feat(contracts): add tokenIdCounter to SBTTokens

Author: Yash Agrawal

contracts/SBT.sol

@@ -13,6 +13,8 @@ contract SBT is ISBT, ERC721EnumerableUpgradeable {
 
 	/// @dev EOA with rights to allow(add)/disallow(remove) minter.
 	address private _minterUpdater;
+	/// @dev The counter to mint new NFTs and track supply.
+	uint256 private _tokenIdCounter;
 
 	/// @dev EOA with minting rights.
 	mapping(address => bool) private _minters;
@@ -96,6 +98,13 @@ contract SBT is ISBT, ERC721EnumerableUpgradeable {
 		return currentId;
 	}
 
+	/**
+	 * @dev See {IERC721Enumerable-totalSupply}.
+	 */
+	function totalSupply() public view override returns (uint256) {
+		return _tokenIdCounter;
+	}
+
 	function _tokenURI(uint256 tokenId) private view returns (string memory) {
 		require(tokenId < currentIndex(), "Token not found");