SimpleStaking

1// SPDX-License-Identifier: MIT
2pragma solidity ^0.8.20;
3 
4interface IERC20 {
5    function transfer(address to, uint256 amount) external returns (bool);
6    function transferFrom(address from, address to, uint256 amount) external returns (bool);
7}
8 
9contract SimpleStaking {
10    IERC20 public immutable stakingToken;
11    IERC20 public immutable rewardToken;
12    uint256 public immutable rewardRatePerBlock;
13    address public owner;
14 
15    uint256 public totalStaked;
16    uint256 public rewardPerTokenStored;
17    uint256 public lastUpdateBlock;
18 
19    mapping(address => uint256) public staked;
20    mapping(address => uint256) public userRewardPerTokenPaid;
21    mapping(address => uint256) public rewards;
22 
23    event Staked(address indexed user, uint256 amount);
24    event Withdrawn(address indexed user, uint256 amount);
25    event RewardPaid(address indexed user, uint256 reward);
26 
27    constructor(address stakingToken_, address rewardToken_, uint256 rewardRatePerBlock_) {
28        stakingToken = IERC20(stakingToken_);
29        rewardToken = IERC20(rewardToken_);
30        rewardRatePerBlock = rewardRatePerBlock_;
31        owner = msg.sender;
32        lastUpdateBlock = block.number;
33    }
34 
35    function rewardPerToken() public view returns (uint256) {
36        if (totalStaked == 0) return rewardPerTokenStored;
37        return rewardPerTokenStored + ((block.number - lastUpdateBlock) * rewardRatePerBlock * 1e18) / totalStaked;
38    }
39 
40    function earned(address account) public view returns (uint256) {
41        return (staked[account] * (rewardPerToken() - userRewardPerTokenPaid[account])) / 1e18 + rewards[account];
42    }
43 
44    modifier updateReward(address account) {
45        rewardPerTokenStored = rewardPerToken();
46        lastUpdateBlock = block.number;
47        rewards[account] = earned(account);
48        userRewardPerTokenPaid[account] = rewardPerTokenStored;
49        _;
50    }
51 
52    function stake(uint256 amount) external updateReward(msg.sender) {
53        require(amount > 0, "ZERO");
54        totalStaked += amount;
55        staked[msg.sender] += amount;
56        require(stakingToken.transferFrom(msg.sender, address(this), amount), "TRANSFER_FAILED");
57        emit Staked(msg.sender, amount);
58    }
59 
60    function withdraw(uint256 amount) external updateReward(msg.sender) {
61        require(staked[msg.sender] >= amount, "BALANCE");
62        totalStaked -= amount;
63        staked[msg.sender] -= amount;
64        require(stakingToken.transfer(msg.sender, amount), "TRANSFER_FAILED");
65        emit Withdrawn(msg.sender, amount);
66    }
67 
68    function claimReward() external updateReward(msg.sender) {
69        uint256 reward = rewards[msg.sender];
70        require(reward > 0, "NO_REWARD");
71        rewards[msg.sender] = 0;
72        require(rewardToken.transfer(msg.sender, reward), "TRANSFER_FAILED");
73        emit RewardPaid(msg.sender, reward);
74    }
75}