31. Pausable pattern

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Pausable {
    address public owner = msg.sender;
    bool public paused;
    modifier onlyOwner() { require(msg.sender == owner); _; }
    // TODO whenNotPaused modifier
    function pause() external onlyOwner { /* TODO */ }
    function unpause() external onlyOwner { /* TODO */ }
}