// File: contracts/Trader.sol



// SPDX-License-Identifier: BUSL-1.1
pragma solidity >=0.8.15;
import "erc3156/contracts/interfaces/IERC3156FlashBorrower.sol";
import "erc3156/contracts/interfaces/IERC3156FlashLender.sol";
import "@yield-protocol/yieldspace-tv/src/interfaces/IMaturingToken.sol";
import "@yield-protocol/vault-v2/contracts/interfaces/IFYToken.sol";
import "@yield-protocol/yieldspace-tv/src/interfaces/IPool.sol";
import "@yield-protocol/utils-v2/contracts/token/MinimalTransferHelper.sol";
import "@yield-protocol/utils-v2/contracts/access/AccessControl.sol";

interface ITrader {
    function authorize(address grantee) external;
    function retrieve(IERC20 token) external returns (uint256 amount);
    function sellFYToken(IPool pool, uint128 fySold, uint128 minBaseOut) external returns (uint256 cost);
    function buyBase(IPool pool, uint128 baseBought, uint128 maxFyIn) external returns (uint256 cost);
}

contract Trader is ITrader, IERC3156FlashBorrower, AccessControl {
    using MinimalTransferHelper for IERC20;

    enum Trade { SELLFYTOKEN, BUYBASE }

    event FYTokenSold(IPool indexed pool, uint256 fySold, uint256 cost);
    event BaseBought(IPool indexed pool, uint256 baseBought, uint256 cost);

    IERC3156FlashLender immutable public lender;
    uint256 private init;

    /// @dev For simplicity, we use a single flash lender. Euler works well.
    constructor (IERC3156FlashLender lender_) {
        lender = lender_;
        authorize(msg.sender);
    }

    /// @dev Give permission to an address to use this contract
    function authorize(address grantee) override public auth {
        _grantRole(this.authorize.selector, grantee);
        _grantRole(this.retrieve.selector, grantee);
        _grantRole(this.sellFYToken.selector, grantee);
        _grantRole(this.buyBase.selector, grantee);
    }

    /// @dev Drain this contract of a given token.
    function retrieve(IERC20 token) override external auth returns (uint256 amount) {
        amount = token.balanceOf(address(this));
        token.transfer(msg.sender, amount);   
    }

    /// @dev Execute an base flash loan and with it, mint fyToken and sell them to a pool
    function sellFYToken(IPool pool, uint128 fySold, uint128 minBaseOut) override external auth returns (uint256 cost) {
        IERC20 base = pool.base();

        // We will obtain `fySold` by flash borrowing an equal amount of base and using it to mint fyToken at 1:1
        init = base.balanceOf(address(this)); // We use this as a semaphore, and to retrieve return data
        lender.flashLoan(IERC3156FlashBorrower(address(this)), address(base), fySold, abi.encode(Trade.SELLFYTOKEN, pool, 0, minBaseOut));
        cost = init - base.balanceOf(address(this));
        delete init;
        emit FYTokenSold(pool, fySold, cost);
    }

    /// @dev Execute an base flash loan and with it, mint fyToken and buy base from a pool
    function buyBase(IPool pool, uint128 baseBought, uint128 maxFyIn) override external auth returns (uint256 cost) {
        IERC20 base = pool.base();

        // We will flash borrow the base that we need, 
        init = base.balanceOf(address(this)); // We use this as a semaphore, and to retrieve return data
        uint256 fySold = pool.buyBasePreview(baseBought);
        lender.flashLoan(IERC3156FlashBorrower(address(this)), address(base), fySold, abi.encode(Trade.BUYBASE, pool, baseBought, maxFyIn));
        cost = init - base.balanceOf(address(this));
        delete init;
        emit BaseBought(pool, baseBought, cost);
    }

    /**
     * @dev Receive a flash loan and use it to mint fyToken and trade them in a pool.
     * Extra funds to cover loan fees and market losses should be present in this contract before this call
     * @param token The loan currency.
     * @param amount The amount of tokens lent.
     * @return The keccak256 hash of "ERC3156FlashBorrower.onFlashLoan"
     */
    function onFlashLoan(
        address,
        address token,
        uint256 amount,
        uint256,
        bytes memory data
    ) external returns (bytes32) {
        require (init != 0, "Unauthorized");
        (Trade trade, IPool pool, uint128 baseOut, uint128 limit) = abi.decode(data, (Trade, IPool, uint128, uint128));
        IFYToken fyToken = IFYToken(address(pool.fyToken()));
        IERC20 base = pool.base();
        require(address(base) == token, "Mismatched pool");

        // Get join from fyToken
        IJoin join = fyToken.join();

        // Approve the lender to take any funds
        IERC20(token).approve(msg.sender, type(uint256).max);

        // We mint fyToken at 1:1
        base.safeTransfer(address(join), amount);
        fyToken.mintWithUnderlying(address(pool), amount);

        // We sell the fyToken to repay the flash loan
        if (trade == Trade.SELLFYTOKEN) pool.sellFYToken(address(this), limit);
        else pool.buyBase(address(this), baseOut, limit);

        return keccak256("ERC3156FlashBorrower.onFlashLoan");
    }
}

// File: erc3156/contracts/interfaces/IERC3156FlashBorrower.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.9.0;


interface IERC3156FlashBorrower {

    /**
     * @dev Receive a flash loan.
     * @param initiator The initiator of the loan.
     * @param token The loan currency.
     * @param amount The amount of tokens lent.
     * @param fee The additional amount of tokens to repay.
     * @param data Arbitrary data structure, intended to contain user-defined parameters.
     * @return The keccak256 hash of "ERC3156FlashBorrower.onFlashLoan"
     */
    function onFlashLoan(
        address initiator,
        address token,
        uint256 amount,
        uint256 fee,
        bytes calldata data
    ) external returns (bytes32);
}

// File: erc3156/contracts/interfaces/IERC3156FlashLender.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.9.0;
import "./IERC3156FlashBorrower.sol";


interface IERC3156FlashLender {

    /**
     * @dev The amount of currency available to be lended.
     * @param token The loan currency.
     * @return The amount of `token` that can be borrowed.
     */
    function maxFlashLoan(
        address token
    ) external view returns (uint256);

    /**
     * @dev The fee to be charged for a given loan.
     * @param token The loan currency.
     * @param amount The amount of tokens lent.
     * @return The amount of `token` to be charged for the loan, on top of the returned principal.
     */
    function flashFee(
        address token,
        uint256 amount
    ) external view returns (uint256);

    /**
     * @dev Initiate a flash loan.
     * @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
     * @param token The loan currency.
     * @param amount The amount of tokens lent.
     * @param data Arbitrary data structure, intended to contain user-defined parameters.
     */
    function flashLoan(
        IERC3156FlashBorrower receiver,
        address token,
        uint256 amount,
        bytes calldata data
    ) external returns (bool);
}
// File: @yield-protocol/yieldspace-tv/src/interfaces/IMaturingToken.sol



// SPDX-License-Identifier: MIT
pragma solidity >=0.8.15;
import "@yield-protocol/utils-v2/contracts/token/IERC20.sol";

interface IMaturingToken is IERC20 {
    function maturity() external view returns (uint256);
}
// File: @yield-protocol/yieldspace-tv/src/interfaces/IPool.sol



// SPDX-License-Identifier: MIT
pragma solidity >= 0.8.0;
import "@yield-protocol/utils-v2/contracts/token/IERC20.sol";
import "@yield-protocol/utils-v2/contracts/token/IERC2612.sol";
import {IMaturingToken} from "./IMaturingToken.sol";
import {IERC20Metadata} from  "@yield-protocol/utils-v2/contracts/token/ERC20.sol";

interface IPool is IERC20, IERC2612 {
    function baseToken() external view returns(IERC20Metadata);
    function base() external view returns(IERC20);
    function burn(address baseTo, address fyTokenTo, uint256 minRatio, uint256 maxRatio) external returns (uint256, uint256, uint256);
    function burnForBase(address to, uint256 minRatio, uint256 maxRatio) external returns (uint256, uint256);
    function buyBase(address to, uint128 baseOut, uint128 max) external returns(uint128);
    function buyBasePreview(uint128 baseOut) external view returns(uint128);
    function buyFYToken(address to, uint128 fyTokenOut, uint128 max) external returns(uint128);
    function buyFYTokenPreview(uint128 fyTokenOut) external view returns(uint128);
    function currentCumulativeRatio() external view returns (uint256 currentCumulativeRatio_, uint256 blockTimestampCurrent);
    function cumulativeRatioLast() external view returns (uint256);
    function fyToken() external view returns(IMaturingToken);
    function g1() external view returns(int128);
    function g2() external view returns(int128);
    function getC() external view returns (int128);
    function getCurrentSharePrice() external view returns (uint256);
    function getCache() external view returns (uint104 baseCached, uint104 fyTokenCached, uint32 blockTimestampLast, uint16 g1Fee_);
    function getBaseBalance() external view returns(uint128);
    function getFYTokenBalance() external view returns(uint128);
    function getSharesBalance() external view returns(uint128);
    function init(address to) external returns (uint256, uint256, uint256);
    function maturity() external view returns(uint32);
    function mint(address to, address remainder, uint256 minRatio, uint256 maxRatio) external returns (uint256, uint256, uint256);
    function mu() external view returns (int128);
    function mintWithBase(address to, address remainder, uint256 fyTokenToBuy, uint256 minRatio, uint256 maxRatio) external returns (uint256, uint256, uint256);
    function retrieveBase(address to) external returns(uint128 retrieved);
    function retrieveFYToken(address to) external returns(uint128 retrieved);
    function retrieveShares(address to) external returns(uint128 retrieved);
    function scaleFactor() external view returns(uint96);
    function sellBase(address to, uint128 min) external returns(uint128);
    function sellBasePreview(uint128 baseIn) external view returns(uint128);
    function sellFYToken(address to, uint128 min) external returns(uint128);
    function sellFYTokenPreview(uint128 fyTokenIn) external view returns(uint128);
    function setFees(uint16 g1Fee_) external;
    function sharesToken() external view returns(IERC20Metadata);
    function ts() external view returns(int128);
    function wrap(address receiver) external returns (uint256 shares);
    function wrapPreview(uint256 assets) external view returns (uint256 shares);
    function unwrap(address receiver) external returns (uint256 assets);
    function unwrapPreview(uint256 shares) external view returns (uint256 assets);
    /// Returns the max amount of FYTokens that can be sold to the pool
    function maxFYTokenIn() external view returns (uint128) ;
    /// Returns the max amount of FYTokens that can be bought from the pool
    function maxFYTokenOut() external view returns (uint128) ;
    /// Returns the max amount of Base that can be sold to the pool
    function maxBaseIn() external view returns (uint128) ;
    /// Returns the max amount of Base that can be bought from the pool
    function maxBaseOut() external view returns (uint128);
    /// Returns the result of the total supply invariant function
    function invariant() external view returns (uint128);
}
// File: @yield-protocol/vault-v2/contracts/interfaces/IFYToken.sol



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

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

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

    /// @dev Unix time at which redemption of fyToken for underlying are possible
    function maturity() external view 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/utils-v2/contracts/token/MinimalTransferHelper.sol



// SPDX-License-Identifier: MIT
// Taken from https://github.com/Uniswap/uniswap-lib/blob/master/contracts/libraries/TransferHelper.sol

pragma solidity >=0.6.0;

import "./IERC20.sol";
import "../utils/RevertMsgExtractor.sol";


// helper methods for transferring ERC20 tokens that do not consistently return true/false
library MinimalTransferHelper {
    /// @notice Transfers tokens from msg.sender to a recipient
    /// @dev Errors with the underlying revert message if transfer fails
    /// @param token The contract address of the token which will be transferred
    /// @param to The recipient of the transfer
    /// @param value The value of the transfer
    function safeTransfer(
        IERC20 token,
        address to,
        uint256 value
    ) internal {
        (bool success, bytes memory data) = address(token).call(abi.encodeWithSelector(IERC20.transfer.selector, to, value));
        if (!(success && (data.length == 0 || abi.decode(data, (bool))))) revert(RevertMsgExtractor.getRevertMsg(data));
    }
}
// File: @yield-protocol/utils-v2/contracts/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/utils-v2/contracts/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);
}
// File: @yield-protocol/utils-v2/contracts/token/ERC20.sol



// SPDX-License-Identifier: MIT
// Inspired on token.sol from DappHub. Natspec adpated from OpenZeppelin.

pragma solidity ^0.8.0;
import "./IERC20Metadata.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}.
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of 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.
 * 
 * Calls to {transferFrom} do not check for allowance if the caller is the owner
 * of the funds. This allows to reduce the number of approvals that are necessary.
 *
 * Finally, {transferFrom} does not decrease the allowance if it is set to
 * type(uint256).max. This reduces the gas costs without any likely impact.
 */
contract ERC20 is IERC20Metadata {
    uint256                                           internal  _totalSupply;
    mapping (address => uint256)                      internal  _balanceOf;
    mapping (address => mapping (address => uint256)) internal  _allowance;
    string                                            public override name = "???";
    string                                            public override symbol = "???";
    uint8                                             public override decimals = 18;

    /**
     *  @dev Sets the values for {name}, {symbol} and {decimals}.
     */
    constructor(string memory name_, string memory symbol_, uint8 decimals_) {
        name = name_;
        symbol = symbol_;
        decimals = decimals_;
    }

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

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

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

    /**
     * @dev See {IERC20-approve}.
     */
    function approve(address spender, uint wad) external virtual override returns (bool) {
        return _setAllowance(msg.sender, spender, wad);
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - the caller must have a balance of at least `wad`.
     */
    function transfer(address dst, uint wad) external virtual override returns (bool) {
        return _transfer(msg.sender, dst, wad);
    }

    /**
     * @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}.
     *
     * Requirements:
     *
     * - `src` must have a balance of at least `wad`.
     * - the caller is not `src`, it must have allowance for ``src``'s tokens of at least
     * `wad`.
     */
    /// if_succeeds {:msg "TransferFrom - decrease allowance"} msg.sender != src ==> old(_allowance[src][msg.sender]) >= wad;
    function transferFrom(address src, address dst, uint wad) external virtual override returns (bool) {
        _decreaseAllowance(src, wad);

        return _transfer(src, dst, wad);
    }

    /**
     * @dev Moves tokens `wad` from `src` to `dst`.
     * 
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `src` must have a balance of at least `amount`.
     */
    /// if_succeeds {:msg "Transfer - src decrease"} old(_balanceOf[src]) >= _balanceOf[src];
    /// if_succeeds {:msg "Transfer - dst increase"} _balanceOf[dst] >= old(_balanceOf[dst]);
    /// if_succeeds {:msg "Transfer - supply"} old(_balanceOf[src]) + old(_balanceOf[dst]) == _balanceOf[src] + _balanceOf[dst];
    function _transfer(address src, address dst, uint wad) internal virtual returns (bool) {
        require(_balanceOf[src] >= wad, "ERC20: Insufficient balance");
        unchecked { _balanceOf[src] = _balanceOf[src] - wad; }
        _balanceOf[dst] = _balanceOf[dst] + wad;

        emit Transfer(src, dst, wad);

        return true;
    }

    /**
     * @dev Sets the allowance granted to `spender` by `owner`.
     *
     * Emits an {Approval} event indicating the updated allowance.
     */
    function _setAllowance(address owner, address spender, uint wad) internal virtual returns (bool) {
        _allowance[owner][spender] = wad;
        emit Approval(owner, spender, wad);

        return true;
    }

    /**
     * @dev Decreases the allowance granted to the caller by `src`, unless src == msg.sender or _allowance[src][msg.sender] == MAX
     *
     * Emits an {Approval} event indicating the updated allowance, if the allowance is updated.
     *
     * Requirements:
     *
     * - `spender` must have allowance for the caller of at least
     * `wad`, unless src == msg.sender
     */
    /// if_succeeds {:msg "Decrease allowance - underflow"} old(_allowance[src][msg.sender]) <= _allowance[src][msg.sender];
    function _decreaseAllowance(address src, uint wad) internal virtual returns (bool) {
        if (src != msg.sender) {
            uint256 allowed = _allowance[src][msg.sender];
            if (allowed != type(uint).max) {
                require(allowed >= wad, "ERC20: Insufficient approval");
                unchecked { _setAllowance(src, msg.sender, allowed - wad); }
            }
        }

        return true;
    }

    /** @dev Creates `wad` tokens and assigns them to `dst`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     */
    /// if_succeeds {:msg "Mint - balance overflow"} old(_balanceOf[dst]) >= _balanceOf[dst];
    /// if_succeeds {:msg "Mint - supply overflow"} old(_totalSupply) >= _totalSupply;
    function _mint(address dst, uint wad) internal virtual returns (bool) {
        _balanceOf[dst] = _balanceOf[dst] + wad;
        _totalSupply = _totalSupply + wad;
        emit Transfer(address(0), dst, wad);

        return true;
    }

    /**
     * @dev Destroys `wad` tokens from `src`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `src` must have at least `wad` tokens.
     */
    /// if_succeeds {:msg "Burn - balance underflow"} old(_balanceOf[src]) <= _balanceOf[src];
    /// if_succeeds {:msg "Burn - supply underflow"} old(_totalSupply) <= _totalSupply;
    function _burn(address src, uint wad) internal virtual returns (bool) {
        unchecked {
            require(_balanceOf[src] >= wad, "ERC20: Insufficient balance");
            _balanceOf[src] = _balanceOf[src] - wad;
            _totalSupply = _totalSupply - wad;
            emit Transfer(src, address(0), wad);
        }

        return true;
    }
}
// File: @yield-protocol/utils-v2/contracts/token/IERC2612.sol



// SPDX-License-Identifier: MIT
// Code adapted from https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2237/
pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC2612 standard as defined in the EIP.
 *
 * Adds the {permit} method, which can be used to change one's
 * {IERC20-allowance} without having to send a transaction, by signing a
 * message. This allows users to spend tokens without having to hold Ether.
 *
 * See https://eips.ethereum.org/EIPS/eip-2612.
 */
interface IERC2612 {
    /**
     * @dev Sets `amount` 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:
     *
     * - `owner` cannot be the zero address.
     * - `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 amount, uint256 deadline, uint8 v, bytes32 r, bytes32 s) external;

    /**
     * @dev Returns the current ERC2612 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);
}

// File: @yield-protocol/utils-v2/contracts/token/IERC20Metadata.sol



// SPDX-License-Identifier: MIT
// Taken from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/extensions/IERC20Metadata.sol

pragma solidity ^0.8.0;

import "./IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 */
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: @yield-protocol/vault-v2/contracts/interfaces/IJoin.sol



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

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

    /// @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);
}

// File: @yield-protocol/utils-v2/contracts/utils/RevertMsgExtractor.sol



// SPDX-License-Identifier: MIT
// Taken from https://github.com/sushiswap/BoringSolidity/blob/441e51c0544cf2451e6116fe00515e71d7c42e2c/contracts/BoringBatchable.sol

pragma solidity >=0.6.0;


library RevertMsgExtractor {
    /// @dev Helper function to extract a useful revert message from a failed call.
    /// If the returned data is malformed or not correctly abi encoded then this call can fail itself.
    function getRevertMsg(bytes memory returnData)
        internal pure
        returns (string memory)
    {
        // If the _res length is less than 68, then the transaction failed silently (without a revert message)
        if (returnData.length < 68) return "Transaction reverted silently";

        assembly {
            // Slice the sighash.
            returnData := add(returnData, 0x04)
        }
        return abi.decode(returnData, (string)); // All that remains is the revert string
    }
}