SushiSwap Staking Rewards

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Contains the implementation of Rewarder for SushiSwap's MasterChefV2 contract and helper RewardsManager contract for simplifying its management using DAO voting. Rewarder based on Synthetix's StakingRewards.sol contract which Lido has already used in Curve's liquidity pool.

Core Contracts

StakingRewards.sol

To use StakingRewards contract as a base contract for SushiRewarder next changes were applied to StakingRewards.sol contract:

• Methods stake(uint256 amount), withdraw(uint256 amount), and exit() were removed. MasterChefV2 will take control over this operations.
• External method getReward() was replaced with the internal method _payReward(address user, address recipient) which allows paying rewards of the user to another recipient's address.
• Since reward might be paid to address different from user's address event RewardPaid(address indexed user, uint256 reward) was changed in a next manner RewardPaid(address indexed user, address indexed recipient, uint256 reward).
• Events Staked and Withdrawn were removed as not used anymore.
• Method totalSupply() was marked as abstract and its visibility was changed to public.
• Variable _totalSupply was removed and all its usages were replaced with totalSupply() view.
• Constructor of the contract became internal cause the contract is abstract now and can't be deployed.
• Visibility of _balances variable was changed from private to internal. This is necessary to make it accessible in the child contracts.

The above changes don't touch rewards calculation logic and only modifies the interface of a contract to make it possible to use it as a base contract for different rewarder contracts. For example, we can implement the current Lido's Curve contract using the modified StakingRewards contract as a base contract, or implement a rewarder for SushiSwap's liquidity pool.

StakingRewardsSushi.sol

Inherits logic of StakingRewards contract and implements Sushi's IRewarder interface to make it possible to use as a rewarder in MasterChefV2 contract.

To be used in MasterChefV2 contract it has to implement next interface:

interface IRewarder {
    function onSushiReward(
        uint256 pid,
        address user,
        address recipient,
        uint256 sushiAmount,
        uint256 newLpAmount
    ) external;

    function pendingTokens(
        uint256 pid,
        address user,
        uint256 sushiAmount
    ) external view returns (IERC20[] memory, uint256[] memory);
}

Method pendingTokens is used by SushiSwaps's UI and must return a tuple with a list of rewardTokens distributes by the rewarder and a list of amounts of tokens gained by the user. In current implementation SushiStakingRewards distributes only one rewardsToken, and returns next value from pendingTokens method: ([rewardsToken], [earned(msg.sender)])

Method onSushiReward is executed on the distribution of rewards with the user and the amount of Sushi given out being specified or on any change of balance of user's lpTokens. In the current implementation, this method validates that method was called by MasterChefV2 contract with correct pid value, calls method _payReward(user, recipient) and updates user balance.

To be deployable SushiStakingRewards implements abstract method totalSupply() from StakingRewards.sol contract in next way:

function totalSupply() public view returns (uint256) {
    return stakingToken.balanceOf(MASTERCHEF_V2);
}

where MASTERCHEF_V2 is an address of MasterChefV2 contract.

RewardsManager.vy

This contract simplifies operations with reward periods of StakingRewards contracts for DAO. Was used without any changes from the original repository.