using System;
using System.Threading;
using System.Threading.Tasks;
using ytLive.Models;
using ytLive.Services.Compositor;

namespace ytLive.Services.Encoder;

/// <summary>
/// The live frame producer (TASK 4 ship step 5): the bridge between the capture
/// managers + compositor and the encoder. While live it snapshots the active
/// scene each tick, resolves every element to its latest frame, composites it
/// into the tier's output frame, and paces frames into the encoder at the tier's
/// FPS. All collaborators are constructor-injected seams (scene, resolver,
/// options, encoder factory, pacing delay) so the pump stays free of WPF and of
/// the capture managers and is fully hermetic in tests.
///
/// The RTMP URL comes from the options provider: until the live-stream create
/// flow lands (TASK 5) it yields null, so go-live runs the existing visual flow
/// without actually pushing.
/// </summary>
public sealed class FramePump : IDisposable
{
    private readonly Func<Scene?> _sceneProvider;
    private readonly Func<SceneElement, VideoFrame?> _frameResolver;
    private readonly Func<CompositorOptions> _compositorOptions;
    private readonly Func<EncoderOptions?> _encoderOptions;
    private readonly Func<IFfmpegEncoder> _encoderFactory;
    private readonly Action<string>? _log;
    private readonly Func<TimeSpan, CancellationToken, Task> _pacingDelay;
    private readonly Func<(VideoFrame? Frame, SocialBarPosition Position)>? _socialBar;
    private readonly TransitionService? _transition;
    private readonly SceneGraph? _sceneGraph;
    private readonly SceneCompositor _compositor = new();

    // Master-buffer scratch pool (take-4 starvation fix, slice 2 of 2): a fresh
    // 8.3MB byte[] every tick is ~500MB/s of LOH churn — GC stalls masquerading
    // as render cost. The pump pools ONLY buffers it handed out (reference-equality
    // set), so bake-cache / social-bar / static-cache frames are never touched;
    // SubmitFrameAsync copies the bytes to the encoder's stdin before returning,
    // so recycling after submit is safe (MyMistakes recipe).
    private readonly HashSet<byte[]> _ownedScratch = new(ReferenceEqualityComparer.Instance);
    private readonly List<byte[]> _freeScratch = new();
    private const int MaxScratchPooled = 4;

    private byte[] AcquireScratch(int size)
    {
        for (var i = _freeScratch.Count - 1; i >= 0; i--)
        {
            if (_freeScratch[i].Length != size) continue;
            var buffer = _freeScratch[i];
            _freeScratch.RemoveAt(i);
            return buffer;
        }
        var fresh = new byte[size];
        _ownedScratch.Add(fresh);
        return fresh;
    }

    private void ReleaseScratch(byte[]? buffer)
    {
        if (buffer == null || !_ownedScratch.Contains(buffer)) return;
        if (_freeScratch.Count >= MaxScratchPooled || _freeScratch.Contains(buffer)) return;
        _freeScratch.Add(buffer);
    }

    // Windows sleep quantum (take-9 finding, 2026-09-04): Task.Delay rounds every
    // request up to the system clock tick (~15.6ms default — learn.microsoft.com/en-us/
    // dotnet/api/system.threading.tasks.task.delay: "approximately 15 milliseconds on
    // Windows systems"), so a pacer requesting 3-15ms actually sleeps 15.6ms. Takes
    // 5-9 measured work ~25ms but period ~37ms: one padded wait per frame hid every
    // compositor improvement. Established media-app practice (game-loop/OBS canon —
    // stackoverflow.com/questions/5441464; and raise the resolution for the session —
    // learn.microsoft.com/en-us/windows/win32/api/timeapi/nf-timeapi-timebeginperiod):
    // timeBeginPeriod(1) while the pump runs, sleep only the BULK of the remainder,
    // and spin the last ~2ms across the deadline.
    [System.Runtime.InteropServices.DllImport("winmm.dll")]
    private static extern uint timeBeginPeriod(uint uMilliseconds);
    [System.Runtime.InteropServices.DllImport("winmm.dll")]
    private static extern uint timeEndPeriod(uint uMilliseconds);
    private static readonly long SpinTailTicks = System.Diagnostics.Stopwatch.Frequency * 2 / 1000; // 2ms

    private readonly object _gate = new();
    private IFfmpegEncoder? _encoder;
    private CancellationTokenSource? _cts;
    private Task? _pumpTask;
    private bool _started;
    private long _outputIndex;

    /// <summary>Captured by <see cref="ProbeRender"/> when a render exceeds ~20ms —
    /// the 2026-09-12 half-speed-render probe. Appended (once) to the next stats or
    /// stall line, then cleared.</summary>
    private string _renderDetail = "";

    /// <summary>Forwards the encoder's parsed health — ship step 6 binds this to the bottom bar.</summary>
    public event EventHandler<StreamHealth>? HealthUpdated;

    /// <summary>Raised when the encoder cannot start or dies mid-stream. The pump stops itself.</summary>
    public event EventHandler<string>? Failed;

    public FramePump(
        Func<Scene?> sceneProvider,
        Func<SceneElement, VideoFrame?> frameResolver,
        Func<CompositorOptions> compositorOptions,
        Func<EncoderOptions?> encoderOptions,
        Func<IFfmpegEncoder> encoderFactory,
        Action<string>? log = null,
        Func<TimeSpan, CancellationToken, Task>? pacingDelay = null,
        Func<(VideoFrame? Frame, SocialBarPosition Position)>? socialBar = null,
        TransitionService? transition = null,
        SceneGraph? sceneGraph = null)
    {
        _sceneProvider = sceneProvider ?? throw new ArgumentNullException(nameof(sceneProvider));
        _frameResolver = frameResolver ?? throw new ArgumentNullException(nameof(frameResolver));
        _compositorOptions = compositorOptions ?? throw new ArgumentNullException(nameof(compositorOptions));
        _encoderOptions = encoderOptions ?? throw new ArgumentNullException(nameof(encoderOptions));
        _encoderFactory = encoderFactory ?? throw new ArgumentNullException(nameof(encoderFactory));
        _log = log;
        _pacingDelay = pacingDelay ?? ((delay, ct) => Task.Delay(delay, ct));
        _socialBar = socialBar;
        _transition = transition;
        _sceneGraph = sceneGraph;
    }

    public bool IsRunning { get; private set; }

    /// <summary>Never throws: failures are logged and surfaced via <see cref="Failed"/>,
    /// so the VM can fire-and-forget it from a sync command handler.</summary>
    public async Task StartAsync(CancellationToken cancellationToken = default)
    {
        lock (_gate)
        {
            if (_started) return;
            _started = true;
        }

        IFfmpegEncoder? encoder = null;
        try
        {
            var options = _encoderOptions();
            if (options == null)
            {
                _log?.Invoke("FramePump: no output configured (neither streaming nor recording) — encoder skipped");
                lock (_gate) _started = false;
                return;
            }

            encoder = _encoderFactory();
            encoder.HealthUpdated += OnHealthUpdated;
            encoder.ProcessFailed += OnProcessFailed;
            await encoder.StartAsync(options, cancellationToken);

            lock (_gate)
            {
                _encoder = encoder;
            }

            // IsRunning must be true before the loop starts: the loop reads it on
            // its first iteration, and with a completed-task delay it can run
            // synchronously on this thread before PumpAsync even returns.
            IsRunning = true;
            _cts = new CancellationTokenSource();
            // The loop runs on the thread pool ON PURPOSE (take-8 finding, 2026-09-04):
            // Task.Run installs no SynchronizationContext, so every await continuation
            // stays off the UI dispatcher. Before this, the pump inherited the UI
            // thread's sync context (StartAsync is fired from a command handler), so
            // "render 22ms, wait 10ms" was the producer sitting in the dispatcher
            // queue behind the live preview it is meant to be independent of — the
            // stats quantum fix made the wait VISIBLE; this removes its cause.
            // OBS's video threads are dedicated for exactly this reason.
            _pumpTask = Task.Run(() => PumpAsync(options, _cts.Token));
            _log?.Invoke($"FramePump started ({options.Width}×{options.Height} @ {options.Fps} fps)");
        }
        catch (Exception ex)
        {
            _log?.Invoke($"FramePump: start failed: {ex.Message}");
            if (encoder != null)
            {
                encoder.HealthUpdated -= OnHealthUpdated;
                encoder.ProcessFailed -= OnProcessFailed;
                try
                {
                    encoder.Dispose();
                }
                catch (Exception disposeEx)
                {
                    _log?.Invoke($"FramePump: disposing failed encoder: {disposeEx.Message}");
                }
            }
            lock (_gate)
            {
                _started = false;
                IsRunning = false;
            }
            Failed?.Invoke(this, ex.Message);
        }
    }

    public async Task StopAsync(CancellationToken cancellationToken = default)
    {
        IFfmpegEncoder? encoder;
        Task? pump;
        lock (_gate)
        {
            if (!_started && _encoder == null) return;
            _started = false;
            IsRunning = false;
            encoder = _encoder;
            pump = _pumpTask;
            _cts?.Cancel();
        }

        // Stop the encoder BEFORE awaiting the pump: closing its stdin unblocks a
        // write stuck on pipe backpressure, otherwise the pump could await forever.
        if (encoder != null)
        {
            try
            {
                await encoder.StopAsync(cancellationToken);
            }
            catch (Exception ex)
            {
                _log?.Invoke($"FramePump: encoder stop failed: {ex.Message}");
            }
        }

        if (pump != null)
        {
            try
            {
                await pump;
            }
            catch (Exception ex)
            {
                _log?.Invoke($"FramePump: pump loop faulted during stop: {ex.Message}");
            }
        }

        if (encoder != null)
        {
            encoder.HealthUpdated -= OnHealthUpdated;
            encoder.ProcessFailed -= OnProcessFailed;
            try
            {
                encoder.Dispose();
            }
            catch (Exception ex)
            {
                _log?.Invoke($"FramePump: encoder dispose failed: {ex.Message}");
            }
        }

        lock (_gate)
        {
            _encoder = null;
            _cts = null;
            _pumpTask = null;
        }
        _log?.Invoke("FramePump stopped");
    }

    public void Dispose()
    {
        try
        {
            StopAsync().GetAwaiter().GetResult();
        }
        catch (Exception ex)
        {
            _log?.Invoke($"FramePump: dispose failed: {ex.Message}");
        }
        _freeScratch.Clear();
        _ownedScratch.Clear();
    }

    private async Task PumpAsync(EncoderOptions options, CancellationToken ct)
    {
        var interval = TimeSpan.FromSeconds(1d / Math.Max(1, options.Fps));
        var lastTick = System.Diagnostics.Stopwatch.StartNew();

        // Deadline pacing (2026-09-03, take-3 fix): the frame interval is a DEADLINE,
        // not an afterthought sleep — the OBS libobs video-io.c pattern (researched
        // before coding; see https://github.com/obsproject/obs-studio/blob/master/
        // libobs/media-io/video-io.c). The old loop slept the FULL interval after
        // each render, so period = render + submit + interval: at take-3's 258ms
        // render that was 3.6fps stamped into a 60fps container — rawvideo stamps by
        // arrival, so 30 wall-seconds muxed as a 2.1s time-lapse, no error anywhere.
        var intervalTicks = Math.Max(1, (long)Math.Round(interval.TotalSeconds * System.Diagnostics.Stopwatch.Frequency));
        var nextTick = System.Diagnostics.Stopwatch.GetTimestamp();

        // Stage timing (2026-09-01, take two): rawvideo carries no per-frame
        // timestamps — ffmpeg stamps frames by ARRIVAL at the declared fps. A producer
        // slower than the declared rate yields a time-lapsed, short file (observed:
        // 39 frames in 27 wall-seconds ≈ 30x at 60fps) with no error anywhere.
        // Log the render/submit split every 5s so the next take names the stage.
        var renderSw = new System.Diagnostics.Stopwatch();
        var submitSw = new System.Diagnostics.Stopwatch();
        var waitSw = new System.Diagnostics.Stopwatch();
        // Resolve-vs-composite split (2026-09-04, take-6 ambiguity): "render" was a
        // black box — the stats line now reports resolver time separately so a take
        // names the stage (get-frame vs blit) instead of feeding another guess.
        var resolveSw = new System.Diagnostics.Stopwatch();
        long renderTicks = 0, submitTicks = 0, resolveTicks = 0, waitTicks = 0, worstRender = 0, worstSubmit = 0;
        int statFrames = 0;
        int stalls = 0;
        var statsNext = DateTime.UtcNow + TimeSpan.FromSeconds(5);
        void ReportStats()
        {
            if (DateTime.UtcNow < statsNext) return;
            var target = 5d / interval.TotalSeconds; // frames expected per window
            IFfmpegEncoder? encoder;
            lock (_gate) encoder = _encoder;
            var dropped = encoder == null ? 0 : encoder.DroppedFrames;
            var detail = _renderDetail;
            _renderDetail = "";
            _log?.Invoke(statFrames == 0
                ? "FramePump stats: NO frames produced in 5s (loop stalled?)" + (detail.Length > 0 ? " | " + detail : "")
                : $"FramePump stats: {statFrames}/{target:F0} frames per 5s, " +
                  $"avg render {renderTicks / (double)System.Diagnostics.Stopwatch.Frequency * 1000 / statFrames:F1}ms " +
                  $"(resolve {resolveTicks / (double)System.Diagnostics.Stopwatch.Frequency * 1000 / statFrames:F1}), " +
                  $"avg submit {submitTicks / (double)System.Diagnostics.Stopwatch.Frequency * 1000 / statFrames:F1}ms, "
                  + $"avg wait {waitTicks / (double)System.Diagnostics.Stopwatch.Frequency * 1000 / statFrames:F1}ms, "
                  + $"worst render {worstRender / (double)System.Diagnostics.Stopwatch.Frequency * 1000:F1}ms, "
                  + $"worst submit {worstSubmit / (double)System.Diagnostics.Stopwatch.Frequency * 1000:F1}ms, "
                  + $"dropped {dropped}, stalls {stalls}" + (detail.Length > 0 ? " | " + detail : ""));
            worstRender = 0;
            worstSubmit = 0;
            renderTicks = submitTicks = resolveTicks = waitTicks = 0;
            statFrames = 0;
            stalls = 0;
            statsNext = DateTime.UtcNow + TimeSpan.FromSeconds(5);
        }

        // One wrapper shared by every render of the run — resolve time accumulates
        // inside the render measurement, and the stats line reports the split.
        timeBeginPeriod(1); // pairs with timeEndPeriod in the finally — see field note
        var previousGcMode = System.Runtime.GCSettings.LatencyMode;
        System.Runtime.GCSettings.LatencyMode = System.Runtime.GCLatencyMode.SustainedLowLatency;
        VideoFrame? TimedResolver(SceneElement element)
        {
            resolveSw.Restart();
            var frame = _frameResolver(element);
            resolveSw.Stop();
            resolveTicks += resolveSw.ElapsedTicks;
            return frame;
        }

        try
        {
            while (!ct.IsCancellationRequested)
            {
                var scene = _sceneProvider();
                if (scene != null)
                {
                    var iterStart = System.Diagnostics.Stopwatch.GetTimestamp();
                    var compositorOptions = _compositorOptions();
                    VideoFrame? socialBarFrame = null;
                    var socialBarTop = 0;
                    if (_socialBar != null)
                    {
                        var (barFrame, position) = _socialBar();
                        socialBarFrame = barFrame;
                        if (barFrame != null)
                            socialBarTop = position == SocialBarPosition.Top
                                ? 0
                                : compositorOptions.SourceRectHeight - barFrame.Height;
                    }

                    VideoFrame frame;
                    var scratchSize = compositorOptions.SourceRectWidth
                        * compositorOptions.SourceRectHeight * 4;
                    // The transition "from" frame lives in TransitionService.FromFrame
                    // (captured at Start by the VM). The old per-tick fromScene render
                    // here was dead weight — a full extra scene composite every
                    // transition tick that BlendFrame never read; removed with the
                    // pooling change because its buffer's only consumer was its own release.
                    renderSw.Restart();
                    var scratch = AcquireScratch(scratchSize);
                    frame = RenderScene(scene, compositorOptions, socialBarFrame, socialBarTop, scratch, TimedResolver);
                    if (_transition is { Active: true } transition)
                    {
                        frame = transition.BlendFrame(frame);
                        transition.Tick(lastTick.Elapsed.TotalMilliseconds);
                    }
                    // Restarted EVERY frame (transition or not): a transition begun
                    // after idle must not inherit a giant ElapsedMs and complete
                    // instantly on its first Tick.
                    lastTick.Restart();
                    renderSw.Stop();
                    renderTicks += renderSw.ElapsedTicks;
                    if (renderSw.ElapsedTicks > worstRender) worstRender = renderSw.ElapsedTicks;

                    IFfmpegEncoder? encoder;
                    lock (_gate) encoder = _encoder;
                    if (encoder == null) break;

                    // Deadline pacing, OBS duplicate-on-lag (slice 15): emit ONE frame per
                    // deadline slot — a fresh composite when the render kept up, a REPEAT
                    // of this iteration's latest composite for every slot the render
                    // overran. The OBS model never leaves a wall-time hole: libobs
                    // media-io/video-io.c runs on its own clock and duplicates the latest
                    // frame when the video thread lags, logging "lagged frames due to
                    // rendering lag/stalls" — never skipped time (docs.obsproject.com/
                    // backend-design: "If the video frame queue is full, it will duplicate
                    // the last frame"). Slice 10 chose the opposite for freshness: an
                    // overrun SKIPPED the missed slots, so a 60fps-authoring pump emitting
                    // one frame per 35ms overrun authored ~1.7x playback (ty-1726: 163
                    // video frames for 2.93s of audio) and ended the video 0.22s before the
                    // audio tail. Counting duplicates instead of skips keeps recording
                    // duration == wall duration (no acceleration, no audio tail cut) at the
                    // cost of a short judder during a stall — the accepted trade. The burst
                    // is microseconds (the enqueue never blocks, and the loop is clamped to
                    // deadlineNow) so it can't smear the way the take-9 blocking burst did.
                    var deadlineNow = System.Diagnostics.Stopwatch.GetTimestamp();
                    while (!ct.IsCancellationRequested && deadlineNow >= nextTick)
                    {
                        // Burned-in frame counter (slice 10 judge): a clock-independent
                        // pacing witness burned literally into the composite. Decode the
                        // recording and read the bottom-right strip: the number must
                        // advance +1 per authored frame and jump only by counted drops
                        // (queue overflow). Burned here — on the buffer finally submitted,
                        // which the enqueue's snapshot copies before the next iteration
                        // rewrites it — so every file frame carries its own index and a
                        // fast-render iteration that submitted nothing leaves no phantom
                        // gap (the slice-10 unconditional bump before the gate could).
                        _outputIndex++;
                        BurnFrameIndex(frame.BgraPixels, frame.Width, frame.Height, _outputIndex);

                        submitSw.Restart();
                        await encoder.SubmitFrameAsync(frame, ct);
                        submitSw.Stop();
                        statFrames++;
                        submitTicks += submitSw.ElapsedTicks;
                        if (submitSw.ElapsedTicks > worstSubmit) worstSubmit = submitSw.ElapsedTicks;
                        nextTick += intervalTicks;
                    }

                    // SubmitFrameAsync copied the bytes into the encoder's queue — the
                    // tick's buffers are recyclable once the enqueue snapshot them.
                    // The free-list Contains guard keeps the Cut path (BlendFrame
                    // returns toFrame itself, aliasing scratch) safe.
                    ReleaseScratch(frame.BgraPixels);
                    ReleaseScratch(scratch);

                    // Sleep the BULK of the remainder, SPIN the 2ms tail — never hand
                    // a sub-tick remainder to the sleep quantum (the timeBeginPeriod
                    // note). If the renderer already ate the budget there is nothing
                    // left to sleep and the loop renders the next frame straight away.
                    waitSw.Restart();
                    var ahead = nextTick - System.Diagnostics.Stopwatch.GetTimestamp();
                    if (ahead > SpinTailTicks)
                        await _pacingDelay(TimeSpan.FromSeconds(
                            (ahead - SpinTailTicks) / (double)System.Diagnostics.Stopwatch.Frequency), ct);
                    while (!ct.IsCancellationRequested
                           && System.Diagnostics.Stopwatch.GetTimestamp() < nextTick)
                        Thread.SpinWait(400);
                    waitSw.Stop();
                    waitTicks += waitSw.ElapsedTicks;

                    // Stall logger (slice 10): an iteration spanning more than two full
                    // intervals is the old bug's fingerprint — name the stage instead of
                    // guessing. With the queue, submit should be ~1ms, so a stall here
                    // means RENDER or RESOLVE (the stage terms of the last take).
                    var iterWall = System.Diagnostics.Stopwatch.GetTimestamp() - iterStart;
                    if (iterWall > 2 * intervalTicks)
                    {
                        stalls++;
                        var detail = _renderDetail;
                        _renderDetail = "";
                        _log?.Invoke($"FramePump stall: iteration {iterWall / (double)System.Diagnostics.Stopwatch.Frequency * 1000:F0}ms " +
                            $"(> 2× the {interval.TotalMilliseconds:F0}ms interval): worst render " +
                            $"{worstRender / (double)System.Diagnostics.Stopwatch.Frequency * 1000:F0}ms, worst submit " +
                            $"{worstSubmit / (double)System.Diagnostics.Stopwatch.Frequency * 1000:F0}ms, dropped {encoder.DroppedFrames}" +
                            (detail.Length > 0 ? " | " + detail : ""));
                    }
                    ReportStats();
                }
            }
        }
        catch (OperationCanceledException)
        {
            // normal stop
        }
        catch (Exception ex)
        {
            // A failure while the pump is supposed to run (encoder died under us,
            // scene provider faulted, ...) stops the pump and surfaces once.
            if (ct.IsCancellationRequested)
            {
                _log?.Invoke($"FramePump: pump exited during stop: {ex.Message}");
            }
            else
            {
                _log?.Invoke($"FramePump: pump loop faulted: {ex.Message}");
                Failed?.Invoke(this, ex.Message);
            }
        }
        finally
        {
            System.Runtime.GCSettings.LatencyMode = previousGcMode;
            timeEndPeriod(1);
            lock (_gate) IsRunning = false;
        }
    }

    private void OnHealthUpdated(object? sender, StreamHealth health) => HealthUpdated?.Invoke(this, health);

    /// <summary>Render a scene, using the baked-crust optimization when a <see cref="SceneGraph"/>
    /// is wired in: bake/cache the static layers below the split point, then composite the
    /// dynamic/above-split layers per frame. Without a SceneGraph, falls back to a full render
    /// (identical output — see SceneCompositorTests). <paramref name="scratch"/> is a pooled
    /// master buffer when supplied; the fully-static path returns the bake-cache frame itself
    /// (never pooled — the release side checks owned-by-reference).</summary>
    private VideoFrame RenderScene(
        Scene scene,
        CompositorOptions options,
        VideoFrame? socialBarFrame,
        int socialBarTop,
        byte[]? scratch = null,
        Func<SceneElement, VideoFrame?>? resolver = null)
    {
        resolver ??= _frameResolver;
        if (_sceneGraph == null)
        {
            var sw = System.Diagnostics.Stopwatch.StartNew();
            var frame = _compositor.Render(scene, resolver, null, options, socialBarFrame, socialBarTop, scratch: scratch);
            ProbeRender("full-no-graph", scene, -1, sw.ElapsedMilliseconds, 0);
            return frame;
        }

        var split = _sceneGraph.GetSplitPoint(scene);
        if (split == scene.Elements.Count)
        {
            // Fully static scene: bake once, reuse.
            var sw = System.Diagnostics.Stopwatch.StartNew();
            var baked = _sceneGraph.GetBakedBase(scene, _frameResolver, _compositorOptions);
            if (baked != null)
            {
                var stretched = StretchMath.BilinearScale(baked, options.OutputWidth, options.OutputHeight);
                ProbeRender("fully-static", scene, split, sw.ElapsedMilliseconds, (int)sw.ElapsedMilliseconds);
                return stretched;
            }
        }

        var swBase = System.Diagnostics.Stopwatch.StartNew();
        var baseFrame = _sceneGraph.GetBakedBase(scene, _frameResolver, _compositorOptions);
        if (baseFrame != null)
        {
            var frame = SceneCompositor.CompositeLayers(
                baseFrame, scene, split, resolver, options, socialBarFrame, socialBarTop, scratch: scratch);
            ProbeRender("base+layers", scene, split, swBase.ElapsedMilliseconds, 0);
            return frame;
        }

        // No static base (first layer is dynamic or empty scene) — full render.
        var swFull = System.Diagnostics.Stopwatch.StartNew();
        var frame2 = _compositor.Render(scene, resolver, null, options, socialBarFrame, socialBarTop, scratch: scratch);
        ProbeRender("full-render", scene, split, swFull.ElapsedMilliseconds, 0);
        return frame2;
    }

    /// <summary>2026-09-12 half-speed-render probe: the pump only produces ~27fps
    /// (render ~35ms vs the 16.7ms deadline), and rawvideo muxes at the DECLARED fps,
    /// so every take muxes at ~half its wall length (the truncation complaint). This
    /// names WHICH compositor path ate the slow frame so the fix targets the real
    /// stage. Records only when a frame takes ≥20ms (or carries the previous detail).</summary>
    private void ProbeRender(string path, Scene scene, int split, long totalMs, int bakeMs)
    {
        if (totalMs < 20 && _renderDetail.Length == 0) return;
        var dynamics = 0;
        foreach (var e in scene.Elements)
            if (e.Kind == ElementKind.Dynamic) dynamics++;
        _renderDetail = $"render={path} split={split} elements={scene.Elements.Count} dynamic={dynamics}" +
                        (bakeMs > 0 ? $" bakeMs={bakeMs}" : "") + $" totalMs={totalMs}";
    }

    // Dot-matrix digits (5×7, one row per raster line, '1' = lit) burned into the
    // bottom-right of every composite. Basic OCR-safe shapes, sized so the strip is
    // a 36×8 white box in the corner of a 1920×1080 frame — readable with a zoomed
    // player, invisible at normal size.
    private static readonly string[][] DigitGlyphs =
    {
        new[] { "01110","10001","10001","10001","10001","10001","01110" }, // 0
        new[] { "00100","01100","00100","00100","00100","00100","01110" }, // 1
        new[] { "01110","10001","00001","00010","00100","01000","11111" }, // 2
        new[] { "11111","00001","00010","00110","00001","10001","01110" }, // 3
        new[] { "00010","00110","01010","10010","11111","00010","00010" }, // 4
        new[] { "11111","10000","11110","00001","00001","10001","01110" }, // 5
        new[] { "01110","10001","10000","11110","10001","10001","01110" }, // 6
        new[] { "11111","00001","00010","00100","01000","01000","01000" }, // 7
        new[] { "01110","10001","10001","01110","10001","10001","01110" }, // 8
        new[] { "01110","10001","10001","01111","00001","10001","01110" }, // 9
    };

    private static void BurnFrameIndex(byte[] bgra, int width, int height, long index)
    {
        const int digitW = 5, digitH = 7, gap = 1, margin = 2, digitCount = 6;
        var stripW = digitCount * (digitW + gap) - gap;
        var left = width - margin - stripW;
        var top = height - margin - digitH;

        // Solid white box under the digits — the underlying scene can be anything.
        for (var y = top; y < top + digitH; y++)
            for (var x = left; x < left + stripW; x++)
            {
                var i = (y * width + x) * 4;
                bgra[i] = 255;
                bgra[i + 1] = 255;
                bgra[i + 2] = 255;
            }

        var text = index.ToString("D6");
        for (var d = 0; d < digitCount; d++)
        {
            var glyph = DigitGlyphs[text[d] - '0'];
            for (var row = 0; row < digitH; row++)
                for (var col = 0; col < digitW; col++)
                {
                    if (glyph[row][col] != '1') continue;
                    var i = ((top + row) * width + (left + d * (digitW + gap) + col)) * 4;
                    bgra[i] = 0;
                    bgra[i + 1] = 0;
                    bgra[i + 2] = 0;
                }
        }
    }

    private void OnProcessFailed(object? sender, string message)
    {
        _log?.Invoke($"FramePump: encoder process failed: {message}");
        Failed?.Invoke(this, message);
        _ = StopAsync();
    }
}