// File: contracts/Shifter.sol



// SPDX-License-Identifier: BUSL-1.1
pragma solidity >=0.8.15;

import "@yield-protocol/vault-v2/src/interfaces/ICauldron.sol";
import "@yield-protocol/vault-v2/src/interfaces/DataTypes.sol";
import "@yield-protocol/utils-v2/src/access/AccessControl.sol";
import "@yield-protocol/utils-v2/src/utils/Cast.sol";


/// @title Shifter
/// @notice Shift vaults from one series to another
contract Shifter is AccessControl {
    using Cast for *;

    event Shifted(bytes12 indexed vaultId, bytes6 indexed oldSeriesId, bytes6 indexed newSeriesId);

    ICauldron public immutable cauldron;

    constructor(ICauldron cauldron_) {
        cauldron = cauldron_;
    }

    /// @dev Shift a vault from one series to another
    /// @param vaultId The vault to shift
    /// @param seriesId The new series
    function shift(bytes12 vaultId, bytes6 seriesId) external auth {
        DataTypes.Vault memory vault = cauldron.vaults(vaultId);
        DataTypes.Balances memory balances = cauldron.balances(vaultId);
        cauldron.pour(vaultId, 0, -(balances.art.i128()));
        cauldron.tweak(vaultId, seriesId, vault.ilkId);
        cauldron.pour(vaultId, 0, balances.art.i128());
        emit Shifted(vaultId, vault.seriesId, seriesId);
    }
}

// File: @yield-protocol/vault-v2/src/interfaces/ICauldron.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "./IFYToken.sol";
import "./IOracle.sol";
import "./DataTypes.sol";

interface ICauldron {
    /// @dev Variable rate lending oracle for an underlying
    function lendingOracles(bytes6 baseId) external view returns (IOracle);

    /// @dev An user can own one or more Vaults, with each vault being able to borrow from a single series.
    function vaults(bytes12 vault)
        external
        view
        returns (DataTypes.Vault memory);

    /// @dev Series available in Cauldron.
    function series(bytes6 seriesId)
        external
        view
        returns (DataTypes.Series memory);

    /// @dev Assets available in Cauldron.
    function assets(bytes6 assetsId) external view returns (address);

    /// @dev Each vault records debt and collateral balances_.
    function balances(bytes12 vault)
        external
        view
        returns (DataTypes.Balances memory);


    // @dev Assets that are approved as collateral for a series
    function ilks(bytes6 seriesId, bytes6 assetId)
        external
        view
        returns (bool);

    /// @dev Max, min and sum of debt per underlying and collateral.
    function debt(bytes6 baseId, bytes6 ilkId)
        external
        view
        returns (DataTypes.Debt memory);

    // @dev Spot price oracle addresses and collateralization ratios
    function spotOracles(bytes6 baseId, bytes6 ilkId)
        external
        view
        returns (DataTypes.SpotOracle memory);

    /// @dev Create a new vault, linked to a series (and therefore underlying) and up to 5 collateral types
    function build(
        address owner,
        bytes12 vaultId,
        bytes6 seriesId,
        bytes6 ilkId
    ) external returns (DataTypes.Vault memory);

    /// @dev Destroy an empty vault. Used to recover gas costs.
    function destroy(bytes12 vault) external;

    /// @dev Change a vault series and/or collateral types.
    function tweak(
        bytes12 vaultId,
        bytes6 seriesId,
        bytes6 ilkId
    ) external returns (DataTypes.Vault memory);

    /// @dev Give a vault to another user.
    function give(bytes12 vaultId, address receiver)
        external
        returns (DataTypes.Vault memory);

    /// @dev Move collateral and debt between vaults.
    function stir(
        bytes12 from,
        bytes12 to,
        uint128 ink,
        uint128 art
    ) external returns (DataTypes.Balances memory, DataTypes.Balances memory);

    /// @dev Manipulate a vault debt and collateral.
    function pour(
        bytes12 vaultId,
        int128 ink,
        int128 art
    ) external returns (DataTypes.Balances memory);

    /// @dev Change series and debt of a vault.
    /// The module calling this function also needs to buy underlying in the pool for the new series, and sell it in pool for the old series.
    function roll(
        bytes12 vaultId,
        bytes6 seriesId,
        int128 art
    ) external returns (DataTypes.Vault memory, DataTypes.Balances memory);

    /// @dev Reduce debt and collateral from a vault, ignoring collateralization checks.
    function slurp(
        bytes12 vaultId,
        uint128 ink,
        uint128 art
    ) external returns (DataTypes.Balances memory);

    // ==== Helpers ====

    /// @dev Convert a debt amount for a series from base to fyToken terms.
    /// @notice Think about rounding if using, since we are dividing.
    function debtFromBase(bytes6 seriesId, uint128 base)
        external
        returns (uint128 art);

    /// @dev Convert a debt amount for a series from fyToken to base terms
    function debtToBase(bytes6 seriesId, uint128 art)
        external
        returns (uint128 base);

    // ==== Accounting ====

    /// @dev Record the borrowing rate at maturity for a series
    function mature(bytes6 seriesId) external;

    /// @dev Retrieve the rate accrual since maturity, maturing if necessary.
    function accrual(bytes6 seriesId) external returns (uint256);

    /// @dev Return the collateralization level of a vault. It will be negative if undercollateralized.
    function level(bytes12 vaultId) external returns (int256);
}

// File: @yield-protocol/vault-v2/src/interfaces/DataTypes.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "./IFYToken.sol";
import "./IOracle.sol";

library DataTypes {
    // ======== Cauldron data types ========
    struct Series {
        IFYToken fyToken; // Redeemable token for the series.
        bytes6 baseId; // Asset received on redemption.
        uint32 maturity; // Unix time at which redemption becomes possible.
        // bytes2 free
    }

    struct Debt {
        uint96 max; // Maximum debt accepted for a given underlying, across all series
        uint24 min; // Minimum debt accepted for a given underlying, across all series
        uint8 dec; // Multiplying factor (10**dec) for max and min
        uint128 sum; // Current debt for a given underlying, across all series
    }

    struct SpotOracle {
        IOracle oracle; // Address for the spot price oracle
        uint32 ratio; // Collateralization ratio to multiply the price for
        // bytes8 free
    }

    struct Vault {
        address owner;
        bytes6 seriesId; // Each vault is related to only one series, which also determines the underlying.
        bytes6 ilkId; // Asset accepted as collateral
    }

    struct Balances {
        uint128 art; // Debt amount
        uint128 ink; // Collateral amount
    }

    // ======== Witch data types ========
    struct Auction {
        address owner;
        uint32 start;
        bytes6 baseId; // We cache the baseId here
        uint128 ink;
        uint128 art;
        address auctioneer;
        bytes6 ilkId; // We cache the ilkId here
        bytes6 seriesId; // We cache the seriesId here
    }

    struct Line {
        uint32 duration; // Time that auctions take to go to minimal price and stay there
        uint64 vaultProportion; // Proportion of the vault that is available each auction (1e18 = 100%)
        uint64 collateralProportion; // Proportion of collateral that is sold at auction start (1e18 = 100%)
    }

    struct Limits {
        uint128 max; // Maximum concurrent auctioned collateral
        uint128 sum; // Current concurrent auctioned collateral
    }
}

library VRDataTypes {
    struct Vault {
        address owner;
        bytes6 baseId; // Each variable rate vault is related to only one base.
        bytes6 ilkId; // Asset accepted as collateral
    }
}
// File: @yield-protocol/utils-v2/src/utils/Cast.sol



// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.13;

library Cast {
    ///@dev library for safe casting of value types

    function b12(bytes32 x) internal pure returns (bytes12 y) {
        require(bytes32(y = bytes12(x)) == x, "Cast overflow");
    }

    function b6(bytes32 x) internal pure returns (bytes6 y) {
        require(bytes32(y = bytes6(x)) == x, "Cast overflow");
    }

    function u256(int256 x) internal pure returns (uint256 y) {
        require(x >= 0, "Cast overflow");
        y = uint256(x);
    }

    function i256(uint256 x) internal pure returns (int256 y) {
        require(x <= uint256(type(int256).max), "Cast overflow");
        y = int256(x);
    }

    function u128(uint256 x) internal pure returns (uint128 y) {
        require(x <= type(uint128).max, "Cast overflow");
        y = uint128(x);
    }

    function u128(int256 x) internal pure returns (uint128 y) {
        require(x >= 0, "Cast overflow");
        y = uint128(uint256(x));
    }

    function i128(uint256 x) internal pure returns (int128) {
        require(x <= uint256(int256(type(int128).max)), "Cast overflow");
        return int128(int256(x));
    }

    function i128(int256 x) internal pure returns (int128) {
        require(x <= type(int128).max, "Cast overflow");
        require(x >= type(int128).min, "Cast overflow");
        return int128(x);
    }

    function u112(uint256 x) internal pure returns (uint112 y) {
        require(x <= type(uint112).max, "Cast overflow");
        y = uint112(x);
    }

    function u104(uint256 x) internal pure returns (uint104 y) {
        require(x <= type(uint104).max, "Cast overflow");
        y = uint104(x);
    }

    function u96(uint256 x) internal pure returns (uint96 y) {
        require(x <= type(uint96).max, "Cast overflow");
        y = uint96(x);
    }

    function u32(uint256 x) internal pure returns (uint32 y) {
        require(x <= type(uint32).max, "Cast overflow");
        y = uint32(x);
    }
}

// File: @yield-protocol/utils-v2/src/access/AccessControl.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms.
 *
 * Roles are referred to by their `bytes4` identifier. These are expected to be the 
 * signatures for all the functions in the contract. Special roles should be exposed
 * in the external API and be unique:
 *
 * ```
 * bytes4 public constant ROOT = 0x00000000;
 * ```
 *
 * Roles represent restricted access to a function call. For that purpose, use {auth}:
 *
 * ```
 * function foo() public auth {
 *     ...
 * }
 * ```
 *
 * 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 `ROOT`, 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 `ROOT` 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.
 */
contract AccessControl {
    struct RoleData {
        mapping (address => bool) members;
        bytes4 adminRole;
    }

    mapping (bytes4 => RoleData) private _roles;

    bytes4 public constant ROOT = 0x00000000;
    bytes4 public constant ROOT4146650865 = 0x00000000; // Collision protection for ROOT, test with ROOT12007226833()
    bytes4 public constant LOCK = 0xFFFFFFFF;           // Used to disable further permissioning of a function
    bytes4 public constant LOCK8605463013 = 0xFFFFFFFF; // Collision protection for LOCK, test with LOCK10462387368()

    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role
     *
     * `ROOT` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes4 indexed role, bytes4 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call.
     */
    event RoleGranted(bytes4 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(bytes4 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Give msg.sender the ROOT role and create a LOCK role with itself as the admin role and no members. 
     * Calling setRoleAdmin(msg.sig, LOCK) means no one can grant that msg.sig role anymore.
     */
    constructor () {
        _grantRole(ROOT, msg.sender);   // Grant ROOT to msg.sender
        _setRoleAdmin(LOCK, LOCK);      // Create the LOCK role by setting itself as its own admin, creating an independent role tree
    }

    /**
     * @dev Each function in the contract has its own role, identified by their msg.sig signature.
     * ROOT can give and remove access to each function, lock any further access being granted to
     * a specific action, or even create other roles to delegate admin control over a function.
     */
    modifier auth() {
        require (_hasRole(msg.sig, msg.sender), "Access denied");
        _;
    }

    /**
     * @dev Allow only if the caller has been granted the admin role of `role`.
     */
    modifier admin(bytes4 role) {
        require (_hasRole(_getRoleAdmin(role), msg.sender), "Only admin");
        _;
    }

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes4 role, address account) external view returns (bool) {
        return _hasRole(role, account);
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes4 role) external view returns (bytes4) {
        return _getRoleAdmin(role);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.

     * If ``role``'s admin role is not `adminRole` emits a {RoleAdminChanged} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function setRoleAdmin(bytes4 role, bytes4 adminRole) external virtual admin(role) {
        _setRoleAdmin(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.
     */
    function grantRole(bytes4 role, address account) external virtual admin(role) {
        _grantRole(role, account);
    }

    
    /**
     * @dev Grants all of `role` in `roles` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - For each `role` in `roles`, the caller must have ``role``'s admin role.
     */
    function grantRoles(bytes4[] memory roles, address account) external virtual {
        for (uint256 i = 0; i < roles.length; i++) {
            require (_hasRole(_getRoleAdmin(roles[i]), msg.sender), "Only admin");
            _grantRole(roles[i], account);
        }
    }

    /**
     * @dev Sets LOCK as ``role``'s admin role. LOCK has no members, so this disables admin management of ``role``.

     * Emits a {RoleAdminChanged} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function lockRole(bytes4 role) external virtual admin(role) {
        _setRoleAdmin(role, LOCK);
    }

    /**
     * @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(bytes4 role, address account) external virtual admin(role) {
        _revokeRole(role, account);
    }

    /**
     * @dev Revokes all of `role` in `roles` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - For each `role` in `roles`, the caller must have ``role``'s admin role.
     */
    function revokeRoles(bytes4[] memory roles, address account) external virtual {
        for (uint256 i = 0; i < roles.length; i++) {
            require (_hasRole(_getRoleAdmin(roles[i]), msg.sender), "Only admin");
            _revokeRole(roles[i], 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 granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes4 role, address account) external virtual {
        require(account == msg.sender, "Renounce only for self");

        _revokeRole(role, account);
    }

    function _hasRole(bytes4 role, address account) internal view returns (bool) {
        return _roles[role].members[account];
    }

    function _getRoleAdmin(bytes4 role) internal view returns (bytes4) {
        return _roles[role].adminRole;
    }

    function _setRoleAdmin(bytes4 role, bytes4 adminRole) internal virtual {
        if (_getRoleAdmin(role) != adminRole) {
            _roles[role].adminRole = adminRole;
            emit RoleAdminChanged(role, adminRole);
        }
    }

    function _grantRole(bytes4 role, address account) internal {
        if (!_hasRole(role, account)) {
            _roles[role].members[account] = true;
            emit RoleGranted(role, account, msg.sender);
        }
    }

    function _revokeRole(bytes4 role, address account) internal {
        if (_hasRole(role, account)) {
            _roles[role].members[account] = false;
            emit RoleRevoked(role, account, msg.sender);
        }
    }
}
// File: @yield-protocol/vault-v2/src/interfaces/IFYToken.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "./IERC5095.sol";
import "./IJoin.sol";
import "./IOracle.sol";

interface IFYToken is IERC5095 {

    /// @dev Oracle for the savings rate.
    function oracle() view external returns (IOracle);

    /// @dev Source of redemption funds.
    function join() view external returns (IJoin); 

    /// @dev Asset to be paid out on redemption.
    function underlying() view external returns (address);

    /// @dev Yield id of the asset to be paid out on redemption.
    function underlyingId() view external returns (bytes6);

    /// @dev Time at which redemptions are enabled.
    function maturity() view external returns (uint256);

    /// @dev Spot price (exchange rate) between the base and an interest accruing token at maturity, set to 2^256-1 before maturity
    function chiAtMaturity() view external returns (uint256);
    
    /// @dev Record price data at maturity
    function mature() external;

    /// @dev Mint fyToken providing an equal amount of underlying to the protocol
    function mintWithUnderlying(address to, uint256 amount) external;

    /// @dev Burn fyToken after maturity for an amount of underlying.
    function redeem(address to, uint256 amount) external returns (uint256);

    /// @dev Mint fyToken.
    /// This function can only be called by other Yield contracts, not users directly.
    /// @param to Wallet to mint the fyToken in.
    /// @param fyTokenAmount Amount of fyToken to mint.
    function mint(address to, uint256 fyTokenAmount) external;

    /// @dev Burn fyToken.
    /// This function can only be called by other Yield contracts, not users directly.
    /// @param from Wallet to burn the fyToken from.
    /// @param fyTokenAmount Amount of fyToken to burn.
    function burn(address from, uint256 fyTokenAmount) external;
}

// File: @yield-protocol/vault-v2/src/interfaces/IOracle.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IOracle {
    /**
     * @notice Doesn't refresh the price, but returns the latest value available without doing any transactional operations
     * @param base The asset in which the `amount` to be converted is represented
     * @param quote The asset in which the converted `value` will be represented
     * @param amount The amount to be converted from `base` to `quote`
     * @return value The converted value of `amount` from `base` to `quote`
     * @return updateTime The timestamp when the conversion price was taken
     */
    function peek(
        bytes32 base,
        bytes32 quote,
        uint256 amount
    ) external view returns (uint256 value, uint256 updateTime);

    /**
     * @notice Does whatever work or queries will yield the most up-to-date price, and returns it.
     * @param base The asset in which the `amount` to be converted is represented
     * @param quote The asset in which the converted `value` will be represented
     * @param amount The amount to be converted from `base` to `quote`
     * @return value The converted value of `amount` from `base` to `quote`
     * @return updateTime The timestamp when the conversion price was taken
     */
    function get(
        bytes32 base,
        bytes32 quote,
        uint256 amount
    ) external returns (uint256 value, uint256 updateTime);
}

// File: @yield-protocol/vault-v2/src/interfaces/IERC5095.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.8.13;

import "@yield-protocol/utils-v2/src/token/IERC20.sol";

interface IERC5095 is IERC20 {
    /// @dev Asset that is returned on redemption.
    function underlying() external view returns (address underlyingAddress);

    /// @dev Unix time at which redemption of fyToken for underlying are possible
    function maturity() external view returns (uint256 timestamp);

    /// @dev Converts a specified amount of principal to underlying
    function convertToUnderlying(uint256 principalAmount) external returns (uint256 underlyingAmount);

    /// @dev Converts a specified amount of underlying to principal
    function convertToPrincipal(uint256 underlyingAmount) external returns (uint256 principalAmount);

    /// @dev Gives the maximum amount an address holder can redeem in terms of the principal
    function maxRedeem(address holder) external view returns (uint256 maxPrincipalAmount);

    /// @dev Gives the amount in terms of underlying that the princiapl amount can be redeemed for plus accrual
    function previewRedeem(uint256 principalAmount) external returns (uint256 underlyingAmount);

    /// @dev Burn fyToken after maturity for an amount of principal.
    function redeem(uint256 principalAmount, address to, address from) external returns (uint256 underlyingAmount);

    /// @dev Gives the maximum amount an address holder can withdraw in terms of the underlying
    function maxWithdraw(address holder) external returns (uint256 maxUnderlyingAmount);

    /// @dev Gives the amount in terms of principal that the underlying amount can be withdrawn for plus accrual
    function previewWithdraw(uint256 underlyingAmount) external returns (uint256 principalAmount);

    /// @dev Burn fyToken after maturity for an amount of underlying.
    function withdraw(uint256 underlyingAmount, address to, address from) external returns (uint256 principalAmount);
}

// File: @yield-protocol/vault-v2/src/interfaces/IJoin.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "@yield-protocol/utils-v2/src/token/IERC20.sol";

interface IJoin {
    /// @dev asset managed by this contract
    function asset() external view returns (address);

    /// @dev amount of assets held by this contract
    function storedBalance() external view returns (uint256);

    /// @dev Add tokens to this contract.
    function join(address user, uint128 wad) external returns (uint128);

    /// @dev Remove tokens to this contract.
    function exit(address user, uint128 wad) external returns (uint128);

    /// @dev Retrieve any tokens other than the `asset`. Useful for airdropped tokens.
    function retrieve(IERC20 token, address to) external;
}

// File: @yield-protocol/utils-v2/src/token/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

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

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

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

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

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

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

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