feat(ui): add TreeView<TItem> component with core rendering, expand/collapse, ARIA (R1-R4, R14)

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

@@ -0,0 +1,106 @@
+@* Reusable hierarchical tree view with expand/collapse, ARIA roles, and guide lines *@
+@typeparam TItem
+
+@if (_items is null || _items.Count == 0)
+{
+    if (EmptyContent != null)
+    {
+        @EmptyContent
+    }
+}
+else
+{
+    <ul role="tree" class="tv-root @(ShowGuideLines ? "tv-guides" : "")">
+        @foreach (var item in _items)
+        {
+            RenderNode(item, 0);
+        }
+    </ul>
+}
+
+@{ void RenderNode(TItem item, int depth)
+    {
+        var key = KeySelector(item);
+        var children = ChildrenSelector(item);
+        var isBranch = HasChildrenSelector(item);
+        var isExpanded = _expandedKeys.Contains(key);
+
+        <li role="treeitem" @key="key"
+            aria-expanded="@(isBranch ? (isExpanded ? "true" : "false") : null)">
+            <div class="tv-row" style="padding-left: @(depth * IndentPx)px">
+                @if (isBranch)
+                {
+                    <span class="tv-toggle" @onclick="() => ToggleExpand(key)">@(isExpanded ? "\u2212" : "+")</span>
+                }
+                else
+                {
+                    <span class="tv-spacer"></span>
+                }
+                <span class="tv-content">
+                    @NodeContent(item)
+                </span>
+            </div>
+            @if (isBranch && isExpanded && children is { Count: > 0 })
+            {
+                <ul role="group">
+                    @foreach (var child in children)
+                    {
+                        RenderNode(child, depth + 1);
+                    }
+                </ul>
+            }
+        </li>
+    }
+}
+
+@code {
+    private IReadOnlyList<TItem>? _items;
+    private HashSet<object> _expandedKeys = new();
+    private bool _initialExpansionApplied;
+
+    [Parameter, EditorRequired] public IReadOnlyList<TItem> Items { get; set; } = [];
+    [Parameter, EditorRequired] public Func<TItem, IReadOnlyList<TItem>> ChildrenSelector { get; set; } = default!;
+    [Parameter, EditorRequired] public Func<TItem, bool> HasChildrenSelector { get; set; } = default!;
+    [Parameter, EditorRequired] public Func<TItem, object> KeySelector { get; set; } = default!;
+    [Parameter, EditorRequired] public RenderFragment<TItem> NodeContent { get; set; } = default!;
+    [Parameter] public RenderFragment? EmptyContent { get; set; }
+    [Parameter] public int IndentPx { get; set; } = 24;
+    [Parameter] public bool ShowGuideLines { get; set; } = true;
+    [Parameter] public Func<TItem, bool>? InitiallyExpanded { get; set; }
+
+    protected override void OnParametersSet()
+    {
+        _items = Items;
+
+        if (!_initialExpansionApplied && InitiallyExpanded != null && _items is { Count: > 0 })
+        {
+            _initialExpansionApplied = true;
+            ApplyInitialExpansion(_items);
+        }
+    }
+
+    private void ApplyInitialExpansion(IReadOnlyList<TItem> items)
+    {
+        foreach (var item in items)
+        {
+            if (InitiallyExpanded!(item))
+            {
+                _expandedKeys.Add(KeySelector(item));
+            }
+
+            var children = ChildrenSelector(item);
+            if (children is { Count: > 0 })
+            {
+                ApplyInitialExpansion(children);
+            }
+        }
+    }
+
+    private void ToggleExpand(object key)
+    {
+        if (!_expandedKeys.Remove(key))
+        {
+            _expandedKeys.Add(key);
+        }
+    }
+}