using Avalonia;
using Avalonia.Headless;
using Avalonia.Media;
using DodoSSH.Client.App.Layout.Tests;

[assembly: AvaloniaTestApplication(typeof(HeadlessApp))]

namespace DodoSSH.Client.App.Layout.Tests;

/// <summary>
/// Builds the real application for a headless renderer.
/// </summary>
/// <remarks>
/// <para>
/// <see cref="DodoSshApp"/> itself, not a stand-in, because the thing being measured is how the shipped
/// styles lay out — a harness with its own theme would measure a window nobody sees. Its
/// <c>OnFrameworkInitializationCompleted</c> only composes the object graph when the lifetime is a classic
/// desktop one, and a headless session's is not, so loading it here brings the Fluent theme and the dark
/// variant and starts no vault, no listener and no browser.
/// </para>
/// <para>
/// Skia rather than the headless drawing stub, which is the one deliberate cost in this file. The stub's
/// font manager returns invented glyph metrics, and text height is an input to every stacked panel in this
/// window — measuring against it would produce numbers that are self-consistent and unrelated to the
/// application. With Skia and the same Inter font the application registers, a measured height is the
/// height a user gets.
/// </para>
/// </remarks>
internal static class HeadlessApp
{
    /// <summary>Found by name; <see cref="AvaloniaTestApplicationAttribute"/> is the contract.</summary>
    /// <remarks>
    /// <para>
    /// The default family is named explicitly, because the paragraph above was describing an intention
    /// rather than what happened. <c>WithInterFont</c> registers a font collection; it does not make it
    /// the default. Avalonia resolves that from the platform — which is to say from whatever the machine
    /// has installed — so a suite whose whole job is measuring text was measuring Segoe UI on a
    /// developer's Windows and DejaVu on their Linux, and treating the two numbers as one.
    /// </para>
    /// <para>
    /// On a machine with no fonts at all it does not merely differ, it stops: <c>FontManager</c> throws
    /// "Default font family name can't be null or empty" during <c>AppBuilder.SetupUnsafe</c>, before any
    /// test body runs. That is how a container CI runner reports all sixty-eight of these as failures with
    /// not one assertion among them. Naming a font costs the runner nothing, because it travels inside the
    /// package rather than on the host — true of Inter before this and of Montserrat now.
    /// </para>
    /// </remarks>
    public static AppBuilder BuildAvaloniaApp() =>
        AppBuilder.Configure<DodoSshApp>()
            .UseSkia()
            .UseHeadless(new AvaloniaHeadlessPlatformOptions { UseHeadlessDrawing = false })
            .WithInterFont()
            .With(new FontManagerOptions
            {
                DefaultFamilyName = DefaultFamily,
                FontFallbacks = [new FontFallback { FontFamily = new FontFamily(InterFamily) }],
            });

    /// <summary>The family <c>Program.BuildAvaloniaApp</c> asks the font manager to default to.</summary>
    /// <remarks>
    /// Kept in step with <c>Program.BuildAvaloniaApp</c> by hand, and it matters that they agree: a
    /// harness pinning a different default from the one the application runs with would certify heights
    /// for a window nobody sees, which is the failure the opening paragraph of this file is about. It was
    /// Inter until the v3 design; now it is Montserrat, embedded the same way, and Inter moves down to
    /// <see cref="InterFamily"/> as the fallback both <c>BuildAvaloniaApp</c> methods name it as.
    /// </remarks>
    internal const string DefaultFamily = "avares://DodoSSH.Client.Shell/Assets/Fonts#Montserrat";

    /// <summary>The family <c>WithInterFont</c> registers.</summary>
    /// <remarks>
    /// No longer the default — see <see cref="DefaultFamily"/> — but still registered and still named
    /// here, because it is still the fallback both heads' <c>BuildAvaloniaApp</c> fall back to, and a test
    /// measuring a glyph Montserrat does not cover has to fall back to the same font the application does.
    /// </remarks>
    internal const string InterFamily = "avares://Avalonia.Fonts.Inter/Assets#Inter";
}