Tether USD Bridged ZEB20 (USDT.z)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.26;

/*
  Blynex USD (USDB)
  - Fixed supply ERC20 token
  - 100,000,000,000 tokens minted once to deployer
  - No owner, no admin functions, no pausing, no limits
  - Fully decentralized: nobody can change anything after deployment
*/

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address to, 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 from, address to, 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 BlynexUSD is IERC20 {
    string private constant _name = "Tether USD Bridged ZEB20";
    string private constant _symbol = "USDT.z";
    uint8 private constant _decimals = 6;
    uint256 private immutable _totalSupply;

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

    constructor() {
        uint256 supply = 100_000_000_000 * 10 ** uint256(_decimals);
        _totalSupply = supply;
        _balances[msg.sender] = supply;
        emit Transfer(address(0), msg.sender, supply);
    }

    // ERC20 standard functions

    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];
    }

    function transfer(address to, uint256 amount) public override returns (bool) {
        _transfer(msg.sender, to, 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 from, address to, uint256 amount) public override returns (bool) {
        uint256 currentAllowance = _allowances[from][msg.sender];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        _approve(from, msg.sender, currentAllowance - amount);
        _transfer(from, to, amount);
        return true;
    }

    // Internal helpers

    function _transfer(address from, address to, uint256 amount) internal {
        require(from != address(0), "ERC20: transfer from zero address");
        require(to != address(0), "ERC20: transfer to zero address");
        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - amount;
        }
        _balances[to] += amount;
        emit Transfer(from, to, amount);
    }

    function _approve(address owner, address spender, uint256 amount) internal {
        require(owner != address(0), "ERC20: approve from zero address");
        require(spender != address(0), "ERC20: approve to zero address");
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
}