feat: add support for fetching purchased tokenID

src/DeployDataset.sol

@@ -37,6 +37,10 @@ contract DatasetToken is ERC1155, Ownable, ReentrancyGuard {
     // The Bonding Curve contract
     DatasetBondingCurve public bondingCurve;
 
+    // Mapping to track purchased tokens by address
+    mapping(address => uint256[]) private _purchasedTokens;
+    mapping(address => mapping(uint256 => bool)) private _hasPurchased;
+
     // Events
     event DatasetTokenMinted(
         address[] owners,
@@ -169,6 +173,10 @@ contract DatasetToken is ERC1155, Ownable, ReentrancyGuard {
      */
     function purchaseDataset(uint256 tokenId) external payable nonReentrant {
         require(isListed[tokenId], "Dataset is not listed for sale");
+        require(
+            !_hasPurchased[msg.sender][tokenId],
+            "Already purchased this dataset"
+        );
         uint256 currentPrice = bondingCurve.getCurrentPrice(tokenId);
         require(msg.value == currentPrice, "Incorrect payment amount");
 
@@ -188,6 +196,10 @@ contract DatasetToken is ERC1155, Ownable, ReentrancyGuard {
             require(success, "Payment transfer failed");
         }
 
+        // Record the purchase
+        _purchasedTokens[msg.sender].push(tokenId);
+        _hasPurchased[msg.sender][tokenId] = true;
+
         // Record the purchase in the bonding curve
         bondingCurve.recordPurchase(tokenId);
 
@@ -202,6 +214,30 @@ contract DatasetToken is ERC1155, Ownable, ReentrancyGuard {
         emit DatasetPurchased(tokenId, msg.sender, sellers, amounts);
     }
 
+    /**
+     * @dev Get all token IDs purchased by an address
+     * @param buyer The address to check
+     * @return tokens Array of token IDs purchased by the buyer
+     */
+    function getPurchasedTokens(
+        address buyer
+    ) public view returns (uint256[] memory tokens) {
+        return _purchasedTokens[buyer];
+    }
+
+    /**
+     * @dev Check if an address has purchased a specific token
+     * @param buyer The address to check
+     * @param tokenId The token ID to check
+     * @return bool True if the address has purchased the token
+     */
+    function hasPurchased(
+        address buyer,
+        uint256 tokenId
+    ) external view returns (bool) {
+        return _hasPurchased[buyer][tokenId];
+    }
+
     /**
      * @dev Get token IDs by tag
      */

test/DatasetToken.t.sol

@@ -385,4 +385,78 @@ contract DatasetTokenTest is Test {
             "Price should increase by 1.5x after purchase"
         );
     }
+
+    function test_PurchaseTracking() public {
+        // First mint a token
+        vm.startPrank(owner);
+        datasetToken.mintDatasetToken(
+            shares,
+            DATASET_NAME,
+            DATASET_DESC,
+            CONTENT_HASH,
+            IPFS_HASH,
+            PRICE,
+            TAGS
+        );
+
+        // Mint a second token
+        datasetToken.mintDatasetToken(
+            shares,
+            "Second Dataset",
+            DATASET_DESC,
+            CONTENT_HASH,
+            IPFS_HASH,
+            PRICE,
+            TAGS
+        );
+        vm.stopPrank();
+
+        // Purchase first token with user3
+        vm.startPrank(user3);
+        vm.deal(user3, PRICE * 2);
+        datasetToken.purchaseDataset{value: PRICE}(0);
+
+        // Verify purchase tracking
+        uint256[] memory purchasedTokens = datasetToken.getPurchasedTokens(
+            user3
+        );
+        assertEq(purchasedTokens.length, 1, "Should have one purchased token");
+        assertEq(purchasedTokens[0], 0, "Should have purchased token 0");
+        assertTrue(
+            datasetToken.hasPurchased(user3, 0),
+            "Should have purchased token 0"
+        );
+        assertFalse(
+            datasetToken.hasPurchased(user3, 1),
+            "Should not have purchased token 1"
+        );
+
+        // Purchase second token
+        datasetToken.purchaseDataset{value: PRICE}(1);
+
+        // Verify updated purchase tracking
+        purchasedTokens = datasetToken.getPurchasedTokens(user3);
+        assertEq(purchasedTokens.length, 2, "Should have two purchased tokens");
+        assertEq(purchasedTokens[0], 0, "First purchase should be token 0");
+        assertEq(purchasedTokens[1], 1, "Second purchase should be token 1");
+        assertTrue(
+            datasetToken.hasPurchased(user3, 0),
+            "Should have purchased token 0"
+        );
+        assertTrue(
+            datasetToken.hasPurchased(user3, 1),
+            "Should have purchased token 1"
+        );
+        vm.stopPrank();
+
+        // Verify no purchases for other users
+        uint256[] memory user1Purchases = datasetToken.getPurchasedTokens(
+            user1
+        );
+        assertEq(user1Purchases.length, 0, "User1 should have no purchases");
+        assertFalse(
+            datasetToken.hasPurchased(user1, 0),
+            "User1 should not have purchased token 0"
+        );
+    }
 }