using System.Runtime.CompilerServices;
using ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared;

namespace ZB.MOM.WW.OtOpcUa.AdminUI.Uns;

/// <summary>
///     Caches each <see cref="RawNode"/>'s context-menu item list (R04 P5). <c>RawTree</c> used to build a
///     fresh list (and fresh closures) per node on every render, and hand it to that row's
///     <c>ContextMenu</c> as a new reference each time. The cache is keyed weakly on the node instance, so
///     a reload (which replaces the child nodes) drops the stale entries with the nodes, and it rebuilds
///     when anything the menu depends on (picker mode, the node's enabled state) differs.
/// </summary>
public sealed class RawNodeMenuCache
{
    private readonly ConditionalWeakTable<RawNode, Entry> _entries = new();

    /// <summary>Returns the cached menu for <paramref name="node"/>, building it on first use or after a dependency changed.</summary>
    /// <param name="node">The node.</param>
    /// <param name="pickerMode">Whether the tree is in picker mode (picker menus differ entirely).</param>
    /// <param name="build">Builds the menu for the node.</param>
    /// <returns>The menu items.</returns>
    public IReadOnlyList<ContextMenuItem> GetOrBuild(
        RawNode node, bool pickerMode, Func<RawNode, IReadOnlyList<ContextMenuItem>> build)
    {
        if (_entries.TryGetValue(node, out var entry)
            && entry.PickerMode == pickerMode
            && entry.Enabled == node.Enabled)
        {
            return entry.Items;
        }

        var items = build(node);
        _entries.AddOrUpdate(node, new Entry(pickerMode, node.Enabled, items));
        return items;
    }

    private sealed record Entry(bool PickerMode, bool Enabled, IReadOnlyList<ContextMenuItem> Items);
}