chore: some minor improvements to GraphPayments and tests

Signed-off-by: Tomás Migone <[email protected]>

Author: tmigone

Diff for: packages/horizon/contracts/interfaces/IGraphPayments.sol

@@ -57,9 +57,10 @@ interface IGraphPayments {
     /**
      * @notice Collects funds from a payer.
      * It will pay cuts to all relevant parties and forward the rest to the receiver.
+     * Note that the collected amount can be zero.
      * @param paymentType The type of payment as defined in {IGraphPayments}
      * @param receiver The address of the receiver
-     * @param tokens The amount of tokens being collected
+     * @param tokens The amount of tokens being collected.
      * @param dataService The address of the data service
      * @param dataServiceCut The data service cut in PPM
      */

Diff for: packages/horizon/contracts/payments/GraphPayments.sol

@@ -23,6 +23,8 @@ import { GraphDirectory } from "../utilities/GraphDirectory.sol";
 contract GraphPayments is Initializable, MulticallUpgradeable, GraphDirectory, IGraphPayments {
     using TokenUtils for IGraphToken;
     using PPMMath for uint256;
+
+    /// @notice Protocol payment cut in PPM
     uint256 public immutable PROTOCOL_PAYMENT_CUT;
 
     /**

Diff for: packages/horizon/test/payments/GraphPayments.t.sol

@@ -291,4 +291,33 @@ contract GraphPaymentsTest is HorizonStakingSharedTest {
         );
         vm.stopPrank();
     }
+
+    function testCollect_ViaMulticall(uint256 amount) public useIndexer {
+        amount = bound(amount, 1, MAX_STAKING_TOKENS / 2); // Divide by 2 as we'll make two calls
+
+        address escrowAddress = address(escrow);
+        mint(escrowAddress, amount * 2);
+        vm.startPrank(escrowAddress);
+        approve(address(payments), amount * 2);
+
+        bytes[] memory data = new bytes[](2);
+        data[0] = abi.encodeWithSelector(
+            payments.collect.selector,
+            IGraphPayments.PaymentTypes.QueryFee,
+            users.indexer,
+            amount,
+            subgraphDataServiceAddress,
+            100_000 // 10%
+        );
+        data[1] = abi.encodeWithSelector(
+            payments.collect.selector,
+            IGraphPayments.PaymentTypes.IndexingFee,
+            users.indexer,
+            amount,
+            subgraphDataServiceAddress,
+            200_000 // 20%
+        );
+
+        payments.multicall(data);
+    }
 }