@* Lazy tree component with per-node text filter. Driver-agnostic — consumes
   IBrowserSessionService for root/expand. Selected node is bound back to parent
   via OnNodeSelected EventCallback. *@
@using ZB.MOM.WW.OtOpcUa.AdminUI.Browsing
@using ZB.MOM.WW.OtOpcUa.Commons.Browsing
@inject IBrowserSessionService BrowserService

<div class="border rounded p-2" style="max-height:420px; overflow:auto; min-height:240px">
    @if (_loading)
    {
        <div class="text-muted small"><span class="spinner-border spinner-border-sm me-1"></span>Loading&hellip;</div>
    }
    else if (_error is not null)
    {
        <div class="text-danger small">@_error</div>
    }
    else if (_roots is null || _roots.Count == 0)
    {
        <div class="text-muted small">No nodes.</div>
    }
    else
    {
        @foreach (var n in _roots) { @RenderNode(n, 0) }
    }
</div>

@code {
    /// <summary>The browse-session token returned by IBrowserSessionService.OpenAsync.</summary>
    [Parameter, EditorRequired] public Guid SessionToken { get; set; }

    /// <summary>The currently-selected node's NodeId, for visual selection highlighting.</summary>
    [Parameter] public string SelectedNodeId { get; set; } = "";

    /// <summary>Fired when the user clicks a leaf (or any node — caller decides what to do with it).</summary>
    [Parameter] public EventCallback<BrowseNode> OnNodeSelected { get; set; }

    private bool _loading = true;
    private string? _error;
    private List<TreeItem>? _roots;

    protected override async Task OnInitializedAsync()
    {
        await LoadRootAsync();
    }

    private async Task LoadRootAsync()
    {
        try
        {
            var roots = await BrowserService.RootAsync(SessionToken, default);
            _roots = roots.Select(n => new TreeItem(n)).ToList();
        }
        catch (Exception ex) { _error = ex.Message; }
        finally { _loading = false; }
    }

    private async Task ToggleAsync(TreeItem item)
    {
        item.Expanded = !item.Expanded;
        if (item.Expanded && !item.Loaded) await ExpandAsync(item);
    }

    private async Task ExpandAsync(TreeItem item)
    {
        if (item.Loaded || item.Loading) return;
        item.Loading = true; StateHasChanged();
        try
        {
            var kids = await BrowserService.ExpandAsync(SessionToken, item.Node.NodeId, default);
            item.Children = kids.Select(k => new TreeItem(k)).ToList();
            item.Loaded = true;
        }
        catch (Exception ex) { item.Error = ex.Message; }
        finally { item.Loading = false; StateHasChanged(); }
    }

    private async Task SelectAsync(TreeItem item)
    {
        SelectedNodeId = item.Node.NodeId;
        await OnNodeSelected.InvokeAsync(item.Node);
    }

    private RenderFragment RenderNode(TreeItem item, int depth) => __builder =>
    {
        var indent = $"padding-left:{depth * 18}px";
        var selectedCls = SelectedNodeId == item.Node.NodeId ? "bg-primary-subtle" : "";
        <div class="d-flex align-items-center gap-1 py-1 @selectedCls" style="@indent">
            @if (item.Node.Kind == BrowseNodeKind.Folder && item.Node.HasChildrenHint)
            {
                <button type="button" class="btn btn-sm btn-link p-0"
                        @onclick="@(() => ToggleAsync(item))" style="width:18px">
                    @(item.Expanded ? "▼" : "▶")
                </button>
            }
            else
            {
                <span style="width:18px"></span>
            }
            <a href="#" @onclick="@(() => SelectAsync(item))" @onclick:preventDefault
               class="text-decoration-none mono small">@item.Node.DisplayName</a>
            @if (item.Node.Kind == BrowseNodeKind.Leaf)
            {
                <span class="chip chip-idle ms-1" style="font-size:0.7rem">leaf</span>
            }
        </div>
        @if (item.Expanded && item.Loading)
        {
            <div class="small text-muted" style="@($"padding-left:{(depth + 1) * 18}px")">
                <span class="spinner-border spinner-border-sm me-1"></span>Loading&hellip;
            </div>
        }
        else if (item.Expanded && item.Error is not null)
        {
            <div class="small text-danger" style="@($"padding-left:{(depth + 1) * 18}px")">
                @item.Error
            </div>
        }
        else if (item.Expanded && item.Loaded && item.Children is { Count: > 0 })
        {
            <input type="text" class="form-control form-control-sm mt-1"
                   placeholder="filter children..."
                   style="@($"width:calc(100% - {(depth + 2) * 18}px); margin-left:{(depth + 2) * 18}px")"
                   @bind="item.Filter" @bind:event="oninput" />
            @foreach (var c in FilterChildren(item))
            {
                @RenderNode(c, depth + 1)
            }
        }
    };

    private static IEnumerable<TreeItem> FilterChildren(TreeItem item)
    {
        if (item.Children is null) yield break;
        var f = item.Filter?.Trim();
        foreach (var c in item.Children)
        {
            if (string.IsNullOrEmpty(f)) { yield return c; continue; }
            if (c.Node.DisplayName.Contains(f, StringComparison.OrdinalIgnoreCase) ||
                c.Node.NodeId.Contains(f, StringComparison.OrdinalIgnoreCase))
                yield return c;
        }
    }

    private sealed class TreeItem(BrowseNode node)
    {
        public BrowseNode Node { get; } = node;
        public bool Expanded { get; set; }
        public bool Loaded { get; set; }
        public bool Loading { get; set; }
        public string? Error { get; set; }
        public List<TreeItem>? Children { get; set; }
        public string? Filter { get; set; }
    }
}