organized_contracts/03/030c096222e8746193408e3a8fa65f7bc051c4f680bcd589ee5b476401fcb951/main.sol

// This contract is part of Zellic’s smart contract dataset, which is a collection of publicly available contract code gathered as of March 2023.

// SPDX-License-Identifier: GPL-2.0-or-later
pragma solidity >=0.8.0;


// ====================================================================
// |     ______                   _______                             |
// |    / _____________ __  __   / ____(_____  ____ _____  ________   |
// |   / /_  / ___/ __ `| |/_/  / /_  / / __ \/ __ `/ __ \/ ___/ _ \  |
// |  / __/ / /  / /_/ _>  <   / __/ / / / / / /_/ / / / / /__/  __/  |
// | /_/   /_/   \__,_/_/|_|  /_/   /_/_/ /_/\__,_/_/ /_/\___/\___/   |
// |                                                                  |
// ====================================================================
// ============================== frxETH ==============================
// ====================================================================
// Frax Finance: https://github.com/FraxFinance

// Primary Author(s)
// Jack Corddry: https://github.com/corddry
// Nader Ghazvini: https://github.com/amirnader-ghazvini 

// Reviewer(s) / Contributor(s)
// Sam Kazemian: https://github.com/samkazemian
// Dennis: https://github.com/denett
// Travis Moore: https://github.com/FortisFortuna
// Jamie Turley: https://github.com/jyturley

/// @title Stablecoin pegged to Ether for use within the Frax ecosystem
/** @notice Does not accrue ETH 2.0 staking yield: it must be staked at the sfrxETH contract first.

    ETH -> frxETH conversion is permanent, so a market will develop for the latter.

    Withdraws are not live (as of deploy time) so loosely pegged to eth but is possible will float */
/// @dev frxETH adheres to EIP-712/EIP-2612 and can use permits

// OpenZeppelin Contracts (last updated v4.7.0) (token/ERC20/ERC20.sol)

// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)

/**

 * @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);
}

// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.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);
}

// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with 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;
    }
}

/**

 * @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].

 *

 * 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}.

     *

     * The default value of {decimals} is 18. To select a different value for

     * {decimals} you should overload it.

     *

     * 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 value {ERC20} uses, unless this function is

     * 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 {}
}

// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/extensions/draft-ERC20Permit.sol)

// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/draft-IERC20Permit.sol)

/**

 * @dev Interface of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in

 * https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].

 *

 * Adds the {permit} method, which can be used to change an account's ERC20 allowance (see {IERC20-allowance}) by

 * presenting a message signed by the account. By not relying on {IERC20-approve}, the token holder account doesn't

 * need to send a transaction, and thus is not required to hold Ether at all.

 */
interface IERC20Permit {
    /**

     * @dev Sets `value` as the allowance of `spender` over ``owner``'s tokens,

     * given ``owner``'s signed approval.

     *

     * IMPORTANT: The same issues {IERC20-approve} has related to transaction

     * ordering also apply here.

     *

     * Emits an {Approval} event.

     *

     * Requirements:

     *

     * - `spender` cannot be the zero address.

     * - `deadline` must be a timestamp in the future.

     * - `v`, `r` and `s` must be a valid `secp256k1` signature from `owner`

     * over the EIP712-formatted function arguments.

     * - the signature must use ``owner``'s current nonce (see {nonces}).

     *

     * For more information on the signature format, see the

     * https://eips.ethereum.org/EIPS/eip-2612#specification[relevant EIP

     * section].

     */
    function permit(

        address owner,

        address spender,

        uint256 value,

        uint256 deadline,

        uint8 v,

        bytes32 r,

        bytes32 s

    ) external;

    /**
     * @dev Returns the current nonce for `owner`. This value must be
     * included whenever a signature is generated for {permit}.
     *
     * Every successful call to {permit} increases ``owner``'s nonce by one. This

     * prevents a signature from being used multiple times.

     */

    function nonces(address owner) external view returns (uint256);



    /**

     * @dev Returns the domain separator used in the encoding of the signature for {permit}, as defined by {EIP712}.

     */

    // solhint-disable-next-line func-name-mixedcase

    function DOMAIN_SEPARATOR() external view returns (bytes32);

}



// OpenZeppelin Contracts (last updated v4.7.0) (utils/cryptography/ECDSA.sol)



// OpenZeppelin Contracts (last updated v4.7.0) (utils/Strings.sol)



// OpenZeppelin Contracts (last updated v4.7.0) (utils/math/Math.sol)



/**

 * @dev Standard math utilities missing in the Solidity language.

 */

library Math {

    enum Rounding {

        Down, // Toward negative infinity

        Up, // Toward infinity

        Zero // Toward zero

    }



    /**

     * @dev Returns the largest of two numbers.

     */

    function max(uint256 a, uint256 b) internal pure returns (uint256) {

        return a > b ? a : b;

    }



    /**

     * @dev Returns the smallest of two numbers.

     */

    function min(uint256 a, uint256 b) internal pure returns (uint256) {

        return a < b ? a : b;

    }



    /**

     * @dev Returns the average of two numbers. The result is rounded towards

     * zero.

     */

    function average(uint256 a, uint256 b) internal pure returns (uint256) {

        // (a + b) / 2 can overflow.

        return (a & b) + (a ^ b) / 2;

    }



    /**

     * @dev Returns the ceiling of the division of two numbers.

     *

     * This differs from standard division with `/` in that it rounds up instead

     * of rounding down.

     */

    function ceilDiv(uint256 a, uint256 b) internal pure returns (uint256) {

        // (a + b - 1) / b can overflow on addition, so we distribute.

        return a == 0 ? 0 : (a - 1) / b + 1;

    }



    /**

     * @notice Calculates floor(x * y / denominator) with full precision. Throws if result overflows a uint256 or denominator == 0

     * @dev Original credit to Remco Bloemen under MIT license (https://xn--2-umb.com/21/muldiv)

     * with further edits by Uniswap Labs also under MIT license.

     */

    function mulDiv(

        uint256 x,

        uint256 y,

        uint256 denominator

    ) internal pure returns (uint256 result) {

        unchecked {

            // 512-bit multiply [prod1 prod0] = x * y. Compute the product mod 2^256 and mod 2^256 - 1, then use

            // use the Chinese Remainder Theorem to reconstruct the 512 bit result. The result is stored in two 256

            // variables such that product = prod1 * 2^256 + prod0.

            uint256 prod0; // Least significant 256 bits of the product

            uint256 prod1; // Most significant 256 bits of the product

            assembly {

                let mm := mulmod(x, y, not(0))

                prod0 := mul(x, y)

                prod1 := sub(sub(mm, prod0), lt(mm, prod0))

            }



            // Handle non-overflow cases, 256 by 256 division.

            if (prod1 == 0) {

                return prod0 / denominator;

            }



            // Make sure the result is less than 2^256. Also prevents denominator == 0.

            require(denominator > prod1);



            ///////////////////////////////////////////////

            // 512 by 256 division.

            ///////////////////////////////////////////////



            // Make division exact by subtracting the remainder from [prod1 prod0].

            uint256 remainder;

            assembly {

                // Compute remainder using mulmod.

                remainder := mulmod(x, y, denominator)



                // Subtract 256 bit number from 512 bit number.

                prod1 := sub(prod1, gt(remainder, prod0))

                prod0 := sub(prod0, remainder)

            }



            // Factor powers of two out of denominator and compute largest power of two divisor of denominator. Always >= 1.

            // See https://cs.stackexchange.com/q/138556/92363.



            // Does not overflow because the denominator cannot be zero at this stage in the function.

            uint256 twos = denominator & (~denominator + 1);

            assembly {

                // Divide denominator by twos.

                denominator := div(denominator, twos)



                // Divide [prod1 prod0] by twos.

                prod0 := div(prod0, twos)



                // Flip twos such that it is 2^256 / twos. If twos is zero, then it becomes one.

                twos := add(div(sub(0, twos), twos), 1)

            }



            // Shift in bits from prod1 into prod0.

            prod0 |= prod1 * twos;



            // Invert denominator mod 2^256. Now that denominator is an odd number, it has an inverse modulo 2^256 such

            // that denominator * inv = 1 mod 2^256. Compute the inverse by starting with a seed that is correct for

            // four bits. That is, denominator * inv = 1 mod 2^4.

            uint256 inverse = (3 * denominator) ^ 2;



            // Use the Newton-Raphson iteration to improve the precision. Thanks to Hensel's lifting lemma, this also works
            // in modular arithmetic, doubling the correct bits in each step.
            inverse *= 2 - denominator * inverse; // inverse mod 2^8
            inverse *= 2 - denominator * inverse; // inverse mod 2^16
            inverse *= 2 - denominator * inverse; // inverse mod 2^32
            inverse *= 2 - denominator * inverse; // inverse mod 2^64
            inverse *= 2 - denominator * inverse; // inverse mod 2^128
            inverse *= 2 - denominator * inverse; // inverse mod 2^256

            // Because the division is now exact we can divide by multiplying with the modular inverse of denominator.
            // This will give us the correct result modulo 2^256. Since the preconditions guarantee that the outcome is
            // less than 2^256, this is the final result. We don't need to compute the high bits of the result and prod1
            // is no longer required.
            result = prod0 * inverse;
            return result;
        }
    }

    /**

     * @notice Calculates x * y / denominator with full precision, following the selected rounding direction.

     */
    function mulDiv(

        uint256 x,

        uint256 y,

        uint256 denominator,

        Rounding rounding

    ) internal pure returns (uint256) {
        uint256 result = mulDiv(x, y, denominator);
        if (rounding == Rounding.Up && mulmod(x, y, denominator) > 0) {
            result += 1;
        }
        return result;
    }

    /**

     * @dev Returns the square root of a number. If the number is not a perfect square, the value is rounded down.

     *

     * Inspired by Henry S. Warren, Jr.'s "Hacker's Delight" (Chapter 11).

     */
    function sqrt(uint256 a) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        // For our first guess, we get the biggest power of 2 which is smaller than the square root of the target.
        //
        // We know that the "msb" (most significant bit) of our target number `a` is a power of 2 such that we have
        // `msb(a) <= a < 2*msb(a)`. This value can be written `msb(a)=2**k` with `k=log2(a)`.
        //
        // This can be rewritten `2**log2(a) <= a < 2**(log2(a) + 1)`
        // → `sqrt(2**k) <= sqrt(a) < sqrt(2**(k+1))`
        // → `2**(k/2) <= sqrt(a) < 2**((k+1)/2) <= 2**(k/2 + 1)`
        //
        // Consequently, `2**(log2(a) / 2)` is a good first approximation of `sqrt(a)` with at least 1 correct bit.
        uint256 result = 1 << (log2(a) >> 1);

        // At this point `result` is an estimation with one bit of precision. We know the true value is a uint128,
        // since it is the square root of a uint256. Newton's method converges quadratically (precision doubles at
        // every iteration). We thus need at most 7 iteration to turn our partial result with one bit of precision
        // into the expected uint128 result.
        unchecked {
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            return min(result, a / result);
        }
    }

    /**

     * @notice Calculates sqrt(a), following the selected rounding direction.

     */
    function sqrt(uint256 a, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = sqrt(a);
            return result + (rounding == Rounding.Up && result * result < a ? 1 : 0);
        }
    }

    /**

     * @dev Return the log in base 2, rounded down, of a positive value.

     * Returns 0 if given 0.

     */
    function log2(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >> 128 > 0) {
                value >>= 128;
                result += 128;
            }
            if (value >> 64 > 0) {
                value >>= 64;
                result += 64;
            }
            if (value >> 32 > 0) {
                value >>= 32;
                result += 32;
            }
            if (value >> 16 > 0) {
                value >>= 16;
                result += 16;
            }
            if (value >> 8 > 0) {
                value >>= 8;
                result += 8;
            }
            if (value >> 4 > 0) {
                value >>= 4;
                result += 4;
            }
            if (value >> 2 > 0) {
                value >>= 2;
                result += 2;
            }
            if (value >> 1 > 0) {
                result += 1;
            }
        }
        return result;
    }

    /**

     * @dev Return the log in base 2, following the selected rounding direction, of a positive value.

     * Returns 0 if given 0.

     */
    function log2(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log2(value);
            return result + (rounding == Rounding.Up && 1 << result < value ? 1 : 0);
        }
    }

    /**

     * @dev Return the log in base 10, rounded down, of a positive value.

     * Returns 0 if given 0.

     */
    function log10(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >= 10**64) {
                value /= 10**64;
                result += 64;
            }
            if (value >= 10**32) {
                value /= 10**32;
                result += 32;
            }
            if (value >= 10**16) {
                value /= 10**16;
                result += 16;
            }
            if (value >= 10**8) {
                value /= 10**8;
                result += 8;
            }
            if (value >= 10**4) {
                value /= 10**4;
                result += 4;
            }
            if (value >= 10**2) {
                value /= 10**2;
                result += 2;
            }
            if (value >= 10**1) {
                result += 1;
            }
        }
        return result;
    }

    /**

     * @dev Return the log in base 10, following the selected rounding direction, of a positive value.

     * Returns 0 if given 0.

     */
    function log10(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log10(value);
            return result + (rounding == Rounding.Up && 10**result < value ? 1 : 0);
        }
    }

    /**

     * @dev Return the log in base 256, rounded down, of a positive value.

     * Returns 0 if given 0.

     *

     * Adding one to the result gives the number of pairs of hex symbols needed to represent `value` as a hex string.

     */
    function log256(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >> 128 > 0) {
                value >>= 128;
                result += 16;
            }
            if (value >> 64 > 0) {
                value >>= 64;
                result += 8;
            }
            if (value >> 32 > 0) {
                value >>= 32;
                result += 4;
            }
            if (value >> 16 > 0) {
                value >>= 16;
                result += 2;
            }
            if (value >> 8 > 0) {
                result += 1;
            }
        }
        return result;
    }

    /**

     * @dev Return the log in base 10, following the selected rounding direction, of a positive value.

     * Returns 0 if given 0.

     */
    function log256(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log256(value);
            return result + (rounding == Rounding.Up && 1 << (result << 3) < value ? 1 : 0);
        }
    }
}

/**

 * @dev String operations.

 */
library Strings {
    bytes16 private constant _SYMBOLS = "0123456789abcdef";
    uint8 private constant _ADDRESS_LENGTH = 20;

    /**

     * @dev Converts a `uint256` to its ASCII `string` decimal representation.

     */
    function toString(uint256 value) internal pure returns (string memory) {
        unchecked {
            uint256 length = Math.log10(value) + 1;
            string memory buffer = new string(length);
            uint256 ptr;
            /// @solidity memory-safe-assembly
            assembly {
                ptr := add(buffer, add(32, length))
            }
            while (true) {
                ptr--;
                /// @solidity memory-safe-assembly
                assembly {
                    mstore8(ptr, byte(mod(value, 10), _SYMBOLS))
                }
                value /= 10;
                if (value == 0) break;
            }
            return buffer;
        }
    }

    /**

     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.

     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        unchecked {
            return toHexString(value, Math.log256(value) + 1);
        }
    }

    /**

     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.

     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }

    /**

     * @dev Converts an `address` with fixed length of 20 bytes to its not checksummed ASCII `string` hexadecimal representation.

     */
    function toHexString(address addr) internal pure returns (string memory) {
        return toHexString(uint256(uint160(addr)), _ADDRESS_LENGTH);
    }
}

/**

 * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.

 *

 * These functions can be used to verify that a message was signed by the holder

 * of the private keys of a given address.

 */
library ECDSA {
    enum RecoverError {
        NoError,
        InvalidSignature,
        InvalidSignatureLength,
        InvalidSignatureS,
        InvalidSignatureV // Deprecated in v4.8
    }

    function _throwError(RecoverError error) private pure {
        if (error == RecoverError.NoError) {
            return; // no error: do nothing
        } else if (error == RecoverError.InvalidSignature) {
            revert("ECDSA: invalid signature");
        } else if (error == RecoverError.InvalidSignatureLength) {
            revert("ECDSA: invalid signature length");
        } else if (error == RecoverError.InvalidSignatureS) {
            revert("ECDSA: invalid signature 's' value");
        }
    }

    /**

     * @dev Returns the address that signed a hashed message (`hash`) with

     * `signature` or error string. This address can then be used for verification purposes.

     *

     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:

     * this function rejects them by requiring the `s` value to be in the lower

     * half order, and the `v` value to be either 27 or 28.

     *

     * IMPORTANT: `hash` _must_ be the result of a hash operation for the

     * verification to be secure: it is possible to craft signatures that

     * recover to arbitrary addresses for non-hashed data. A safe way to ensure

     * this is by receiving a hash of the original message (which may otherwise

     * be too long), and then calling {toEthSignedMessageHash} on it.

     *

     * Documentation for signature generation:

     * - with https://web3js.readthedocs.io/en/v1.3.4/web3-eth-accounts.html#sign[Web3.js]

     * - with https://docs.ethers.io/v5/api/signer/#Signer-signMessage[ethers]

     *

     * _Available since v4.3._

     */
    function tryRecover(bytes32 hash, bytes memory signature) internal pure returns (address, RecoverError) {
        if (signature.length == 65) {
            bytes32 r;
            bytes32 s;
            uint8 v;
            // ecrecover takes the signature parameters, and the only way to get them
            // currently is to use assembly.
            /// @solidity memory-safe-assembly
            assembly {
                r := mload(add(signature, 0x20))
                s := mload(add(signature, 0x40))
                v := byte(0, mload(add(signature, 0x60)))
            }
            return tryRecover(hash, v, r, s);
        } else {
            return (address(0), RecoverError.InvalidSignatureLength);
        }
    }

    /**

     * @dev Returns the address that signed a hashed message (`hash`) with

     * `signature`. This address can then be used for verification purposes.

     *

     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:

     * this function rejects them by requiring the `s` value to be in the lower

     * half order, and the `v` value to be either 27 or 28.

     *

     * IMPORTANT: `hash` _must_ be the result of a hash operation for the

     * verification to be secure: it is possible to craft signatures that

     * recover to arbitrary addresses for non-hashed data. A safe way to ensure

     * this is by receiving a hash of the original message (which may otherwise

     * be too long), and then calling {toEthSignedMessageHash} on it.

     */
    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, signature);
        _throwError(error);
        return recovered;
    }

    /**

     * @dev Overload of {ECDSA-tryRecover} that receives the `r` and `vs` short-signature fields separately.

     *

     * See https://eips.ethereum.org/EIPS/eip-2098[EIP-2098 short signatures]

     *

     * _Available since v4.3._

     */
    function tryRecover(

        bytes32 hash,

        bytes32 r,

        bytes32 vs

    ) internal pure returns (address, RecoverError) {
        bytes32 s = vs & bytes32(0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff);
        uint8 v = uint8((uint256(vs) >> 255) + 27);
        return tryRecover(hash, v, r, s);
    }

    /**

     * @dev Overload of {ECDSA-recover} that receives the `r and `vs` short-signature fields separately.

     *

     * _Available since v4.2._

     */
    function recover(

        bytes32 hash,

        bytes32 r,

        bytes32 vs

    ) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, r, vs);
        _throwError(error);
        return recovered;
    }

    /**

     * @dev Overload of {ECDSA-tryRecover} that receives the `v`,

     * `r` and `s` signature fields separately.

     *

     * _Available since v4.3._

     */
    function tryRecover(

        bytes32 hash,

        uint8 v,

        bytes32 r,

        bytes32 s

    ) internal pure returns (address, RecoverError) {
        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
        // the valid range for s in (301): 0 < s < secp256k1n ÷ 2 + 1, and for v in (302): v ∈ {27, 28}. Most
        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
        //
        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
        // these malleable signatures as well.
        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
            return (address(0), RecoverError.InvalidSignatureS);
        }

        // If the signature is valid (and not malleable), return the signer address
        address signer = ecrecover(hash, v, r, s);
        if (signer == address(0)) {
            return (address(0), RecoverError.InvalidSignature);
        }

        return (signer, RecoverError.NoError);
    }

    /**

     * @dev Overload of {ECDSA-recover} that receives the `v`,

     * `r` and `s` signature fields separately.

     */
    function recover(

        bytes32 hash,

        uint8 v,

        bytes32 r,

        bytes32 s

    ) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, v, r, s);
        _throwError(error);
        return recovered;
    }

    /**

     * @dev Returns an Ethereum Signed Message, created from a `hash`. This

     * produces hash corresponding to the one signed with the

     * https://eth.wiki/json-rpc/API#eth_sign[`eth_sign`]

     * JSON-RPC method as part of EIP-191.

     *

     * See {recover}.

     */
    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
        // 32 is the length in bytes of hash,
        // enforced by the type signature above
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
    }

    /**

     * @dev Returns an Ethereum Signed Message, created from `s`. This

     * produces hash corresponding to the one signed with the

     * https://eth.wiki/json-rpc/API#eth_sign[`eth_sign`]

     * JSON-RPC method as part of EIP-191.

     *

     * See {recover}.

     */
    function toEthSignedMessageHash(bytes memory s) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n", Strings.toString(s.length), s));
    }

    /**

     * @dev Returns an Ethereum Signed Typed Data, created from a

     * `domainSeparator` and a `structHash`. This produces hash corresponding

     * to the one signed with the

     * https://eips.ethereum.org/EIPS/eip-712[`eth_signTypedData`]

     * JSON-RPC method as part of EIP-712.

     *

     * See {recover}.

     */
    function toTypedDataHash(bytes32 domainSeparator, bytes32 structHash) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
    }
}

/**

 * @dev https://eips.ethereum.org/EIPS/eip-712[EIP 712] is a standard for hashing and signing of typed structured data.

 *

 * The encoding specified in the EIP is very generic, and such a generic implementation in Solidity is not feasible,

 * thus this contract does not implement the encoding itself. Protocols need to implement the type-specific encoding

 * they need in their contracts using a combination of `abi.encode` and `keccak256`.

 *

 * This contract implements the EIP 712 domain separator ({_domainSeparatorV4}) that is used as part of the encoding

 * scheme, and the final step of the encoding to obtain the message digest that is then signed via ECDSA

 * ({_hashTypedDataV4}).

 *

 * The implementation of the domain separator was designed to be as efficient as possible while still properly updating

 * the chain id to protect against replay attacks on an eventual fork of the chain.

 *

 * NOTE: This contract implements the version of the encoding known as "v4", as implemented by the JSON RPC method

 * https://docs.metamask.io/guide/signing-data.html[`eth_signTypedDataV4` in MetaMask].

 *

 * _Available since v3.4._

 */
abstract contract EIP712 {
    /* solhint-disable var-name-mixedcase */
    // Cache the domain separator as an immutable value, but also store the chain id that it corresponds to, in order to
    // invalidate the cached domain separator if the chain id changes.
    bytes32 private immutable _CACHED_DOMAIN_SEPARATOR;
    uint256 private immutable _CACHED_CHAIN_ID;
    address private immutable _CACHED_THIS;

    bytes32 private immutable _HASHED_NAME;
    bytes32 private immutable _HASHED_VERSION;
    bytes32 private immutable _TYPE_HASH;

    /* solhint-enable var-name-mixedcase */

    /**

     * @dev Initializes the domain separator and parameter caches.

     *

     * The meaning of `name` and `version` is specified in

     * https://eips.ethereum.org/EIPS/eip-712#definition-of-domainseparator[EIP 712]:

     *

     * - `name`: the user readable name of the signing domain, i.e. the name of the DApp or the protocol.

     * - `version`: the current major version of the signing domain.

     *

     * NOTE: These parameters cannot be changed except through a xref:learn::upgrading-smart-contracts.adoc[smart

     * contract upgrade].

     */
    constructor(string memory name, string memory version) {
        bytes32 hashedName = keccak256(bytes(name));
        bytes32 hashedVersion = keccak256(bytes(version));
        bytes32 typeHash = keccak256(
            "EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"
        );
        _HASHED_NAME = hashedName;
        _HASHED_VERSION = hashedVersion;
        _CACHED_CHAIN_ID = block.chainid;
        _CACHED_DOMAIN_SEPARATOR = _buildDomainSeparator(typeHash, hashedName, hashedVersion);
        _CACHED_THIS = address(this);
        _TYPE_HASH = typeHash;
    }

    /**

     * @dev Returns the domain separator for the current chain.

     */
    function _domainSeparatorV4() internal view returns (bytes32) {
        if (address(this) == _CACHED_THIS && block.chainid == _CACHED_CHAIN_ID) {
            return _CACHED_DOMAIN_SEPARATOR;
        } else {
            return _buildDomainSeparator(_TYPE_HASH, _HASHED_NAME, _HASHED_VERSION);
        }
    }

    function _buildDomainSeparator(

        bytes32 typeHash,

        bytes32 nameHash,

        bytes32 versionHash

    ) private view returns (bytes32) {
        return keccak256(abi.encode(typeHash, nameHash, versionHash, block.chainid, address(this)));
    }

    /**

     * @dev Given an already https://eips.ethereum.org/EIPS/eip-712#definition-of-hashstruct[hashed struct], this

     * function returns the hash of the fully encoded EIP712 message for this domain.

     *

     * This hash can be used together with {ECDSA-recover} to obtain the signer of a message. For example:

     *

     * ```solidity

     * bytes32 digest = _hashTypedDataV4(keccak256(abi.encode(

     *     keccak256("Mail(address to,string contents)"),

     *     mailTo,

     *     keccak256(bytes(mailContents))

     * )));

     * address signer = ECDSA.recover(digest, signature);

     * ```

     */
    function _hashTypedDataV4(bytes32 structHash) internal view virtual returns (bytes32) {
        return ECDSA.toTypedDataHash(_domainSeparatorV4(), structHash);
    }
}

// OpenZeppelin Contracts v4.4.1 (utils/Counters.sol)

/**

 * @title Counters

 * @author Matt Condon (@shrugs)

 * @dev Provides counters that can only be incremented, decremented or reset. This can be used e.g. to track the number

 * of elements in a mapping, issuing ERC721 ids, or counting request ids.

 *

 * Include with `using Counters for Counters.Counter;`

 */
library Counters {
    struct Counter {
        // This variable should never be directly accessed by users of the library: interactions must be restricted to
        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
        // this feature: see https://github.com/ethereum/solidity/issues/4637
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        unchecked {
            counter._value += 1;
        }
    }

    function decrement(Counter storage counter) internal {
        uint256 value = counter._value;
        require(value > 0, "Counter: decrement overflow");
        unchecked {
            counter._value = value - 1;
        }
    }

    function reset(Counter storage counter) internal {
        counter._value = 0;
    }
}

/**

 * @dev Implementation of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in

 * https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].

 *

 * Adds the {permit} method, which can be used to change an account's ERC20 allowance (see {IERC20-allowance}) by

 * presenting a message signed by the account. By not relying on `{IERC20-approve}`, the token holder account doesn't

 * need to send a transaction, and thus is not required to hold Ether at all.

 *

 * _Available since v3.4._

 */
abstract contract ERC20Permit is ERC20, IERC20Permit, EIP712 {
    using Counters for Counters.Counter;

    mapping(address => Counters.Counter) private _nonces;

    // solhint-disable-next-line var-name-mixedcase
    bytes32 private constant _PERMIT_TYPEHASH =
        keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    /**

     * @dev In previous versions `_PERMIT_TYPEHASH` was declared as `immutable`.

     * However, to ensure consistency with the upgradeable transpiler, we will continue

     * to reserve a slot.

     * @custom:oz-renamed-from _PERMIT_TYPEHASH

     */
    // solhint-disable-next-line var-name-mixedcase
    bytes32 private _PERMIT_TYPEHASH_DEPRECATED_SLOT;

    /**

     * @dev Initializes the {EIP712} domain separator using the `name` parameter, and setting `version` to `"1"`.

     *

     * It's a good idea to use the same `name` that is defined as the ERC20 token name.

     */
    constructor(string memory name) EIP712(name, "1") {}

    /**

     * @dev See {IERC20Permit-permit}.

     */
    function permit(

        address owner,

        address spender,

        uint256 value,

        uint256 deadline,

        uint8 v,

        bytes32 r,

        bytes32 s

    ) public virtual override {
        require(block.timestamp <= deadline, "ERC20Permit: expired deadline");

        bytes32 structHash = keccak256(abi.encode(_PERMIT_TYPEHASH, owner, spender, value, _useNonce(owner), deadline));

        bytes32 hash = _hashTypedDataV4(structHash);

        address signer = ECDSA.recover(hash, v, r, s);
        require(signer == owner, "ERC20Permit: invalid signature");

        _approve(owner, spender, value);
    }

    /**

     * @dev See {IERC20Permit-nonces}.

     */
    function nonces(address owner) public view virtual override returns (uint256) {
        return _nonces[owner].current();
    }

    /**

     * @dev See {IERC20Permit-DOMAIN_SEPARATOR}.

     */
    // solhint-disable-next-line func-name-mixedcase
    function DOMAIN_SEPARATOR() external view override returns (bytes32) {
        return _domainSeparatorV4();
    }

    /**

     * @dev "Consume a nonce": return the current value and increment.

     *

     * _Available since v4.1._

     */
    function _useNonce(address owner) internal virtual returns (uint256 current) {
        Counters.Counter storage nonce = _nonces[owner];
        current = nonce.current();
        nonce.increment();
    }
}

// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC20/extensions/ERC20Burnable.sol)

/**

 * @dev Extension of {ERC20} that allows token holders to destroy both their own

 * tokens and those that they have an allowance for, in a way that can be

 * recognized off-chain (via event analysis).

 */
abstract contract ERC20Burnable is Context, ERC20 {
    /**

     * @dev Destroys `amount` tokens from the caller.

     *

     * See {ERC20-_burn}.

     */
    function burn(uint256 amount) public virtual {
        _burn(_msgSender(), amount);
    }

    /**

     * @dev Destroys `amount` tokens from `account`, deducting from the caller's

     * allowance.

     *

     * See {ERC20-_burn} and {ERC20-allowance}.

     *

     * Requirements:

     *

     * - the caller must have allowance for ``accounts``'s tokens of at least

     * `amount`.

     */
    function burnFrom(address account, uint256 amount) public virtual {
        _spendAllowance(account, _msgSender(), amount);
        _burn(account, amount);
    }
}

// https://docs.synthetix.io/contracts/Owned
// NO NEED TO AUDIT
contract Owned {
    address public owner;
    address public nominatedOwner;

    constructor (address _owner) {
        require(_owner != address(0), "Owner address cannot be 0");
        owner = _owner;
        emit OwnerChanged(address(0), _owner);
    }

    function nominateNewOwner(address _owner) external onlyOwner {
        nominatedOwner = _owner;
        emit OwnerNominated(_owner);
    }

    function acceptOwnership() external {
        require(msg.sender == nominatedOwner, "You must be nominated before you can accept ownership");
        emit OwnerChanged(owner, nominatedOwner);
        owner = nominatedOwner;
        nominatedOwner = address(0);
    }

    modifier onlyOwner {
        require(msg.sender == owner, "Only the contract owner may perform this action");
        _;
    }

    event OwnerNominated(address newOwner);
    event OwnerChanged(address oldOwner, address newOwner);
}

/// @title Parent contract for frxETH.sol
/** @notice Combines Openzeppelin's ERC20Permit and ERC20Burnable with Synthetix's Owned. 

    Also includes a list of authorized minters */
/// @dev frxETH adheres to EIP-712/EIP-2612 and can use permits
contract ERC20PermitPermissionedMint is ERC20Permit, ERC20Burnable, Owned {
    // Core
    address public timelock_address;

    // Minters
    address[] public minters_array; // Allowed to mint
    mapping(address => bool) public minters; // Mapping is also used for faster verification

    /* ========== CONSTRUCTOR ========== */

    constructor(
        address _creator_address,
        address _timelock_address,
        string memory _name,
        string memory _symbol
    ) 
    ERC20(_name, _symbol)
    ERC20Permit(_name) 
    Owned(_creator_address)
    {
      timelock_address = _timelock_address;
    }

    /* ========== MODIFIERS ========== */

    modifier onlyByOwnGov() {
        require(msg.sender == timelock_address || msg.sender == owner, "Not owner or timelock");
        _;
    }

    modifier onlyMinters() {
       require(minters[msg.sender] == true, "Only minters");
        _;
    } 

    /* ========== RESTRICTED FUNCTIONS ========== */

    // Used by minters when user redeems
    function minter_burn_from(address b_address, uint256 b_amount) public onlyMinters {
        super.burnFrom(b_address, b_amount);
        emit TokenMinterBurned(b_address, msg.sender, b_amount);
    }

    // This function is what other minters will call to mint new tokens 
    function minter_mint(address m_address, uint256 m_amount) public onlyMinters {
        super._mint(m_address, m_amount);
        emit TokenMinterMinted(msg.sender, m_address, m_amount);
    }

    // Adds whitelisted minters 
    function addMinter(address minter_address) public onlyByOwnGov {
        require(minter_address != address(0), "Zero address detected");

        require(minters[minter_address] == false, "Address already exists");
        minters[minter_address] = true; 
        minters_array.push(minter_address);

        emit MinterAdded(minter_address);
    }

    // Remove a minter 
    function removeMinter(address minter_address) public onlyByOwnGov {
        require(minter_address != address(0), "Zero address detected");
        require(minters[minter_address] == true, "Address nonexistant");
        
        // Delete from the mapping
        delete minters[minter_address];

        // 'Delete' from the array by setting the address to 0x0
        for (uint i = 0; i < minters_array.length; i++){ 
            if (minters_array[i] == minter_address) {
                minters_array[i] = address(0); // This will leave a null in the array and keep the indices the same
                break;
            }
        }

        emit MinterRemoved(minter_address);
    }

    function setTimelock(address _timelock_address) public onlyByOwnGov {
        require(_timelock_address != address(0), "Zero address detected"); 
        timelock_address = _timelock_address;
        emit TimelockChanged(_timelock_address);
    }

    /* ========== EVENTS ========== */
    
    event TokenMinterBurned(address indexed from, address indexed to, uint256 amount);
    event TokenMinterMinted(address indexed from, address indexed to, uint256 amount);
    event MinterAdded(address minter_address);
    event MinterRemoved(address minter_address);
    event TimelockChanged(address timelock_address);
}

contract frxETH is ERC20PermitPermissionedMint {

    /* ========== CONSTRUCTOR ========== */
    constructor(
      address _creator_address,
      address _timelock_address
    ) 
    ERC20PermitPermissionedMint(_creator_address, _timelock_address, "Frax Ether", "frxETH") 
    {}

}