contract MixinStakingPoolRewards is
    MixinAbstract,
    MixinCumulativeRewards
{
    using LibSafeMath for uint256;

    /// @dev Withdraws the caller's WETH rewards that have accumulated
    ///      until the last epoch.
    /// @param poolId Unique id of pool.
    function withdrawDelegatorRewards(bytes32 poolId)
        external
    {
        _withdrawAndSyncDelegatorRewards(poolId, msg.sender);
    }

    /// @dev Computes the reward balance in ETH of the operator of a pool.
    /// @param poolId Unique id of pool.
    /// @return totalReward Balance in ETH.
    function computeRewardBalanceOfOperator(bytes32 poolId)
        external
        view
        returns (uint256 reward)
    {
        // Because operator rewards are immediately withdrawn as WETH
        // on finalization, the only factor in this function are unfinalized
        // rewards.
        IStructs.Pool memory pool = _poolById[poolId];
        // Get any unfinalized rewards.
        (uint256 unfinalizedTotalRewards, uint256 unfinalizedMembersStake) =
            _getUnfinalizedPoolRewards(poolId);

        // Get the operators' portion.
        (reward,) = _computePoolRewardsSplit(
            pool.operatorShare,
            unfinalizedTotalRewards,
            unfinalizedMembersStake
        );
        return reward;
    }

    /// @dev Computes the reward balance in ETH of a specific member of a pool.
    /// @param poolId Unique id of pool.
    /// @param member The member of the pool.
    /// @return totalReward Balance in ETH.
    function computeRewardBalanceOfDelegator(bytes32 poolId, address member)
        external
        view
        returns (uint256 reward)
    {
        IStructs.Pool memory pool = _poolById[poolId];
        // Get any unfinalized rewards.
        (uint256 unfinalizedTotalRewards, uint256 unfinalizedMembersStake) =
            _getUnfinalizedPoolRewards(poolId);

        // Get the members' portion.
        (, uint256 unfinalizedMembersReward) = _computePoolRewardsSplit(
            pool.operatorShare,
            unfinalizedTotalRewards,
            unfinalizedMembersStake
        );
        return _computeDelegatorReward(
            poolId,
            member,
            unfinalizedMembersReward,
            unfinalizedMembersStake
        );
    }

    /// @dev Syncs rewards for a delegator. This includes withdrawing rewards
    ///      rewards and adding/removing dependencies on cumulative rewards.
    /// @param poolId Unique id of pool.
    /// @param member of the pool.
    function _withdrawAndSyncDelegatorRewards(
        bytes32 poolId,
        address member
    )
        internal
    {
        // Ensure the pool is finalized.
        _assertPoolFinalizedLastEpoch(poolId);

        // Compute balance owed to delegator
        uint256 balance = _computeDelegatorReward(
            poolId,
            member,
            // No unfinalized values because we ensured the pool is already
            // finalized.
            0,
            0
        );

        // Sync the delegated stake balance. This will ensure future calls of
        // `_computeDelegatorReward` during this epoch will return 0, 
        // preventing a delegator from withdrawing more than once an epoch.
        _delegatedStakeToPoolByOwner[member][poolId] =
            _loadCurrentBalance(_delegatedStakeToPoolByOwner[member][poolId]);

        // Withdraw non-0 balance
        if (balance != 0) {
            // Decrease the balance of the pool
            _decreasePoolRewards(poolId, balance);

            // Withdraw the member's WETH balance
            getWethContract().transfer(member, balance);
        }

        // Ensure a cumulative reward entry exists for this epoch,
        // copying the previous epoch's CR if one doesn't exist already.
        _updateCumulativeReward(poolId);
    }

    /// @dev Handles a pool's reward at the current epoch.
    ///      This will split the reward between the operator and members,
    ///      depositing them into their respective vaults, and update the
    ///      accounting needed to allow members to withdraw their individual
    ///      rewards.
    /// @param poolId Unique Id of pool.
    /// @param reward received by the pool.
    /// @param membersStake the amount of non-operator delegated stake that
    ///        will split the  reward.
    /// @return operatorReward Portion of `reward` given to the pool operator.
    /// @return membersReward Portion of `reward` given to the pool members.
    function _syncPoolRewards(
        bytes32 poolId,
        uint256 reward,
        uint256 membersStake
    )
        internal
        returns (uint256 operatorReward, uint256 membersReward)
    {
        IStructs.Pool memory pool = _poolById[poolId];

        // Split the reward between operator and members
        (operatorReward, membersReward) = _computePoolRewardsSplit(
            pool.operatorShare,
            reward,
            membersStake
        );

        if (operatorReward > 0) {
            // Transfer the operator's weth reward to the operator
            getWethContract().transfer(pool.operator, operatorReward);
        }

        if (membersReward > 0) {
            // Increase the balance of the pool
            _increasePoolRewards(poolId, membersReward);
            // Create a cumulative reward entry at the current epoch.
            _addCumulativeReward(poolId, membersReward, membersStake);
        }

        return (operatorReward, membersReward);
    }

    /// @dev Compute the split of a pool reward between the operator and members
    ///      based on the `operatorShare` and `membersStake`.
    /// @param operatorShare The fraction of rewards owed to the operator,
    ///        in PPM.
    /// @param totalReward The pool reward.
    /// @param membersStake The amount of member (non-operator) stake delegated
    ///        to the pool in the epoch the rewards were earned.
    /// @return operatorReward Portion of `totalReward` given to the pool operator.
    /// @return membersReward Portion of `totalReward` given to the pool members.
    function _computePoolRewardsSplit(
        uint32 operatorShare,
        uint256 totalReward,
        uint256 membersStake
    )
        internal
        pure
        returns (uint256 operatorReward, uint256 membersReward)
    {
        if (membersStake == 0) {
            operatorReward = totalReward;
        } else {
            operatorReward = LibMath.getPartialAmountCeil(
                uint256(operatorShare),
                PPM_DENOMINATOR,
                totalReward
            );
            membersReward = totalReward.safeSub(operatorReward);
        }
        return (operatorReward, membersReward);
    }

    /// @dev Computes the reward balance in ETH of a specific member of a pool.
    /// @param poolId Unique id of pool.
    /// @param member of the pool.
    /// @param unfinalizedMembersReward Unfinalized total members reward (if any).
    /// @param unfinalizedMembersStake Unfinalized total members stake (if any).
    /// @return reward Balance in WETH.
    function _computeDelegatorReward(
        bytes32 poolId,
        address member,
        uint256 unfinalizedMembersReward,
        uint256 unfinalizedMembersStake
    )
        private
        view
        returns (uint256 reward)
    {
        uint256 currentEpoch_ = currentEpoch;
        IStructs.StoredBalance memory delegatedStake = _delegatedStakeToPoolByOwner[member][poolId];

        // There can be no rewards if the last epoch when stake was stored is
        // equal to the current epoch, because all prior rewards, including
        // rewards finalized this epoch have been claimed.
        if (delegatedStake.currentEpoch == currentEpoch_) {
            return 0;
        }

        // We account for rewards over 3 intervals, below.

        // 1/3 Unfinalized rewards earned in `currentEpoch - 1`.
        reward = _computeUnfinalizedDelegatorReward(
            delegatedStake,
            currentEpoch_,
            unfinalizedMembersReward,
            unfinalizedMembersStake
        );

        // 2/3 Finalized rewards earned in epochs [`delegatedStake.currentEpoch + 1` .. `currentEpoch - 1`]
        uint256 delegatedStakeNextEpoch = uint256(delegatedStake.currentEpoch).safeAdd(1);
        reward = reward.safeAdd(
            _computeMemberRewardOverInterval(
                poolId,
                delegatedStake.currentEpochBalance,
                delegatedStake.currentEpoch,
                delegatedStakeNextEpoch
            )
        );

        // 3/3 Finalized rewards earned in epoch `delegatedStake.currentEpoch`.
        reward = reward.safeAdd(
            _computeMemberRewardOverInterval(
                poolId,
                delegatedStake.nextEpochBalance,
                delegatedStakeNextEpoch,
                currentEpoch_
            )
        );

        return reward;
    }

    /// @dev Computes the unfinalized rewards earned by a delegator in the last epoch.
    /// @param delegatedStake Amount of stake delegated to pool by a specific staker
    /// @param currentEpoch_ The epoch in which this call is executing
    /// @param unfinalizedMembersReward Unfinalized total members reward (if any).
    /// @param unfinalizedMembersStake Unfinalized total members stake (if any).
    /// @return reward Balance in WETH.
    function _computeUnfinalizedDelegatorReward(
        IStructs.StoredBalance memory delegatedStake,
        uint256 currentEpoch_,
        uint256 unfinalizedMembersReward,
        uint256 unfinalizedMembersStake
    )
        private
        pure
        returns (uint256)
    {
        // If there are unfinalized rewards this epoch, compute the member's
        // share.
        if (unfinalizedMembersReward == 0 || unfinalizedMembersStake == 0) {
            return 0;
        }

        // Unfinalized rewards are always earned from stake in
        // the prior epoch so we want the stake at `currentEpoch_-1`.
        uint256 unfinalizedStakeBalance = delegatedStake.currentEpoch >= currentEpoch_.safeSub(1) ?
            delegatedStake.currentEpochBalance :
            delegatedStake.nextEpochBalance;

        // Sanity check to save gas on computation
        if (unfinalizedStakeBalance == 0) {
            return 0;
        }

        // Compute unfinalized reward
        return LibMath.getPartialAmountFloor(
            unfinalizedMembersReward,
            unfinalizedMembersStake,
            unfinalizedStakeBalance
        );
    }

    /// @dev Increases rewards for a pool.
    /// @param poolId Unique id of pool.
    /// @param amount Amount to increment rewards by.
    function _increasePoolRewards(bytes32 poolId, uint256 amount)
        private
    {
        rewardsByPoolId[poolId] = rewardsByPoolId[poolId].safeAdd(amount);
        wethReservedForPoolRewards = wethReservedForPoolRewards.safeAdd(amount);
    }

    /// @dev Decreases rewards for a pool.
    /// @param poolId Unique id of pool.
    /// @param amount Amount to decrement rewards by.
    function _decreasePoolRewards(bytes32 poolId, uint256 amount)
        private
    {
        rewardsByPoolId[poolId] = rewardsByPoolId[poolId].safeSub(amount);
        wethReservedForPoolRewards = wethReservedForPoolRewards.safeSub(amount);
    }
}
function _computePoolRewardsSplit(
    uint32 operatorShare,
    uint256 totalReward,
    uint256 membersStake
)
    internal
    pure
    returns (uint256 operatorReward, uint256 membersReward)
{
    if (membersStake == 0) {
        operatorReward = totalReward;
    } else {
        operatorReward = LibMath.getPartialAmountCeil(
            uint256(operatorShare),
            PPM_DENOMINATOR,
            totalReward
        );
        membersReward = totalReward.safeSub(operatorReward);
    }
    return (operatorReward, membersReward);
}

/// @dev Compute the split of a pool reward between the operator and members
///      based on the `operatorShare` and `membersStake`.
/// @param operatorShare The fraction of rewards owed to the operator,
///        in PPM.
/// @param totalReward The pool reward.
/// @param membersStake The amount of member (non-operator) stake delegated
///        to the pool in the epoch the rewards were earned.
/// @return operatorReward Portion of `totalReward` given to the pool operator.
/// @return membersReward Portion of `totalReward` given to the pool members.