// SPDX-License-Identifier: MIT

pragma solidity ^0.8.4;

interface IST20 {
    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);
}

library SafeMath {
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return a - b;
    }
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }
    function _msgData() internal view virtual returns (bytes calldata) {
        this;
        return msg.data;
    }
}

abstract contract Ownable is Context {
    address private _owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    constructor () {
        _owner = _msgSender();
        emit OwnershipTransferred(address(0), _owner);
    }
    function owner() public view virtual returns (address) {
        return _owner;
    }
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

interface STPayable {
    function pay(string memory serviceName) external payable;
}

abstract contract TokenGenerator {
    constructor (address payable receiver, string memory serviceName) payable {
        STPayable(receiver).pay{value: msg.value}(serviceName);
    }
}

contract ST_Standard_Token is Ownable, IST20, TokenGenerator {
    using SafeMath for uint256;
    mapping (address => uint256) private _balances;
    mapping (address => mapping (address => uint256)) private _allowances;
    uint256 private _totalSupply;
    string private _name;
    string private _symbol;
    uint256 private _decimals;

    constructor (string memory name, string memory symbol, uint256 decimals, uint256 supply, address payable feeReceiver) TokenGenerator(feeReceiver, "ST_Standard_Token") payable public {
        _name = name;
        _symbol = symbol;
        _decimals = decimals;
        _totalSupply = supply;
        _balances[_msgSender()] = _totalSupply;
        emit Transfer(address(0), _msgSender(), _totalSupply);
    }
    function name() external view returns (string memory) {
        return _name;
    }
    function symbol() external view returns (string memory) {
        return _symbol;
    }
    function decimals() external view returns (uint256) {
        return _decimals;
    }
    function totalSupply() external view override returns (uint256) {
        return _totalSupply;
    }
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "IST20: approve from the zero address");
        require(spender != address(0), "IST20: approve to the zero address");
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender] + addedValue);
        return true;
    }
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        uint256 currentAllowance = _allowances[_msgSender()][spender];
        require(currentAllowance >= subtractedValue, "IST20: decreased allowance below zero");
        _approve(_msgSender(), spender, currentAllowance - subtractedValue);
        return true;
    }
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "IST20: mint to the zero address");
        _beforeTokenTransfer(address(0), account, amount);
        _totalSupply += amount;
        _balances[account] += amount;
        emit Transfer(address(0), account, amount);
    }
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "IST20: burn from the zero address");
        _beforeTokenTransfer(account, address(0), amount);
        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "IST20: burn amount exceeds balance");
        _balances[account] = accountBalance - amount;
        _balances[address(0)] += amount;
        emit Transfer(account, address(0), amount);
    }
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "IST20: transfer from the zero address");
        require(recipient != address(0), "IST20: transfer to the zero address");
        _beforeTokenTransfer(sender, recipient, amount);
        uint256 senderBalance = _balances[sender];
        require(senderBalance >= amount, "IST20: transfer amount exceeds balance");
        _balances[sender] = senderBalance - amount;
        _balances[recipient] += amount;
        emit Transfer(sender, recipient, amount);
    }
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        uint256 currentAllowance = _allowances[sender][_msgSender()];
        require(currentAllowance >= amount, "IST20: transfer amount exceeds allowance");
        _approve(sender, _msgSender(), currentAllowance - amount);
        return true;
    }

    // ------------------------------------------------------------------------
    // Function to Withdraw Tokens sent by mistake to the Token Contract Address.
    // Only the Contract owner can withdraw the Tokens.
    // ------------------------------------------------------------------------
    function WithdrawTokens(address tokenAddress, uint256 tokenAmount) public virtual onlyOwner {
        IST20(tokenAddress).transfer(owner(), tokenAmount);
    }
}