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



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * 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);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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/Strings.sol



// 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);
    }
}

// File: @solv/v2-solidity-utils/contracts/access/AdminControl.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

import "../openzeppelin/utils/ContextUpgradeable.sol";
import "../openzeppelin/proxy/Initializable.sol";

abstract contract AdminControl is Initializable, ContextUpgradeable {

    event NewAdmin(address oldAdmin, address newAdmin);
    event NewPendingAdmin(address oldPendingAdmin, address newPendingAdmin);

    address public admin;
    address public pendingAdmin;

    modifier onlyAdmin() {
        require(_msgSender() == admin, "only admin");
        _;
    }

    function __AdminControl_init(address admin_) internal initializer {
        admin = admin_;
    }

    function setPendingAdmin(address newPendingAdmin_) external virtual onlyAdmin {
        emit NewPendingAdmin(pendingAdmin, newPendingAdmin_);
        pendingAdmin = newPendingAdmin_;        
    }

    function acceptAdmin() external virtual {
        require(_msgSender() == pendingAdmin, "only pending admin");
        emit NewAdmin(admin, pendingAdmin);
        admin = pendingAdmin;
        pendingAdmin = address(0);
    }

}
// File: @solv/v2-solidity-utils/contracts/helpers/ERC20TransferHelper.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;
import "../misc/Constants.sol";

interface ERC20Interface {
    function balanceOf(address account) external view returns (uint256);

    function transfer(address recipient, uint256 amount)
        external
        returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);
}

// helper methods for interacting with ERC20 tokens and sending ETH that do not consistently return true/false
library ERC20TransferHelper {
    function doTransferIn(
        address underlying,
        address from,
        uint256 amount
    ) internal returns (uint256) {
        if (underlying == Constants.ETH_ADDRESS) {
            // Sanity checks
            require(tx.origin == from || msg.sender == from, "sender mismatch");
            require(msg.value == amount, "value mismatch");

            return amount;
        } else {
            require(msg.value == 0, "don't support msg.value");
            uint256 balanceBefore = ERC20Interface(underlying).balanceOf(
                address(this)
            );
            (bool success, bytes memory data) = underlying.call(
                abi.encodeWithSelector(
                    ERC20Interface.transferFrom.selector,
                    from,
                    address(this),
                    amount
                )
            );
            require(
                success && (data.length == 0 || abi.decode(data, (bool))),
                "STF"
            );

            // Calculate the amount that was *actually* transferred
            uint256 balanceAfter = ERC20Interface(underlying).balanceOf(
                address(this)
            );
            require(
                balanceAfter >= balanceBefore,
                "TOKEN_TRANSFER_IN_OVERFLOW"
            );
            return balanceAfter - balanceBefore; // underflow already checked above, just subtract
        }
    }

    function doTransferOut(
        address underlying,
        address payable to,
        uint256 amount
    ) internal {
        if (underlying == Constants.ETH_ADDRESS) {
            (bool success, ) = to.call{value: amount}(new bytes(0));
            require(success, "STE");
        } else {
            (bool success, bytes memory data) = underlying.call(
                abi.encodeWithSelector(
                    ERC20Interface.transfer.selector,
                    to,
                    amount
                )
            );
            require(
                success && (data.length == 0 || abi.decode(data, (bool))),
                "ST"
            );
        }
    }

    function getCashPrior(address underlying_) internal view returns (uint256) {
        if (underlying_ == Constants.ETH_ADDRESS) {
            uint256 startingBalance = sub(address(this).balance, msg.value);
            return startingBalance;
        } else {
            ERC20Interface token = ERC20Interface(underlying_);
            return token.balanceOf(address(this));
        }
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }
}

// File: @solv/v2-solidity-utils/contracts/misc/BokkyPooBahsDateTimeLibrary.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.9.0;

// ----------------------------------------------------------------------------
// BokkyPooBah's DateTime Library v1.01
//
// A gas-efficient Solidity date and time library
//
// https://github.com/bokkypoobah/BokkyPooBahsDateTimeLibrary
//
// Tested date range 1970/01/01 to 2345/12/31
//
// Conventions:
// Unit      | Range         | Notes
// :-------- |:-------------:|:-----
// timestamp | >= 0          | Unix timestamp, number of seconds since 1970/01/01 00:00:00 UTC
// year      | 1970 ... 2345 |
// month     | 1 ... 12      |
// day       | 1 ... 31      |
// hour      | 0 ... 23      |
// minute    | 0 ... 59      |
// second    | 0 ... 59      |
// dayOfWeek | 1 ... 7       | 1 = Monday, ..., 7 = Sunday
//
//
// Enjoy. (c) BokkyPooBah / Bok Consulting Pty Ltd 2018-2019. The MIT Licence.
// ----------------------------------------------------------------------------

library BokkyPooBahsDateTimeLibrary {

    uint constant SECONDS_PER_DAY = 24 * 60 * 60;
    uint constant SECONDS_PER_HOUR = 60 * 60;
    uint constant SECONDS_PER_MINUTE = 60;
    int constant OFFSET19700101 = 2440588;

    uint constant DOW_MON = 1;
    uint constant DOW_TUE = 2;
    uint constant DOW_WED = 3;
    uint constant DOW_THU = 4;
    uint constant DOW_FRI = 5;
    uint constant DOW_SAT = 6;
    uint constant DOW_SUN = 7;

    // ------------------------------------------------------------------------
    // Calculate the number of days from 1970/01/01 to year/month/day using
    // the date conversion algorithm from
    //   http://aa.usno.navy.mil/faq/docs/JD_Formula.php
    // and subtracting the offset 2440588 so that 1970/01/01 is day 0
    //
    // days = day
    //      - 32075
    //      + 1461 * (year + 4800 + (month - 14) / 12) / 4
    //      + 367 * (month - 2 - (month - 14) / 12 * 12) / 12
    //      - 3 * ((year + 4900 + (month - 14) / 12) / 100) / 4
    //      - offset
    // ------------------------------------------------------------------------
    function _daysFromDate(uint year, uint month, uint day) internal pure returns (uint _days) {
        require(year >= 1970);
        int _year = int(year);
        int _month = int(month);
        int _day = int(day);

        int __days = _day
          - 32075
          + 1461 * (_year + 4800 + (_month - 14) / 12) / 4
          + 367 * (_month - 2 - (_month - 14) / 12 * 12) / 12
          - 3 * ((_year + 4900 + (_month - 14) / 12) / 100) / 4
          - OFFSET19700101;

        _days = uint(__days);
    }

    // ------------------------------------------------------------------------
    // Calculate year/month/day from the number of days since 1970/01/01 using
    // the date conversion algorithm from
    //   http://aa.usno.navy.mil/faq/docs/JD_Formula.php
    // and adding the offset 2440588 so that 1970/01/01 is day 0
    //
    // int L = days + 68569 + offset
    // int N = 4 * L / 146097
    // L = L - (146097 * N + 3) / 4
    // year = 4000 * (L + 1) / 1461001
    // L = L - 1461 * year / 4 + 31
    // month = 80 * L / 2447
    // dd = L - 2447 * month / 80
    // L = month / 11
    // month = month + 2 - 12 * L
    // year = 100 * (N - 49) + year + L
    // ------------------------------------------------------------------------
    function _daysToDate(uint _days) internal pure returns (uint year, uint month, uint day) {
        int __days = int(_days);

        int L = __days + 68569 + OFFSET19700101;
        int N = 4 * L / 146097;
        L = L - (146097 * N + 3) / 4;
        int _year = 4000 * (L + 1) / 1461001;
        L = L - 1461 * _year / 4 + 31;
        int _month = 80 * L / 2447;
        int _day = L - 2447 * _month / 80;
        L = _month / 11;
        _month = _month + 2 - 12 * L;
        _year = 100 * (N - 49) + _year + L;

        year = uint(_year);
        month = uint(_month);
        day = uint(_day);
    }

    function timestampFromDate(uint year, uint month, uint day) internal pure returns (uint timestamp) {
        timestamp = _daysFromDate(year, month, day) * SECONDS_PER_DAY;
    }
    function timestampFromDateTime(uint year, uint month, uint day, uint hour, uint minute, uint second) internal pure returns (uint timestamp) {
        timestamp = _daysFromDate(year, month, day) * SECONDS_PER_DAY + hour * SECONDS_PER_HOUR + minute * SECONDS_PER_MINUTE + second;
    }
    function timestampToDate(uint timestamp) internal pure returns (uint year, uint month, uint day) {
        (year, month, day) = _daysToDate(timestamp / SECONDS_PER_DAY);
    }
    function timestampToDateTime(uint timestamp) internal pure returns (uint year, uint month, uint day, uint hour, uint minute, uint second) {
        (year, month, day) = _daysToDate(timestamp / SECONDS_PER_DAY);
        uint secs = timestamp % SECONDS_PER_DAY;
        hour = secs / SECONDS_PER_HOUR;
        secs = secs % SECONDS_PER_HOUR;
        minute = secs / SECONDS_PER_MINUTE;
        second = secs % SECONDS_PER_MINUTE;
    }

    function isValidDate(uint year, uint month, uint day) internal pure returns (bool valid) {
        if (year >= 1970 && month > 0 && month <= 12) {
            uint daysInMonth = _getDaysInMonth(year, month);
            if (day > 0 && day <= daysInMonth) {
                valid = true;
            }
        }
    }
    function isValidDateTime(uint year, uint month, uint day, uint hour, uint minute, uint second) internal pure returns (bool valid) {
        if (isValidDate(year, month, day)) {
            if (hour < 24 && minute < 60 && second < 60) {
                valid = true;
            }
        }
    }
    function isLeapYear(uint timestamp) internal pure returns (bool leapYear) {
        (uint year,,) = _daysToDate(timestamp / SECONDS_PER_DAY);
        leapYear = _isLeapYear(year);
    }
    function _isLeapYear(uint year) internal pure returns (bool leapYear) {
        leapYear = ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0);
    }
    function isWeekDay(uint timestamp) internal pure returns (bool weekDay) {
        weekDay = getDayOfWeek(timestamp) <= DOW_FRI;
    }
    function isWeekEnd(uint timestamp) internal pure returns (bool weekEnd) {
        weekEnd = getDayOfWeek(timestamp) >= DOW_SAT;
    }
    function getDaysInMonth(uint timestamp) internal pure returns (uint daysInMonth) {
        (uint year, uint month,) = _daysToDate(timestamp / SECONDS_PER_DAY);
        daysInMonth = _getDaysInMonth(year, month);
    }
    function _getDaysInMonth(uint year, uint month) internal pure returns (uint daysInMonth) {
        if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) {
            daysInMonth = 31;
        } else if (month != 2) {
            daysInMonth = 30;
        } else {
            daysInMonth = _isLeapYear(year) ? 29 : 28;
        }
    }
    // 1 = Monday, 7 = Sunday
    function getDayOfWeek(uint timestamp) internal pure returns (uint dayOfWeek) {
        uint _days = timestamp / SECONDS_PER_DAY;
        dayOfWeek = (_days + 3) % 7 + 1;
    }

    function getYear(uint timestamp) internal pure returns (uint year) {
        (year,,) = _daysToDate(timestamp / SECONDS_PER_DAY);
    }
    function getMonth(uint timestamp) internal pure returns (uint month) {
        (,month,) = _daysToDate(timestamp / SECONDS_PER_DAY);
    }
    function getDay(uint timestamp) internal pure returns (uint day) {
        (,,day) = _daysToDate(timestamp / SECONDS_PER_DAY);
    }
    function getHour(uint timestamp) internal pure returns (uint hour) {
        uint secs = timestamp % SECONDS_PER_DAY;
        hour = secs / SECONDS_PER_HOUR;
    }
    function getMinute(uint timestamp) internal pure returns (uint minute) {
        uint secs = timestamp % SECONDS_PER_HOUR;
        minute = secs / SECONDS_PER_MINUTE;
    }
    function getSecond(uint timestamp) internal pure returns (uint second) {
        second = timestamp % SECONDS_PER_MINUTE;
    }

    function addYears(uint timestamp, uint _years) internal pure returns (uint newTimestamp) {
        (uint year, uint month, uint day) = _daysToDate(timestamp / SECONDS_PER_DAY);
        year += _years;
        uint daysInMonth = _getDaysInMonth(year, month);
        if (day > daysInMonth) {
            day = daysInMonth;
        }
        newTimestamp = _daysFromDate(year, month, day) * SECONDS_PER_DAY + timestamp % SECONDS_PER_DAY;
        require(newTimestamp >= timestamp);
    }
    function addMonths(uint timestamp, uint _months) internal pure returns (uint newTimestamp) {
        (uint year, uint month, uint day) = _daysToDate(timestamp / SECONDS_PER_DAY);
        month += _months;
        year += (month - 1) / 12;
        month = (month - 1) % 12 + 1;
        uint daysInMonth = _getDaysInMonth(year, month);
        if (day > daysInMonth) {
            day = daysInMonth;
        }
        newTimestamp = _daysFromDate(year, month, day) * SECONDS_PER_DAY + timestamp % SECONDS_PER_DAY;
        require(newTimestamp >= timestamp);
    }
    function addDays(uint timestamp, uint _days) internal pure returns (uint newTimestamp) {
        newTimestamp = timestamp + _days * SECONDS_PER_DAY;
        require(newTimestamp >= timestamp);
    }
    function addHours(uint timestamp, uint _hours) internal pure returns (uint newTimestamp) {
        newTimestamp = timestamp + _hours * SECONDS_PER_HOUR;
        require(newTimestamp >= timestamp);
    }
    function addMinutes(uint timestamp, uint _minutes) internal pure returns (uint newTimestamp) {
        newTimestamp = timestamp + _minutes * SECONDS_PER_MINUTE;
        require(newTimestamp >= timestamp);
    }
    function addSeconds(uint timestamp, uint _seconds) internal pure returns (uint newTimestamp) {
        newTimestamp = timestamp + _seconds;
        require(newTimestamp >= timestamp);
    }

    function subYears(uint timestamp, uint _years) internal pure returns (uint newTimestamp) {
        (uint year, uint month, uint day) = _daysToDate(timestamp / SECONDS_PER_DAY);
        year -= _years;
        uint daysInMonth = _getDaysInMonth(year, month);
        if (day > daysInMonth) {
            day = daysInMonth;
        }
        newTimestamp = _daysFromDate(year, month, day) * SECONDS_PER_DAY + timestamp % SECONDS_PER_DAY;
        require(newTimestamp <= timestamp);
    }
    function subMonths(uint timestamp, uint _months) internal pure returns (uint newTimestamp) {
        (uint year, uint month, uint day) = _daysToDate(timestamp / SECONDS_PER_DAY);
        uint yearMonth = year * 12 + (month - 1) - _months;
        year = yearMonth / 12;
        month = yearMonth % 12 + 1;
        uint daysInMonth = _getDaysInMonth(year, month);
        if (day > daysInMonth) {
            day = daysInMonth;
        }
        newTimestamp = _daysFromDate(year, month, day) * SECONDS_PER_DAY + timestamp % SECONDS_PER_DAY;
        require(newTimestamp <= timestamp);
    }
    function subDays(uint timestamp, uint _days) internal pure returns (uint newTimestamp) {
        newTimestamp = timestamp - _days * SECONDS_PER_DAY;
        require(newTimestamp <= timestamp);
    }
    function subHours(uint timestamp, uint _hours) internal pure returns (uint newTimestamp) {
        newTimestamp = timestamp - _hours * SECONDS_PER_HOUR;
        require(newTimestamp <= timestamp);
    }
    function subMinutes(uint timestamp, uint _minutes) internal pure returns (uint newTimestamp) {
        newTimestamp = timestamp - _minutes * SECONDS_PER_MINUTE;
        require(newTimestamp <= timestamp);
    }
    function subSeconds(uint timestamp, uint _seconds) internal pure returns (uint newTimestamp) {
        newTimestamp = timestamp - _seconds;
        require(newTimestamp <= timestamp);
    }

    function diffYears(uint fromTimestamp, uint toTimestamp) internal pure returns (uint _years) {
        require(fromTimestamp <= toTimestamp);
        (uint fromYear,,) = _daysToDate(fromTimestamp / SECONDS_PER_DAY);
        (uint toYear,,) = _daysToDate(toTimestamp / SECONDS_PER_DAY);
        _years = toYear - fromYear;
    }
    function diffMonths(uint fromTimestamp, uint toTimestamp) internal pure returns (uint _months) {
        require(fromTimestamp <= toTimestamp);
        (uint fromYear, uint fromMonth,) = _daysToDate(fromTimestamp / SECONDS_PER_DAY);
        (uint toYear, uint toMonth,) = _daysToDate(toTimestamp / SECONDS_PER_DAY);
        _months = toYear * 12 + toMonth - fromYear * 12 - fromMonth;
    }
    function diffDays(uint fromTimestamp, uint toTimestamp) internal pure returns (uint _days) {
        require(fromTimestamp <= toTimestamp);
        _days = (toTimestamp - fromTimestamp) / SECONDS_PER_DAY;
    }
    function diffHours(uint fromTimestamp, uint toTimestamp) internal pure returns (uint _hours) {
        require(fromTimestamp <= toTimestamp);
        _hours = (toTimestamp - fromTimestamp) / SECONDS_PER_HOUR;
    }
    function diffMinutes(uint fromTimestamp, uint toTimestamp) internal pure returns (uint _minutes) {
        require(fromTimestamp <= toTimestamp);
        _minutes = (toTimestamp - fromTimestamp) / SECONDS_PER_MINUTE;
    }
    function diffSeconds(uint fromTimestamp, uint toTimestamp) internal pure returns (uint _seconds) {
        require(fromTimestamp <= toTimestamp);
        _seconds = toTimestamp - fromTimestamp;
    }
}
// File: @solv/v2-solidity-utils/contracts/misc/Constants.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

library Constants {
    enum ClaimType {
        LINEAR,
        ONE_TIME,
        STAGED
    }

    enum VoucherType {
        STANDARD_VESTING,
        FLEXIBLE_DATE_VESTING,
        BOUNDING,
        DREAM
    }

    uint32 internal constant FULL_PERCENTAGE = 10000;
    
    address internal constant ETH_ADDRESS =
        0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
    address internal constant ZERO_ADDRESS = 
        0x0000000000000000000000000000000000000000;
}

// File: @solv/v2-solidity-utils/contracts/misc/StringConvertor.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

import '@openzeppelin/contracts/utils/Strings.sol';
import '@openzeppelin/contracts/math/SafeMath.sol';
import './BokkyPooBahsDateTimeLibrary.sol';

library StringConvertor {

    using Strings for uint256;
    using SafeMath for uint256;

    /**
     * @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);
    }

    function uint2decimal(uint256 self, uint8 decimals) 
        internal
        pure
        returns (bytes memory)
    {
        uint256 base = 10 ** decimals;
        string memory round = self.div(base).toString();
        string memory fraction = self.mod(base).toString();
        uint256 fractionLength = bytes(fraction).length;

        bytes memory fullStr = abi.encodePacked(round, '.');
        if (fractionLength < decimals) {
            for (uint8 i = 0; i < decimals - fractionLength; i++) {
                fullStr = abi.encodePacked(fullStr, '0');
            }
        }

        return abi.encodePacked(fullStr, fraction);
    }

    function trim(bytes memory self, uint256 cutLength) 
        internal 
        pure
        returns (bytes memory newString)
    {
        newString = new bytes(self.length - cutLength);
        uint256 index = newString.length;
        while (index-- > 0) {
            newString[index] = self[index];
        }
    }

    function addThousandsSeparator(bytes memory self) 
        internal
        pure
        returns (bytes memory newString) 
    {
        uint256 roundLength = 0;
        for (uint256 i = 0; i < self.length; i++) {
            if (self[i] != '.') {
                roundLength++;
            } else {
                break;
            }
        }

        if (roundLength <= 3) {
            newString = self;
        } else {
            newString = new bytes(self.length + (roundLength - 1) / 3);
            uint256 newIndex = 0;
            for (uint256 oriIndex = 0; oriIndex < self.length; oriIndex++) {
                newString[newIndex++] = self[oriIndex];
                if (oriIndex < roundLength - 1 && (roundLength - oriIndex - 1) % 3 == 0) {
                    newString[newIndex++] = ',';
                }
            }
        }
    }

    function addressToString(address self) 
        internal 
        pure 
        returns (string memory) 
    {
        bytes32 value = bytes32(uint256(self));
        bytes memory alphabet = "0123456789abcdef";

        bytes memory str = new bytes(42);
        str[0] = '0';
        str[1] = 'x';
        for (uint i = 0; i < 20; i++) {
            str[2+i*2] = alphabet[uint8(value[i + 12] >> 4)];
            str[3+i*2] = alphabet[uint8(value[i + 12] & 0x0f)];
        }
        return string(str);
    }

    function datetimeToString(uint256 timestamp) 
        internal
        pure
        returns (string memory)
    {
        (uint256 year, uint256 month, uint256 day, uint256 hour, uint256 minute, uint256 second)
            = BokkyPooBahsDateTimeLibrary.timestampToDateTime(timestamp);
        return 
            string(
                abi.encodePacked(
                    year.toString(), '/', 
                    month < 10 ? '0' : '', month.toString(), '/', 
                    day < 10 ? '0' : '', day.toString(), ' ',
                    hour < 10 ? '0' : '', hour.toString(), ':', 
                    minute < 10 ? '0' : '', minute.toString(), ':',
                    second < 10 ? '0' : '',  second.toString()
                )
            );
    }

    function dateToString(uint256 timestamp)
        internal
        pure
        returns (string memory)
    {
        (uint256 year, uint256 month, uint256 day)
            = BokkyPooBahsDateTimeLibrary.timestampToDate(timestamp);
        return 
            string(
                abi.encodePacked(
                    year.toString(), '/', 
                    month < 10 ? '0' : '', month.toString(), '/', 
                    day < 10 ? '0' : '', day.toString()
                )
            );
    }

    function uintArray2str(uint64[] memory array) 
        internal 
        pure 
        returns (string memory) 
    {
        bytes memory pack = abi.encodePacked('[');
        for (uint256 i = 0; i < array.length; i++) {
            if (i == array.length - 1) {
                pack = abi.encodePacked(pack, uint256(array[i]).toString());
            } else {
                pack = abi.encodePacked(pack, uint256(array[i]).toString(), ',');
            }
        }
        return string(abi.encodePacked(pack, ']'));
    }

    function percentArray2str(uint32[] memory array) 
        internal 
        pure 
        returns (string memory) 
    {
        bytes memory pack = abi.encodePacked('[');
        for (uint256 i = 0; i < array.length; i++) {
            bytes memory percent = abi.encodePacked('"', uint2decimal(array[i], 2), '%"');

            if (i == array.length - 1) {
                pack = abi.encodePacked(pack, percent);
            } else {
                pack = abi.encodePacked(pack, percent, ',');
            }
        }
        return string(abi.encodePacked(pack, ']'));
    }

}
// File: @solv/v2-solidity-utils/contracts/openzeppelin/introspection/ERC165Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC165Upgradeable.sol";
import "../proxy/Initializable.sol";

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
abstract contract ERC165Upgradeable is Initializable, IERC165Upgradeable {
    /*
     * 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;

    function __ERC165_init() internal initializer {
        __ERC165_init_unchained();
    }

    function __ERC165_init_unchained() internal initializer {
        // 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;
    }
    uint256[49] private __gap;
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/introspection/IERC165Upgradeable.sol



// 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 IERC165Upgradeable {
    /**
     * @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);
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/math/SafeMathUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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 SafeMathUpgradeable {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * 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);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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: @solv/v2-solidity-utils/contracts/openzeppelin/proxy/Initializable.sol



// SPDX-License-Identifier: MIT

// solhint-disable-next-line compiler-version
pragma solidity >=0.4.24 <0.8.0;

import "../utils/AddressUpgradeable.sol";

/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 *
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {UpgradeableProxy-constructor}.
 *
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 */
abstract 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 protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(_initializing || _isConstructor() || !_initialized, "Initializable: contract is already 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) {
        return !AddressUpgradeable.isContract(address(this));
    }
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/token/ERC20/ERC20Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/ContextUpgradeable.sol";
import "./IERC20Upgradeable.sol";
import "../../math/SafeMathUpgradeable.sol";
import "../../proxy/Initializable.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 ERC20Upgradeable is Initializable, ContextUpgradeable, IERC20Upgradeable {
    using SafeMathUpgradeable for uint256;

    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.
     */
    function __ERC20_init(string memory name_, string memory symbol_) internal initializer {
        __Context_init_unchained();
        __ERC20_init_unchained(name_, symbol_);
    }

    function __ERC20_init_unchained(string memory name_, string memory symbol_) internal initializer {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

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

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual 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 virtual returns (uint8) {
        return _decimals;
    }

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

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual 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 virtual {
        _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 { }
    uint256[44] private __gap;
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/token/ERC20/IERC20Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20Upgradeable {
    /**
     * @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: @solv/v2-solidity-utils/contracts/openzeppelin/token/ERC721/ERC721Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/ContextUpgradeable.sol";
import "./IERC721Upgradeable.sol";
import "./IERC721MetadataUpgradeable.sol";
import "./IERC721EnumerableUpgradeable.sol";
import "./IERC721ReceiverUpgradeable.sol";
import "../../introspection/ERC165Upgradeable.sol";
import "../../math/SafeMathUpgradeable.sol";
import "../../utils/AddressUpgradeable.sol";
import "../../utils/EnumerableSetUpgradeable.sol";
import "../../utils/EnumerableMapUpgradeable.sol";
import "../../utils/StringsUpgradeable.sol";
import "../../proxy/Initializable.sol";

/**
 * @title ERC721 Non-Fungible Token Standard basic implementation
 * @dev see https://eips.ethereum.org/EIPS/eip-721
 */
contract ERC721Upgradeable is Initializable, ContextUpgradeable, ERC165Upgradeable, IERC721Upgradeable, IERC721MetadataUpgradeable, IERC721EnumerableUpgradeable {
    using SafeMathUpgradeable for uint256;
    using AddressUpgradeable for address;
    using EnumerableSetUpgradeable for EnumerableSetUpgradeable.UintSet;
    using EnumerableMapUpgradeable for EnumerableMapUpgradeable.UintToAddressMap;
    using StringsUpgradeable for uint256;

    // Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
    // which can be also obtained as `IERC721Receiver(0).onERC721Received.selector`
    bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;

    // Mapping from holder address to their (enumerable) set of owned tokens
    mapping (address => EnumerableSetUpgradeable.UintSet) private _holderTokens;

    // Enumerable mapping from token ids to their owners
    EnumerableMapUpgradeable.UintToAddressMap private _tokenOwners;

    // Mapping from token ID to approved address
    mapping (uint256 => address) private _tokenApprovals;

    // Mapping from owner to operator approvals
    mapping (address => mapping (address => bool)) private _operatorApprovals;

    // Token name
    string private _name;

    // Token symbol
    string private _symbol;

    // Optional mapping for token URIs
    mapping (uint256 => string) private _tokenURIs;

    // Base URI
    string private _baseURI;

    /*
     *     bytes4(keccak256('balanceOf(address)')) == 0x70a08231
     *     bytes4(keccak256('ownerOf(uint256)')) == 0x6352211e
     *     bytes4(keccak256('approve(address,uint256)')) == 0x095ea7b3
     *     bytes4(keccak256('getApproved(uint256)')) == 0x081812fc
     *     bytes4(keccak256('setApprovalForAll(address,bool)')) == 0xa22cb465
     *     bytes4(keccak256('isApprovedForAll(address,address)')) == 0xe985e9c5
     *     bytes4(keccak256('transferFrom(address,address,uint256)')) == 0x23b872dd
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256)')) == 0x42842e0e
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)')) == 0xb88d4fde
     *
     *     => 0x70a08231 ^ 0x6352211e ^ 0x095ea7b3 ^ 0x081812fc ^
     *        0xa22cb465 ^ 0xe985e9c5 ^ 0x23b872dd ^ 0x42842e0e ^ 0xb88d4fde == 0x80ac58cd
     */
    bytes4 private constant _INTERFACE_ID_ERC721 = 0x80ac58cd;

    /*
     *     bytes4(keccak256('name()')) == 0x06fdde03
     *     bytes4(keccak256('symbol()')) == 0x95d89b41
     *     bytes4(keccak256('tokenURI(uint256)')) == 0xc87b56dd
     *
     *     => 0x06fdde03 ^ 0x95d89b41 ^ 0xc87b56dd == 0x5b5e139f
     */
    bytes4 private constant _INTERFACE_ID_ERC721_METADATA = 0x5b5e139f;

    /*
     *     bytes4(keccak256('totalSupply()')) == 0x18160ddd
     *     bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) == 0x2f745c59
     *     bytes4(keccak256('tokenByIndex(uint256)')) == 0x4f6ccce7
     *
     *     => 0x18160ddd ^ 0x2f745c59 ^ 0x4f6ccce7 == 0x780e9d63
     */
    bytes4 private constant _INTERFACE_ID_ERC721_ENUMERABLE = 0x780e9d63;

    /**
     * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
     */
    function __ERC721_init(string memory name_, string memory symbol_) internal initializer {
        __Context_init_unchained();
        __ERC165_init_unchained();
        __ERC721_init_unchained(name_, symbol_);
    }

    function __ERC721_init_unchained(string memory name_, string memory symbol_) internal initializer {
        _name = name_;
        _symbol = symbol_;

        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(_INTERFACE_ID_ERC721);
        _registerInterface(_INTERFACE_ID_ERC721_METADATA);
        _registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
    }

    /**
     * @dev See {IERC721-balanceOf}.
     */
    function balanceOf(address owner) public view virtual override returns (uint256) {
        require(owner != address(0), "ERC721: balance query for the zero address");
        return _holderTokens[owner].length();
    }

    /**
     * @dev See {IERC721-ownerOf}.
     */
    function ownerOf(uint256 tokenId) public view virtual override returns (address) {
        return _tokenOwners.get(tokenId, "ERC721: owner query for nonexistent token");
    }

    /**
     * @dev See {IERC721Metadata-name}.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev See {IERC721Metadata-symbol}.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
        require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");

        string memory _tokenURI = _tokenURIs[tokenId];
        string memory base = baseURI();

        // If there is no base URI, return the token URI.
        if (bytes(base).length == 0) {
            return _tokenURI;
        }
        // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
        if (bytes(_tokenURI).length > 0) {
            return string(abi.encodePacked(base, _tokenURI));
        }
        // If there is a baseURI but no tokenURI, concatenate the tokenID to the baseURI.
        return string(abi.encodePacked(base, tokenId.toString()));
    }

    /**
    * @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 virtual returns (string memory) {
        return _baseURI;
    }

    /**
     * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
        return _holderTokens[owner].at(index);
    }

    /**
     * @dev See {IERC721Enumerable-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        // _tokenOwners are indexed by tokenIds, so .length() returns the number of tokenIds
        return _tokenOwners.length();
    }

    /**
     * @dev See {IERC721Enumerable-tokenByIndex}.
     */
    function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
        (uint256 tokenId, ) = _tokenOwners.at(index);
        return tokenId;
    }

    /**
     * @dev See {IERC721-approve}.
     */
    function approve(address to, uint256 tokenId) public virtual override {
        address owner = ERC721Upgradeable.ownerOf(tokenId);
        require(to != owner, "ERC721: approval to current owner");

        require(_msgSender() == owner || ERC721Upgradeable.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 virtual 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 virtual 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 virtual override returns (bool) {
        return _operatorApprovals[owner][operator];
    }

    /**
     * @dev See {IERC721-transferFrom}.
     */
    function transferFrom(address from, address to, uint256 tokenId) public virtual override {
        //solhint-disable-next-line max-line-length
        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 virtual override {
        safeTransferFrom(from, to, tokenId, "");
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public virtual 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 virtual {
        _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`),
     * and stop existing when they are burned (`_burn`).
     */
    function _exists(uint256 tokenId) internal view virtual returns (bool) {
        return _tokenOwners.contains(tokenId);
    }

    /**
     * @dev Returns whether `spender` is allowed to manage `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual returns (bool) {
        require(_exists(tokenId), "ERC721: operator query for nonexistent token");
        address owner = ERC721Upgradeable.ownerOf(tokenId);
        return (spender == owner || getApproved(tokenId) == spender || ERC721Upgradeable.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 virtual {
        _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 virtual {
        _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 virtual {
        require(to != address(0), "ERC721: mint to the zero address");
        require(!_exists(tokenId), "ERC721: token already minted");

        _beforeTokenTransfer(address(0), to, tokenId);

        _holderTokens[to].add(tokenId);

        _tokenOwners.set(tokenId, to);

        emit Transfer(address(0), 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 virtual {
        address owner = ERC721Upgradeable.ownerOf(tokenId); // internal owner

        _beforeTokenTransfer(owner, address(0), tokenId);

        // Clear approvals
        _approve(address(0), tokenId);

        // Clear metadata (if any)
        if (bytes(_tokenURIs[tokenId]).length != 0) {
            delete _tokenURIs[tokenId];
        }

        _holderTokens[owner].remove(tokenId);

        _tokenOwners.remove(tokenId);

        emit Transfer(owner, address(0), 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 virtual {
        require(ERC721Upgradeable.ownerOf(tokenId) == from, "ERC721: transfer of token that is not own"); // internal owner
        require(to != address(0), "ERC721: transfer to the zero address");

        _beforeTokenTransfer(from, to, tokenId);

        // Clear approvals from the previous owner
        _approve(address(0), tokenId);

        _holderTokens[from].remove(tokenId);
        _holderTokens[to].add(tokenId);

        _tokenOwners.set(tokenId, to);

        emit Transfer(from, to, tokenId);
    }

    /**
     * @dev Sets `_tokenURI` as the tokenURI of `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _setTokenURI(uint256 tokenId, string memory _tokenURI) internal virtual {
        require(_exists(tokenId), "ERC721Metadata: URI set of nonexistent token");
        _tokenURIs[tokenId] = _tokenURI;
    }

    /**
     * @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 virtual {
        _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()) {
            return true;
        }
        bytes memory returndata = to.functionCall(abi.encodeWithSelector(
            IERC721ReceiverUpgradeable(to).onERC721Received.selector,
            _msgSender(),
            from,
            tokenId,
            _data
        ), "ERC721: transfer to non ERC721Receiver implementer");
        bytes4 retval = abi.decode(returndata, (bytes4));
        return (retval == _ERC721_RECEIVED);
    }

    /**
     * @dev Approve `to` to operate on `tokenId`
     *
     * Emits an {Approval} event.
     */
    function _approve(address to, uint256 tokenId) internal virtual {
        _tokenApprovals[tokenId] = to;
        emit Approval(ERC721Upgradeable.ownerOf(tokenId), to, tokenId); // internal owner
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning.
     *
     * Calling conditions:
     *
     * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
     * transferred to `to`.
     * - When `from` is zero, `tokenId` will be minted for `to`.
     * - When `to` is zero, ``from``'s `tokenId` will be burned.
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal virtual { }
    uint256[41] private __gap;
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/token/ERC721/IERC721EnumerableUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "./IERC721Upgradeable.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721EnumerableUpgradeable is IERC721Upgradeable {

    /**
     * @dev Returns the total amount of tokens stored by the contract.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns a token ID owned by `owner` at a given `index` of its token list.
     * Use along with {balanceOf} to enumerate all of ``owner``'s tokens.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) external view returns (uint256 tokenId);

    /**
     * @dev Returns a token ID at a given `index` of all the tokens stored by the contract.
     * Use along with {totalSupply} to enumerate all tokens.
     */
    function tokenByIndex(uint256 index) external view returns (uint256);
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/token/ERC721/IERC721MetadataUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "./IERC721Upgradeable.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721MetadataUpgradeable is IERC721Upgradeable {

    /**
     * @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);
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/token/ERC721/IERC721ReceiverUpgradeable.sol



// 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 IERC721ReceiverUpgradeable {
    /**
     * @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);
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/token/ERC721/IERC721Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

import "../../introspection/IERC165Upgradeable.sol";

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721Upgradeable is IERC165Upgradeable {
    /**
     * @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;
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/utils/AddressUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library AddressUpgradeable {
    /**
     * @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);
    }

    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);
            }
        }
    }
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/utils/ContextUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;
import "../proxy/Initializable.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 ContextUpgradeable is Initializable {
    function __Context_init() internal initializer {
        __Context_init_unchained();
    }

    function __Context_init_unchained() internal initializer {
    }
    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;
    }
    uint256[50] private __gap;
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/utils/EnumerableMapUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Library for managing an enumerable variant of Solidity's
 * https://solidity.readthedocs.io/en/latest/types.html#mapping-types[`mapping`]
 * type.
 *
 * Maps have the following properties:
 *
 * - Entries are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Entries are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableMap for EnumerableMap.UintToAddressMap;
 *
 *     // Declare a set state variable
 *     EnumerableMap.UintToAddressMap private myMap;
 * }
 * ```
 *
 * As of v3.0.0, only maps of type `uint256 -> address` (`UintToAddressMap`) are
 * supported.
 */
library EnumerableMapUpgradeable {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Map type with
    // bytes32 keys and values.
    // The Map implementation uses private functions, and user-facing
    // implementations (such as Uint256ToAddressMap) are just wrappers around
    // the underlying Map.
    // This means that we can only create new EnumerableMaps for types that fit
    // in bytes32.

    struct MapEntry {
        bytes32 _key;
        bytes32 _value;
    }

    struct Map {
        // Storage of map keys and values
        MapEntry[] _entries;

        // Position of the entry defined by a key in the `entries` array, plus 1
        // because index 0 means a key is not in the map.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Adds a key-value pair to a map, or updates the value for an existing
     * key. O(1).
     *
     * Returns true if the key was added to the map, that is if it was not
     * already present.
     */
    function _set(Map storage map, bytes32 key, bytes32 value) private returns (bool) {
        // We read and store the key's index to prevent multiple reads from the same storage slot
        uint256 keyIndex = map._indexes[key];

        if (keyIndex == 0) { // Equivalent to !contains(map, key)
            map._entries.push(MapEntry({ _key: key, _value: value }));
            // The entry is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            map._indexes[key] = map._entries.length;
            return true;
        } else {
            map._entries[keyIndex - 1]._value = value;
            return false;
        }
    }

    /**
     * @dev Removes a key-value pair from a map. O(1).
     *
     * Returns true if the key was removed from the map, that is if it was present.
     */
    function _remove(Map storage map, bytes32 key) private returns (bool) {
        // We read and store the key's index to prevent multiple reads from the same storage slot
        uint256 keyIndex = map._indexes[key];

        if (keyIndex != 0) { // Equivalent to contains(map, key)
            // To delete a key-value pair from the _entries array in O(1), we swap the entry to delete with the last one
            // in the array, and then remove the last entry (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = keyIndex - 1;
            uint256 lastIndex = map._entries.length - 1;

            // When the entry to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            MapEntry storage lastEntry = map._entries[lastIndex];

            // Move the last entry to the index where the entry to delete is
            map._entries[toDeleteIndex] = lastEntry;
            // Update the index for the moved entry
            map._indexes[lastEntry._key] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved entry was stored
            map._entries.pop();

            // Delete the index for the deleted slot
            delete map._indexes[key];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the key is in the map. O(1).
     */
    function _contains(Map storage map, bytes32 key) private view returns (bool) {
        return map._indexes[key] != 0;
    }

    /**
     * @dev Returns the number of key-value pairs in the map. O(1).
     */
    function _length(Map storage map) private view returns (uint256) {
        return map._entries.length;
    }

   /**
    * @dev Returns the key-value pair stored at position `index` in the map. O(1).
    *
    * Note that there are no guarantees on the ordering of entries inside the
    * array, and it may change when more entries are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Map storage map, uint256 index) private view returns (bytes32, bytes32) {
        require(map._entries.length > index, "EnumerableMap: index out of bounds");

        MapEntry storage entry = map._entries[index];
        return (entry._key, entry._value);
    }

    /**
     * @dev Tries to returns the value associated with `key`.  O(1).
     * Does not revert if `key` is not in the map.
     */
    function _tryGet(Map storage map, bytes32 key) private view returns (bool, bytes32) {
        uint256 keyIndex = map._indexes[key];
        if (keyIndex == 0) return (false, 0); // Equivalent to contains(map, key)
        return (true, map._entries[keyIndex - 1]._value); // All indexes are 1-based
    }

    /**
     * @dev Returns the value associated with `key`.  O(1).
     *
     * Requirements:
     *
     * - `key` must be in the map.
     */
    function _get(Map storage map, bytes32 key) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, "EnumerableMap: nonexistent key"); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }

    /**
     * @dev Same as {_get}, with a custom error message when `key` is not in the map.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {_tryGet}.
     */
    function _get(Map storage map, bytes32 key, string memory errorMessage) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, errorMessage); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }

    // UintToAddressMap

    struct UintToAddressMap {
        Map _inner;
    }

    /**
     * @dev Adds a key-value pair to a map, or updates the value for an existing
     * key. O(1).
     *
     * Returns true if the key was added to the map, that is if it was not
     * already present.
     */
    function set(UintToAddressMap storage map, uint256 key, address value) internal returns (bool) {
        return _set(map._inner, bytes32(key), bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the key was removed from the map, that is if it was present.
     */
    function remove(UintToAddressMap storage map, uint256 key) internal returns (bool) {
        return _remove(map._inner, bytes32(key));
    }

    /**
     * @dev Returns true if the key is in the map. O(1).
     */
    function contains(UintToAddressMap storage map, uint256 key) internal view returns (bool) {
        return _contains(map._inner, bytes32(key));
    }

    /**
     * @dev Returns the number of elements in the map. O(1).
     */
    function length(UintToAddressMap storage map) internal view returns (uint256) {
        return _length(map._inner);
    }

   /**
    * @dev Returns the element stored at position `index` in the set. O(1).
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintToAddressMap storage map, uint256 index) internal view returns (uint256, address) {
        (bytes32 key, bytes32 value) = _at(map._inner, index);
        return (uint256(key), address(uint160(uint256(value))));
    }

    /**
     * @dev Tries to returns the value associated with `key`.  O(1).
     * Does not revert if `key` is not in the map.
     *
     * _Available since v3.4._
     */
    function tryGet(UintToAddressMap storage map, uint256 key) internal view returns (bool, address) {
        (bool success, bytes32 value) = _tryGet(map._inner, bytes32(key));
        return (success, address(uint160(uint256(value))));
    }

    /**
     * @dev Returns the value associated with `key`.  O(1).
     *
     * Requirements:
     *
     * - `key` must be in the map.
     */
    function get(UintToAddressMap storage map, uint256 key) internal view returns (address) {
        return address(uint160(uint256(_get(map._inner, bytes32(key)))));
    }

    /**
     * @dev Same as {get}, with a custom error message when `key` is not in the map.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryGet}.
     */
    function get(UintToAddressMap storage map, uint256 key, string memory errorMessage) internal view returns (address) {
        return address(uint160(uint256(_get(map._inner, bytes32(key), errorMessage))));
    }
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/utils/EnumerableSetUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Library for managing
 * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
 * types.
 *
 * Sets have the following properties:
 *
 * - Elements are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Elements are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableSet for EnumerableSet.AddressSet;
 *
 *     // Declare a set state variable
 *     EnumerableSet.AddressSet private mySet;
 * }
 * ```
 *
 * As of v3.3.0, sets of type `bytes32` (`Bytes32Set`), `address` (`AddressSet`)
 * and `uint256` (`UintSet`) are supported.
 */
library EnumerableSetUpgradeable {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Set type with
    // bytes32 values.
    // The Set implementation uses private functions, and user-facing
    // implementations (such as AddressSet) are just wrappers around the
    // underlying Set.
    // This means that we can only create new EnumerableSets for types that fit
    // in bytes32.

    struct Set {
        // Storage of set values
        bytes32[] _values;

        // Position of the value in the `values` array, plus 1 because index 0
        // means a value is not in the set.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            // The value is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        // We read and store the value's index to prevent multiple reads from the same storage slot
        uint256 valueIndex = set._indexes[value];

        if (valueIndex != 0) { // Equivalent to contains(set, value)
            // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
            // the array, and then remove the last element (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;

            // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            bytes32 lastvalue = set._values[lastIndex];

            // Move the last value to the index where the value to delete is
            set._values[toDeleteIndex] = lastvalue;
            // Update the index for the moved value
            set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved value was stored
            set._values.pop();

            // Delete the index for the deleted slot
            delete set._indexes[value];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[index];
    }

    // Bytes32Set

    struct Bytes32Set {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _add(set._inner, value);
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _remove(set._inner, value);
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(Bytes32Set storage set, bytes32 value) internal view returns (bool) {
        return _contains(set._inner, value);
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(Bytes32Set storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(Bytes32Set storage set, uint256 index) internal view returns (bytes32) {
        return _at(set._inner, index);
    }

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint160(uint256(_at(set._inner, index))));
    }


    // UintSet

    struct UintSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/utils/ReentrancyGuardUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;
import "../proxy/Initializable.sol";

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuardUpgradeable is Initializable {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    function __ReentrancyGuard_init() internal initializer {
        __ReentrancyGuard_init_unchained();
    }

    function __ReentrancyGuard_init_unchained() internal initializer {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
    uint256[49] private __gap;
}

// File: @solv/v2-solidity-utils/contracts/openzeppelin/utils/StringsUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev String operations.
 */
library StringsUpgradeable {
    /**
     * @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);
    }
}

// File: @solv/v2-solver/contracts/interface/ISolver.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

interface ISolver {

    event SetOperationPaused (
        address product,
        string operation,
        bool setPaused
    );


    function isSolver() external pure returns (bool);

    function setOperationPaused(address product_, string calldata operation_, bool setPaused_) external;

    function operationAllowed(string calldata operation_, bytes calldata data_) external returns (uint256);

    function operationVerify(string calldata operation_, bytes calldata data_) external returns (uint256);
    
}
// File: @solv/v2-vnft-core/contracts/VNFTCoreV2.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

import "@solv/v2-solidity-utils/contracts/openzeppelin/token/ERC721/ERC721Upgradeable.sol";
import "@solv/v2-solidity-utils/contracts/openzeppelin/utils/EnumerableSetUpgradeable.sol";
import "./interface/IVNFT.sol";
import "./interface/optional/IVNFTMetadata.sol";

abstract contract VNFTCoreV2 is IVNFT, IVNFTMetadata, ERC721Upgradeable {
    using SafeMathUpgradeable for uint256;
    using AddressUpgradeable for address;
    using EnumerableSetUpgradeable for EnumerableSetUpgradeable.UintSet;

    struct ApproveUnits {
        address[] approvals;
        mapping(address => uint256) allowances;
    }

    /// @dev tokenId => units
    mapping(uint256 => uint256) internal _units;

    /// @dev tokenId => operator => units
    mapping(uint256 => ApproveUnits) private _tokenApprovalUnits;

    /// @dev slot => tokenIds
    mapping(uint256 => EnumerableSetUpgradeable.UintSet) private _slotTokens;

    uint8 internal _unitDecimals;

    function _initialize(
        string memory name_,
        string memory symbol_,
        uint8 unitDecimals_
    ) internal virtual {
        ERC721Upgradeable.__ERC721_init(name_, symbol_);
        ERC165Upgradeable._registerInterface(type(IVNFT).interfaceId);
        _unitDecimals = unitDecimals_;
    }

    function _safeTransferUnitsFrom(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 targetTokenId_,
        uint256 transferUnits_,
        bytes memory data_
    ) internal virtual {
        _transferUnitsFrom(
            from_,
            to_,
            tokenId_,
            targetTokenId_,
            transferUnits_
        );
        require(
            _checkOnVNFTReceived(
                from_,
                to_,
                targetTokenId_,
                transferUnits_,
                data_
            ),
            "to non VNFTReceiver implementer"
        );
    }

    function _transferUnitsFrom(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 targetTokenId_,
        uint256 transferUnits_
    ) internal virtual {
        require(from_ == ownerOf(tokenId_), "source token owner mismatch");
        require(to_ != address(0), "transfer to the zero address");

        _beforeTransferUnits(
            from_,
            to_,
            tokenId_,
            targetTokenId_,
            transferUnits_
        );

        // approve all后可不需要approve units
        if (_msgSender() != from_ && !isApprovedForAll(from_, _msgSender())) {
            _tokenApprovalUnits[tokenId_].allowances[
                _msgSender()
            ] = _tokenApprovalUnits[tokenId_].allowances[_msgSender()].sub(
                transferUnits_,
                "transfer units exceeds allowance"
            );
        }

        _units[tokenId_] = _units[tokenId_].sub(
            transferUnits_,
            "transfer excess units"
        );

        if (!_exists(targetTokenId_)) {
            _mintUnits(to_, targetTokenId_, _slotOf(tokenId_), transferUnits_);
        } else {
            require(
                ownerOf(targetTokenId_) == to_,
                "target token owner mismatch"
            );
            require(
                _slotOf(tokenId_) == _slotOf(targetTokenId_),
                "slot mismatch"
            );
            _units[targetTokenId_] = _units[targetTokenId_].add(transferUnits_);
        }

        emit TransferUnits(
            from_,
            to_,
            tokenId_,
            targetTokenId_,
            transferUnits_
        );
    }

    function _merge(uint256 tokenId_, uint256 targetTokenId_) internal virtual {
        require(
            _isApprovedOrOwner(_msgSender(), tokenId_),
            "VNFT: not owner nor approved"
        );
        require(tokenId_ != targetTokenId_, "self merge not allowed");
        require(_slotOf(tokenId_) == _slotOf(targetTokenId_), "slot mismatch");

        address owner = ownerOf(tokenId_);
        require(owner == ownerOf(targetTokenId_), "not same owner");

        uint256 mergeUnits = _units[tokenId_];
        _units[targetTokenId_] = _units[tokenId_].add(_units[targetTokenId_]);
        _burn(tokenId_);

        emit Merge(owner, tokenId_, targetTokenId_, mergeUnits);
    }

    function _split(
        uint256 tokenId_,
        uint256 newTokenId_,
        uint256 splitUnits_
    ) internal virtual {
        require(
            _isApprovedOrOwner(_msgSender(), tokenId_),
            "VNFT: not owner nor approved"
        );
        require(!_exists(newTokenId_), "new token already exists");

        _units[tokenId_] = _units[tokenId_].sub(splitUnits_);

        address owner = ownerOf(tokenId_);
        _mintUnits(owner, newTokenId_, _slotOf(tokenId_), splitUnits_);

        emit Split(owner, tokenId_, newTokenId_, splitUnits_);
    }

    function _mintUnits(
        address minter_,
        uint256 tokenId_,
        uint256 slot_,
        uint256 units_
    ) internal virtual {
        if (!_exists(tokenId_)) {
            ERC721Upgradeable._mint(minter_, tokenId_);
            _slotTokens[slot_].add(tokenId_);
        }

        _units[tokenId_] = _units[tokenId_].add(units_);
        emit TransferUnits(address(0), minter_, 0, tokenId_, units_);
    }

    function _burn(uint256 tokenId_) internal virtual override {
        address owner = ownerOf(tokenId_);
        uint256 slot = _slotOf(tokenId_);
        uint256 burnUnits = _units[tokenId_];

        _slotTokens[slot].remove(tokenId_);
        delete _units[tokenId_];

        ERC721Upgradeable._burn(tokenId_);
        emit TransferUnits(owner, address(0), tokenId_, 0, burnUnits);
    }

    function _burnUnits(uint256 tokenId_, uint256 burnUnits_)
        internal
        virtual
        returns (uint256 balance)
    {
        address owner = ownerOf(tokenId_);
        _units[tokenId_] = _units[tokenId_].sub(
            burnUnits_,
            "burn excess units"
        );

        emit TransferUnits(owner, address(0), tokenId_, 0, burnUnits_);
        return _units[tokenId_];
    }

    function approve(
        address to_,
        uint256 tokenId_,
        uint256 allowance_
    ) public virtual override {
        require(_msgSender() == ownerOf(tokenId_), "VNFT: only owner");
        _approveUnits(to_, tokenId_, allowance_);
    }

    function allowance(uint256 tokenId_, address spender_)
        public
        view
        virtual
        override
        returns (uint256)
    {
        return _tokenApprovalUnits[tokenId_].allowances[spender_];
    }

    /**
     * @dev Approve `to_` to operate on `tokenId_` within range of `allowance_`
     */
    function _approveUnits(
        address to_,
        uint256 tokenId_,
        uint256 allowance_
    ) internal virtual {
        if (_tokenApprovalUnits[tokenId_].allowances[to_] == 0) {
            _tokenApprovalUnits[tokenId_].approvals.push(to_);
        }
        _tokenApprovalUnits[tokenId_].allowances[to_] = allowance_;
        emit ApprovalUnits(to_, tokenId_, allowance_);
    }

    /**
     * @dev Clear existing approveUnits for `tokenId_`, including approved addresses and their approved units.
     */
    function _clearApproveUnits(uint256 tokenId_) internal virtual {
        ApproveUnits storage approveUnits = _tokenApprovalUnits[tokenId_];
        for (uint256 i = 0; i < approveUnits.approvals.length; i++) {
            delete approveUnits.allowances[approveUnits.approvals[i]];
            delete approveUnits.approvals[i];
        }
    }

    function unitDecimals() public view override returns (uint8) {
        return _unitDecimals;
    }

    function unitsInSlot(uint256 slot_)
        public
        view
        override
        returns (uint256 units_)
    {
        for (uint256 i = 0; i < tokensInSlot(slot_); i++) {
            units_ = units_.add(unitsInToken(tokenOfSlotByIndex(slot_, i)));
        }
    }

    function unitsInToken(uint256 tokenId_)
        public
        view
        virtual
        override
        returns (uint256)
    {
        return _units[tokenId_];
    }

    function tokensInSlot(uint256 slot_)
        public
        view
        override
        returns (uint256)
    {
        return _slotTokens[slot_].length();
    }

    function tokenOfSlotByIndex(uint256 slot_, uint256 index_)
        public
        view
        override
        returns (uint256)
    {
        return _slotTokens[slot_].at(index_);
    }

    function slotOf(uint256 tokenId_) public view override returns (uint256) {
        return _slotOf(tokenId_);
    }

    function _slotOf(uint256 tokenId_) internal view virtual returns (uint256);

    /**
     * @dev Before transferring or burning a token, the existing approveUnits should be cleared.
     */
    function _beforeTokenTransfer(
        address from_,
        address to_,
        uint256 tokenId_
    ) internal virtual override {
        if (from_ != address(0)) {
            _clearApproveUnits(tokenId_);
        }
    }

    function _beforeTransferUnits(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 targetTokenId_,
        uint256 transferUnits_
    ) internal virtual {}

    function _checkOnVNFTReceived(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 units_,
        bytes memory _data
    ) internal returns (bool) {
        if (!to_.isContract()) {
            return true;
        }
        bytes memory returndata = to_.functionCall(
            abi.encodeWithSelector(
                IVNFTReceiver(to_).onVNFTReceived.selector,
                _msgSender(),
                from_,
                tokenId_,
                units_,
                _data
            ),
            "non VNFTReceiver implementer"
        );
        bytes4 retval = abi.decode(returndata, (bytes4));
        /*b382cdcd  =>  onVNFTReceived(address,address,uint256,uint256,bytes)*/
        return (retval == type(IVNFTReceiver).interfaceId);
    }
}

// File: @solv/v2-vnft-core/contracts/interface/IVNFT.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

/* is ERC721, ERC165 */
interface IVNFT {
    event TransferUnits(
        address indexed from,
        address indexed to,
        uint256 indexed tokenId,
        uint256 targetTokenId,
        uint256 transferUnits
    );

    event Split(
        address indexed owner,
        uint256 indexed tokenId,
        uint256 newTokenId,
        uint256 splitUnits
    );

    event Merge(
        address indexed owner,
        uint256 indexed tokenId,
        uint256 indexed targetTokenId,
        uint256 mergeUnits
    );

    event ApprovalUnits(
        address indexed approval,
        uint256 indexed tokenId,
        uint256 allowance
    );

    function slotOf(uint256 tokenId) external view returns (uint256 slot);

    function unitDecimals() external view returns (uint8);

    function unitsInSlot(uint256 slot) external view returns (uint256);

    function tokensInSlot(uint256 slot)
        external
        view
        returns (uint256 tokenCount);

    function tokenOfSlotByIndex(uint256 slot, uint256 index)
        external
        view
        returns (uint256 tokenId);

    function unitsInToken(uint256 tokenId)
        external
        view
        returns (uint256 units);

    function approve(
        address to,
        uint256 tokenId,
        uint256 units
    ) external;

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

    function split(uint256 tokenId, uint256[] calldata units)
        external
        returns (uint256[] memory newTokenIds);

    function merge(uint256[] calldata tokenIds, uint256 targetTokenId) external;

    function transferFrom(
        address from,
        address to,
        uint256 tokenId,
        uint256 units
    ) external returns (uint256 newTokenId);

    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        uint256 units,
        bytes calldata data
    ) external returns (uint256 newTokenId);

    function transferFrom(
        address from,
        address to,
        uint256 tokenId,
        uint256 targetTokenId,
        uint256 units
    ) external;

    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        uint256 targetTokenId,
        uint256 units,
        bytes calldata data
    ) external;
}

interface IVNFTReceiver {
    function onVNFTReceived(
        address operator,
        address from,
        uint256 tokenId,
        uint256 units,
        bytes calldata data
    ) external returns (bytes4);
}

// File: @solv/v2-vnft-core/contracts/interface/optional/IVNFTMetadata.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

interface IVNFTMetadata /* is IERC721Metadata */ {
    function contractURI() external view returns (string memory);
    function slotURI(uint256 slot) external view returns (string memory);
}
// File: @solv/v2-voucher-core/contracts/VoucherCore.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

import "@solv/v2-solidity-utils/contracts/access/AdminControl.sol";
import "@solv/v2-solidity-utils/contracts/misc/Constants.sol";
import "@solv/v2-vnft-core/contracts/VNFTCoreV2.sol";

abstract contract VoucherCore is VNFTCoreV2, AdminControl {
    /// @dev tokenId => slot
    mapping(uint256 => uint256) public voucherSlotMapping;

    uint32 public nextTokenId;

    function _initialize(
        string memory name_,
        string memory symbol_,
        uint8 unitDecimals_
    ) internal override {
        AdminControl.__AdminControl_init(_msgSender());
        VNFTCoreV2._initialize(name_, symbol_, unitDecimals_);
        nextTokenId = 1;
    }

    function _generateTokenId() internal virtual returns (uint256) {
        return nextTokenId++;
    }

    function split(uint256 tokenId_, uint256[] calldata splitUnits_)
        public
        virtual
        override
        returns (uint256[] memory newTokenIds)
    {
        require(splitUnits_.length > 0, "empty splitUnits");
        newTokenIds = new uint256[](splitUnits_.length);

        for (uint256 i = 0; i < splitUnits_.length; i++) {
            uint256 newTokenId = _generateTokenId();
            newTokenIds[i] = newTokenId;
            VNFTCoreV2._split(tokenId_, newTokenId, splitUnits_[i]);
            voucherSlotMapping[newTokenId] = voucherSlotMapping[tokenId_];
        }
    }

    function merge(uint256[] calldata tokenIds_, uint256 targetTokenId_)
        public
        virtual
        override
    {
        require(tokenIds_.length > 0, "empty tokenIds");
        for (uint256 i = 0; i < tokenIds_.length; i++) {
            VNFTCoreV2._merge(tokenIds_[i], targetTokenId_);
            delete voucherSlotMapping[tokenIds_[i]];
        }
    }

    /**
     * @notice Transfer part of units of a Voucher to target address.
     * @param from_ Address of the Voucher sender
     * @param to_ Address of the Voucher recipient
     * @param tokenId_ Id of the Voucher to transfer
     * @param transferUnits_ Amount of units to transfer
     */
    function transferFrom(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 transferUnits_
    ) public virtual override returns (uint256 newTokenId) {
        newTokenId = _generateTokenId();
        _transferUnitsFrom(from_, to_, tokenId_, newTokenId, transferUnits_);
    }

    /**
     * @notice Transfer part of units of a Voucher to another Voucher.
     * @param from_ Address of the Voucher sender
     * @param to_ Address of the Voucher recipient
     * @param tokenId_ Id of the Voucher to transfer
     * @param targetTokenId_ Id of the Voucher to receive
     * @param transferUnits_ Amount of units to transfer
     */
    function transferFrom(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 targetTokenId_,
        uint256 transferUnits_
    ) public virtual override {
        require(_exists(targetTokenId_), "target token not exists");
        _transferUnitsFrom(
            from_,
            to_,
            tokenId_,
            targetTokenId_,
            transferUnits_
        );
    }

    function safeTransferFrom(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 transferUnits_,
        bytes memory data_
    ) public virtual override returns (uint256 newTokenId) {
        newTokenId = transferFrom(from_, to_, tokenId_, transferUnits_);
        require(
            _checkOnVNFTReceived(from_, to_, newTokenId, transferUnits_, data_),
            "to non VNFTReceiver"
        );
        return newTokenId;
    }

    function safeTransferFrom(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 targetTokenId_,
        uint256 transferUnits_,
        bytes memory data_
    ) public virtual override {
        transferFrom(from_, to_, tokenId_, targetTokenId_, transferUnits_);
        require(
            _checkOnVNFTReceived(
                from_,
                to_,
                targetTokenId_,
                transferUnits_,
                data_
            ),
            "to non VNFTReceiver"
        );
    }

    function _transferUnitsFrom(
        address from_,
        address to_,
        uint256 tokenId_,
        uint256 targetTokenId_,
        uint256 transferUnits_
    ) internal virtual override {
        VNFTCoreV2._transferUnitsFrom(
            from_,
            to_,
            tokenId_,
            targetTokenId_,
            transferUnits_
        );
        voucherSlotMapping[targetTokenId_] = voucherSlotMapping[tokenId_];
    }

    function _mint(
        address minter_,
        uint256 slot_,
        uint256 units_
    ) internal virtual returns (uint256 tokenId) {
        tokenId = _generateTokenId();
        voucherSlotMapping[tokenId] = slot_;
        VNFTCoreV2._mintUnits(minter_, tokenId, slot_, units_);
    }

    function burn(uint256 tokenId_) external virtual {
        require(_msgSender() == ownerOf(tokenId_), "only owner");
        _burnVoucher(tokenId_);
    }

    function _burnVoucher(uint256 tokenId_) internal virtual {
        delete voucherSlotMapping[tokenId_];
        VNFTCoreV2._burn(tokenId_);
    }

    function _slotOf(uint256 tokenId_)
        internal
        view
        virtual
        override
        returns (uint256)
    {
        return voucherSlotMapping[tokenId_];
    }

    function owner() external view virtual returns (address) {
        return admin;
    }

    function voucherType() external view virtual returns (Constants.VoucherType) {}

}

// File: base64-sol/base64.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0;

/// @title Base64
/// @author Brecht Devos - <brecht@loopring.org>
/// @notice Provides functions for encoding/decoding base64
library Base64 {
    string internal constant TABLE_ENCODE = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
    bytes  internal constant TABLE_DECODE = hex"0000000000000000000000000000000000000000000000000000000000000000"
                                            hex"00000000000000000000003e0000003f3435363738393a3b3c3d000000000000"
                                            hex"00000102030405060708090a0b0c0d0e0f101112131415161718190000000000"
                                            hex"001a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132330000000000";

    function encode(bytes memory data) internal pure returns (string memory) {
        if (data.length == 0) return '';

        // load the table into memory
        string memory table = TABLE_ENCODE;

        // multiply by 4/3 rounded up
        uint256 encodedLen = 4 * ((data.length + 2) / 3);

        // add some extra buffer at the end required for the writing
        string memory result = new string(encodedLen + 32);

        assembly {
            // set the actual output length
            mstore(result, encodedLen)

            // prepare the lookup table
            let tablePtr := add(table, 1)

            // input ptr
            let dataPtr := data
            let endPtr := add(dataPtr, mload(data))

            // result ptr, jump over length
            let resultPtr := add(result, 32)

            // run over the input, 3 bytes at a time
            for {} lt(dataPtr, endPtr) {}
            {
                // read 3 bytes
                dataPtr := add(dataPtr, 3)
                let input := mload(dataPtr)

                // write 4 characters
                mstore8(resultPtr, mload(add(tablePtr, and(shr(18, input), 0x3F))))
                resultPtr := add(resultPtr, 1)
                mstore8(resultPtr, mload(add(tablePtr, and(shr(12, input), 0x3F))))
                resultPtr := add(resultPtr, 1)
                mstore8(resultPtr, mload(add(tablePtr, and(shr( 6, input), 0x3F))))
                resultPtr := add(resultPtr, 1)
                mstore8(resultPtr, mload(add(tablePtr, and(        input,  0x3F))))
                resultPtr := add(resultPtr, 1)
            }

            // padding with '='
            switch mod(mload(data), 3)
            case 1 { mstore(sub(resultPtr, 2), shl(240, 0x3d3d)) }
            case 2 { mstore(sub(resultPtr, 1), shl(248, 0x3d)) }
        }

        return result;
    }

    function decode(string memory _data) internal pure returns (bytes memory) {
        bytes memory data = bytes(_data);

        if (data.length == 0) return new bytes(0);
        require(data.length % 4 == 0, "invalid base64 decoder input");

        // load the table into memory
        bytes memory table = TABLE_DECODE;

        // every 4 characters represent 3 bytes
        uint256 decodedLen = (data.length / 4) * 3;

        // add some extra buffer at the end required for the writing
        bytes memory result = new bytes(decodedLen + 32);

        assembly {
            // padding with '='
            let lastBytes := mload(add(data, mload(data)))
            if eq(and(lastBytes, 0xFF), 0x3d) {
                decodedLen := sub(decodedLen, 1)
                if eq(and(lastBytes, 0xFFFF), 0x3d3d) {
                    decodedLen := sub(decodedLen, 1)
                }
            }

            // set the actual output length
            mstore(result, decodedLen)

            // prepare the lookup table
            let tablePtr := add(table, 1)

            // input ptr
            let dataPtr := data
            let endPtr := add(dataPtr, mload(data))

            // result ptr, jump over length
            let resultPtr := add(result, 32)

            // run over the input, 4 characters at a time
            for {} lt(dataPtr, endPtr) {}
            {
               // read 4 characters
               dataPtr := add(dataPtr, 4)
               let input := mload(dataPtr)

               // write 3 bytes
               let output := add(
                   add(
                       shl(18, and(mload(add(tablePtr, and(shr(24, input), 0xFF))), 0xFF)),
                       shl(12, and(mload(add(tablePtr, and(shr(16, input), 0xFF))), 0xFF))),
                   add(
                       shl( 6, and(mload(add(tablePtr, and(shr( 8, input), 0xFF))), 0xFF)),
                               and(mload(add(tablePtr, and(        input , 0xFF))), 0xFF)
                    )
                )
                mstore(resultPtr, shl(232, output))
                resultPtr := add(resultPtr, 3)
            }
        }

        return result;
    }
}

// File: contracts/BondPool.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;
pragma abicoder v2;

import "@solv/v2-solidity-utils/contracts/access/AdminControl.sol";
import "@solv/v2-solidity-utils/contracts/openzeppelin/utils/ReentrancyGuardUpgradeable.sol";
import "@solv/v2-solidity-utils/contracts/openzeppelin/utils/EnumerableSetUpgradeable.sol";
import "@solv/v2-solidity-utils/contracts/openzeppelin/math/SafeMathUpgradeable.sol";
import "@solv/v2-solidity-utils/contracts/helpers/ERC20TransferHelper.sol";
import "@solv/v2-solidity-utils/contracts/openzeppelin/token/ERC20/ERC20Upgradeable.sol";
import "./interface/IBondPool.sol";

contract BondPool is IBondPool, AdminControl, ReentrancyGuardUpgradeable {
    
    using SafeMathUpgradeable for uint256;
    using EnumerableSetUpgradeable for EnumerableSetUpgradeable.UintSet;

    mapping(uint256 => SlotDetail) internal _slotDetails;

    mapping(address => EnumerableSetUpgradeable.UintSet) internal _issuerSlots;

    mapping(uint256 => uint256) public slotBalances;

    uint8 public valueDecimals;

    address public fundCurrency;

    address public voucher;

    string public issuerName;

    modifier onlyVoucher() {
        require(_msgSender() == voucher, "only voucher");
        _;
    }

    function initialize(uint8 valueDecimals_, address fundCurrency_, string calldata issuerName_) external initializer {
        AdminControl.__AdminControl_init(_msgSender());
        valueDecimals = valueDecimals_;
        fundCurrency = fundCurrency_;
        issuerName = issuerName_;
    }

    function createSlot(
        address issuer_,
        uint64 effectiveTime_,
        uint64 maturity_
    ) external onlyVoucher returns (uint256 slot) {
        validateSlotParams(issuer_, effectiveTime_, maturity_);

        slot = getSlot(issuer_, effectiveTime_, maturity_);
        require(!_slotDetails[slot].isValid, "slot already existed");

        SlotDetail storage slotDetail = _slotDetails[slot];
        slotDetail.issuer = issuer_;
        slotDetail.effectiveTime = effectiveTime_;
        slotDetail.maturity = maturity_;
        slotDetail.isValid = true;

        _issuerSlots[issuer_].add(slot);

        emit CreateSlot(slot, issuer_, effectiveTime_, maturity_);
    }

    function validateSlotParams(
        address issuer_,
        uint64 effectiveTime_,
        uint64 maturity_
    ) public pure {
        require(issuer_ != address(0), "issuer cannot be 0 address");
        require(effectiveTime_ > 0 && effectiveTime_ < maturity_, "invalid time");
    }

    function mint(
        address minter_,
        uint256 slot_,
        uint256 mintValue_
    ) external override nonReentrant onlyVoucher {
        require(minter_ != address(0), "minter cannot be 0 address");
        require(mintValue_ != 0, "mint value cannot be 0");
        SlotDetail storage slotDetail = _slotDetails[slot_];
        require(slotDetail.isValid, "invalid slot");
        require(
            !slotDetail.isIssuerRefunded && block.timestamp < slotDetail.maturity, 
            "non-mintable slot"
        );

        slotDetail.totalValue = slotDetail.totalValue.add(mintValue_);
        emit Mint(minter_, slot_, mintValue_);
    }

    function refund(uint256 slot_) external override nonReentrant {
        SlotDetail storage slotDetail = _slotDetails[slot_];
        require(slotDetail.isValid, "invalid slot");
        require(!slotDetail.isIssuerRefunded, "already refunded");

        slotDetail.isIssuerRefunded = true;

        uint8 currencyDecimals = ERC20Upgradeable(fundCurrency).decimals();
        uint256 currencyAmount = slotDetail.totalValue.mul(10**currencyDecimals).div(10**valueDecimals);

        slotBalances[slot_] = slotBalances[slot_].add(currencyAmount);
        ERC20TransferHelper.doTransferIn(fundCurrency,_msgSender(),currencyAmount);

        emit Refund(slot_, _msgSender(), currencyAmount);
    }

    function claim(uint256 slot_, address to_, uint256 claimValue_)
        external
        override
        onlyVoucher
        nonReentrant
        returns (uint256 claimCurrencyAmount)
    {
        SlotDetail storage slotDetail = _slotDetails[slot_];
        require(slotDetail.isValid, "invalid slot");
        require(slotDetail.isIssuerRefunded, "not refunded");

        claimCurrencyAmount = claimValue_
            .mul(10 ** ERC20Upgradeable(fundCurrency).decimals())
            .div(10 ** valueDecimals);

        if (claimCurrencyAmount > 0) {
            uint256 reservedCurrencyAmount = slotBalances[slot_];
            if (claimCurrencyAmount > reservedCurrencyAmount) {
                claimCurrencyAmount = reservedCurrencyAmount;
            }
            slotBalances[slot_] = reservedCurrencyAmount.sub(claimCurrencyAmount);
            ERC20TransferHelper.doTransferOut(fundCurrency, payable(to_), claimCurrencyAmount);
        }
    }

    function getSlot(
        address issuer_,
        uint64 effectiveTime_,
        uint64 maturity_
    ) public view returns (uint256) {
        return
            uint256(
                keccak256(
                    abi.encode(
                        voucher,
                        issuer_,
                        effectiveTime_,
                        maturity_
                    )
                )
            );
    }

    function getSlotDetail(uint256 slot_) external view returns (SlotDetail memory) {
        return _slotDetails[slot_];
    }

    function getIssuerSlots(address issuer_) external view returns (uint256[] memory slots) {
        slots = new uint256[](_issuerSlots[issuer_].length());
        for (uint256 i = 0; i < slots.length; i++) {
            slots[i] = _issuerSlots[issuer_].at(i);
        }
    }

    function getIssuerSlotDetails(address issuer_) external view returns (SlotDetail[] memory slotDetails) {
        slotDetails = new SlotDetail[](_issuerSlots[issuer_].length());
        for (uint256 i = 0; i < slotDetails.length; i++) {
            slotDetails[i] = _slotDetails[_issuerSlots[issuer_].at(i)];
        }
    }

    function setVoucher(address newVoucher_) external onlyAdmin {
        require(newVoucher_ != address(0), "new voucher cannot be 0 address");
        emit NewVoucher(voucher, newVoucher_);
        voucher = newVoucher_;
    }
    
}

// File: contracts/BondVoucher.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;
pragma abicoder v2;

import "@solv/v2-solidity-utils/contracts/openzeppelin/utils/ReentrancyGuardUpgradeable.sol";
import "@solv/v2-solidity-utils/contracts/openzeppelin/utils/EnumerableSetUpgradeable.sol";
import "@solv/v2-voucher-core/contracts/VoucherCore.sol";
import "@solv/v2-solver/contracts/interface/ISolver.sol";
import "./BondPool.sol";
import "./interface/IVNFTDescriptor.sol";
import "./interface/IBondVoucher.sol";

contract BondVoucher is IBondVoucher, VoucherCore, ReentrancyGuardUpgradeable {

    using SafeMathUpgradeable for uint256;
    using EnumerableSetUpgradeable for EnumerableSetUpgradeable.AddressSet;

    BondPool public bondPool;

    IVNFTDescriptor public voucherDescriptor;

    ISolver public solver;

    EnumerableSetUpgradeable.AddressSet internal _managers;

    modifier onlyManager {
        require(_managers.contains(_msgSender()), "only manager");
        _;
    }

    function initialize(
        address bondPool_,
        address voucherDescriptor_,
        address solver_,
        uint8 unitDecimals_,
        string calldata name_,
        string calldata symbol_
    )
        external
        initializer
    {
        ReentrancyGuardUpgradeable.__ReentrancyGuard_init();
        VoucherCore._initialize(name_, symbol_, unitDecimals_);

        bondPool = BondPool(bondPool_);
        voucherDescriptor = IVNFTDescriptor(voucherDescriptor_);
        solver = ISolver(solver_);

        ERC165Upgradeable._registerInterface(type(IBondVoucher).interfaceId);
    }

    function mint(
        address issuer_,
        uint64 effectiveTime_,
        uint64 maturity_,
        uint256 mintValue_
    ) 
        external 
        override 
        onlyManager
        nonReentrant
        returns (uint256 slot, uint256 tokenId) 
    {
        uint256 err = solver.operationAllowed(
            "mint", 
            abi.encode(
                _msgSender(),
                issuer_,
                effectiveTime_, 
                maturity_
            )
        );
        require(err == 0, "Solver: not allowed");

        slot = getSlot(issuer_, effectiveTime_, maturity_);
        if (!getSlotDetail(slot).isValid) {
            bondPool.createSlot(issuer_, effectiveTime_, maturity_);
        }

        bondPool.mint(_msgSender(), slot, mintValue_);
        tokenId = VoucherCore._mint(_msgSender(), slot, mintValue_);

        solver.operationVerify(
            "mint", 
            abi.encode(_msgSender(), issuer_, slot, tokenId, mintValue_)
        );
    }

    function claimAll(uint256 tokenId_) external override {
        claim(tokenId_, unitsInToken(tokenId_));
    }
    
    function claim(uint256 tokenId_, uint256 claimUnits_) public override {
        claimTo(tokenId_, _msgSender(), claimUnits_);
    }

    function claimTo(uint256 tokenId_, address to_, uint256 claimUnits_) public override nonReentrant {
        require(_msgSender() == ownerOf(tokenId_), "only owner");
        require(claimUnits_ <= unitsInToken(tokenId_), "over claim");

        uint256 err = solver.operationAllowed(
            "claim",
            abi.encode(_msgSender(), tokenId_, to_, claimUnits_)
        );
        require(err == 0, "Solver: not allowed");

        uint256 claimCurrencyAmount = bondPool.claim(voucherSlotMapping[tokenId_], to_, claimUnits_);

        if (claimUnits_ == unitsInToken(tokenId_)) {
            _burnVoucher(tokenId_);
        } else {
            _burnUnits(tokenId_, claimUnits_);
        }

        solver.operationVerify(
            "claim",
            abi.encode(_msgSender(), tokenId_, to_, claimUnits_)
        );

        emit Claim(tokenId_, to_, claimUnits_, claimCurrencyAmount);
    }

    function getSlot(
        address issuer_,
        uint64 effectiveTime_,
        uint64 maturity_
    ) 
        public  
        view 
        override 
        returns (uint256) 
    {
        return bondPool.getSlot(issuer_, effectiveTime_, maturity_);
    }

    function getSlotDetail(uint256 slot_) public view override returns (IBondPool.SlotDetail memory) {
        return bondPool.getSlotDetail(slot_);
    }

    function getIssuerSlots(address issuer_) external view override returns (uint256[] memory slots) {
        return bondPool.getIssuerSlots(issuer_);
    }
    
    function contractURI() external view override returns (string memory) {
        return voucherDescriptor.contractURI();
    }

    function slotURI(uint256 slot_) external view override returns (string memory) {
        return voucherDescriptor.slotURI(slot_);
    }

    function tokenURI(uint256 tokenId_) public view virtual override returns (string memory) {
        require(_exists(tokenId_), "token not exists");
        return voucherDescriptor.tokenURI(tokenId_);
    }

    function getSnapshot(uint256 tokenId_)
        public
        override
        view
        returns (BondVoucherSnapshot memory snapshot)
    {
        snapshot.tokenId = tokenId_;
        snapshot.parValue = unitsInToken(tokenId_);
        snapshot.slotDetail = bondPool.getSlotDetail(voucherSlotMapping[tokenId_]);
    }

    function setVoucherDescriptor(address newDescriptor_) external onlyAdmin {
        require(newDescriptor_ != address(0), "newDescriptor can not be 0 address");
        emit SetDescriptor(address(voucherDescriptor), newDescriptor_);
        voucherDescriptor = IVNFTDescriptor(newDescriptor_);
    }

    function setSolver(ISolver newSolver_) external onlyAdmin {
        require(newSolver_.isSolver(), "invalid solver");
        emit SetSolver(address(solver), address(newSolver_));
        solver = newSolver_;
    }

    function setManager(address newManager_, bool enabled_) external onlyAdmin {
        require(newManager_ != address(0), "manager can not be 0 address");
        emit SetManager(newManager_, enabled_);
        if (enabled_) {
            _managers.add(newManager_);
        } else {
            _managers.remove(newManager_);
        }
    }

    function voucherType() external pure override returns (Constants.VoucherType) {
        return Constants.VoucherType.BOUNDING;
    }

    function version() external pure returns (string memory) {
        return "1.0.1";
    }
}

// File: contracts/BondVoucherDescriptor.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;
pragma abicoder v2;

import "@solv/v2-solidity-utils/contracts/access/AdminControl.sol";
import "@solv/v2-solidity-utils/contracts/misc/StringConvertor.sol";
import "@solv/v2-solidity-utils/contracts/misc/BokkyPooBahsDateTimeLibrary.sol";
import "@solv/v2-solidity-utils/contracts/openzeppelin/token/ERC20/ERC20Upgradeable.sol";
import "./interface/IVNFTDescriptor.sol";
import "./interface/IVoucherSVG.sol";
import "./BondVoucher.sol";
import "./BondPool.sol";
import "base64-sol/base64.sol";

contract BondVoucherDescriptor is IVNFTDescriptor, AdminControl {

    event SetVoucherSVG(
        address indexed voucher,
        address oldVoucherSVG,
        address newVoucherSVG
    );

    event SetBondWarrant(
        address indexed voucher,
        uint256 indexed slot,
        string bondWarrant
    );

    using StringConvertor for address;
    using StringConvertor for uint256;
    using StringConvertor for bytes;

    // BondVoucher address => VoucherSVG address
    // Mapping value of 0x0 is defined as default VoucherSVG
    mapping(address => address) public voucherSVGs;

    // BondVoucher address => slot => bond warrant
    mapping(address => mapping(uint256 => string)) public bondWarrants;


    function initialize(address defaultVoucherSVG_) external initializer {
        AdminControl.__AdminControl_init(_msgSender());
        setVoucherSVG(address(0), defaultVoucherSVG_);
    }

    function setVoucherSVG(address voucher_, address voucherSVG_) public onlyAdmin {
        emit SetVoucherSVG(voucher_, voucherSVGs[voucher_], voucherSVG_);
        voucherSVGs[voucher_] = voucherSVG_;
    }

    function setBondWarrant(address voucher_, uint256 slot_, string calldata bondWarrant) external onlyAdmin {
        emit SetBondWarrant(voucher_, slot_, bondWarrant);
        bondWarrants[voucher_][slot_] = bondWarrant;
    }

    function contractURI() external view override returns (string memory) { 
        BondVoucher voucher = BondVoucher(_msgSender());
        return string(
            abi.encodePacked(
                'data:application/json;{"name":"', voucher.name(),
                '","description":"', _contractDescription(voucher),
                '","unitDecimals":"', uint256(voucher.unitDecimals()).toString(),
                '","properties":{}}'
            )
        );
    }

    function slotURI(uint256 slot_) external view override returns (string memory) {
        BondVoucher voucher = BondVoucher(_msgSender());
        BondPool pool = voucher.bondPool();
        BondPool.SlotDetail memory slotDetail = pool.getSlotDetail(slot_);

        return string(
            abi.encodePacked(
                'data:application/json;{"unitsInSlot":"', voucher.unitsInSlot(slot_).toString(),
                '","tokensInSlot":"', voucher.tokensInSlot(slot_).toString(),
                '","properties":', _properties(pool, slot_, slotDetail),
                '}'
            )
        );
    }

    function tokenURI(uint256 tokenId_)
        external
        view
        virtual
        override
        returns (string memory)
    {
        BondVoucher voucher = BondVoucher(_msgSender());
        BondPool pool = voucher.bondPool();

        uint256 slot = voucher.slotOf(tokenId_);
        BondPool.SlotDetail memory slotDetail = pool.getSlotDetail(slot);
        
        bytes memory name = abi.encodePacked(voucher.name(), ' #', tokenId_.toString());

        address voucherSVG = voucherSVGs[_msgSender()];
        if (voucherSVG == address(0)) {
            voucherSVG = voucherSVGs[address(0)];
        }
        string memory image = IVoucherSVG(voucherSVG).generateSVG(_msgSender(), tokenId_);

        return
            string(
                abi.encodePacked(
                    "data:application/json;base64,",
                    Base64.encode(
                        abi.encodePacked(
                            '{"name":"', name, 
                            '","description":"', _tokenDescription(voucher, tokenId_),
                            '","image":"data:image/svg+xml;base64,', Base64.encode(bytes(image)),
                            '","balance":"', voucher.unitsInToken(tokenId_).toString(),
                            '","slot":"', slot.toString(),
                            '","properties":', _properties(pool, slot, slotDetail),
                            '}'
                        )
                    )
                )
            );
    }

    function _contractDescription(BondVoucher voucher) 
        private 
        view
        returns (bytes memory)
    {
        return abi.encodePacked(
            voucher.name(), '\\n\\n',
            _descVoucher(), '\\n\\n', 
            _descAlert(), '\\n\\n', 
            _descProtocol()
        );
    }

    function _tokenDescription(
        BondVoucher voucher, 
        uint256 tokenId
    )
        private
        view
        returns (bytes memory)
    {
        return abi.encodePacked(
            voucher.name(), ' #', tokenId.toString(), '. \\n\\n',
            _descVoucher(), '\\n\\n', 
            abi.encodePacked(
                '- Voucher Address: ', address(voucher).addressToString(), '\\n',
                '- Pool Address: ', address(voucher.bondPool()).addressToString(), '\\n',
                "- Borrowed asset's address: ", voucher.bondPool().fundCurrency().addressToString()
            ),
            '\\n\\n',
            _descAlert()
        );
    }

    function _descAlert() private pure returns (string memory) {
        return
            string(
                abi.encodePacked(
                    unicode'⚠️ ', 
                    'Before you buy or make an offer: ',
                    '\\n\\n',
                    'Please be aware that the price displayed on this platform may not reflect the latest price change. For reliable price data, collateral report and repayment details, please visit the Solv dApp at app.solv.finance.'
                )
            );
    }

    function _descVoucher() private pure returns (string memory) {
        return 
            string(
                abi.encodePacked(
                    'Credit Bond is an ERC-3525-powered bond SFT to bridge TradFi with DeFi, tailor-made for crypto institutions such as market makers, VCs, and asset management protocols seeking to bootstrap liquidity, exercise market-neutral trading strategies, or fund operational expenses.',
                    '\\n\\n', 
                    'Credit Bond provides credit enhancement optionality including custody, collateral, insurance, bringing flexibility to build up credit profiles and fast-tracking lending processes. Institutional borrowers can issue a Credit Bond to get funded, customizing key financial terms in a no-code front end.',
                    '\\n\\n',
                    'To learn more about the Bond Voucher, read this doc: https://docs.solv.finance/solv-documentation/featured-products/bond-for-institutions'
                )
            );
    }

    function _descProtocol() private pure returns (string memory) {
        return 'Solv Protocol is the decentralized platform for creating, managing and trading Financial NFTs.';
    }

    function _properties(
        BondPool pool,
        uint256 slot,
        BondPool.SlotDetail memory slotDetail
    ) 
        private
        view
        returns (bytes memory data) 
    {
        string memory bondWarrant = bondWarrants[_msgSender()][slot];
        if (bytes(bondWarrant).length == 0) {
            bondWarrant = bondWarrants[_msgSender()][0];
        }

        return 
            abi.encodePacked(
                '{"issuer":"', slotDetail.issuer.addressToString(),
                '","issuerName":"', pool.issuerName(), 
                '","fundCurrency":"', pool.fundCurrency().addressToString(), 
                '","totalValue":"', _formatValue(slotDetail.totalValue, pool.valueDecimals()),
                '","effectiveTime":"', uint256(slotDetail.effectiveTime).datetimeToString(),
                '","maturity":"', uint256(slotDetail.maturity).datetimeToString(),
                '","bondWarrant":"', bondWarrant,
                '"}'
            );
    }

    function _formatValue(uint256 value, uint8 decimals) private pure returns (bytes memory) {
        return value.uint2decimal(decimals).trim(decimals - 2).addThousandsSeparator();
    }

}

// File: contracts/interface/IBondPool.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

interface IBondPool {

    struct SlotDetail {
        address issuer;
        uint256 totalValue;
        uint64 effectiveTime;
        uint64 maturity;
        bool isIssuerRefunded;
        bool isValid;
    }

    event NewVoucher(address oldVoucher, address newVoucher);

    event CreateSlot(
        uint256 indexed slot,
        address indexed issuer,
        uint64 effectiveTime,
        uint64 maturity
    );

    event Mint(
        address indexed minter,
        uint256 indexed slot,
        uint256 value
    );

    event Refund(uint256 indexed slot, address sender, uint256 refundAmount);

    function mint(
        address minter_,
        uint256 slot_,
        uint256 mintValue_
    ) external;

    function claim(
        uint256 slot_,
        address to_,
        uint256 claimValue_
    ) external returns (uint256);

    function refund(uint256 slot_) external;

}

// File: contracts/interface/IBondVoucher.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;
pragma abicoder v2;

import "./IBondPool.sol";

interface IBondVoucher {

    struct BondVoucherSnapshot {
        IBondPool.SlotDetail slotDetail;
        uint256 tokenId;
        uint256 parValue;
    }

    event SetDescriptor(address oldDescriptor, address newDescriptor);

    event SetSolver(address oldSolver, address newSolver);

    event SetManager(address manager, bool enabled);

    event Claim (
        uint256 indexed tokenId,
        address indexed to,
        uint256 claimUnits,
        uint256 claimCurrencyAmount
    );

    function mint(
        address issuer_,
        uint64 effectiveTime_,
        uint64 maturity_,
        uint256 mintValue_
    ) 
        external 
        returns (uint256 slot, uint256 tokenId);

    function claimAll(uint256 tokenId_) external;
    
    function claim(uint256 tokenId_, uint256 claimUnits_) external;

    function claimTo(uint256 tokenId_, address to_, uint256 claimUnits_) external;

    function getSlot(
        address issuer_,
        uint64 effectiveTime_,
        uint64 maturity_
    ) 
        external
        view 
        returns (uint256 slot);

    function getSlotDetail(uint256 slot_) 
        external 
        view 
        returns (IBondPool.SlotDetail memory);

    function getIssuerSlots(address issuer_) 
        external 
        view 
        returns (uint256[] memory slots);

    function getSnapshot(uint256 tokenId_)
        external
        view
        returns (BondVoucherSnapshot memory);

}
// File: contracts/interface/IVNFTDescriptor.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

interface IVNFTDescriptor {

    function contractURI() external view returns (string memory);
    function slotURI(uint256 slot) external view returns (string memory);
    function tokenURI(uint256 tokenId) external view returns (string memory);

}

// File: contracts/interface/IVoucherSVG.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.7.6;

interface IVoucherSVG {

    function generateSVG(address voucher_, uint256 tokenId_) external view returns (string memory);

}