claim and reserve test

claimReserve.sol

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

import '@openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol';
import '@openzeppelin/contracts/access/Ownable.sol';

contract Reserve is ERC721Enumerable, Ownable {

    string _baseTokenURI;
    uint256 private _price = 0.04 ether;
    mapping(address => uint256) public claimMap;

    constructor(string memory baseURI) ERC721("Reserve", "R")  {
        setBaseURI(baseURI);
    }

    // pay at the point of reserving
    // should stop ppl reserving and never claiming
    function reserve(uint256 num) public payable {
        require(num < 21,                       "You can adopt a maximum of 20");
        require(msg.value >= _price * num,      "Ether sent is not correct");
        claimMap[msg.sender] += num;
    }

    // limit claim to help prevent gassing out
    function claim(uint256 num) public {
        uint256 supply = totalSupply();
        uint256 claimCount = claimMap[msg.sender];

        require(num >= claimCount,              "Cant claim more than you own");
        require(num < 21,                       "You can claim a maximum of 20");

        for (uint256 i; i < claimCount; i++) {
            _safeMint(msg.sender, supply + i);
        }

        // account for the claim
        claimMap[msg.sender] -= num;
    }

    // standard minting
    function adopt(uint256 num) public payable {
        uint256 supply = totalSupply();
        require(num < 21,                       "You can adopt a maximum of 20");
        require(msg.value >= _price * num,      "Ether sent is not correct");

        for (uint256 i; i < num; i++) {
            _safeMint(msg.sender, supply + i);
        }
    }

    function _baseURI() internal view virtual override returns (string memory) {
        return _baseTokenURI;
    }

    function setBaseURI(string memory baseURI) public onlyOwner {
        _baseTokenURI = baseURI;
    }

    function getReservedCount() public view returns (uint256){
        return claimMap[msg.sender];
    }
}

Code is not fully unit tested. Just a small experiment based on this tweet
https://twitter.com/0xfoobar/status/1434574225214296065