There is a canonical position staking contract, Staker.

struct Incentive {
  uint128 totalRewardUnclaimed;
  uint128 numberOfStakes;
  uint160 totalSecondsClaimedX128;
}

struct Deposit {
  address owner;
  uint96 numberOfStakes;
}

struct Stake {
  uint160 secondsPerLiquidityInsideInitialX128;
  uint128 liquidity;
}

State:

IUniswapV3Factory public immutable factory;
INonfungiblePositionManager public immutable nonfungiblePositionManager;

/// @dev bytes32 refers to the return value of IncentiveId.compute
mapping(bytes32 => Incentive) public incentives;

/// @dev deposits[tokenId] => Deposit
mapping(uint256 => Deposit) public deposits;

/// @dev stakes[tokenId][incentiveHash] => Stake
mapping(uint256 => mapping(bytes32 => Stake)) public stakes;

/// @dev rewards[rewardToken][msg.sender] => uint256
mapping(address => mapping(address => uint256)) public rewards;

Params:

struct CreateIncentiveParams {
  address rewardToken;
  address pool;
  uint256 startTime;
  uint256 endTime;
  uint128 totalReward;
}

struct EndIncentiveParams {
  address creator;
  address rewardToken;
  address pool;
  uint256 startTime;
  uint256 endTime;
}

createIncentive creates a liquidity mining incentive program. The key used to look up an Incentive is the hash of its immutable properties.

Check:

• Incentive with these params does not already exist
• Timestamps: params.endTime >= params.startTime, params.startTime >= block.timestamp
• Incentive with this ID does not already exist.

Effects:

• Sets incentives[key] = Incentive(totalRewardUnclaimed=totalReward, totalSecondsClaimedX128=0, rewardToken=rewardToken)

Interaction:

• Transfers params.totalReward from msg.sender to self.
  • Make sure there is a check here and it fails if the transfer fails
• Emits IncentiveCreated

endIncentive can be called by anyone to end an Incentive after the endTime has passed, transferring totalRewardUnclaimed of rewardToken back to refundee.

Check:

• block.timestamp > params.endTime
• Incentive exists (incentive.totalRewardUnclaimed != 0)

Effects:

• deletes incentives[key] (This is a new change)

Interactions:

• safeTransfers totalRewardUnclaimed of rewardToken to the incentive creator msg.sender
• emits IncentiveEnded

Interactions

• nonfungiblePositionManager.safeTransferFrom(sender, this, tokenId)
  • This transfer triggers the onERC721Received hook

Check:

• Make sure sender is univ3 nft

Effects:

• Creates a deposit for the token setting deposit owner to from.
  • Setting owner to from ensures that the owner of the token also owns the deposit. Approved addresses and operators may first transfer the token to themselves before depositing for deposit ownership.
• If data.length>0, stakes the token in one or more incentives

Checks

• Check that a Deposit exists for the token and that msg.sender is the owner on that Deposit.
• Check that numberOfStakes on that Deposit is 0.

Effects

• Delete the Deposit delete deposits[tokenId].

Interactions

• safeTransferFrom the token to to with data.
• emit DepositTransferred(token, deposit.owner, address(0))

Check:

• deposits[params.tokenId].owner == msg.sender
• Make sure incentive actually exists and has reward that could be claimed (incentive.rewardToken != address(0))
  • Check if this check can check totalRewardUnclaimed instead
• Make sure token not already staked

Interactions

• msg.sender to withdraw all of their reward balance in a specific token to a specified to address.

• emit RewardClaimed(to, reward)

To unstake an NFT, you call unstakeToken, which takes all the same arguments as stake.

Checks

• It checks that you are the owner of the Deposit
• It checks that there exists a Stake for the provided key (with exists=true).

Effects

• Deletes the Stake.
• Decrements numberOfStakes for the Deposit by 1.
• totalRewardsUnclaimed is decremented by reward.
• totalSecondsClaimed is incremented by seconds.
• Increments rewards[rewardToken][msg.sender] by the amount given by getRewardInfo.

• It computes secondsInsideX128 (the total liquidity seconds for which rewards are owed) for a given Stake, by:

  • usingsnapshotCumulativesInside from the Uniswap v3 core contract to get secondsPerLiquidityInRangeX128, and subtracting secondsPerLiquidityInRangeInitialX128.
  • Multiplying that by stake.liquidity to get the total seconds accrued by the liquidity in that period

• Note that X128 means it's a UQ32X128.

• It computes totalSecondsUnclaimed by taking max(endTime, block.timestamp) - startTime, casting it as a Q128, and subtracting totalSecondsClaimedX128.

• It computes rewardRate for the Incentive casting incentive.totalRewardUnclaimed as a Q128, then dividing it by totalSecondsUnclaimedX128.

• reward is then calculated as secondsInsideX128 times the rewardRate, scaled down to a regular uint128.