using System.Windows;
using System.Windows.Media;

namespace ytLive.Helpers;

/// <summary>Resolves a design token for code that cannot bind — view-model state colours (the
/// top bar, the health banner, the meters, toast tints). The values live once, in
/// <c>Themes/Tokens.xaml</c>; this reads them from the application resources.
///
/// <para>Why not a Brush field per colour: a second list in C# would drift from the theme. Why not
/// OutputPalette: that one exists for the frame-pump thread, which must not touch resources; these
/// properties are read by bindings on the UI thread.</para>
///
/// <para>Without an Application (unit tests, design-time) a neutral grey comes back: visibly wrong
/// rather than silently plausible, and never a crash.</para></summary>
internal static class ThemeBrush
{
    private static readonly SolidColorBrush Missing = Frozen(Color.FromRgb(0x80, 0x80, 0x80));

    /// <summary>The brush for a token key, e.g. <c>ThemeBrush.Get("Brush.Primary")</c>.</summary>
    public static SolidColorBrush Get(string key)
        => Application.Current?.TryFindResource(key) as SolidColorBrush ?? Missing;

    /// <summary>The token's colour as a browser-style hex string, for APIs that take one
    /// (Notification.Wpf's <c>NotificationColor.FromHex</c>, for instance).</summary>
    public static string Hex(string key)
    {
        var c = Get(key).Color;
        return c.A == 255
            ? $"#{c.R:x2}{c.G:x2}{c.B:x2}"
            : $"#{c.A:x2}{c.R:x2}{c.G:x2}{c.B:x2}";
    }

    private static SolidColorBrush Frozen(Color colour)
    {
        var brush = new SolidColorBrush(colour);
        brush.Freeze();
        return brush;
    }
}