defi-protocol-templates

SKILL.md

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event Withdrawn(address indexed user, uint256 amount);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)

```solidity
// 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");
        _mint(msg.sender, shares);
        _update(
            token0.balanceOf(address(this)),
            token1.balanceOf(address(this))
        );

        emit Mint(msg.sender, shares);
    }

    function removeLiquidity(uint256 shares) external returns (uint256 amount0, uint256 amount1) {
        uint256 bal0 = token0.balanceOf(address(this));
        uint256 bal1 = token1.balanceOf(address(this));

        amount0 = (shares * bal0) / totalSupply;
        amount1 = (shares * bal1) / totalSupply;

        require(amount0 > 0 && amount1 > 0, "Amount0 or amount1 = 0");

        _burn(msg.sender, shares);
        _update(bal0 - amount0, bal1 - amount1);

        token0.transfer(msg.sender, amount0);
        token1.transfer(msg.sender, amount1);

        emit Burn(msg.sender, shares);
    }

    function swap(address tokenIn, uint256 amountIn) external returns (uint256 amountOut) {
        require(tokenIn == address(token0) || tokenIn == address(token1), "Invalid token");

        bool isToken0 = tokenIn == address(token0);
        (IERC20 tokenIn_, IERC20 tokenOut, uint256 resIn, uint256 resOut) = isToken0
            ? (token0, token1, reserve0, reserve1)
            : (token1, token0, reserve1, reserve0);

        tokenIn_.transferFrom(msg.sender, address(this), amountIn);

        // 0.3% fee
        uint256 amountInWithFee = (amountIn * 997) / 1000;
        amountOut = (resOut * amountInWithFee) / (resIn + amountInWithFee);

        tokenOut.transfer(msg.sender, amountOut);

        _update(
            token0.balanceOf(address(this)),
            token1.balanceOf(address(this))
        );

        emit Swap(msg.sender, isToken0 ? amountIn : 0, isToken0 ? 0 : amountIn, isToken0 ? 0 : amountOut, isToken0 ? amountOut : 0);
    }

    function _mint(address to, uint256 amount) private {
        balanceOf[to] += amount;
        totalSupply += amount;
    }

    function _burn(address from, uint256 amount) private {
        balanceOf[from] -= amount;
        totalSupply -= amount;
    }

    function _update(uint256 res0, uint256 res1) private {
        reserve0 = res0;
        reserve1 = res1;
    }

    function sqrt(uint256 y) private pure returns (uint256 z) {
        if (y > 3) {
            z = y;
            uint256 x = y / 2 + 1;
            while (x < z) {
                z = x;
                x = (y / x + x) / 2;
            }
        } else if (y != 0) {
            z = 1;
        }
    }

    function min(uint256 x, uint256 y) private pure returns (uint256) {
        return x <= y ? x : y;
    }
}

Additional patterns and templates

More detailed templates and worked examples live in references/details.md. Read that file for the full pattern library.