// File: src/vaults/VaultPauser/HashnoteVaultPauser.sol



// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import {
    SafeERC20
} from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
import {IVaultPauser} from "../../interfaces/IVaultPauser.sol";
import {Vault} from "../../libraries/Vault.sol";
import {IHashnoteThetaVault} from "../../interfaces/IHashnoteThetaVault.sol";
import {IWETH} from "../../interfaces/IWETH.sol";
import {ShareMath} from "../../libraries/ShareMath.sol";

contract HashnoteVaultPauser is Ownable, IVaultPauser {
    using SafeERC20 for IERC20;

    /************************************************
     *  NON UPGRADEABLE STORAGE
     ***********************************************/

    /// @notice Stores all the vault's paused positions
    struct PauseReceipt {
        uint16 round;
        uint128 shares;
    }

    mapping(address => mapping(address => PauseReceipt)) public pausedPositions;
    mapping(address => bool) private registeredVaults;

    /************************************************
     *  IMMUTABLES & CONSTANTS
     ***********************************************/
    /// @notice WETH9 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2
    address public immutable WETH;
    address public immutable STETH;

    address public stethVault;
    address public keeper;
    /************************************************
     *  EVENTS
     ***********************************************/

    event Pause(
        address indexed account,
        address indexed vaultAddress,
        uint256 share,
        uint256 round
    );

    event Resume(
        address indexed account,
        address indexed vaultAddress,
        uint256 withdrawAmount
    );

    event Withdraw(
        address indexed account,
        address indexed vaultAddress,
        uint256 withdrawAmount
    );

    event ProcessWithdrawal(address indexed vaultAddress, uint256 round);

    /************************************************
     *  CONSTRUCTOR & INITIALIZATION
     ***********************************************/

    /**
     * @notice Initializes the contract with immutable variables
     */
    constructor(
        address _keeper,
        address _weth,
        address _steth
    ) {
        require(_keeper != address(0), "!_keeper");
        require(_weth != address(0), "!_weth");
        require(_steth != address(0), "!_steth");

        keeper = _keeper;
        WETH = _weth;
        STETH = _steth;
    }

    /**
     * @dev Throws if called by any account other than the keeper.
     */
    modifier onlyKeeper() {
        require(msg.sender == keeper, "!keeper");
        _;
    }

    /************************************************
     *  GETTERS
     ***********************************************/

    function getPausePosition(address _vaultAddress, address _userAddress)
        external
        view
        returns (PauseReceipt memory)
    {
        return pausedPositions[_vaultAddress][_userAddress];
    }

    /************************************************
     *  SETTERS
     ***********************************************/

    /**
     * @notice Sets the new keeper
     * @param _newKeeper is the address of the new keeper
     */
    function setNewKeeper(address _newKeeper) external onlyOwner {
        require(_newKeeper != address(0), "!newKeeper");
        keeper = _newKeeper;
    }

    /**
     * @notice add vault into registered vaults
     * @param _vaultAddress is the address of the new vault to be registered
     */
    function addVault(address _vaultAddress) external onlyOwner {
        registeredVaults[_vaultAddress] = true;
    }

    /**
     * @notice sets steth vaults
     * @param _newVault is the address of the new vault to be registered
     */
    function setStEthVault(address _newVault) external onlyOwner {
        require(_newVault != address(0), "!newVault");
        stethVault = _newVault;
    }

    /************************************************
     *  VAULT OPERATIONS
     ***********************************************/

    /**
     * @notice pause position from vault by redeem all the shares from vault to Pauser
     * @param _account user's address
     * @param _amount the amount of shares
     */
    function pausePosition(address _account, uint256 _amount)
        external
        override
    {
        address currentVaultAddress = msg.sender;
        IHashnoteThetaVault currentVault = IHashnoteThetaVault(currentVaultAddress);

        // check if vault is registered
        require(
            registeredVaults[currentVaultAddress],
            "Vault is not registered"
        );

        PauseReceipt storage pausedPosition =
            pausedPositions[currentVaultAddress][_account];

        // check if position is paused
        require(
            pausedPosition.shares == 0 && pausedPosition.round == 0,
            "Position is paused"
        );

        uint16 round = currentVault.vaultState().round;

        require(_amount < type(uint128).max, "_amount overflow");

        pausedPositions[currentVaultAddress][_account] = PauseReceipt({
            round: round,
            shares: uint128(_amount)
        });

        emit Pause(_account, currentVaultAddress, _amount, round);

        // transfer from user to pauser
        IERC20(currentVaultAddress).safeTransferFrom(
            _account,
            address(this),
            _amount
        );

        currentVault.initiateWithdraw(_amount);
    }

    /**
     * @notice resume user's position into vault by making a deposit
     * @param _vaultAddress vault's address
     */
    function resumePositionOrWithdraw(address _vaultAddress, address _destination) external override {
        require(_destination != address(0), "!destination");

        IHashnoteThetaVault currentVault = IHashnoteThetaVault(_vaultAddress);

        // check if vault is registered
        require(registeredVaults[_vaultAddress], "Vault is not registered");

        // get params and round
        Vault.VaultParams memory currentParams = currentVault.vaultParams();
        uint256 round = currentVault.vaultState().round;

        PauseReceipt storage pauseReceipt =
            pausedPositions[_vaultAddress][msg.sender];
        uint256 pauseReceiptRound = pauseReceipt.round;

        // check if round is closed before resuming position
        require(pauseReceiptRound < round, "Round not closed yet");
        uint256 totalWithdrawAmount =
            ShareMath.sharesToAsset(
                pauseReceipt.shares,
                currentVault.roundPricePerShare(pauseReceiptRound),
                currentParams.decimals
            );

        // delete position once transfer (revert to zero)
        delete pausedPositions[_vaultAddress][msg.sender];

        // stETH transfers suffer from an off-by-1 error
        // since we received STETH , we shall deposit using STETH instead of ETH
        if (_vaultAddress == stethVault) {
            totalWithdrawAmount = totalWithdrawAmount - 3;

            IERC20(STETH).safeApprove(_destination, totalWithdrawAmount);

            if (_vaultAddress == _destination) {
                emit Resume(msg.sender, _vaultAddress, totalWithdrawAmount - 1);
                currentVault.depositYieldTokenFor(totalWithdrawAmount, msg.sender);
            } else {
                emit Withdraw(msg.sender, _vaultAddress, totalWithdrawAmount);
                IERC20(STETH).safeTransfer(_destination, totalWithdrawAmount);
            }

        } else {
            address asset = currentParams.asset;
            // if asset is ETH, we will convert it into WETH before depositing
            if (asset == WETH) {
                IWETH(WETH).deposit{value: totalWithdrawAmount}();
            }
            IERC20(asset).safeApprove(_destination, totalWithdrawAmount);

            if (_vaultAddress == _destination) {
                emit Resume(msg.sender, _vaultAddress, totalWithdrawAmount);
                currentVault.depositFor(totalWithdrawAmount, msg.sender);
            } else {
                emit Withdraw(msg.sender, _vaultAddress, totalWithdrawAmount);
                IERC20(asset).safeTransfer(_destination, totalWithdrawAmount);
            }
        }
    }

    /**
     * @notice process withdrawals by completing in a batch
     * @param _vaultAddress vault's address to be processed
     */
    function processWithdrawal(address _vaultAddress) external onlyKeeper {
        IHashnoteThetaVault currentVault = IHashnoteThetaVault(_vaultAddress);
        // we can only process withdrawal after closing the previous round
        // hence round should be - 1
        emit ProcessWithdrawal(
            _vaultAddress,
            currentVault.vaultState().round - 1
        );
        currentVault.completeWithdraw();
    }

    /**
     * @notice Recovery function that returns an ERC20 token to the recipient
     * @param token is the ERC20 token to recover from the vault
     * @param recipient is the recipient of the recovered tokens
     */
    function recoverTokens(address token, address recipient) external onlyOwner {
        require(recipient != address(0), "!recipient");
        require(recipient != address(this), "Recipient cannot be vault");

        IERC20(token).safeTransfer(
            recipient,
            IERC20(token).balanceOf(address(this))
        );
    }

    fallback() external payable {}

    receive() external payable {}
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

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

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

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

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

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

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

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

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../../../utils/Address.sol";

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

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

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

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

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

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

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

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

// File: @openzeppelin/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../utils/Context.sol";

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _setOwner(_msgSender());
    }

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

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _setOwner(address(0));
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _setOwner(newOwner);
    }

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// File: src/interfaces/IVaultPauser.sol



// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

interface IVaultPauser {
    /// @notice pause vault position of an account with max amount
    /// @param _account the address of user
    /// @param _amount amount of shares
    function pausePosition(address _account, uint256 _amount) external;

    /// @notice resume vault position of an account with max amount
    /// @param _vaultAddress the address of vault
    function resumePositionOrWithdraw(address _vaultAddress, address _destination) external;
}

// File: src/libraries/Vault.sol



// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

library Vault {
    /************************************************
     *  IMMUTABLES & CONSTANTS
     ***********************************************/

    // Fees are 6-decimal places. For example: 20 * 10**6 = 20%
    uint256 internal constant FEE_MULTIPLIER = 10**6;

    // Premium discount has 1-decimal place. For example: 80 * 10**1 = 80%. Which represents a 20% discount.
    uint256 internal constant PREMIUM_DISCOUNT_MULTIPLIER = 10;

    // Otokens have 8 decimal places.
    uint256 internal constant OTOKEN_DECIMALS = 8;

    // Percentage of funds allocated to options is 2 decimal places. 10 * 10**2 = 10%
    uint256 internal constant OPTION_ALLOCATION_MULTIPLIER = 10**2;

    // Placeholder uint value to prevent cold writes
    uint256 internal constant PLACEHOLDER_UINT = 1;

    struct VaultParams {
        // Option type the vault is selling
        bool isPut;
        // Token decimals for vault shares
        uint8 decimals;
        // Asset used in Theta / Delta Vault
        address asset;
        // Underlying asset of the options sold by vault
        address underlying;
        // asset that the strike price is denominated in
        address strike;
        // Minimum supply of the vault shares issued, for ETH it's 10**10
        uint56 minimumSupply;
        // Vault cap
        uint104 cap;
    }

    struct OptionState {
        // Option that the vault is shorting / longing in the next cycle
        address nextOption;
        // Option that the vault is currently shorting / longing
        address currentOption;
        // The timestamp when the `nextOption` can be used by the vault
        uint32 nextOptionReadyAt;
    }

    struct VaultState {
        // 32 byte slot 1
        //  Current round number. `round` represents the number of `period`s elapsed.
        uint16 round;
        // Amount that is currently locked for selling options
        uint104 lockedAmount;
        // Amount that was locked for selling options in the previous round
        // used for calculating performance fee deduction
        uint104 lastLockedAmount;
        // 32 byte slot 2
        // Stores the total tally of how much of `asset` there is
        // to be used to mint rTHETA tokens
        uint128 totalPending;
        // Total amount of queued withdrawal shares from previous rounds (doesn't include the current round)
        uint128 queuedWithdrawShares;
    }

    struct DepositReceipt {
        // Maximum of 65535 rounds. Assuming 1 round is 7 days, maximum is 1256 years.
        uint16 round;
        // Deposit amount, max 20,282,409,603,651 or 20 trillion ETH deposit
        uint104 amount;
        // Unredeemed shares balance
        uint128 unredeemedShares;
    }

    struct Withdrawal {
        // Maximum of 65535 rounds. Assuming 1 round is 7 days, maximum is 1256 years.
        uint16 round;
        // Number of shares withdrawn
        uint128 shares;
    }

    struct AuctionSellOrder {
        // Amount of `asset` token offered in auction
        uint96 sellAmount;
        // Amount of oToken requested in auction
        uint96 buyAmount;
        // User Id of delta vault in latest gnosis auction
        uint64 userId;
    }
}

// File: src/interfaces/IHashnoteThetaVault.sol



// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

import {Vault} from "../libraries/Vault.sol";

interface IHashnoteThetaVault {
    function currentOption() external view returns (address);

    function nextOption() external view returns (address);

    function vaultParams() external view returns (Vault.VaultParams memory);

    function vaultState() external view returns (Vault.VaultState memory);

    function optionState() external view returns (Vault.OptionState memory);

    function optionAuctionID() external view returns (uint256);

    function pricePerShare() external view returns (uint256);

    function roundPricePerShare(uint256) external view returns (uint256);

    function depositFor(uint256 amount, address creditor) external;

    function initiateWithdraw(uint256 numShares) external;

    function completeWithdraw() external;

    function maxRedeem() external;

    function depositYieldTokenFor(uint256 amount, address creditor) external;

    function symbol() external view returns (string calldata);
}

// File: src/interfaces/IWETH.sol



// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

interface IWETH {
    function deposit() external payable;

    function withdraw(uint256) external;

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

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

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

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

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

    function decimals() external view returns (uint256);
}

// File: src/libraries/ShareMath.sol



// SPDX-License-Identifier: MIT
pragma solidity =0.8.4;

import {SafeMath} from "@openzeppelin/contracts/utils/math/SafeMath.sol";
import {Vault} from "./Vault.sol";

library ShareMath {
    using SafeMath for uint256;

    uint256 internal constant PLACEHOLDER_UINT = 1;

    function assetToShares(
        uint256 assetAmount,
        uint256 assetPerShare,
        uint256 decimals
    ) internal pure returns (uint256) {
        // If this throws, it means that vault's roundPricePerShare[currentRound] has not been set yet
        // which should never happen.
        // Has to be larger than 1 because `1` is used in `initRoundPricePerShares` to prevent cold writes.
        require(assetPerShare > PLACEHOLDER_UINT, "Invalid assetPerShare");

        return assetAmount.mul(10**decimals).div(assetPerShare);
    }

    function sharesToAsset(
        uint256 shares,
        uint256 assetPerShare,
        uint256 decimals
    ) internal pure returns (uint256) {
        // If this throws, it means that vault's roundPricePerShare[currentRound] has not been set yet
        // which should never happen.
        // Has to be larger than 1 because `1` is used in `initRoundPricePerShares` to prevent cold writes.
        require(assetPerShare > PLACEHOLDER_UINT, "Invalid assetPerShare");

        return shares.mul(assetPerShare).div(10**decimals);
    }

    /**
     * @notice Returns the shares unredeemed by the user given their DepositReceipt
     * @param depositReceipt is the user's deposit receipt
     * @param currentRound is the `round` stored on the vault
     * @param assetPerShare is the price in asset per share
     * @param decimals is the number of decimals the asset/shares use
     * @return unredeemedShares is the user's virtual balance of shares that are owed
     */
    function getSharesFromReceipt(
        Vault.DepositReceipt memory depositReceipt,
        uint256 currentRound,
        uint256 assetPerShare,
        uint256 decimals
    ) internal pure returns (uint256 unredeemedShares) {
        if (depositReceipt.round > 0 && depositReceipt.round < currentRound) {
            uint256 sharesFromRound =
                assetToShares(depositReceipt.amount, assetPerShare, decimals);

            return
                uint256(depositReceipt.unredeemedShares).add(sharesFromRound);
        }
        return depositReceipt.unredeemedShares;
    }

    function pricePerShare(
        uint256 totalSupply,
        uint256 totalBalance,
        uint256 pendingAmount,
        uint256 decimals
    ) internal pure returns (uint256) {
        uint256 singleShare = 10**decimals;
        return
            totalSupply > 0
                ? singleShare.mul(totalBalance.sub(pendingAmount)).div(
                    totalSupply
                )
                : singleShare;
    }

    /************************************************
     *  HELPERS
     ***********************************************/

    function assertUint104(uint256 num) internal pure {
        require(num <= type(uint104).max, "Overflow uint104");
    }

    function assertUint128(uint256 num) internal pure {
        require(num <= type(uint128).max, "Overflow uint128");
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

        uint256 size;
        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");

        (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");

        (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");

        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal 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

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is no longer needed starting with Solidity 0.8. The compiler
 * now has built in overflow checking.
 */
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) {
        unchecked {
            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) {
        unchecked {
            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) {
        unchecked {
            // 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) {
        unchecked {
            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) {
        unchecked {
            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) {
        return a + b;
    }

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

    /**
     * @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.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        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) {
        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) {
        unchecked {
            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.
     *
     * 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) {
        unchecked {
            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) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}