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



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

pragma solidity ^0.8.0;

import "./IAccessControl.sol";
import "../utils/Context.sol";
import "../utils/Strings.sol";
import "../utils/introspection/ERC165.sol";

/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms. This is a lightweight version that doesn't allow enumerating role
 * members except through off-chain means by accessing the contract event logs. Some
 * applications may benefit from on-chain enumerability, for those cases see
 * {AccessControlEnumerable}.
 *
 * Roles are referred to by their `bytes32` identifier. These should be exposed
 * in the external API and be unique. The best way to achieve this is by
 * using `public constant` hash digests:
 *
 * ```solidity
 * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
 * ```
 *
 * Roles can be used to represent a set of permissions. To restrict access to a
 * function call, use {hasRole}:
 *
 * ```solidity
 * function foo() public {
 *     require(hasRole(MY_ROLE, msg.sender));
 *     ...
 * }
 * ```
 *
 * Roles can be granted and revoked dynamically via the {grantRole} and
 * {revokeRole} functions. Each role has an associated admin role, and only
 * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
 *
 * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
 * that only accounts with this role will be able to grant or revoke other
 * roles. More complex role relationships can be created by using
 * {_setRoleAdmin}.
 *
 * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
 * grant and revoke this role. Extra precautions should be taken to secure
 * accounts that have been granted it. We recommend using {AccessControlDefaultAdminRules}
 * to enforce additional security measures for this role.
 */
abstract contract AccessControl is Context, IAccessControl, ERC165 {
    struct RoleData {
        mapping(address => bool) members;
        bytes32 adminRole;
    }

    mapping(bytes32 => RoleData) private _roles;

    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

    /**
     * @dev Modifier that checks that an account has a specific role. Reverts
     * with a standardized message including the required role.
     *
     * The format of the revert reason is given by the following regular expression:
     *
     *  /^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/
     *
     * _Available since v4.1._
     */
    modifier onlyRole(bytes32 role) {
        _checkRole(role);
        _;
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IAccessControl).interfaceId || super.supportsInterface(interfaceId);
    }

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) public view virtual override returns (bool) {
        return _roles[role].members[account];
    }

    /**
     * @dev Revert with a standard message if `_msgSender()` is missing `role`.
     * Overriding this function changes the behavior of the {onlyRole} modifier.
     *
     * Format of the revert message is described in {_checkRole}.
     *
     * _Available since v4.6._
     */
    function _checkRole(bytes32 role) internal view virtual {
        _checkRole(role, _msgSender());
    }

    /**
     * @dev Revert with a standard message if `account` is missing `role`.
     *
     * The format of the revert reason is given by the following regular expression:
     *
     *  /^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/
     */
    function _checkRole(bytes32 role, address account) internal view virtual {
        if (!hasRole(role, account)) {
            revert(
                string(
                    abi.encodePacked(
                        "AccessControl: account ",
                        Strings.toHexString(account),
                        " is missing role ",
                        Strings.toHexString(uint256(role), 32)
                    )
                )
            );
        }
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) public view virtual override returns (bytes32) {
        return _roles[role].adminRole;
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     *
     * May emit a {RoleGranted} event.
     */
    function grantRole(bytes32 role, address account) public virtual override onlyRole(getRoleAdmin(role)) {
        _grantRole(role, account);
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     *
     * May emit a {RoleRevoked} event.
     */
    function revokeRole(bytes32 role, address account) public virtual override onlyRole(getRoleAdmin(role)) {
        _revokeRole(role, account);
    }

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been revoked `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     *
     * May emit a {RoleRevoked} event.
     */
    function renounceRole(bytes32 role, address account) public virtual override {
        require(account == _msgSender(), "AccessControl: can only renounce roles for self");

        _revokeRole(role, account);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event. Note that unlike {grantRole}, this function doesn't perform any
     * checks on the calling account.
     *
     * May emit a {RoleGranted} event.
     *
     * [WARNING]
     * ====
     * This function should only be called from the constructor when setting
     * up the initial roles for the system.
     *
     * Using this function in any other way is effectively circumventing the admin
     * system imposed by {AccessControl}.
     * ====
     *
     * NOTE: This function is deprecated in favor of {_grantRole}.
     */
    function _setupRole(bytes32 role, address account) internal virtual {
        _grantRole(role, account);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.
     *
     * Emits a {RoleAdminChanged} event.
     */
    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
        bytes32 previousAdminRole = getRoleAdmin(role);
        _roles[role].adminRole = adminRole;
        emit RoleAdminChanged(role, previousAdminRole, adminRole);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * Internal function without access restriction.
     *
     * May emit a {RoleGranted} event.
     */
    function _grantRole(bytes32 role, address account) internal virtual {
        if (!hasRole(role, account)) {
            _roles[role].members[account] = true;
            emit RoleGranted(role, account, _msgSender());
        }
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * Internal function without access restriction.
     *
     * May emit a {RoleRevoked} event.
     */
    function _revokeRole(bytes32 role, address account) internal virtual {
        if (hasRole(role, account)) {
            _roles[role].members[account] = false;
            emit RoleRevoked(role, account, _msgSender());
        }
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/IAccessControl.sol)

pragma solidity ^0.8.0;

/**
 * @dev External interface of AccessControl declared to support ERC165 detection.
 */
interface IAccessControl {
    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
     *
     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call, an admin role
     * bearer except when using {AccessControl-_setupRole}.
     */
    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Emitted when `account` is revoked `role`.
     *
     * `sender` is the account that originated the contract call:
     *   - if using `revokeRole`, it is the admin role bearer
     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
     */
    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) external view returns (bool);

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {AccessControl-_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) external view returns (bytes32);

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) external;

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) external;

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) external;
}

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



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

pragma solidity ^0.8.0;

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

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

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

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

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

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

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
    }

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

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

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// File: @openzeppelin/contracts/interfaces/IERC20Metadata.sol



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

pragma solidity ^0.8.0;

import "../token/ERC20/extensions/IERC20Metadata.sol";

// File: @openzeppelin/contracts/security/Pausable.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (security/Pausable.sol)

pragma solidity ^0.8.0;

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

/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor() {
        _paused = false;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        _requireNotPaused();
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        _requirePaused();
        _;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Throws if the contract is paused.
     */
    function _requireNotPaused() internal view virtual {
        require(!paused(), "Pausable: paused");
    }

    /**
     * @dev Throws if the contract is not paused.
     */
    function _requirePaused() internal view virtual {
        require(paused(), "Pausable: not paused");
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

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



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

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * The default value of {decimals} is 18. To change this, you should override
 * this function so it returns a different value.
 *
 * We have followed general OpenZeppelin Contracts guidelines: functions revert
 * instead returning `false` on failure. This behavior is nonetheless
 * conventional and does not conflict with the expectations of ERC20
 * applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

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

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

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

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

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5.05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the default value returned by this function, unless
     * it's overridden.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual override returns (uint8) {
        return 18;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address to, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address from, address to, uint256 amount) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, amount);
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, allowance(owner, spender) + addedValue);
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        address owner = _msgSender();
        uint256 currentAllowance = allowance(owner, spender);
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `from` to `to`.
     *
     * This internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     */
    function _transfer(address from, address to, uint256 amount) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(from, to, amount);

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

        emit Transfer(from, to, amount);

        _afterTokenTransfer(from, to, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

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

        _afterTokenTransfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

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

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

        _afterTokenTransfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

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

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual {}

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * has been transferred to `to`.
     * - when `from` is zero, `amount` tokens have been minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens have been burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _afterTokenTransfer(address from, address to, uint256 amount) internal virtual {}
}

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



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

pragma solidity ^0.8.0;

import "../IERC20.sol";

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

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

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

// File: @openzeppelin/contracts/token/ERC20/extensions/IERC20Permit.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/extensions/IERC20Permit.sol)

pragma solidity ^0.8.0;

/**
 * @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);
}

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



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

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

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

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

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

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

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

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

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

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/utils/SafeERC20.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../extensions/IERC20Permit.sol";
import "../../../utils/Address.sol";

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

    /**
     * @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. Compatible with tokens that require the approval to be set to
     * 0 before setting it to a non-zero value.
     */
    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));
    }
}

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



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

pragma solidity ^0.8.1;

/**
 * @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);
        }
    }
}

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



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

pragma solidity ^0.8.0;

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

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

// File: @openzeppelin/contracts/utils/introspection/ERC165.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)

pragma solidity ^0.8.0;

import "./IERC165.sol";

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
 * for the additional interface id that will be supported. For example:
 *
 * ```solidity
 * function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
 *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
 * }
 * ```
 *
 * Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
 */
abstract contract ERC165 is IERC165 {
    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IERC165).interfaceId;
    }
}

// File: @openzeppelin/contracts/utils/introspection/IERC165.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/introspection/IERC165.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (utils/math/Math.sol)

pragma solidity ^0.8.0;

/**
 * @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) {
                // Solidity will revert if denominator == 0, unlike the div opcode on its own.
                // The surrounding unchecked block does not change this fact.
                // See https://docs.soliditylang.org/en/latest/control-structures.html#checked-or-unchecked-arithmetic.
                return prod0 / denominator;
            }

            // Make sure the result is less than 2^256. Also prevents denominator == 0.
            require(denominator > prod1, "Math: mulDiv overflow");

            ///////////////////////////////////////////////
            // 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 256, 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);
        }
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (utils/math/SafeMath.sol)

pragma solidity ^0.8.0;

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

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is generally not needed starting with Solidity 0.8, since the compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

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

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.8.0) (utils/math/SignedMath.sol)

pragma solidity ^0.8.0;

/**
 * @dev Standard signed math utilities missing in the Solidity language.
 */
library SignedMath {
    /**
     * @dev Returns the largest of two signed numbers.
     */
    function max(int256 a, int256 b) internal pure returns (int256) {
        return a > b ? a : b;
    }

    /**
     * @dev Returns the smallest of two signed numbers.
     */
    function min(int256 a, int256 b) internal pure returns (int256) {
        return a < b ? a : b;
    }

    /**
     * @dev Returns the average of two signed numbers without overflow.
     * The result is rounded towards zero.
     */
    function average(int256 a, int256 b) internal pure returns (int256) {
        // Formula from the book "Hacker's Delight"
        int256 x = (a & b) + ((a ^ b) >> 1);
        return x + (int256(uint256(x) >> 255) & (a ^ b));
    }

    /**
     * @dev Returns the absolute unsigned value of a signed value.
     */
    function abs(int256 n) internal pure returns (uint256) {
        unchecked {
            // must be unchecked in order to support `n = type(int256).min`
            return uint256(n >= 0 ? n : -n);
        }
    }
}

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



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

pragma solidity ^0.8.0;

import "./math/Math.sol";
import "./math/SignedMath.sol";

/**
 * @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 `int256` to its ASCII `string` decimal representation.
     */
    function toString(int256 value) internal pure returns (string memory) {
        return string(abi.encodePacked(value < 0 ? "-" : "", toString(SignedMath.abs(value))));
    }

    /**
     * @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 Returns true if the two strings are equal.
     */
    function equal(string memory a, string memory b) internal pure returns (bool) {
        return keccak256(bytes(a)) == keccak256(bytes(b));
    }
}

// File: contracts/interfaces/IInterestRateModel.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.18;

interface IInterestRateModel {
	function getSupplyInterestRate(
		uint256 totalSupply,
		uint256 totalBorrow
	) external pure returns (uint);
}

// File: contracts/interfaces/ILiquidatePool.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.18;

interface ILiquidatePool {
	function liquidateSTBT(address caller, uint256 stbtAmount) external;

	function flashLiquidateSTBTByCurve(
		uint256 stbtAmount,
		int128 j,
		uint256 minReturn,
		address receiver
	) external;
}

// File: contracts/interfaces/IMigrator.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.18;

interface IMigrator {}

// File: contracts/interfaces/ISTBT.sol



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

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/interfaces/IERC20Metadata.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

interface IERC1644 is IERC20 {
	// Controller Events
	event ControllerTransfer(
		address _controller,
		address indexed _from,
		address indexed _to,
		uint256 _value,
		bytes _data,
		bytes _operatorData
	);

	event ControllerRedemption(
		address _controller,
		address indexed _tokenHolder,
		uint256 _value,
		bytes _data,
		bytes _operatorData
	);

	// Controller Operation
	function isControllable() external view returns (bool);

	function controllerTransfer(
		address _from,
		address _to,
		uint256 _value,
		bytes calldata _data,
		bytes calldata _operatorData
	) external;

	function controllerRedeem(
		address _tokenHolder,
		uint256 _value,
		bytes calldata _data,
		bytes calldata _operatorData
	) external;
}

interface IERC1643 {
	// Document Events
	event DocumentRemoved(bytes32 indexed _name, string _uri, bytes32 _documentHash);
	event DocumentUpdated(bytes32 indexed _name, string _uri, bytes32 _documentHash);

	// Document Management
	function getDocument(bytes32 _name) external view returns (string memory, bytes32, uint256);

	function setDocument(bytes32 _name, string calldata _uri, bytes32 _documentHash) external;

	function removeDocument(bytes32 _name) external;

	function getAllDocuments() external view returns (bytes32[] memory);
}

interface IERC1594 is IERC20 {
	// Issuance / Redemption Events
	event Issued(address indexed _operator, address indexed _to, uint256 _value, bytes _data);
	event Redeemed(address indexed _operator, address indexed _from, uint256 _value, bytes _data);

	// Transfers
	function transferWithData(address _to, uint256 _value, bytes calldata _data) external;

	function transferFromWithData(
		address _from,
		address _to,
		uint256 _value,
		bytes calldata _data
	) external;

	// Token Issuance
	function isIssuable() external view returns (bool);

	function issue(address _tokenHolder, uint256 _value, bytes calldata _data) external;

	// Token Redemption
	function redeem(uint256 _value, bytes calldata _data) external;

	function redeemFrom(address _tokenHolder, uint256 _value, bytes calldata _data) external;

	// Transfer Validity
	function canTransfer(
		address _to,
		uint256 _value,
		bytes calldata _data
	) external view returns (bool, uint8, bytes32);

	function canTransferFrom(
		address _from,
		address _to,
		uint256 _value,
		bytes calldata _data
	) external view returns (bool, uint8, bytes32);
}

interface ISTBT is IERC20, IERC20Metadata, IERC1594, IERC1643, IERC1644 {
	struct Permission {
		bool sendAllowed; // default: true
		bool receiveAllowed;
		// Address holder’s KYC will be validated till this time, after that the holder needs to re-KYC.
		uint64 expiryTime; // default:0 validated forever
	}

	function setIssuer(address _issuer) external;

	function setController(address _controller) external;

	function setModerator(address _moderator) external;

	function setMinDistributeInterval(uint64 interval) external;

	function setMaxDistributeRatio(uint64 ratio) external;

	function setPermission(address addr, Permission calldata permission) external;

	function distributeInterests(
		int256 _distributedInterest,
		uint interestFromTime,
		uint interestToTime
	) external;

	function increaseAllowance(address _spender, uint256 _addedValue) external returns (bool);

	function decreaseAllowance(address _spender, uint256 _subtractedValue) external returns (bool);

	function sharesOf(address _account) external view returns (uint256);

	function getSharesByAmount(uint256 _amount) external view returns (uint256 result);

	function getAmountByShares(uint256 _shares) external view returns (uint256 result);
}

// File: contracts/rUSTP.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.18;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/utils/math/SafeMath.sol";

/**
 * @title Interest-bearing ERC20-like token for TProtocol.
 *
 * This contract is abstract. To make the contract deployable override the
 * `_getTotalSupplyrUSTP` function. `rUSTPool.sol` contract inherits rUSTP and defines
 * the `_getTotalSupplyrUSTP` function.
 *
 * rUSTP balances are dynamic and represent the holder's share in the total amount
 * of Ether controlled by the protocol. Account shares aren't normalized, so the
 * contract also stores the sum of all shares to calculate each account's token balance
 * which equals to:
 *
 *   shares[account] * _getTotalSupplyrUSTP() / _getTotalShares()
 *
 * For example, assume that we have:
 *
 *   _getTotalSupplyrUSTP() -> 10 rUSTP
 *   sharesOf(user1) -> 100
 *   sharesOf(user2) -> 400
 *
 * Therefore:
 *
 *   balanceOf(user1) -> 2 tokens which corresponds 2 rUSTP
 *   balanceOf(user2) -> 8 tokens which corresponds 8 rUSTP
 *
 * Since balances of all token holders change when the amount of total supplied rUSTP
 * changes, this token cannot fully implement ERC20 standard: it only emits `Transfer`
 * events upon explicit transfer between holders. In contrast, when total amount of
 * pooled Ether increases, no `Transfer` events are generated: doing so would require
 * emitting an event for each token holder and thus running an unbounded loop.
 */

abstract contract rUSTP is ERC20 {
	using SafeMath for uint256;
	uint256 private totalShares;

	/**
	 * @dev rUSTP balances are dynamic and are calculated based on the accounts' shares
	 * and the total amount of Ether controlled by the protocol. Account shares aren't
	 * normalized, so the contract also stores the sum of all shares to calculate
	 * each account's token balance which equals to:
	 *
	 *   shares[account] * _getTotalSupplyrUSTP() / _getTotalShares()
	 */
	mapping(address => uint256) private shares;

	/**
	 * @dev Allowances are nominated in tokens, not token shares.
	 */
	mapping(address => mapping(address => uint256)) private allowances;

	/**
	 * @notice An executed shares transfer from `sender` to `recipient`.
	 *
	 * @dev emitted in pair with an ERC20-defined `Transfer` event.
	 */
	event TransferShares(address indexed from, address indexed to, uint256 sharesValue);

	/**
	 * @notice An executed `burnShares` request
	 *
	 * @dev Reports simultaneously burnt shares amount
	 * and corresponding rUSTP amount.
	 * The rUSTP amount is calculated twice: before and after the burning incurred rebase.
	 *
	 * @param account holder of the burnt shares
	 * @param preRebaseTokenAmount amount of rUSTP the burnt shares corresponded to before the burn
	 * @param postRebaseTokenAmount amount of rUSTP the burnt shares corresponded to after the burn
	 * @param sharesAmount amount of burnt shares
	 */
	event SharesBurnt(
		address indexed account,
		uint256 preRebaseTokenAmount,
		uint256 postRebaseTokenAmount,
		uint256 sharesAmount
	);

	/**
	 * @return the number of decimals for getting user representation of a token amount.
	 */
	function decimals() public pure override returns (uint8) {
		return 18;
	}

	/**
	 * @return the amount of tokens in existence.
	 *
	 * @dev Always equals to `_getTotalSupplyrUSTP()` since token amount
	 * is pegged to the total amount of rUSTP controlled by the protocol.
	 */
	function totalSupply() public view override returns (uint256) {
		return _getTotalSupplyrUSTP();
	}

	/**
	 * @return the amount of tokens owned by the `_account`.
	 *
	 * @dev Balances are dynamic and equal the `_account`'s share in the amount of the
	 * total rUSTP controlled by the protocol. See `sharesOf`.
	 */
	function balanceOf(address _account) public view override returns (uint256) {
		return getrUSTPAmountByShares(_sharesOf(_account));
	}

	/**
	 * @return the total amount of shares in existence.
	 *
	 * @dev The sum of all accounts' shares can be an arbitrary number, therefore
	 * it is necessary to store it in order to calculate each account's relative share.
	 */
	function getTotalShares() public view returns (uint256) {
		return _getTotalShares();
	}

	/**
	 * @return the amount of shares owned by `_account`.
	 */
	function sharesOf(address _account) external view returns (uint256) {
		return _sharesOf(_account);
	}

	/**
	 * @return the amount of shares that corresponds to `_rUSTPAmount` protocol-supplied rUSTP.
	 */
	function getSharesByrUSTPAmount(uint256 _rUSTPAmount) public view returns (uint256) {
		uint256 totalSupplyrUSTP = _getTotalSupplyrUSTP();
		return
			totalSupplyrUSTP == 0 ? 0 : _rUSTPAmount.mul(_getTotalShares()).div(totalSupplyrUSTP);
	}

	/**
	 * @return the amount of rUSTP that corresponds to `_sharesAmount` token shares.
	 */
	function getrUSTPAmountByShares(uint256 _sharesAmount) public view returns (uint256) {
		uint256 totalSharesAmount = _getTotalShares();
		return
			totalSharesAmount == 0
				? 0
				: _sharesAmount.mul(_getTotalSupplyrUSTP()).div(totalSharesAmount);
	}

	/**
	 * @notice Moves `_sharesAmount` token shares from the caller's account to the `_recipient` account.
	 *
	 * @return amount of transferred tokens.
	 * Emits a `TransferShares` event.
	 * Emits a `Transfer` event.
	 *
	 * Requirements:
	 *
	 * - `_recipient` cannot be the zero address.
	 * - the caller must have at least `_sharesAmount` shares.
	 * - the contract must not be paused.
	 *
	 * @dev The `_sharesAmount` argument is the amount of shares, not tokens.
	 */
	function transferShares(address _recipient, uint256 _sharesAmount) external returns (uint256) {
		_transferShares(msg.sender, _recipient, _sharesAmount);
		uint256 tokensAmount = getrUSTPAmountByShares(_sharesAmount);
		_emitTransferEvents(msg.sender, _recipient, tokensAmount, _sharesAmount);
		return tokensAmount;
	}

	/**
	 * @return the total amount of rUSTP.
	 * @dev This is used for calculating tokens from shares and vice versa.
	 * @dev This function is required to be implemented in a derived contract.
	 */
	function _getTotalSupplyrUSTP() internal view virtual returns (uint256);

	/**
	 * @notice Moves `_amount` tokens from `_sender` to `_recipient`.
	 * Emits a `Transfer` event.
	 * Emits a `TransferShares` event.
	 */
	function _transfer(address _sender, address _recipient, uint256 _amount) internal override {
		uint256 _sharesToTransfer = getSharesByrUSTPAmount(_amount);
		_transferShares(_sender, _recipient, _sharesToTransfer);
		_emitTransferEvents(_sender, _recipient, _amount, _sharesToTransfer);
	}

	/**
	 * @return the total amount of shares in existence.
	 */
	function _getTotalShares() internal view returns (uint256) {
		return totalShares;
	}

	/**
	 * @return the amount of shares owned by `_account`.
	 */
	function _sharesOf(address _account) internal view returns (uint256) {
		return shares[_account];
	}

	/**
	 * @notice Moves `_sharesAmount` shares from `_sender` to `_recipient`.
	 *
	 * Requirements:
	 *
	 * - `_sender` cannot be the zero address.
	 * - `_recipient` cannot be the zero address.
	 * - `_sender` must hold at least `_sharesAmount` shares.
	 * - the contract must not be paused.
	 */
	function _transferShares(address _sender, address _recipient, uint256 _sharesAmount) internal {
		require(_sender != address(0), "TRANSFER_FROM_THE_ZERO_ADDRESS");
		require(_recipient != address(0), "TRANSFER_TO_THE_ZERO_ADDRESS");

		uint256 currentSenderShares = shares[_sender];
		require(_sharesAmount <= currentSenderShares, "TRANSFER_AMOUNT_EXCEEDS_BALANCE");

		shares[_sender] = currentSenderShares.sub(_sharesAmount);
		shares[_recipient] = shares[_recipient].add(_sharesAmount);
	}

	/**
	 * @notice Creates `_sharesAmount` shares and assigns them to `_recipient`, increasing the total amount of shares.
	 * @dev This doesn't increase the token total supply.
	 *
	 * NB: The method doesn't check protocol pause relying on the external enforcement.
	 *
	 * Requirements:
	 *
	 * - `_recipient` cannot be the zero address.
	 * - the contract must not be paused.
	 */
	function _mintShares(
		address _recipient,
		uint256 _sharesAmount
	) internal returns (uint256 newTotalShares) {
		require(_recipient != address(0), "MINT_TO_ZERO_ADDR");

		newTotalShares = _getTotalShares().add(_sharesAmount);
		totalShares = newTotalShares;

		shares[_recipient] = shares[_recipient].add(_sharesAmount);

		// Notice: we're not emitting a Transfer event from the zero address here since shares mint
		// works by taking the amount of tokens corresponding to the minted shares from all other
		// token holders, proportionally to their share. The total supply of the token doesn't change
		// as the result. This is equivalent to performing a send from each other token holder's
		// address to `address`, but we cannot reflect this as it would require sending an unbounded
		// number of events.
	}

	/**
	 * @notice Destroys `_sharesAmount` shares from `_account`'s holdings, decreasing the total amount of shares.
	 * @dev This doesn't decrease the token total supply.
	 *
	 * Requirements:
	 *
	 * - `_account` cannot be the zero address.
	 * - `_account` must hold at least `_sharesAmount` shares.
	 * - the contract must not be paused.
	 */
	function _burnShares(
		address _account,
		uint256 _sharesAmount
	) internal returns (uint256 newTotalShares) {
		require(_account != address(0), "BURN_FROM_ZERO_ADDR");

		uint256 accountShares = shares[_account];
		require(_sharesAmount <= accountShares, "BALANCE_EXCEEDED");

		uint256 preRebaseTokenAmount = getrUSTPAmountByShares(_sharesAmount);

		newTotalShares = _getTotalShares().sub(_sharesAmount);
		totalShares = newTotalShares;

		shares[_account] = accountShares.sub(_sharesAmount);

		uint256 postRebaseTokenAmount = getrUSTPAmountByShares(_sharesAmount);

		emit SharesBurnt(_account, preRebaseTokenAmount, postRebaseTokenAmount, _sharesAmount);

		// Notice: we're not emitting a Transfer event to the zero address here since shares burn
		// works by redistributing the amount of tokens corresponding to the burned shares between
		// all other token holders. The total supply of the token doesn't change as the result.
		// This is equivalent to performing a send from `address` to each other token holder address,
		// but we cannot reflect this as it would require sending an unbounded number of events.

		// We're emitting `SharesBurnt` event to provide an explicit rebase log record nonetheless.
	}

	/**
	 * @dev Emits {Transfer} and {TransferShares} events
	 */
	function _emitTransferEvents(
		address _from,
		address _to,
		uint _tokenAmount,
		uint256 _sharesAmount
	) internal {
		emit Transfer(_from, _to, _tokenAmount);
		emit TransferShares(_from, _to, _sharesAmount);
	}
}

// File: contracts/rUSTPool.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.18;

import "@openzeppelin/contracts/access/AccessControl.sol";
import "@openzeppelin/contracts/security/Pausable.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "@openzeppelin/contracts/utils/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

import "./interfaces/ISTBT.sol";
import "./interfaces/IInterestRateModel.sol";
import "./interfaces/ILiquidatePool.sol";
import "./interfaces/IMigrator.sol";
import "./rUSTP.sol";

contract rUSTPool is rUSTP, AccessControl, Pausable {
	using SafeERC20 for IERC20;
	using SafeMath for uint256;

	bytes32 public constant POOL_MANAGER_ROLE = keccak256("POOL_MANAGER_ROLE");

	uint256 public lastCheckpoint;
	// Used to calculate the interest base.
	uint256 public constant APR_COEFFICIENT = 1e8;
	// Used to calculate the fee base.
	uint256 public constant FEE_COEFFICIENT = 1e8;
	// Used to calculate shares of STBT deposited by users.
	uint256 public totalDepositedSharesSTBT;
	// Used to calculate total supply of rUSTP.
	uint256 public totalSupplyrUSTP;

	uint256 public safeCollateralRate = 101 * 1e18;
	uint256 public reserveFactor;

	bool public migrating;

	// Used to record the user's STBT shares.
	mapping(address => uint256) public depositedSharesSTBT;
	// Used to record the user's loan shares of rUSTP.
	mapping(address => uint256) borrowedShares;
	uint256 public totalBorrowShares;
	uint256 public totalBorrowrUSTP;

	mapping(address => bool) liquidateProvider;
	// Used to be a flash liquidate provider
	mapping(address => bool) flashLiquidateProvider;
	mapping(address => bool) pendingFlashLiquidateProvider;

	// We assume that the interest rate will not exceed 10%.
	uint256 public constant maxInterestRate = APR_COEFFICIENT / 10;

	// collateral token.
	ISTBT public stbt;
	// Used to mint rUSTP.
	IERC20 public usdc;
	// interest rate model
	IInterestRateModel public interestRateModel;
	ILiquidatePool public liquidatePool;

	IMigrator public migrator;

	// the claimable fee for protocol
	// reserves will be claim with rUSTP.
	uint256 public totalUnclaimReserves;

	event SupplySTBT(address indexed user, uint256 amount, uint256 shares, uint256 timestamp);
	event SupplyUSDC(address indexed user, uint256 amount, uint256 timestamp);
	event Mint(address indexed user, uint256 amount, uint256 timestamp);
	event Burn(address indexed user, uint256 amount, uint256 timestamp);
	event WithdrawSTBT(address indexed user, uint256 amount, uint256 shares, uint256 timestamp);
	event WithdrawUSDC(address indexed user, uint256 amount, uint256 timestamp);
	event BorrowUSDC(address indexed user, uint256 amount, uint256 timestamp);
	event RepayUSDC(address indexed user, uint256 amount, uint256 timestamp);

	event ReservesAdded(uint256 addAmount, uint256 newTotalUnclaimReserves);
	event LiquidationRecord(
		address liquidator,
		address indexed borrower,
		uint256 rUSTPAmount,
		uint256 timestamp
	);

	event SafeCollateralRateChanged(uint256 newSafeRatio);

	// 0 is not, 1 is pending, 2 is a provider.
	event FlashLiquidateProvider(address user, uint8 status);
	event NewLiquidateProvider(address user, bool status);

	event MintDebt(address indexed user, uint256 amount, uint256 shareAmount, uint256 timestamp);
	event BurnDebt(address indexed user, uint256 amount, uint256 shareAmount, uint256 timestamp);

	constructor(
		address admin,
		ISTBT _stbt,
		IERC20 _usdc
	) ERC20("Interest-bearing USD of TProtocol", "rUSTP") {
		_setupRole(DEFAULT_ADMIN_ROLE, admin);
		stbt = _stbt;
		usdc = _usdc;
		migrating = true;
	}

	modifier realizeInterest() {
		if (totalSupplyrUSTP != 0) {
			uint256 totalInterest = getRPS().mul(block.timestamp.sub(lastCheckpoint));
			uint256 reserves = totalInterest.mul(reserveFactor).div(FEE_COEFFICIENT);

			totalSupplyrUSTP = totalSupplyrUSTP.add(totalInterest).sub(reserves);
			totalUnclaimReserves = totalUnclaimReserves.add(reserves);
			totalBorrowrUSTP = totalBorrowrUSTP.add(totalInterest);

			emit ReservesAdded(reserves, totalUnclaimReserves);
		}
		lastCheckpoint = block.timestamp;
		_;
	}

	/**
	 * @notice Pause the contract. Revert if already paused.
	 */
	function pause() external onlyRole(DEFAULT_ADMIN_ROLE) {
		_pause();
	}

	/**
	 * @notice Unpause the contract. Revert if already unpaused.
	 */
	function unpause() external onlyRole(DEFAULT_ADMIN_ROLE) {
		_unpause();
	}

	/**
	 * @dev to set the liquidate pool
	 * @param _address the address of liquidate pool
	 */
	function initLiquidatePool(
		address _address
	) external onlyRole(DEFAULT_ADMIN_ROLE) realizeInterest {
		require(address(liquidatePool) == address(0), "initialized.");
		liquidatePool = ILiquidatePool(_address);
	}

	/**
	 * @dev to set the migrator
	 * @param _address the address of migrator
	 */
	function initMigrator(address _address) external onlyRole(DEFAULT_ADMIN_ROLE) {
		require(address(migrator) == address(0), "initialized");
		require(migrating, "migration has been done");
		migrator = IMigrator(_address);
	}

	/**
	 * @dev to revoke migrator
	 */
	function revokeMigrator() external onlyRole(DEFAULT_ADMIN_ROLE) {
		require(migrating, "migration has been done");
		migrator = IMigrator(address(0));
		migrating = false;
	}

	/**
	 * @dev claim protocol's reserves fee
	 * @param _receiver the address be used to receive reserves fee.
	 */
	function claimReservesFee(
		address _receiver
	) external realizeInterest onlyRole(DEFAULT_ADMIN_ROLE) {
		_mintrUSTP(_receiver, totalUnclaimReserves);
		totalUnclaimReserves = 0;
	}

	/**
	 * @dev to set the rate of manager fee
	 * @param _reserveFactor the rate. it should be multiply 10**6
	 */
	function setReserveFactor(
		uint256 _reserveFactor
	) external onlyRole(POOL_MANAGER_ROLE) realizeInterest {
		require(_reserveFactor <= FEE_COEFFICIENT, "reserve factor should be less than 100%.");
		reserveFactor = _reserveFactor;
	}

	/**
	 * @dev to set interest rate model
	 * @param _interestRateModel the model address
	 */
	function setInterestRateModel(
		IInterestRateModel _interestRateModel
	) external onlyRole(POOL_MANAGER_ROLE) realizeInterest {
		// To ensure 100% utilization.
		uint256 supplyInterestRate = _interestRateModel.getSupplyInterestRate(
			totalSupplyrUSTP,
			totalSupplyrUSTP
		);
		require(
			supplyInterestRate <= maxInterestRate,
			"interest rate should be less than maxInterestRate."
		);
		interestRateModel = _interestRateModel;
	}

	/**
	 * @notice  safeCollateralRate
	 */
	function setSafeCollateralRate(
		uint256 newSafeRatio
	) external onlyRole(POOL_MANAGER_ROLE) realizeInterest {
		require(newSafeRatio >= 101 * 1e18, "Safe CollateralRate should more than 101%");
		safeCollateralRate = newSafeRatio;
		emit SafeCollateralRateChanged(newSafeRatio);
	}

	/**
	 * @notice Supply USDC.
	 * Emits a `SupplyUSDC` event.
	 *
	 * @param _amount the amount of USDC
	 */
	function supplyUSDC(uint256 _amount) external whenNotPaused realizeInterest {
		require(_amount > 0, "Supply USDC should more then 0.");
		usdc.transferFrom(msg.sender, address(this), _amount);

		// convert to rUSTP.
		uint256 convertTorUSTP = _amount.mul(1e12);

		_mintrUSTP(msg.sender, convertTorUSTP);

		emit SupplyUSDC(msg.sender, _amount, block.timestamp);
	}

	/**
	 * @notice Supply STBT.
	 * Emits a `SupplySTBT` event.
	 *
	 * @param _amount the amount of STBT.
	 */
	function supplySTBT(uint256 _amount) external whenNotPaused realizeInterest {
		require(_amount > 0, "Supply STBT should more then 0.");
		_supplySTBTFor(_amount, msg.sender);
	}

	/**
	 * @notice Supply STBT for others.
	 * Emits a `SupplySTBT` event.
	 *
	 * @param _amount the amount of STBT.
	 * @param _receiver receiver
	 */

	function supplySTBTFor(
		uint256 _amount,
		address _receiver
	) external whenNotPaused realizeInterest {
		require(_amount > 0, "Supply STBT should more then 0.");
		_supplySTBTFor(_amount, _receiver);
	}

	function _supplySTBTFor(uint256 _amount, address _receiver) internal {
		uint256 beforeShares = stbt.sharesOf(address(this));
		stbt.transferFrom(msg.sender, address(this), _amount);
		uint256 afterShares = stbt.sharesOf(address(this));

		uint256 userDepositedShares = afterShares.sub(beforeShares);

		totalDepositedSharesSTBT += userDepositedShares;
		depositedSharesSTBT[_receiver] += userDepositedShares;

		emit SupplySTBT(_receiver, _amount, userDepositedShares, block.timestamp);
	}

	/**
	 * @notice Withdraw STBT to an address.
	 * Emits a `WithdrawSTBT` event.
	 *
	 * @param _amount the amount of STBT.
	 */
	function withdrawSTBT(uint256 _amount) external whenNotPaused realizeInterest {
		require(_amount > 0, "Withdraw STBT should more then 0.");

		uint256 withdrawShares = stbt.getSharesByAmount(_amount);
		totalDepositedSharesSTBT -= withdrawShares;
		depositedSharesSTBT[msg.sender] -= withdrawShares;

		_requireIsSafeCollateralRate(msg.sender);
		stbt.transfer(msg.sender, _amount);

		emit WithdrawSTBT(msg.sender, _amount, withdrawShares, block.timestamp);
	}

	/**
	 * @notice Withdraw all STBT to an address.
	 * Emits a `WithdrawSTBT` event.
	 *
	 */
	function withdrawAllSTBT() external whenNotPaused realizeInterest {
		uint256 withdrawShares = depositedSharesSTBT[msg.sender];
		require(withdrawShares > 0, "Withdraw STBT should more then 0.");
		uint256 _amount = stbt.getAmountByShares(withdrawShares);

		totalDepositedSharesSTBT -= withdrawShares;
		depositedSharesSTBT[msg.sender] = 0;

		_requireIsSafeCollateralRate(msg.sender);
		stbt.transfer(msg.sender, _amount);

		emit WithdrawSTBT(msg.sender, _amount, withdrawShares, block.timestamp);
	}

	/**
	 * @notice Withdraw USDC to an address.
	 * rUSTP:USDC always 1:1.
	 * Emits a `WithdrawUSDC` event.
	 *
	 * @param _amount the amount of USDC.
	 */
	function withdrawUSDC(uint256 _amount) external whenNotPaused realizeInterest {
		require(_amount > 0, "Withdraw USDC should more then 0.");

		// convert to rUSTP.
		uint256 convertTorUSTP = _amount.mul(10 ** 12);

		_burnrUSTP(msg.sender, convertTorUSTP);
		usdc.transfer(msg.sender, _amount);

		emit WithdrawUSDC(msg.sender, _amount, block.timestamp);
	}

	/**
	 * @notice Withdraw all USDC to an address.
	 * rUSTP:USDC always 1:1.
	 * Emits a `WithdrawUSDC` event.
	 *
	 */
	function withdrawAllUSDC() external whenNotPaused realizeInterest {
		uint256 _amount = balanceOf(msg.sender);
		require(_amount > 0, "Withdraw USDC should more then 0.");

		// convert to USDC.
		uint256 convertToUSDC = _amount.div(10 ** 12);

		_burnrUSTP(msg.sender, _amount);

		if (convertToUSDC > 0) {
			usdc.transfer(msg.sender, convertToUSDC);
		}

		emit WithdrawUSDC(msg.sender, convertToUSDC, block.timestamp);
	}

	/**
	 * @notice Borrow USDC to an address.
	 * Emits a `BorrowUSDC` event.
	 *
	 * @param _amount the amount of USDC.
	 */
	function borrowUSDC(uint256 _amount) external whenNotPaused realizeInterest {
		require(_amount > 0, "Borrow USDC should more then 0.");

		// convert to rUSTP.
		uint256 convertTorUSTP = _amount.mul(10 ** 12);

		_mintrUSTPDebt(msg.sender, convertTorUSTP);
		_requireIsSafeCollateralRate(msg.sender);

		usdc.safeTransfer(msg.sender, _amount);

		emit BorrowUSDC(msg.sender, _amount, block.timestamp);
	}

	/**
	 * @notice Repay USDC from user
	 * Emits a `RepayUSDC` event.
	 *
	 * @param _amount the amount of USDC.
	 */
	function repayUSDC(uint256 _amount) external whenNotPaused realizeInterest {
		require(_amount > 0, "Repay USDC should more then 0.");

		usdc.transferFrom(msg.sender, address(this), _amount);
		// convert to rUSTP.
		uint256 convertTorUSTP = _amount.mul(1e12);

		_burnrUSTPDebt(msg.sender, convertTorUSTP);

		emit RepayUSDC(msg.sender, _amount, block.timestamp);
	}

	/**
	 * @notice Repay all USDC from user
	 * Emits a `RepayUSDC` event.
	 *
	 */
	function repayAll() external whenNotPaused realizeInterest {
		uint256 userBorrowShares = borrowedShares[msg.sender];
		require(userBorrowShares > 0, "Repay USDC should more then 0.");

		uint256 repayrUSTP = getBorrowrUSTPAmountByShares(userBorrowShares);

		// convert to USDC.
		uint256 convertToUSDC = repayrUSTP.div(1e12) + 1;
		usdc.transferFrom(msg.sender, address(this), convertToUSDC);

		_burnrUSTPDebt(msg.sender, repayrUSTP);

		emit RepayUSDC(msg.sender, convertToUSDC, block.timestamp);
	}

	/**
	 * @notice The sender liquidates the borrowers collateral.
	 * *Can be liquidated at any time*
	 * Emits a `LiquidationRecord` event.
	 *
	 * @param borrower The borrower be liquidated
	 * @param repayAmount The amount of the rUSTP to repay
	 */
	function liquidateBorrow(
		address borrower,
		uint256 repayAmount
	) external whenNotPaused realizeInterest {
		require(liquidateProvider[borrower], "borrower is not a provider.");
		_liquidateProcedure(borrower, repayAmount);
		liquidatePool.liquidateSTBT(msg.sender, repayAmount);

		emit LiquidationRecord(msg.sender, borrower, repayAmount, block.timestamp);
	}

	/**
	 * @notice The sender liquidates the borrowers collateral by Curve.
	 * *Can be liquidated at any time*
	 * Emits a `LiquidationRecord` event.
	 *
	 * @param borrower The borrower be liquidated
	 * @param repayAmount The amount of the rUSTP to repay
	 * @param j token of index for curve pool
	 * @param minReturn the minimum amount of return
	 */
	function flashLiquidateBorrow(
		address borrower,
		uint256 repayAmount,
		int128 j,
		uint256 minReturn
	) external whenNotPaused realizeInterest {
		require(flashLiquidateProvider[borrower], "borrower is not a provider.");
		_liquidateProcedure(borrower, repayAmount);
		liquidatePool.flashLiquidateSTBTByCurve(repayAmount, j, minReturn, msg.sender);

		emit LiquidationRecord(msg.sender, borrower, repayAmount, block.timestamp);
	}

	function _liquidateProcedure(address borrower, uint256 repayAmount) internal {
		require(msg.sender != borrower, "don't liquidate self.");
		uint256 borrowedUSD = getBorrowrUSTPAmountByShares(borrowedShares[borrower]);
		require(borrowedUSD >= repayAmount, "repayAmount should be less than borrower's debt.");
		_burnrUSTP(msg.sender, repayAmount);

		_burnrUSTPDebt(borrower, repayAmount);

		// always assuming STBT:rUSTP is 1:1.
		uint256 liquidateShares = stbt.getSharesByAmount(repayAmount);
		// TODO maybe no need to check.
		require(
			depositedSharesSTBT[borrower] >= liquidateShares,
			"liquidateShares should be less than borrower's deposit."
		);
		totalDepositedSharesSTBT -= liquidateShares;
		depositedSharesSTBT[borrower] -= liquidateShares;

		stbt.transfer(address(liquidatePool), repayAmount);
	}

	/**
	 * @notice User chooses to apply a provider
	 */
	function applyFlashLiquidateProvider() external {
		pendingFlashLiquidateProvider[msg.sender] = true;
		emit FlashLiquidateProvider(msg.sender, 1);
	}

	/**
	 * @notice User chooses to cancel a provider
	 */
	function cancelFlashLiquidateProvider() external {
		pendingFlashLiquidateProvider[msg.sender] = false;
		flashLiquidateProvider[msg.sender] = false;
		emit FlashLiquidateProvider(msg.sender, 0);
	}

	/**
	 * @notice Admin accept a apply for provider
	 */
	function acceptFlashLiquidateProvider(address user) external onlyRole(POOL_MANAGER_ROLE) {
		require(pendingFlashLiquidateProvider[user], "the user did not apply.");
		pendingFlashLiquidateProvider[user] = false;
		flashLiquidateProvider[user] = true;
		emit FlashLiquidateProvider(user, 2);
	}

	/**
	 * @notice Admin add a provider
	 */
	function setLiquidateProvider(address user, bool status) external onlyRole(POOL_MANAGER_ROLE) {
		liquidateProvider[user] = status;
		emit NewLiquidateProvider(user, status);
	}

	/**
	 * @notice Migrate wTBT to rUSTP
	 * @param _user the user of deposit USDC
	 * @param _borrower the user of deposit STBT
	 * @param _amount the amount of migration
	 */
	function migrate(
		address _user,
		address _borrower,
		uint256 _amount
	) external whenNotPaused realizeInterest {
		require(migrating, "migration is done.");
		require(msg.sender == address(migrator), "no authorization.");

		// Mint USTP to user, 1-to-1 stbt
		_mintrUSTP(_user, _amount);

		// supply stbt
		uint256 beforeShares = stbt.sharesOf(address(this));
		stbt.transferFrom(_borrower, address(this), _amount);
		uint256 afterShares = stbt.sharesOf(address(this));

		uint256 userDepositedShares = afterShares.sub(beforeShares);

		totalDepositedSharesSTBT += userDepositedShares;
		depositedSharesSTBT[_borrower] += userDepositedShares;

		// Borrow
		// At migrate. we don't check healthy
		// Deposit stbt for borrower later
		_mintrUSTPDebt(_borrower, _amount);

		emit BorrowUSDC(msg.sender, _amount, block.timestamp);
	}

	/**
	 * @notice Get the borrowed shares of user
	 *
	 * @param user the address of borrower
	 */

	function getBorrowedSharesOf(address user) external view returns (uint256) {
		return borrowedShares[user];
	}

	/**
	 * @notice Get the borrowed amount of user
	 *
	 * @param user the address of borrower
	 */

	function getBorrowedAmount(address user) public view returns (uint256) {
		return getBorrowrUSTPAmountByShares(borrowedShares[user]);
	}

	/**
	 * @return the amount of borrow shares that corresponds to `_rUSTPAmount` protocol-borrowed rUSTP.
	 */
	function getBorrowSharesByrUSTPAmount(uint256 _rUSTPAmount) public view returns (uint256) {
		return
			totalBorrowrUSTP == 0 ? 0 : _rUSTPAmount.mul(totalBorrowShares).div(totalBorrowrUSTP);
	}

	/**
	 * @return the amount of borrow rUSTP that corresponds to `_sharesAmount` borrow shares.
	 */
	function getBorrowrUSTPAmountByShares(uint256 _sharesAmount) public view returns (uint256) {
		return
			totalBorrowShares == 0 ? 0 : _sharesAmount.mul(totalBorrowrUSTP).div(totalBorrowShares);
	}

	/**
	 * @dev mint rUSTP for _receiver.
	 * Emits`Mint` and `Transfer` event.
	 *
	 * @param _receiver the address be used to receive rUSTP.
	 * @param _amount the amount of rUSTP.
	 */
	function _mintrUSTP(address _receiver, uint256 _amount) internal {
		uint256 sharesAmount = getSharesByrUSTPAmount(_amount);
		if (sharesAmount == 0) {
			//rUSTP shares are 1:1 to USDC at first.
			sharesAmount = _amount;
		}
		_mintShares(_receiver, sharesAmount);
		totalSupplyrUSTP += _amount;
		emit Mint(msg.sender, _amount, block.timestamp);
		emit Transfer(address(0), _receiver, _amount);
	}

	/**
	 * @dev burn rUSTP from _receiver.
	 * Emits`Burn` and `Transfer` event.
	 *
	 * @param _account the address be used to burn rUSTP.
	 * @param _amount the amount of rUSTP.
	 */
	function _burnrUSTP(address _account, uint256 _amount) internal {
		uint256 sharesAmount = getSharesByrUSTPAmount(_amount);
		require(sharesAmount > 0, "shares should be more then 0.");
		_burnShares(_account, sharesAmount);
		totalSupplyrUSTP -= _amount;
		emit Burn(msg.sender, _amount, block.timestamp);
		emit Transfer(_account, address(0), _amount);
	}

	/**
	 * @dev mint rUSTP debt for _receiver.
	 *
	 * @param _receiver the address be used to receive rUSTP debt.
	 * @param _amount the amount of rUSTP.
	 */
	function _mintrUSTPDebt(address _receiver, uint256 _amount) internal {
		uint256 borrowShares = getBorrowSharesByrUSTPAmount(_amount);
		if (borrowShares == 0) {
			borrowShares = _amount;
		}
		borrowedShares[_receiver] += borrowShares;
		totalBorrowShares += borrowShares;

		totalBorrowrUSTP += _amount;

		require(totalBorrowrUSTP <= totalSupplyrUSTP, "shold be less then supply of rUSTP.");

		emit MintDebt(msg.sender, _amount, borrowShares, block.timestamp);
	}

	/**
	 * @dev burn rUSTP debt from _receiver.
	 *
	 * @param _account the address be used to burn rUSTP.
	 * @param _amount the amount of rUSTP.
	 */
	function _burnrUSTPDebt(address _account, uint256 _amount) internal {
		uint256 borrowShares = getBorrowSharesByrUSTPAmount(_amount);
		require(borrowShares > 0, "shares should be more then 0.");
		borrowedShares[_account] -= borrowShares;
		totalBorrowShares -= borrowShares;

		totalBorrowrUSTP -= _amount;

		emit BurnDebt(msg.sender, _amount, borrowShares, block.timestamp);
	}

	/**
	 * @notice total supply of rUSTP.
	 */
	function _getTotalSupplyrUSTP() internal view override returns (uint256) {
		return totalSupplyrUSTP;
	}

	/**
	 * @dev Return USD value of STBT
	 * it should be equal to $1.
	 * maybe possible through the oracle.
	 */
	function _stbtPrice() internal pure returns (uint256) {
		return 1e18;
	}

	/**
	 * @dev The USD value of the collateral asset must be higher than safeCollateralRate.
	 */
	function _requireIsSafeCollateralRate(address user) internal view {
		uint256 borrowedAmount = getBorrowedAmount(user);
		if (borrowedAmount == 0) {
			return;
		}
		require(
			(stbt.getAmountByShares(depositedSharesSTBT[user]).mul(_stbtPrice()).mul(100) /
				borrowedAmount) >= safeCollateralRate,
			"Cannot be lower than the safeCollateralRate."
		);
	}

	/**
	 * @dev revolutions per second
	 */
	function getRPS() public view returns (uint256) {
		uint256 _totalSupplyrUSTP = _getTotalSupplyrUSTP();
		uint256 supplyInterestRate = interestRateModel.getSupplyInterestRate(
			_totalSupplyrUSTP,
			getrUSTPAmountByShares(totalBorrowShares)
		);
		if (supplyInterestRate >= maxInterestRate) {
			supplyInterestRate = maxInterestRate;
		}
		return supplyInterestRate.mul(_totalSupplyrUSTP).div(365 days).div(APR_COEFFICIENT);
	}
}