using Silk.NET.Core;
using Silk.NET.Windowing;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;

namespace AcDream.App.Rendering;

/// <summary>
/// Applies acdream's window icon to the native window.
/// </summary>
/// <remarks>
/// <para>
/// The icon art is the retail mosswart head (Setup <c>0x02000B4F</c> part 14,
/// skin <c>0x05001E11</c>) rendered offline by <c>tools/IconForge</c>; only the
/// baked PNGs ship. See <c>assets/icons/README.md</c>.
/// </para>
/// <para>
/// The PNGs are <b>embedded</b> rather than copied next to the binary, unlike
/// the shader/markup assets in this project. Two reasons: a window icon has no
/// sensible runtime fallback if the file is missing, and embedding keeps it
/// intact under single-file publish. The cost is a few tens of KB in the
/// assembly.
/// </para>
/// <para>
/// Several sizes are handed over at once because the window manager picks the
/// closest match per surface — the title bar wants ~16px while Alt-Tab and the
/// taskbar want 32-256px, and letting the WM choose beats shipping one size and
/// having it resampled badly.
/// </para>
/// </remarks>
internal static class WindowIconLoader
{
    // Ordered small -> large purely for readability; the window manager selects
    // by size, not by position.
    private static readonly string[] ResourceNames =
    {
        "AcDream.App.Rendering.Icons.acdream-client-16.png",
        "AcDream.App.Rendering.Icons.acdream-client-32.png",
        "AcDream.App.Rendering.Icons.acdream-client-48.png",
        "AcDream.App.Rendering.Icons.acdream-client-256.png",
    };

    /// <summary>
    /// Decode the embedded icon set and hand it to the window.
    /// </summary>
    /// <param name="window">
    /// A window that has already been initialized. Silk's <c>Window.Create</c>
    /// returns an uninitialized object — <c>IWindow.Initialize</c> is what
    /// "creates the window on the underlying platform" — so this must be called
    /// from <c>Load</c> or later.
    /// </param>
    public static void Apply(IWindow window)
    {
        ArgumentNullException.ThrowIfNull(window);

        // Named explicitly rather than left to the catch below. Calling too
        // early throws a generic InvalidOperationException whose message says
        // nothing about icons, and the symptom — GLFW falling back to the
        // stock Windows application icon while the executable's own PE icon
        // still shows in Explorer — looks like a packaging problem rather than
        // an ordering one. That misdirection already cost one shipped build.
        if (!window.IsInitialized)
        {
            Console.Error.WriteLine(
                "window icon: refusing to set an icon on an uninitialized window — "
                + "call WindowIconLoader.Apply from the Load callback, not next to "
                + "Window.Create.");
            return;
        }

        RawImage[] images;
        try
        {
            images = Decode();
        }
        catch (Exception failure)
        {
            // A missing or corrupt embedded resource is a build defect, not a
            // runtime condition — say so loudly rather than shipping a silent
            // catch, but do not take the client down over cosmetics.
            Console.Error.WriteLine($"window icon: could not decode embedded icons — {failure}");
            return;
        }

        if (images.Length == 0)
        {
            Console.Error.WriteLine("window icon: no embedded icon resources found");
            return;
        }

        try
        {
            window.SetWindowIcon(images.AsSpan());
        }
        catch (Exception failure)
        {
            // Wayland has no window-icon protocol and GLFW reports the request
            // as unsupported there. That is a platform fact, not a bug, and it
            // must not be fatal — but it is still worth printing so an
            // unexpectedly icon-less window on a supported platform is
            // traceable rather than mysterious.
            Console.Error.WriteLine($"window icon: platform rejected the icon — {failure.Message}");
        }
    }

    private static RawImage[] Decode()
    {
        var assembly = typeof(WindowIconLoader).Assembly;
        var decoded = new List<RawImage>(ResourceNames.Length);

        foreach (string name in ResourceNames)
        {
            using Stream? stream = assembly.GetManifestResourceStream(name);
            if (stream is null)
            {
                Console.Error.WriteLine($"window icon: embedded resource missing — {name}");
                continue;
            }

            using var image = Image.Load<Rgba32>(stream);
            var pixels = new byte[image.Width * image.Height * 4];
            image.CopyPixelDataTo(pixels);
            decoded.Add(new RawImage(image.Width, image.Height, pixels));
        }

        return decoded.ToArray();
    }
}