Discussion on: [Feedback] The Pitfalls of Developing on XDC Network: A Critical Assessment

function _msgData() internal view virtual returns (bytes memory) {
    this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
    return msg.data;
}

uint256 private _status;

constructor() {
    _status = _NOT_ENTERED;
}

modifier nonReentrant() {
    require(_status != _ENTERED, "ReentrancyGuard: reentrant call");
    _status = _ENTERED;
    _;
    _status = _NOT_ENTERED;
}

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

constructor () {
    address msgSender = _msgSender();
    _owner = msgSender;
    emit OwnershipTransferred(address(0), msgSender);
}

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

modifier onlyOwner() {
    require(_owner == _msgSender(), "Ownable: caller is not the owner");
    _;
}

function renounceOwnership() public virtual onlyOwner {
    emit OwnershipTransferred(_owner, address(0));
    _owner = address(0);
}

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

// we want to track who has already migrated to V2
mapping(address => bool) private claimed;
address public immutable deadWallet = 0x000000000000000000000000000000000000dEaD;

IERC20 public tokenV1; //address of the old version
IERC20 public tokenV2; //address of the new version
uint256 public rate; // 1 token V1 ---> 1 * rate token V2

bool public migrationStarted;

/// @notice Emits event every time someone migrates
event MigrateToV2(address addr, uint256 amount);

/// @param tokenAddressV1 The address of old version
/// @param tokenAddressV2 The address of new version
/// @param _rate The rate between old and new version
constructor(IERC20 tokenAddressV1, IERC20 tokenAddressV2, uint256 _rate) {
    tokenV2 = tokenAddressV2;
    tokenV1 = tokenAddressV1;
    rate = _rate;
}

/// @notice Enables the migration
function startMigration() external onlyOwner{
    require(migrationStarted == false, "Migration is already enabled");
    migrationStarted = true;
}

/// @notice Disable the migration
function stopMigration() external onlyOwner{
    require(migrationStarted == true, "Migration is already disabled");
    migrationStarted = false;
}

/// @notice Updates "tokenV1", "tokenV2" and the "rate"
/// @param tokenV1addr The address of old version
/// @param tokenV2addr The address of new version
/// @param _rate The rate between old and new version
function setTokenV1andV2(IERC20 tokenV1addr, IERC20 tokenV2addr, uint256 _rate) external onlyOwner{
    tokenV1 = tokenV1addr;
    tokenV2 = tokenV2addr;
    rate = _rate;
}

/// @notice Withdraws remaining tokens
function withdrawTokens(uint256 amount) external onlyOwner{
    require(migrationStarted == false, "Impossible to withdraw tokens if migration still enabled");
    tokenV2.transfer(msg.sender, amount * 10**(tokenV2.decimals()));
}

/// @param v1amount The amount of tokens to migrate
/// @notice Migrates from old version to new one
///   User must call "approve" function on tokenV1 contract
///   passing this contract address as "sender".
///   Old tokens will be sent to burn
function migrateToV2(uint256 v1amount) public nonReentrant(){
    require(migrationStarted == true, 'Migration not started yet');
    uint256 amount = v1amount * 10 ** tokenV1.decimals();
    uint256 userV1Balance = tokenV1.balanceOf(msg.sender);
    require(userV1Balance >= amount, 'You must hold V1 tokens to migrate');
    uint256 amtToMigrate = v1amount * rate * 10 ** tokenV2.decimals();
    require(tokenV2.balanceOf(address(this)) >= amtToMigrate, 'No enough V2 liquidity');
    tokenV1.transferFrom(msg.sender, deadWallet, amount);
    tokenV2.transfer(msg.sender, amtToMigrate);
    emit MigrateToV2(msg.sender, amtToMigrate);
}