add: ERC721Enumerable Interfaces (#196)

Author: KukretiShubham

contracts/interfaces/ISTokensManager.sol

@@ -183,4 +183,25 @@ interface ISTokensManager {
 	 * @return uint256 current token id
 	 */
 	function currentIndex() external view returns (uint256);
+
+	/// @notice Count NFTs tracked by this contract
+    /// @return A count of valid NFTs tracked by this contract, where each one of
+    ///  them has an assigned and queryable owner not equal to the zero address
+    function totalSupply() external view returns (uint256);
+
+	/// @notice Enumerate valid NFTs
+    /// @dev Throws if `_index` >= `totalSupply()`.
+    /// @param _index A counter less than `totalSupply()`
+    /// @return The token identifier for the `_index`th NFT,
+    ///  (sort order not specified)
+    function tokenByIndex(uint256 _index) external view returns (uint256);
+
+	/// @notice Enumerate NFTs assigned to an owner
+    /// @dev Throws if `_index` >= `balanceOf(_owner)` or if
+    ///  `_owner` is the zero address, representing invalid NFTs.
+    /// @param _owner An address where we are interested in NFTs owned by them
+    /// @param _index A counter less than `balanceOf(_owner)`
+    /// @return The token identifier for the `_index`th NFT assigned to `_owner`,
+    ///   (sort order not specified)
+    function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);
 }

contracts/interfaces/ISTokensManagerV2.sol

@@ -172,4 +172,25 @@ interface ISTokensManagerV2 is ISTokensManagerStruct {
 	 * @return uint256 current token id
 	 */
 	function currentIndex() external view returns (uint256);
+
+	/// @notice Count NFTs tracked by this contract
+    /// @return A count of valid NFTs tracked by this contract, where each one of
+    ///  them has an assigned and queryable owner not equal to the zero address
+    function totalSupply() external view returns (uint256);
+
+	/// @notice Enumerate valid NFTs
+    /// @dev Throws if `_index` >= `totalSupply()`.
+    /// @param _index A counter less than `totalSupply()`
+    /// @return The token identifier for the `_index`th NFT,
+    ///  (sort order not specified)
+    function tokenByIndex(uint256 _index) external view returns (uint256);
+
+	/// @notice Enumerate NFTs assigned to an owner
+    /// @dev Throws if `_index` >= `balanceOf(_owner)` or if
+    ///  `_owner` is the zero address, representing invalid NFTs.
+    /// @param _owner An address where we are interested in NFTs owned by them
+    /// @param _index A counter less than `balanceOf(_owner)`
+    /// @return The token identifier for the `_index`th NFT assigned to `_owner`,
+    ///   (sort order not specified)
+    function tokenOfOwnerByIndex(address _owner, uint256 _index) external view returns (uint256);
 }