prevent discount rate manipulation

src/TermDiscountRateAdapter.sol

@@ -4,22 +4,27 @@ pragma solidity ^0.8.18;
 import {ITermDiscountRateAdapter} from "./interfaces/term/ITermDiscountRateAdapter.sol";
 import {ITermController, AuctionMetadata} from "./interfaces/term/ITermController.sol";
 import {ITermRepoToken} from "./interfaces/term/ITermRepoToken.sol";
+import "@openzeppelin/contracts-upgradeable/contracts/access/AccessControlUpgradeable.sol";
 
 /**
  * @title TermDiscountRateAdapter
  * @notice Adapter contract to retrieve discount rates for Term repo tokens
  * @dev This contract implements the ITermDiscountRateAdapter interface and interacts with the Term Controller
  */
-contract TermDiscountRateAdapter is ITermDiscountRateAdapter {
+contract TermDiscountRateAdapter is ITermDiscountRateAdapter, AccessControlUpgradeable {
+    bytes32 public constant ADMIN_ROLE = keccak256("ADMIN_ROLE");
+
     /// @notice The Term Controller contract
     ITermController public immutable TERM_CONTROLLER;
+    mapping(address => mapping (bytes32 => bool)) public rateInvalid;
 
     /**
      * @notice Constructor to initialize the TermDiscountRateAdapter
      * @param termController_ The address of the Term Controller contract
      */
-    constructor(address termController_) {
+    constructor(address termController_, address adminWallet_) {
         TERM_CONTROLLER = ITermController(termController_);
+        _grantRole(ADMIN_ROLE, adminWallet_);
     }
 
     /**
@@ -33,8 +38,51 @@ contract TermDiscountRateAdapter is ITermDiscountRateAdapter {
         (AuctionMetadata[] memory auctionMetadata, ) = TERM_CONTROLLER.getTermAuctionResults(ITermRepoToken(repoToken).termRepoId());
 
         uint256 len = auctionMetadata.length;
-        require(len > 0);
+        require(len > 0, "No auctions found");
+
+        if (len > 1) {
+            uint256 latestAuctionTime = auctionMetadata[len - 1].auctionClearingBlockTimestamp;
+            if ((block.timestamp - latestAuctionTime) < 30 minutes) {
+                for (int256 i = int256(len) - 1; i >= 0; i--) {
+                    if (!rateInvalid[repoToken][auctionMetadata[uint256(i)].termAuctionId]) {
+                        return auctionMetadata[uint256(i)].auctionClearingRate;
+                    }
+                }
+                revert("No valid auction rate found within the last 30 minutes");
+            }
+        }
+
+        require(!rateInvalid[repoToken][auctionMetadata[0].termAuctionId], "Most recent auction rate is invalid");
+        return auctionMetadata[0].auctionClearingRate;
+    }
+
+    /**
+    * @notice Invalidates the result of a specific auction for a given repo token
+    * @dev This function is used to mark auction results as invalid, typically in cases of suspected manipulation
+    * @param repoToken The address of the repo token associated with the auction
+    * @param termAuctionId The unique identifier of the term auction to be invalidated
+    * @custom:access Restricted to accounts with the ADMIN_ROLE
+    */
+    function invalidateAuctionResult(address repoToken, bytes32 termAuctionId) external onlyRole(ADMIN_ROLE) {
+        // Fetch the auction metadata for the given repo token
+        (AuctionMetadata[] memory auctionMetadata, ) = TERM_CONTROLLER.getTermAuctionResults(ITermRepoToken(repoToken).termRepoId());
+
+        // Check if the termAuctionId exists in the metadata
+        bool auctionExists = false;
+        for (uint256 i = 0; i < auctionMetadata.length; i++) {
+            if (auctionMetadata[i].termAuctionId == termAuctionId) {
+                auctionExists = true;
+                break;
+            }
+        }
+
+        // Revert if the auction doesn't exist
+        require(auctionExists, "Auction ID not found in metadata");
+
+        // Check if the rate is already invalidated
+        require(!rateInvalid[repoToken][termAuctionId], "Rate already invalidated");
 
-        return auctionMetadata[len - 1].auctionClearingRate;
+        // Invalidate the rate
+        rateInvalid[repoToken][termAuctionId] = true;
     }
 }