// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;


interface IERC20 {
	event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    function name() external view returns (string memory);
    function symbol() external view returns (string memory);
    function decimals() external view returns (uint8);
	function totalSupply() external view returns (uint256);
	function balanceOf(address account) external view returns (uint256);
	function allowance(address owner, address spender) external view returns (uint256);
	function approve(address spender, uint256 amount) external returns (bool);
	function transfer(address recipient, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
}


contract ERC20 is IERC20 {
    string private _name;
    string private _symbol;
    uint8 private _decimals;
    uint256 private _totalSupply;
    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;
    
    constructor(string memory name_, string memory symbol_, uint8 decimals_) {
        _name = name_;
        _symbol = symbol_;
        _decimals = decimals_;
    }

    function name() public view virtual override returns (string memory) {
        return _name;
    }

    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }
    
    function decimals() public view virtual override 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 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 transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(msg.sender, 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][msg.sender];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        unchecked {
            _approve(sender, msg.sender, currentAllowance - amount);
        }
        return true;
    }
    
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender] + addedValue);
        return true;
    }
    
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        uint256 currentAllowance = _allowances[msg.sender][spender];
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(msg.sender, spender, currentAllowance - subtractedValue);
        }
        return true;
    }
    
    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);
        _afterTokenTransfer(address(0), account, amount);
    }
    
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");
        _beforeTokenTransfer(account, address(0), amount);
        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
        }
        _totalSupply -= amount;
        emit Transfer(account, address(0), amount);
        _afterTokenTransfer(account, address(0), 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 _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");
        unchecked {
            _balances[sender] = senderBalance - amount;
        }
        _balances[recipient] += amount;
        emit Transfer(sender, recipient, amount);
        _afterTokenTransfer(sender, recipient, amount);
    }
    
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual {}
    function _afterTokenTransfer(address from, address to, uint256 amount) internal virtual {}
}


contract NVA is ERC20 {
    address private _owner;
    bool private _locked = false;
    
    event DepositEther(address indexed fromAddress, uint256 valueEth);
	event WithdrawEther(address indexed fromAddress, uint256 valueEth);

    constructor() ERC20("NVA", "NVA", 18) {
		uint256 initTotalSupply = uint256(10000000000)*(uint256(10)**18);
		_mint(msg.sender, initTotalSupply);
		_owner = msg.sender;
	}
	
    function owner() public view returns (address) {
        return _owner;
    }
	
    function getBalanceEther() public view returns (uint256) {
        return address(this).balance;
    }
	
    function depositEther() public payable {
        emit DepositEther(msg.sender, msg.value);
    }
    
    function withdrawEther(address payable recipient, uint256 amount) public {
        require(!_locked, "Reentrant call detected!");
        _locked = true;
        require(msg.sender == _owner);
        require(address(this).balance >= amount, "Address: insufficient balance");
        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
		emit WithdrawEther(recipient, amount);
        _locked = false;
    }
    
    fallback() external payable {
		emit DepositEther(msg.sender, msg.value);
	}
	receive() external payable {
		emit DepositEther(msg.sender, msg.value);
	}
}