// SPDX-License-Identifier: MIT
pragma solidity =0.8.7;

/**
 * @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.
 *
 * _Available since v4.1._
 */
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 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).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
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 Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
	address private _owner;

	event OwnershipTransferred(
		address indexed previousOwner,
		address indexed newOwner
	);

	/**
	 * @dev Initializes the contract setting the deployer as the initial owner.
	 */
	constructor() {
		_setOwner(_msgSender());
	}

	/**
	 * @dev Returns the address of the current owner.
	 */
	function owner() public view virtual returns (address) {
		return _owner;
	}

	/**
	 * @dev Throws if called by any account other than the owner.
	 */
	modifier onlyOwner() {
		require(owner() == _msgSender(), "Ownable: caller is not the owner");
		_;
	}

	/**
	 * @dev Leaves the contract without owner. It will not be possible to call
	 * `onlyOwner` functions anymore. Can only be called by the current owner.
	 *
	 * NOTE: Renouncing ownership will leave the contract without an owner,
	 * thereby removing any functionality that is only available to the owner.
	 */
	function renounceOwnership() public virtual onlyOwner {
		_setOwner(address(0));
	}

	/**
	 * @dev Transfers ownership of the contract to a new account (`newOwner`).
	 * Can only be called by the current owner.
	 */
	function transferOwnership(address newOwner) public virtual onlyOwner {
		require(
			newOwner != address(0),
			"Ownable: new owner is the zero address"
		);
		_setOwner(newOwner);
	}

	function _setOwner(address newOwner) private {
		address oldOwner = _owner;
		_owner = newOwner;
		emit OwnershipTransferred(oldOwner, newOwner);
	}
}

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin Contracts guidelines: functions revert
 * instead returning `false` on failure. This behavior is nonetheless
 * conventional and does not conflict with the expectations of ERC20
 * applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20, IERC20Metadata {
	mapping(address => uint256) private _balances;

	mapping(address => mapping(address => uint256)) private _allowances;

	uint256 private _totalSupply;

	string private _name;
	string private _symbol;

	/**
	 * @dev Sets the values for {name} and {symbol}.
	 *
	 * The default value of {decimals} is 18. To select a different value for
	 * {decimals} you should overload it.
	 *
	 * All two of these values are immutable: they can only be set once during
	 * construction.
	 */
	constructor(string memory name_, string memory symbol_) {
		_name = name_;
		_symbol = symbol_;
	}

	/**
	 * @dev Returns the name of the token.
	 */
	function name() public view virtual override returns (string memory) {
		return _name;
	}

	/**
	 * @dev Returns the symbol of the token, usually a shorter version of the
	 * name.
	 */
	function symbol() public view virtual override returns (string memory) {
		return _symbol;
	}

	/**
	 * @dev Returns the number of decimals used to get its user representation.
	 * For example, if `decimals` equals `2`, a balance of `505` tokens should
	 * be displayed to a user as `5.05` (`505 / 10 ** 2`).
	 *
	 * Tokens usually opt for a value of 18, imitating the relationship between
	 * Ether and Wei. This is the value {ERC20} uses, unless this function is
	 * overridden;
	 *
	 * NOTE: This information is only used for _display_ purposes: it in
	 * no way affects any of the arithmetic of the contract, including
	 * {IERC20-balanceOf} and {IERC20-transfer}.
	 */
	function decimals() public view virtual override returns (uint8) {
		return 18;
	}

	/**
	 * @dev See {IERC20-totalSupply}.
	 */
	function totalSupply() public view virtual override returns (uint256) {
		return _totalSupply;
	}

	/**
	 * @dev See {IERC20-balanceOf}.
	 */
	function balanceOf(address account)
		public
		view
		virtual
		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
		virtual
		override
		returns (bool)
	{
		_transfer(_msgSender(), recipient, amount);
		return true;
	}

	/**
	 * @dev See {IERC20-allowance}.
	 */
	function allowance(address owner, address spender)
		public
		view
		virtual
		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
		virtual
		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 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 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
		virtual
		returns (bool)
	{
		_approve(
			_msgSender(),
			spender,
			_allowances[_msgSender()][spender] + 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
		virtual
		returns (bool)
	{
		uint256 currentAllowance = _allowances[_msgSender()][spender];
		require(
			currentAllowance >= subtractedValue,
			"ERC20: decreased allowance below zero"
		);
		unchecked {
			_approve(_msgSender(), spender, currentAllowance - subtractedValue);
		}

		return true;
	}

	/**
	 * @dev Moves `amount` of tokens from `sender` to `recipient`.
	 *
	 * This 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 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);
	}

	/** @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:
	 *
	 * - `account` cannot be the zero address.
	 */
	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);
	}

	/**
	 * @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 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);
	}

	/**
	 * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
	 *
	 * This 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 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);
	}

	/**
	 * @dev Hook that is called before any transfer of tokens. This includes
	 * minting and burning.
	 *
	 * Calling conditions:
	 *
	 * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
	 * will be transferred to `to`.
	 * - when `from` is zero, `amount` tokens will be minted for `to`.
	 * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
	 * - `from` and `to` are never both zero.
	 *
	 * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
	 */
	function _beforeTokenTransfer(
		address from,
		address to,
		uint256 amount
	) internal virtual {}

	/**
	 * @dev Hook that is called after any transfer of tokens. This includes
	 * minting and burning.
	 *
	 * Calling conditions:
	 *
	 * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
	 * has been transferred to `to`.
	 * - when `from` is zero, `amount` tokens have been minted for `to`.
	 * - when `to` is zero, `amount` of ``from``'s tokens have been burned.
	 * - `from` and `to` are never both zero.
	 *
	 * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
	 */
	function _afterTokenTransfer(
		address from,
		address to,
		uint256 amount
	) internal virtual {}
}

contract VentToken is Ownable, ERC20 {
	constructor() ERC20("VENT", "VENT") {
		_mint(msg.sender, 250_000_000 ether);
	}

	function burn(uint256 _amount) public onlyOwner {
		_burn(msg.sender, _amount);
	}
}