f: fix underflow

Author: matiasedgeandnode

packages/horizon/contracts/interfaces/IRecurringCollector.sol

@@ -259,6 +259,14 @@ interface IRecurringCollector is IAuthorizable, IPaymentsCollector {
      */
     error RecurringCollectorInvalidCollectData(bytes invalidData);
 
+    /**
+     * Thrown when calling collect() on a payer canceled agreement
+     * where the final collection has already been done
+     * @param agreementId The agreement ID
+     * @param finalCollectionAt The timestamp when the final collection was done
+     */
+    error RecurringCollectorFinalCollectionDone(bytes16 agreementId, uint256 finalCollectionAt);
+
     /**
      * Thrown when interacting with an agreement that has an incorrect state
      * @param agreementId The agreement ID

packages/horizon/contracts/payments/collectors/RecurringCollector.sol

@@ -340,10 +340,13 @@ contract RecurringCollector is EIP712, GraphDirectory, Authorizable, IRecurringC
         bytes16 _agreementId,
         uint256 _tokens
     ) private view returns (uint256) {
-        uint256 collectionSeconds = _agreement.state == AgreementState.CanceledByPayer
+        // if canceled by the payer allow collection up to the cancelation time
+        uint256 collectionEnd = _agreement.state == AgreementState.CanceledByPayer
             ? _agreement.canceledAt
             : block.timestamp;
-        collectionSeconds -= _agreementCollectionStartAt(_agreement);
+        uint256 collectionStart = _agreementCollectionStartAt(_agreement);
+        require(collectionEnd > collectionStart, RecurringCollectorFinalCollectionDone(_agreementId, collectionStart));
+        uint256 collectionSeconds = collectionEnd - collectionStart;
         require(
             collectionSeconds >= _agreement.minSecondsPerCollection,
             RecurringCollectorCollectionTooSoon(

packages/horizon/test/unit/payments/recurring-collector/collect.t.sol

@@ -142,7 +142,7 @@ contract RecurringCollectorCollectTest is RecurringCollectorSharedTest {
         vm.prank(accepted.rca.dataService);
         _recurringCollector.collect(IGraphPayments.PaymentTypes.IndexingFee, data);
 
-        uint256 collectionSeconds = boundSkipCeil(unboundedCollectionSeconds, accepted.rca.minSecondsPerCollection - 1);
+        uint256 collectionSeconds = boundSkip(unboundedCollectionSeconds, 1, accepted.rca.minSecondsPerCollection - 1);
         skip(collectionSeconds);
 
         IRecurringCollector.CollectParams memory collectParams = _generateCollectParams(