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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/ERC20.sol)

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.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.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * The default value of {decimals} is 18. To change this, you should override
 * this function so it returns a different value.
 *
 * We have followed general OpenZeppelin Contracts guidelines: functions revert
 * instead returning `false` on failure. This behavior is nonetheless
 * conventional and does not conflict with the expectations of ERC20
 * applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

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

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override 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 default value returned by this function, unless
     * it's overridden.
     *
     * 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 override returns (uint8) {
        return 18;
    }

    /**
     * @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:
     *
     * - `to` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address to, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, 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}.
     *
     * NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, 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}.
     *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address from, address to, uint256 amount) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, amount);
        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) {
        address owner = _msgSender();
        _approve(owner, spender, allowance(owner, spender) + 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) {
        address owner = _msgSender();
        uint256 currentAllowance = allowance(owner, spender);
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `from` to `to`.
     *
     * This 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:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     */
    function _transfer(address from, address to, uint256 amount) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(from, to, amount);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - amount;
            // Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
            // decrementing then incrementing.
            _balances[to] += amount;
        }

        emit Transfer(from, to, amount);

        _afterTokenTransfer(from, to, 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:
     *
     * - `account` 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 += amount;
        unchecked {
            // Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
            _balances[account] += amount;
        }
        emit Transfer(address(0), account, amount);

        _afterTokenTransfer(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);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
            // Overflow not possible: amount <= accountBalance <= totalSupply.
            _totalSupply -= amount;
        }

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(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 Updates `owner` s allowance for `spender` based on spent `amount`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    function _spendAllowance(address owner, address spender, uint256 amount) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - amount);
            }
        }
    }

    /**
     * @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 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 {}

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * has been transferred to `to`.
     * - when `from` is zero, `amount` tokens have been minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens have been 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 _afterTokenTransfer(address from, address to, uint256 amount) internal virtual {}
}

// File: @openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @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);

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

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

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: contracts/interface/IsQWN.sol



// SPDX-License-Identifier: AGPL-3.0
pragma solidity 0.8.19;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

interface IsQWN is IERC20 {
    function rebase(uint256 amount_, uint epoch_) external returns (uint256);

    function circulatingSupply() external view returns (uint256);

    function gonsForBalance(uint amount) external view returns (uint);

    function balanceForGons(uint gons) external view returns (uint);

    function index() external view returns (uint);
}

// File: contracts/interface/IStaking.sol



// SPDX-License-Identifier: AGPL-3.0
pragma solidity 0.8.19;

interface IStaking {
    function stake(address _to, uint256 _amount) external;

    function unstake(address _to, uint256 _amount) external;

    function rebase() external;

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

// File: contracts/token/sQWN.sol



// SPDX-License-Identifier: AGPL-3.0
pragma solidity 0.8.19;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "../interface/IsQWN.sol";
import "../interface/IStaking.sol";

/// @title   sQWN
/// @notice  Staked QWN
contract sQWN is IsQWN, ERC20 {
    /// EVENTS ///

    event LogSupply(uint256 indexed epoch, uint256 totalSupply);
    event LogRebase(uint256 indexed epoch, uint256 rebase, uint256 index);
    event LogStakingContractUpdated(address stakingContract);

    /// MODIFIERS ///

    modifier onlyStakingContract() {
        require(
            msg.sender == stakingContract,
            "StakingContract:  call is not staking contract"
        );
        _;
    }

    /// DATA STRUCTURES ///

    struct Rebase {
        uint256 epoch;
        uint256 rebase; // 18 decimals
        uint256 totalStakedBefore;
        uint256 totalStakedAfter;
        uint256 amountRebased;
        uint256 index;
        uint256 blockNumberOccured;
    }

    /// STATE VARIABLES ///

    address internal initializer;
    address public treasury;
    address public stakingContract; // balance used to calc rebase

    uint256 internal _totalSupply;
    uint256 internal INDEX; // Index Gons - tracks rebase growth

    uint256 private constant MAX_UINT256 = type(uint256).max;
    uint256 private constant INITIAL_FRAGMENTS_SUPPLY = 250_000 * 10 ** 9;

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

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

    uint256 private _gonsPerFragment;

    Rebase[] public rebases; // past rebase data

    mapping(address => uint256) private _gonBalances;

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

    /// CONSTRUCTOR ///

    constructor() ERC20("Staked QWN", "sQWN") {
        initializer = msg.sender;
        _totalSupply = INITIAL_FRAGMENTS_SUPPLY;
        _gonsPerFragment = TOTAL_GONS / _totalSupply;
    }

    function decimals() public view virtual override returns (uint8) {
        return 9;
    }

    /// INITIALIZATION ///

    /// @notice        Sets initial index
    /// @param _index  Initial index
    function setIndex(uint256 _index) external {
        require(
            msg.sender == initializer,
            "Initializer:  caller is not initializer"
        );
        require(INDEX == 0, "Cannot set INDEX again");
        INDEX = gonsForBalance(_index);
    }

    /// @notice                  Initialize contract
    /// @param _stakingContract  Address of staking contract
    /// @param _treasury         Address of treasury
    function initialize(address _stakingContract, address _treasury) external {
        require(
            msg.sender == initializer,
            "Initializer:  caller is not initializer"
        );

        require(_stakingContract != address(0), "Zero address: Staking");
        stakingContract = _stakingContract;
        _gonBalances[stakingContract] = TOTAL_GONS;

        require(_treasury != address(0), "Zero address: Treasury");
        treasury = _treasury;

        emit Transfer(address(0x0), stakingContract, _totalSupply);
        emit LogStakingContractUpdated(stakingContract);

        initializer = address(0);
    }

    /// REBASE ///

    /// @notice             Increases sQWN supply
    /// @param amount_      Amount to rebase for
    /// @param epoch_       Epoch number
    /// @return _newSupply  New total supply
    function rebase(
        uint256 amount_,
        uint256 epoch_
    ) public override onlyStakingContract returns (uint256 _newSupply) {
        uint256 rebaseAmount;
        uint256 circulatingSupply_ = circulatingSupply();
        if (amount_ == 0) {
            emit LogSupply(epoch_, _totalSupply);
            emit LogRebase(epoch_, 0, index());
            return _totalSupply;
        } else if (circulatingSupply_ > 0) {
            rebaseAmount = (amount_ * _totalSupply) / circulatingSupply_;
        } else {
            rebaseAmount = amount_;
        }

        _totalSupply = _totalSupply + rebaseAmount;

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

        _gonsPerFragment = TOTAL_GONS / _totalSupply;

        _storeRebase(circulatingSupply_, amount_, epoch_);

        return _totalSupply;
    }

    /// @notice                      Stores rebase
    /// @param previousCirculating_  Previous circ supply
    /// @param profit_               Amount of profic for epoch
    /// @param epoch_                Epoch number
    function _storeRebase(
        uint256 previousCirculating_,
        uint256 profit_,
        uint256 epoch_
    ) internal {
        uint256 rebasePercent;
        if (previousCirculating_ > 0)
            rebasePercent = (profit_ * 1e18) / previousCirculating_;
        rebases.push(
            Rebase({
                epoch: epoch_,
                rebase: rebasePercent, // 18 decimals
                totalStakedBefore: previousCirculating_,
                totalStakedAfter: circulatingSupply(),
                amountRebased: profit_,
                index: index(),
                blockNumberOccured: block.number
            })
        );

        emit LogSupply(epoch_, _totalSupply);
        emit LogRebase(epoch_, rebasePercent, index());
    }

    /// MUTATIVE FUNCTIONS ///

    /// @notice       Transfer sQWN from msg.sender
    /// @param to     Address sending sQWN to
    /// @param value  Amount of sQWN to send
    function transfer(
        address to,
        uint256 value
    ) public override(IERC20, ERC20) returns (bool) {
        uint256 gonValue = value * _gonsPerFragment;

        _gonBalances[msg.sender] = _gonBalances[msg.sender] - gonValue;
        _gonBalances[to] = _gonBalances[to] + gonValue;

        emit Transfer(msg.sender, to, value);
        return true;
    }

    /// @notice       Transfer sQWN
    /// @param from   Address sending sQWN from
    /// @param to     Address sending sQWN to
    /// @param value  Amount of sQWN to send
    function transferFrom(
        address from,
        address to,
        uint256 value
    ) public override(IERC20, ERC20) returns (bool) {
        _allowedValue[from][msg.sender] =
            _allowedValue[from][msg.sender] -
            value;
        emit Approval(from, msg.sender, _allowedValue[from][msg.sender]);

        uint256 gonValue = gonsForBalance(value);
        _gonBalances[from] = _gonBalances[from] - gonValue;
        _gonBalances[to] = _gonBalances[to] + gonValue;

        emit Transfer(from, to, value);
        return true;
    }

    function approve(
        address spender,
        uint256 value
    ) public override(IERC20, ERC20) returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    function increaseAllowance(
        address spender,
        uint256 addedValue
    ) public override returns (bool) {
        _approve(
            msg.sender,
            spender,
            _allowedValue[msg.sender][spender] + addedValue
        );
        return true;
    }

    function decreaseAllowance(
        address spender,
        uint256 subtractedValue
    ) public override returns (bool) {
        uint256 oldValue = _allowedValue[msg.sender][spender];
        if (subtractedValue >= oldValue) {
            _approve(msg.sender, spender, 0);
        } else {
            _approve(msg.sender, spender, oldValue - subtractedValue);
        }
        return true;
    }

    /// INTERNAL FUNCTIONS ///

    function _approve(
        address owner,
        address spender,
        uint256 value
    ) internal virtual override {
        _allowedValue[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    /// VIEW FUNCTIONS ///

    /// @notice       Returns balance of an address
    /// @param who    Address of who to get balance from
    function balanceOf(
        address who
    ) public view override(IERC20, ERC20) returns (uint256) {
        return _gonBalances[who] / _gonsPerFragment;
    }

    /// @notice        Returns calculation of gons for amount of sQWN
    /// @param amount  Amount of sQWN to calculate gons for
    function gonsForBalance(
        uint256 amount
    ) public view override returns (uint256) {
        return amount * _gonsPerFragment;
    }

    /// @notice      Returns calculation of balance for gons amount
    /// @param gons  Amount of gons to calculate sQWN for
    function balanceForGons(
        uint256 gons
    ) public view override returns (uint256) {
        return gons / _gonsPerFragment;
    }

    /// @notice  Returns sQWN circulating supply (Total Supply - Staking Contract Balance)
    function circulatingSupply() public view override returns (uint256) {
        return _totalSupply - balanceOf(stakingContract);
    }

    /// @notice  Returns current sQWN index
    function index() public view override returns (uint256) {
        return balanceForGons(INDEX);
    }

    function allowance(
        address owner_,
        address spender
    ) public view override(IERC20, ERC20) returns (uint256) {
        return _allowedValue[owner_][spender];
    }
}