// SPDX-License-Identifier: MIT
pragma solidity ^0.8.21;

import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/Pausable.sol";

// Multi-Factor Authentication (MFA) Contract
contract MFA is Ownable, Pausable {
    using ECDSA for bytes32;

    mapping(address => string) public userSecrets;
    mapping(address => uint256) public lastVerificationTimestamp;

    event SecretSet(address indexed user, string secret);
    event VerificationAttempt(address indexed user, bool success);

    constructor() Ownable() Pausable() {}

    function setSecret(string memory secret) external onlyOwner whenNotPaused {
        userSecrets[msg.sender] = secret;
        emit SecretSet(msg.sender, secret);
    }

    function generateTOTPCode(uint256 timestamp) internal view returns (uint256) {
        require(bytes(userSecrets[msg.sender]).length > 0, "MFA secret not set");

        bytes32 key = keccak256(abi.encodePacked(userSecrets[msg.sender]));
        bytes32 data = keccak256(abi.encodePacked(timestamp / 30)); // 30 seconds interval
        bytes memory signature = ECDSA.toEthSignedMessageHash(data).recover(key);

        uint256 totpCode = uint256(uint8(signature[19])) & 0x0F;
        totpCode = (totpCode << 8) | uint256(uint8(signature[20]));
        totpCode = (totpCode << 8) | uint256(uint8(signature[21]));
        totpCode = (totpCode << 8) | uint256(uint8(signature[22]));
        totpCode = totpCode % 1000000; // 6-digit code

        return totpCode;
    }

    function verifyCode(uint256 code) external view returns (bool) {
        uint256 currentTimestamp = block.timestamp;
        uint256 previousTimestamp = currentTimestamp - 30; // Consider a 30-second window

        // Verify the current and previous TOTP codes
        bool success = (code == generateTOTPCode(currentTimestamp) || code == generateTOTPCode(previousTimestamp));

        emit VerificationAttempt(msg.sender, success);

        // Update last verification timestamp
        lastVerificationTimestamp[msg.sender] = currentTimestamp;

        return success;
    }

    // Additional functions can be added for enhanced MFA features

    // Pause and unpause functions for emergency situations
    function pauseContract() external onlyOwner {
        _pause();
    }

    function unpauseContract() external onlyOwner {
        _unpause();
    }
}