// File: src/Grok.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.22;

import {ERC20, IERC20} from "openzeppelin/token/ERC20/ERC20.sol";
import {Ownable} from "openzeppelin/access/Ownable.sol";

// https://t.me/GrokPortal
// https://twitter.com/xGrokAI

interface IUniswapV2Router02 {
    function factory() external pure returns (address);

    function WETH() external pure returns (address);

    function swapExactTokensForETHSupportingFeeOnTransferTokens(
        uint256 amountIn,
        uint256 amountOutMin,
        address[] calldata path,
        address to,
        uint256 deadline
    ) external;

    function addLiquidityETH(
        address token,
        uint256 amountTokenDesired,
        uint256 amountTokenMin,
        uint256 amountETHMin,
        address to,
        uint256 deadline
    ) external payable returns (uint256 amountToken, uint256 amountETH, uint256 liquidity);
}

interface UniswapUniversalRouter {}

interface IUniswapV2Factory {
    function createPair(address tokenA, address tokenB) external returns (address pair);
}

contract Grok is ERC20, Ownable {
    // errors
    error ErrAlreadySetup();
    error ErrAlreadyLaunched();
    error ErrMaxBalance();
    error ErrMaxTx();
    error ErrInvalidFees();
    error ErrInvalidSwapThreshold();
    error ErrAddressZero();
    error ErrZeroValue();
    error ErrZeroToken();
    error ErrTradingNotStarted();

    // states
    address constant FEE_RECEIVER = 0x4e8a7E4867348435ADDF373F0343A72478D8E47b;

    uint256 public constant MAX_SUPPLY = 1 * 1e9 ether;
    IUniswapV2Router02 public constant UNISWAP_V2_ROUTER =
        IUniswapV2Router02(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);

    uint256 private constant INITIAL_MAX_TRANSACTION_AMOUNT = 3 * 1e7 ether; // 3% from total supply maxTransactionAmountTxn
    uint256 private constant INITIAL_MAX_WALLET = 3 * 1e7 ether; // 3% from total supply maxWallet

    uint256 private constant INITIAL_BUY_FEE = 15;
    uint256 private constant INITIAL_SELL_FEE = 30;

    address public uniswapPair;
    mapping(address => bool) private _limitExempted;
    mapping(address => bool) private _feeExempted;

    uint256 public maxWallet;
    uint256 public maxTx;

    address public feeReceiver;
    uint256 public buyFee;
    uint256 public sellFee;
    uint256 private _swapThreshold;

    bool private _isSwapping;
    bool public tradingStarted;

    constructor() ERC20(unicode"GrōkAI", unicode"GROK") {
        // set states
        _limitExempted[tx.origin] = true;
        _limitExempted[address(0)] = true;
        _limitExempted[address(0xdead)] = true;
        _limitExempted[address(this)] = true;
        _limitExempted[address(UNISWAP_V2_ROUTER)] = true;

        _feeExempted[address(this)] = true;
        _feeExempted[tx.origin] = true;

        maxWallet = INITIAL_MAX_WALLET;
        maxTx = INITIAL_MAX_TRANSACTION_AMOUNT;

        buyFee = INITIAL_BUY_FEE;
        sellFee = INITIAL_SELL_FEE;
        feeReceiver = FEE_RECEIVER;
        _swapThreshold = MAX_SUPPLY / 100;

        // mint
        _mint(tx.origin, MAX_SUPPLY);
    }

    receive() external payable {}

    fallback() external payable {}

    // erc20
    function _beforeTokenTransfer(address from_, address to_, uint256 amount_) internal view override {
        // check limits max wallet
        if (!_limitExempted[to_]) {
            if (balanceOf(to_) + amount_ > maxWallet) {
                revert ErrMaxBalance();
            }
        }

        // check max tx
        if (!_limitExempted[from_]) {
            if (amount_ > maxTx) {
                revert ErrMaxTx();
            }
        }

        // check trading started
        if (!tradingStarted) {
            if (!_feeExempted[from_] && !_feeExempted[to_]) {
                revert ErrTradingNotStarted();
            }
        }
    }

    function _transfer(address from_, address to_, uint256 amount_) internal override {
        // check
        if (to_ == address(0)) revert ErrAddressZero();

        // zero amount
        if (amount_ == 0) {
            super._transfer(from_, to_, 0);
            return;
        }

        // swap
        if (
            !_isSwapping && balanceOf(address(this)) >= _swapThreshold && from_ != uniswapPair && !_feeExempted[from_]
                && !_feeExempted[to_]
        ) {
            _isSwapping = true;
            _swap();
            _isSwapping = false;
        }

        // fees
        uint256 fees = 0;
        if (!_isSwapping && !_feeExempted[from_] && !_feeExempted[to_]) {
            uint256 _sellTax = sellFee;
            uint256 _buyTax = buyFee;

            // on sell
            if (to_ == uniswapPair && _sellTax > 0) {
                fees = (amount_ * _sellTax) / 100;
                super._transfer(from_, address(this), fees);
            }
            // on buy
            else if (from_ == uniswapPair && _buyTax > 0) {
                fees = (amount_ * _buyTax) / 100;
                super._transfer(from_, address(this), fees);
            }
        }
        super._transfer(from_, to_, amount_ - fees);
    }

    // owners
    function launch(uint256 tokenAmount_) external payable onlyOwner {
        // check if already launched
        if (uniswapPair != address(0)) revert ErrAlreadyLaunched();

        // check token & value
        if (msg.value == 0) revert ErrZeroValue();
        if (tokenAmount_ == 0) revert ErrZeroToken();

        // transfer token
        _transfer(msg.sender, address(this), tokenAmount_);

        // create pair
        IUniswapV2Router02 __router = UNISWAP_V2_ROUTER;
        address __uniswapPair = IUniswapV2Factory(__router.factory()).createPair(address(this), __router.WETH());

        // update state
        _limitExempted[__uniswapPair] = true;

        // approve tokens
        _approve(address(this), address(__router), type(uint256).max);
        _approve(address(this), address(__uniswapPair), type(uint256).max);
        IERC20(__uniswapPair).approve(address(__router), type(uint256).max);

        // add liq
        __router.addLiquidityETH{value: address(this).balance}(
            address(this), balanceOf(address(this)), 0, 0, owner(), block.timestamp
        );

        uniswapPair = __uniswapPair;
    }

    function clearStuck() external onlyOwner {
        (bool success,) = payable(msg.sender).call{value: address(this).balance}("");
        require(success);
    }

    function clearStuckToken() external onlyOwner {
        _transfer(address(this), msg.sender, balanceOf(address(this)));
    }

    function setLimitExempted(address addr_, bool exempted_) external onlyOwner {
        _limitExempted[addr_] = exempted_;
    }

    function setFeeExempted(address addr_, bool exempted_) external onlyOwner {
        _feeExempted[addr_] = exempted_;
    }

    function setMaxWallet(uint256 maxWallet_) external onlyOwner {
        maxWallet = maxWallet_;
    }

    function setMaxTx(uint256 maxTx_) external onlyOwner {
        maxTx = maxTx_;
    }

    function setFeeReceiver(address addr_) external onlyOwner {
        feeReceiver = addr_;
    }

    function setFees(uint256 buyFee_, uint256 sellFee_) external onlyOwner {
        if (buyFee_ > 100 || sellFee_ > 100) {
            revert ErrInvalidFees();
        }

        sellFee = sellFee_;
        buyFee = buyFee_;
    }

    function setSwapThreshold(uint256 swapThreshold_) external onlyOwner {
        uint256 __totalSupply = MAX_SUPPLY;
        if (swapThreshold_ < __totalSupply / 1000 || swapThreshold_ > __totalSupply / 20) {
            revert ErrInvalidSwapThreshold();
        }
        _swapThreshold = swapThreshold_;
    }

    function enableTrading() external onlyOwner {
        tradingStarted = true;
    }

    // internal
    function _swapTokensForEth(uint256 tokenAmount) private {
        IUniswapV2Router02 __swapRouter = UNISWAP_V2_ROUTER;

        // generate the uniswap pair path of token -> weth
        address[] memory path = new address[](2);
        path[0] = address(this);
        path[1] = __swapRouter.WETH();

        _approve(address(this), address(__swapRouter), tokenAmount);

        // make the swap
        __swapRouter.swapExactTokensForETHSupportingFeeOnTransferTokens(
            tokenAmount, 0, path, address(this), block.timestamp
        );
    }

    function _swap() private {
        uint256 __contractBalance = balanceOf(address(this));
        uint256 __swapThreshold = _swapThreshold;

        // nothing to swap
        if (__contractBalance == 0) {
            return;
        }

        // swap amount
        uint256 __swapAmount = __contractBalance;
        if (__swapAmount > __swapThreshold * 20) {
            __swapAmount = __swapThreshold * 20;
        }

        // swap to ETH
        _swapTokensForEth(__swapAmount);

        // send
        uint256 __balance = address(this).balance;
        (bool success,) = payable(address(feeReceiver)).call{value: __balance}("");
    }
}

// File: lib/openzeppelin-contracts/contracts/token/ERC20/ERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.8.0) (token/ERC20/ERC20.sol)

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";

/**
 * @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.openzeppelin.com/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:
     *
     * - `to` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address to, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, 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}.
     *
     * NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, 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}.
     *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, 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) {
        address owner = _msgSender();
        _approve(owner, spender, allowance(owner, 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) {
        address owner = _msgSender();
        uint256 currentAllowance = allowance(owner, spender);
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `from` to `to`.
     *
     * 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:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     */
    function _transfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(from, to, amount);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - amount;
            // Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
            // decrementing then incrementing.
            _balances[to] += amount;
        }

        emit Transfer(from, to, amount);

        _afterTokenTransfer(from, to, 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;
        unchecked {
            // Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
            _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;
            // Overflow not possible: amount <= accountBalance <= totalSupply.
            _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 Updates `owner` s allowance for `spender` based on spent `amount`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    function _spendAllowance(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - 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 {}
}

// File: lib/openzeppelin-contracts/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (access/Ownable.sol)

pragma solidity ^0.8.0;

import "../utils/Context.sol";

/**
 * @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() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        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 {
        _transferOwnership(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");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// File: lib/openzeppelin-contracts/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @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 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 `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, 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 `from` to `to` 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 from,
        address to,
        uint256 amount
    ) external returns (bool);
}

// File: lib/openzeppelin-contracts/contracts/token/ERC20/extensions/IERC20Metadata.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @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);
}

// File: lib/openzeppelin-contracts/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

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).
 *
 * 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;
    }
}