Fix Platzhalter Editer im TemplateDesigner

LehrerApp.TemplateDesigner/DesignerViewModel.cs

@@ -60,6 +60,8 @@ public partial class DesignerViewModel : ObservableObject
     public ObservableCollection<DesignerAsset> AssetItems { get; } = [];
     public ObservableCollection<StarterTemplateItem> StarterTemplates { get; } = [];
 
+    public DesignerViewModel() => SelectedPlaceholder = Placeholders.FirstOrDefault();
+
     public void Reset()
     {
         TemplateId = "neue-vorlage"; TemplateName = "Neue Vorlage"; Description = "";
@@ -83,7 +85,7 @@ public partial class DesignerViewModel : ObservableObject
         Id = TemplateId.Trim(), Name = TemplateName.Trim(), Description = Description.Trim(),
         PageSize = new((float)PageWidth, (float)PageHeight, Unit), LayoutFile = "layout.tpl",
         Metadata = BuildMetadata(),
-        Placeholders = Placeholders.Select(x => new PlaceholderDefinition(x.Name.Trim(), x.Type, x.Required)).ToList(),
+        Placeholders = BuildPlaceholders(),
     };
 
     public LoadedTemplate BuildLoaded()
@@ -106,6 +108,24 @@ public partial class DesignerViewModel : ObservableObject
     public ITemplateDataProvider BuildDataProvider() => new DesignerDataProvider(Placeholders.ToDictionary(
         x => x.Name.Trim(), x => x.ToValue(), StringComparer.Ordinal));
 
+    public DesignerPlaceholder AddPlaceholder()
+    {
+        var existing = Placeholders.Select(x => x.Name).ToHashSet(StringComparer.Ordinal);
+        var index = Placeholders.Count + 1;
+        while (existing.Contains($"Feld{index}")) index++;
+        var placeholder = new DesignerPlaceholder($"Feld{index}", PlaceholderType.Text, false, "Beispiel");
+        Placeholders.Add(placeholder); SelectedPlaceholder = placeholder; CanExport = false;
+        SetStatus($"Platzhalter „{placeholder.Name}“ angelegt. Details können jetzt bearbeitet werden.", false);
+        return placeholder;
+    }
+
+    public void RemoveSelectedPlaceholder()
+    {
+        if (SelectedPlaceholder is not { } selected) return;
+        Placeholders.Remove(selected); SelectedPlaceholder = null; CanExport = false;
+        SetStatus($"Platzhalter „{selected.Name}“ entfernt.", false);
+    }
+
     public void Load(LoadedTemplate template, string layoutSource)
     {
         TemplateId = template.Manifest.Id; TemplateName = template.Manifest.Name; Description = template.Manifest.Description;
@@ -118,6 +138,7 @@ public partial class DesignerViewModel : ObservableObject
         Placeholders.Clear();
         foreach (var placeholder in template.Manifest.Placeholders)
             Placeholders.Add(new(placeholder.Name, placeholder.Type, placeholder.Required, DesignerPlaceholder.SampleFor(placeholder.Type)));
+        SelectedPlaceholder = Placeholders.FirstOrDefault();
         Assets.Clear(); AssetItems.Clear();
         foreach (var asset in template.Assets) AddOrReplaceAsset(asset.Key, asset.Value, keepName: true);
         RefreshAssetUsage();
@@ -163,6 +184,20 @@ public partial class DesignerViewModel : ObservableObject
         return result;
     }
 
+    private List<PlaceholderDefinition> BuildPlaceholders()
+    {
+        var names = new HashSet<string>(StringComparer.Ordinal);
+        var result = new List<PlaceholderDefinition>(Placeholders.Count);
+        foreach (var placeholder in Placeholders)
+        {
+            var name = placeholder.Name.Trim();
+            if (name.Length == 0) throw new InvalidDataException("Ein Platzhaltername darf nicht leer sein.");
+            if (!names.Add(name)) throw new InvalidDataException($"Platzhalter „{name}“ ist mehrfach definiert.");
+            result.Add(new(name, placeholder.Type, placeholder.Required));
+        }
+        return result;
+    }
+
     private static ITemplateDataProvider BuildSampleDataProvider(TemplateManifest manifest) =>
         new DesignerDataProvider(manifest.Placeholders.ToDictionary(x => x.Name,
             x => new DesignerPlaceholder(x.Name, x.Type, x.Required, DesignerPlaceholder.SampleFor(x.Type)).ToValue(),