abstract contract ERC721EnumerableOptimized is
  ERC721,
  IERC721Enumerable
{
  // Mapping from owner to list of owned token IDs
  mapping(address => mapping(uint256 => uint256)) private _ownedTokens;

  // Mapping from token ID to index of the owner tokens list
  mapping(uint256 => uint256) private _ownedTokensIndex;

  /**
   * @dev See {IERC165-supportsInterface}.
   */
  function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC721) returns (bool) {
    return interfaceId == type(IERC721Enumerable).interfaceId || super.supportsInterface(interfaceId);
  }

  /**
   * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
   */
  function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
    require(index < ERC721.balanceOf(owner), "ERC721Enumerable: owner index out of bounds");
    return _ownedTokens[owner][index];
  }

  /**
   * @dev See {IERC721Enumerable-totalSupply}.
   *
   *  As another aggressive gas cost optimization, we leave this to be implemented in the top-level
   *  minting contract.
   */
  function totalSupply() public view virtual override returns (uint256);

  /**
   * @dev See {IERC721Enumerable-tokenByIndex}.
   */
  function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
    require(index < totalSupply(), "ERC721Enumerable: global index out of bounds");
    return index + 1;
  }

  /**
   * @dev Hook that is called before any token transfer. This includes minting
   * and burning.
   *
   * Calling conditions:
   *
   * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
   * transferred to `to`.
   * - When `from` is zero, `tokenId` will be minted for `to`.
   * - We assume burning is not supported, so `to` cannot be the zero address.
   *
   * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
   */
  function _beforeTokenTransfer(
    address from,
    address to,
    uint256 tokenId
  ) internal virtual override {
    super._beforeTokenTransfer(from, to, tokenId);

    if (
      from != address(0) &&
      from != to
    ) {
      _removeTokenFromOwnerEnumeration(from, tokenId);
    }

    if (to != from) {
      _addTokenToOwnerEnumeration(to, tokenId);
    }
  }

  /**
   * @dev Private function to add a token to this extension's ownership-tracking data structures.
   * @param to address representing the new owner of the given token ID
   * @param tokenId uint256 ID of the token to be added to the tokens list of the given address
   */
  function _addTokenToOwnerEnumeration(address to, uint256 tokenId) private {
    uint256 length = ERC721.balanceOf(to);
    _ownedTokens[to][length] = tokenId;
    _ownedTokensIndex[tokenId] = length;
  }

  /**
   * @dev Private function to remove a token from this extension's ownership-tracking data structures. Note that
   * while the token is not assigned a new owner, the `_ownedTokensIndex` mapping is _not_ updated: this allows for
   * gas optimizations e.g. when performing a transfer operation (avoiding double writes).
   * This has O(1) time complexity, but alters the order of the _ownedTokens array.
   * @param from address representing the previous owner of the given token ID
   * @param tokenId uint256 ID of the token to be removed from the tokens list of the given address
   */
  function _removeTokenFromOwnerEnumeration(address from, uint256 tokenId) private {
    // To prevent a gap in from's tokens array, we store the last token in the index of the token to delete, and
    // then delete the last slot (swap and pop).

    uint256 lastTokenIndex = ERC721.balanceOf(from) - 1;
    uint256 tokenIndex = _ownedTokensIndex[tokenId];

    // When the token to delete is the last token, the swap operation is unnecessary
    if (tokenIndex != lastTokenIndex) {
      uint256 lastTokenId = _ownedTokens[from][lastTokenIndex];

      _ownedTokens[from][tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
      _ownedTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index
    }

    // This also deletes the contents at the last position of the array
    delete _ownedTokensIndex[tokenId];
    delete _ownedTokens[from][lastTokenIndex];
  }
}
/**
 * @title ERC721EnumerableOptimized
 * @author the-torn
 *
 * @notice Implementation of the ERC721Enumerable interface, gas-optimized for NFTs where:
 *   - Minting is sequential, beginning with token ID 1.
 *   - Burning is impossible.
 *
 *  IMPORTANT: Do not use this contract with NFTs where the above two conditions are not guaranteed.
 *
 *  Based on the OpenZeppelin ERC721Enumerable implementation (MIT license).
 *  https://github.com/OpenZeppelin/openzeppelin-contracts/blob/aefcb3e8aa4ee8da8e2b7022ffe4dcb57fbb0fdf/contracts/token/ERC721/extensions/ERC721Enumerable.sol
 */
function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
  require(index < ERC721.balanceOf(owner), "ERC721Enumerable: owner index out of bounds");
  return _ownedTokens[owner][index];
}

/**
 * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
 */