// 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: 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/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);

}
// File: contracts/svgs/DefaultBondVoucherSVG.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/Constants.sol";
import "@solv/v2-solidity-utils/contracts/misc/StringConvertor.sol";
import "@solv/v2-solidity-utils/contracts/openzeppelin/token/ERC20/ERC20Upgradeable.sol";
import "../interface/IVoucherSVG.sol";
import "../BondVoucher.sol";
import "../BondPool.sol";

contract DefaultBondVoucherSVG is IVoucherSVG, AdminControl {

    using StringConvertor for uint256;
    using StringConvertor for bytes;
    
    struct SVGParams {
        address voucher;
        string voucherName;
        string issuerName;
        string currencyTokenSymbol;
        uint256 tokenId;
        uint256 parValue;
        uint64 effectiveTime;
        uint64 maturity;
        uint8 valueDecimals;
    }

    /// @dev voucher => claimType => background colors
    mapping(address => mapping(uint8 => string[])) public voucherBgColors;

    constructor(
        string[] memory linearBgColors_, 
        string[] memory onetimeBgColors_, 
        string[] memory stagedBgColors_
    ) {
        __AdminControl_init(_msgSender());
        setVoucherBgColors(address(0), linearBgColors_, onetimeBgColors_, stagedBgColors_);
    }

    function setVoucherBgColors(
        address voucher_,
        string[] memory linearBgColors_, 
        string[] memory onetimeBgColors_, 
        string[] memory stagedBgColors_
    )
        public 
        onlyAdmin 
    {
        voucherBgColors[voucher_][uint8(Constants.ClaimType.LINEAR)] = linearBgColors_;
        voucherBgColors[voucher_][uint8(Constants.ClaimType.ONE_TIME)] = onetimeBgColors_;
        voucherBgColors[voucher_][uint8(Constants.ClaimType.STAGED)] = stagedBgColors_;
    }
    
    function generateSVG(address voucher_, uint256 tokenId_) 
        external 
        virtual 
        override
        view 
        returns (string memory) 
    {
        BondVoucher bondVoucher = BondVoucher(voucher_);
        BondPool bondPool = bondVoucher.bondPool();

        BondVoucher.BondVoucherSnapshot memory snapshot = bondVoucher.getSnapshot(tokenId_);
        ERC20Upgradeable currencyToken = ERC20Upgradeable(bondPool.fundCurrency());

        SVGParams memory svgParams;
        svgParams.voucher = voucher_;
        svgParams.voucherName = bondVoucher.name();
        svgParams.issuerName = bondPool.issuerName();
        svgParams.currencyTokenSymbol = currencyToken.symbol();
        svgParams.tokenId = tokenId_;
        svgParams.parValue = snapshot.parValue;
        svgParams.effectiveTime = snapshot.slotDetail.effectiveTime;
        svgParams.maturity = snapshot.slotDetail.maturity;
        svgParams.valueDecimals = bondPool.valueDecimals();
        return _generateSVG(svgParams);
    }

    function _generateSVG(SVGParams memory params) 
        internal 
        virtual 
        view 
        returns (string memory) 
    {
        return 
            string(
                abi.encodePacked(
                    '<svg width="600px" height="400px" viewBox="0 0 600 400" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">',
                        _generateDefs(params),
                        '<g stroke-width="1" fill="none" fill-rule="evenodd" font-family="Arial">',
                            _generateBackground(params),
                            _generateTitle(params),
                            _generateMaturity(params),
                        '</g>',
                    '</svg>'
                )
            );
    }

    function _generateDefs(SVGParams memory params) internal virtual view returns (string memory) {
        string memory color0 = voucherBgColors[params.voucher][1].length > 0 ?
                               voucherBgColors[params.voucher][1][0] :
                               voucherBgColors[address(0)][1][0];
        string memory color1 = voucherBgColors[params.voucher][1].length > 1 ?
                               voucherBgColors[params.voucher][1][1] :
                               voucherBgColors[address(0)][1][1];

        return 
            string(
                abi.encodePacked(
                    '<defs>',
                        abi.encodePacked(
                            '<linearGradient x1="0" y1="50%" x2="100%" y2="50%" id="lg-1">',
                                '<stop stop-color="', color0, '" offset="0%"></stop>',
                                '<stop stop-color="', color1, '" offset="100%"></stop>',
                            '</linearGradient>',
                            '<linearGradient x1="0" y1="50%" x2="100%" y2="50%" id="lg-2">',
                                '<stop stop-color="#000000" stop-opacity="0" offset="0%"></stop>',
                                '<stop stop-color="#000000" offset="40%"></stop>',
                                '<stop stop-color="#000000" offset="55%"></stop>',
                                '<stop stop-color="#000000" stop-opacity="0" offset="100%"></stop>',
                            '</linearGradient>'
                        ),
                        abi.encodePacked(
                            '<linearGradient x1="0" y1="50%" x2="100%" y2="50%" id="lg-3">',
                                '<stop stop-color="#FFFFFF" stop-opacity="0" offset="0%"></stop>',
                                '<stop stop-color="#FFFFFF" offset="50%"></stop>',
                                '<stop stop-color="#FFFFFF" stop-opacity="0" offset="100%"></stop>',
                            '</linearGradient>',
                            '<linearGradient x1="82%" y1="18%" x2="25%" y2="65%" id="lg-4">',
                                '<stop stop-color="#FFFFFF" offset="0%"></stop>',
                                '<stop stop-color="#FFFFFF" stop-opacity="0" offset="100%"></stop>',
                            '</linearGradient>',
                            '<path id="text-path-a" d="M30 12 H570 A18 18 0 0 1 588 30 V370 A18 18 0 0 1 570 388 H30 A18 18 0 0 1 12 370 V30 A18 18 0 0 1 30 12 Z"/>'
                        ),
                    '</defs>'
                )
            );
    }

    function _generateBackground(SVGParams memory params) internal pure virtual returns (string memory) {
        return 
            string(
                abi.encodePacked(
                    // outline
                    '<rect fill="url(#lg-1)" x="0" y="0" width="600" height="400" rx="24"></rect>',
                    // border
                    '<rect stroke="#FFFFFF" x="16.5" y="16.5" width="567" height="367" rx="16"></rect>',
                    abi.encodePacked(
                        // rolling text
                        '<g text-rendering="optimizeSpeed" opacity="0.5" font-size="10" fill="#FFFFFF">',
                            '<text><textPath startOffset="-100%" xlink:href="#text-path-a">Issued by ', params.issuerName, '<animate additive="sum" attributeName="startOffset" from="0%" to="100%" begin="0s" dur="30s" repeatCount="indefinite"/></textPath></text>',
                            '<text><textPath startOffset="0%" xlink:href="#text-path-a">Issued by ', params.issuerName, '<animate additive="sum" attributeName="startOffset" from="0%" to="100%" begin="0s" dur="30s" repeatCount="indefinite"/></textPath></text>',
                            '<text><textPath startOffset="50%" xlink:href="#text-path-a">Powered by Solv Protocol<animate additive="sum" attributeName="startOffset" from="0%" to="100%" begin="0s" dur="30s" repeatCount="indefinite"/></textPath></text>',
                            '<text><textPath startOffset="-50%" xlink:href="#text-path-a">Powered by Solv Protocol<animate additive="sum" attributeName="startOffset" from="0%" to="100%" begin="0s" dur="30s" repeatCount="indefinite"/></textPath></text>',
                        '</g>'
                    ),
                    // bonding curve
                    '<g transform="translate(40, 92)">',
                        '<path d="M0,127 C0,127 0,127 0,127 L260,128 L260,128 L467,7" stroke="url(#lg-2)" stroke-width="20" opacity="0.1" stroke-linecap="round" stroke-linejoin="round"></path>',
                        '<polyline stroke="url(#lg-3)" stroke-width="6" stroke-linecap="round" stroke-linejoin="round" points="47 127 260 127 479 0"></polyline>',
                        '<path d="M413.3,12.5 L397,34 C385,19 385,19 385,19 L411,9.5 C412,9 414.5,9.5 413.5,12 Z" fill="url(#lg-4)" transform="rotate(-356)"></path>',
                        '<circle stroke="#FFFFFF" stroke-width="4" fill="#3CBF45" cx="260" cy="127.5" r="7"></circle>',
                    '</g>'
                )
            );
    }

    function _generateTitle(SVGParams memory params) internal pure virtual returns (string memory) {
        string memory tokenIdStr = params.tokenId.toString();
        uint256 tokenIdLeftMargin = 526 - 18 * bytes(tokenIdStr).length;
        return 
            string(
                abi.encodePacked(
                    '<text fill="#FFFFFF">',
                        '<tspan x="40" y="65" font-size="28">', params.voucherName, '</tspan>',
                        '<tspan x="40" y="120" font-size="36">', 
                            _formatValue(params.parValue, params.valueDecimals), 
                            '<tspan font-size="28"> ', params.currencyTokenSymbol, '</tspan>', 
                        '</tspan>',
                        '<tspan font-size="32" x="', tokenIdLeftMargin.toString(), '" y="69"># ', tokenIdStr, '</tspan>',
                    '</text>'
                )
            );
    }

    function _generateMaturity(SVGParams memory params) internal pure virtual returns (string memory) {
        return
            string(
                abi.encodePacked(
                    '<text font-size="14" fill="#FFFFFF">',
                        '<tspan x="40" y="350">Start Date: ',
                            uint256(params.effectiveTime).dateToString(),
                        '</tspan>',
                        '<tspan x="400" y="350">Maturity Date: ',
                            uint256(params.maturity).dateToString(),
                        '</tspan>',
                    '</text>'
                )
            );
    }

    function _formatValue(uint256 value, uint8 decimals) private pure returns (bytes memory) {
        return value.uint2decimal(decimals).trim(decimals - 4).addThousandsSeparator();
    }

}