invoices: refactor cancelHTLCs to apply all updates in one place

This commit changes cancelHTLCs such that all updates are gathered and
applied in the same function. This is part of a larger refactor to
gather all invoice changes later to be used in the invoice updater.

invoices/update_invoice.go

@@ -126,7 +126,30 @@ func cancelHTLCs(invoice *Invoice, updateTime time.Time,
 		// Tally this into the set of HTLCs that need to be updated on
 		// disk, but once again, only if this is an AMP invoice.
 		if invoice.IsAMP() {
-			cancelHtlcsAmp(invoice, htlcsAmpUpdate, htlc, key)
+			// Process the cancellation of the HTLC that belongs to
+			// an AMP HTLC set. We'll need to update the meta data
+			// in the  main invoice, and also apply the new update
+			// to the update map.
+
+			setID := htlc.AMP.Record.SetID()
+			// First, we'll update the state of the entire HTLC set
+			// to cancelled.
+			newAmpState := getUpdatedInvoiceAmpState(
+				invoice, setID, key, HtlcStateCanceled,
+				htlc.Amt,
+			)
+
+			invoice.AMPState[setID] = newAmpState
+
+			// We'll only decrement the total amount paid if the
+			// invoice was already in the accepted state.
+			if invoice.AmtPaid != 0 {
+				invoice.AmtPaid -= htlc.Amt
+			}
+
+			applyCancelHtlcsAmp(
+				invoice, setID, key, htlc, htlcsAmpUpdate,
+			)
 		}
 	}
 
@@ -582,24 +605,12 @@ func getUpdatedInvoiceAmpState(invoice *Invoice, setID SetID,
 	return ampState
 }
 
-// cancelHtlcsAmp processes a cancellation of an HTLC that belongs to an AMP
-// HTLC set. We'll need to update the meta data in the  main invoice, and also
-// apply the new update to the update MAP, since all the HTLCs for a given HTLC
-// set need to be written in-line with each other.
-func cancelHtlcsAmp(invoice *Invoice,
-	updateMap map[SetID]map[models.CircuitKey]*InvoiceHTLC,
-	htlc *InvoiceHTLC, circuitKey models.CircuitKey) {
-
-	setID := htlc.AMP.Record.SetID()
-
-	// First, we'll update the state of the entire HTLC set
-	// to cancelled.
-	newAmpState := getUpdatedInvoiceAmpState(
-		invoice, setID, circuitKey, HtlcStateCanceled,
-		htlc.Amt,
-	)
-
-	invoice.AMPState[setID] = newAmpState
+// applyCancelHtlcsAmp applies the cancellation update to the update map, since
+// all the HTLCs for a given HTLC set need to be written in-line with each
+// other.
+func applyCancelHtlcsAmp(invoice *Invoice, setID [32]byte,
+	circuitKey models.CircuitKey, htlc *InvoiceHTLC,
+	updateMap map[SetID]map[models.CircuitKey]*InvoiceHTLC) {
 
 	if _, ok := updateMap[setID]; !ok {
 		// Only HTLCs in the accepted state, can be cancelled, but we
@@ -620,12 +631,6 @@ func cancelHtlcsAmp(invoice *Invoice,
 	// Finally, include the newly cancelled HTLC in the set of HTLCs we
 	// need to cancel.
 	updateMap[setID][circuitKey] = htlc
-
-	// We'll only decrement the total amount paid if the invoice was
-	// already in the accepted state.
-	if invoice.AmtPaid != 0 {
-		invoice.AmtPaid -= htlc.Amt
-	}
 }
 
 // canCancelSingleHtlc validates cancellation of a single HTLC. If nil is