Contract Source Code:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.0;

import {ERC20} from "solmate/src/tokens/ERC20.sol";
import {SafeTransferLib} from "solmate/src/utils/SafeTransferLib.sol";

contract SbeeStaking {
    using SafeTransferLib for ERC20;
    using Cast for uint256;

    event Staked(address user, uint256 amount);
    event Unstaked(address user, uint256 amount);
    event Claimed(address user, uint256 amount);
    event RewardsPerTokenUpdated(uint256 accumulated);
    event UserRewardsUpdated(address user, uint256 rewards, uint256 checkpoint);

    struct RewardsPerToken {
        uint128 accumulated;
        uint128 lastUpdated;
    }

    struct UserRewards {
        uint128 accumulated;
        uint128 checkpoint;
        uint256 totalEarned;
    }

    ERC20 public immutable stakingToken;
    uint256 public totalStaked;
    uint256 public totalStakers;
    mapping(address => uint256) public userStake;

    uint256 public immutable rewardsRate;
    uint256 public immutable stakingStart;
    uint256 public immutable stakingEnd;

    RewardsPerToken public rewardsPerToken;
    mapping(address => UserRewards) public accumulatedRewards;

    constructor(
        ERC20 _stakingToken,
        uint256 _stakingStart,
        uint256 _stakingEnd,
        uint256 totalRewards
    ) {
        stakingToken = _stakingToken;
        stakingStart = _stakingStart;
        stakingEnd = _stakingEnd;
        rewardsRate = totalRewards / (_stakingEnd - _stakingStart);
        rewardsPerToken.lastUpdated = _stakingStart.u128();
    }

    function _calculateRewardsPerToken(
        RewardsPerToken memory rewardsPerTokenIn
    ) internal view returns (RewardsPerToken memory) {
        RewardsPerToken memory rewardsPerTokenOut = RewardsPerToken(
            rewardsPerTokenIn.accumulated,
            rewardsPerTokenIn.lastUpdated
        );
        uint256 _totalStaked = totalStaked;

        if (block.timestamp < stakingStart) return rewardsPerTokenOut;

        uint256 updateTime = block.timestamp < stakingEnd
            ? block.timestamp
            : stakingEnd;
        uint256 elapsed = updateTime - rewardsPerTokenIn.lastUpdated;

        if (elapsed == 0) return rewardsPerTokenOut;
        rewardsPerTokenOut.lastUpdated = updateTime.u128();

        if (totalStaked == 0) return rewardsPerTokenOut;

        rewardsPerTokenOut.accumulated = (rewardsPerTokenIn.accumulated +
            (1e18 * elapsed * rewardsRate) /
            _totalStaked).u128();
        return rewardsPerTokenOut;
    }

    function _calculateUserRewards(
        uint256 _staked,
        uint256 earlierCheckpoint,
        uint256 latterCheckpoint
    ) internal pure returns (uint256) {
        return (_staked * (latterCheckpoint - earlierCheckpoint)) / 1e18;
    }

    function _updateRewardsPerToken()
        internal
        returns (RewardsPerToken memory)
    {
        RewardsPerToken memory rewardsPerTokenIn = rewardsPerToken;
        RewardsPerToken memory rewardsPerTokenOut = _calculateRewardsPerToken(
            rewardsPerTokenIn
        );

        if (rewardsPerTokenIn.lastUpdated == rewardsPerTokenOut.lastUpdated)
            return rewardsPerTokenOut;

        rewardsPerToken = rewardsPerTokenOut;
        emit RewardsPerTokenUpdated(rewardsPerTokenOut.accumulated);

        return rewardsPerTokenOut;
    }

    function _updateUserRewards(
        address user
    ) internal returns (UserRewards memory) {
        RewardsPerToken memory _rewardsPerToken = _updateRewardsPerToken();
        UserRewards memory _userRewards = accumulatedRewards[user];

        if (_userRewards.checkpoint == _rewardsPerToken.lastUpdated)
            return _userRewards;

        uint256 earnedSinceLastUpdate = _calculateUserRewards(
            userStake[user],
            _userRewards.checkpoint,
            _rewardsPerToken.accumulated
        );
        _userRewards.accumulated += earnedSinceLastUpdate.u128();
        _userRewards.totalEarned += earnedSinceLastUpdate.u128();
        _userRewards.checkpoint = _rewardsPerToken.accumulated;

        accumulatedRewards[user] = _userRewards;
        emit UserRewardsUpdated(
            user,
            _userRewards.accumulated,
            _userRewards.checkpoint
        );

        return _userRewards;
    }

    function _stake(address user, uint256 amount) internal {
        _updateUserRewards(user);
        if (userStake[user] == 0) {
            totalStakers++;
        }
        totalStaked += amount;
        userStake[user] += amount;
        stakingToken.safeTransferFrom(user, address(this), amount);
        emit Staked(user, amount);
    }

    function _unstake(address user, uint256 amount) internal {
        require(userStake[user] >= amount, "Insufficient staked amount");
        _updateUserRewards(user);
        if (userStake[user] == amount) {
            totalStakers--;
        }
        totalStaked -= amount;
        userStake[user] -= amount;
        stakingToken.safeTransfer(user, amount);
        emit Unstaked(user, amount);
    }

    function _claim(address user, uint256 amount) internal {
        uint256 rewardsAvailable = _updateUserRewards(msg.sender).accumulated;

        accumulatedRewards[user].accumulated = (rewardsAvailable - amount)
            .u128();

        stakingToken.safeTransfer(user, amount);
        emit Claimed(user, amount);
    }

    function stake(uint256 amount) public virtual {
        _stake(msg.sender, amount);
    }

    function unstake(uint256 amount) public virtual {
        _unstake(msg.sender, amount);
    }

    function claim() public virtual returns (uint256) {
        uint256 claimed = _updateUserRewards(msg.sender).accumulated;
        _claim(msg.sender, claimed);
        return claimed;
    }

    function currentRewardsPerToken() public view returns (uint256) {
        return _calculateRewardsPerToken(rewardsPerToken).accumulated;
    }

    function currentUserRewards(address user) public view returns (uint256) {
        UserRewards memory accumulatedRewards_ = accumulatedRewards[user];
        RewardsPerToken memory rewardsPerToken_ = _calculateRewardsPerToken(
            rewardsPerToken
        );
        return
            accumulatedRewards_.accumulated +
            _calculateUserRewards(
                userStake[user],
                accumulatedRewards_.checkpoint,
                rewardsPerToken_.accumulated
            );
    }
}

library Cast {
    function u128(uint256 x) internal pure returns (uint128 y) {
        require(x <= type(uint128).max, "Cast overflow");
        y = uint128(x);
    }
}

// SPDX-License-Identifier: AGPL-3.0-only
pragma solidity >=0.8.0;

/// @notice Modern and gas efficient ERC20 + EIP-2612 implementation.
/// @author Solmate (https://github.com/transmissions11/solmate/blob/main/src/tokens/ERC20.sol)
/// @author Modified from Uniswap (https://github.com/Uniswap/uniswap-v2-core/blob/master/contracts/UniswapV2ERC20.sol)
/// @dev Do not manually set balances without updating totalSupply, as the sum of all user balances must not exceed it.
abstract contract ERC20 {
    /*//////////////////////////////////////////////////////////////
                                 EVENTS
    //////////////////////////////////////////////////////////////*/

    event Transfer(address indexed from, address indexed to, uint256 amount);

    event Approval(address indexed owner, address indexed spender, uint256 amount);

    /*//////////////////////////////////////////////////////////////
                            METADATA STORAGE
    //////////////////////////////////////////////////////////////*/

    string public name;

    string public symbol;

    uint8 public immutable decimals;

    /*//////////////////////////////////////////////////////////////
                              ERC20 STORAGE
    //////////////////////////////////////////////////////////////*/

    uint256 public totalSupply;

    mapping(address => uint256) public balanceOf;

    mapping(address => mapping(address => uint256)) public allowance;

    /*//////////////////////////////////////////////////////////////
                            EIP-2612 STORAGE
    //////////////////////////////////////////////////////////////*/

    uint256 internal immutable INITIAL_CHAIN_ID;

    bytes32 internal immutable INITIAL_DOMAIN_SEPARATOR;

    mapping(address => uint256) public nonces;

    /*//////////////////////////////////////////////////////////////
                               CONSTRUCTOR
    //////////////////////////////////////////////////////////////*/

    constructor(
        string memory _name,
        string memory _symbol,
        uint8 _decimals
    ) {
        name = _name;
        symbol = _symbol;
        decimals = _decimals;

        INITIAL_CHAIN_ID = block.chainid;
        INITIAL_DOMAIN_SEPARATOR = computeDomainSeparator();
    }

    /*//////////////////////////////////////////////////////////////
                               ERC20 LOGIC
    //////////////////////////////////////////////////////////////*/

    function approve(address spender, uint256 amount) public virtual returns (bool) {
        allowance[msg.sender][spender] = amount;

        emit Approval(msg.sender, spender, amount);

        return true;
    }

    function transfer(address to, uint256 amount) public virtual returns (bool) {
        balanceOf[msg.sender] -= amount;

        // Cannot overflow because the sum of all user
        // balances can't exceed the max uint256 value.
        unchecked {
            balanceOf[to] += amount;
        }

        emit Transfer(msg.sender, to, amount);

        return true;
    }

    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public virtual returns (bool) {
        uint256 allowed = allowance[from][msg.sender]; // Saves gas for limited approvals.

        if (allowed != type(uint256).max) allowance[from][msg.sender] = allowed - amount;

        balanceOf[from] -= amount;

        // Cannot overflow because the sum of all user
        // balances can't exceed the max uint256 value.
        unchecked {
            balanceOf[to] += amount;
        }

        emit Transfer(from, to, amount);

        return true;
    }

    /*//////////////////////////////////////////////////////////////
                             EIP-2612 LOGIC
    //////////////////////////////////////////////////////////////*/

    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public virtual {
        require(deadline >= block.timestamp, "PERMIT_DEADLINE_EXPIRED");

        // Unchecked because the only math done is incrementing
        // the owner's nonce which cannot realistically overflow.
        unchecked {
            address recoveredAddress = ecrecover(
                keccak256(
                    abi.encodePacked(
                        "\x19\x01",
                        DOMAIN_SEPARATOR(),
                        keccak256(
                            abi.encode(
                                keccak256(
                                    "Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"
                                ),
                                owner,
                                spender,
                                value,
                                nonces[owner]++,
                                deadline
                            )
                        )
                    )
                ),
                v,
                r,
                s
            );

            require(recoveredAddress != address(0) && recoveredAddress == owner, "INVALID_SIGNER");

            allowance[recoveredAddress][spender] = value;
        }

        emit Approval(owner, spender, value);
    }

    function DOMAIN_SEPARATOR() public view virtual returns (bytes32) {
        return block.chainid == INITIAL_CHAIN_ID ? INITIAL_DOMAIN_SEPARATOR : computeDomainSeparator();
    }

    function computeDomainSeparator() internal view virtual returns (bytes32) {
        return
            keccak256(
                abi.encode(
                    keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
                    keccak256(bytes(name)),
                    keccak256("1"),
                    block.chainid,
                    address(this)
                )
            );
    }

    /*//////////////////////////////////////////////////////////////
                        INTERNAL MINT/BURN LOGIC
    //////////////////////////////////////////////////////////////*/

    function _mint(address to, uint256 amount) internal virtual {
        totalSupply += amount;

        // Cannot overflow because the sum of all user
        // balances can't exceed the max uint256 value.
        unchecked {
            balanceOf[to] += amount;
        }

        emit Transfer(address(0), to, amount);
    }

    function _burn(address from, uint256 amount) internal virtual {
        balanceOf[from] -= amount;

        // Cannot underflow because a user's balance
        // will never be larger than the total supply.
        unchecked {
            totalSupply -= amount;
        }

        emit Transfer(from, address(0), amount);
    }
}

// SPDX-License-Identifier: AGPL-3.0-only
pragma solidity >=0.8.0;

import {ERC20} from "../tokens/ERC20.sol";

/// @notice Safe ETH and ERC20 transfer library that gracefully handles missing return values.
/// @author Solmate (https://github.com/transmissions11/solmate/blob/main/src/utils/SafeTransferLib.sol)
/// @dev Use with caution! Some functions in this library knowingly create dirty bits at the destination of the free memory pointer.
/// @dev Note that none of the functions in this library check that a token has code at all! That responsibility is delegated to the caller.
library SafeTransferLib {
    /*//////////////////////////////////////////////////////////////
                             ETH OPERATIONS
    //////////////////////////////////////////////////////////////*/

    function safeTransferETH(address to, uint256 amount) internal {
        bool success;

        /// @solidity memory-safe-assembly
        assembly {
            // Transfer the ETH and store if it succeeded or not.
            success := call(gas(), to, amount, 0, 0, 0, 0)
        }

        require(success, "ETH_TRANSFER_FAILED");
    }

    /*//////////////////////////////////////////////////////////////
                            ERC20 OPERATIONS
    //////////////////////////////////////////////////////////////*/

    function safeTransferFrom(
        ERC20 token,
        address from,
        address to,
        uint256 amount
    ) internal {
        bool success;

        /// @solidity memory-safe-assembly
        assembly {
            // Get a pointer to some free memory.
            let freeMemoryPointer := mload(0x40)

            // Write the abi-encoded calldata into memory, beginning with the function selector.
            mstore(freeMemoryPointer, 0x23b872dd00000000000000000000000000000000000000000000000000000000)
            mstore(add(freeMemoryPointer, 4), and(from, 0xffffffffffffffffffffffffffffffffffffffff)) // Append and mask the "from" argument.
            mstore(add(freeMemoryPointer, 36), and(to, 0xffffffffffffffffffffffffffffffffffffffff)) // Append and mask the "to" argument.
            mstore(add(freeMemoryPointer, 68), amount) // Append the "amount" argument. Masking not required as it's a full 32 byte type.

            success := and(
                // Set success to whether the call reverted, if not we check it either
                // returned exactly 1 (can't just be non-zero data), or had no return data.
                or(and(eq(mload(0), 1), gt(returndatasize(), 31)), iszero(returndatasize())),
                // We use 100 because the length of our calldata totals up like so: 4 + 32 * 3.
                // We use 0 and 32 to copy up to 32 bytes of return data into the scratch space.
                // Counterintuitively, this call must be positioned second to the or() call in the
                // surrounding and() call or else returndatasize() will be zero during the computation.
                call(gas(), token, 0, freeMemoryPointer, 100, 0, 32)
            )
        }

        require(success, "TRANSFER_FROM_FAILED");
    }

    function safeTransfer(
        ERC20 token,
        address to,
        uint256 amount
    ) internal {
        bool success;

        /// @solidity memory-safe-assembly
        assembly {
            // Get a pointer to some free memory.
            let freeMemoryPointer := mload(0x40)

            // Write the abi-encoded calldata into memory, beginning with the function selector.
            mstore(freeMemoryPointer, 0xa9059cbb00000000000000000000000000000000000000000000000000000000)
            mstore(add(freeMemoryPointer, 4), and(to, 0xffffffffffffffffffffffffffffffffffffffff)) // Append and mask the "to" argument.
            mstore(add(freeMemoryPointer, 36), amount) // Append the "amount" argument. Masking not required as it's a full 32 byte type.

            success := and(
                // Set success to whether the call reverted, if not we check it either
                // returned exactly 1 (can't just be non-zero data), or had no return data.
                or(and(eq(mload(0), 1), gt(returndatasize(), 31)), iszero(returndatasize())),
                // We use 68 because the length of our calldata totals up like so: 4 + 32 * 2.
                // We use 0 and 32 to copy up to 32 bytes of return data into the scratch space.
                // Counterintuitively, this call must be positioned second to the or() call in the
                // surrounding and() call or else returndatasize() will be zero during the computation.
                call(gas(), token, 0, freeMemoryPointer, 68, 0, 32)
            )
        }

        require(success, "TRANSFER_FAILED");
    }

    function safeApprove(
        ERC20 token,
        address to,
        uint256 amount
    ) internal {
        bool success;

        /// @solidity memory-safe-assembly
        assembly {
            // Get a pointer to some free memory.
            let freeMemoryPointer := mload(0x40)

            // Write the abi-encoded calldata into memory, beginning with the function selector.
            mstore(freeMemoryPointer, 0x095ea7b300000000000000000000000000000000000000000000000000000000)
            mstore(add(freeMemoryPointer, 4), and(to, 0xffffffffffffffffffffffffffffffffffffffff)) // Append and mask the "to" argument.
            mstore(add(freeMemoryPointer, 36), amount) // Append the "amount" argument. Masking not required as it's a full 32 byte type.

            success := and(
                // Set success to whether the call reverted, if not we check it either
                // returned exactly 1 (can't just be non-zero data), or had no return data.
                or(and(eq(mload(0), 1), gt(returndatasize(), 31)), iszero(returndatasize())),
                // We use 68 because the length of our calldata totals up like so: 4 + 32 * 2.
                // We use 0 and 32 to copy up to 32 bytes of return data into the scratch space.
                // Counterintuitively, this call must be positioned second to the or() call in the
                // surrounding and() call or else returndatasize() will be zero during the computation.
                call(gas(), token, 0, freeMemoryPointer, 68, 0, 32)
            )
        }

        require(success, "APPROVE_FAILED");
    }
}