexed epoch, uint256 totalSupply);
    event LogMonetaryPolicyUpdated(address monetaryPolicy);

    // Used for authentication
    address public monetaryPolicy;

    modifier onlyMonetaryPolicy() {
        require(msg.sender == monetaryPolicy);
        _;
    }

    bool private rebasePausedDeprecated;
    bool private tokenPausedDeprecated;

    modifier validRecipient(address to) {
        require(to != address(0x0));
        require(to != address(this));
        _;
    }

    uint256 private constant DECIMALS = 9;
    uint256 private constant MAX_UINT256 = ~uint256(0);
    uint256 private constant INITIAL_FRAGMENTS_SUPPLY = 10 * 10**6 * 10**DECIMALS; // 10 million (locked in this base contract)

    // TOTAL_GONS is a multiple of INITIAL_FRAGMENTS_SUPPLY so that _gonsPerFragment is an integer.
    // Use the highest value that fits in a uint256 for max granularity.
    uint256 private constant TOTAL_GONS = MAX_UINT256 - (MAX_UINT256 % INITIAL_FRAGMENTS_SUPPLY);

    // MAX_SUPPLY = maximum integer < (sqrt(4*TOTAL_GONS + 1) - 1) / 2
    uint256 private constant MAX_SUPPLY = ~uint128(0);  // (2^128) - 1

    uint256 private _totalSupply;
    uint256 private _gonsPerFragment;
    mapping(address => uint256) private _gonBalances;

    // This is denominated in Fragments, because the gons-fragments conversion might change before
    // it's fully paid.
    mapping (address => mapping (address => uint256)) private _allowedFragments;

    mapping (address => bool) public minters;

    function addMinter(address _minter) public onlyOwner {
        minters[_minter] = true;
    }

    function removeMinter(address _minter) public onlyOwner {
        minters[_minter] = false;
    }

    function mint(address account, uint amount) public {
        require(minters[msg.sender], "!minter");
        require(account != address(0x0), "ERC20: mint to the zero address");
        uint256 gonValue = amount.mul(_gonsPerFragment);
        _totalSupply = _totalSupply.add(amount);
        _gonBalances[account] = _gonBalances[account].add(gonValue);
        emit Transfer(address(0x0), account, amount);
    }

    function burn(uint amount) public {
        require(msg.sender != address(0x0), "ERC20: burn from the zero address");
        uint256 gonValue = amount.mul(_gonsPerFragment);
        _gonBalances[msg.sender] = _gonBalances[msg.sender].sub(gonValue);
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(address(0x0), msg.sender, amount);
    }

    /**
     * @param monetaryPolicy_ The address of the monetary policy contract to use for authentication.
     */
    function setMonetaryPolicy(address monetaryPolicy_)
    external
    onlyOwner
    {
        monetaryPolicy = monetaryPolicy_;
        emit LogMonetaryPolicyUpdated(monetaryPolicy_);
    }

    /**
     * @dev Notifies Fragments contract about a new rebase cycle.
     * @param supplyDelta The number of new fragment tokens to add into circulation via expansion.
     * @return The total number of fragments after the supply adjustment.
     */
    function rebase(uint256 epoch, int256 supplyDelta)
    external
    onlyMonetaryPolicy
    returns (uint256)
    {
        if (supplyDelta == 0) {
            emit LogRebase(epoch, _totalSupply);
            return _totalSupply;
        }

        if (supplyDelta < 0) {
            _totalSupply = _totalSupply.sub(uint256(supplyDelta.abs()));
        } else {
            _totalSupply = _totalSupply.add(uint256(supplyDelta));
        }

        if (_totalSupply > MAX_SUPPLY) {
            _totalSupply = MAX_SUPPLY;
        }

        _gonsPerFragment = TOTAL_GONS.div(_totalSupply);

        // From this point forward, _gonsPerFragment is taken as the source of truth.
        // We recalculate a new _totalSupply to be in agreement with the _gonsPerFragment
        // conversion rate.
        // This means our applied supplyDelta can deviate from the requested supplyDelta,
        // but this deviation is guaranteed to be < (_totalSupply^2)/(TOTAL_GONS - _totalSupply).
        //
        // In the case of _totalSupply <= MAX_UINT128 (our current supply cap), this
        // deviation is guaranteed to be < 1, so we can omit this step. If the supply cap is
        // ever increased, it must be re-included.
        // _totalSupply = TOTAL_GONS.div(_gonsPerFragment)

        emit LogRebase(epoch, _totalSupply);
        return _totalSupply;
    }

    function initialize(address owner_)
    public
    initializer
    {
        ERC20Detailed.initialize("Value USD", "vUSD", uint8(DECIMALS));
        Ownable.initialize(owner_);

        rebasePausedDeprecated = false;
        tokenPausedDeprecated = false;

        _totalSupply = INITIAL_FRAGMENTS_SUPPLY;
        _gonBalances[address(this)] = TOTAL_GONS;
        _gonsPerFragment = TOTAL_GONS.div(_totalSupply);

        emit Transfer(address(0x0), owner_, _totalSupply);
    }

    /**
     * @return The total number of fragments.
     */
    function totalSupply()
    public
    view
    returns (uint256)
    {
        return _totalSupply;
    }

    /**
     * @param who The address to query.
     * @return The balance of the specified address.
     */
    function balanceOf(address who)
    public
    view
    returns (uint256)
    {
        return _gonBalances[who].div(_gonsPerFragment);
    }

    /**
     * @dev Transfer tokens to a specified address.
     * @param to The address to transfer to.
     * @param value The amount to be transferred.
     * @return True on success, false otherwise.
     */
    function transfer(address to, uint256 value)
    public
    validRecipient(to)
    returns (bool)
    {
        uint256 gonValue = value.mul(_gonsPerFragment);
        _gonBalances[msg.sender] = _gonBalances[msg.sender].sub(gonValue);
        _gonBalances[to] = _gonBalances[to].add(gonValue);
        emit Transfer(msg.sender, to, value);
        return true;
    }

    /**
     * @dev Function to check the amount of tokens that an owner has allowed to a spender.
     * @param owner_ The address which owns the funds.
     * @param spender The address which will spend the funds.
     * @return The number of tokens still available for the spender.
     */
    function allowance(address owner_, address spender)
    public
    view
    returns (uint256)
    {
        return _allowedFragments[owner_][spender];
    }

    /**
     * @dev Transfer tokens from one address to another.
     * @param from The address you want to send tokens from.
     * @param to The address you want to transfer to.
     * @param value The amount of tokens to be transferred.
     */
    function transferFrom(address from, address to, uint256 value)
    public
    validRecipient(to)
    returns (bool)
    {
        _allowedFragments[from][msg.sender] = _allowedFragments[from][msg.sender].sub(value);

        uint256 gonValue = value.mul(_gonsPerFragment);
        _gonBalances[from] = _gonBalances[from].sub(gonValue);
        _gonBalances[to] = _gonBalances[to].add(gonValue);
        emit Transfer(from, to, value);

        return true;
    }

    /**
     * @dev Approve the passed address to spend the specified amount of tokens on behalf of
     * msg.sender. This method is included for ERC20 compatibility.
     * increaseAllowance and decreaseAllowance should be used instead.
     * Changing an allowance with this method brings the risk that someone may transfer both
     * the old and the new allowance - if they are both greater than zero - if a transfer
     * transaction is mined before the later approve() call is mined.
     *
     * @param spender The address which will spend the funds.
     * @param value The amount of tokens to be spent.
     */
    function approve(address spender, uint256 value)
    public
    returns (bool)
    {
        _allowedFragments[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }

    /**
     * @dev Increase the amount of tokens that an owner has allowed to a spender.
     * This method should be used instead of approve() to avoid the double approval vulnerability
     * described above.
     * @param spender The address which will spend the funds.
     * @param addedValue The amount of tokens to increase the allowance by.
     */
    function increaseAllowance(address spender, uint256 addedValue)
    public
    returns (bool)
    {
        _allowedFragments[msg.sender][spender] =
        _allowedFragments[msg.sender][spender].add(addedValue);
        emit Approval(msg.sender, spender, _allowedFragments[msg.sender][spender]);
        return true;
    }

    /**
     * @dev Decrease the amount of tokens that an owner has allowed to a spender.
     *
     * @param spender The address which will spend the funds.
     * @param subtractedValue The amount of tokens to decrease the allowance by.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue)
    public
    returns (bool)
    {
        uint256 oldValue = _allowedFragments[msg.sender][spender];
        if (subtractedValue >= oldValue) {
            _allowedFragments[msg.sender][spender] = 0;
        } else {
            _allowedFragments[msg.sender][spender] = oldValue.sub(subtractedValue);
        }
        emit Approval(msg.sender, spender, _allowedFragments[msg.sender][spender]);
        return true;
    }
}

// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.7.6;
import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
import "@openzeppelin/contracts/token/ERC721/IERC721Metadata.sol";
import "@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol";
import "@openzeppelin/contracts/introspection/ERC165.sol";
import "@openzeppelin/contracts/utils/Address.sol";
import "@openzeppelin/contracts/utils/Strings.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/Pausable.sol";
import "./lib/InfluenceSettings.sol";
/**
 * @dev Contract that models each asteroid as an ERC721, non-fungible token.
 */
contract AsteroidToken is ERC165, IERC721, IERC721Metadata, Ownable, Pausable {
  using Address for address;
  using Strings for uint256;
  // Mapping from tokenId to owner address
  mapping (uint => address) private _tokenOwners;
  // Mapping from address to number of owned tokens
  mapping (address => uint) private _balances;
  // Mapping from token ID to approved address
  mapping (uint => address) private _tokenApprovals;
  // Mapping from owner to operator approvals
  mapping (address => mapping (address => bool)) private _operatorApprovals;
  // Mapping indicating allowed managers
  mapping (address => bool) private _managers;
  // Token name
  string private _name;
  // Token symbol
  string private _symbol;
  // Base URI
  string private _baseURI;
  /**
   * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
   */
  constructor (string memory name_, string memory symbol_) {
      _name = name_;
      _symbol = symbol_;
      // register the supported interfaces to conform to ERC721 via ERC165
      _registerInterface(type(IERC721).interfaceId);
      _registerInterface(type(IERC721Metadata).interfaceId);
  }
  // Modifier to check if calling contract has the correct minting role
   modifier onlyManagers {
     require(isManager(_msgSender()), "Only managers can call this function");
     _;
   }
  /**
   * @dev Add a new account / contract that can mint / burn asteroids
   * @param _manager Address of the new manager
   */
  function addManager(address _manager) external onlyOwner {
    _managers[_manager] = true;
  }
  /**
   * @dev Remove a current manager
   * @param _manager Address of the manager to be removed
   */
  function removeManager(address _manager) external onlyOwner {
    _managers[_manager] = false;
  }
  /**
   * @dev Checks if an address is a manager
   * @param _manager Address of contract / account to check
   */
  function isManager(address _manager) public view returns (bool) {
    return _managers[_manager];
  }
  /**
   * @dev Pauses the contract and prevents transfers / burns
   */
  function pause() external onlyOwner {
    _pause();
  }
  /**
   * @dev Unpauses the contract allowing transfers / burns
   */
  function unpause() external onlyOwner {
    _unpause();
  }
  /**
   * @dev Allowed managers (including sale contract) can mint initial asterodis
   * @param _to The purchaser's address
   * @param _tokenId The token ID to mint
   */
  function mint(address _to, uint256 _tokenId) external onlyManagers {
    _safeMint(_to, _tokenId);
  }
  /**
   * @dev Burns a token
   * @param _tokenId uint256 ID of the token being burned
   */
  function burn(uint256 _tokenId) external onlyManagers {
    _burn(_tokenId);
  }
  /**
   * @dev See {IERC721-balanceOf}.
   */
  function balanceOf(address owner) public view override returns (uint256) {
    require(owner != address(0), "ERC721: balance query for the zero address");
    return _balances[owner];
  }
  /**
   * @dev See {IERC721-ownerOf}.
   */
  function ownerOf(uint256 tokenId) public view override returns (address) {
    require(tokenId > 0 && tokenId <= InfluenceSettings.TOTAL_ASTEROIDS);
    return _tokenOwners[tokenId];
  }
  /**
   * @dev See {IERC721Metadata-name}.
   */
  function name() public view override returns (string memory) {
    return _name;
  }
  /**
   * @dev See {IERC721Metadata-symbol}.
   */
  function symbol() public view override returns (string memory) {
    return _symbol;
  }
  /**
   * @dev See {IERC721Metadata-tokenURI}.
   */
  function tokenURI(uint256 tokenId) public view override returns (string memory) {
    require(tokenId > 0 && tokenId <= InfluenceSettings.TOTAL_ASTEROIDS);
    string memory base = baseURI();
    return string(abi.encodePacked(base, tokenId.toString()));
  }
  /**
   * @dev External interface to set the base URI for all token IDs.
   */
  function setBaseURI(string memory baseURI_) external onlyOwner {
    _setBaseURI(baseURI_);
  }
  /**
  * @dev Returns the base URI set via {_setBaseURI}. This will be
  * automatically added as a prefix in {tokenURI} to each token's URI, or
  * to the token ID if no specific URI is set for that token ID.
  */
  function baseURI() public view returns (string memory) {
    return _baseURI;
  }
  /**
   * @dev See {IERC721Enumerable-totalSupply}. Enumerable extension is not implemented fully,
   * but totalSupply is included for better compatibility.
   */
  function totalSupply() public pure returns (uint256) {
    return InfluenceSettings.TOTAL_ASTEROIDS;
  }
  /**
   * @dev See {IERC721-approve}.
   */
  function approve(address to, uint256 tokenId) public override {
    address owner = ownerOf(tokenId);
    require(to != owner, "ERC721: approval to current owner");
    require(_msgSender() == owner || isApprovedForAll(owner, _msgSender()),
      "ERC721: approve caller is not owner nor approved for all"
    );
    _approve(to, tokenId);
  }
  /**
   * @dev See {IERC721-getApproved}.
   */
  function getApproved(uint256 tokenId) public view override returns (address) {
    require(_exists(tokenId), "ERC721: approved query for nonexistent token");
    return _tokenApprovals[tokenId];
  }
  /**
   * @dev See {IERC721-setApprovalForAll}.
   */
  function setApprovalForAll(address operator, bool approved) public override {
    require(operator != _msgSender(), "ERC721: approve to caller");
    _operatorApprovals[_msgSender()][operator] = approved;
    emit ApprovalForAll(_msgSender(), operator, approved);
  }
  /**
   * @dev See {IERC721-isApprovedForAll}.
   */
  function isApprovedForAll(address owner, address operator) public view override returns (bool) {
    return _operatorApprovals[owner][operator];
  }
  /**
   * @dev See {IERC721-transferFrom}.
   */
  function transferFrom(address from, address to, uint256 tokenId) public override {
    require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
    _transfer(from, to, tokenId);
  }
  /**
   * @dev See {IERC721-safeTransferFrom}.
   */
  function safeTransferFrom(address from, address to, uint256 tokenId) public override {
    safeTransferFrom(from, to, tokenId, "");
  }
  /**
   * @dev See {IERC721-safeTransferFrom}.
   */
  function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public override {
    require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
    _safeTransfer(from, to, tokenId, _data);
  }
  /**
   * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
   * are aware of the ERC721 protocol to prevent tokens from being forever locked.
   *
   * `_data` is additional data, it has no specified format and it is sent in call to `to`.
   *
   * This internal function is equivalent to {safeTransferFrom}, and can be used to e.g.
   * implement alternative mechanisms to perform token transfer, such as signature-based.
   *
   * Requirements:
   *
   * - `from` cannot be the zero address.
   * - `to` cannot be the zero address.
   * - `tokenId` token must exist and be owned by `from`.
   * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
   *
   * Emits a {Transfer} event.
   */
  function _safeTransfer(address from, address to, uint256 tokenId, bytes memory _data) internal {
    _transfer(from, to, tokenId);
    require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
  }
  /**
   * @dev Returns whether `tokenId` exists.
   *
   * Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
   *
   * Tokens start existing when they are minted (`_mint`).
   */
  function _exists(uint256 tokenId) internal view returns (bool) {
    return _tokenOwners[tokenId] != address(0);
  }
  /**
   * @dev Returns whether `spender` is allowed to manage `tokenId`.
   *
   * Requirements:
   *
   * - `tokenId` must exist.
   */
  function _isApprovedOrOwner(address spender, uint256 tokenId) internal view returns (bool) {
    require(_exists(tokenId), "ERC721: operator query for nonexistent token");
    address owner = ownerOf(tokenId);
    return (spender == owner || getApproved(tokenId) == spender || isApprovedForAll(owner, spender));
  }
  /**
   * @dev Safely mints `tokenId` and transfers it to `to`.
   *
   * Requirements:
   d*
   * - `tokenId` must not exist.
   * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received},
   * which is called upon a safe transfer.
   *
   * Emits a {Transfer} event.
   */
  function _safeMint(address to, uint256 tokenId) internal {
    _safeMint(to, tokenId, "");
  }
  /**
   * @dev Same as {xref-ERC721-_safeMint-address-uint256-}[`_safeMint`], with an additional `data` parameter which is
   * forwarded in {IERC721Receiver-onERC721Received} to contract recipients.
   */
  function _safeMint(address to, uint256 tokenId, bytes memory _data) internal onlyManagers {
    _mint(to, tokenId);
    require(_checkOnERC721Received(address(0), to, tokenId, _data),
      "ERC721: transfer to non ERC721Receiver implementer"
    );
  }
  /**
   * @dev Mints `tokenId` and transfers it to `to`.
   *
   * WARNING: Usage of this method is discouraged, use {_safeMint} whenever possible
   *
   * Requirements:
   *
   * - `tokenId` must not exist.
   * - `to` cannot be the zero address.
   *
   * Emits a {Transfer} event.
   */
  function _mint(address to, uint256 tokenId) internal whenNotPaused {
    require(tokenId > 0 && tokenId <= InfluenceSettings.TOTAL_ASTEROIDS, "Invalid token ID");
    require(to != address(0), "ERC721: mint to the zero address");
    require(!_exists(tokenId), "ERC721: token already minted");
    _balances[to]++;
    _tokenOwners[tokenId] = to;
    emit Transfer(address(0), to, tokenId);
  }
  /**
   * @dev Transfers `tokenId` from `from` to `to`.
   *  As opposed to {transferFrom}, this imposes no restrictions on msg.sender.
   *
   * Requirements:
   *
   * - `to` cannot be the zero address.
   * - `tokenId` token must be owned by `from`.
   *
   * Emits a {Transfer} event.
   */
  function _transfer(address from, address to, uint256 tokenId) internal whenNotPaused {
    require(ownerOf(tokenId) == from, "ERC721: transfer of token that is not own");
    require(to != address(0), "ERC721: transfer to the zero address");
    require(_balances[from] > 0); // Avoid overflows
    // Clear approvals from the previous owner
    _approve(address(0), tokenId);
    _balances[from] -= 1;
    _balances[to] += 1;
    _tokenOwners[tokenId] = to;
    emit Transfer(from, to, tokenId);
  }
  /**
   * @dev Destroys `tokenId`.
   * The approval is cleared when the token is burned.
   *
   * Requirements:
   *
   * - `tokenId` must exist.
   *
   * Emits a {Transfer} event.
   */
  function _burn(uint256 tokenId) internal whenNotPaused {
    require(_exists(tokenId), "ERC721: token not minted yet");
    address owner = ownerOf(tokenId);
    require(_balances[owner] > 0); // Avoid overflow
    // Clear approvals
    _approve(address(0), tokenId);
    _balances[owner] -= 1;
    delete _tokenOwners[tokenId];
    emit Transfer(owner, address(0), tokenId);
  }
  /**
   * @dev Internal function to set the base URI for all token IDs. It is
   * automatically added as a prefix to the value returned in {tokenURI},
   * or to the token ID if {tokenURI} is empty.
   */
  function _setBaseURI(string memory baseURI_) internal {
    _baseURI = baseURI_;
  }
  /**
   * @dev Internal function to invoke {IERC721Receiver-onERC721Received} on a target address.
   * The call is not executed if the target address is not a contract.
   *
   * @param from address representing the previous owner of the given token ID
   * @param to target address that will receive the tokens
   * @param tokenId uint256 ID of the token to be transferred
   * @param _data bytes optional data to send along with the call
   * @return bool whether the call correctly returned the expected magic value
   */
  function _checkOnERC721Received(
    address from,
    address to,
    uint256 tokenId,
    bytes memory _data
  ) private returns (bool) {
    if (to.isContract()) {
      try IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data) returns (bytes4 retval) {
        return retval == IERC721Receiver(to).onERC721Received.selector;
      } catch (bytes memory reason) {
        if (reason.length == 0) {
          revert("ERC721: transfer to non ERC721Receiver implementer");
        } else {
          // solhint-disable-next-line no-inline-assembly
          assembly {
            revert(add(32, reason), mload(reason))
          }
        }
      }
    } else {
      return true;
    }
  }
  function _approve(address to, uint256 tokenId) private {
    _tokenApprovals[tokenId] = to;
    emit Approval(ownerOf(tokenId), to, tokenId);
  }
}
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.7.0;
library InfluenceSettings {
  // Game constants
  bytes32 public constant MASTER_SEED = "influence";
  uint32 public constant MAX_RADIUS = 375142; // in meters
  uint32 public constant START_TIMESTAMP = 1609459200; // Zero date timestamp for orbits
  uint public constant TOTAL_ASTEROIDS = 250000;
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }
    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }
    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }
    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
import "./IERC165.sol";
/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
abstract contract ERC165 is IERC165 {
    /*
     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
     */
    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
    /**
     * @dev Mapping of interface ids to whether or not it's supported.
     */
    mapping(bytes4 => bool) private _supportedInterfaces;
    constructor () internal {
        // Derived contracts need only register support for their own interfaces,
        // we register support for ERC165 itself here
        _registerInterface(_INTERFACE_ID_ERC165);
    }
    /**
     * @dev See {IERC165-supportsInterface}.
     *
     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return _supportedInterfaces[interfaceId];
    }
    /**
     * @dev Registers the contract as an implementer of the interface defined by
     * `interfaceId`. Support of the actual ERC165 interface is automatic and
     * registering its interface id is not required.
     *
     * See {IERC165-supportsInterface}.
     *
     * Requirements:
     *
     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
     */
    function _registerInterface(bytes4 interfaceId) internal virtual {
        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
        _supportedInterfaces[interfaceId] = true;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.2 <0.8.0;
import "../../introspection/IERC165.sol";
/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
     */
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
    /**
     * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
     */
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
    /**
     * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
     */
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
    /**
     * @dev Returns the number of tokens in ``owner``'s account.
     */
    function balanceOf(address owner) external view returns (uint256 balance);
    /**
     * @dev Returns the owner of the `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function ownerOf(uint256 tokenId) external view returns (address owner);
    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId) external;
    /**
     * @dev Transfers `tokenId` token from `from` to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address from, address to, uint256 tokenId) external;
    /**
     * @dev Gives permission to `to` to transfer `tokenId` token to another account.
     * The approval is cleared when the token is transferred.
     *
     * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
     *
     * Requirements:
     *
     * - The caller must own the token or be an approved operator.
     * - `tokenId` must exist.
     *
     * Emits an {Approval} event.
     */
    function approve(address to, uint256 tokenId) external;
    /**
     * @dev Returns the account approved for `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function getApproved(uint256 tokenId) external view returns (address operator);
    /**
     * @dev Approve or remove `operator` as an operator for the caller.
     * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
     *
     * Requirements:
     *
     * - The `operator` cannot be the caller.
     *
     * Emits an {ApprovalForAll} event.
     */
    function setApprovalForAll(address operator, bool _approved) external;
    /**
     * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
     *
     * See {setApprovalForAll}
     */
    function isApprovedForAll(address owner, address operator) external view returns (bool);
    /**
      * @dev Safely transfers `tokenId` token from `from` to `to`.
      *
      * Requirements:
      *
      * - `from` cannot be the zero address.
      * - `to` cannot be the zero address.
      * - `tokenId` token must exist and be owned by `from`.
      * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
      * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
      *
      * Emits a {Transfer} event.
      */
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.2 <0.8.0;
import "./IERC721.sol";
/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Metadata is IERC721 {
    /**
     * @dev Returns the token collection name.
     */
    function name() external view returns (string memory);
    /**
     * @dev Returns the token collection symbol.
     */
    function symbol() external view returns (string memory);
    /**
     * @dev Returns the Uniform Resource Identifier (URI) for `tokenId` token.
     */
    function tokenURI(uint256 tokenId) external view returns (string memory);
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
interface IERC721Receiver {
    /**
     * @dev Whenever an {IERC721} `tokenId` token is transferred to this contract via {IERC721-safeTransferFrom}
     * by `operator` from `from`, this function is called.
     *
     * It must return its Solidity selector to confirm the token transfer.
     * If any other value is returned or the interface is not implemented by the recipient, the transfer will be reverted.
     *
     * The selector can be obtained in Solidity with `IERC721.onERC721Received.selector`.
     */
    function onERC721Received(address operator, address from, uint256 tokenId, bytes calldata data) external returns (bytes4);
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.2 <0.8.0;
/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.
        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }
    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");
        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }
    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }
    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }
    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly
                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
import "./Context.sol";
/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);
    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);
    bool private _paused;
    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor () internal {
        _paused = false;
    }
    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }
    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        require(!paused(), "Pausable: paused");
        _;
    }
    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        require(paused(), "Pausable: not paused");
        _;
    }
    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }
    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}
// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;
/**
 * @dev String operations.
 */
library Strings {
    /**
     * @dev Converts a `uint256` to its ASCII `string` representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol
        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        uint256 index = digits - 1;
        temp = value;
        while (temp != 0) {
            buffer[index--] = bytes1(uint8(48 + temp % 10));
            temp /= 10;
        }
        return string(buffer);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

// File: @openzeppelin/contracts/GSN/Context.sol

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: @openzeppelin/contracts/math/SafeMath.sol

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/utils/Address.sol

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies in extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/ERC20.sol

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;
    using Address for address;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name, string memory symbol) public {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

// File: @openzeppelin/contracts/token/ERC20/SafeERC20.sol

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    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));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @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).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: contracts/VALUE/ValueLiquidityToken.sol

/**
 * @notice Value Liquidity (VALUE) with Governance Alpha
 */
contract ValueLiquidityToken is ERC20 {
    using SafeERC20 for IERC20;
    using SafeMath for uint256;

    IERC20 public yfv;

    address public governance;
    uint256 public cap;
    uint256 public yfvLockedBalance;
    mapping(address => bool) public minters;

    event Deposit(address indexed dst, uint amount);
    event Withdrawal(address indexed src, uint amount);

    constructor (IERC20 _yfv, uint256 _cap) public ERC20("Value Liquidity", "VALUE") {
        governance = msg.sender;
        yfv = _yfv;
        cap = _cap;
    }

    function mint(address _to, uint256 _amount) public {
        require(msg.sender == governance || minters[msg.sender], "!governance && !minter");
        _mint(_to, _amount);
        _moveDelegates(address(0), _delegates[_to], _amount);
    }

    function burn(uint256 _amount) public {
        _burn(msg.sender, _amount);
        _moveDelegates(_delegates[msg.sender], address(0), _amount);
    }

    function burnFrom(address _account, uint256 _amount) public {
        uint256 decreasedAllowance = allowance(_account, msg.sender).sub(_amount, "ERC20: burn amount exceeds allowance");
        _approve(_account, msg.sender, decreasedAllowance);
        _burn(_account, _amount);
        _moveDelegates(_delegates[_account], address(0), _amount);
    }

    function setGovernance(address _governance) public {
        require(msg.sender == governance, "!governance");
        governance = _governance;
    }

    function addMinter(address _minter) public {
        require(msg.sender == governance, "!governance");
        minters[_minter] = true;
    }

    function removeMinter(address _minter) public {
        require(msg.sender == governance, "!governance");
        minters[_minter] = false;
    }

    function setCap(uint256 _cap) public {
        require(msg.sender == governance, "!governance");
        require(_cap.add(yfvLockedBalance) >= totalSupply(), "_cap (plus yfvLockedBalance) is below current supply");
        cap = _cap;
    }

    function deposit(uint256 _amount) public {
        yfv.safeTransferFrom(msg.sender, address(this), _amount);
        yfvLockedBalance = yfvLockedBalance.add(_amount);
        _mint(msg.sender, _amount);
        _moveDelegates(address(0), _delegates[msg.sender], _amount);
        Deposit(msg.sender, _amount);
    }

    function withdraw(uint256 _amount) public {
        yfvLockedBalance = yfvLockedBalance.sub(_amount, "There is not enough locked YFV to withdraw");
        yfv.safeTransfer(msg.sender, _amount);
        _burn(msg.sender, _amount);
        _moveDelegates(_delegates[msg.sender], address(0), _amount);
        Withdrawal(msg.sender, _amount);
    }

    // This function allows governance to take unsupported tokens out of the contract.
    // This is in an effort to make someone whole, should they seriously mess up.
    // There is no guarantee governance will vote to return these.
    // It also allows for removal of airdropped tokens.
    function governanceRecoverUnsupported(IERC20 _token, address _to, uint256 _amount) external {
        require(msg.sender == governance, "!governance");
        if (_token == yfv) {
            uint256 yfvBalance = yfv.balanceOf(address(this));
            require(_amount <= yfvBalance.sub(yfvLockedBalance), "cant withdraw more then stuck amount");
        }
        _token.safeTransfer(_to, _amount);
    }

    /**
     * @dev See {ERC20-_beforeTokenTransfer}.
     *
     * Requirements:
     *
     * - minted tokens must not cause the total supply to go over the cap.
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override {
        super._beforeTokenTransfer(from, to, amount);

        if (from == address(0)) {// When minting tokens
            require(totalSupply().add(amount) <= cap.add(yfvLockedBalance), "ERC20Capped: cap exceeded");
        }
    }

    // Copied and modified from YAM code:
    // https://github.com/yam-finance/yam-protocol/blob/master/contracts/token/YAMGovernanceStorage.sol
    // https://github.com/yam-finance/yam-protocol/blob/master/contracts/token/YAMGovernance.sol
    // Which is copied and modified from COMPOUND:
    // https://github.com/compound-finance/compound-protocol/blob/master/contracts/Governance/Comp.sol

    /// @dev A record of each accounts delegate
    mapping(address => address) internal _delegates;

    /// @notice A checkpoint for marking number of votes from a given block
    struct Checkpoint {
        uint32 fromBlock;
        uint256 votes;
    }

    /// @notice A record of votes checkpoints for each account, by index
    mapping(address => mapping(uint32 => Checkpoint)) public checkpoints;

    /// @notice The number of checkpoints for each account
    mapping(address => uint32) public numCheckpoints;

    /// @notice The EIP-712 typehash for the contract's domain
    bytes32 public constant DOMAIN_TYPEHASH = keccak256("EIP712Domain(string name,uint256 chainId,address verifyingContract)");

    /// @notice The EIP-712 typehash for the delegation struct used by the contract
    bytes32 public constant DELEGATION_TYPEHASH = keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");

    /// @notice A record of states for signing / validating signatures
    mapping(address => uint) public nonces;

    /// @notice An event thats emitted when an account changes its delegate
    event DelegateChanged(address indexed delegator, address indexed fromDelegate, address indexed toDelegate);

    /// @notice An event thats emitted when a delegate account's vote balance changes
    event DelegateVotesChanged(address indexed delegate, uint previousBalance, uint newBalance);

    /**
     * @notice Delegate votes from `msg.sender` to `delegatee`
     * @param delegator The address to get delegatee for
     */
    function delegates(address delegator)
    external
    view
    returns (address)
    {
        return _delegates[delegator];
    }

    /**
     * @notice Delegate votes from `msg.sender` to `delegatee`
     * @param delegatee The address to delegate votes to
     */
    function delegate(address delegatee) external {
        return _delegate(msg.sender, delegatee);
    }

    /**
     * @notice Delegates votes from signatory to `delegatee`
     * @param delegatee The address to delegate votes to
     * @param nonce The contract state required to match the signature
     * @param expiry The time at which to expire the signature
     * @param v The recovery byte of the signature
     * @param r Half of the ECDSA signature pair
     * @param s Half of the ECDSA signature pair
     */
    function delegateBySig(
        address delegatee,
        uint nonce,
        uint expiry,
        uint8 v,
        bytes32 r,
        bytes32 s
    )
        external
    {
        bytes32 domainSeparator = keccak256(
            abi.encode(
                DOMAIN_TYPEHASH,
                keccak256(bytes(name())),
                getChainId(),
                address(this)
            )
        );

        bytes32 structHash = keccak256(
            abi.encode(
                DELEGATION_TYPEHASH,
                delegatee,
                nonce,
                expiry
            )
        );

        bytes32 digest = keccak256(
            abi.encodePacked(
                "\x19\x01",
                domainSeparator,
                structHash
            )
        );
        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "VALUE::delegateBySig: invalid signature");
        require(nonce == nonces[signatory]++, "VALUE::delegateBySig: invalid nonce");
        require(now <= expiry, "VALUE::delegateBySig: signature expired");
        return _delegate(signatory, delegatee);
    }

    /**
     * @notice Gets the current votes balance for `account`
     * @param account The address to get votes balance
     * @return The number of current votes for `account`
     */
    function getCurrentVotes(address account)
        external
        view
        returns (uint256)
    {
        uint32 nCheckpoints = numCheckpoints[account];
        return nCheckpoints > 0 ? checkpoints[account][nCheckpoints - 1].votes : 0;
    }

    /**
     * @notice Determine the prior number of votes 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 account The address of the account to check
     * @param blockNumber The block number to get the vote balance at
     * @return The number of votes the account had as of the given block
     */
    function getPriorVotes(address account, uint blockNumber)
        external
        view
        returns (uint256)
    {
        require(blockNumber < block.number, "VALUE::getPriorVotes: not yet determined");

        uint32 nCheckpoints = numCheckpoints[account];
        if (nCheckpoints == 0) {
            return 0;
        }

        // First check most recent balance
        if (checkpoints[account][nCheckpoints - 1].fromBlock <= blockNumber) {
            return checkpoints[account][nCheckpoints - 1].votes;
        }

        // Next check implicit zero balance
        if (checkpoints[account][0].fromBlock > blockNumber) {
            return 0;
        }

        uint32 lower = 0;
        uint32 upper = nCheckpoints - 1;
        while (upper > lower) {
            uint32 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
            Checkpoint memory cp = checkpoints[account][center];
            if (cp.fromBlock == blockNumber) {
                return cp.votes;
            } else if (cp.fromBlock < blockNumber) {
                lower = center;
            } else {
                upper = center - 1;
            }
        }
        return checkpoints[account][lower].votes;
    }

    function _delegate(address delegator, address delegatee)
        internal
    {
        address currentDelegate = _delegates[delegator];
        uint256 delegatorBalance = balanceOf(delegator); // balance of underlying VALUEs (not scaled);
        _delegates[delegator] = delegatee;

        emit DelegateChanged(delegator, currentDelegate, delegatee);

        _moveDelegates(currentDelegate, delegatee, delegatorBalance);
    }

    function _moveDelegates(address srcRep, address dstRep, uint256 amount) internal {
        if (srcRep != dstRep && amount > 0) {
            if (srcRep != address(0)) {
                // decrease old representative
                uint32 srcRepNum = numCheckpoints[srcRep];
                uint256 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
                uint256 srcRepNew = srcRepOld.sub(amount);
                _writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
            }

            if (dstRep != address(0)) {
                // increase new representative
                uint32 dstRepNum = numCheckpoints[dstRep];
                uint256 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
                uint256 dstRepNew = dstRepOld.add(amount);
                _writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
            }
        }
    }

    function _writeCheckpoint(
        address delegatee,
        uint32 nCheckpoints,
        uint256 oldVotes,
        uint256 newVotes
    )
        internal
    {
        uint32 blockNumber = safe32(block.number, "VALUE::_writeCheckpoint: block number exceeds 32 bits");

        if (nCheckpoints > 0 && checkpoints[delegatee][nCheckpoints - 1].fromBlock == blockNumber) {
            checkpoints[delegatee][nCheckpoints - 1].votes = newVotes;
        } else {
            checkpoints[delegatee][nCheckpoints] = Checkpoint(blockNumber, newVotes);
            numCheckpoints[delegatee] = nCheckpoints + 1;
        }

        emit DelegateVotesChanged(delegatee, oldVotes, newVotes);
    }

    function safe32(uint n, string memory errorMessage) internal pure returns (uint32) {
        require(n < 2 ** 32, errorMessage);
        return uint32(n);
    }

    function getChainId() internal pure returns (uint) {
        uint256 chainId;
        assembly {chainId := chainid()}
        return chainId;
    }
}

/*
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                                                             Copyright by 1inch Corporation
                                                                 https://1inch.exchange

---
Deployer wallet address:
0x7E1E3334130355799F833ffec2D731BCa3E68aF6

Signed raw transaction for chainId 1:
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---
*/
// File: @openzeppelin/contracts/math/Math.sol

pragma solidity ^0.6.0;

/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    /**
     * @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, so we distribute
        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol

pragma solidity ^0.6.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: contracts/ChiToken.sol

pragma solidity ^0.6.0;





abstract contract ERC20WithoutTotalSupply is IERC20 {
    using SafeMath for uint256;

    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function allowance(address owner, address spender) public view override returns (uint256) {
        return _allowances[owner][spender];
    }

    function transfer(address recipient, uint256 amount) public override returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    function approve(address spender, uint256 amount) public override returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address sender, address recipient, uint256 amount) public override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    function _transfer(address sender, address recipient, uint256 amount) internal {
        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    function _approve(address owner, address spender, uint256 amount) internal {
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    function _mint(address account, uint256 amount) internal {
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    function _burn(address account, uint256 amount) internal {
        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        emit Transfer(account, address(0), amount);
    }

    function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(account, msg.sender, _allowances[account][msg.sender].sub(amount, "ERC20: burn amount exceeds allowance"));
    }
}


contract ChiToken is IERC20, ERC20WithoutTotalSupply {
    string constant public name = "Chi Gastoken by 1inch";
    string constant public symbol = "CHI";
    uint8 constant public decimals = 0;

    uint256 public totalMinted;
    uint256 public totalBurned;

    function totalSupply() public view override returns(uint256) {
        return totalMinted.sub(totalBurned);
    }

    function mint(uint256 value) public {
        uint256 offset = totalMinted;
        assembly {
            mstore(0, 0x746d4946c0e9F43F4Dee607b0eF1fA1c3318585733ff6000526015600bf30000)

            for {let i := div(value, 32)} i {i := sub(i, 1)} {
                pop(create2(0, 0, 30, add(offset, 0))) pop(create2(0, 0, 30, add(offset, 1)))
                pop(create2(0, 0, 30, add(offset, 2))) pop(create2(0, 0, 30, add(offset, 3)))
                pop(create2(0, 0, 30, add(offset, 4))) pop(create2(0, 0, 30, add(offset, 5)))
                pop(create2(0, 0, 30, add(offset, 6))) pop(create2(0, 0, 30, add(offset, 7)))
                pop(create2(0, 0, 30, add(offset, 8))) pop(create2(0, 0, 30, add(offset, 9)))
                pop(create2(0, 0, 30, add(offset, 10))) pop(create2(0, 0, 30, add(offset, 11)))
                pop(create2(0, 0, 30, add(offset, 12))) pop(create2(0, 0, 30, add(offset, 13)))
                pop(create2(0, 0, 30, add(offset, 14))) pop(create2(0, 0, 30, add(offset, 15)))
                pop(create2(0, 0, 30, add(offset, 16))) pop(create2(0, 0, 30, add(offset, 17)))
                pop(create2(0, 0, 30, add(offset, 18))) pop(create2(0, 0, 30, add(offset, 19)))
                pop(create2(0, 0, 30, add(offset, 20))) pop(create2(0, 0, 30, add(offset, 21)))
                pop(create2(0, 0, 30, add(offset, 22))) pop(create2(0, 0, 30, add(offset, 23)))
                pop(create2(0, 0, 30, add(offset, 24))) pop(create2(0, 0, 30, add(offset, 25)))
                pop(create2(0, 0, 30, add(offset, 26))) pop(create2(0, 0, 30, add(offset, 27)))
                pop(create2(0, 0, 30, add(offset, 28))) pop(create2(0, 0, 30, add(offset, 29)))
                pop(create2(0, 0, 30, add(offset, 30))) pop(create2(0, 0, 30, add(offset, 31)))
                offset := add(offset, 32)
            }

            for {let i := and(value, 0x1F)} i {i := sub(i, 1)} {
                pop(create2(0, 0, 30, offset))
                offset := add(offset, 1)
            }
        }

        _mint(msg.sender, value);
        totalMinted = offset;
    }

    function computeAddress2(uint256 salt) public view returns (address) {
        bytes32 _data = keccak256(
            abi.encodePacked(bytes1(0xff), address(this), salt, bytes32(0x3c1644c68e5d6cb380c36d1bf847fdbc0c7ac28030025a2fc5e63cce23c16348))
        );
        return address(uint256(_data));
    }

    function _destroyChildren(uint256 value) internal {
        uint256 _totalBurned = totalBurned;
        for (uint256 i = 0; i < value; i++) {
            computeAddress2(_totalBurned + i).call("");
        }
        totalBurned = _totalBurned + value;
    }

    function free(uint256 value) public returns (uint256)  {
        _burn(msg.sender, value);
        _destroyChildren(value);
        return value;
    }

    function freeUpTo(uint256 value) public returns (uint256) {
        return free(Math.min(value, balanceOf(msg.sender)));
    }

    function freeFrom(address from, uint256 value) public returns (uint256) {
        _burnFrom(from, value);
        _destroyChildren(value);
        return value;
    }

    function freeFromUpTo(address from, uint256 value) public returns (uint256) {
        return freeFrom(from, Math.min(Math.min(value, balanceOf(from)), allowance(from, msg.sender)));
    }
}

pragma solidity ^0.5.0;

contract YFVReferral {
    mapping(address => address) public referrers; // account_address -> referrer_address
    mapping(address => uint256) public referredCount; // referrer_address -> num_of_referred

    event Referral(address indexed referrer, address indexed farmer);

    // Standard contract ownership transfer.
    address public owner;
    address private nextOwner;

    mapping(address => bool) public isAdmin;

    constructor () public {
        owner = msg.sender;
    }

    // Standard modifier on methods invokable only by contract owner.
    modifier onlyOwner {
        require(msg.sender == owner, "OnlyOwner methods called by non-owner.");
        _;
    }

    modifier onlyAdmin {
        require(isAdmin[msg.sender], "OnlyAdmin methods called by non-admin.");
        _;
    }

    // Standard contract ownership transfer implementation,
    function approveNextOwner(address _nextOwner) external onlyOwner {
        require(_nextOwner != owner, "Cannot approve current owner.");
        nextOwner = _nextOwner;
    }

    function acceptNextOwner() external {
        require(msg.sender == nextOwner, "Can only accept preapproved new owner.");
        owner = nextOwner;
    }

    function setReferrer(address farmer, address referrer) public onlyAdmin {
        if (referrers[farmer] == address(0) && referrer != address(0)) {
            referrers[farmer] = referrer;
            referredCount[referrer] += 1;
            emit Referral(referrer, farmer);
        }
    }

    function getReferrer(address farmer) public view returns (address) {
        return referrers[farmer];
    }

    // Set admin status.
    function setAdminStatus(address _admin, bool _status) external onlyOwner {
        isAdmin[_admin] = _status;
    }

    event EmergencyERC20Drain(address token, address owner, uint256 amount);

    // owner can drain tokens that are sent here by mistake
    function emergencyERC20Drain(ERC20 token, uint amount) external onlyOwner {
        emit EmergencyERC20Drain(address(token), owner, amount);
        token.transfer(owner, amount);
    }
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 {
    function totalSupply() public view returns (uint256);

    function balanceOf(address _who) public view returns (uint256);

    function transfer(address _to, uint256 _value) public returns (bool);

    function allowance(address _owner, address _spender) public view returns (uint256);

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool);

    function approve(address _spender, uint256 _value) public returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}