// File: openzeppelin-solidity-2.3.0/contracts/ownership/Ownable.sol

pragma solidity ^0.5.0;

/**
 * @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.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be aplied to your functions to restrict their use to
 * the owner.
 */
contract Ownable {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        _owner = msg.sender;
        emit OwnershipTransferred(address(0), _owner);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Returns true if the caller is the current owner.
     */
    function isOwner() public view returns (bool) {
        return msg.sender == _owner;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * > Note: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = 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 onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: openzeppelin-solidity-2.3.0/contracts/token/ERC20/IERC20.sol

pragma solidity ^0.5.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see `ERC20Detailed`.
 */
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.
     *
     * > 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: openzeppelin-solidity-2.3.0/contracts/math/SafeMath.sol

pragma solidity ^0.5.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @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) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        uint256 c = a - b;

        return c;
    }

    /**
     * @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) {
        // 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-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts 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) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, "SafeMath: division by zero");
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts 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) {
        require(b != 0, "SafeMath: modulo by zero");
        return a % b;
    }
}

// File: openzeppelin-solidity-2.3.0/contracts/token/ERC20/ERC20.sol

pragma solidity ^0.5.0;



/**
 * @dev Implementation of the `IERC20` interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using `_mint`.
 * For a generic mechanism see `ERC20Mintable`.
 *
 * *For a detailed writeup see our guide [How to implement supply
 * mechanisms](https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226).*
 *
 * 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.
 *
 * 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 IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    /**
     * @dev See `IERC20.totalSupply`.
     */
    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See `IERC20.balanceOf`.
     */
    function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See `IERC20.transfer`.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    /**
     * @dev See `IERC20.allowance`.
     */
    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See `IERC20.approve`.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 value) public returns (bool) {
        _approve(msg.sender, spender, value);
        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`;
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `value`.
     * - the caller must have allowance for `sender`'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(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 returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].add(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 returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is 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:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _balances[sender] = _balances[sender].sub(amount);
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, 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
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

     /**
     * @dev Destoys `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 value) internal {
        require(account != address(0), "ERC20: burn from the zero address");

        _totalSupply = _totalSupply.sub(value);
        _balances[account] = _balances[account].sub(value);
        emit Transfer(account, address(0), value);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is 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 value) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    /**
     * @dev Destoys `amount` tokens from `account`.`amount` is then deducted
     * from the caller's allowance.
     *
     * See `_burn` and `_approve`.
     */
    function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(account, msg.sender, _allowances[account][msg.sender].sub(amount));
    }
}

// File: openzeppelin-solidity-2.3.0/contracts/math/Math.sol

pragma solidity ^0.5.0;

/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    /**
     * @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, so we distribute
        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
    }
}

// File: openzeppelin-solidity-2.3.0/contracts/utils/ReentrancyGuard.sol

pragma solidity ^0.5.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the `nonReentrant` modifier
 * available, which can be aplied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 */
contract ReentrancyGuard {
    /// @dev counter to allow mutex lock with only one SSTORE operation
    uint256 private _guardCounter;

    constructor () internal {
        // The counter starts at one to prevent changing it from zero to a non-zero
        // value, which is a more expensive operation.
        _guardCounter = 1;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        _guardCounter += 1;
        uint256 localCounter = _guardCounter;
        _;
        require(localCounter == _guardCounter, "ReentrancyGuard: reentrant call");
    }
}

// File: contracts/BankConfig.sol

pragma solidity 0.5.16;

interface BankConfig {
    /// @dev Return minimum ETH debt size per position.
    function minDebtSize() external view returns (uint256);

    /// @dev Return the interest rate per second, using 1e18 as denom.
    function getInterestRate(uint256 debt, uint256 floating) external view returns (uint256);

    /// @dev Return the bps rate for reserve pool.
    function getReservePoolBps() external view returns (uint256);

    /// @dev Return the bps rate for Avada Kill caster.
    function getKillBps() external view returns (uint256);

    /// @dev Return whether the given address is a goblin.
    function isGoblin(address goblin) external view returns (bool);

    /// @dev Return whether the given goblin accepts more debt. Revert on non-goblin.
    function acceptDebt(address goblin) external view returns (bool);

    /// @dev Return the work factor for the goblin + ETH debt, using 1e4 as denom. Revert on non-goblin.
    function workFactor(address goblin, uint256 debt) external view returns (uint256);

    /// @dev Return the kill factor for the goblin + ETH debt, using 1e4 as denom. Revert on non-goblin.
    function killFactor(address goblin, uint256 debt) external view returns (uint256);
}

// File: contracts/Goblin.sol

pragma solidity 0.5.16;

interface Goblin {
    /// @dev Work on a (potentially new) position. Optionally send ETH back to Bank.
    function work(uint256 id, address user, uint256 debt, bytes calldata data) external payable;

    /// @dev Re-invest whatever the goblin is working on.
    function reinvest() external;

    /// @dev Return the amount of ETH wei to get back if we are to liquidate the position.
    function health(uint256 id) external view returns (uint256);

    /// @dev Liquidate the given position to ETH. Send all ETH back to Bank.
    function liquidate(uint256 id) external;
}

// File: contracts/SafeToken.sol

pragma solidity 0.5.16;

interface ERC20Interface {
    function balanceOf(address user) external view returns (uint256);
}

library SafeToken {
    function myBalance(address token) internal view returns (uint256) {
        return ERC20Interface(token).balanceOf(address(this));
    }

    function balanceOf(address token, address user) internal view returns (uint256) {
        return ERC20Interface(token).balanceOf(user);
    }

    function safeApprove(address token, address to, uint256 value) internal {
        // bytes4(keccak256(bytes('approve(address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x095ea7b3, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), "!safeApprove");
    }

    function safeTransfer(address token, address to, uint256 value) internal {
        // bytes4(keccak256(bytes('transfer(address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0xa9059cbb, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), "!safeTransfer");
    }

    function safeTransferFrom(address token, address from, address to, uint256 value) internal {
        // bytes4(keccak256(bytes('transferFrom(address,address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x23b872dd, from, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), "!safeTransferFrom");
    }

    function safeTransferETH(address to, uint256 value) internal {
        (bool success, ) = to.call.value(value)(new bytes(0));
        require(success, "!safeTransferETH");
    }
}

// File: contracts/Bank.sol

pragma solidity 0.5.16;









contract Bank is ERC20, ReentrancyGuard, Ownable {
    /// @notice Libraries
    using SafeToken for address;
    using SafeMath for uint256;

    /// @notice Events
    event AddDebt(uint256 indexed id, uint256 debtShare);
    event RemoveDebt(uint256 indexed id, uint256 debtShare);
    event Work(uint256 indexed id, uint256 loan);
    event Kill(uint256 indexed id, address indexed killer, uint256 prize, uint256 left);

    string public name = "Interest Bearing ETH";
    string public symbol = "ibETH";
    uint8 public decimals = 18;

    struct Position {
        address goblin;
        address owner;
        uint256 debtShare;
    }

    BankConfig public config;
    mapping (uint256 => Position) public positions;
    uint256 public nextPositionID = 1;

    uint256 public glbDebtShare;
    uint256 public glbDebtVal;
    uint256 public lastAccrueTime;
    uint256 public reservePool;

    /// @dev Require that the caller must be an EOA account to avoid flash loans.
    modifier onlyEOA() {
        require(msg.sender == tx.origin, "not eoa");
        _;
    }

    /// @dev Add more debt to the global debt pool.
    modifier accrue(uint256 msgValue) {
        if (now > lastAccrueTime) {
            uint256 interest = pendingInterest(msgValue);
            uint256 toReserve = interest.mul(config.getReservePoolBps()).div(10000);
            reservePool = reservePool.add(toReserve);
            glbDebtVal = glbDebtVal.add(interest);
            lastAccrueTime = now;
        }
        _;
    }

    constructor(BankConfig _config) public {
        config = _config;
        lastAccrueTime = now;
    }

    /// @dev Return the pending interest that will be accrued in the next call.
    /// @param msgValue Balance value to subtract off address(this).balance when called from payable functions.
    function pendingInterest(uint256 msgValue) public view returns (uint256) {
        if (now > lastAccrueTime) {
            uint256 timePast = now.sub(lastAccrueTime);
            uint256 balance = address(this).balance.sub(msgValue);
            uint256 ratePerSec = config.getInterestRate(glbDebtVal, balance);
            return ratePerSec.mul(glbDebtVal).mul(timePast).div(1e18);
        } else {
            return 0;
        }
    }

    /// @dev Return the ETH debt value given the debt share. Be careful of unaccrued interests.
    /// @param debtShare The debt share to be converted.
    function debtShareToVal(uint256 debtShare) public view returns (uint256) {
        if (glbDebtShare == 0) return debtShare; // When there's no share, 1 share = 1 val.
        return debtShare.mul(glbDebtVal).div(glbDebtShare);
    }

    /// @dev Return the debt share for the given debt value. Be careful of unaccrued interests.
    /// @param debtVal The debt value to be converted.
    function debtValToShare(uint256 debtVal) public view returns (uint256) {
        if (glbDebtShare == 0) return debtVal; // When there's no share, 1 share = 1 val.
        return debtVal.mul(glbDebtShare).div(glbDebtVal);
    }

    /// @dev Return ETH value and debt of the given position. Be careful of unaccrued interests.
    /// @param id The position ID to query.
    function positionInfo(uint256 id) public view returns (uint256, uint256) {
        Position storage pos = positions[id];
        return (Goblin(pos.goblin).health(id), debtShareToVal(pos.debtShare));
    }

    /// @dev Return the total ETH entitled to the token holders. Be careful of unaccrued interests.
    function totalETH() public view returns (uint256) {
        return address(this).balance.add(glbDebtVal).sub(reservePool);
    }

    /// @dev Add more ETH to the bank. Hope to get some good returns.
    function deposit() external payable accrue(msg.value) nonReentrant {
        uint256 total = totalETH().sub(msg.value);
        uint256 share = total == 0 ? msg.value : msg.value.mul(totalSupply()).div(total);
        _mint(msg.sender, share);
    }

    /// @dev Withdraw ETH from the bank by burning the share tokens.
    function withdraw(uint256 share) external accrue(0) nonReentrant {
        uint256 amount = share.mul(totalETH()).div(totalSupply());
        _burn(msg.sender, share);
        SafeToken.safeTransferETH(msg.sender, amount);
    }

    /// @dev Create a new farming position to unlock your yield farming potential.
    /// @param id The ID of the position to unlock the earning. Use ZERO for new position.
    /// @param goblin The address of the authorized goblin to work for this position.
    /// @param loan The amount of ETH to borrow from the pool.
    /// @param maxReturn The max amount of ETH to return to the pool.
    /// @param data The calldata to pass along to the goblin for more working context.
    function work(uint256 id, address goblin, uint256 loan, uint256 maxReturn, bytes calldata data)
        external payable
        onlyEOA accrue(msg.value) nonReentrant
    {
        // 1. Sanity check the input position, or add a new position of ID is 0.
        if (id == 0) {
            id = nextPositionID++;
            positions[id].goblin = goblin;
            positions[id].owner = msg.sender;
        } else {
            require(id < nextPositionID, "bad position id");
            require(positions[id].goblin == goblin, "bad position goblin");
            require(positions[id].owner == msg.sender, "not position owner");
        }
        emit Work(id, loan);
        // 2. Make sure the goblin can accept more debt and remove the existing debt.
        require(config.isGoblin(goblin), "not a goblin");
        require(loan == 0 || config.acceptDebt(goblin), "goblin not accept more debt");
        uint256 debt = _removeDebt(id).add(loan);
        // 3. Perform the actual work, using a new scope to avoid stack-too-deep errors.
        uint256 back;
        {
            uint256 sendETH = msg.value.add(loan);
            require(sendETH <= address(this).balance, "insufficient ETH in the bank");
            uint256 beforeETH = address(this).balance.sub(sendETH);
            Goblin(goblin).work.value(sendETH)(id, msg.sender, debt, data);
            back = address(this).balance.sub(beforeETH);
        }
        // 4. Check and update position debt.
        uint256 lessDebt = Math.min(debt, Math.min(back, maxReturn));
        debt = debt.sub(lessDebt);
        if (debt > 0) {
            require(debt >= config.minDebtSize(), "too small debt size");
            uint256 health = Goblin(goblin).health(id);
            uint256 workFactor = config.workFactor(goblin, debt);
            require(health.mul(workFactor) >= debt.mul(10000), "bad work factor");
            _addDebt(id, debt);
        } else {
            require(Goblin(goblin).health(id) == 0, "zero debt but nonzero health");
        }
        // 5. Return excess ETH back.
        if (back > lessDebt) SafeToken.safeTransferETH(msg.sender, back - lessDebt);
    }

    /// @dev Kill the given to the position. Liquidate it immediately if killFactor condition is met.
    /// @param id The position ID to be killed.
    function kill(uint256 id) external onlyEOA accrue(0) nonReentrant {
        // 1. Verify that the position is eligible for liquidation.
        Position storage pos = positions[id];
        require(pos.debtShare > 0, "no debt");
        uint256 debt = _removeDebt(id);
        uint256 health = Goblin(pos.goblin).health(id);
        uint256 killFactor = config.killFactor(pos.goblin, debt);
        require(health.mul(killFactor) < debt.mul(10000), "can't liquidate");
        // 2. Perform liquidation and compute the amount of ETH received.
        uint256 beforeETH = address(this).balance;
        Goblin(pos.goblin).liquidate(id);
        uint256 back = address(this).balance.sub(beforeETH);
        uint256 prize = back.mul(config.getKillBps()).div(10000);
        uint256 rest = back.sub(prize);
        // 3. Clear position debt and return funds to liquidator and position owner.
        if (prize > 0) SafeToken.safeTransferETH(msg.sender, prize);
        uint256 left = rest > debt ? rest - debt : 0;
        if (left > 0) SafeToken.safeTransferETH(pos.owner, left);
        emit Kill(id, msg.sender, prize, left);
    }

    /// @dev Internal function to add the given debt value to the given position.
    function _addDebt(uint256 id, uint256 debtVal) internal {
        Position storage pos = positions[id];
        uint256 debtShare = debtValToShare(debtVal);
        pos.debtShare = pos.debtShare.add(debtShare);
        glbDebtShare = glbDebtShare.add(debtShare);
        glbDebtVal = glbDebtVal.add(debtVal);
        emit AddDebt(id, debtShare);
    }

    /// @dev Internal function to clear the debt of the given position. Return the debt value.
    function _removeDebt(uint256 id) internal returns (uint256) {
        Position storage pos = positions[id];
        uint256 debtShare = pos.debtShare;
        if (debtShare > 0) {
            uint256 debtVal = debtShareToVal(debtShare);
            pos.debtShare = 0;
            glbDebtShare = glbDebtShare.sub(debtShare);
            glbDebtVal = glbDebtVal.sub(debtVal);
            emit RemoveDebt(id, debtShare);
            return debtVal;
        } else {
            return 0;
        }
    }

    /// @dev Update bank configuration to a new address. Must only be called by owner.
    /// @param _config The new configurator address.
    function updateConfig(BankConfig _config) external onlyOwner {
        config = _config;
    }

    /// @dev Withdraw ETH reserve for underwater positions to the given address.
    /// @param to The address to transfer ETH to.
    /// @param value The number of ETH tokens to withdraw. Must not exceed `reservePool`.
    function withdrawReserve(address to, uint256 value) external onlyOwner nonReentrant {
        reservePool = reservePool.sub(value);
        SafeToken.safeTransferETH(to, value);
    }

    /// @dev Reduce ETH reserve, effectively giving them to the depositors.
    /// @param value The number of ETH reserve to reduce.
    function reduceReserve(uint256 value) external onlyOwner {
        reservePool = reservePool.sub(value);
    }

    /// @dev Recover ERC20 tokens that were accidentally sent to this smart contract.
    /// @param token The token contract. Can be anything. This contract should not hold ERC20 tokens.
    /// @param to The address to send the tokens to.
    /// @param value The number of tokens to transfer to `to`.
    function recover(address token, address to, uint256 value) external onlyOwner nonReentrant {
        token.safeTransfer(to, value);
    }

    /// @dev Fallback function to accept ETH. Goblins will send ETH back the pool.
    function() external payable {}
}