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

contract DataStorage {
    mapping(address => string) public storedData;
    mapping(string => bool) private dataExists;
    address public admin;

    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);

    constructor() {
        admin = msg.sender;
    }

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

    function setData(string memory _data) public {
        require(bytes(_data).length <= 9, "Data length exceeds 9 characters");
        require(!dataExists[_data], "Data already exists");

        storedData[msg.sender] = _data;
        dataExists[_data] = true;

        emit DataStored(msg.sender, _data);
    }

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

    function transferToNewContract(address _newContract) public onlyAdmin {
        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 onlyAdmin {
        require(_newAdmin != address(0), "Invalid admin address");
        emit AdminChanged(admin, _newAdmin);
        admin = _newAdmin;
    }
}