Contract Source Code:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "../Utility/owner.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";

interface IERC20 {
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
    function approve(address spender, uint256 amount) external returns (bool);
    function transfer(address to, uint256 amount) external returns (bool);
    function decimals() external view returns (uint8);
}

contract BV2toBV3Swap is Owner, ReentrancyGuard {
    IERC20 public bv2Token;
    IERC20 public bv3Token;
    uint256 public totalBV2Swapped;
    uint256 public bv3Counter;

    function setBV2TokenAddress(address _bv2TokenAddress) external onlyOwner {
        bv2Token = IERC20(_bv2TokenAddress);
    }

    function setBV3TokenAddress(address _bv3TokenAddress) external onlyOwner {
        bv3Token = IERC20(_bv3TokenAddress);
    }

    function approveBV2() external {
        uint256 maxUint = type(uint256).max;
        bv2Token.approve(address(this), maxUint);
    }

    // Users must approve this contract to spend their BV2 tokens before calling this function
    function swapBV2ForBV3(uint256 _bv2Amount) external nonReentrant {
        require(bv2Token.decimals() == 10, "BV2 token does not have 10 decimals");
        require(bv3Token.decimals() == 18, "BV3 token does not have 18 decimals");

        uint256 bv3Amount = (_bv2Amount * (10 ** 8)) * 2; // Convert BV2 amount to BV3 amount

        require(bv2Token.transferFrom(msg.sender, address(this), _bv2Amount), "Failed to transfer BV2 tokens");
        require(bv3Token.transfer(msg.sender, bv3Amount), "Failed to transfer BV3 tokens");

        totalBV2Swapped += _bv2Amount;
    }

    // View function to see the total BV2 tokens swapped
    function getTotalBV2Swapped() external view returns (uint256) {
        return totalBV2Swapped;
    }

    // Function to allow the owner to withdraw BV3 tokens using transferFrom
    function withdrawBV3(uint256 _amount) external onlyOwner {
        require(bv3Token.transferFrom(address(this), msg.sender, _amount), "Failed to withdraw BV3 tokens");
        bv3Counter -= _amount;
    }

    // Function for the owner to send BV3 tokens using transferFrom and adjust the BV3 counter
    function sendBV3(address _from, uint256 _amount) external onlyOwner {
        require(bv3Token.transferFrom(_from, address(this), _amount), "Failed to send BV3 tokens");
        bv3Counter += _amount;
    }


    function getBV3Counter() external view returns (uint256) {
        return bv3Counter;
    }

    // Other functions and code...
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (security/ReentrancyGuard.sol)

pragma solidity ^0.8.0;

/**
 * @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 making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        _nonReentrantBefore();
        _;
        _nonReentrantAfter();
    }

    function _nonReentrantBefore() private {
        // On the first call to nonReentrant, _status will be _NOT_ENTERED
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;
    }

    function _nonReentrantAfter() private {
        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Returns true if the reentrancy guard is currently set to "entered", which indicates there is a
     * `nonReentrant` function in the call stack.
     */
    function _reentrancyGuardEntered() internal view returns (bool) {
        return _status == _ENTERED;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Owner {
    address public _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor() {
        _owner = msg.sender;
        emit OwnershipTransferred(address(0), _owner);
    }

    modifier onlyOwner() {
        require(isOwner(), "You are not the owner");
        _;
    }

    function transferOwnership(address newOwner) public onlyOwner {
        require(newOwner != address(0), "New owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }


    function isOwner() public view returns (bool) {
        return msg.sender == _owner;
    }


    function getOwner() public view returns (address) {
        return _owner;
    }

}