blockchain-expert

Blockchain Expert

Expert guidance for blockchain development, smart contracts, Web3 applications, DeFi protocols, and cryptocurrency systems.

Core Concepts

Blockchain Fundamentals

• Distributed ledger technology
• Consensus mechanisms (PoW, PoS, PoA)
• Cryptographic hashing
• Public/private key cryptography
• Transaction validation
• Block structure and chain

Smart Contracts

• Solidity programming
• Gas optimization
• Security patterns
• Upgradeable contracts
• Testing and auditing
• Contract interactions

Web3 & DeFi

• Decentralized applications (dApps)
• DeFi protocols (AMM, lending, staking)
• NFTs and token standards
• Layer 2 solutions
• Cross-chain bridges
• Wallet integration

Smart Contract Development

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

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

contract SimpleToken is ERC20, Ownable, ReentrancyGuard {
    uint256 public constant MAX_SUPPLY = 1000000 * 10**18;

    mapping(address => bool) public minters;

    event MinterAdded(address indexed minter);
    event MinterRemoved(address indexed minter);

    modifier onlyMinter() {
        require(minters[msg.sender], "Not a minter");
        _;
    }

    constructor() ERC20("SimpleToken", "SMPL") {
        minters[msg.sender] = true;
    }

    function mint(address to, uint256 amount) external onlyMinter {
        require(totalSupply() + amount <= MAX_SUPPLY, "Max supply exceeded");
        _mint(to, amount);
    }

    function burn(uint256 amount) external {
        _burn(msg.sender, amount);
    }

    function addMinter(address minter) external onlyOwner {
        minters[minter] = true;
        emit MinterAdded(minter);
    }

    function removeMinter(address minter) external onlyOwner {
        minters[minter] = false;
        emit MinterRemoved(minter);
    }
}

// Staking Contract
contract StakingPool is ReentrancyGuard {
    IERC20 public stakingToken;
    IERC20 public rewardToken;

    uint256 public rewardRate = 100; // Reward tokens 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;

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

    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];
    }

    modifier updateReward(address account) {
        rewardPerTokenStored = rewardPerToken();
        lastUpdateTime = block.timestamp;
        if (account != address(0)) {
            rewards[account] = earned(account);
            userRewardPerTokenPaid[account] = rewardPerTokenStored;
        }
        _;
    }

    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);
    }

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

    function getReward() external nonReentrant updateReward(msg.sender) {
        uint256 reward = rewards[msg.sender];
        if (reward > 0) {
            rewards[msg.sender] = 0;
            rewardToken.transfer(msg.sender, reward);
        }
    }
}