feat(ui): add sessionStorage persistence for TreeView expansion state (R11)

src/ScadaLink.CentralUI/Components/Shared/TreeView.razor

@@ -1,5 +1,6 @@
 @* Reusable hierarchical tree view with expand/collapse, ARIA roles, and guide lines *@
 @typeparam TItem
+@inject IJSRuntime JSRuntime
 
 @if (_items is null || _items.Count == 0)
 {
@@ -58,6 +59,7 @@ else
     private IReadOnlyList<TItem>? _items;
     private HashSet<object> _expandedKeys = new();
     private bool _initialExpansionApplied;
+    private bool _storageLoaded;
 
     [Parameter, EditorRequired] public IReadOnlyList<TItem> Items { get; set; } = [];
     [Parameter, EditorRequired] public Func<TItem, IReadOnlyList<TItem>> ChildrenSelector { get; set; } = default!;
@@ -72,6 +74,7 @@ else
     [Parameter] public object? SelectedKey { get; set; }
     [Parameter] public EventCallback<object?> SelectedKeyChanged { get; set; }
     [Parameter] public string SelectedCssClass { get; set; } = "bg-primary bg-opacity-10";
+    [Parameter] public string? StorageKey { get; set; }
 
     protected override void OnParametersSet()
     {
@@ -79,8 +82,40 @@ else
 
         if (!_initialExpansionApplied && InitiallyExpanded != null && _items is { Count: > 0 })
         {
-            _initialExpansionApplied = true;
+            // Only apply InitiallyExpanded when there is no StorageKey, or storage
-            ApplyInitialExpansion(_items);
+            // has already been checked and returned nothing (no prior state).
+            if (StorageKey == null || (_storageLoaded && _expandedKeys.Count == 0))
+            {
+                _initialExpansionApplied = true;
+                ApplyInitialExpansion(_items);
+            }
+        }
+    }
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
+    {
+        if (firstRender && StorageKey != null)
+        {
+            var json = await JSRuntime.InvokeAsync<string?>("treeviewStorage.load", StorageKey);
+            _storageLoaded = true;
+
+            if (json != null)
+            {
+                var keys = System.Text.Json.JsonSerializer.Deserialize<List<string>>(json);
+                if (keys != null)
+                {
+                    _expandedKeys = new HashSet<object>(keys);
+                    _initialExpansionApplied = true;
+                }
+            }
+            else if (InitiallyExpanded != null && _items is { Count: > 0 } && !_initialExpansionApplied)
+            {
+                // Storage returned null (no prior state) — fall back to InitiallyExpanded
+                _initialExpansionApplied = true;
+                ApplyInitialExpansion(_items);
+            }
+
+            StateHasChanged();
         }
     }
 
@@ -107,6 +142,18 @@ else
         {
             _expandedKeys.Add(key);
         }
+
+        PersistExpandedState();
+    }
+
+    private void PersistExpandedState()
+    {
+        if (StorageKey != null)
+        {
+            var keys = _expandedKeys.Select(k => k.ToString()!).ToList();
+            var json = System.Text.Json.JsonSerializer.Serialize(keys);
+            _ = JSRuntime.InvokeVoidAsync("treeviewStorage.save", StorageKey, json);
+        }
     }
 
     private async Task OnContentClick(object key)

src/ScadaLink.CentralUI/wwwroot/js/treeview-storage.js

@@ -0,0 +1,8 @@
+window.treeviewStorage = {
+    save: function (storageKey, keysJson) {
+        sessionStorage.setItem("treeview:" + storageKey, keysJson);
+    },
+    load: function (storageKey) {
+        return sessionStorage.getItem("treeview:" + storageKey);
+    }
+};

src/ScadaLink.Host/Components/App.razor

@@ -92,6 +92,7 @@
             }
         });
     </script>
+    <script src="/js/treeview-storage.js"></script>
     <script src="/lib/bootstrap/js/bootstrap.bundle.min.js"></script>
 </body>
 </html>

tests/ScadaLink.CentralUI.Tests/TreeViewTests.cs

@@ -33,7 +33,8 @@ public class TreeViewTests : BunitContext
         bool selectable = false,
         object? selectedKey = null,
         Action<object?>? onSelectedKeyChanged = null,
-        string? selectedCssClass = null)
+        string? selectedCssClass = null,
+        string? storageKey = null)
     {
         return Render<TreeView<TestNode>>(parameters =>
         {
@@ -61,6 +62,11 @@ public class TreeViewTests : BunitContext
             {
                 parameters.Add(p => p.SelectedCssClass, selectedCssClass);
             }
+
+            if (storageKey != null)
+            {
+                parameters.Add(p => p.StorageKey, storageKey);
+            }
         });
     }
 
@@ -317,4 +323,64 @@ public class TreeViewTests : BunitContext
         var alphaLi = cut.FindAll("li[role='treeitem']")[0];
         Assert.Equal("true", alphaLi.GetAttribute("aria-selected"));
     }
+
+    [Fact]
+    public void SessionStorage_NullKey_NoJsInteropCalls()
+    {
+        var cut = RenderTreeView();
+
+        // Expand Alpha
+        cut.Find(".tv-toggle").Click();
+
+        // No JS interop calls should have been made
+        Assert.Empty(JSInterop.Invocations);
+    }
+
+    [Fact]
+    public void SessionStorage_Set_ExpandWritesToStorage()
+    {
+        JSInterop.Setup<string?>("treeviewStorage.load", _ => true).SetResult(null);
+        JSInterop.SetupVoid("treeviewStorage.save", _ => true);
+
+        var cut = RenderTreeView(storageKey: "test-tree");
+
+        // Expand Alpha
+        cut.Find(".tv-toggle").Click();
+
+        // Verify save was called
+        var saveInvocations = JSInterop.Invocations
+            .Where(i => i.Identifier == "treeviewStorage.save")
+            .ToList();
+        Assert.Single(saveInvocations);
+    }
+
+    [Fact]
+    public void SessionStorage_RestoresExpandedOnMount()
+    {
+        JSInterop.Setup<string?>("treeviewStorage.load", _ => true).SetResult("[\"a\"]");
+        JSInterop.SetupVoid("treeviewStorage.save", _ => true);
+
+        var cut = RenderTreeView(storageKey: "test-tree");
+
+        // Alpha's children should be visible because "a" was restored from storage
+        var labels = cut.FindAll(".node-label");
+        Assert.Contains(labels, l => l.TextContent == "Alpha-1");
+        Assert.Contains(labels, l => l.TextContent == "Alpha-2");
+    }
+
+    [Fact]
+    public void SessionStorage_TakesPrecedenceOverInitiallyExpanded()
+    {
+        // Storage returns empty array — meaning user explicitly collapsed everything
+        JSInterop.Setup<string?>("treeviewStorage.load", _ => true).SetResult("[]");
+        JSInterop.SetupVoid("treeviewStorage.save", _ => true);
+
+        var cut = RenderTreeView(
+            storageKey: "test-tree",
+            initiallyExpanded: n => n.Key == "a");
+
+        // Alpha should NOT be expanded — storage (empty) wins over InitiallyExpanded
+        var labels = cut.FindAll(".node-label");
+        Assert.DoesNotContain(labels, l => l.TextContent == "Alpha-1");
+    }
 }