Prevent negative payment

lib/ui/app/dialogs/error_dialog.dart

@@ -20,7 +20,7 @@ class ErrorDialog extends StatelessWidget {
     final store = StoreProvider.of<AppState>(context);
 
     return AlertDialog(
-      title: Text(localization.anErrorOccurred),
+      title: Text(localization.error),
       content: error != null ? Text(error.toString()) : SizedBox(),
       actions: [
         if (clearErrorOnDismiss && !Config.DEMO_MODE)

lib/ui/client/edit/client_edit.dart

@@ -53,11 +53,9 @@ class _ClientEditState extends State<ClientEdit>
       onSavePressed: (context) {
         final bool isValid = _formKey.currentState.validate();
 
-        /*
         setState(() {
-          autoValidate = !isValid ?? false;
+          //autoValidate = !isValid;
         });
-         */
 
         if (!isValid) {
           return;

lib/ui/payment/edit/payment_edit_vm.dart

@@ -8,6 +8,7 @@ import 'package:invoiceninja_flutter/redux/ui/pref_state.dart';
 import 'package:invoiceninja_flutter/redux/ui/ui_actions.dart';
 import 'package:invoiceninja_flutter/ui/app/dialogs/error_dialog.dart';
 import 'package:invoiceninja_flutter/ui/payment/view/payment_view_vm.dart';
+import 'package:invoiceninja_flutter/utils/localization.dart';
 import 'package:invoiceninja_flutter/utils/platforms.dart';
 import 'package:redux/redux.dart';
 import 'package:invoiceninja_flutter/redux/payment/payment_actions.dart';
@@ -70,6 +71,18 @@ class PaymentEditVM {
         store.dispatch(UpdateCurrentRoute(state.uiState.previousRoute));
       },
       onSavePressed: (BuildContext context) {
+        double amount = 0;
+        payment.invoices.forEach((invoice) => amount += invoice.amount);
+        payment.credits.forEach((credit) => amount -= credit.amount);
+        if (amount < 0) {
+          showDialog<ErrorDialog>(
+              context: context,
+              builder: (BuildContext context) {
+                return ErrorDialog(
+                    AppLocalization.of(context).negativePaymentError);
+              });
+          return null;
+        }
         final Completer<PaymentEntity> completer = Completer<PaymentEntity>();
         store.dispatch(
             SavePaymentRequest(completer: completer, payment: payment));

lib/utils/i18n.dart

@@ -15,6 +15,8 @@ mixin LocalizationsProvider on LocaleCodeAware {
   static final Map<String, Map<String, String>> _localizedValues = {
     'en': {
       // STARTER: lang key - do not remove comment
+      'negative_payment_error':
+          'The credit amount cannot exceed the payment amount',
       'view_changes': 'View Changes',
       'force_update': 'Force Update',
       'force_update_help':
@@ -4673,6 +4675,9 @@ mixin LocalizationsProvider on LocaleCodeAware {
 
   String get viewChanges => _localizedValues[localeCode]['view_changes'] ?? '';
 
+  String get negativePaymentError =>
+      _localizedValues[localeCode]['negative_payment_error'] ?? '';
+
   String lookup(String key) {
     final lookupKey = toSnakeCase(key);