using AcDream.App;
using AcDream.App.Composition;
using Silk.NET.Core.Contexts;
using Silk.NET.OpenGL;

namespace AcDream.App.Tests.Composition;

/// <summary>
/// Campaign V slice V6h: the graphics handle composition tests hand to a phase.
///
/// <para>The phases now select their backend arm from
/// <see cref="GameWindowGraphics"/> rather than from a bare <c>GL</c> reference,
/// so a test that means "compose the OpenGL arm" has to say so. The GL instance
/// is never called: every composition test supplies a stub factory that ignores
/// its context argument, and the loader below would fault if anything did — which
/// is the point. It is a token identifying the arm, not a driver.</para>
/// </summary>
internal sealed class TestGameWindowGraphics : GameWindowGraphics
{
    private readonly GL? _gl;

    private TestGameWindowGraphics(RenderBackendKind backend, GL? gl)
    {
        Backend = backend;
        _gl = gl;
    }

    /// <summary>Selects the OpenGL arm, with a context token no test dereferences.</summary>
    public static TestGameWindowGraphics OpenGl { get; } =
        new(RenderBackendKind.Gl, new GL(new UnusableNativeContext()));

    /// <summary>Selects the Vulkan arm: no GL context exists.</summary>
    public static TestGameWindowGraphics Vulkan { get; } =
        new(RenderBackendKind.Vulkan, null);

    public override RenderBackendKind Backend { get; }

    public override GL? Gl => _gl;

    public override void Dispose()
    {
    }

    private sealed class UnusableNativeContext : INativeContext
    {
        public nint GetProcAddress(string proc, int? slot = null) =>
            throw new InvalidOperationException(
                $"A composition test called GL entry point '{proc}'. " +
                "Test graphics are a backend token, not a driver.");

        public bool TryGetProcAddress(string proc, out nint addr, int? slot = null)
        {
            addr = 0;
            return false;
        }

        public void Dispose()
        {
        }
    }
}