acdream/src/AcDream.App/Rendering/GlTextureConstructionTransaction.cs

namespace AcDream.App.Rendering;

internal interface IGlTextureNameApi
{
    uint GenTexture();
    void DeleteTexture(uint texture);
}

internal sealed class GlTextureNameApi(Silk.NET.OpenGL.GL gl) : IGlTextureNameApi
{
    public uint GenTexture() =>
        GlResourceCommand.CreateTexture(gl, "terrain construction texture");

    public void DeleteTexture(uint texture) =>
        GlResourceCommand.DeleteTexture(
            gl,
            texture,
            $"delete terrain construction texture {texture}");
}

/// <summary>
/// Retains every texture name immediately after allocation until the complete
/// aggregate owner has been constructed. A failed factory rolls names back in
/// reverse acquisition order and attempts every deletion.
/// </summary>
internal sealed class GlTextureConstructionTransaction(IGlTextureNameApi api)
    : IRetryableResourceCleanup
{
    private readonly List<uint> _ownedNames = [];
    private bool _finished;

    public bool IsCleanupComplete => _finished;

    public uint Allocate()
    {
        if (_finished)
            throw new InvalidOperationException("The texture construction transaction is finished.");

        uint texture = api.GenTexture();
        if (texture == 0)
            throw new InvalidOperationException("OpenGL returned no texture name.");
        _ownedNames.Add(texture);
        return texture;
    }

    public void Commit()
    {
        if (_finished)
            throw new InvalidOperationException("The texture construction transaction is finished.");
        _ownedNames.Clear();
        _finished = true;
    }

    public void Rollback()
    {
        if (_finished)
            return;

        List<Exception>? failures = null;
        for (int i = _ownedNames.Count - 1; i >= 0; i--)
        {
            uint texture = _ownedNames[i];
            try
            {
                api.DeleteTexture(texture);
                _ownedNames.RemoveAt(i);
            }
            catch (Exception failure)
            {
                (failures ??= []).Add(new InvalidOperationException(
                    $"Texture construction rollback could not delete OpenGL name {texture}.",
                    failure));
            }
        }

        if (failures is not null)
            throw new AggregateException(
                "Texture construction rollback did not release every allocated OpenGL name.",
                failures);

        _finished = true;
    }

    public void RetryCleanup() => Rollback();
}