// SPDX-License-Identifier: MIT
pragma solidity 0.8.0; 

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}


/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}


/**
 * @dev Implementation of the DGMV Token
 *  
 */
contract DGMV is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

    mapping(address => mapping(address => uint256)) private _allowances;

    string constant private _name = "DigiMetaverse";
    string constant private _symbol = "DGMV";
    uint8  constant private _decimal = 18;
    uint256 constant private _totalSupply = 1000000000 * (10 ** _decimal); // 1 Billion tokens
    
    /**
     * @dev Sets the values for {name}, {symbol}, {total supply} and {decimal}.
     */
    constructor() {
        _balances[_msgSender()] = _totalSupply;
         emit Transfer(address(0), _msgSender(), _totalSupply);
    }
    
    /**
     * @dev Returns Name of the token
     */
    function name() external view virtual override returns (string memory) {
        return _name;
    }
    
    /**
     * @dev Returns the symbol of the token, usually a shorter version of the name.
     */
    function symbol() external view virtual override returns (string memory) {
        return _symbol;
    }
    
    /**
     * @dev Returns the number of decimals used to get its user representation
     */
    function decimals() external view virtual override returns (uint8) {
        return _decimal;
    }
    
    /**
     * @dev This will give the total number of tokens in existence.
     */
    function totalSupply() external view virtual override returns (uint256) {
        return _totalSupply;
    }
    
    /**
     * @dev Gets the balance of the specified address.
     */
    function balanceOf(address account) external view virtual override returns (uint256) {
        return _balances[account];
    }
    
    /**
     * @dev Transfer token to a specified address and Emits a Transfer event.
     */
    function transfer(address recipient, uint256 amount) external virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }
    
    /**
     * @dev Function to check the number of tokens that an owner allowed to a spender
     */
    function allowance(address owner, address spender) external view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }
    
    /**
     * @dev Function to allow anyone to spend a token from your account and Emits an Approval event.
     */
    function approve(address spender, uint256 amount) external virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }
    
    /**
     * @dev Function to transfer allowed token from other's account
     */
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external virtual override returns (bool) {
        _transfer(sender, recipient, amount);

        uint256 currentAllowance = _allowances[sender][_msgSender()];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        unchecked {
            _approve(sender, _msgSender(), currentAllowance - amount);
        }

        return true;
    }
    
    /**
     * @dev Function to increase the allowance of another account
     */
    function increaseAllowance(address spender, uint256 addedValue) external virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender] + addedValue);
        return true;
    }
    
    /**
     * @dev Function to decrease the allowance of another account
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) external virtual returns (bool) {
        uint256 currentAllowance = _allowances[_msgSender()][spender];
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(_msgSender(), spender, currentAllowance - subtractedValue);
        }
        return true;
    }
    
    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");
        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);
    }

    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);
    } 
}