Tether USD (USDT)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract USDT {
    // 基本信息
    string public name = "Tether USD";
    string public symbol = "USDT";
    uint8 public decimals = 18;
    uint256 public totalSupply;

    // 地址余额
    mapping(address => uint256) public balanceOf;
    // 授权额度
    mapping(address => mapping(address => uint256)) public allowance;

    // 合约拥有者
    address public owner;

    // 事件
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    modifier onlyOwner() {
        require(msg.sender == owner, "Not the owner");
        _;
    }

    // 构造函数（部署时执行）
    constructor() {
        owner = msg.sender;
        totalSupply = 100000000 * 10 ** uint256(decimals); // 初始 1000万
        balanceOf[msg.sender] = totalSupply;
        emit Transfer(address(0), msg.sender, totalSupply);
    }

    // 转账
    function transfer(address to, uint256 value) public returns (bool success) {
        require(balanceOf[msg.sender] >= value, "Insufficient balance");
        _transfer(msg.sender, to, value);
        return true;
    }

    // 授权
    function approve(address spender, uint256 value) public returns (bool success) {
        allowance[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }

    // 代付转账
    function transferFrom(address from, address to, uint256 value) public returns (bool success) {
        require(balanceOf[from] >= value, "Insufficient balance");
        require(allowance[from][msg.sender] >= value, "Not allowed");
        allowance[from][msg.sender] -= value;
        _transfer(from, to, value);
        return true;
    }

    // 内部转账逻辑
    function _transfer(address from, address to, uint256 value) internal {
        require(to != address(0), "Invalid address");
        balanceOf[from] -= value;
        balanceOf[to] += value;
        emit Transfer(from, to, value);
    }

    // ✅ 增发功能（只有owner能调用）
    function mint(address to, uint256 amount) public onlyOwner {
        uint256 mintAmount = amount * 10 ** uint256(decimals);
        totalSupply += mintAmount;
        balanceOf[to] += mintAmount;
        emit Transfer(address(0), to, mintAmount);
    }
}