// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IERC20 {
    function totalSupply() external pure 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 ERC20Token is IERC20 {
    string public constant name = "reproduce";
    string public constant symbol = "XYXX";
    uint8 public constant decimals = 18;
    uint256 private constant _initialSupply = 8000000000 * (10 ** uint256(decimals));
    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    constructor() {
        _balances[msg.sender] = _initialSupply;
        emit Transfer(address(0), msg.sender, _initialSupply);
    }

    function totalSupply() external pure override returns (uint256) {
        return _initialSupply;
    }

    function balanceOf(address account) external view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) external override returns (bool) {
        require(recipient != address(0), "ERC20: transfer to the zero address");
        require(amount <= _balances[msg.sender], "ERC20: transfer amount exceeds balance");
        
        _balances[msg.sender] -= amount;
        _balances[recipient] += amount;
        
        emit Transfer(msg.sender, recipient, amount);
        return true;
    }

    function allowance(address owner, address spender) external view override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) external override returns (bool) {
        _allowances[msg.sender][spender] = amount;
        
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address sender, address recipient, uint256 amount) external override returns (bool) {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");
        require(amount <= _balances[sender], "ERC20: transfer amount exceeds balance");
        require(amount <= _allowances[sender][msg.sender], "ERC20: transfer amount exceeds allowance");
        
        _balances[sender] -= amount;
        _balances[recipient] += amount;
        _allowances[sender][msg.sender] -= amount;
        
        emit Transfer(sender, recipient, amount);
        return true;
    }
}