using AcDream.App.Rendering.Gpu;

namespace AcDream.App.Rendering;

/// <summary>
/// Campaign V slice V4a: exposes whichever <see cref="IGpuFrame"/> is
/// currently open, so renderers ported onto the RHI (<see cref="TextRenderer"/>,
/// <see cref="DebugLineRenderer"/> today) can reach it without a stored
/// window/delegate back-reference. Non-null exactly between a
/// <see cref="GpuDeviceFrameLifetime.BeginFrame"/> and its matching
/// <see cref="GpuDeviceFrameLifetime.EndFrame"/>.
/// </summary>
internal interface ICurrentGpuFrameSource
{
    IGpuFrame? CurrentFrame { get; }
}

/// <summary>
/// Drives <see cref="IGpuDevice.BeginFrame"/>/<see cref="IGpuFrame.End"/> once
/// per rendered frame, additively over the existing
/// <see cref="GpuFrameFlightController"/>-driven fence/slot bracket:
/// <see cref="GlGpuDevice"/>'s own <c>BeginFrame</c> already calls straight
/// through to the frame-flight controller it was constructed with (see its
/// class comment), so routing the production
/// <see cref="RenderFrameOrchestrator"/>'s <see cref="IRenderFrameLifetime"/>
/// through the device instead of the controller directly changes nothing about
/// the existing fence-wait/slot-rotation contract — it only additionally
/// yields the <see cref="IGpuFrame"/> that ported renderers need, which
/// <see cref="GpuFrameFlightController.BeginFrame"/> alone could not supply.
/// No clears move, no framebuffer binding changes, and the frame graph's
/// phase order is untouched.
/// </summary>
internal sealed class GpuDeviceFrameLifetime : IRenderFrameLifetime, ICurrentGpuFrameSource
{
    private readonly IGpuDevice _device;

    public GpuDeviceFrameLifetime(IGpuDevice device) =>
        _device = device ?? throw new ArgumentNullException(nameof(device));

    public IGpuFrame? CurrentFrame { get; private set; }

    public void BeginFrame() => CurrentFrame = _device.BeginFrame();

    public void EndFrame()
    {
        IGpuFrame? frame = CurrentFrame;
        CurrentFrame = null;
        frame?.End();
    }
}