Show warning when changing recurring invoice start date

resources/lang/en/texts.php

@@ -1305,6 +1305,11 @@ $LANG = array(
     'canada' => 'Canada',
     'accept_debit_cards' => 'Accept Debit Cards',
     'debit_cards' => 'Debit Cards',
+
+    'warn_start_date_changed' => 'The next invoice will be sent on the new start date.',
+    'original_start_date' => 'Original start date',
+    'new_start_date' => 'New start date',
+
 );
 
 return $LANG;

resources/views/invoices/edit.blade.php

@@ -809,6 +809,7 @@
             var invoice = {!! $invoice !!};
             ko.mapping.fromJS(invoice, model.invoice().mapping, model.invoice);
             model.invoice().is_recurring({{ $invoice->is_recurring ? '1' : '0' }});
+            model.invoice().start_date_orig(model.invoice().start_date());
 
             @if ($invoice->id)
                 var invitationContactIds = {!! json_encode($invitationContactIds) !!};
@@ -1192,13 +1193,25 @@
 	}
 
 	function onSaveClick() {
-		if (model.invoice().is_recurring() && {{ $invoice ? 'false' : 'true' }}) {
+		if (model.invoice().is_recurring()) {
+            // warn invoice will be emailed when saving new recurring invoice
+            if ({{ $invoice->exists() ? 'false' : 'true' }}) {
                 if (confirm("{!! trans("texts.confirm_recurring_email_$entityType") !!}" + '\n\n' + getSendToEmails() + '\n' + "{!! trans("texts.confirm_recurring_timing") !!}")) {
                     submitAction('');
                 }
-		} else {
-            preparePdfData('');
+                return;
+            // warn invoice will be emailed again if start date is changed
+            } else if (model.invoice().start_date() != model.invoice().start_date_orig()) {
+                if (confirm("{!! trans("texts.warn_start_date_changed") !!}" + '\n\n'
+                    + "{!! trans("texts.original_start_date") !!}: " + model.invoice().start_date_orig() + '\n'
+                    + "{!! trans("texts.new_start_date") !!}: " + model.invoice().start_date())) {
+                        submitAction('');
                 }
+                return;
+            }
+        }
+
+        preparePdfData('');
     }
 
     function getSendToEmails() {

resources/views/invoices/knockout.blade.php

@@ -180,6 +180,7 @@ function InvoiceModel(data) {
     self.due_date = ko.observable('');
     self.recurring_due_date = ko.observable('');
     self.start_date = ko.observable('');
+    self.start_date_orig = ko.observable('');
     self.end_date = ko.observable('');
     self.last_sent_date = ko.observable('');
     self.tax_name1 = ko.observable();