This contract implement ERC721 for KBPsystem's NFT collection. This includes several functions like setting the URI, withdrawal of contract funds and checking if available contract funds

KBPsystemNFT.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.2;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";

/***
* @title KBPsystem NFT contract
* @author Koleen BP
* @notice This contracts handles the NFT implementation for KBPsystem NFT collections
*/
contract KBPPunk is ERC721, ERC721Enumerable, ERC721URIStorage, Ownable {
    using Counters for Counters.Counter;

    Counters.Counter private _tokenIdCounter;
    uint256 public mintRate = 0.01 ether;
    uint public MAX_SUPPLY = 10000;

    constructor() ERC721("KBP-Punk", "KBPNFT") {}

    function _baseURI() internal pure override returns (string memory) {
        return "https://gateway.pinata.cloud/ipfs/QmYpwYV3V9nFQLt524A5JuL7NgHCzvLHCA5sqjgVd1xSdz/";
    }

   function _burn(uint256 tokenId) internal override(ERC721, ERC721URIStorage) {
        super._burn(tokenId);
    }

        function tokenURI(uint256 tokenId)
        public
        view
        override(ERC721, ERC721URIStorage)
        returns (string memory)
    {
        return super.tokenURI(tokenId);
    }

    function safeMint(address to, string memory uri) public payable returns (uint256){
        require(totalSupply() <= MAX_SUPPLY, "Allowable number of NFTs has been met.");
        require(msg.value > mintRate, "Ether sent is not enough to mint NFT");
        _tokenIdCounter.increment();
        uint256 tokenId = _tokenIdCounter.current();

        _safeMint(to, tokenId);
        _setTokenURI(tokenId, uri);
        return tokenId;
    }

    // @notice Withdraw function. This will withdraw all the funds from the contract from the minting
     function withdraw() public onlyOwner {
        require(address(this).balance > 0, "Contract Balance: 0; Nothing to withdraw here!");
        payable(owner()).transfer(address(this).balance);
    }


    // @notice Fetched the current contract balance or total ethers sent to this contract 
    function getContractBalance() public view returns(uint256) {
        return address(this).balance;
    }

    // The following functions are overrides required by Solidity.

    function _beforeTokenTransfer(address from, address to, uint256 tokenId)
        internal
        override(ERC721, ERC721Enumerable)
    {
        super._beforeTokenTransfer(from, to, tokenId);
    }

    function supportsInterface(bytes4 interfaceId)
        public
        view
        override(ERC721, ERC721Enumerable)
        returns (bool)
    {
        return super.supportsInterface(interfaceId);
    }
    
}