fix/confusing maths

src/DerolasAuction.sol

@@ -8,6 +8,8 @@ import {IBalancerVaultAdmin} from "./interfaces/IBalancerVaultAdmin.sol";
 
 import {SafeTransferLib} from "./libraries/SafeTransferLib.sol";
 
+error NoAvailableIncentiveBalance();
+
 /// @dev Round point struct.
 /// @notice Stores information about a specific round
 struct RoundPoint {
@@ -275,9 +277,11 @@ contract DerolasAuction {
         }
 
         // Calculate rewards
-        uint256 amount = (donation * roundPoints[claimRound].availableRewards) / totalRoundDonations;
+
         uint256 claimedAmount = roundToClaimed[claimRound][account];
-        return amount - claimedAmount;
+        if (claimedAmount > 0) return 0; // Already claimed
+        uint256 amount = (donation * roundPoints[claimRound].availableRewards) / totalRoundDonations;
+        return amount;
     }
 
     /// @dev Estimates ticket percentage.
@@ -307,8 +311,10 @@ contract DerolasAuction {
 
         uint256 curRound = currentRound;
         require(msg.value >= roundPoints[curRound].minDonation, "Donation amount is less than the minimum donation");
+        uint256 allocatedRewards = this.getAllocatedIncentives();
         require(
-            IToken(incentiveTokenAddress).balanceOf(address(this)) >= roundPoints[curRound].availableRewards,
+            IToken(incentiveTokenAddress).balanceOf(address(this))
+                >= roundPoints[curRound].availableRewards + allocatedRewards,
             "Not enough rewards to play the game"
         );
 
@@ -417,11 +423,31 @@ contract DerolasAuction {
     /// @dev withdraws the incentive token balance.
     /// @notice This function allows the owner to withdraw the incentive token balance from the contract.
     function withdrawIncentiveTokenBalance() external {
+        require(_locked == 1, "ReentrancyGuard");
+        _locked = 2;
+        // check what is promised to participants in the current round and the claim round
+        uint256 allocatedRewards = this.getAllocatedIncentives();
+
         require(msg.sender == owner, "Unauthorized account");
-        uint256 incentiveBalance = IToken(incentiveTokenAddress).balanceOf(address(this));
-        require(incentiveBalance > 0, "No incentive token balance to withdraw");
+        uint256 incentiveBalance = IToken(incentiveTokenAddress).balanceOf(address(this)) - allocatedRewards;
+        if (incentiveBalance == 0) revert NoAvailableIncentiveBalance();
         SafeTransferLib.safeTransfer(incentiveTokenAddress, owner, incentiveBalance);
         emit TopUpIncentiveWithdrawn(incentiveBalance);
+        _locked = 1;
+    }
+
+    /// @dev gets allocated Incentives
+    /// @return allocatedRewards Allocated rewards.
+    function getAllocatedIncentives() external view returns (uint256 allocatedRewards) {
+        uint256 curRound = currentRound;
+        uint256 claimRound = curRound - 1;
+
+        if (roundPoints[claimRound].totalDonated > 0) {
+            allocatedRewards += roundPoints[claimRound].availableRewards;
+        }
+        if (roundPoints[curRound].totalDonated > 0) {
+            allocatedRewards += roundPoints[curRound].availableRewards;
+        }
     }
 
     /// @dev Gets service multisig nonces.

test/DerolasAuction.t.sol

@@ -2,7 +2,7 @@
 pragma solidity ^0.8.30;
 
 import {Test} from "lib/forge-std/src/Test.sol";
-import {DerolasAuction, GameState} from "src/DerolasAuction.sol";
+import {DerolasAuction, GameState, NoAvailableIncentiveBalance} from "src/DerolasAuction.sol";
 import {IToken} from "src/interfaces/IToken.sol";
 import {IBalancerVaultAdmin} from "src/interfaces/IBalancerVaultAdmin.sol";
 
@@ -321,7 +321,7 @@ contract TestDerolasAuctionContract is Test {
 
     function testCanWithdrawIncentiveBalance() public {
         // Check that the owner can withdraw incentives
-        vm.expectRevert("No incentive token balance to withdraw");
+        vm.expectRevert(NoAvailableIncentiveBalance.selector);
         c.withdrawIncentiveTokenBalance();
 
         this.testTopupIncentivesBalance(); // Ensure incentives are topped up