using System.Collections.Concurrent;
using System.IO;
using System.Windows;
using System.Windows.Media;

namespace DeskCore;

/// <summary>Lädt Icons auf einem eigenen STA-Thread (Shell-COM braucht STA) und cached sie.</summary>
public static class IconLoader
{
    private static readonly ConcurrentDictionary<string, ImageSource?> _cache = new(StringComparer.OrdinalIgnoreCase);
    private static readonly BlockingCollection<(IconItem Item, int Size)> _queue = new();

    static IconLoader()
    {
        var t = new Thread(Work) { IsBackground = true, Name = "IconLoader" };
        t.SetApartmentState(ApartmentState.STA);
        t.Start();
    }

    private static string Key(string path, int size)
    {
        DateTime stamp;
        try { stamp = File.GetLastWriteTimeUtc(path); } catch { stamp = default; }
        return $"{size}|{stamp.Ticks}|{path}";
    }

    /// <summary>Setzt das Icon sofort aus dem Cache oder lädt es im Hintergrund nach.</summary>
    public static void Load(IconItem item, int size)
    {
        if (_cache.TryGetValue(Key(item.Path, size), out var icon)) item.Icon = icon;
        else _queue.Add((item, size));
    }

    private static void Work()
    {
        foreach (var (item, size) in _queue.GetConsumingEnumerable())
        {
            var key = Key(item.Path, size);
            if (!_cache.TryGetValue(key, out var icon))
            {
                icon = ShellIcon.Get(item.Path, size);
                _cache[key] = icon;
            }
            var result = icon;
            Application.Current?.Dispatcher.BeginInvoke(() => item.Icon = result);
        }
    }
}