DeFi Protocol Templates

Production-ready templates for common DeFi protocols including staking, AMMs, governance, and flash loans.

When to Use This Skill

• Building staking platforms with reward distribution
• Implementing AMM (Automated Market Maker) protocols
• Creating governance token systems
• Integrating flash loan functionality

Staking Contract

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

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract StakingRewards is ReentrancyGuard, Ownable {
    IERC20 public stakingToken;
    IERC20 public rewardsToken;

    uint256 public rewardRate = 100; // Rewards per second
    uint256 public lastUpdateTime;
    uint256 public rewardPerTokenStored;

    mapping(address => uint256) public userRewardPerTokenPaid;
    mapping(address => uint256) public rewards;
    mapping(address => uint256) public balances;

    uint256 private _totalSupply;

    event Staked(address indexed user, uint256 amount);
    event Withdrawn(address indexed user, uint256 amount);
    event RewardPaid(address indexed user, uint256 reward);

    constructor(address _stakingToken, address _rewardsToken) {
        stakingToken = IERC20(_stakingToken);
        rewardsToken = IERC20(_rewardsToken);
    }

    modifier updateReward(address account) {
        rewardPerTokenStored = rewardPerToken();
        lastUpdateTime = block.timestamp;

        if (account != address(0)) {
            rewards[account] = earned(account);
            userRewardPerTokenPaid[account] = rewardPerTokenStored;
        }
        _;
    }

    function rewardPerToken() public view returns (uint256) {
        if (_totalSupply == 0) {
            return rewardPerTokenStored;
        }
        return rewardPerTokenStored +
            ((block.timestamp - lastUpdateTime) * rewardRate * 1e18) / _totalSupply;
    }

    function earned(address account) public view returns (uint256) {
        return (balances[account] *
            (rewardPerToken() - userRewardPerTokenPaid[account])) / 1e18 +
            rewards[account];
    }

    function stake(uint256 amount) external nonReentrant updateReward(msg.sender) {
        require(amount > 0, "Cannot stake 0");
        _totalSupply += amount;
        balances[msg.sender] += amount;
        stakingToken.transferFrom(msg.sender, address(this), amount);
        emit Staked(msg.sender, amount);
    }

    function withdraw(uint256 amount) public nonReentrant updateReward(msg.sender) {
        require(amount > 0, "Cannot withdraw 0");
        _totalSupply -= amount;
        balances[msg.sender] -= amount;
        stakingToken.transfer(msg.sender, amount);
        emit Withdrawn(msg.sender, amount);
    }

    function getReward() public nonReentrant updateReward(msg.sender) {
        uint256 reward = rewards[msg.sender];
        if (reward > 0) {
            rewards[msg.sender] = 0;
            rewardsToken.transfer(msg.sender, reward);
            emit RewardPaid(msg.sender, reward);
        }
    }

    function exit() external {
        withdraw(balances[msg.sender]);
        getReward();
    }
}

AMM (Automated Market Maker)

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

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract SimpleAMM {
    IERC20 public token0;
    IERC20 public token1;

    uint256 public reserve0;
    uint256 public reserve1;

    uint256 public totalSupply;
    mapping(address => uint256) public balanceOf;

    event Mint(address indexed to, uint256 amount);
    event Burn(address indexed from, uint256 amount);
    event Swap(address indexed trader, uint256 amount0In, uint256 amount1In, uint256 amount0Out, uint256 amount1Out);

    constructor(address _token0, address _token1) {
        token0 = IERC20(_token0);
        token1 = IERC20(_token1);
    }

    function addLiquidity(uint256 amount0, uint256 amount1) external returns (uint256 shares) {
        token0.transferFrom(msg.sender, address(this), amount0);
        token1.transferFrom(msg.sender, address(this), amount1);

        if (totalSupply == 0) {
            shares = sqrt(amount0 * amount1);
        } else {
            shares = min(
                (amount0 * totalSupply) / reserve0,
                (amount1 * totalSupply) / reserve1
            );
        }

        require(shares > 0, "Shares = 0");

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