Mengimplementasikan Vault Contract

Vault adalah kontrak yang menerima token ERC20 dari pengguna dan memberikan "shares" sebagai bukti kepemilikan proporsional. Konsep ini adalah fondasi dari banyak DeFi protocol seperti yield aggregator.

Buat file src/MyVault.sol:

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

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

contract MyVault is ReentrancyGuard {
    IERC20 public immutable token;

    uint256 public totalShares;
    mapping(address => uint256) public shares;

    // Custom errors
    error ZeroAmount();
    error InsufficientShares(uint256 requested, uint256 available);
    error ZeroSharesMinted();

    // Events
    event Deposited(address indexed user, uint256 amount, uint256 sharesMinted);
    event Withdrawn(address indexed user, uint256 shares, uint256 amountReturned);

    constructor(address _token) {
        token = IERC20(_token);
    }

    function deposit(uint256 amount) external nonReentrant {
        if (amount == 0) revert ZeroAmount();

        uint256 sharesToMint;
        uint256 totalTokenBalance = token.balanceOf(address(this));

        if (totalShares == 0 || totalTokenBalance == 0) {
            // Deposit pertama: shares = amount (1:1)
            sharesToMint = amount;
        } else {
            // Shares proporsional terhadap total balance saat ini
            sharesToMint = (amount * totalShares) / totalTokenBalance;
        }

        if (sharesToMint == 0) revert ZeroSharesMinted();

        totalShares += sharesToMint;
        shares[msg.sender] += sharesToMint;

        token.transferFrom(msg.sender, address(this), amount);

        emit Deposited(msg.sender, amount, sharesToMint);
    }

    function withdraw(uint256 sharesToBurn) external nonReentrant {
        if (sharesToBurn == 0) revert ZeroAmount();
        if (sharesToBurn > shares[msg.sender])
            revert InsufficientShares(sharesToBurn, shares[msg.sender]);

        uint256 amountToReturn =
            (sharesToBurn * token.balanceOf(address(this))) / totalShares;

        totalShares -= sharesToBurn;
        shares[msg.sender] -= sharesToBurn;

        token.transfer(msg.sender, amountToReturn);

        emit Withdrawn(msg.sender, sharesToBurn, amountToReturn);
    }
}