// File: contracts/Rewards.sol



// SPDX-License-Identifier: Apache-2.0
pragma solidity 0.7.6;
pragma experimental ABIEncoderV2;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "./interfaces/IKernel.sol";

contract Rewards is Ownable {
    using SafeMath for uint256;

    uint256 constant decimals = 10 ** 18;

    struct Pull {
        address source;
        uint256 startTs;
        uint256 endTs;
        uint256 totalDuration;
        uint256 totalAmount;
    }

    Pull public pullFeature;
    bool public disabled;
    uint256 public lastPullTs;

    uint256 public balanceBefore;
    uint256 public currentMultiplier;

    mapping(address => uint256) public userMultiplier;
    mapping(address => uint256) public owed;

    IKernel public kernel;
    IERC20 public rewardToken;

    event Claim(address indexed user, uint256 amount);

    constructor(address _owner, address _token, address _kernel) {
        require(_token != address(0), "reward token must not be 0x0");
        require(_kernel != address(0), "kernel address must not be 0x0");

        transferOwnership(_owner);

        rewardToken = IERC20(_token);
        kernel = IKernel(_kernel);
    }

    // registerUserAction is called by the Kernel every time the user does a deposit or withdrawal in order to
    // account for the changes in reward that the user should get
    // it updates the amount owed to the user without transferring the funds
    function registerUserAction(address user) public {
        require(msg.sender == address(kernel), 'only callable by kernel');

        _calculateOwed(user);
    }

    // claim calculates the currently owed reward and transfers the funds to the user
    function claim() public returns (uint256){
        _calculateOwed(msg.sender);

        uint256 amount = owed[msg.sender];
        require(amount > 0, "nothing to claim");

        owed[msg.sender] = 0;

        rewardToken.transfer(msg.sender, amount);

        // acknowledge the amount that was transferred to the user
        ackFunds();

        emit Claim(msg.sender, amount);

        return amount;
    }

    // ackFunds checks the difference between the last known balance of `token` and the current one
    // if it goes up, the multiplier is re-calculated
    // if it goes down, it only updates the known balance
    function ackFunds() public {
        uint256 balanceNow = rewardToken.balanceOf(address(this));

        if (balanceNow == 0 || balanceNow <= balanceBefore) {
            balanceBefore = balanceNow;
            return;
        }

        uint256 totalStakedEntr = kernel.entrStaked();
        // if there's no entr staked, it doesn't make sense to ackFunds because there's nobody to distribute them to
        // and the calculation would fail anyways due to division by 0
        if (totalStakedEntr == 0) {
            return;
        }

        uint256 diff = balanceNow.sub(balanceBefore);
        uint256 multiplier = currentMultiplier.add(diff.mul(decimals).div(totalStakedEntr));

        balanceBefore = balanceNow;
        currentMultiplier = multiplier;
    }

    // setupPullToken is used to setup the rewards system; only callable by contract owner
    // set source to address(0) to disable the functionality
    function setupPullToken(address source, uint256 startTs, uint256 endTs, uint256 amount) public {
        require(msg.sender == owner(), "!owner");
        require(!disabled, "contract is disabled");

        if (pullFeature.source != address(0)) {
            require(source == address(0), "contract is already set up, source must be 0x0");
            disabled = true;
        } else {
            require(source != address(0), "contract is not setup, source must be != 0x0");
        }

        if (source == address(0)) {
            require(startTs == 0, "disable contract: startTs must be 0");
            require(endTs == 0, "disable contract: endTs must be 0");
            require(amount == 0, "disable contract: amount must be 0");
        } else {
            require(endTs > startTs, "setup contract: endTs must be greater than startTs");
            require(amount > 0, "setup contract: amount must be greater than 0");
        }

        pullFeature.source = source;
        pullFeature.startTs = startTs;
        pullFeature.endTs = endTs;
        pullFeature.totalDuration = endTs.sub(startTs);
        pullFeature.totalAmount = amount;

        if (lastPullTs < startTs) {
            lastPullTs = startTs;
        }
    }

    // setKernel sets the address of the EnterDao Kernel into the state variable
    function setKernel(address _kernel) public {
        require(_kernel != address(0), 'kernel address must not be 0x0');
        require(msg.sender == owner(), '!owner');

        kernel = IKernel(_kernel);
    }

    // _pullToken calculates the amount based on the time passed since the last pull relative
    // to the total amount of time that the pull functionality is active and executes a transferFrom from the
    // address supplied as `pullTokenFrom`, if enabled
    function _pullToken() internal {
        if (
            pullFeature.source == address(0) ||
            block.timestamp < pullFeature.startTs
        ) {
            return;
        }

        uint256 timestampCap = pullFeature.endTs;
        if (block.timestamp < pullFeature.endTs) {
            timestampCap = block.timestamp;
        }

        if (lastPullTs >= timestampCap) {
            return;
        }

        uint256 timeSinceLastPull = timestampCap.sub(lastPullTs);
        uint256 shareToPull = timeSinceLastPull.mul(decimals).div(pullFeature.totalDuration);
        uint256 amountToPull = pullFeature.totalAmount.mul(shareToPull).div(decimals);

        lastPullTs = block.timestamp;
        rewardToken.transferFrom(pullFeature.source, address(this), amountToPull);
    }

    // _calculateOwed calculates and updates the total amount that is owed to an user and updates the user's multiplier
    // to the current value
    // it automatically attempts to pull the token from the source and acknowledge the funds
    function _calculateOwed(address user) internal {
        _pullToken();
        ackFunds();

        uint256 reward = _userPendingReward(user);

        owed[user] = owed[user].add(reward);
        userMultiplier[user] = currentMultiplier;
    }

    // _userPendingReward calculates the reward that should be based on the current multiplier / anything that's not included in the `owed[user]` value
    // it does not represent the entire reward that's due to the user unless added on top of `owed[user]`
    function _userPendingReward(address user) internal view returns (uint256) {
        uint256 multiplier = currentMultiplier.sub(userMultiplier[user]);

        return kernel.balanceOf(user).mul(multiplier).div(decimals);
    }
}

// File: @openzeppelin/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../utils/Context.sol";
/**
 * @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.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the 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 virtual 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 virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * 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);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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;
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

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

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

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

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

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

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

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

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

// File: contracts/interfaces/IKernel.sol



// SPDX-License-Identifier: Apache-2.0
pragma solidity 0.7.6;
pragma experimental ABIEncoderV2;

import "../libraries/LibKernelStorage.sol";

interface IKernel {
    // deposit allows a user to add more entr to his staked balance
    function deposit(uint256 amount) external;

    // withdraw allows a user to withdraw funds if the balance is not locked
    function withdraw(uint256 amount) external;

    // lock a user's currently staked balance until timestamp & add the bonus to his voting power
    function lock(uint256 timestamp) external;

    // delegate allows a user to delegate his voting power to another user
    function delegate(address to) external;

    // stopDelegate allows a user to take back the delegated voting power
    function stopDelegate() external;

    // lock the balance of a proposal creator until the voting ends; only callable by DAO
    function lockCreatorBalance(address user, uint256 timestamp) external;

    // balanceOf returns the current ENTR balance of a user (bonus not included)
    function balanceOf(address user) external view returns (uint256);

    // balanceAtTs returns the amount of ENTR that the user currently staked (bonus NOT included)
    function balanceAtTs(address user, uint256 timestamp) external view returns (uint256);

    // stakeAtTs returns the Stake object of the user that was valid at `timestamp`
    function stakeAtTs(address user, uint256 timestamp) external view returns (LibKernelStorage.Stake memory);

    // votingPower returns the voting power (bonus included) + delegated voting power for a user at the current block
    function votingPower(address user) external view returns (uint256);

    // votingPowerAtTs returns the voting power (bonus included) + delegated voting power for a user at a point in time
    function votingPowerAtTs(address user, uint256 timestamp) external view returns (uint256);

    // entrStaked returns the total raw amount of ENTR staked at the current block
    function entrStaked() external view returns (uint256);

    // entrStakedAtTs returns the total raw amount of ENTR users have deposited into the contract
    // it does not include any bonus
    function entrStakedAtTs(uint256 timestamp) external view returns (uint256);

    // delegatedPower returns the total voting power that a user received from other users
    function delegatedPower(address user) external view returns (uint256);

    // delegatedPowerAtTs returns the total voting power that a user received from other users at a point in time
    function delegatedPowerAtTs(address user, uint256 timestamp) external view returns (uint256);

    // multiplierAtTs calculates the multiplier at a given timestamp based on the user's stake a the given timestamp
    // it includes the decay mechanism
    function multiplierAtTs(address user, uint256 timestamp) external view returns (uint256);

    // userLockedUntil returns the timestamp until the user's balance is locked
    function userLockedUntil(address user) external view returns (uint256);

    // userDidDelegate returns the address to which a user delegated their voting power; address(0) if not delegated
    function userDelegatedTo(address user) external view returns (address);
    
}

// File: @openzeppelin/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: contracts/libraries/LibKernelStorage.sol



// SPDX-License-Identifier: Apache-2.0
pragma solidity 0.7.6;
pragma experimental ABIEncoderV2;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "../interfaces/IRewards.sol";

library LibKernelStorage {
    bytes32 constant STORAGE_POSITION = keccak256("com.enterdao.kernel.storage");

    struct Checkpoint {
        uint256 timestamp;
        uint256 amount;
    }

    struct Stake {
        uint256 timestamp;
        uint256 amount;
        uint256 expiryTimestamp;
        address delegatedTo;
    }

    struct Storage {
        bool initialized;

        // mapping of user address to history of Stake objects
        // every user action creates a new object in the history
        mapping(address => Stake[]) userStakeHistory;

        // array of entr staked Checkpoint
        // deposits/withdrawals create a new object in the history (max one per block)
        Checkpoint[] entrStakedHistory;

        // mapping of user address to history of delegated power
        // every delegate/stopDelegate call create a new checkpoint (max one per block)
        mapping(address => Checkpoint[]) delegatedPowerHistory;

        IERC20 entr;
        IRewards rewards;
    }

    function kernelStorage() internal pure returns (Storage storage ds) {
        bytes32 position = STORAGE_POSITION;
        assembly {
            ds.slot := position
        }
    }
}

// File: contracts/interfaces/IRewards.sol



// SPDX-License-Identifier: Apache-2.0
pragma solidity 0.7.6;
pragma experimental ABIEncoderV2;

interface IRewards {
    function registerUserAction(address user) external;
}