pragma solidity 0.5.16;


/**
 * @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.
     *
     * 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);
}

/**
 * @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) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        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-contracts/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) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        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) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message 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.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following 
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @dev Converts an `address` into `address payable`. Note that this is
     * simply a type cast: the actual underlying value is not changed.
     *
     * _Available since v2.4.0._
     */
    function toPayable(address account) internal pure returns (address payable) {
        return address(uint160(account));
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     *
     * _Available since v2.4.0._
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-call-value
        (bool success, ) = recipient.call.value(amount)("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
}

library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves.

        // A Solidity high level call has three parts:
        //  1. The target address is checked to verify it contains contract code
        //  2. The call itself is made, and success asserted
        //  3. The return value is decoded, which in turn checks the size of the returned data.
        // solhint-disable-next-line max-line-length
        require(address(token).isContract(), "SafeERC20: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = address(token).call(data);
        require(success, "SafeERC20: low-level call failed");

        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

contract ReentrancyGuard {
    bool private _notEntered;

    constructor () internal {
        // Storing an initial non-zero value makes deployment a bit more
        // expensive, but in exchange the refund on every call to nonReentrant
        // will be lower in amount. Since refunds are capped to a percetange of
        // the total transaction's gas, it is best to keep them low in cases
        // like this one, to increase the likelihood of the full refund coming
        // into effect.
        _notEntered = true;
    }

    /**
     * @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() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_notEntered, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _notEntered = false;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _notEntered = true;
    }
}

contract StakingTokenWrapper is ReentrancyGuard {

    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    IERC20 public stakingToken;

    uint256 private _totalSupply;
    mapping(address => uint256) private _balances;

    /**
     * @dev TokenWrapper constructor
     * @param _stakingToken Wrapped token to be staked
     */
    constructor(address _stakingToken) internal {
        stakingToken = IERC20(_stakingToken);
    }

    /**
     * @dev Get the total amount of the staked token
     * @return uint256 total supply
     */
    function totalSupply()
        public
        view
        returns (uint256)
    {
        return _totalSupply;
    }

    /**
     * @dev Get the balance of a given account
     * @param _account User for which to retrieve balance
     */
    function balanceOf(address _account)
        public
        view
        returns (uint256)
    {
        return _balances[_account];
    }

    /**
     * @dev Deposits a given amount of StakingToken from sender
     * @param _amount Units of StakingToken
     */
    function _stake(address _beneficiary, uint256 _amount)
        internal
        nonReentrant
    {
        _totalSupply = _totalSupply.add(_amount);
        _balances[_beneficiary] = _balances[_beneficiary].add(_amount);
        stakingToken.safeTransferFrom(msg.sender, address(this), _amount);
    }

    /**
     * @dev Withdraws a given stake from sender
     * @param _amount Units of StakingToken
     */
    function _withdraw(uint256 _amount)
        internal
        nonReentrant
    {
        _totalSupply = _totalSupply.sub(_amount);
        _balances[msg.sender] = _balances[msg.sender].sub(_amount);
        stakingToken.safeTransfer(msg.sender, _amount);
    }
}

contract ModuleKeys {

    // Governance
    // ===========
                                                // Phases
    // keccak256("Governance");                 // 2.x
    bytes32 internal constant KEY_GOVERNANCE = 0x9409903de1e6fd852dfc61c9dacb48196c48535b60e25abf92acc92dd689078d;
    //keccak256("Staking");                     // 1.2
    bytes32 internal constant KEY_STAKING = 0x1df41cd916959d1163dc8f0671a666ea8a3e434c13e40faef527133b5d167034;
    //keccak256("ProxyAdmin");                  // 1.0
    bytes32 internal constant KEY_PROXY_ADMIN = 0x96ed0203eb7e975a4cbcaa23951943fa35c5d8288117d50c12b3d48b0fab48d1;

    // mStable
    // =======
    // keccak256("OracleHub");                  // 1.2
    bytes32 internal constant KEY_ORACLE_HUB = 0x8ae3a082c61a7379e2280f3356a5131507d9829d222d853bfa7c9fe1200dd040;
    // keccak256("Manager");                    // 1.2
    bytes32 internal constant KEY_MANAGER = 0x6d439300980e333f0256d64be2c9f67e86f4493ce25f82498d6db7f4be3d9e6f;
    //keccak256("Recollateraliser");            // 2.x
    bytes32 internal constant KEY_RECOLLATERALISER = 0x39e3ed1fc335ce346a8cbe3e64dd525cf22b37f1e2104a755e761c3c1eb4734f;
    //keccak256("MetaToken");                   // 1.1
    bytes32 internal constant KEY_META_TOKEN = 0xea7469b14936af748ee93c53b2fe510b9928edbdccac3963321efca7eb1a57a2;
    // keccak256("SavingsManager");             // 1.0
    bytes32 internal constant KEY_SAVINGS_MANAGER = 0x12fe936c77a1e196473c4314f3bed8eeac1d757b319abb85bdda70df35511bf1;
}

interface INexus {
    function governor() external view returns (address);
    function getModule(bytes32 key) external view returns (address);

    function proposeModule(bytes32 _key, address _addr) external;
    function cancelProposedModule(bytes32 _key) external;
    function acceptProposedModule(bytes32 _key) external;
    function acceptProposedModules(bytes32[] calldata _keys) external;

    function requestLockModule(bytes32 _key) external;
    function cancelLockModule(bytes32 _key) external;
    function lockModule(bytes32 _key) external;
}

contract Module is ModuleKeys {

    INexus public nexus;

    /**
     * @dev Initialises the Module by setting publisher addresses,
     *      and reading all available system module information
     */
    constructor(address _nexus) internal {
        require(_nexus != address(0), "Nexus is zero address");
        nexus = INexus(_nexus);
    }

    /**
     * @dev Modifier to allow function calls only from the Governor.
     */
    modifier onlyGovernor() {
        require(msg.sender == _governor(), "Only governor can execute");
        _;
    }

    /**
     * @dev Modifier to allow function calls only from the Governance.
     *      Governance is either Governor address or Governance address.
     */
    modifier onlyGovernance() {
        require(
            msg.sender == _governor() || msg.sender == _governance(),
            "Only governance can execute"
        );
        _;
    }

    /**
     * @dev Modifier to allow function calls only from the ProxyAdmin.
     */
    modifier onlyProxyAdmin() {
        require(
            msg.sender == _proxyAdmin(), "Only ProxyAdmin can execute"
        );
        _;
    }

    /**
     * @dev Modifier to allow function calls only from the Manager.
     */
    modifier onlyManager() {
        require(msg.sender == _manager(), "Only manager can execute");
        _;
    }

    /**
     * @dev Returns Governor address from the Nexus
     * @return Address of Governor Contract
     */
    function _governor() internal view returns (address) {
        return nexus.governor();
    }

    /**
     * @dev Returns Governance Module address from the Nexus
     * @return Address of the Governance (Phase 2)
     */
    function _governance() internal view returns (address) {
        return nexus.getModule(KEY_GOVERNANCE);
    }

    /**
     * @dev Return Staking Module address from the Nexus
     * @return Address of the Staking Module contract
     */
    function _staking() internal view returns (address) {
        return nexus.getModule(KEY_STAKING);
    }

    /**
     * @dev Return ProxyAdmin Module address from the Nexus
     * @return Address of the ProxyAdmin Module contract
     */
    function _proxyAdmin() internal view returns (address) {
        return nexus.getModule(KEY_PROXY_ADMIN);
    }

    /**
     * @dev Return MetaToken Module address from the Nexus
     * @return Address of the MetaToken Module contract
     */
    function _metaToken() internal view returns (address) {
        return nexus.getModule(KEY_META_TOKEN);
    }

    /**
     * @dev Return OracleHub Module address from the Nexus
     * @return Address of the OracleHub Module contract
     */
    function _oracleHub() internal view returns (address) {
        return nexus.getModule(KEY_ORACLE_HUB);
    }

    /**
     * @dev Return Manager Module address from the Nexus
     * @return Address of the Manager Module contract
     */
    function _manager() internal view returns (address) {
        return nexus.getModule(KEY_MANAGER);
    }

    /**
     * @dev Return SavingsManager Module address from the Nexus
     * @return Address of the SavingsManager Module contract
     */
    function _savingsManager() internal view returns (address) {
        return nexus.getModule(KEY_SAVINGS_MANAGER);
    }

    /**
     * @dev Return Recollateraliser Module address from the Nexus
     * @return  Address of the Recollateraliser Module contract (Phase 2)
     */
    function _recollateraliser() internal view returns (address) {
        return nexus.getModule(KEY_RECOLLATERALISER);
    }
}

interface IRewardsDistributionRecipient {
    function notifyRewardAmount(uint256 reward) external;
    function getRewardToken() external view returns (IERC20);
}

contract RewardsDistributionRecipient is IRewardsDistributionRecipient, Module {

    // @abstract
    function notifyRewardAmount(uint256 reward) external;
    function getRewardToken() external view returns (IERC20);

    // This address has the ability to distribute the rewards
    address public rewardsDistributor;

    /** @dev Recipient is a module, governed by mStable governance */
    constructor(address _nexus, address _rewardsDistributor)
        internal
        Module(_nexus)
    {
        rewardsDistributor = _rewardsDistributor;
    }

    /**
     * @dev Only the rewards distributor can notify about rewards
     */
    modifier onlyRewardsDistributor() {
        require(msg.sender == rewardsDistributor, "Caller is not reward distributor");
        _;
    }

    /**
     * @dev Change the rewardsDistributor - only called by mStable governor
     * @param _rewardsDistributor   Address of the new distributor
     */
    function setRewardsDistribution(address _rewardsDistributor)
        external
        onlyGovernor
    {
        rewardsDistributor = _rewardsDistributor;
    }
}

library StableMath {

    using SafeMath for uint256;

    /**
     * @dev Scaling unit for use in specific calculations,
     * where 1 * 10**18, or 1e18 represents a unit '1'
     */
    uint256 private constant FULL_SCALE = 1e18;

    /**
     * @notice Token Ratios are used when converting between units of bAsset, mAsset and MTA
     * Reasoning: Takes into account token decimals, and difference in base unit (i.e. grams to Troy oz for gold)
     * @dev bAsset ratio unit for use in exact calculations,
     * where (1 bAsset unit * bAsset.ratio) / ratioScale == x mAsset unit
     */
    uint256 private constant RATIO_SCALE = 1e8;

    /**
     * @dev Provides an interface to the scaling unit
     * @return Scaling unit (1e18 or 1 * 10**18)
     */
    function getFullScale() internal pure returns (uint256) {
        return FULL_SCALE;
    }

    /**
     * @dev Provides an interface to the ratio unit
     * @return Ratio scale unit (1e8 or 1 * 10**8)
     */
    function getRatioScale() internal pure returns (uint256) {
        return RATIO_SCALE;
    }

    /**
     * @dev Scales a given integer to the power of the full scale.
     * @param x   Simple uint256 to scale
     * @return    Scaled value a to an exact number
     */
    function scaleInteger(uint256 x)
        internal
        pure
        returns (uint256)
    {
        return x.mul(FULL_SCALE);
    }

    /***************************************
              PRECISE ARITHMETIC
    ****************************************/

    /**
     * @dev Multiplies two precise units, and then truncates by the full scale
     * @param x     Left hand input to multiplication
     * @param y     Right hand input to multiplication
     * @return      Result after multiplying the two inputs and then dividing by the shared
     *              scale unit
     */
    function mulTruncate(uint256 x, uint256 y)
        internal
        pure
        returns (uint256)
    {
        return mulTruncateScale(x, y, FULL_SCALE);
    }

    /**
     * @dev Multiplies two precise units, and then truncates by the given scale. For example,
     * when calculating 90% of 10e18, (10e18 * 9e17) / 1e18 = (9e36) / 1e18 = 9e18
     * @param x     Left hand input to multiplication
     * @param y     Right hand input to multiplication
     * @param scale Scale unit
     * @return      Result after multiplying the two inputs and then dividing by the shared
     *              scale unit
     */
    function mulTruncateScale(uint256 x, uint256 y, uint256 scale)
        internal
        pure
        returns (uint256)
    {
        // e.g. assume scale = fullScale
        // z = 10e18 * 9e17 = 9e36
        uint256 z = x.mul(y);
        // return 9e38 / 1e18 = 9e18
        return z.div(scale);
    }

    /**
     * @dev Multiplies two precise units, and then truncates by the full scale, rounding up the result
     * @param x     Left hand input to multiplication
     * @param y     Right hand input to multiplication
     * @return      Result after multiplying the two inputs and then dividing by the shared
     *              scale unit, rounded up to the closest base unit.
     */
    function mulTruncateCeil(uint256 x, uint256 y)
        internal
        pure
        returns (uint256)
    {
        // e.g. 8e17 * 17268172638 = 138145381104e17
        uint256 scaled = x.mul(y);
        // e.g. 138145381104e17 + 9.99...e17 = 138145381113.99...e17
        uint256 ceil = scaled.add(FULL_SCALE.sub(1));
        // e.g. 13814538111.399...e18 / 1e18 = 13814538111
        return ceil.div(FULL_SCALE);
    }

    /**
     * @dev Precisely divides two units, by first scaling the left hand operand. Useful
     *      for finding percentage weightings, i.e. 8e18/10e18 = 80% (or 8e17)
     * @param x     Left hand input to division
     * @param y     Right hand input to division
     * @return      Result after multiplying the left operand by the scale, and
     *              executing the division on the right hand input.
     */
    function divPrecisely(uint256 x, uint256 y)
        internal
        pure
        returns (uint256)
    {
        // e.g. 8e18 * 1e18 = 8e36
        uint256 z = x.mul(FULL_SCALE);
        // e.g. 8e36 / 10e18 = 8e17
        return z.div(y);
    }


    /***************************************
                  RATIO FUNCS
    ****************************************/

    /**
     * @dev Multiplies and truncates a token ratio, essentially flooring the result
     *      i.e. How much mAsset is this bAsset worth?
     * @param x     Left hand operand to multiplication (i.e Exact quantity)
     * @param ratio bAsset ratio
     * @return      Result after multiplying the two inputs and then dividing by the ratio scale
     */
    function mulRatioTruncate(uint256 x, uint256 ratio)
        internal
        pure
        returns (uint256 c)
    {
        return mulTruncateScale(x, ratio, RATIO_SCALE);
    }

    /**
     * @dev Multiplies and truncates a token ratio, rounding up the result
     *      i.e. How much mAsset is this bAsset worth?
     * @param x     Left hand input to multiplication (i.e Exact quantity)
     * @param ratio bAsset ratio
     * @return      Result after multiplying the two inputs and then dividing by the shared
     *              ratio scale, rounded up to the closest base unit.
     */
    function mulRatioTruncateCeil(uint256 x, uint256 ratio)
        internal
        pure
        returns (uint256)
    {
        // e.g. How much mAsset should I burn for this bAsset (x)?
        // 1e18 * 1e8 = 1e26
        uint256 scaled = x.mul(ratio);
        // 1e26 + 9.99e7 = 100..00.999e8
        uint256 ceil = scaled.add(RATIO_SCALE.sub(1));
        // return 100..00.999e8 / 1e8 = 1e18
        return ceil.div(RATIO_SCALE);
    }


    /**
     * @dev Precisely divides two ratioed units, by first scaling the left hand operand
     *      i.e. How much bAsset is this mAsset worth?
     * @param x     Left hand operand in division
     * @param ratio bAsset ratio
     * @return      Result after multiplying the left operand by the scale, and
     *              executing the division on the right hand input.
     */
    function divRatioPrecisely(uint256 x, uint256 ratio)
        internal
        pure
        returns (uint256 c)
    {
        // e.g. 1e14 * 1e8 = 1e22
        uint256 y = x.mul(RATIO_SCALE);
        // return 1e22 / 1e12 = 1e10
        return y.div(ratio);
    }

    /***************************************
                    HELPERS
    ****************************************/

    /**
     * @dev Calculates minimum of two numbers
     * @param x     Left hand input
     * @param y     Right hand input
     * @return      Minimum of the two inputs
     */
    function min(uint256 x, uint256 y)
        internal
        pure
        returns (uint256)
    {
        return x > y ? y : x;
    }

    /**
     * @dev Calculated maximum of two numbers
     * @param x     Left hand input
     * @param y     Right hand input
     * @return      Maximum of the two inputs
     */
    function max(uint256 x, uint256 y)
        internal
        pure
        returns (uint256)
    {
        return x > y ? x : y;
    }

    /**
     * @dev Clamps a value to an upper bound
     * @param x           Left hand input
     * @param upperBound  Maximum possible value to return
     * @return            Input x clamped to a maximum value, upperBound
     */
    function clamp(uint256 x, uint256 upperBound)
        internal
        pure
        returns (uint256)
    {
        return x > upperBound ? upperBound : x;
    }
}

/**
 * @title  StakingRewards
 * @author Originally: Synthetix (forked from /Synthetixio/synthetix/contracts/StakingRewards.sol)
 *         Audit: https://github.com/sigp/public-audits/blob/master/synthetix/unipool/review.pdf
 *         Changes by: Stability Labs Pty. Ltd.
 * @notice Rewards stakers of a given LP token (a.k.a StakingToken) with RewardsToken, on a pro-rata basis
 * @dev    Uses an ever increasing 'rewardPerTokenStored' variable to distribute rewards
 * each time a write action is called in the contract. This allows for passive reward accrual.
 *         Changes:
 *           - Cosmetic (comments, readability)
 *           - Addition of getRewardToken()
 *           - Changing of `StakingTokenWrapper` funcs from `super.stake` to `_stake`
 *           - Introduced a `stake(_beneficiary)` function to enable contract wrappers to stake on behalf
 */
contract StakingRewards is StakingTokenWrapper, RewardsDistributionRecipient {

    using StableMath for uint256;

    IERC20 public rewardsToken;

    uint256 public constant DURATION = 7 days;

    // Timestamp for current period finish
    uint256 public periodFinish = 0;
    // RewardRate for the rest of the PERIOD
    uint256 public rewardRate = 0;
    // Last time any user took action
    uint256 public lastUpdateTime = 0;
    // Ever increasing rewardPerToken rate, based on % of total supply
    uint256 public rewardPerTokenStored = 0;
    mapping(address => uint256) public userRewardPerTokenPaid;
    mapping(address => uint256) public rewards;

    event RewardAdded(uint256 reward);
    event Staked(address indexed user, uint256 amount, address payer);
    event Withdrawn(address indexed user, uint256 amount);
    event RewardPaid(address indexed user, uint256 reward);

    /** @dev StakingRewards is a TokenWrapper and RewardRecipient */
    constructor(
        address _nexus,
        address _stakingToken,
        address _rewardsToken,
        address _rewardsDistributor
    )
        public
        StakingTokenWrapper(_stakingToken)
        RewardsDistributionRecipient(_nexus, _rewardsDistributor)
    {
        rewardsToken = IERC20(_rewardsToken);
    }

    /** @dev Updates the reward for a given address, before executing function */
    modifier updateReward(address _account) {
        // Setting of global vars
        uint256 newRewardPerToken = rewardPerToken();
        // If statement protects against loss in initialisation case
        if(newRewardPerToken > 0) {
            rewardPerTokenStored = newRewardPerToken;
            lastUpdateTime = lastTimeRewardApplicable();
            // Setting of personal vars based on new globals
            if (_account != address(0)) {
                rewards[_account] = earned(_account);
                userRewardPerTokenPaid[_account] = newRewardPerToken;
            }
        }
        _;
    }

    /***************************************
                    ACTIONS
    ****************************************/

    /**
     * @dev Stakes a given amount of the StakingToken for the sender
     * @param _amount Units of StakingToken
     */
    function stake(uint256 _amount)
        external
    {
        _stake(msg.sender, _amount);
    }

    /**
     * @dev Stakes a given amount of the StakingToken for a given beneficiary
     * @param _beneficiary Staked tokens are credited to this address
     * @param _amount      Units of StakingToken
     */
    function stake(address _beneficiary, uint256 _amount)
        external
    {
        _stake(_beneficiary, _amount);
    }

    /**
     * @dev Internally stakes an amount by depositing from sender,
     * and crediting to the specified beneficiary
     * @param _beneficiary Staked tokens are credited to this address
     * @param _amount      Units of StakingToken
     */
    function _stake(address _beneficiary, uint256 _amount)
        internal
        updateReward(_beneficiary)
    {
        require(_amount > 0, "Cannot stake 0");
        super._stake(_beneficiary, _amount);
        emit Staked(_beneficiary, _amount, msg.sender);
    }

    /**
     * @dev Withdraws stake from pool and claims any rewards
     */
    function exit() external {
        withdraw(balanceOf(msg.sender));
        claimReward();
    }

    /**
     * @dev Withdraws given stake amount from the pool
     * @param _amount Units of the staked token to withdraw
     */
    function withdraw(uint256 _amount)
        public
        updateReward(msg.sender)
    {
        require(_amount > 0, "Cannot withdraw 0");
        _withdraw(_amount);
        emit Withdrawn(msg.sender, _amount);
    }

    /**
     * @dev Claims outstanding rewards for the sender.
     * First updates outstanding reward allocation and then transfers.
     */
    function claimReward()
        public
        updateReward(msg.sender)
    {
        uint256 reward = rewards[msg.sender];
        if (reward > 0) {
            rewards[msg.sender] = 0;
            rewardsToken.transfer(msg.sender, reward);
            emit RewardPaid(msg.sender, reward);
        }
    }


    /***************************************
                    GETTERS
    ****************************************/

    /**
     * @dev Gets the RewardsToken
     */
    function getRewardToken()
        external
        view
        returns (IERC20)
    {
        return rewardsToken;
    }

    /**
     * @dev Gets the last applicable timestamp for this reward period
     */
    function lastTimeRewardApplicable()
        public
        view
        returns (uint256)
    {
        return StableMath.min(block.timestamp, periodFinish);
    }

    /**
     * @dev Calculates the amount of unclaimed rewards per token since last update,
     * and sums with stored to give the new cumulative reward per token
     * @return 'Reward' per staked token
     */
    function rewardPerToken()
        public
        view
        returns (uint256)
    {
        // If there is no StakingToken liquidity, avoid div(0)
        uint256 stakedTokens = totalSupply();
        if (stakedTokens == 0) {
            return rewardPerTokenStored;
        }
        // new reward units to distribute = rewardRate * timeSinceLastUpdate
        uint256 rewardUnitsToDistribute = rewardRate.mul(lastTimeRewardApplicable().sub(lastUpdateTime));
        // new reward units per token = (rewardUnitsToDistribute * 1e18) / totalTokens
        uint256 unitsToDistributePerToken = rewardUnitsToDistribute.divPrecisely(stakedTokens);
        // return summed rate
        return rewardPerTokenStored.add(unitsToDistributePerToken);
    }

    /**
     * @dev Calculates the amount of unclaimed rewards a user has earned
     * @param _account User address
     * @return Total reward amount earned
     */
    function earned(address _account)
        public
        view
        returns (uint256)
    {
        // current rate per token - rate user previously received
        uint256 userRewardDelta = rewardPerToken().sub(userRewardPerTokenPaid[_account]);
        // new reward = staked tokens * difference in rate
        uint256 userNewReward = balanceOf(_account).mulTruncate(userRewardDelta);
        // add to previous rewards
        return rewards[_account].add(userNewReward);
    }


    /***************************************
                    ADMIN
    ****************************************/

    /**
     * @dev Notifies the contract that new rewards have been added.
     * Calculates an updated rewardRate based on the rewards in period.
     * @param _reward Units of RewardToken that have been added to the pool
     */
    function notifyRewardAmount(uint256 _reward)
        external
        onlyRewardsDistributor
        updateReward(address(0))
    {
        uint256 currentTime = block.timestamp;
        // If previous period over, reset rewardRate
        if (currentTime >= periodFinish) {
            rewardRate = _reward.div(DURATION);
        }
        // If additional reward to existing period, calc sum
        else {
            uint256 remaining = periodFinish.sub(currentTime);
            uint256 leftover = remaining.mul(rewardRate);
            rewardRate = _reward.add(leftover).div(DURATION);
        }

        lastUpdateTime = currentTime;
        periodFinish = currentTime.add(DURATION);

        emit RewardAdded(_reward);
    }
}

{
  "compilationTarget": {
    "StakingRewards.sol": "StakingRewards"
  },
  "evmVersion": "istanbul",
  "libraries": {},
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}