TeleWave/backend/src/TeleWave.Infrastructure/Media/FfmpegMediaProcessor.cs

using System.Globalization;
using System.Text.Json;
using Microsoft.Extensions.Options;
using TeleWave.Application.Common.Interfaces;

namespace TeleWave.Infrastructure.Media;

/// <summary>
/// Нормализация (H.264/AAC 1080p) и нарезка исходника на HLS-сегменты через ffmpeg. Длительность
/// добивается чёрным кадром + тишиной до кратности длине сегмента — ключевой инвариант эфирной
/// математики (см. docs/media-storage-and-streaming.md).
/// </summary>
public sealed class FfmpegMediaProcessor(
    MediaPathResolver paths,
    IOptions<StorageOptions> storageOptions,
    IOptions<MediaOptions> mediaOptions
) : IMediaProcessor
{
    private const int MaxWidth = 1920;
    private readonly StorageOptions _storage = storageOptions.Value;
    private readonly MediaOptions _media = mediaOptions.Value;

    public async Task<MediaProcessingResult> ProcessAsync(
        Guid assetId,
        string extension,
        CancellationToken cancellationToken
    )
    {
        var originalPath = paths.OriginalPath(assetId, extension);
        if (!File.Exists(originalPath))
            throw new FileNotFoundException("Исходник для обработки не найден.", originalPath);

        var probe = await ProbeAsync(originalPath, cancellationToken);
        var segmentSeconds = _storage.SegmentSeconds;

        // Целевая длительность — вверх до кратности длине сегмента.
        var target = Math.Ceiling(probe.Duration / segmentSeconds) * segmentSeconds;
        var pad = target - probe.Duration;

        var assetDir = paths.AssetDir(assetId);
        if (Directory.Exists(assetDir))
            Directory.Delete(assetDir, recursive: true);
        Directory.CreateDirectory(assetDir);

        var (outWidth, outHeight) = ScaleDown(probe.Width, probe.Height);
        var args = BuildFfmpegArgs(originalPath, assetDir, segmentSeconds, target, pad);

        var result = await ProcessRunner.RunAsync(
            _media.FfmpegPath,
            args,
            lowPriority: true,
            TimeSpan.FromSeconds(_media.TranscodeTimeoutSeconds),
            cancellationToken
        );
        if (result.ExitCode != 0)
            throw new InvalidOperationException(
                $"ffmpeg завершился с кодом {result.ExitCode}: {Tail(result.StdErr)}"
            );

        var playlist = Path.Combine(assetDir, "index.m3u8");
        if (!File.Exists(playlist))
            throw new InvalidOperationException("ffmpeg не создал плейлист index.m3u8.");

        var segmentCount = Directory.GetFiles(assetDir, "seg*.ts").Length;
        if (segmentCount == 0)
            throw new InvalidOperationException("ffmpeg не создал ни одного сегмента.");

        return new MediaProcessingResult(
            TimeSpan.FromSeconds(target),
            segmentSeconds,
            segmentCount,
            outWidth,
            outHeight,
            "h264",
            "aac",
            paths.AssetRelativePath(assetId)
        );
    }

    private List<string> BuildFfmpegArgs(
        string input,
        string assetDir,
        int segmentSeconds,
        double target,
        double pad
    )
    {
        var padding = pad > 0.001;
        var vfilter = $"scale='min({MaxWidth},iw)':-2";
        if (padding)
            vfilter += $",tpad=stop_duration={Fmt(pad)}:stop_mode=add:color=black";

        var args = new List<string>
        {
            "-hide_banner",
            "-nostdin",
            "-y",
            "-i",
            input,
            "-threads",
            _media.TranscodeThreads.ToString(CultureInfo.InvariantCulture),
            "-c:v",
            "libx264",
            "-preset",
            "veryfast",
            "-crf",
            "21",
            "-maxrate",
            "4500k",
            "-bufsize",
            "9000k",
            "-vf",
            vfilter,
            "-force_key_frames",
            $"expr:gte(t,n_forced*{segmentSeconds.ToString(CultureInfo.InvariantCulture)})",
            "-sc_threshold",
            "0",
            "-c:a",
            "aac",
            "-b:a",
            "128k",
            "-ac",
            "2",
            "-ar",
            "48000",
        };

        // Аудиофильтры: нормализация громкости (EBU R128, чтобы все ролики звучали одинаково) и,
        // при добивке хвоста, тишина apad. Порядок: сначала loudnorm по реальному звуку, потом apad.
        var afilters = new List<string>();
        if (_media.NormalizeLoudness)
            afilters.Add(
                $"loudnorm=I={_media.LoudnessTargetLufs.ToString(CultureInfo.InvariantCulture)}:TP=-1.5:LRA=11"
            );
        if (padding)
            afilters.Add($"apad=pad_dur={Fmt(pad)}");

        if (afilters.Count > 0)
        {
            args.Add("-af");
            args.Add(string.Join(",", afilters));
        }

        if (padding)
        {
            args.Add("-t");
            args.Add(Fmt(target));
        }

        args.AddRange([
            "-f",
            "hls",
            "-hls_time",
            segmentSeconds.ToString(CultureInfo.InvariantCulture),
            "-hls_playlist_type",
            "vod",
            "-hls_list_size",
            "0",
            "-hls_segment_filename",
            Path.Combine(assetDir, "seg%05d.ts"),
            Path.Combine(assetDir, "index.m3u8"),
        ]);

        return args;
    }

    private async Task<ProbeInfo> ProbeAsync(string path, CancellationToken cancellationToken)
    {
        var result = await ProcessRunner.RunAsync(
            _media.FfprobePath,
            ["-v", "quiet", "-print_format", "json", "-show_format", "-show_streams", path],
            lowPriority: false,
            TimeSpan.FromSeconds(_media.ProbeTimeoutSeconds),
            cancellationToken
        );
        if (result.ExitCode != 0)
            throw new InvalidOperationException(
                $"ffprobe завершился с кодом {result.ExitCode}: {Tail(result.StdErr)}"
            );

        using var doc = JsonDocument.Parse(result.StdOut);
        var root = doc.RootElement;

        double duration = 0;
        if (
            root.TryGetProperty("format", out var format)
            && format.TryGetProperty("duration", out var durEl)
            && double.TryParse(
                durEl.GetString(),
                NumberStyles.Float,
                CultureInfo.InvariantCulture,
                out var parsed
            )
        )
            duration = parsed;

        int width = 0,
            height = 0;
        var hasVideo = false;
        if (root.TryGetProperty("streams", out var streams))
        {
            foreach (var stream in streams.EnumerateArray())
            {
                if (!stream.TryGetProperty("codec_type", out var typeEl))
                    continue;
                if (typeEl.GetString() == "video" && !hasVideo)
                {
                    hasVideo = true;
                    width = stream.TryGetProperty("width", out var w) ? w.GetInt32() : 0;
                    height = stream.TryGetProperty("height", out var h) ? h.GetInt32() : 0;
                }
            }
        }

        if (duration <= 0)
            throw new InvalidOperationException("Не удалось определить длительность файла.");
        if (!hasVideo || width <= 0 || height <= 0)
            throw new InvalidOperationException("В файле не найдена видеодорожка.");

        return new ProbeInfo(duration, width, height);
    }

    private static (int Width, int Height) ScaleDown(int width, int height)
    {
        if (width <= MaxWidth)
            return (width, height);
        var scaledHeight = (int)Math.Round((double)height * MaxWidth / width);
        if (scaledHeight % 2 != 0)
            scaledHeight++;
        return (MaxWidth, scaledHeight);
    }

    private static string Fmt(double value) =>
        value.ToString("0.###", CultureInfo.InvariantCulture);

    private static string Tail(string text)
    {
        text = text.Trim();
        const int max = 500;
        return text.Length <= max ? text : text[^max..];
    }

    private sealed record ProbeInfo(double Duration, int Width, int Height);
}