Smart Contract

//SPDX-License-Identifier: UNLICENSED pragma solidity ^0.8.7;

contract NftTokenMint {

  address public minter;

  //Mappings
  // TokenId to Address
  mapping(uint256=>address) public tokenOwner;

  //Address to NFT Total
  mapping(address=>uint256) public ownedTokensBalance;

  //Events
  event Sent(address from, address to, uint256 tokenId);

  //Setting up the contract creator has a unique minter;
  constructor() {
      minter = msg.sender;
  }

  // Aux function to control if token already exists in mapping of this contract.
  function _exists(uint256 tokenId) public view returns(bool) {
      address owner = tokenOwner[tokenId];

      return owner != address(0);
  }

  // Function to mint a NFT anexing a owner to this token and adding a balance to address sender
  function mint(uint256 tokenId) public {
      require(!_exists(tokenId), "ERROR: Token already exist!");
      require(msg.sender == minter, "ERROR: You are not a minter!");

      tokenOwner[tokenId] = msg.sender;
      ownedTokensBalance[msg.sender] += 1;

  }

  // Function to check addres of token owner
  function _ownerOf(uint256 tokenId) internal view returns(address) {
      address owner = tokenOwner[tokenId];
      require(owner != address(0), "ERROR: Invalid token!");

      return owner;
  }

  // Functino to send a NFT to other owner
  function send(address receiver, uint256 tokenId) public {
      require(_ownerOf(tokenId) == msg.sender);
      require(receiver != address(0), "ERROR: Wrong receiver!");

      tokenOwner[tokenId] = receiver;
      ownedTokensBalance[receiver] += 1;
      ownedTokensBalance[msg.sender] -= 1;

      emit Sent(msg.sender, receiver, tokenId);
  }

}