ENS с проверками

ens_domen.sol

pragma solidity ^0.8.0;  
//SPDX-License-Identifier: GPL-3.0 

contract EnsDomen {

  constructor() {
    owner = msg.sender;
  }

  receive() external payable {}
  fallback() external {}

  modifier checkOwner() {
    require(msg.sender == owner, 'You are not the owner!');
    _;
  }

  modifier checkPeriod(uint _period) {
    require(_period < 11 && _period >  0, 'Unsupported period!');
    _;
  }

  address internal owner;
  uint public priceOneYear = 100;
  uint public coefficient = 2;

  function setPrice(uint _price) public checkOwner {
    priceOneYear = _price;
  }

  function setCoefficient(uint _coefficient) public checkOwner {
    coefficient = _coefficient;
  }

  struct Domen {
    uint timestamp;
    uint amount;
    address addr;
    uint period;
  }
  
  mapping(string => Domen) public domenStructure;

  function createDomen(string memory _name, uint _period) public payable checkPeriod(_period) {
    require(msg.value == (priceOneYear * _period), 'Wrong amount!');
    if (domenStructure[_name].amount != 0) {
        if (!checkExpire(_name)) {
          revert("Domen is busy");
        }
    }
    Domen memory domen = Domen(block.timestamp, msg.value, msg.sender, _period);
    domenStructure[_name] = domen;
  }

  function viewDomen(string memory _name) public view returns(address) {
    return domenStructure[_name].addr;
  }

  function renewDomen(string memory _name, uint _period) public payable checkPeriod(_period) {
    require(msg.sender == domenStructure[_name].addr, 'You are not the domen owner!');
    require(msg.value == (priceOneYear * _period * coefficient), 'Wrong amount!');
    domenStructure[_name].amount += msg.value;
    domenStructure[_name].period += _period;
  }

  function withdrawMoney(address payable _to) public checkOwner {
    _to.transfer(address(this).balance);
  }

  function checkExpire(string memory _name) public view returns(bool) {
    uint _periodDifference = block.timestamp - domenStructure[_name].timestamp;
    bool isExpired = _periodDifference > domenStructure[_name].period * 365*24*60*60;
    return isExpired;
  }

}