NFT.sol

pragma solidity ^0.7.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract NFT is ERC721 {
  
  uint _tokenCounter;
  mapping (uint => uint) public itemValue;
  uint maxValue = 10000; // Max value of an item

  constructor() ERC721("Super NFT", "SPRNFT") {}

  /**
    Returns an random number
  */
  function random() private view returns (uint) { 
        return uint(keccak256(abi.encodePacked(block.difficulty, block.timestamp, block.number)));
  }

  function myItems() external view returns (uint[] memory items) {
    // Returns an array of items that the user owns
    items = new uint[](balanceOf(msg.sender));
    uint _counter = 0;
    for(uint i = 1; i < _tokenCounter; i++) { // i = 1 because the token counter is increased before the id is assigned
      if(ownerOf(i) == msg.sender) { // if the user owns the item
        items[_counter] = i; // add the item to the array
        _counter++; // increase the counter
      }
    }
    return items;
  }

  function getItem() payable public returns (uint256) {
    require(msg.value == 0.5 ether); // 0.5 AVAX is the cost of an item
    uint256 newItemId = _tokenCounter; // Get the current counter value
    _tokenCounter++; // Increase the counter
    _mint(msg.sender, newItemId); // Mint the new item to the player
    itemValue[newItemId] = random() % maxValue; // Set the item value to a random number modulus used to make sure that the value isn't bigger than maxValue
    return newItemId; // Return the new item id
  }
}