feat(finance): display transaction reference length as it is restricted to 140 chars

jdav_web/finance/admin.py

@@ -1,4 +1,5 @@
 from django.contrib import admin, messages
+from django.utils.safestring import mark_safe
 from django import forms
 from django.forms import Textarea, ClearableFileInput
 from django.http import HttpResponse, HttpResponseRedirect
@@ -112,11 +113,22 @@ class StatementUnSubmittedAdmin(CommonAdminMixin, admin.ModelAdmin):
 
 class TransactionOnSubmittedStatementInline(admin.TabularInline):
     model = Transaction
-    fields = ['amount', 'member', 'reference', 'ledger']
+    fields = ['amount', 'member', 'reference', 'text_length_warning', 'ledger']
     formfield_overrides = {
         TextField: {'widget': Textarea(attrs={'rows': 1, 'cols': 40})}
     }
+    readonly_fields = ['text_length_warning']
     extra = 0
+    
+    def text_length_warning(self, obj):
+        """Display reference length, warn if exceeds 140 characters."""
+        len_reference = len(obj.reference)
+        len_string = f"{len_reference}/140"
+        if len_reference > 140:
+            return mark_safe(f'<span style="color: red;">{len_string}</span>')
+        
+        return len_string
+    text_length_warning.short_description = "Länge"
 
 
 class BillOnSubmittedStatementInline(BillOnStatementInline):