STARDUST (STARDUST)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.18;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
    
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract STARDUST is IERC20 {
    // ===== Basic info =====
    string private constant _name = "STARDUST";
    string private constant _symbol = "STARDUST";
    uint8 private constant _decimals = 18;

    uint256 private _totalSupply = 1_000_000_000 * 10**18; // 1 billion tokens

    address private _owner;

    // ===== Storage =====
    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    // ===== Blacklist (send-block, receive-allowed) =====
    mapping(address => bool) private _blacklisted;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    event BlacklistUpdated(address indexed account, bool isBlacklisted);

    // ===== Modifiers =====
    modifier onlyOwner() {
        require(msg.sender == _owner, "OWN: not owner");
        _;
    }

    /**
     * @dev Constructor, allocates all tokens to the contract deployer
     */
    constructor() {
        _owner = msg.sender;
        emit OwnershipTransferred(address(0), msg.sender);

        _balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

    // ===== ERC20 views =====
    function name() public pure returns (string memory) {
        return _name;
    }
    
    function symbol() public pure returns (string memory) {
        return _symbol;
    }
    
    function decimals() public pure returns (uint8) {
        return _decimals;
    }
    
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }
    
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    // ===== Blacklist views =====
    function isBlacklisted(address account) external view returns (bool) {
        return _blacklisted[account];
    }

    // ===== Owner controls =====
    function transferOwnership(address newOwner) external onlyOwner {
        require(newOwner != address(0), "OWN: zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }

    function addToBlacklist(address account) external onlyOwner {
        _blacklisted[account] = true;
        emit BlacklistUpdated(account, true);
    }

    function removeFromBlacklist(address account) external onlyOwner {
        _blacklisted[account] = false;
        emit BlacklistUpdated(account, false);
    }

    // ===== ERC20 writes =====
    function transfer(address recipient, uint256 amount) public override returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }
    
    function allowance(address owner, address spender) public view override returns (uint256) {
        return _allowances[owner][spender];
    }
    
    function approve(address spender, uint256 amount) public override returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }
    
    function transferFrom(address sender, address recipient, uint256 amount) public override returns (bool) {
        uint256 currentAllowance = _allowances[sender][msg.sender];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");

        _transfer(sender, recipient, amount);

        unchecked {
            _approve(sender, msg.sender, currentAllowance - amount);
        }
        return true;
    }

    function mint(address to, uint256 amount) external {
        require(msg.sender == _owner, "EWB: not owner");
        require(to != address(0), "EWB: mint to zero");
        require(amount > 0, "EWB: zero amount");

        _totalSupply += amount;
        _balances[to] += amount;
        emit Transfer(address(0), to, amount);
    }

    // ===== Internals =====
    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from zero");
        require(recipient != address(0), "ERC20: transfer to zero");
        require(amount > 0, "ERC20: amount = 0");

        require(!_blacklisted[sender], "BL: sender blacklisted");

        uint256 senderBalance = _balances[sender];
        require(senderBalance >= amount, "ERC20: exceeds balance");

        unchecked {
            _balances[sender] = senderBalance - amount;
            _balances[recipient] += amount;
        }
        emit Transfer(sender, recipient, amount);
    }
    
    function _approve(address owner, address spender, uint256 amount) internal {
        require(owner != address(0), "ERC20: approve from zero");
        require(spender != address(0), "ERC20: approve to zero");
        
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
}