pragma solidity 0.6.12;


/**
 * @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);
}

/**
 * @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);
    }
}

/**
 * @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.
     */
    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.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        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.
     */
    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 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].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

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

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

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

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // 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. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        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");
        }
    }
}

/**
 * @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");
    }
}

interface IRewardsDistributionRecipient {
    function notifyRewardAmount(address _rewardToken, uint256 reward) external;
}

interface IWrappedERC20 {
    function wrap(address _to, uint _amount) external;
    function unwrap(address _to, uint _amount) external;
}

// A multistakingreward contract that allows stakers to staking a single token and recieve various reward tokens.
// Forked from the Uniswap staking reward contract at https://etherscan.io/address/0x7FBa4B8Dc5E7616e59622806932DBea72537A56b#code
// with the following changes:
// - Expand from single reward token to a list of reward tokens
// - allow governance to rescue unclaimed tokens
contract MultiStakingRewards is IRewardsDistributionRecipient, ReentrancyGuard {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    /* ========== STRUCTS ========== */

    // Info of each reward pool.
    struct RewardPool {
        IERC20 rewardToken;                                 // Address of reward token.
        uint256 periodFinish;                               // timestamp of when this reward pool finishes distribution
        uint256 rewardRate;                                 // amount of rewards distributed per unit of time
        uint256 rewardsDuration;                            // duration of distribution
        uint256 lastUpdateTime;                             // timestamp of when reward info was last updated
        uint256 rewardPerTokenStored;                       // current rewards per token based on total rewards and total staked
        mapping(address => uint256) userRewardPerTokenPaid; // amount of rewards per token already paided out to user
        mapping(address => uint256) rewards;                // amount of rewards user has earned
        bool isActive;                                      // mark if the pool is active
    }

    /* ========== STATE VARIABLES ========== */

    address public rewardsDistribution;
    address public governance;

    IERC20 public stakingToken;
    IWrappedERC20 public wStakingToken; // wrapped stakingToken is used to reward stakers with more stakingToken

    uint256 public totalSupply;
    mapping(address => uint256) public balances;

    mapping(address => RewardPool) public rewardPools; // reward token to reward pool mapping
    address[] public activeRewardPools; // list of reward tokens that are distributing rewards

    /* ========== CONSTRUCTOR ========== */

    constructor(address _stakingToken, address _wStakingToken, address _rewardsDistribution) public {
        stakingToken = IERC20(_stakingToken);
        wStakingToken = IWrappedERC20(_wStakingToken);
        rewardsDistribution = _rewardsDistribution;
        governance = msg.sender;
    }

    /* ========== VIEWS ========== */

    function activeRewardPoolsLength() external view returns (uint256) {
        return activeRewardPools.length;
    }

    function lastTimeRewardApplicable(address _rewardToken) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return Math.min(block.timestamp, pool.periodFinish);
    }

    function rewardPerToken(address _rewardToken) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        if (totalSupply == 0) {
            return pool.rewardPerTokenStored;
        }
        return
            pool.rewardPerTokenStored.add(
                lastTimeRewardApplicable(_rewardToken).sub(pool.lastUpdateTime).mul(pool.rewardRate).mul(1e18).div(totalSupply)
            );
    }

    function earned(address _rewardToken, address _account) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return balances[_account].mul(rewardPerToken(_rewardToken).sub(pool.userRewardPerTokenPaid[_account])).div(1e18).add(pool.rewards[_account]);
    }

    function getRewardForDuration(address _rewardToken) external view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return pool.rewardRate.mul(pool.rewardsDuration);
    }

    function periodFinish(address _rewardToken) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return pool.periodFinish;
    }

    function rewardRate(address _rewardToken) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return pool.rewardRate;
    }

    function rewardsDuration(address _rewardToken) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return pool.rewardsDuration;
    }

    function lastUpdateTime(address _rewardToken) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return pool.lastUpdateTime;
    }

    function rewardPerTokenStored(address _rewardToken) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return pool.rewardPerTokenStored;
    }

    function userRewardPerTokenPaid(address _rewardToken, address _account) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return pool.userRewardPerTokenPaid[_account];
    }

    function rewards(address _rewardToken, address _account) public view returns (uint256) {
        RewardPool storage pool = rewardPools[_rewardToken];
        return pool.rewards[_account];
    }

    /* ========== MUTATIVE FUNCTIONS ========== */

    function stake(uint256 amount) external nonReentrant updateActiveRewards(msg.sender) {
        require(amount > 0, "Cannot stake 0");
        totalSupply = totalSupply.add(amount);
        balances[msg.sender] = balances[msg.sender].add(amount);
        stakingToken.safeTransferFrom(msg.sender, address(this), amount);
        emit Staked(msg.sender, amount);
    }

    function withdraw(uint256 amount) public nonReentrant updateActiveRewards(msg.sender) {
        require(amount > 0, "Cannot withdraw 0");
        totalSupply = totalSupply.sub(amount);
        balances[msg.sender] = balances[msg.sender].sub(amount);
        stakingToken.safeTransfer(msg.sender, amount);
        emit Withdrawn(msg.sender, amount);
    }

    function getReward(address _rewardToken) external nonReentrant updateReward(_rewardToken, msg.sender) {
        _getReward(_rewardToken);
    }

    function getAllActiveRewards() public nonReentrant updateActiveRewards(msg.sender) {
        for (uint i = 0; i < activeRewardPools.length; i++) {
            _getReward(activeRewardPools[i]);
        }
    }

    function _getReward(address _rewardToken) internal {
        RewardPool storage pool = rewardPools[_rewardToken];
        require(pool.isActive, "pool is inactive");

        uint256 reward = pool.rewards[msg.sender];
        if (reward > 0) {
            pool.rewards[msg.sender] = 0;
            // If reward token is wrapped version of staking token, auto unwrap into underlying to user
            if (address(pool.rewardToken) == address(wStakingToken)) {
                wStakingToken.unwrap(msg.sender, reward);
            } else {
                pool.rewardToken.safeTransfer(msg.sender, reward);
            }
            emit RewardPaid(address(pool.rewardToken), msg.sender, reward);
        }
    }

    function exit() external {
        withdraw(balances[msg.sender]);
        getAllActiveRewards();
    }

    /* ========== RESTRICTED FUNCTIONS ========== */

    function notifyRewardAmount(address _rewardToken, uint256 _amount) external override onlyRewardsDistribution updateReward(_rewardToken, address(0)) {
        RewardPool storage pool = rewardPools[_rewardToken];

        if (block.timestamp >= pool.periodFinish) {
            pool.rewardRate = _amount.div(pool.rewardsDuration);
        } else {
            uint256 remaining = pool.periodFinish.sub(block.timestamp);
            uint256 leftover = remaining.mul(pool.rewardRate);
            pool.rewardRate = _amount.add(leftover).div(pool.rewardsDuration);
        }

        // Ensure the provided reward amount is not more than the balance in the contract.
        // This keeps the reward rate in the right range, preventing overflows due to
        // very high values of rewardRate in the earned and rewardsPerToken functions;
        // Reward + leftover must be less than 2^256 / 10^18 to avoid overflow.
        uint balance = pool.rewardToken.balanceOf(address(this));
        require(pool.rewardRate <= balance.div(pool.rewardsDuration), "Provided reward too high");

        pool.lastUpdateTime = block.timestamp;
        pool.periodFinish = block.timestamp.add(pool.rewardsDuration);

        emit RewardAdded(_rewardToken, _amount);
    }

    // Add new reward pool to list
    // NOTE: DO NOT add same pool twice while active.
    function addRewardPool(
        address _rewardToken,
        uint256 _rewardsDuration
    )
        external
        onlyGov
    {
      rewardPools[_rewardToken] = RewardPool({
          rewardToken: IERC20(_rewardToken),
          periodFinish: 0,
          rewardRate: 0,
          rewardsDuration: _rewardsDuration,
          lastUpdateTime: 0,
          rewardPerTokenStored: 0,
          isActive: true
      });

      activeRewardPools.push(_rewardToken);
    }

    // Remove pool from active list
    function inactivateRewardPool(address _rewardToken) external onlyGov {
        // find the index
        uint indexToDelete = 0;
        bool found = false;
        for (uint i = 0; i < activeRewardPools.length; i++) {
            if (activeRewardPools[i] == _rewardToken) {
                indexToDelete = i;
                found = true;
                break;
            }
        }

        require(found, "element not found");
        _inactivateRewardPool(indexToDelete);
    }

    // In case the list gets so large and make iteration impossible
    function inactivateRewardPoolByIndex(uint256 _index) external onlyGov {
        _inactivateRewardPool(_index);
    }

    function _inactivateRewardPool(uint256 _index) internal {
        RewardPool storage pool = rewardPools[activeRewardPools[_index]];
        pool.isActive = false;
        // we don't care about the ordering of the active reward pool array
        // so we can just swap the element to delete with the last element
        activeRewardPools[_index] = activeRewardPools[activeRewardPools.length - 1];
        activeRewardPools.pop();
    }

    // Allow governance to rescue unclaimed inactive rewards
    function rescue(address _rewardToken) external onlyGov {
        require(_rewardToken != address(stakingToken), "Cannot withdraw staking token");
        RewardPool storage pool = rewardPools[_rewardToken];
        require(pool.isActive == false, "Cannot withdraw active reward token");

        uint _balance = IERC20(_rewardToken).balanceOf(address(this));
        IERC20(_rewardToken).safeTransfer(governance, _balance);
    }

    /* ========== RESTRICTED FUNCTIONS ========== */

    function setRewardsDistribution(address _rewardsDistribution) external {
        require(msg.sender == governance, "!governance");
        rewardsDistribution = _rewardsDistribution;
    }

    function setGov(address _gov) external {
        require(msg.sender == governance, "!governance");
        governance = _gov;
    }

    /* ========== MODIFIERS ========== */

    modifier updateActiveRewards(address _account) {
        for (uint i = 0; i < activeRewardPools.length; i++) {
            RewardPool storage pool = rewardPools[activeRewardPools[i]];

            pool.rewardPerTokenStored = rewardPerToken(address(pool.rewardToken));
            pool.lastUpdateTime = lastTimeRewardApplicable(address(pool.rewardToken));
            if (_account != address(0)) {
                pool.rewards[_account] = earned(address(pool.rewardToken), _account);
                pool.userRewardPerTokenPaid[_account] = pool.rewardPerTokenStored;
            }
        }
        _;
    }

    modifier updateReward(address _rewardToken, address _account) {
        RewardPool storage pool = rewardPools[_rewardToken];

        pool.rewardPerTokenStored = rewardPerToken(address(pool.rewardToken));
        pool.lastUpdateTime = lastTimeRewardApplicable(address(pool.rewardToken));
        if (_account != address(0)) {
            pool.rewards[_account] = earned(address(pool.rewardToken), _account);
            pool.userRewardPerTokenPaid[_account] = pool.rewardPerTokenStored;
        }
        _;
    }

    modifier onlyGov() {
        require(msg.sender == governance, "!governance");
        _;
    }

    modifier onlyRewardsDistribution() {
        require(msg.sender == rewardsDistribution, "!rewardsDistribution");
        _;
    }

    /* ========== EVENTS ========== */

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