add getter to get last payment Id made in the system

contracts/CreditStation.sol

@@ -196,6 +196,12 @@ contract CreditStation is AccessManaged, Pausable, IVersioned, ICreditStation {
         return _paymentsByUser.length(user);
     }
 
+    /// @notice Gets the last paymentId made in the system
+    /// @return paymentId returns the last payment ID made in the system
+    function getLastPaymentId() external view override returns (PaymentId paymentId) {
+        return _previous(_nextPaymentId);
+    }
+
     /// @notice Gets the last payment made by a user
     /// @param user The address of the buyer
     /// @return paymentId returns the last payment ID if there is one, reverts otherwise
@@ -280,4 +286,11 @@ contract CreditStation is AccessManaged, Pausable, IVersioned, ICreditStation {
     function _next(PaymentId id) private pure returns (PaymentId next) {
         return PaymentId.wrap(PaymentId.unwrap(id) + 1);
     }
+
+    /// @notice Get payment ID previous before the provided one
+    /// @param id The payment ID
+    /// @return previous The previous payment ID
+    function _previous(PaymentId id) private pure returns (PaymentId previous) {
+        return PaymentId.wrap(PaymentId.unwrap(id) - 1);
+    }
 }

contracts/interfaces/ICreditStation.sol

@@ -66,6 +66,9 @@ interface ICreditStation {
     function getLastPayment(
         address user
     ) external view returns (PaymentId paymentId);
+    /// @notice Gets the last paymentId made in the system
+    /// @return paymentId returns the last payment ID made in the system
+    function getLastPaymentId() external view returns (PaymentId paymentId);
     /// @notice Gets the payment IDs made by a user within a specific range (MAX 10_000 each query)
     /// @param user The address of the buyer
     /// @param startIndex The start index (inclusive) of the payments to get

test/CreditStation.ts

@@ -76,6 +76,8 @@ describe("CreditStation", () => {
             creditStation,
             "InvalidIndices"
         );
+
+        await creditStation.getLastPaymentId().should.eventually.be.equal(2n);
     });
 
     it("should revert when getting non-existing payment info", async () => {