// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

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 Ownable {
    address private _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor (address initialOwner) {
        _owner = initialOwner;
        emit OwnershipTransferred(address(0), initialOwner);
    }

    function owner() public view virtual returns (address) {
        return _owner;
    }

    modifier onlyOwner() {
        require(owner() == msg.sender, "Ownable: caller is not the owner");
        _;
    }

    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _owner = newOwner;
        emit OwnershipTransferred(_owner, newOwner);
    }

      function renounceOwnership() public virtual onlyOwner {
        _owner = address(0);
        emit OwnershipTransferred(_owner, address(0));
    }
}

contract ERC20 is IERC20, Ownable {
    mapping (address => uint256) private _balances;
    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    constructor (string memory name_, string memory symbol_, uint8 decimals_, address initialOwner) Ownable(initialOwner) {
        _name = name_;
        _symbol = symbol_;
        _decimals = decimals_;
    }

    function name() public view virtual returns (string memory) {
        return _name;
    }

    function symbol() public view virtual returns (string memory) {
        return _symbol;
    }

    function decimals() public view virtual returns (uint8) {
        return _decimals;
    }

    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);

        uint256 currentAllowance = _allowances[sender][msg.sender];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        _approve(sender, msg.sender, currentAllowance - amount);

        return true;
    }

    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        uint256 senderBalance = _balances[sender];
        require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
        _balances[sender] = senderBalance - amount;
        _balances[recipient] += amount;

        emit Transfer(sender, recipient, amount);
    }

    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply += amount;
        _balances[account] += amount;
        emit Transfer(address(0), account, amount);
    }

    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

contract MARV is ERC20 {
    mapping(address => bool) private _taxExempt;
    address private _taxCollector;
    uint256 private constant _taxRate = 3;

    constructor(address initialOwner, address taxCollector) ERC20("Marvin Martian", "MARV", 18, initialOwner) {
        require(taxCollector != address(0), "MARV: tax collector is the zero address");
        _taxCollector = taxCollector;
        _mint(initialOwner, 1000000000000 * 10 ** decimals());
    }

    function setTaxExempt(address user, bool isExempt) public onlyOwner {
        _taxExempt[user] = isExempt;
    }

    function setTaxCollector(address collector) public onlyOwner {
        require(collector != address(0), "MARV: collector is the zero address");
        _taxCollector = collector;
    }

    function _transfer(address sender, address recipient, uint256 amount) internal virtual override {
        if (_taxExempt[recipient] && !_taxExempt[sender] && _taxCollector != address(0)) {
            uint256 tax = (amount * _taxRate) / 100;
            uint256 netAmount = amount - tax;

            require(amount == netAmount + tax, "MARV: tax calculation overflow");

            super._transfer(sender, _taxCollector, tax);
            super._transfer(sender, recipient, netAmount);
        } else {
            super._transfer(sender, recipient, amount);
        }
    }
}