contract CoinVoyageDiamond is Context, IERC20, Ownable {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

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

    string private _name = "Coin Voyage Diamond";
    string private _symbol = "ZS";
    uint8 private _decimals = 6;

    uint256 private _outOfGameSupply = 0;
    uint256 private _lastMonthSupply = 0;
    uint256 private _lastMonth = 0;

    address private _admin;

    event Withdraw(uint256 account);
    event Deposit(uint256 account);

    constructor () public {
    }

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

    function symbol() public view returns (string memory) {
        return _symbol;
    }

    function decimals() public view returns (uint8) {
        return _decimals;
    }

    function admin() public view returns (address) {
        return _admin;
    }

    function setAdmin(address who) public onlyOwner {
        _admin = who;
    }

    /**
     * @dev Withdraw `amount` tokens from `account` to `who`, increases the
     * total supply.
     *
     * Requirements
     *
     * - `account` is a number of format 309XXXXX
     */
    function withdrawFromGame(uint256 account, address who, uint256 amount) public {
        require(msg.sender == _admin, "Only admin can withdraw");
        require(_outOfGameSupply + amount <= totalSupply(), "Should not exceed totalSupply");
        _mint(who, amount);
        emit Withdraw(account);
    }

    /**
     * @dev Deposit `amount` tokens back to `account`, reducing the
     * total supply.
     *
     * Requirements
     *
     * - `account` is a number of format 309XXXXX
     * - msg.sender must have at least `amount` tokens.
     */
    function depositToGame(uint256 account, uint256 amount) public {
        _burn(msg.sender, amount);
        emit Deposit(account);
    }

    // Gets the supply of the game at a certain month.
    function getMonthlySupply(uint256 month) public pure returns(uint256) {
        if (month == 0) return 0;

        uint256 amount = 1e6 * 1e6;

        for (uint256 i = 0; i < month - 1; ++i) {
            amount = amount * 99 / 100;
        }

        return amount;
    }

    function addMonthlySupply(uint256 month) public {
        require(msg.sender == _admin, "Only admin can add");

        uint256 initialDay = 18430;  // June 16, 2020
        uint256 today = now / (1 days);
        require(month < (today - initialDay) / 30 + 1);
        require(month > _lastMonth);

        _lastMonthSupply += getMonthlySupply(month);
        _lastMonth = month;
    }
  
    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        uint256 initialDay = 18430;  // June 18, 2020
        uint256 today = now / (1 days);
        uint256 supply = _lastMonthSupply;
        
        uint256 month = _lastMonth;
        uint256 monthlySupply = 0;
        
        for (uint256 i = _lastMonth * 30; i < today - initialDay; ++i) {
            if (i / 30 + 1 > month || monthlySupply == 0) {
                month = i / 30 + 1;
                monthlySupply = getMonthlySupply(month);
            }

            supply += monthlySupply / 30;
        }

        return supply;
    }
    
    function outOfGameSupply() public view returns (uint256) {
        return _outOfGameSupply;
    }
  
    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }
    
    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for `sender`'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");

        _outOfGameSupply = _outOfGameSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: burn from the zero address");

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _outOfGameSupply = _outOfGameSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal {
        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 decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
    _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
    return true;
}

/**
 * @dev Atomically decreases the allowance granted to `spender` by the caller.
 *
 * This is an alternative to {approve} that can be used as a mitigation for
 * problems described in {IERC20-approve}.
 *
 * Emits an {Approval} event indicating the updated allowance.
 *
 * Requirements:
 *
 * - `spender` cannot be the zero address.
 * - `spender` must have allowance for the caller of at least
 * `subtractedValue`.
 */