namespace ytLive.Services.Encoder;

/// <summary>
/// Builds the FFmpeg command line for a live RTMP push (TASK 4 ship step 3):
/// raw BGRA frames via stdin (paced by the frame pump — the pump holds a strict
/// CFR cadence, so <c>-re</c> would only add a second, fighting pacer), real
/// audio via the named pipe
/// (TASK 9 — the mixer streams f32le at 48 kHz stereo into <c>\\.\pipe\&lt;name&gt;</c>;
/// WASAPI loopback + the mic ride the pipe instead of the old anullsrc silence),
/// H.264 + AAC encoding, FLV muxing to the ingestion URL. Pure — the encoder
/// just starts <c>ffmpeg.exe [Build(...)]</c>.
/// </summary>
public static class FfmpegArgs
{
    public static IReadOnlyList<string> Build(EncoderOptions options, string videoEncoder)
    {
        var args = new List<string>
        {
            "-hide_banner", "-loglevel", "info",
            "-stats", "-stats_period", "0.5",
            "-f", "rawvideo", "-pix_fmt", "bgra",
            "-video_size", $"{options.RawWidth}x{options.RawHeight}",
            "-framerate", options.Fps.ToString(),
            "-i", "pipe:0",
            "-f", "f32le", "-ar", options.AudioSampleRate.ToString(),
            "-ac", options.AudioChannels.ToString(),
            "-i", $@"\\.\pipe\{options.AudioPipeName}",
        };

        // Each output is a self-contained block: its own -map, codec options,
        // format, and destination. Record+stream encodes the video twice off the
        // one raw input pipe (cheap on NVENC).
        if (options.StreamEnabled)
        {
            AddVideoTags(args, options, videoEncoder);
            args.AddRange(["-c:a", "aac", "-b:a", "128k",
                "-ar", options.AudioSampleRate.ToString(), "-ac", options.AudioChannels.ToString()]);
            args.AddRange(["-f", "flv", options.RtmpUrl]);
        }

        if (options.RecordEnabled)
        {
            AddVideoTags(args, options, videoEncoder);
            args.AddRange(["-c:a", "aac",
                "-ar", options.AudioSampleRate.ToString(), "-ac", options.AudioChannels.ToString()]);
            // TASK 32·4: FRAGMENTED mp4. A plain MP4 writes its index (moov) at the end, so a
            // power cut or a killed process leaves the video bytes on disk in a file nothing can
            // open — the whole recording, not the tail. Fragmented writes the index first and
            // flushes a playable fragment at every keyframe, so an interrupted file still plays up
            // to the last fragment. Record block only: the FLV stream output has no index.
            args.AddRange(["-movflags", "+frag_keyframe+empty_moov+default_base_moof"]);
            args.AddRange(["-f", "mp4", options.RecordPath!]);
        }

        // TASK 65: the replay buffer is a third mux of the same encoded frames. Fragmented MP4 on
        // stdout (stats already own stderr) — one fragment per second, so a clip can start anywhere
        // inside the chosen window instead of at the last 4-second keyframe.
        if (options.ClipBuffer != null)
        {
            AddVideoTags(args, options, videoEncoder);
            args.AddRange(["-c:a", "aac",
                "-ar", options.AudioSampleRate.ToString(), "-ac", options.AudioChannels.ToString()]);
            args.AddRange(["-movflags", "+frag_keyframe+empty_moov+default_base_moof"]);
            args.AddRange(["-frag_duration", "1000000"]);
            args.AddRange(["-f", "mp4", "pipe:1"]);
        }

        return args;
    }

    private static void AddVideoTags(List<string> args, EncoderOptions options, string videoEncoder)
    {
        var gop = options.GopSize;
        args.AddRange(["-map", "0:v", "-map", "1:a"]);
        if (options.RawWidth != options.Width || options.RawHeight != options.Height)
        {
            args.AddRange(["-vf", $"scale={options.Width}:{options.Height}:flags=bilinear,setsar=1"]);
        }
        args.AddRange(["-c:v", videoEncoder]);
        args.AddRange(["-b:v", $"{options.BitrateKbps}k", "-maxrate", $"{options.BitrateKbps}k",
            "-bufsize", $"{options.BitrateKbps * 2}k"]);
        args.AddRange(["-g", gop.ToString(), "-keyint_min", gop.ToString(),
            "-sc_threshold", "0", "-bf", "0", "-pix_fmt", "yuv420p"]);
    }
}