using System.IO;
using System.Windows.Threading;

namespace DeskCore;

/// <summary>
/// Beobachtet Desktop und Kategorie-Ordner. Meldet Änderungen gebündelt (statt bei jedem einzelnen Ereignis)
/// und sammelt neu auf dem Desktop aufgetauchte Elemente für die automatische Sortierung.
/// </summary>
public sealed class Watcher : IDisposable
{
    private readonly List<FileSystemWatcher> _watchers = [];
    private readonly DispatcherTimer _changedTimer;
    private readonly DispatcherTimer _newTimer;
    private readonly HashSet<string> _newOnDesktop = new(StringComparer.OrdinalIgnoreCase);
    private readonly object _lock = new();

    /// <summary>Irgendetwas hat sich geändert (UI-Thread).</summary>
    public event Action? Changed;
    /// <summary>Neue Elemente auf dem Desktop (UI-Thread, nach kurzer Wartezeit).</summary>
    public event Action<List<string>>? NewOnDesktop;

    public Watcher(Dispatcher dispatcher)
    {
        _changedTimer = new DispatcherTimer(TimeSpan.FromMilliseconds(350), DispatcherPriority.Background, (_, _) =>
        {
            _changedTimer!.Stop();
            Changed?.Invoke();
        }, dispatcher);
        _changedTimer.Stop();

        // Etwas länger warten: Installer legen Verknüpfungen oft in mehreren Schritten an
        _newTimer = new DispatcherTimer(TimeSpan.FromSeconds(2), DispatcherPriority.Background, (_, _) =>
        {
            _newTimer!.Stop();
            List<string> items;
            lock (_lock) { items = _newOnDesktop.ToList(); _newOnDesktop.Clear(); }
            items = items.Where(p => (File.Exists(p) || Directory.Exists(p)) && !Storage.CreatedByApp(p)).ToList();
            if (items.Count > 0) NewOnDesktop?.Invoke(items);
        }, dispatcher);
        _newTimer.Stop();

        Directory.CreateDirectory(Storage.Root);
        Add(Storage.UserDesktop, false, true);
        Add(Storage.PublicDesktop, false, true);
        Add(Storage.Root, true, false);
    }

    private void Add(string dir, bool subdirs, bool isDesktop)
    {
        if (!Directory.Exists(dir)) return;
        try
        {
            var w = new FileSystemWatcher(dir)
            {
                IncludeSubdirectories = subdirs,
                NotifyFilter = NotifyFilters.FileName | NotifyFilters.DirectoryName | NotifyFilters.LastWrite,
                InternalBufferSize = 64 * 1024,
            };
            FileSystemEventHandler onChange = (_, e) =>
            {
                Poke();
                if (isDesktop && e.ChangeType == WatcherChangeTypes.Created) NoteNew(e.FullPath);
            };
            w.Created += onChange;
            w.Deleted += onChange;
            w.Changed += onChange;
            w.Renamed += (_, e) => { Poke(); if (isDesktop) NoteNew(e.FullPath); };
            w.Error += (_, _) => Poke();
            w.EnableRaisingEvents = true;
            _watchers.Add(w);
        }
        catch { }
    }

    private void NoteNew(string path)
    {
        var name = Path.GetFileName(path);
        if (name.StartsWith('~') || name.EndsWith(".tmp", StringComparison.OrdinalIgnoreCase) ||
            name.Equals("desktop.ini", StringComparison.OrdinalIgnoreCase)) return;
        lock (_lock) _newOnDesktop.Add(path);
        _newTimer.Dispatcher.BeginInvoke(() => { _newTimer.Stop(); _newTimer.Start(); });
    }

    private void Poke() => _changedTimer.Dispatcher.BeginInvoke(() => { _changedTimer.Stop(); _changedTimer.Start(); });

    public void Dispose()
    {
        foreach (var w in _watchers) w.Dispose();
        _changedTimer.Stop();
        _newTimer.Stop();
    }
}

public static class AutoSorter
{
    /// <summary>Erste passende Regel → Kategoriename (nur existierende Kategorien).</summary>
    public static string? Match(string path)
    {
        var name = Storage.DisplayName(path);
        var cats = Storage.Categories();
        foreach (var r in AppSettings.Current.Rules)
        {
            if (string.IsNullOrWhiteSpace(r.Contains)) continue;
            if (!name.Contains(r.Contains.Trim(), StringComparison.CurrentCultureIgnoreCase)) continue;
            var cat = cats.FirstOrDefault(c => string.Equals(c, r.Category, StringComparison.OrdinalIgnoreCase));
            if (cat is not null) return cat;
        }
        return null;
    }
}