using System.Windows;
using System.Windows.Media;
using Microsoft.Win32;

namespace DeskCore;

/// <summary>Übernimmt Hell/Dunkel-Modus und Akzentfarbe von Windows – auch live, wenn man sie ändert.</summary>
public static class Theme
{
    public static bool IsLight { get; private set; } = true;

    /// <summary>Vom Benutzer gewählter Modus; "System" folgt der Windows-Einstellung.</summary>
    public static DesignMode Mode => AppSettings.Current.Design;

    public static void Init()
    {
        Apply();
        SystemEvents.UserPreferenceChanged += (_, e) =>
        {
            if (e.Category is UserPreferenceCategory.General or UserPreferenceCategory.Color or UserPreferenceCategory.VisualStyle)
                Application.Current.Dispatcher.BeginInvoke(Apply);
        };
    }

    public static void Apply()
    {
        IsLight = Mode switch
        {
            DesignMode.Light => true,
            DesignMode.Dark => false,
            _ => ReadDword(@"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize", "AppsUseLightTheme") != 0,
        };
        var res = Application.Current.Resources;
        res.MergedDictionaries[0] = new ResourceDictionary
        {
            Source = new Uri($"pack://application:,,,/Themes/Colors.{(IsLight ? "Light" : "Dark")}.xaml")
        };

        // DWM speichert die Akzentfarbe als ABGR
        int abgr = ReadDword(@"Software\Microsoft\Windows\DWM", "AccentColor") is var v and not -1 ? v : unchecked((int)0xFFD77800);
        var accent = Color.FromRgb((byte)abgr, (byte)(abgr >> 8), (byte)(abgr >> 16));

        // Wie Windows 11: im Hellmodus etwas dunkler + weiße Schrift, im Dunkelmodus deutlich heller + schwarze Schrift
        var a = IsLight ? Mix(accent, Colors.Black, 0.12) : Mix(accent, Colors.White, 0.45);
        res["AccentBrush"] = Brush(a);
        res["AccentHoverBrush"] = Brush(IsLight ? Mix(a, Colors.White, 0.1) : Mix(a, Colors.Black, 0.1));
        res["OnAccentBrush"] = Brush(IsLight ? Colors.White : Colors.Black);
        res["AccentSubtleBrush"] = Brush(Color.FromArgb(IsLight ? (byte)0x22 : (byte)0x30, a.R, a.G, a.B));
        res["AccentSubtleStrokeBrush"] = Brush(Color.FromArgb(IsLight ? (byte)0x55 : (byte)0x60, a.R, a.G, a.B));
        Changed?.Invoke();
    }

    public static event Action? Changed;

    private static int ReadDword(string key, string name)
    {
        try
        {
            using var k = Registry.CurrentUser.OpenSubKey(key);
            return k?.GetValue(name) is int i ? i : -1;
        }
        catch { return -1; }
    }

    private static Color Mix(Color c, Color with, double t) => Color.FromRgb(
        (byte)(c.R + (with.R - c.R) * t), (byte)(c.G + (with.G - c.G) * t), (byte)(c.B + (with.B - c.B) * t));

    private static SolidColorBrush Brush(Color c)
    {
        var b = new SolidColorBrush(c);
        b.Freeze();
        return b;
    }
}