using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Web;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Instances;

namespace ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared;

/// <summary>
/// A combobox that picks one instance out of a site's area tree: a text field over a
/// dropdown panel hosting <see cref="TreeView{TItem}"/> across the forest that
/// <see cref="InstanceTreeBuilder"/> builds from the site's areas and instances.
///
/// <para>
/// It replaces the flat instance <c>&lt;select&gt;</c> on Flow Debugger and Debug View,
/// where a site with a few hundred instances made the list unusable. The panel opens
/// with every area collapsed so the operator drills down; an outside click closes it
/// through a transparent fixed backdrop (no JavaScript, the same pattern
/// <see cref="TreeView{TItem}"/> uses for its context menu).
/// </para>
///
/// <para>
/// Typing in the field filters the forest to the instances whose <c>UniqueName</c> contains
/// the text plus their ancestor areas, force-expanded so every match is on screen; clearing
/// the text restores the full forest, collapsed. <c>Enter</c> picks the first instance the
/// operator can actually see (document order, skipping collapsed branches), <c>ArrowDown</c>
/// hands keyboard navigation to the tree's own roving tabindex, and <c>Escape</c> closes
/// without changing the selection. The filter never survives a close or a pick.
/// </para>
///
/// <para>
/// A parent that swaps <see cref="Areas"/>/<see cref="Instances"/> (a site change)
/// closes the panel and re-derives the field text from the current selection, clearing
/// it when the selected instance is not in the new list. A parent that changes
/// <see cref="SelectedInstanceId"/> (a deep link or a localStorage restore) updates the
/// field text while the panel is closed.
/// </para>
/// </summary>
public partial class InstancePicker
{
    /// <summary>
    /// The site's areas, flat and linked by <see cref="Area.ParentAreaId"/>; null is treated
    /// as empty. Compared by REFERENCE: a new list object means "the site changed" and closes
    /// the panel, drops the filter and re-derives the field text. Hold a stable reference and
    /// only hand the picker a new list when the underlying set actually changed — rebuilding
    /// the list on every parent render would close the panel out from under the operator.
    /// </summary>
    [Parameter]
    public IReadOnlyList<Area>? Areas { get; set; }

    /// <summary>
    /// The site's instances; null is treated as empty. Compared by REFERENCE on the same
    /// contract as <see cref="Areas"/> — pass a stable reference and only replace it when the
    /// underlying set changed.
    /// </summary>
    [Parameter]
    public IReadOnlyList<Instance>? Instances { get; set; }

    /// <summary>Id of the currently selected instance; <c>0</c> means nothing is selected.</summary>
    [Parameter]
    public int SelectedInstanceId { get; set; }

    /// <summary>Raised with the instance id when the operator picks a row.</summary>
    [Parameter]
    public EventCallback<int> SelectedInstanceIdChanged { get; set; }

    /// <summary>Disables the field and the chevron; the panel can no longer be opened.</summary>
    [Parameter]
    public bool Disabled { get; set; }

    /// <summary>
    /// Maps an instance to the text shown on its row and, once picked, in the field.
    /// Defaults to <see cref="Instance.UniqueName"/>. Note that searching always matches
    /// on <c>UniqueName</c> (the builder's contract), whatever this renders.
    /// </summary>
    [Parameter]
    public Func<Instance, string>? ItemLabel { get; set; }

    /// <summary>
    /// <c>data-test</c> root for the control: <c>{prefix}-picker</c>, <c>-input</c>,
    /// <c>-toggle</c>, <c>-panel</c>, <c>-backdrop</c> and <c>-row</c> (instance rows also
    /// carry <c>data-instance-id</c>).
    /// </summary>
    [Parameter]
    public string DataTestPrefix { get; set; } = "instance";

    /// <summary>Placeholder shown in the field while nothing is selected.</summary>
    [Parameter]
    public string Placeholder { get; set; } = "Search or browse instances…";

    private readonly string _idSuffix = Guid.NewGuid().ToString("N")[..8];

    private bool _open;
    private string _text = string.Empty;

    /// <summary>
    /// The name filter applied to the forest. Empty until the search box lands; kept
    /// separate from <see cref="_text"/> so a selected label never doubles as a filter.
    /// </summary>
    private string _filter = string.Empty;

    private bool _hasFilter;
    private IReadOnlyList<InstanceTreeNode> _roots = [];
    private TreeView<InstanceTreeNode>? _tree;

    /// <summary>Bulk expansion the tree owes the current filter, applied after the next render.</summary>
    private enum PendingTreeAction
    {
        /// <summary>Nothing to do.</summary>
        None,

        /// <summary>Open every branch so the filtered matches are all on screen.</summary>
        ExpandAll,

        /// <summary>Close every branch, back to the drill-down starting point.</summary>
        CollapseAll,
    }

    // The TreeView only exists once the panel has rendered, so keyboard/typing work that
    // targets it is deferred to OnAfterRenderAsync through these two flags.
    private PendingTreeAction _pendingTreeAction;
    private bool _pendingTreeFocus;

    // Last parameter values seen, so OnParametersSet can tell a real change from a
    // parent that simply re-rendered with the same lists and selection.
    private IReadOnlyList<Area>? _lastAreas;
    private IReadOnlyList<Instance>? _lastInstances;
    private int _lastSelectedId;
    private bool _parametersSeen;

    private string _inputId => $"ip-{_idSuffix}-input";

    private string _panelId => $"ip-{_idSuffix}-panel";

    /// <inheritdoc />
    protected override void OnParametersSet()
    {
        var listsChanged = !_parametersSeen
            || !ReferenceEquals(_lastAreas, Areas)
            || !ReferenceEquals(_lastInstances, Instances);
        var selectionChanged = !_parametersSeen || _lastSelectedId != SelectedInstanceId;

        _parametersSeen = true;
        _lastAreas = Areas;
        _lastInstances = Instances;
        _lastSelectedId = SelectedInstanceId;

        if (!listsChanged && !selectionChanged) return;

        var selected = CurrentSelection();

        if (listsChanged)
        {
            // A site change: drop any filter, rebuild, and close unconditionally — the panel
            // is showing the OLD site's tree, so leaving it open would be showing a lie even
            // when the selected instance happens to exist in the new list too.
            _filter = string.Empty;
            Rebuild();
            _open = false;
            _text = selected is null ? string.Empty : LabelOf(selected);
        }
        else if (!_open)
        {
            _text = selected is null ? string.Empty : LabelOf(selected);
        }
    }

    /// <inheritdoc />
    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        var action = _pendingTreeAction;
        var focus = _pendingTreeFocus;
        _pendingTreeAction = PendingTreeAction.None;
        _pendingTreeFocus = false;

        // The panel may have closed again in the same batch (a pick, an Escape), taking
        // the tree with it — there is nothing left to expand or focus.
        if (!_open || _tree is null) return;

        // ExpandAll/CollapseAll re-render the TREE, not this component, so consuming the
        // flag here cannot loop back into another picker render.
        switch (action)
        {
            case PendingTreeAction.ExpandAll:
                _tree.ExpandAll();
                break;
            case PendingTreeAction.CollapseAll:
                _tree.CollapseAll();
                break;
        }

        if (focus) await _tree.FocusFirstVisibleAsync();
    }

    /// <summary>The instance <see cref="SelectedInstanceId"/> points at, or null when unresolved.</summary>
    private Instance? CurrentSelection() =>
        SelectedInstanceId == 0 ? null : Instances?.FirstOrDefault(i => i.Id == SelectedInstanceId);

    /// <summary>Rebuilds the forest for the current filter.</summary>
    private void Rebuild()
    {
        _hasFilter = !string.IsNullOrWhiteSpace(_filter);
        _roots = InstanceTreeBuilder.Build(Areas, Instances, _filter);
    }

    private string LabelOf(Instance instance) => ItemLabel?.Invoke(instance) ?? instance.UniqueName;

    private string RowLabel(InstanceTreeNode node) =>
        node.Instance is { } instance ? LabelOf(instance) : node.Label;

    private void Open()
    {
        if (Disabled || _open) return;
        _open = true;
    }

    private void Toggle()
    {
        if (Disabled) return;
        if (_open) Close(); else _open = true;
    }

    private void Close()
    {
        _open = false;
        if (_hasFilter)
        {
            _filter = string.Empty;
            Rebuild();
        }

        var selected = CurrentSelection();
        _text = selected is null ? string.Empty : LabelOf(selected);
    }

    /// <summary>
    /// Every keystroke retypes the filter: the field text IS the filter while the operator
    /// is typing, and the panel opens if it was closed. The rebuilt forest is expanded when
    /// something is being searched for and collapsed back to the drill-down view when the
    /// text is cleared — both after the next render, once the tree exists.
    /// </summary>
    private void OnInput(ChangeEventArgs e)
    {
        if (Disabled) return;

        _text = e.Value?.ToString() ?? string.Empty;
        _filter = _text;
        _open = true;
        Rebuild();
        _pendingTreeAction = _hasFilter ? PendingTreeAction.ExpandAll : PendingTreeAction.CollapseAll;
    }

    /// <summary>
    /// The field's keyboard surface. Deliberately no <c>preventDefault</c>: Blazor's flag is
    /// all-or-nothing per element, and neither default is harmful here (Enter in a text input
    /// outside a form does nothing; ArrowDown just moves the caret) — while suppressing Tab
    /// would break getting out of the control.
    /// </summary>
    private Task OnInputKeyDown(KeyboardEventArgs e)
    {
        if (Disabled) return Task.CompletedTask;

        switch (e.Key)
        {
            case "Enter" when _open:
                return FirstVisibleInstance() is { } instance ? SelectAsync(instance) : Task.CompletedTask;

            case "Escape" when _open:
                Close();
                break;

            case "ArrowDown":
                _open = true;
                _pendingTreeFocus = true;
                break;
        }

        return Task.CompletedTask;
    }

    /// <summary>
    /// The first instance leaf in document order among the rows the operator can actually
    /// see — a collapsed area's contents are skipped, matching what Enter appears to pick.
    /// With a filter active every branch is expanded, so this degrades to plain document
    /// order over the filtered forest.
    /// </summary>
    private Instance? FirstVisibleInstance() => FirstVisibleInstance(_roots);

    private Instance? FirstVisibleInstance(IReadOnlyList<InstanceTreeNode> nodes)
    {
        foreach (var node in nodes)
        {
            if (node.Instance is { } instance) return instance;
            if (!node.HasChildren) continue;

            // Before the tree's first render the filter's pending ExpandAll decides visibility.
            var expanded = _tree?.IsExpanded(node.Key) ?? _hasFilter;
            if (expanded && FirstVisibleInstance(node.Children) is { } hit) return hit;
        }

        return null;
    }

    private Task OnRowClickAsync(InstanceTreeNode node)
    {
        if (node.Instance is { } instance) return SelectAsync(instance);

        _tree?.ToggleExpanded(node.Key);
        return Task.CompletedTask;
    }

    private async Task SelectAsync(Instance instance)
    {
        _text = LabelOf(instance);
        _open = false;
        if (_hasFilter)
        {
            _filter = string.Empty;
            Rebuild();
        }

        await SelectedInstanceIdChanged.InvokeAsync(instance.Id);
    }
}