#include <torchaudio/csrc/ffmpeg/stream_writer/audio_output_stream.h>

namespace torchaudio::io {

namespace {

FilterGraph get_audio_filter(
    AVSampleFormat src_fmt,
    AVCodecContext* codec_ctx) {
  auto desc = [&]() -> std::string {
    if (src_fmt == codec_ctx->sample_fmt) {
      return "anull";
    } else {
      std::stringstream ss;
      ss << "aformat=" << av_get_sample_fmt_name(codec_ctx->sample_fmt);
      return ss.str();
    }
  }();

  FilterGraph p{AVMEDIA_TYPE_AUDIO};
  p.add_audio_src(
      src_fmt,
      codec_ctx->time_base,
      codec_ctx->sample_rate,
      codec_ctx->channel_layout);
  p.add_sink();
  p.add_process(desc);
  p.create_filter();
  return p;
}

AVFramePtr get_audio_frame(
    AVSampleFormat src_fmt,
    AVCodecContext* codec_ctx,
    int default_frame_size = 10000) {
  AVFramePtr frame{};
  frame->pts = 0;
  frame->format = src_fmt;
  frame->channel_layout = codec_ctx->channel_layout;
  frame->sample_rate = codec_ctx->sample_rate;
  frame->nb_samples =
      codec_ctx->frame_size ? codec_ctx->frame_size : default_frame_size;
  if (frame->nb_samples) {
    int ret = av_frame_get_buffer(frame, 0);
    TORCH_CHECK(
        ret >= 0,
        "Error allocating an audio buffer (",
        av_err2string(ret),
        ").");
  }
  return frame;
}

} // namespace

AudioOutputStream::AudioOutputStream(
    AVFormatContext* format_ctx,
    AVSampleFormat src_fmt,
    AVCodecContextPtr&& codec_ctx_)
    : OutputStream(
          format_ctx,
          codec_ctx_,
          get_audio_filter(src_fmt, codec_ctx_)),
      src_frame(get_audio_frame(src_fmt, codec_ctx_)),
      frame_capacity(src_frame->nb_samples),
      codec_ctx(std::move(codec_ctx_)) {}

namespace {

void validate_audio_input(
    enum AVSampleFormat fmt,
    AVCodecContext* ctx,
    const torch::Tensor& t) {
  auto dtype = t.dtype().toScalarType();
  switch (fmt) {
    case AV_SAMPLE_FMT_U8:
      TORCH_CHECK(
          dtype == c10::ScalarType::Byte, "Expected Tensor of uint8 type.");
      break;
    case AV_SAMPLE_FMT_S16:
      TORCH_CHECK(
          dtype == c10::ScalarType::Short, "Expected Tensor of int16 type.");
      break;
    case AV_SAMPLE_FMT_S32:
      TORCH_CHECK(
          dtype == c10::ScalarType::Int, "Expected Tensor of int32 type.");
      break;
    case AV_SAMPLE_FMT_S64:
      TORCH_CHECK(
          dtype == c10::ScalarType::Long, "Expected Tensor of int64 type.");
      break;
    case AV_SAMPLE_FMT_FLT:
      TORCH_CHECK(
          dtype == c10::ScalarType::Float, "Expected Tensor of float32 type.");
      break;
    case AV_SAMPLE_FMT_DBL:
      TORCH_CHECK(
          dtype == c10::ScalarType::Double, "Expected Tensor of float64 type.");
      break;
    default:
      TORCH_CHECK(
          false,
          "Internal error: Audio encoding stream is not properly configured.");
  }
  TORCH_CHECK(t.device().is_cpu(), "Input tensor has to be on CPU.");
  TORCH_CHECK(t.dim() == 2, "Input Tensor has to be 2D.");
  const auto num_channels = t.size(1);
  TORCH_CHECK(
      num_channels == ctx->channels,
      "Expected waveform with ",
      ctx->channels,
      " channels. Found ",
      num_channels);
}

} // namespace

void AudioOutputStream::write_chunk(const torch::Tensor& waveform) {
  validate_audio_input(
      static_cast<AVSampleFormat>(src_frame->format), codec_ctx, waveform);

  AVRational time_base{1, codec_ctx->sample_rate};

  using namespace torch::indexing;
  for (int64_t i = 0; i < waveform.size(0); i += frame_capacity) {
    auto chunk = waveform.index({Slice(i, i + frame_capacity), Slice()});
    auto num_frames = chunk.size(0);
    auto byte_size = chunk.numel() * chunk.element_size();
    chunk = chunk.reshape({-1}).contiguous();

    // TODO: make writable
    // https://ffmpeg.org/doxygen/4.1/muxing_8c_source.html#l00334
    TORCH_CHECK(
        av_frame_is_writable(src_frame),
        "Internal Error: frame is not writable.");

    memcpy(src_frame->data[0], chunk.data_ptr(), byte_size);
    src_frame->pts += av_rescale_q(num_frames, time_base, codec_ctx->time_base);
    src_frame->nb_samples = num_frames;
    process_frame(src_frame);
  }
}

} // namespace torchaudio::io
