accounts: add new IncreaseAccountBalance Store method

And use it instead of UpdateAccount in the InterceptorService's
invoiceUpdate method.

accounts/interface.go

@@ -230,6 +230,11 @@ type Store interface {
 	AddAccountInvoice(ctx context.Context, id AccountID,
 		hash lntypes.Hash) error
 
+	// IncreaseAccountBalance increases the balance of the account with the
+	// given ID by the given amount.
+	IncreaseAccountBalance(ctx context.Context, id AccountID,
+		amount lnwire.MilliSatoshi) error
+
 	// RemoveAccount finds an account by its ID and removes it from the¨
 	// store.
 	RemoveAccount(ctx context.Context, id AccountID) error

accounts/service.go

@@ -592,21 +592,13 @@ func (s *InterceptorService) invoiceUpdate(ctx context.Context,
 		return nil
 	}
 
-	account, err := s.store.Account(ctx, acctID)
-	if err != nil {
-		return s.disableAndErrorfUnsafe(
-			"error fetching account: %w", err,
-		)
-	}
-
 	// If we get here, the current account has the invoice associated with
 	// it that was just paid. Credit the amount to the account and update it
 	// in the DB.
-	account.CurrentBalance += int64(invoice.AmountPaid)
-	if err := s.store.UpdateAccount(ctx, account); err != nil {
-		return s.disableAndErrorfUnsafe(
-			"error updating account: %w", err,
-		)
+	err := s.store.IncreaseAccountBalance(ctx, acctID, invoice.AmountPaid)
+	if err != nil {
+		return s.disableAndErrorfUnsafe("error updating account: %w",
+			err)
 	}
 
 	// We've now fully processed the invoice and don't need to keep it

accounts/store_kvdb.go

@@ -233,6 +233,22 @@ func (s *BoltStore) AddAccountInvoice(_ context.Context, id AccountID,
 	return s.updateAccount(id, update)
 }
 
+// IncreaseAccountBalance increases the balance of the account with the given ID
+// by the given amount.
+//
+// NOTE: This is part of the Store interface.
+func (s *BoltStore) IncreaseAccountBalance(_ context.Context, id AccountID,
+	amount lnwire.MilliSatoshi) error {
+
+	update := func(account *OffChainBalanceAccount) error {
+		account.CurrentBalance += int64(amount)
+
+		return nil
+	}
+
+	return s.updateAccount(id, update)
+}
+
 func (s *BoltStore) updateAccount(id AccountID,
 	updateFn func(*OffChainBalanceAccount) error) error {
 

accounts/store_test.go

@@ -205,6 +205,29 @@ func TestAccountUpdateMethods(t *testing.T) {
 
 		assertInvoices(hash1, hash2)
 	})
+
+	t.Run("IncreaseAccountBalance", func(t *testing.T) {
+		store := NewTestDB(t)
+
+		acct, err := store.NewAccount(ctx, 123, time.Time{}, "foo")
+		require.NoError(t, err)
+
+		assertBalance := func(balance int64) {
+			dbAcct, err := store.Account(ctx, acct.ID)
+			require.NoError(t, err)
+			require.EqualValues(t, balance, dbAcct.CurrentBalance)
+		}
+
+		// The account initially has a balance of 123.
+		assertBalance(123)
+
+		// Increase the balance by 100 and assert that the new balance
+		// is 223.
+		err = store.IncreaseAccountBalance(ctx, acct.ID, 100)
+		require.NoError(t, err)
+
+		assertBalance(223)
+	})
 }
 
 // TestLastInvoiceIndexes makes sure the last known invoice indexes can be