using System.Buffers;
using System.Diagnostics;
using System.Threading.Channels;
using ytLive.Helpers;
using ytLive.Models;

namespace ytLive.Services.Encoder;

/// <summary>
/// The default <see cref="IFfmpegEncoder"/>: spawns <c>ffmpeg.exe</c> (resolved via
/// <see cref="IFfmpegLocator"/>), feeds raw BGRA frames into stdin, and parses the
/// <c>-stats</c> progress lines into <see cref="StreamHealth"/>. Encoder choice is
/// probed from the binary's <c>-encoders</c> listing (hardware NVENC/QSV/AMF first,
/// OpenH264 software fallback — never libx264, see the license posture) unless
/// <see cref="EncoderOptions.VideoEncoder"/> forces one.
///
/// Graceful stop = close stdin (EOF) → ffmpeg finalizes the FLV and exits by itself;
/// a watchdogs kill fires only if it hasn't exited shortly after EOF.
/// </summary>
public sealed class FfmpegEncoder : IFfmpegEncoder
{
    public event EventHandler<StreamHealth>? HealthUpdated;
    public event EventHandler<string>? ProcessFailed;

    private readonly IFfmpegLocator _locator;
    private readonly Func<IEncoderProcess> _processFactory;

    private readonly object _gate = new();
    private IEncoderProcess? _process;
    private EncoderOptions? _options;
    private StreamHealth _health = new() { Status = StreamStatus.Offline };
    private Task? _stderrLoop;
    private bool _stopRequested;

    // Pipe decoupling (slice 10, 2026-09-10): a bounded pending-frame queue drained
    // by its own task (the OBS video-thread → encoder-queue model — the encoder's
    // thread never couples back into the video thread; libobs obs-encoder.c). The
    // pump's SubmitFrameAsync now ENQUEUES (copying into a pooled buffer) instead of
    // blocking on WriteAsync when ffmpeg lags the pipe; overflow DROPS the newest
    // frame (skip-newest) and counts it. BoundedChannelFullMode.Wait + TryWrite gives
    // exactly that: when full, TryWrite returns false and the caller drops the item.
    private const int QueueCapacity = 120; // ~2s at the tier's 60fps
    private readonly Channel<PendingWrite> _frames = Channel.CreateBounded<PendingWrite>(
        new BoundedChannelOptions(QueueCapacity) { SingleReader = true });
    private Task? _drainTask;
    private int _droppedBackpressure;

    private readonly record struct PendingWrite(byte[] Buffer, int Length);

    public FfmpegEncoder(
        IFfmpegLocator locator,
        Func<IEncoderProcess>? processFactory = null)
    {
        _locator = locator;
        _processFactory = processFactory ?? (() => new FfmpegEncoderProcess());
    }

    public bool IsRunning { get; private set; }

    /// <summary>Frames dropped by the bounded queue because the drain task couldn't
    /// keep the pipe fed (the encoder lagging the real-time capture rate). The pump
    /// reports this in its stats; the burned-in frame counter in the recording
    /// shows the identical jumps. Distinct from <see cref="StreamHealth.DroppedFrames"/>
    /// (ffmpeg's own progress-derived estimate).</summary>
    public int DroppedFrames => Volatile.Read(ref _droppedBackpressure);

    public async Task StartAsync(EncoderOptions options, CancellationToken cancellationToken = default)
    {
        if (options == null) throw new ArgumentNullException(nameof(options));
        var hasStream = options.StreamEnabled && !string.IsNullOrWhiteSpace(options.RtmpUrl);
        var hasRecord = options.RecordEnabled && !string.IsNullOrWhiteSpace(options.RecordPath);
        if (!hasStream && !hasRecord)
            throw new ArgumentException(
                "At least one output is required — a stream needs an RTMP URL, a recording needs an output path.",
                nameof(options));

        lock (_gate)
        {
            if (IsRunning) throw new InvalidOperationException("The encoder is already running.");
            _options = options;
        }

        var ffmpegPath = await _locator.LocateAsync(cancellationToken).ConfigureAwait(false);
        var encoder = options.VideoEncoder ?? await ProbeEncoderAsync(ffmpegPath, cancellationToken).ConfigureAwait(false);
        var args = FfmpegArgs.Build(options, encoder);

        var startInfo = new ProcessStartInfo
        {
            FileName = ffmpegPath,
            UseShellExecute = false,
            RedirectStandardInput = true,
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            CreateNoWindow = true,
        };
        foreach (var arg in args) startInfo.ArgumentList.Add(arg);

        IEncoderProcess process;
        try
        {
            process = _processFactory();
            process.Start(startInfo);
        }
        catch (Exception ex)
        {
            AppLog.Write(ex, "FFmpeg encoder: failed to start subprocess");
            lock (_gate) _options = null;
            throw;
        }

        lock (_gate)
        {
            _process = process;
            IsRunning = true;
            _health = new StreamHealth { Status = StreamStatus.Streaming };
        }

        _stopRequested = false;
        _stderrLoop = RunStderrLoopAsync(process);
        StartDrainLoop(process);
    }

    /// <summary>
    /// Enqueue one raw BGRA frame for ffmpeg's stdin (slice 10). The caller races
    /// freely (the compositor pump); this never blocks on the pipe. The pixels are
    /// copied into a pooled buffer first because — unlike the old direct write — the
    /// write happens later on the drain thread, so the caller may (and does) recycle
    /// its scratch buffer the moment this returns. When the bounded queue is full the
    /// NEWEST frame is dropped and counted (freshness over coverage; the encoder is
    /// already behind, so the stale-content failure mode never encodes).
    /// </summary>
    public Task SubmitFrameAsync(VideoFrame frame, CancellationToken cancellationToken = default)
    {
        if (frame == null) throw new ArgumentNullException(nameof(frame));
        lock (_gate)
        {
            if (!IsRunning) throw new InvalidOperationException("The encoder is not running.");
        }

        if (cancellationToken.IsCancellationRequested)
            return Task.FromCanceled(cancellationToken);

        var pooled = ArrayPool<byte>.Shared.Rent(frame.BgraPixels.Length);
        Buffer.BlockCopy(frame.BgraPixels, 0, pooled, 0, frame.BgraPixels.Length);
        if (_frames.Writer.TryWrite(new PendingWrite(pooled, frame.BgraPixels.Length)))
            return Task.CompletedTask;

        // Queue full (encoder lagging) or the channel completed during stop — drop the
        // newest and count it. The caller never blocks; the encoder catches up or the
        // session ends with a (reported) short gap instead of a frozen stall.
        ArrayPool<byte>.Shared.Return(pooled);
        Interlocked.Increment(ref _droppedBackpressure);
        return Task.CompletedTask;
    }

    public async Task StopAsync(CancellationToken cancellationToken = default)
    {
        IEncoderProcess? process;
        Task? loop;
        lock (_gate)
        {
            if (!IsRunning) return;
            _stopRequested = true;
            process = _process;
            loop = _stderrLoop;
        }

        // Flush every queued frame, then EOF: TryComplete lets the drain task write
        // the buffered frames, close stdin → ffmpeg finalizes and exits by itself
        // (the "did not exit after EOF" kill below is only the backstop).
        try
        {
            _frames.Writer.TryComplete();
            if (_drainTask != null) await _drainTask.ConfigureAwait(false);
        }
        catch (Exception ex)
        {
            AppLog.Write(ex, "FFmpeg encoder: drain loop faulted during stop");
        }

        try
        {
            using var timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
            timeout.CancelAfter(TimeSpan.FromSeconds(10));
            await process!.WaitForExitAsync(timeout.Token).ConfigureAwait(false);
        }
        catch (OperationCanceledException)
        {
            AppLog.Write("FFmpeg encoder: did not exit after stdin EOF — killing");
            process!.Kill();
        }
        catch (Exception ex)
        {
            AppLog.Write(ex, "FFmpeg encoder: waiting for exit failed");
            process!.Kill();
        }

        try
        {
            if (loop != null) await loop.ConfigureAwait(false);
        }
        catch (Exception ex)
        {
            AppLog.Write(ex, "FFmpeg encoder: stderr loop faulted during stop");
        }

        process.Dispose();

        lock (_gate)
        {
            IsRunning = false;
            _health.Status = StreamStatus.Offline;
            _health.LastError = null;
            _process = null;
            _options = null;
        }

        AppLog.Write($"FFmpeg encoder stopped (exit {process.ExitCode})");
    }

    public void Dispose()
    {
        _frames.Writer.TryComplete(); // unblock a stuck drain loop alongside the kill
        lock (_gate)
        {
            if (!IsRunning) return;
            _process?.Kill();
            _process?.Dispose();
            _process = null;
            IsRunning = false;
        }
    }

    /// <summary>
    /// The drain task (slice 10): owns every stdin write, so pipe backpressure — the
    /// pump's old stall — lives HERE, on a thread the pump never touches. Frames are
    /// written exactly as queued (the pooled array through its recorded length —
    /// ArrayPool may return a larger buffer), returned to the pool after the write
    /// copies into the pipe, and stdin is closed (EOF) once the queue drains.
    /// </summary>
    private void StartDrainLoop(IEncoderProcess process)
    {
        _drainTask = Task.Run(async () =>
        {
            try
            {
                try
                {
                    while (await _frames.Reader.WaitToReadAsync().ConfigureAwait(false))
                    {
                        while (_frames.Reader.TryRead(out var pending))
                        {
                            await process.StandardInput.WriteAsync(pending.Buffer, 0, pending.Length)
                                .ConfigureAwait(false);
                            await process.StandardInput.FlushAsync().ConfigureAwait(false);
                            ArrayPool<byte>.Shared.Return(pending.Buffer);
                        }
                    }
                }
                catch (ChannelClosedException)
                {
                    // channel completed while waiting — fall through to EOF
                }
                catch (Exception ex)
                {
                    AppLog.Write(ex, "FFmpeg encoder: drain loop write faulted");
                }
                finally
                {
                    // EOF on every path — a byte that sits in the pool when the pipe
                    // breaks is garbage anyway, and ffmpeg MUST see the close to finalize.
                    process.StandardInput.Dispose();
                }
            }
            catch (Exception ex)
            {
                AppLog.Write(ex, "FFmpeg encoder: drain loop faulted");
            }
        });
    }

    private async Task<string> ProbeEncoderAsync(string ffmpegPath, CancellationToken cancellationToken)
    {
        try
        {
            var startInfo = new ProcessStartInfo
            {
                FileName = ffmpegPath,
                UseShellExecute = false,
                RedirectStandardOutput = true,
                RedirectStandardError = true,
                CreateNoWindow = true,
            };
            startInfo.ArgumentList.Add("-hide_banner");
            startInfo.ArgumentList.Add("-encoders");

            using var probe = _processFactory();
            probe.Start(startInfo);
            using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
            cts.CancelAfter(TimeSpan.FromSeconds(15));
            var output = await probe.StandardOutput.ReadToEndAsync(cts.Token).ConfigureAwait(false);
            return FfmpegEncoderPicker.Pick(output);
        }
        catch (Exception ex)
        {
            AppLog.Write(ex, "FFmpeg encoder: encoder probe failed — falling back to software");
            return FfmpegEncoderPicker.Preference[^1];
        }
    }

    private Task RunStderrLoopAsync(IEncoderProcess process)
    {
        return Task.Run(async () =>
        {
            try
            {
                while (true)
                {
                    var line = await process.StandardError.ReadLineAsync().ConfigureAwait(false);
                    if (line == null) break;
                    OnStderrLine(process, line);
                }

                // Read the exit code defensively: the stop path disposes the process
                // while this loop may still be waking (2026-09-01 "No process is
                // associated with this object" — a cosmetic race that poisoned the log).
                int exitCode;
                try
                {
                    exitCode = process.ExitCode;
                }
                catch (Exception)
                {
                    exitCode = -1;
                }

                var stillRunning = false;
                var stopping = false;
                lock (_gate)
                {
                    stillRunning = IsRunning;
                    stopping = _stopRequested;
                }
                if (stillRunning && !stopping)
                {
                    // ANY exit we did not ask for is a failure — including code 0.
                    // The old `code != 0` gate let ffmpeg's clean early exit vanish
                    // without a word while the pump kept feeding a corpse
                    // (2026-09-01 first real recording: died at ~0.9s, zero logs).
                    AppLog.Write($"FFmpeg encoder: subprocess exited unexpectedly (code {exitCode})");
                    _health.LastError = $"FFmpeg exited with code {exitCode}";
                    ProcessFailed?.Invoke(this, $"FFmpeg exited with code {exitCode}");
                }
            }
            catch (Exception ex)
            {
                AppLog.Write(ex, "FFmpeg encoder: stderr loop faulted");
            }
        });
    }

    private void OnStderrLine(IEncoderProcess process, string line)
    {
        var progress = FfmpegProgressParser.TryParse(line);
        if (progress == null)
        {
            // THE EYES: everything ffmpeg says that isn't a progress line — startup
            // config, warnings, the real reason it quit. Was silently discarded
            // (2026-09-01: encoder died at ~0.9s, log silent). Truncated so a
            // \r-choked stats blob can't flood; noise now beats blindness.
            var text = line.Trim('\r', ' ', '\t');
            if (text.Length > 0)
                AppLog.Write($"ffmpeg: {(text.Length > 400 ? text[..400] + "…" : text)}");
            return;
        }

        var dropped = Math.Max(0, (long)Math.Round(progress.Value.Fps * progress.Value.Duration.TotalSeconds) - progress.Value.Frame);

        lock (_gate)
        {
            _health.CurrentBitrate = progress.Value.BitrateKbps;
            _health.FPS = progress.Value.Fps;
            _health.DroppedFrames = (int)dropped;
            _health.StreamDuration = progress.Value.Duration;
        }

        HealthUpdated?.Invoke(this, _health);
    }
}