Contract

/**
 *Submitted for verification at Etherscan.io on 2024-03-21
*/

// SPDX-License-Identifier: AGPL-3.0
pragma solidity 0.8.18;

// Math library from https://github.com/ajna-finance/ajna-core/blob/master/src/libraries/internal/Maths.sol

/**
    @title  Maths library
    @notice Internal library containing common maths.
 */
library Maths {
    uint256 internal constant WAD = 1e18;
    uint256 internal constant RAY = 1e27;

    function wmul(uint256 x, uint256 y) internal pure returns (uint256) {
        return (x * y + WAD / 2) / WAD;
    }

    function floorWmul(uint256 x, uint256 y) internal pure returns (uint256) {
        return (x * y) / WAD;
    }

    function ceilWmul(uint256 x, uint256 y) internal pure returns (uint256) {
        return (x * y + WAD - 1) / WAD;
    }

    function wdiv(uint256 x, uint256 y) internal pure returns (uint256) {
        return (x * WAD + y / 2) / y;
    }

    function floorWdiv(uint256 x, uint256 y) internal pure returns (uint256) {
        return (x * WAD) / y;
    }

    function ceilWdiv(uint256 x, uint256 y) internal pure returns (uint256) {
        return (x * WAD + y - 1) / y;
    }

    function ceilDiv(uint256 x, uint256 y) internal pure returns (uint256) {
        return (x + y - 1) / y;
    }

    function max(uint256 x, uint256 y) internal pure returns (uint256) {
        return x >= y ? x : y;
    }

    function min(uint256 x, uint256 y) internal pure returns (uint256) {
        return x <= y ? x : y;
    }

    function wad(uint256 x) internal pure returns (uint256) {
        return x * WAD;
    }

    function rmul(uint256 x, uint256 y) internal pure returns (uint256) {
        return (x * y + RAY / 2) / RAY;
    }

    function rpow(uint256 x, uint256 n) internal pure returns (uint256 z) {
        z = n % 2 != 0 ? x : RAY;

        for (n /= 2; n != 0; n /= 2) {
            x = rmul(x, x);

            if (n % 2 != 0) {
                z = rmul(z, x);
            }
        }
    }

    /*************************/
    /*** Integer Functions ***/
    /*************************/

    function maxInt(int256 x, int256 y) internal pure returns (int256) {
        return x >= y ? x : y;
    }

    function minInt(int256 x, int256 y) internal pure returns (int256) {
        return x <= y ? x : y;
    }
}

contract Governance {
    /// @notice Emitted when the governance address is updated.
    event GovernanceTransferred(
        address indexed previousGovernance,
        address indexed newGovernance
    );

    modifier onlyGovernance() {
        _checkGovernance();
        _;
    }

    /// @notice Checks if the msg sender is the governance.
    function _checkGovernance() internal view virtual {
        require(governance == msg.sender, "!governance");
    }

    /// @notice Address that can set the default base fee and provider
    address public governance;

    constructor(address _governance) {
        governance = _governance;

        emit GovernanceTransferred(address(0), _governance);
    }

    /**
     * @notice Sets a new address as the governance of the contract.
     * @dev Throws if the caller is not current governance.
     * @param _newGovernance The new governance address.
     */
    function transferGovernance(
        address _newGovernance
    ) external virtual onlyGovernance {
        require(_newGovernance != address(0), "ZERO ADDRESS");
        address oldGovernance = governance;
        governance = _newGovernance;

        emit GovernanceTransferred(oldGovernance, _newGovernance);
    }
}

// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/ERC20.sol)

// OpenZeppelin Contracts (last updated v4.9.0) (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 (last updated v4.9.4) (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;
    }

    function _contextSuffixLength() internal view virtual returns (uint256) {
        return 0;
    }
}

/**
 * @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 {}
}

// OpenZeppelin Contracts (last updated v4.9.3) (token/ERC20/utils/SafeERC20.sol)

// OpenZeppelin Contracts (last updated v4.9.4) (token/ERC20/extensions/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.
 *
 * ==== Security Considerations
 *
 * There are two important considerations concerning the use of `permit`. The first is that a valid permit signature
 * expresses an allowance, and it should not be assumed to convey additional meaning. In particular, it should not be
 * considered as an intention to spend the allowance in any specific way. The second is that because permits have
 * built-in replay protection and can be submitted by anyone, they can be frontrun. A protocol that uses permits should
 * take this into consideration and allow a `permit` call to fail. Combining these two aspects, a pattern that may be
 * generally recommended is:
 *
 * ```solidity
 * function doThingWithPermit(..., uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s) public {
 *     try token.permit(msg.sender, address(this), value, deadline, v, r, s) {} catch {}
 *     doThing(..., value);
 * }
 *
 * function doThing(..., uint256 value) public {
 *     token.safeTransferFrom(msg.sender, address(this), value);
 *     ...
 * }
 * ```
 *
 * Observe that: 1) `msg.sender` is used as the owner, leaving no ambiguity as to the signer intent, and 2) the use of
 * `try/catch` allows the permit to fail and makes the code tolerant to frontrunning. (See also
 * {SafeERC20-safeTransferFrom}).
 *
 * Additionally, note that smart contract wallets (such as Argent or Safe) are not able to produce permit signatures, so
 * contracts should have entry points that don't rely on permit.
 */
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].
     *
     * CAUTION: See Security Considerations above.
     */
    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 v4.9.0) (utils/Address.sol)

/**
 * @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
     *
     * Furthermore, `isContract` will also return true if the target contract within
     * the same transaction is already scheduled for destruction by `SELFDESTRUCT`,
     * which only has an effect at the end of a transaction.
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 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://consensys.net/diligence/blog/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/v0.8.0/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 functionCallWithValue(target, data, 0, "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");
        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResultFromTarget(target, 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) {
        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResultFromTarget(target, 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) {
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verify that a low level call to smart-contract was successful, and revert (either by bubbling
     * the revert reason or using the provided one) in case of unsuccessful call or if target was not a contract.
     *
     * _Available since v4.8._
     */
    function verifyCallResultFromTarget(
        address target,
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        if (success) {
            if (returndata.length == 0) {
                // only check isContract if the call was successful and the return data is empty
                // otherwise we already know that it was a contract
                require(isContract(target), "Address: call to non-contract");
            }
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    /**
     * @dev Tool to verify that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason or 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 {
            _revert(returndata, errorMessage);
        }
    }

    function _revert(bytes memory returndata, string memory errorMessage) private pure {
        // 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
            /// @solidity memory-safe-assembly
            assembly {
                let returndata_size := mload(returndata)
                revert(add(32, returndata), returndata_size)
            }
        } else {
            revert(errorMessage);
        }
    }
}

/**
 * @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;

    /**
     * @dev Transfer `value` amount of `token` from the calling contract to `to`. If `token` returns no value,
     * non-reverting calls are assumed to be successful.
     */
    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    /**
     * @dev Transfer `value` amount of `token` from `from` to `to`, spending the approval given by `from` to the
     * calling contract. If `token` returns no value, non-reverting calls are assumed to be successful.
     */
    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));
    }

    /**
     * @dev Increase the calling contract's allowance toward `spender` by `value`. If `token` returns no value,
     * non-reverting calls are assumed to be successful.
     */
    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 oldAllowance = token.allowance(address(this), spender);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, oldAllowance + value));
    }

    /**
     * @dev Decrease the calling contract's allowance toward `spender` by `value`. If `token` returns no value,
     * non-reverting calls are assumed to be successful.
     */
    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");
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, oldAllowance - value));
        }
    }

    /**
     * @dev Set the calling contract's allowance toward `spender` to `value`. If `token` returns no value,
     * non-reverting calls are assumed to be successful. Meant to be used with tokens that require the approval
     * to be set to zero before setting it to a non-zero value, such as USDT.
     */
    function forceApprove(IERC20 token, address spender, uint256 value) internal {
        bytes memory approvalCall = abi.encodeWithSelector(token.approve.selector, spender, value);

        if (!_callOptionalReturnBool(token, approvalCall)) {
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, 0));
            _callOptionalReturn(token, approvalCall);
        }
    }

    /**
     * @dev Use a ERC-2612 signature to set the `owner` approval toward `spender` on `token`.
     * Revert on invalid signature.
     */
    function safePermit(
        IERC20Permit token,
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal {
        uint256 nonceBefore = token.nonces(owner);
        token.permit(owner, spender, value, deadline, v, r, s);
        uint256 nonceAfter = token.nonces(owner);
        require(nonceAfter == nonceBefore + 1, "SafeERC20: permit did not succeed");
    }

    /**
     * @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");
        require(returndata.length == 0 || abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
    }

    /**
     * @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).
     *
     * This is a variant of {_callOptionalReturn} that silents catches all reverts and returns a bool instead.
     */
    function _callOptionalReturnBool(IERC20 token, bytes memory data) private returns (bool) {
        // 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 cannot use {Address-functionCall} here since this should return false
        // and not revert is the subcall reverts.

        (bool success, bytes memory returndata) = address(token).call(data);
        return
            success && (returndata.length == 0 || abi.decode(returndata, (bool))) && Address.isContract(address(token));
    }
}

// OpenZeppelin Contracts (last updated v4.9.0) (security/ReentrancyGuard.sol)

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

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

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        _nonReentrantBefore();
        _;
        _nonReentrantAfter();
    }

    function _nonReentrantBefore() private {
        // On the first call to nonReentrant, _status will be _NOT_ENTERED
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

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

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

    /**
     * @dev Returns true if the reentrancy guard is currently set to "entered", which indicates there is a
     * `nonReentrant` function in the call stack.
     */
    function _reentrancyGuardEntered() internal view returns (bool) {
        return _status == _ENTERED;
    }
}

interface ITaker {
    function auctionTakeCallback(
        bytes32 _auctionId,
        address _sender,
        uint256 _amountTaken,
        uint256 _amountNeeded,
        bytes calldata _data
    ) external;
}

/// @notice Interface that the optional `hook` contract should implement if the non-standard logic is desired.
interface IHook {
    function kickable(address _fromToken) external view returns (uint256);

    function auctionKicked(address _fromToken) external returns (uint256);

    function preTake(
        address _fromToken,
        uint256 _amountToTake,
        uint256 _amountToPay
    ) external;

    function postTake(
        address _toToken,
        uint256 _amountTaken,
        uint256 _amountPayed
    ) external;
}

/**
 *   @title Auction
 *   @author yearn.fi
 *   @notice General use dutch auction contract for token sales.
 */
contract Auction is Governance, ReentrancyGuard {
    using SafeERC20 for ERC20;

    /// @notice Emitted when a new auction is enabled
    event AuctionEnabled(
        bytes32 auctionId,
        address indexed from,
        address indexed to,
        address indexed auctionAddress
    );

    /// @notice Emitted when an auction is disabled.
    event AuctionDisabled(
        bytes32 auctionId,
        address indexed from,
        address indexed to,
        address indexed auctionAddress
    );

    /// @notice Emitted when auction has been kicked.
    event AuctionKicked(bytes32 auctionId, uint256 available);

    /// @notice Emitted when any amount of an active auction was taken.
    event AuctionTaken(
        bytes32 auctionId,
        uint256 amountTaken,
        uint256 amountLeft
    );

    /// @dev Store address and scaler in one slot.
    struct TokenInfo {
        address tokenAddress;
        uint96 scaler;
    }

    /// @notice Store all the auction specific information.
    struct AuctionInfo {
        TokenInfo fromInfo;
        uint96 kicked;
        address receiver;
        uint128 initialAvailable;
        uint128 currentAvailable;
    }

    /// @notice Store the hook address and each flag in one slot.
    struct Hook {
        address hook;
        bool kickable;
        bool kick;
        bool preTake;
        bool postTake;
    }

    uint256 internal constant WAD = 1e18;

    /// @notice Used for the price decay.
    uint256 internal constant MINUTE_HALF_LIFE =
        0.988514020352896135_356867505 * 1e27; // 0.5^(1/60)

    /// @notice Struct to hold the info for `want`.
    TokenInfo internal wantInfo;

    /// @notice Contract to call during write functions.
    Hook internal hook_;

    /// @notice The amount to start the auction at.
    uint256 public startingPrice;

    /// @notice The time that each auction lasts.
    uint256 public auctionLength;

    /// @notice The minimum time to wait between auction 'kicks'.
    uint256 public auctionCooldown;

    /// @notice Mapping from an auction ID to its struct.
    mapping(bytes32 => AuctionInfo) public auctions;

    /// @notice Array of all the enabled auction for this contract.
    bytes32[] public enabledAuctions;

    constructor() Governance(msg.sender) {}

    /**
     * @notice Initializes the Auction contract with initial parameters.
     * @param _want Address this auction is selling to.
     * @param _hook Address of the hook contract (optional).
     * @param _governance Address of the contract governance.
     * @param _auctionLength Duration of each auction in seconds.
     * @param _auctionCooldown Cooldown period between auctions in seconds.
     * @param _startingPrice Starting price for each auction.
     */
    function initialize(
        address _want,
        address _hook,
        address _governance,
        uint256 _auctionLength,
        uint256 _auctionCooldown,
        uint256 _startingPrice
    ) external virtual {
        require(auctionLength == 0, "initialized");
        require(_want != address(0), "ZERO ADDRESS");
        require(_auctionLength != 0, "length");
        require(_auctionLength < _auctionCooldown, "cooldown");
        require(_startingPrice != 0, "starting price");

        // Cannot have more than 18 decimals.
        uint256 decimals = ERC20(_want).decimals();
        require(decimals <= 18, "unsupported decimals");

        // Set variables
        wantInfo = TokenInfo({
            tokenAddress: _want,
            scaler: uint96(WAD / 10 ** decimals)
        });

        // If we are using a hook.
        if (_hook != address(0)) {
            // All flags default to true.
            hook_ = Hook({
                hook: _hook,
                kickable: true,
                kick: true,
                preTake: true,
                postTake: true
            });
        }

        governance = _governance;
        auctionLength = _auctionLength;
        auctionCooldown = _auctionCooldown;
        startingPrice = _startingPrice;
    }

    /*//////////////////////////////////////////////////////////////
                         VIEW METHODS
    //////////////////////////////////////////////////////////////*/

    /**
     * @notice Get the address of this auctions want token.
     * @return . The want token.
     */
    function want() public view virtual returns (address) {
        return wantInfo.tokenAddress;
    }

    /**
     * @notice Get the address of the hook if any.
     * @return . The hook.
     */
    function hook() external view virtual returns (address) {
        return hook_.hook;
    }

    /**
     * @notice Get the current status of which hooks are being used.
     * @return . If the kickable hook is used.
     * @return . If the kick hook is used.
     * @return . If the preTake hook is used.
     * @return . If the postTake hook is used.
     */
    function getHookFlags()
        external
        view
        virtual
        returns (bool, bool, bool, bool)
    {
        Hook memory _hook = hook_;
        return (_hook.kickable, _hook.kick, _hook.preTake, _hook.postTake);
    }

    /**
     * @notice Get the length of the enabled auctions array.
     */
    function numberOfEnabledAuctions() external view virtual returns (uint256) {
        return enabledAuctions.length;
    }

    /**
     * @notice Get the unique auction identifier.
     * @param _from The address of the token to sell.
     * @return bytes32 A unique auction identifier.
     */
    function getAuctionId(address _from) public view virtual returns (bytes32) {
        return keccak256(abi.encodePacked(_from, want(), address(this)));
    }

    /**
     * @notice Retrieves information about a specific auction.
     * @param _auctionId The unique identifier of the auction.
     * @return _from The address of the token to sell.
     * @return _to The address of the token to buy.
     * @return _kicked The timestamp of the last kick.
     * @return _available The current available amount for the auction.
     */
    function auctionInfo(
        bytes32 _auctionId
    )
        public
        view
        virtual
        returns (
            address _from,
            address _to,
            uint256 _kicked,
            uint256 _available
        )
    {
        AuctionInfo memory auction = auctions[_auctionId];

        return (
            auction.fromInfo.tokenAddress,
            want(),
            auction.kicked,
            auction.kicked + auctionLength > block.timestamp
                ? auction.currentAvailable
                : 0
        );
    }

    /**
     * @notice Get the pending amount available for the next auction.
     * @dev Defaults to the auctions balance of the from token if no hook.
     * @param _auctionId The unique identifier of the auction.
     * @return uint256 The amount that can be kicked into the auction.
     */
    function kickable(
        bytes32 _auctionId
    ) external view virtual returns (uint256) {
        // If not enough time has passed then `kickable` is 0.
        if (auctions[_auctionId].kicked + auctionCooldown > block.timestamp) {
            return 0;
        }

        // Check if we have a hook to call.
        Hook memory _hook = hook_;
        if (_hook.kickable) {
            // If so default to the hooks logic.
            return
                IHook(_hook.hook).kickable(
                    auctions[_auctionId].fromInfo.tokenAddress
                );
        } else {
            // Else just use the full balance of this contract.
            return
                ERC20(auctions[_auctionId].fromInfo.tokenAddress).balanceOf(
                    address(this)
                );
        }
    }

    /**
     * @notice Gets the amount of `want` needed to buy a specific amount of `from`.
     * @param _auctionId The unique identifier of the auction.
     * @param _amountToTake The amount of `from` to take in the auction.
     * @return . The amount of `want` needed to fulfill the take amount.
     */
    function getAmountNeeded(
        bytes32 _auctionId,
        uint256 _amountToTake
    ) external view virtual returns (uint256) {
        return
            _getAmountNeeded(
                auctions[_auctionId],
                _amountToTake,
                block.timestamp
            );
    }

    /**
     * @notice Gets the amount of `want` needed to buy a specific amount of `from` at a specific timestamp.
     * @param _auctionId The unique identifier of the auction.
     * @param _amountToTake The amount `from` to take in the auction.
     * @param _timestamp The specific timestamp for calculating the amount needed.
     * @return . The amount of `want` needed to fulfill the take amount.
     */
    function getAmountNeeded(
        bytes32 _auctionId,
        uint256 _amountToTake,
        uint256 _timestamp
    ) external view virtual returns (uint256) {
        return
            _getAmountNeeded(auctions[_auctionId], _amountToTake, _timestamp);
    }

    /**
     * @dev Return the amount of `want` needed to buy `_amountToTake`.
     */
    function _getAmountNeeded(
        AuctionInfo memory _auction,
        uint256 _amountToTake,
        uint256 _timestamp
    ) internal view virtual returns (uint256) {
        return
            // Scale _amountToTake to 1e18
            (_amountToTake *
                _auction.fromInfo.scaler *
                // Price is always 1e18
                _price(
                    _auction.kicked,
                    _auction.initialAvailable * _auction.fromInfo.scaler,
                    _timestamp
                )) /
            1e18 /
            // Scale back down to want.
            wantInfo.scaler;
    }

    /**
     * @notice Gets the price of the auction at the current timestamp.
     * @param _auctionId The unique identifier of the auction.
     * @return . The price of the auction.
     */
    function price(bytes32 _auctionId) external view virtual returns (uint256) {
        return price(_auctionId, block.timestamp);
    }

    /**
     * @notice Gets the price of the auction at a specific timestamp.
     * @param _auctionId The unique identifier of the auction.
     * @param _timestamp The specific timestamp for calculating the price.
     * @return . The price of the auction.
     */
    function price(
        bytes32 _auctionId,
        uint256 _timestamp
    ) public view virtual returns (uint256) {
        // Get unscaled price and scale it down.
        return
            _price(
                auctions[_auctionId].kicked,
                auctions[_auctionId].initialAvailable *
                    auctions[_auctionId].fromInfo.scaler,
                _timestamp
            ) / wantInfo.scaler;
    }

    /**
     * @dev Internal function to calculate the scaled price based on auction parameters.
     * @param _kicked The timestamp the auction was kicked.
     * @param _available The initial available amount scaled 1e18.
     * @param _timestamp The specific timestamp for calculating the price.
     * @return . The calculated price scaled to 1e18.
     */
    function _price(
        uint256 _kicked,
        uint256 _available,
        uint256 _timestamp
    ) internal view virtual returns (uint256) {
        if (_available == 0) return 0;

        uint256 secondsElapsed = _timestamp - _kicked;

        if (secondsElapsed > auctionLength) return 0;

        // Exponential decay from https://github.com/ajna-finance/ajna-core/blob/master/src/libraries/helpers/PoolHelper.sol
        uint256 hoursComponent = 1e27 >> (secondsElapsed / 3600);
        uint256 minutesComponent = Maths.rpow(
            MINUTE_HALF_LIFE,
            (secondsElapsed % 3600) / 60
        );
        uint256 initialPrice = Maths.wdiv(startingPrice * 1e18, _available);

        return
            (initialPrice * Maths.rmul(hoursComponent, minutesComponent)) /
            1e27;
    }

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

    /**
     * @notice Enables a new auction.
     * @dev Uses governance as the receiver.
     * @param _from The address of the token to be auctioned.
     * @return . The unique identifier of the enabled auction.
     */
    function enable(address _from) external virtual returns (bytes32) {
        return enable(_from, msg.sender);
    }

    /**
     * @notice Enables a new auction.
     * @param _from The address of the token to be auctioned.
     * @param _receiver The address that will receive the funds in the auction.
     * @return _auctionId The unique identifier of the enabled auction.
     */
    function enable(
        address _from,
        address _receiver
    ) public virtual onlyGovernance returns (bytes32 _auctionId) {
        address _want = want();
        require(_from != address(0) && _from != _want, "ZERO ADDRESS");
        require(
            _receiver != address(0) && _receiver != address(this),
            "receiver"
        );
        // Cannot have more than 18 decimals.
        uint256 decimals = ERC20(_from).decimals();
        require(decimals <= 18, "unsupported decimals");

        // Calculate the id.
        _auctionId = getAuctionId(_from);

        require(
            auctions[_auctionId].fromInfo.tokenAddress == address(0),
            "already enabled"
        );

        // Store all needed info.
        auctions[_auctionId].fromInfo = TokenInfo({
            tokenAddress: _from,
            scaler: uint96(WAD / 10 ** decimals)
        });
        auctions[_auctionId].receiver = _receiver;

        // Add to the array.
        enabledAuctions.push(_auctionId);

        emit AuctionEnabled(_auctionId, _from, _want, address(this));
    }

    /**
     * @notice Disables an existing auction.
     * @dev Only callable by governance.
     * @param _from The address of the token being sold.
     */
    function disable(address _from) external virtual {
        disable(_from, 0);
    }

    /**
     * @notice Disables an existing auction.
     * @dev Only callable by governance.
     * @param _from The address of the token being sold.
     * @param _index The index the auctionId is at in the array.
     */
    function disable(
        address _from,
        uint256 _index
    ) public virtual onlyGovernance {
        bytes32 _auctionId = getAuctionId(_from);

        // Make sure the auction was enabled.
        require(
            auctions[_auctionId].fromInfo.tokenAddress != address(0),
            "not enabled"
        );

        // Remove the struct.
        delete auctions[_auctionId];

        // Remove the auction ID from the array.
        bytes32[] memory _enabledAuctions = enabledAuctions;
        if (_enabledAuctions[_index] != _auctionId) {
            // If the _index given is not the id find it.
            for (uint256 i = 0; i < _enabledAuctions.length; ++i) {
                if (_enabledAuctions[i] == _auctionId) {
                    _index = i;
                    break;
                }
            }
        }

        // Move the id to the last spot if not there.
        if (_index < _enabledAuctions.length - 1) {
            _enabledAuctions[_index] = _enabledAuctions[
                _enabledAuctions.length - 1
            ];
            // Update the array.
            enabledAuctions = _enabledAuctions;
        }

        // Pop the id off the array.
        enabledAuctions.pop();

        emit AuctionDisabled(_auctionId, _from, want(), address(this));
    }

    /**
     * @notice Set the flags to be used with hook.
     * @param _kickable If the kickable hook should be used.
     * @param _kick If the kick hook should be used.
     * @param _preTake If the preTake hook should be used.
     * @param _postTake If the postTake should be used.
     */
    function setHookFlags(
        bool _kickable,
        bool _kick,
        bool _preTake,
        bool _postTake
    ) external virtual onlyGovernance {
        address _hook = hook_.hook;
        require(_hook != address(0), "no hook set");

        hook_ = Hook({
            hook: _hook,
            kickable: _kickable,
            kick: _kick,
            preTake: _preTake,
            postTake: _postTake
        });
    }

    /*//////////////////////////////////////////////////////////////
                      PARTICIPATE IN AUCTION
    //////////////////////////////////////////////////////////////*/

    /**
     * @notice Kicks off an auction, updating its status and making funds available for bidding.
     * @param _auctionId The unique identifier of the auction.
     * @return available The available amount for bidding on in the auction.
     */
    function kick(
        bytes32 _auctionId
    ) external virtual nonReentrant returns (uint256 available) {
        address _fromToken = auctions[_auctionId].fromInfo.tokenAddress;
        require(_fromToken != address(0), "not enabled");
        require(
            block.timestamp > auctions[_auctionId].kicked + auctionCooldown,
            "too soon"
        );

        Hook memory _hook = hook_;
        // Use hook if defined.
        if (_hook.kick) {
            available = IHook(_hook.hook).auctionKicked(_fromToken);
        } else {
            // Else just use current balance.
            available = ERC20(_fromToken).balanceOf(address(this));
        }

        require(available != 0, "nothing to kick");

        // Update the auctions status.
        auctions[_auctionId].kicked = uint96(block.timestamp);
        auctions[_auctionId].initialAvailable = uint128(available);
        auctions[_auctionId].currentAvailable = uint128(available);

        emit AuctionKicked(_auctionId, available);
    }

    /**
     * @notice Take the token being sold in a live auction.
     * @dev Defaults to taking the full amount and sending to the msg sender.
     * @param _auctionId The unique identifier of the auction.
     * @return . The amount of fromToken taken in the auction.
     */
    function take(bytes32 _auctionId) external virtual returns (uint256) {
        return _take(_auctionId, type(uint256).max, msg.sender, new bytes(0));
    }

    /**
     * @notice Take the token being sold in a live auction with a specified maximum amount.
     * @dev Uses the sender's address as the receiver.
     * @param _auctionId The unique identifier of the auction.
     * @param _maxAmount The maximum amount of fromToken to take in the auction.
     * @return . The amount of fromToken taken in the auction.
     */
    function take(
        bytes32 _auctionId,
        uint256 _maxAmount
    ) external virtual returns (uint256) {
        return _take(_auctionId, _maxAmount, msg.sender, new bytes(0));
    }

    /**
     * @notice Take the token being sold in a live auction.
     * @param _auctionId The unique identifier of the auction.
     * @param _maxAmount The maximum amount of fromToken to take in the auction.
     * @param _receiver The address that will receive the fromToken.
     * @return _amountTaken The amount of fromToken taken in the auction.
     */
    function take(
        bytes32 _auctionId,
        uint256 _maxAmount,
        address _receiver
    ) external virtual returns (uint256) {
        return _take(_auctionId, _maxAmount, _receiver, new bytes(0));
    }

    /**
     * @notice Take the token being sold in a live auction.
     * @param _auctionId The unique identifier of the auction.
     * @param _maxAmount The maximum amount of fromToken to take in the auction.
     * @param _receiver The address that will receive the fromToken.
     * @param _data The data signify the callback should be used and sent with it.
     * @return _amountTaken The amount of fromToken taken in the auction.
     */
    function take(
        bytes32 _auctionId,
        uint256 _maxAmount,
        address _receiver,
        bytes calldata _data
    ) external virtual returns (uint256) {
        return _take(_auctionId, _maxAmount, _receiver, _data);
    }

    /// @dev Implements the take of the auction.
    function _take(
        bytes32 _auctionId,
        uint256 _maxAmount,
        address _receiver,
        bytes memory _data
    ) internal virtual nonReentrant returns (uint256 _amountTaken) {
        AuctionInfo memory auction = auctions[_auctionId];
        // Make sure the auction is active.
        require(
            auction.kicked + auctionLength >= block.timestamp,
            "not kicked"
        );

        // Max amount that can be taken.
        _amountTaken = auction.currentAvailable > _maxAmount
            ? _maxAmount
            : auction.currentAvailable;

        // Get the amount needed
        uint256 needed = _getAmountNeeded(
            auction,
            _amountTaken,
            block.timestamp
        );

        require(needed != 0, "zero needed");

        // How much is left in this auction.
        uint256 left;
        unchecked {
            left = auction.currentAvailable - _amountTaken;
        }
        auctions[_auctionId].currentAvailable = uint128(left);

        Hook memory _hook = hook_;
        if (_hook.preTake) {
            // Use hook if defined.
            IHook(_hook.hook).preTake(
                auction.fromInfo.tokenAddress,
                _amountTaken,
                needed
            );
        }

        // Send `from`.
        ERC20(auction.fromInfo.tokenAddress).safeTransfer(
            _receiver,
            _amountTaken
        );

        // If the caller has specified data.
        if (_data.length != 0) {
            // Do the callback.
            ITaker(_receiver).auctionTakeCallback(
                _auctionId,
                msg.sender,
                _amountTaken,
                needed,
                _data
            );
        }

        // Cache the want address.
        address _want = want();

        // Pull `want`.
        ERC20(_want).safeTransferFrom(msg.sender, auction.receiver, needed);

        // Post take hook if defined.
        if (_hook.postTake) {
            IHook(_hook.hook).postTake(_want, _amountTaken, needed);
        }

        emit AuctionTaken(_auctionId, _amountTaken, left);
    }
}

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