《纸上谈兵·solidity》第 32 课：DeFi 基础合约

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

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

contract Staking {
    IERC20 public stakingToken;
    IERC20 public rewardToken;

    uint256 public rewardRate = 100; // 每秒奖励数量
    mapping(address => uint256) public staked;
    mapping(address => uint256) public lastUpdate;
    mapping(address => uint256) public rewards;

    constructor(address _stakingToken, address _rewardToken) {
        stakingToken = IERC20(_stakingToken);
        rewardToken = IERC20(_rewardToken);
    }

    function stake(uint256 amount) external {
        _updateReward(msg.sender);
        stakingToken.transferFrom(msg.sender, address(this), amount);
        staked[msg.sender] += amount;
    }

    function withdraw(uint256 amount) external {
        _updateReward(msg.sender);
        staked[msg.sender] -= amount;
        stakingToken.transfer(msg.sender, amount);
    }

    function claimReward() external {
        _updateReward(msg.sender);
        uint256 reward = rewards[msg.sender];
        rewards[msg.sender] = 0;
        rewardToken.transfer(msg.sender, reward);
    }

    function _updateReward(address account) internal {
        if (account != address(0)) {
            uint256 timeDiff = block.timestamp - lastUpdate[account];
            rewards[account] += staked[account] * rewardRate * timeDiff / 1e18;
            lastUpdate[account] = block.timestamp;
        }
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

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

contract SimpleAMM {
    IERC20 public tokenA;
    IERC20 public tokenB;

    uint256 public reserveA;
    uint256 public reserveB;

    constructor(address _tokenA, address _tokenB) {
        tokenA = IERC20(_tokenA);
        tokenB = IERC20(_tokenB);
    }

    function addLiquidity(uint256 amountA, uint256 amountB) external {
        tokenA.transferFrom(msg.sender, address(this), amountA);
        tokenB.transferFrom(msg.sender, address(this), amountB);
        reserveA += amountA;
        reserveB += amountB;
    }

    function swapAforB(uint256 amountIn) external returns (uint256 amountOut) {
        tokenA.transferFrom(msg.sender, address(this), amountIn);
        uint256 newReserveA = reserveA + amountIn;
        // x*y=k => amountOut = reserveB - (k / newReserveA)
        uint256 k = reserveA * reserveB;
        amountOut = reserveB - (k / newReserveA);
        reserveA = newReserveA;
        reserveB -= amountOut;
        tokenB.transfer(msg.sender, amountOut);
    }
}

// Pseudo code
deposit(collateral)  
borrow(asset)  
repay(asset)  
liquidate(user)  // 当抵押价值 < 借出价值 * 安全因子