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

contract e2XUsernames {
    address public owner;

    mapping(address => string) public storedData;
    mapping(string => address) public addressByUser;
    mapping(address => bool) private isAdmin;

    event DataStored(address indexed _from, string _data);
    event AdminChanged(address indexed _previousAdmin, address indexed _newAdmin);
    event DataTransferred(address indexed _from, address indexed _to, string _data);

    modifier onlyAdmin() {
        require(isAdmin[msg.sender], "Only admin can call this function");
        _;
    }

    modifier onlyOwner() {
        require(msg.sender == owner, "Only owner can call this function");
        _;
    }

    constructor() {
        owner = msg.sender;
        isAdmin[msg.sender] = true;
    }

    function e2xData(string memory _data) public {
        require(bytes(_data).length <= 9, "Data length exceeds 9 characters");
        require(addressByUser[_data] == address(0), "User ID already exists");

        storedData[msg.sender] = _data;
        addressByUser[_data] = msg.sender;

        emit DataStored(msg.sender, _data);
    }

    function getData(address _address) public view returns (string memory) {
        return storedData[_address];
    }

    function getAddressByUser(string memory _user) public view returns (address) {
        return addressByUser[_user];
    }

    function transferToNewContract(address _newContract) external onlyOwner {
        require(_newContract != address(0), "Invalid new contract address");

        // Implement logic to transfer data to the new contract
        // For demonstration purposes, emitting an event here
        emit DataTransferred(address(this), _newContract, storedData[msg.sender]);
    }

    function changeAdmin(address _newAdmin) public onlyOwner {
        require(_newAdmin != address(0), "Invalid admin address");
        require(!isAdmin[_newAdmin], "Address is already an admin");

        isAdmin[_newAdmin] = true;
        isAdmin[owner] = false;
        owner = _newAdmin;

        emit AdminChanged(msg.sender, _newAdmin);
    }
}