// File: @openzeppelin\upgrades\contracts\Initializable.sol

pragma solidity >=0.4.24 <0.6.0;


/**
 * @title Initializable
 *
 * @dev Helper contract to support initializer functions. To use it, replace
 * the constructor with a function that has the `initializer` modifier.
 * WARNING: Unlike constructors, initializer functions must be manually
 * invoked. This applies both to deploying an Initializable contract, as well
 * as extending an Initializable contract via inheritance.
 * WARNING: When used with inheritance, manual care must be taken to not invoke
 * a parent initializer twice, or ensure that all initializers are idempotent,
 * because this is not dealt with automatically as with constructors.
 */
contract Initializable {

  /**
   * @dev Indicates that the contract has been initialized.
   */
  bool private initialized;

  /**
   * @dev Indicates that the contract is in the process of being initialized.
   */
  bool private initializing;

  /**
   * @dev Modifier to use in the initializer function of a contract.
   */
  modifier initializer() {
    require(initializing || isConstructor() || !initialized, "Contract instance has already been initialized");

    bool isTopLevelCall = !initializing;
    if (isTopLevelCall) {
      initializing = true;
      initialized = true;
    }

    _;

    if (isTopLevelCall) {
      initializing = false;
    }
  }

  /// @dev Returns true if and only if the function is running in the constructor
  function isConstructor() private view returns (bool) {
    // extcodesize checks the size of the code stored in an address, and
    // address returns the current address. Since the code is still not
    // deployed when running a constructor, any checks on its code size will
    // yield zero, making it an effective way to detect if a contract is
    // under construction or not.
    uint256 cs;
    assembly { cs := extcodesize(address) }
    return cs == 0;
  }

  // Reserved storage space to allow for layout changes in the future.
  uint256[50] private ______gap;
}

// File: @openzeppelin\contracts-ethereum-package\contracts\math\SafeMath.sol

pragma solidity ^0.5.0;

/**
 * @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.
     *
     * _Available since v2.4.0._
     */
    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.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        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.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin\contracts-ethereum-package\contracts\token\ERC20\IERC20.sol

pragma solidity ^0.5.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
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);
}

// File: contracts\UniSwap_ETH_cDAI.sol

// Copyright (C) 2019, 2020 dipeshsukhani, nodarjonashi, toshsharma, suhailg

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 2 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// Visit <https://www.gnu.org/licenses/>for a copy of the GNU Affero General Public License

/**
 * WARNING: This is an upgradable contract. Be careful not to disrupt
 * the existing storage layout when making upgrades to the contract. In particular,
 * existing fields should not be removed and should not have their types changed.
 * The order of field declarations must not be changed, and new fields must be added
 * below all existing declarations.
 *
 * The base contracts and the order in which they are declared must not be changed.
 * New fields must not be added to base contracts (unless the base contract has
 * reserved placeholder fields for this purpose).
 *
 * See https://docs.zeppelinos.org/docs/writing_contracts.html for more info.
*/

pragma solidity ^0.5.0;

///@author DeFiZap
///@notice this contract implements one click conversion from ETH to unipool liquidity tokens (cDAI)

interface IuniswapFactory {
    function getExchange(address token) external view returns (address exchange);
}

interface IuniswapExchange {
    function getEthToTokenInputPrice(uint256 eth_sold) external view returns (uint256 tokens_bought);
    function getTokenToEthInputPrice(uint256 tokens_sold) external view returns (uint256 eth_bought);
    function ethToTokenSwapInput(uint256 min_tokens, uint256 deadline) external payable returns (uint256  tokens_bought);
    function balanceOf(address _owner) external view returns (uint256);
    function transfer(address _to, uint256 _value) external returns (bool);
    function transferFrom(address _from, address _to, uint256 value) external returns (bool);
    function approve(address _spender, uint256 _value) external returns (bool);
    function totalSupply() external view returns (uint256);
    function addLiquidity(uint256 min_liquidity, uint256 max_tokens, uint256 deadline) external payable returns (uint256);
    function removeLiquidity(uint256 amount, uint256 min_eth, uint256 min_tokens, uint256 deadline) external returns (uint256, uint256);
}

interface Compound {
    function approve ( address spender, uint256 amount ) external returns ( bool );
    function mint ( uint256 mintAmount ) external returns ( uint256 );
    function balanceOf(address _owner) external view returns (uint256 balance);
    function transfer(address _to, uint _value) external returns (bool success);
}

interface IOneSplitInterface {

    function getExpectedReturn(
        address fromToken,
        address toToken,
        uint256 amount,
        uint256 parts,
        uint256 disableFlags // 1 - Uniswap, 2 - Kyber, 4 - Bancor, 8 - Oasis, 16 - Compound, 32 - Fulcrum, 64 - Chai, 128 - Aave, 256 - SmartToken
    )
        external
        view
        returns(
            uint256 returnAmount,
            uint256[] memory distribution // [Uniswap, Kyber, Bancor, Oasis]
        );

    function swap(
        address fromToken,
        address toToken,
        uint256 amount,
        uint256 minReturn,
        uint256[] calldata distribution, // [Uniswap, Kyber, Bancor, Oasis]
        uint256 disableFlags // 16 - Compound, 32 - Fulcrum, 64 - Chai, 128 - Aave, 256 - SmartToken
    )
        external
        payable;

    function goodSwap(
        address fromToken,
        address toToken,
        uint256 amount,
        uint256 minReturn,
        uint256 parts,
        uint256 disableFlags // 1 - Uniswap, 2 - Kyber, 4 - Bancor, 8 - Oasis, 16 - Compound, 32 - Fulcrum, 64 - Chai, 128 - Aave, 256 - SmartToken
    )
        external
        payable;
}

contract UniSwap_ETH_CDAIZap is Initializable {
    using SafeMath for uint;
    // state variables

    // - THESE MUST ALWAYS STAY IN THE SAME LAYOUT
    bool private stopped;
    address payable public owner;
    IuniswapFactory public UniSwapFactoryAddress;
    IOneSplitInterface public OneSplitInterfaceAddress;
    IERC20 public NEWDAI_TOKEN_ADDRESS;
    Compound public COMPOUND_TOKEN_ADDRESS;
    address public DAI_TOKEN_ADDRESS;
    address public ETH_TOKEN_ADDRESS;
    address public ONESPLIT_ADDRESS;


    // events
    event ERC20TokenHoldingsOnConversionDaiChai(uint);
    event ERC20TokenHoldingsOnConversionEthDai(uint);
    event LiquidityTokens(uint);

    // circuit breaker modifiers
    modifier stopInEmergency {if (!stopped) _;}
    modifier onlyInEmergency {if (stopped) _;}
    modifier onlyOwner() {
        require(isOwner(), "you are not authorised to call this function");
        _;
    }


    function initialize() initializer public {
        stopped = false;
        owner = msg.sender;
        UniSwapFactoryAddress = IuniswapFactory(0xc0a47dFe034B400B47bDaD5FecDa2621de6c4d95);
        NEWDAI_TOKEN_ADDRESS = IERC20(0x6B175474E89094C44Da98b954EedeAC495271d0F);
        COMPOUND_TOKEN_ADDRESS = Compound(0x5d3a536E4D6DbD6114cc1Ead35777bAB948E3643);
        OneSplitInterfaceAddress = IOneSplitInterface(0xD010B65120E027419586216D25bF86C2c24FCC4a);
        ONESPLIT_ADDRESS = address(0xD010B65120E027419586216D25bF86C2c24FCC4a);
        DAI_TOKEN_ADDRESS = address(0x6B175474E89094C44Da98b954EedeAC495271d0F);
        ETH_TOKEN_ADDRESS = address(0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE);
    }


    function set_new_UniSwapFactoryAddress(address _new_UniSwapFactoryAddress) public onlyOwner {
        UniSwapFactoryAddress = IuniswapFactory(_new_UniSwapFactoryAddress);
    }

    function set_new_DAI_TOKEN_ADDRESS(address _new_DAI_TOKEN_ADDRESS) public onlyOwner {
        NEWDAI_TOKEN_ADDRESS = IERC20(_new_DAI_TOKEN_ADDRESS);
        DAI_TOKEN_ADDRESS = _new_DAI_TOKEN_ADDRESS;
    }

    function set_new_cDAI_TokenContractAddress(address _new_cDAI_TokenContractAddress) public onlyOwner {
        COMPOUND_TOKEN_ADDRESS = Compound(_new_cDAI_TokenContractAddress);
    }

    function set_OneSplitInterfaceAddress(address _new_OneSplitInterfaceAddress) public onlyOwner {
        OneSplitInterfaceAddress = IOneSplitInterface(_new_OneSplitInterfaceAddress);
        ONESPLIT_ADDRESS = _new_OneSplitInterfaceAddress;
    }

    function getExpectedReturn(uint256 eth) public view returns (uint256) {
      uint256 _minReturn = 0;
      (_minReturn, ) = OneSplitInterfaceAddress.getExpectedReturn(ETH_TOKEN_ADDRESS, DAI_TOKEN_ADDRESS, eth, 1, 0);
      return _minReturn;
    }

    function LetsInvest(address _towhomtoissue, uint256 _minReturn) public payable stopInEmergency returns (uint) {
        IERC20 ERC20TokenAddress = IERC20(address(COMPOUND_TOKEN_ADDRESS));
        IuniswapExchange UniSwapExchangeContractAddress = IuniswapExchange(UniSwapFactoryAddress.getExchange(address(COMPOUND_TOKEN_ADDRESS)));

        // determining the portion of the incoming ETH to be converted to the ERC20 Token
        uint conversionPortion = SafeMath.div(SafeMath.mul(msg.value, 505), 1000);
        uint non_conversionPortion = SafeMath.sub(msg.value,conversionPortion);

        if (_minReturn == 0) {
          (_minReturn, ) = OneSplitInterfaceAddress.getExpectedReturn(ETH_TOKEN_ADDRESS, DAI_TOKEN_ADDRESS, conversionPortion, 1, 0);
        }

        OneSplitInterfaceAddress.goodSwap.value(conversionPortion)(ETH_TOKEN_ADDRESS, DAI_TOKEN_ADDRESS, conversionPortion, _minReturn, 1, 0);
        uint tokenBalance = NEWDAI_TOKEN_ADDRESS.balanceOf(address(this));

        require(tokenBalance > 0, "the conversion did not happen as planned");

        // conversion of DAI to cDAI
        uint qty2approve = SafeMath.mul(tokenBalance, 3);
        require(NEWDAI_TOKEN_ADDRESS.approve(address(ERC20TokenAddress), qty2approve));
        COMPOUND_TOKEN_ADDRESS.mint(tokenBalance);
        uint ERC20TokenHoldings = ERC20TokenAddress.balanceOf(address(this));
        require (ERC20TokenHoldings > 0, "the conversion did not happen as planned");
        emit ERC20TokenHoldingsOnConversionDaiChai(ERC20TokenHoldings);
        NEWDAI_TOKEN_ADDRESS.approve(address(ERC20TokenAddress), 0);
        ERC20TokenAddress.approve(address(UniSwapExchangeContractAddress),ERC20TokenHoldings);

        // adding Liquidity
        uint max_tokens_ans = getMaxTokens(address(UniSwapExchangeContractAddress), ERC20TokenAddress, non_conversionPortion);
        UniSwapExchangeContractAddress.addLiquidity.value(non_conversionPortion)(1,max_tokens_ans,SafeMath.add(now,1800));
        ERC20TokenAddress.approve(address(UniSwapExchangeContractAddress),0);

        // transferring Liquidity
        uint LiquityTokenHoldings = UniSwapExchangeContractAddress.balanceOf(address(this));
        emit LiquidityTokens(LiquityTokenHoldings);
        UniSwapExchangeContractAddress.transfer(_towhomtoissue, LiquityTokenHoldings);
        ERC20TokenHoldings = ERC20TokenAddress.balanceOf(address(this));
        ERC20TokenAddress.transfer(_towhomtoissue, ERC20TokenHoldings);
        return LiquityTokenHoldings;
    }

    function Redeem(address _towhomtosend, uint256 _amount) public stopInEmergency returns (uint) {
        // Compound contract address
        IERC20 ERC20TokenAddress = IERC20(address(COMPOUND_TOKEN_ADDRESS));

        // Compound uniswap exchange
        IuniswapExchange UniSwapExchangeContractAddress = IuniswapExchange(UniSwapFactoryAddress.getExchange(address(COMPOUND_TOKEN_ADDRESS)));

        // Send users uni-v1 to contract address (will fail if not approved)
        UniSwapExchangeContractAddress.transferFrom(msg.sender, address(this), _amount);

        // Get min_eth and min_token for removeLiquidity call
        (, uint256 ownerSharesEth, uint256 ownerSharesToken) = getReturn(address(UniSwapExchangeContractAddress), ERC20TokenAddress, _amount);
        // Swap uni-v1 for eth and tokens
        (uint256 eth, uint256 tokens) = UniSwapExchangeContractAddress.removeLiquidity(_amount, ownerSharesEth, ownerSharesToken, SafeMath.add(now,1800));

        // Approve onsplit to take the compound tokens
        ERC20TokenAddress.approve(ONESPLIT_ADDRESS, tokens);
        // Get the expected return in ETH
        (uint256 _minReturn, ) = OneSplitInterfaceAddress.getExpectedReturn(address(COMPOUND_TOKEN_ADDRESS), ETH_TOKEN_ADDRESS, tokens, 1, 0);
        // Swap for the expected ETH
        OneSplitInterfaceAddress.goodSwap.value(0)(address(COMPOUND_TOKEN_ADDRESS), ETH_TOKEN_ADDRESS, tokens, _minReturn, 1, 0);


        ERC20TokenAddress.approve(ONESPLIT_ADDRESS, 0);

        uint256 ethReturn = SafeMath.add(eth, _minReturn);
        (bool result, ) = _towhomtosend.call.value(ethReturn).gas(50000)("");
        require(result, "transfer of ETH failed");
        return ethReturn;
    }

    function getMaxTokens(address _UniSwapExchangeContractAddress, IERC20 _ERC20TokenAddress, uint _value) public view returns (uint) {
        uint contractBalance = _UniSwapExchangeContractAddress.balance;
        uint eth_reserve = SafeMath.sub(contractBalance, _value);
        uint token_reserve = _ERC20TokenAddress.balanceOf(_UniSwapExchangeContractAddress);
        uint token_amount = SafeMath.div(SafeMath.mul(_value,token_reserve),eth_reserve) + 1;
        return token_amount;
    }

    function getEthBalance(address _UniSwapExchangeContractAddress) public view returns (uint) {
      uint ethBalance = _UniSwapExchangeContractAddress.balance;
      return ethBalance;
    }

    function getTokenReserves(address _UniSwapExchangeContractAddress, IERC20 _ERC20TokenAddress) public view returns (uint) {
      uint token_reserve = _ERC20TokenAddress.balanceOf(_UniSwapExchangeContractAddress);
      return token_reserve;
    }


    function getTotalShares(address _UniSwapExchangeContractAddress) public view returns (uint) {
      uint totalShares = IuniswapExchange(_UniSwapExchangeContractAddress).totalSupply();
      return totalShares;
    }

    function getReturn(address _UniSwapExchangeContractAddress, IERC20 _ERC20TokenAddress, uint _value) public view returns (uint, uint, uint) {
        // Token balance in uniswap contract
        uint token_reserve = _ERC20TokenAddress.balanceOf(_UniSwapExchangeContractAddress);
        // ETH balance in uniswap contract
        uint ethBalance = _UniSwapExchangeContractAddress.balance;

        // Get total pool shares
        uint totalShares = IuniswapExchange(_UniSwapExchangeContractAddress).totalSupply();

        // Calculate owner share pool
        uint ownerSharesEth = SafeMath.div(SafeMath.mul(_value, ethBalance), totalShares);
        uint ownerSharesToken = SafeMath.div(SafeMath.mul(_value, token_reserve), totalShares);

        // Calculate eth value
        uint ethBought = IuniswapExchange(_UniSwapExchangeContractAddress).getTokenToEthInputPrice(ownerSharesToken);
        uint ethValue = SafeMath.add(ethBought, ownerSharesEth);

        return (ethValue, ownerSharesEth, ownerSharesToken);
    }

    // incase of half-way error
    function inCaseTokengetsStuck(IERC20 _TokenAddress) onlyOwner public {
        uint qty = _TokenAddress.balanceOf(address(this));
        _TokenAddress.transfer(owner, qty);
    }

    // - fallback function let you / anyone send ETH to this wallet without the need to call any function
    function() external payable {
        if (msg.sender != owner) {
            LetsInvest(msg.sender, 0);
        }
    }

    // - to Pause the contract
    function toggleContractActive() onlyOwner public {
        stopped = !stopped;
    }
    // - to withdraw any ETH balance sitting in the contract
    function withdraw() onlyOwner public{
        owner.transfer(address(this).balance);
    }
    // - to kill the contract
    function destruct() public onlyOwner {
        selfdestruct(owner);
    }
    /**
     * @return true if `msg.sender` is the owner of the contract.
     */
    function isOwner() public view returns (bool) {
        return msg.sender == owner;
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address payable newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address payable newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        owner = newOwner;
    }

}