#include <sstream>

#include "AVIOTensorContext.h"
#include "Encoder.h"
#include "torch/types.h"

extern "C" {
#include <libavutil/opt.h>
#include <libavutil/pixdesc.h>
}

namespace facebook::torchcodec {

namespace {

torch::Tensor validateSamples(const torch::Tensor& samples) {
  TORCH_CHECK(
      samples.dtype() == torch::kFloat32,
      "samples must have float32 dtype, got ",
      samples.dtype());
  TORCH_CHECK(
      samples.dim() == 2,
      "samples must have 2 dimensions, got ",
      samples.dim());

  // We enforce this, but if we get user reports we should investigate whether
  // that's actually needed.
  int numChannels = static_cast<int>(samples.sizes()[0]);
  TORCH_CHECK(
      numChannels <= AV_NUM_DATA_POINTERS,
      "Trying to encode ",
      numChannels,
      " channels, but FFmpeg only supports ",
      AV_NUM_DATA_POINTERS,
      " channels per frame.");

  return samples.contiguous();
}

void validateSampleRate(const AVCodec& avCodec, int sampleRate) {
  const int* supportedSampleRates = getSupportedSampleRates(avCodec);
  if (supportedSampleRates == nullptr) {
    return;
  }

  for (auto i = 0; supportedSampleRates[i] != 0; ++i) {
    if (sampleRate == supportedSampleRates[i]) {
      return;
    }
  }
  std::stringstream supportedRates;
  for (auto i = 0; supportedSampleRates[i] != 0; ++i) {
    if (i > 0) {
      supportedRates << ", ";
    }
    supportedRates << supportedSampleRates[i];
  }

  TORCH_CHECK(
      false,
      "invalid sample rate=",
      sampleRate,
      ". Supported sample rate values are: ",
      supportedRates.str());
}

static const std::vector<AVSampleFormat> preferredFormatsOrder = {
    AV_SAMPLE_FMT_FLTP,
    AV_SAMPLE_FMT_FLT,
    AV_SAMPLE_FMT_DBLP,
    AV_SAMPLE_FMT_DBL,
    AV_SAMPLE_FMT_S64P,
    AV_SAMPLE_FMT_S64,
    AV_SAMPLE_FMT_S32P,
    AV_SAMPLE_FMT_S32,
    AV_SAMPLE_FMT_S16P,
    AV_SAMPLE_FMT_S16,
    AV_SAMPLE_FMT_U8P,
    AV_SAMPLE_FMT_U8};

AVSampleFormat findBestOutputSampleFormat(const AVCodec& avCodec) {
  const AVSampleFormat* supportedSampleFormats =
      getSupportedOutputSampleFormats(avCodec);

  // Find a sample format that the encoder supports. We prefer using FLT[P],
  // since this is the format of the input samples. If FLTP isn't supported
  // then we'll need to convert the AVFrame's format. Our heuristic is to encode
  // into the format with the highest resolution.
  if (supportedSampleFormats == nullptr) {
    // Can't really validate anything in this case, best we can do is hope that
    // FLTP is supported by the encoder. If not, FFmpeg will raise.
    return AV_SAMPLE_FMT_FLTP;
  }

  for (AVSampleFormat preferredFormat : preferredFormatsOrder) {
    for (int i = 0; supportedSampleFormats[i] != -1; ++i) {
      if (supportedSampleFormats[i] == preferredFormat) {
        return preferredFormat;
      }
    }
  }
  // We should always find a match in preferredFormatsOrder, so we should always
  // return earlier. But in the event that a future FFmpeg version defines an
  // additional sample format that isn't in preferredFormatsOrder, we fallback:
  return supportedSampleFormats[0];
}

} // namespace

AudioEncoder::~AudioEncoder() {
  close_avio();
}

void AudioEncoder::close_avio() {
  if (avFormatContext_ && avFormatContext_->pb) {
    if (avFormatContext_->pb->error == 0) {
      avio_flush(avFormatContext_->pb);
    }

    if (!avioContextHolder_) {
      if (avFormatContext_->pb->error == 0) {
        avio_close(avFormatContext_->pb);
      }
      // avoids closing again in destructor, which would segfault.
      avFormatContext_->pb = nullptr;
    }
  }
}

AudioEncoder::AudioEncoder(
    const torch::Tensor& samples,
    int sampleRate,
    std::string_view fileName,
    const AudioStreamOptions& audioStreamOptions)
    : samples_(validateSamples(samples)), inSampleRate_(sampleRate) {
  setFFmpegLogLevel();
  AVFormatContext* avFormatContext = nullptr;
  int status = avformat_alloc_output_context2(
      &avFormatContext, nullptr, nullptr, fileName.data());

  TORCH_CHECK(
      avFormatContext != nullptr,
      "Couldn't allocate AVFormatContext. ",
      "The destination file is ",
      fileName,
      ", check the desired extension? ",
      getFFMPEGErrorStringFromErrorCode(status));
  avFormatContext_.reset(avFormatContext);

  status = avio_open(&avFormatContext_->pb, fileName.data(), AVIO_FLAG_WRITE);
  TORCH_CHECK(
      status >= 0,
      "avio_open failed. The destination file is ",
      fileName,
      ", make sure it's a valid path? ",
      getFFMPEGErrorStringFromErrorCode(status));

  initializeEncoder(audioStreamOptions);
}

AudioEncoder::AudioEncoder(
    const torch::Tensor& samples,
    int sampleRate,
    std::string_view formatName,
    std::unique_ptr<AVIOContextHolder> avioContextHolder,
    const AudioStreamOptions& audioStreamOptions)
    : samples_(validateSamples(samples)),
      inSampleRate_(sampleRate),
      avioContextHolder_(std::move(avioContextHolder)) {
  setFFmpegLogLevel();
  AVFormatContext* avFormatContext = nullptr;
  int status = avformat_alloc_output_context2(
      &avFormatContext, nullptr, formatName.data(), nullptr);

  TORCH_CHECK(
      avFormatContext != nullptr,
      "Couldn't allocate AVFormatContext. ",
      "Check the desired format? Got format=",
      formatName,
      ". ",
      getFFMPEGErrorStringFromErrorCode(status));
  avFormatContext_.reset(avFormatContext);

  avFormatContext_->pb = avioContextHolder_->getAVIOContext();

  initializeEncoder(audioStreamOptions);
}

void AudioEncoder::initializeEncoder(
    const AudioStreamOptions& audioStreamOptions) {
  // We use the AVFormatContext's default codec for that
  // specific format/container.
  const AVCodec* avCodec =
      avcodec_find_encoder(avFormatContext_->oformat->audio_codec);
  TORCH_CHECK(avCodec != nullptr, "Codec not found");

  AVCodecContext* avCodecContext = avcodec_alloc_context3(avCodec);
  TORCH_CHECK(avCodecContext != nullptr, "Couldn't allocate codec context.");
  avCodecContext_.reset(avCodecContext);

  auto desiredBitRate = audioStreamOptions.bitRate;
  if (desiredBitRate.has_value()) {
    TORCH_CHECK(
        *desiredBitRate >= 0, "bit_rate=", *desiredBitRate, " must be >= 0.");
  }
  // bit_rate=None defaults to 0, which is what the FFmpeg CLI seems to use as
  // well when "-b:a" isn't specified.
  avCodecContext_->bit_rate = desiredBitRate.value_or(0);

  outNumChannels_ = static_cast<int>(
      audioStreamOptions.numChannels.value_or(samples_.sizes()[0]));
  validateNumChannels(*avCodec, outNumChannels_);
  // The avCodecContext layout defines the layout of the encoded output, it's
  // not related to the input sampes.
  setDefaultChannelLayout(avCodecContext_, outNumChannels_);

  outSampleRate_ = audioStreamOptions.sampleRate.value_or(inSampleRate_);
  validateSampleRate(*avCodec, outSampleRate_);
  avCodecContext_->sample_rate = outSampleRate_;

  // Input samples are expected to be FLTP. Not all encoders support FLTP, so we
  // may need to convert the samples into a supported output sample format,
  // which is what the `.sample_fmt` defines.
  avCodecContext_->sample_fmt = findBestOutputSampleFormat(*avCodec);

  int status = avcodec_open2(avCodecContext_.get(), avCodec, nullptr);
  TORCH_CHECK(
      status == AVSUCCESS,
      "avcodec_open2 failed: ",
      getFFMPEGErrorStringFromErrorCode(status));

  // We're allocating the stream here. Streams are meant to be freed by
  // avformat_free_context(avFormatContext), which we call in the
  // avFormatContext_'s destructor.
  AVStream* avStream = avformat_new_stream(avFormatContext_.get(), nullptr);
  TORCH_CHECK(avStream != nullptr, "Couldn't create new stream.");
  status = avcodec_parameters_from_context(
      avStream->codecpar, avCodecContext_.get());
  TORCH_CHECK(
      status == AVSUCCESS,
      "avcodec_parameters_from_context failed: ",
      getFFMPEGErrorStringFromErrorCode(status));
  streamIndex_ = avStream->index;

  // If sample rate conversion is needed and the encoder doesn't support
  // variable frame size, we need to create an intermediate FIFO. See
  // [Encoding loop, sample rate conversion and FIFO].
  if (((avCodec->capabilities & AV_CODEC_CAP_VARIABLE_FRAME_SIZE) == 0) &&
      (inSampleRate_ != outSampleRate_)) {
    // frame_size * 2 is a decent default size. FFmpeg automatically
    // re-allocates the fifo if more space is needed.
    auto avAudioFifo = av_audio_fifo_alloc(
        avCodecContext_->sample_fmt,
        outNumChannels_,
        avCodecContext_->frame_size * 2);
    TORCH_CHECK(avAudioFifo != nullptr, "Couldn't create AVAudioFifo.");
    avAudioFifo_.reset(avAudioFifo);
  }
}

torch::Tensor AudioEncoder::encodeToTensor() {
  TORCH_CHECK(
      avioContextHolder_ != nullptr,
      "Cannot encode to tensor, avio tensor context doesn't exist.");
  encode();
  auto avioToTensorContext =
      dynamic_cast<AVIOToTensorContext*>(avioContextHolder_.get());
  TORCH_CHECK(avioToTensorContext != nullptr, "Invalid AVIO context holder.");
  return avioToTensorContext->getOutputTensor();
}

void AudioEncoder::encode() {
  // To be on the safe side we enforce that encode() can only be called once on
  // an encoder object. Whether this is actually necessary is unknown, so this
  // may be relaxed if needed.
  TORCH_CHECK(!encodeWasCalled_, "Cannot call encode() twice.");
  encodeWasCalled_ = true;

  //  Default to 256 like in torchaudio
  int numSamplesAllocatedPerFrame =
      avCodecContext_->frame_size > 0 ? avCodecContext_->frame_size : 256;
  UniqueAVFrame avFrame = allocateAVFrame(
      numSamplesAllocatedPerFrame,
      inSampleRate_,
      static_cast<int>(samples_.sizes()[0]),
      AV_SAMPLE_FMT_FLTP);
  avFrame->pts = 0;

  AutoAVPacket autoAVPacket;

  uint8_t* psamples = static_cast<uint8_t*>(samples_.data_ptr());
  int numSamples = static_cast<int>(samples_.sizes()[1]); // per channel
  int numEncodedSamples = 0; // per channel
  int numBytesPerSample = static_cast<int>(samples_.element_size());
  int numBytesPerChannel = numSamples * numBytesPerSample;

  auto status = avformat_write_header(avFormatContext_.get(), nullptr);
  TORCH_CHECK(
      status == AVSUCCESS,
      "Error in avformat_write_header: ",
      getFFMPEGErrorStringFromErrorCode(status));

  while (numEncodedSamples < numSamples) {
    int numSamplesToEncode =
        std::min(numSamplesAllocatedPerFrame, numSamples - numEncodedSamples);
    int numBytesToEncode = numSamplesToEncode * numBytesPerSample;

    for (int ch = 0; ch < samples_.sizes()[0]; ch++) {
      std::memcpy(
          avFrame->data[ch],
          psamples + ch * numBytesPerChannel,
          numBytesToEncode);
    }
    psamples += numBytesToEncode;

    // Above, we set the AVFrame's .nb_samples to AVCodecContext.frame_size so
    // that the frame buffers are allocated to a big enough size. Here, we reset
    // it to the exact number of samples that need to be encoded, otherwise the
    // encoded frame would contain more samples than necessary and our results
    // wouldn't match the ffmpeg CLI.
    avFrame->nb_samples = numSamplesToEncode;

    UniqueAVFrame convertedAVFrame = maybeConvertAVFrame(avFrame);
    encodeFrameThroughFifo(autoAVPacket, convertedAVFrame);

    numEncodedSamples += numSamplesToEncode;
  }
  TORCH_CHECK(numEncodedSamples == numSamples, "Hmmmmmm something went wrong.");

  flushBuffers();

  status = av_write_trailer(avFormatContext_.get());
  TORCH_CHECK(
      status == AVSUCCESS,
      "Error in: av_write_trailer",
      getFFMPEGErrorStringFromErrorCode(status));

  close_avio();
}

UniqueAVFrame AudioEncoder::maybeConvertAVFrame(const UniqueAVFrame& avFrame) {
  if (static_cast<AVSampleFormat>(avFrame->format) ==
          avCodecContext_->sample_fmt &&
      getNumChannels(avFrame) == outNumChannels_ &&
      avFrame->sample_rate == outSampleRate_) {
    // Note: the clone references the same underlying data, it's a cheap copy.
    return UniqueAVFrame(av_frame_clone(avFrame.get()));
  }

  if (!swrContext_) {
    swrContext_.reset(createSwrContext(
        static_cast<AVSampleFormat>(avFrame->format),
        avCodecContext_->sample_fmt,
        avFrame->sample_rate,
        outSampleRate_,
        avFrame,
        outNumChannels_));
  }
  UniqueAVFrame convertedAVFrame = convertAudioAVFrameSamples(
      swrContext_,
      avFrame,
      avCodecContext_->sample_fmt,
      outSampleRate_,
      outNumChannels_);

  if (avFrame->sample_rate == outSampleRate_) {
    TORCH_CHECK(
        convertedAVFrame->nb_samples == avFrame->nb_samples,
        "convertedAVFrame->nb_samples=",
        convertedAVFrame->nb_samples,
        " differs from ",
        "avFrame->nb_samples=",
        avFrame->nb_samples,
        "This is unexpected, please report on the TorchCodec bug tracker.");
  }
  return convertedAVFrame;
}

void AudioEncoder::encodeFrameThroughFifo(
    AutoAVPacket& autoAVPacket,
    const UniqueAVFrame& avFrame,
    // flushFifo is only set to true in maybeFlushSwrBuffers(), i.e. at the very
    // end of the encoding process when we're flushing buffers. We also want to
    // flush the FIFO so as to not leave any remaining samples in it.
    bool flushFifo) {
  if (avAudioFifo_ == nullptr) {
    encodeFrame(autoAVPacket, avFrame);
    return;
  }
  int numSamplesWritten = av_audio_fifo_write(
      avAudioFifo_.get(),
      reinterpret_cast<void**>(avFrame->data),
      avFrame->nb_samples);
  TORCH_CHECK(
      numSamplesWritten == avFrame->nb_samples,
      "Tried to write ",
      avFrame->nb_samples,
      " samples, but only wrote ",
      numSamplesWritten);

  UniqueAVFrame newavFrame = allocateAVFrame(
      avCodecContext_->frame_size,
      outSampleRate_,
      outNumChannels_,
      avCodecContext_->sample_fmt);

  // Explaining the while bound:
  // - if we're not flushing the FIFO, i.e. in most cases, we want to pull
  //   exactly `frame_size` samples from the FIFO, so we have to stop before it
  //   contains less than `frame_size` samples.
  // - if we're flushing the FIFO, we want to read from the FIFO until the very
  //   last sample it contains.
  //
  // In both cases, for as long as we can, we're trying to pull exatly
  // `frame_size` samples from the FIFO and send each `frame_size`-sized avFrame
  // to encodeFrame(). Only the very last avFrame of the encoding process is
  // allowed to contained less than frame_size samples. That only happens when
  // flushFifo is true.
  while (av_audio_fifo_size(avAudioFifo_.get()) >=
         (flushFifo ? 1 : avCodecContext_->frame_size)) {
    int samplesToRead = std::min(
        av_audio_fifo_size(avAudioFifo_.get()), newavFrame->nb_samples);
    int numSamplesRead = av_audio_fifo_read(
        avAudioFifo_.get(),
        reinterpret_cast<void**>(newavFrame->data),
        samplesToRead);
    TORCH_CHECK(
        numSamplesRead == samplesToRead,
        "Tried to read ",
        samplesToRead,
        " samples, but only read ",
        numSamplesRead);

    newavFrame->nb_samples = numSamplesRead;
    encodeFrame(autoAVPacket, newavFrame);
  }
}

void AudioEncoder::encodeFrame(
    AutoAVPacket& autoAVPacket,
    const UniqueAVFrame& avFrame) {
  if (avFrame != nullptr) {
    avFrame->pts = lastEncodedAVFramePts_;
    lastEncodedAVFramePts_ += avFrame->nb_samples;
  }

  auto status = avcodec_send_frame(avCodecContext_.get(), avFrame.get());
  TORCH_CHECK(
      status == AVSUCCESS,
      "Error while sending frame: ",
      getFFMPEGErrorStringFromErrorCode(status));

  while (status >= 0) {
    ReferenceAVPacket packet(autoAVPacket);
    status = avcodec_receive_packet(avCodecContext_.get(), packet.get());
    if (status == AVERROR(EAGAIN) || status == AVERROR_EOF) {
      if (status == AVERROR_EOF) {
        // Flush the packets that were potentially buffered by
        // av_interleaved_write_frame(). See corresponding block in
        // TorchAudio:
        // https://github.com/pytorch/audio/blob/d60ce09e2c532d5bf2e05619e700ab520543465e/src/libtorio/ffmpeg/stream_writer/encoder.cpp#L21
        status = av_interleaved_write_frame(avFormatContext_.get(), nullptr);
        TORCH_CHECK(
            status == AVSUCCESS,
            "Failed to flush packet: ",
            getFFMPEGErrorStringFromErrorCode(status));
      }
      return;
    }
    TORCH_CHECK(
        status >= 0,
        "Error receiving packet: ",
        getFFMPEGErrorStringFromErrorCode(status));

    packet->stream_index = streamIndex_;

    status = av_interleaved_write_frame(avFormatContext_.get(), packet.get());
    TORCH_CHECK(
        status == AVSUCCESS,
        "Error in av_interleaved_write_frame: ",
        getFFMPEGErrorStringFromErrorCode(status));
  }
}

void AudioEncoder::maybeFlushSwrBuffers(AutoAVPacket& autoAVPacket) {
  // Similar to the decoder's method with the same name, but for encoding this
  // time. That is, when sample conversion is involved, libswresample may have
  // buffered some samples that we now need to flush and send to the encoder.
  if (swrContext_ == nullptr && inSampleRate_ == outSampleRate_) {
    return;
  }
  TORCH_CHECK(
      swrContext_ != nullptr,
      "swrContext is null, but sample rate conversion is needed. ",
      "This is unexpected, please report on the TorchCodec bug tracker.");

  int numRemainingSamples = // this is an upper bound
      swr_get_out_samples(swrContext_.get(), 0);
  if (numRemainingSamples == 0) {
    return;
  }

  UniqueAVFrame avFrame = allocateAVFrame(
      numRemainingSamples,
      outSampleRate_,
      outNumChannels_,
      avCodecContext_->sample_fmt);
  int actualNumRemainingSamples = swr_convert(
      swrContext_.get(), avFrame->data, avFrame->nb_samples, nullptr, 0);
  avFrame->nb_samples = actualNumRemainingSamples;

  // We're potentially sending avFrame through the FIFO (if it exists), in which
  // case we also want to flush the FIFO itself.
  encodeFrameThroughFifo(autoAVPacket, avFrame, /*flushFifo=*/true);
}

void AudioEncoder::flushBuffers() {
  AutoAVPacket autoAVPacket;
  maybeFlushSwrBuffers(autoAVPacket);

  encodeFrame(autoAVPacket, UniqueAVFrame(nullptr));
}

namespace {

torch::Tensor validateFrames(const torch::Tensor& frames) {
  TORCH_CHECK(
      frames.dtype() == torch::kUInt8,
      "frames must have uint8 dtype, got ",
      frames.dtype());
  TORCH_CHECK(
      frames.dim() == 4,
      "frames must have 4 dimensions (N, C, H, W), got ",
      frames.dim());
  TORCH_CHECK(
      frames.sizes()[1] == 3,
      "frame must have 3 channels (R, G, B), got ",
      frames.sizes()[1]);
  return frames.contiguous();
}

AVPixelFormat validatePixelFormat(
    const AVCodec& avCodec,
    const std::string& targetPixelFormat) {
  AVPixelFormat pixelFormat = av_get_pix_fmt(targetPixelFormat.c_str());

  // Validate that the encoder supports this pixel format
  const AVPixelFormat* supportedFormats = getSupportedPixelFormats(avCodec);
  if (supportedFormats != nullptr) {
    for (int i = 0; supportedFormats[i] != AV_PIX_FMT_NONE; ++i) {
      if (supportedFormats[i] == pixelFormat) {
        return pixelFormat;
      }
    }
  }

  std::stringstream errorMsg;
  // av_get_pix_fmt failed to find a pix_fmt
  if (pixelFormat == AV_PIX_FMT_NONE) {
    errorMsg << "Unknown pixel format: " << targetPixelFormat;
  } else {
    errorMsg << "Specified pixel format " << targetPixelFormat
             << " is not supported by the " << avCodec.name << " encoder.";
  }
  // Build error message, similar to FFmpeg's error log
  errorMsg << "\nSupported pixel formats for " << avCodec.name << ":";
  for (int i = 0; supportedFormats[i] != AV_PIX_FMT_NONE; ++i) {
    errorMsg << " " << av_get_pix_fmt_name(supportedFormats[i]);
  }
  TORCH_CHECK(false, errorMsg.str());
}

void tryToValidateCodecOption(
    const AVCodec& avCodec,
    const char* optionName,
    const std::string& value) {
  if (!avCodec.priv_class) {
    return;
  }
  const AVOption* option = av_opt_find2(
      // Convert obj arg from const AVClass* const* to non-const void*
      // First cast to remove const, then cast to void*
      const_cast<void*>(static_cast<const void*>(&avCodec.priv_class)),
      optionName,
      nullptr,
      0,
      AV_OPT_SEARCH_FAKE_OBJ,
      nullptr);
  // If option is not found we cannot validate it, let FFmpeg handle it
  if (!option) {
    return;
  }
  // Validate if option is defined as a numeric type
  if (option->type == AV_OPT_TYPE_INT || option->type == AV_OPT_TYPE_INT64 ||
      option->type == AV_OPT_TYPE_FLOAT || option->type == AV_OPT_TYPE_DOUBLE) {
    try {
      double numericValue = std::stod(value);
      TORCH_CHECK(
          numericValue >= option->min && numericValue <= option->max,
          optionName,
          "=",
          numericValue,
          " is out of valid range [",
          option->min,
          ", ",
          option->max,
          "] for this codec. For more details, run 'ffmpeg -h encoder=",
          avCodec.name,
          "'");
    } catch (const std::invalid_argument&) {
      TORCH_CHECK(
          false,
          "Option ",
          optionName,
          " expects a numeric value but got '",
          value,
          "'");
    }
  }
}

void sortCodecOptions(
    const std::map<std::string, std::string>& extraOptions,
    AVDictionary** codecDict,
    AVDictionary** formatDict) {
  // Accepts a map of options as input, then sorts them into codec options and
  // format options. The sorted options are returned into two separate dicts.
  const AVClass* formatClass = avformat_get_class();
  for (const auto& [key, value] : extraOptions) {
    const AVOption* fmtOpt = av_opt_find2(
        &formatClass,
        key.c_str(),
        nullptr,
        0,
        AV_OPT_SEARCH_CHILDREN | AV_OPT_SEARCH_FAKE_OBJ,
        nullptr);
    if (fmtOpt) {
      av_dict_set(formatDict, key.c_str(), value.c_str(), 0);
    } else {
      // Default to codec option (includes AVCodecContext + encoder-private)
      av_dict_set(codecDict, key.c_str(), value.c_str(), 0);
    }
  }
}
} // namespace

VideoEncoder::~VideoEncoder() {
  // TODO-VideoEncoder: Unify destructor with ~AudioEncoder()
  if (avFormatContext_ && avFormatContext_->pb) {
    if (avFormatContext_->pb->error == 0) {
      avio_flush(avFormatContext_->pb);
    }
    if (!avioContextHolder_) {
      if (avFormatContext_->pb->error == 0) {
        avio_close(avFormatContext_->pb);
      }
      avFormatContext_->pb = nullptr;
    }
  }
  av_dict_free(&avFormatOptions_);
}

VideoEncoder::VideoEncoder(
    const torch::Tensor& frames,
    double frameRate,
    std::string_view fileName,
    const VideoStreamOptions& videoStreamOptions)
    : frames_(validateFrames(frames)), inFrameRate_(frameRate) {
  setFFmpegLogLevel();

  // Allocate output format context
  AVFormatContext* avFormatContext = nullptr;
  int status = avformat_alloc_output_context2(
      &avFormatContext, nullptr, nullptr, fileName.data());

  TORCH_CHECK(
      avFormatContext != nullptr,
      "Couldn't allocate AVFormatContext. ",
      "The destination file is ",
      fileName,
      ", check the desired extension? ",
      getFFMPEGErrorStringFromErrorCode(status));
  avFormatContext_.reset(avFormatContext);

  status = avio_open(&avFormatContext_->pb, fileName.data(), AVIO_FLAG_WRITE);
  TORCH_CHECK(
      status >= 0,
      "avio_open failed. The destination file is ",
      fileName,
      ", make sure it's a valid path? ",
      getFFMPEGErrorStringFromErrorCode(status));
  initializeEncoder(videoStreamOptions);
}

VideoEncoder::VideoEncoder(
    const torch::Tensor& frames,
    double frameRate,
    std::string_view formatName,
    std::unique_ptr<AVIOContextHolder> avioContextHolder,
    const VideoStreamOptions& videoStreamOptions)
    : frames_(validateFrames(frames)),
      inFrameRate_(frameRate),
      avioContextHolder_(std::move(avioContextHolder)) {
  setFFmpegLogLevel();
  // Map mkv -> matroska when used as format name
  formatName = (formatName == "mkv") ? "matroska" : formatName;
  AVFormatContext* avFormatContext = nullptr;
  int status = avformat_alloc_output_context2(
      &avFormatContext, nullptr, formatName.data(), nullptr);

  TORCH_CHECK(
      avFormatContext != nullptr,
      "Couldn't allocate AVFormatContext. ",
      "Check the desired format? Got format=",
      formatName,
      ". ",
      getFFMPEGErrorStringFromErrorCode(status));
  avFormatContext_.reset(avFormatContext);

  avFormatContext_->pb = avioContextHolder_->getAVIOContext();

  initializeEncoder(videoStreamOptions);
}

void VideoEncoder::initializeEncoder(
    const VideoStreamOptions& videoStreamOptions) {
  const AVCodec* avCodec = nullptr;
  // If codec arg is provided, find codec using logic similar to FFmpeg:
  // https://github.com/FFmpeg/FFmpeg/blob/master/fftools/ffmpeg_opt.c#L804-L835
  if (videoStreamOptions.codec.has_value()) {
    const std::string& codec = videoStreamOptions.codec.value();
    // Try to find codec by name ("libx264", "libsvtav1")
    avCodec = avcodec_find_encoder_by_name(codec.c_str());
    // Try to find by codec descriptor ("h264", "av1")
    if (!avCodec) {
      const AVCodecDescriptor* desc =
          avcodec_descriptor_get_by_name(codec.c_str());
      if (desc) {
        avCodec = avcodec_find_encoder(desc->id);
      }
    }
    TORCH_CHECK(
        avCodec != nullptr,
        "Video codec ",
        codec,
        " not found. To see available codecs, run: ffmpeg -encoders");
  } else {
    TORCH_CHECK(
        avFormatContext_->oformat != nullptr,
        "Output format is null, unable to find default codec.");
    avCodec = avcodec_find_encoder(avFormatContext_->oformat->video_codec);
    TORCH_CHECK(avCodec != nullptr, "Video codec not found");
  }

  AVCodecContext* avCodecContext = avcodec_alloc_context3(avCodec);
  TORCH_CHECK(avCodecContext != nullptr, "Couldn't allocate codec context.");
  avCodecContext_.reset(avCodecContext);

  // Store dimension order and input pixel format
  // TODO-VideoEncoder: Remove assumption that tensor in NCHW format
  auto sizes = frames_.sizes();
  inPixelFormat_ = AV_PIX_FMT_GBRP;
  inHeight_ = static_cast<int>(sizes[2]);
  inWidth_ = static_cast<int>(sizes[3]);

  // Use specified dimensions or input dimensions
  // TODO-VideoEncoder: Allow height and width to be set
  outWidth_ = inWidth_;
  outHeight_ = inHeight_;

  if (videoStreamOptions.pixelFormat.has_value()) {
    outPixelFormat_ =
        validatePixelFormat(*avCodec, videoStreamOptions.pixelFormat.value());
  } else {
    const AVPixelFormat* formats = getSupportedPixelFormats(*avCodec);
    // Use first listed pixel format as default (often yuv420p).
    // This is similar to FFmpeg's logic:
    // https://www.ffmpeg.org/doxygen/4.0/decode_8c_source.html#l01087
    // If pixel formats are undefined for some reason, try yuv420p
    outPixelFormat_ = (formats && formats[0] != AV_PIX_FMT_NONE)
        ? formats[0]
        : AV_PIX_FMT_YUV420P;
  }

  // Configure codec parameters
  avCodecContext_->codec_id = avCodec->id;
  avCodecContext_->width = outWidth_;
  avCodecContext_->height = outHeight_;
  avCodecContext_->pix_fmt = outPixelFormat_;
  // TODO-VideoEncoder: Add and utilize output frame_rate option
  avCodecContext_->framerate = av_d2q(inFrameRate_, INT_MAX);
  avCodecContext_->time_base = av_inv_q(avCodecContext_->framerate);

  // Set flag for containers that require extradata to be in the codec context
  if (avFormatContext_->oformat->flags & AVFMT_GLOBALHEADER) {
    avCodecContext_->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  }

  // Apply videoStreamOptions
  AVDictionary* avCodecOptions = nullptr;
  if (videoStreamOptions.extraOptions.has_value()) {
    for (const auto& [key, value] : videoStreamOptions.extraOptions.value()) {
      tryToValidateCodecOption(*avCodec, key.c_str(), value);
    }
    sortCodecOptions(
        videoStreamOptions.extraOptions.value(),
        &avCodecOptions,
        &avFormatOptions_);
  }

  if (videoStreamOptions.crf.has_value()) {
    std::string crfValue = std::to_string(videoStreamOptions.crf.value());
    tryToValidateCodecOption(*avCodec, "crf", crfValue);
    av_dict_set(&avCodecOptions, "crf", crfValue.c_str(), 0);
  }
  if (videoStreamOptions.preset.has_value()) {
    av_dict_set(
        &avCodecOptions,
        "preset",
        videoStreamOptions.preset.value().c_str(),
        0);
  }
  int status = avcodec_open2(avCodecContext_.get(), avCodec, &avCodecOptions);
  av_dict_free(&avCodecOptions);

  TORCH_CHECK(
      status == AVSUCCESS,
      "avcodec_open2 failed: ",
      getFFMPEGErrorStringFromErrorCode(status));

  avStream_ = avformat_new_stream(avFormatContext_.get(), nullptr);
  TORCH_CHECK(avStream_ != nullptr, "Couldn't create new stream.");

  // Set the stream time base to encode correct frame timestamps
  avStream_->time_base = avCodecContext_->time_base;
  // Set the stream frame rate to store correct frame durations for some
  // containers (webm, mkv)
  avStream_->r_frame_rate = avCodecContext_->framerate;

  status = avcodec_parameters_from_context(
      avStream_->codecpar, avCodecContext_.get());
  TORCH_CHECK(
      status == AVSUCCESS,
      "avcodec_parameters_from_context failed: ",
      getFFMPEGErrorStringFromErrorCode(status));
}

void VideoEncoder::encode() {
  // To be on the safe side we enforce that encode() can only be called once
  TORCH_CHECK(!encodeWasCalled_, "Cannot call encode() twice.");
  encodeWasCalled_ = true;

  int status = avformat_write_header(avFormatContext_.get(), &avFormatOptions_);
  TORCH_CHECK(
      status == AVSUCCESS,
      "Error in avformat_write_header: ",
      getFFMPEGErrorStringFromErrorCode(status));

  AutoAVPacket autoAVPacket;
  int numFrames = static_cast<int>(frames_.sizes()[0]);
  for (int i = 0; i < numFrames; ++i) {
    torch::Tensor currFrame = frames_[i];
    UniqueAVFrame avFrame = convertTensorToAVFrame(currFrame, i);
    encodeFrame(autoAVPacket, avFrame);
  }

  flushBuffers();

  status = av_write_trailer(avFormatContext_.get());
  TORCH_CHECK(
      status == AVSUCCESS,
      "Error in av_write_trailer: ",
      getFFMPEGErrorStringFromErrorCode(status));
}

UniqueAVFrame VideoEncoder::convertTensorToAVFrame(
    const torch::Tensor& frame,
    int frameIndex) {
  // Initialize and cache scaling context if it does not exist
  if (!swsContext_) {
    swsContext_.reset(sws_getContext(
        inWidth_,
        inHeight_,
        inPixelFormat_,
        outWidth_,
        outHeight_,
        outPixelFormat_,
        SWS_BICUBIC, // Used by FFmpeg CLI
        nullptr,
        nullptr,
        nullptr));
    TORCH_CHECK(swsContext_ != nullptr, "Failed to create scaling context");
  }

  UniqueAVFrame avFrame(av_frame_alloc());
  TORCH_CHECK(avFrame != nullptr, "Failed to allocate AVFrame");

  // Set output frame properties
  avFrame->format = outPixelFormat_;
  avFrame->width = outWidth_;
  avFrame->height = outHeight_;
  avFrame->pts = frameIndex;

  int status = av_frame_get_buffer(avFrame.get(), 0);
  TORCH_CHECK(status >= 0, "Failed to allocate frame buffer");

  // Need to convert/scale the frame
  // Create temporary frame with input format
  UniqueAVFrame inputFrame(av_frame_alloc());
  TORCH_CHECK(inputFrame != nullptr, "Failed to allocate input AVFrame");

  inputFrame->format = inPixelFormat_;
  inputFrame->width = inWidth_;
  inputFrame->height = inHeight_;

  uint8_t* tensorData = static_cast<uint8_t*>(frame.data_ptr());

  // TODO-VideoEncoder: Reorder tensor if in NHWC format
  int channelSize = inHeight_ * inWidth_;
  // Reorder RGB -> GBR for AV_PIX_FMT_GBRP format
  // TODO-VideoEncoder: Determine if FFmpeg supports planar RGB input format
  inputFrame->data[0] = tensorData + channelSize;
  inputFrame->data[1] = tensorData + (2 * channelSize);
  inputFrame->data[2] = tensorData;

  inputFrame->linesize[0] = inWidth_;
  inputFrame->linesize[1] = inWidth_;
  inputFrame->linesize[2] = inWidth_;

  status = sws_scale(
      swsContext_.get(),
      inputFrame->data,
      inputFrame->linesize,
      0,
      inputFrame->height,
      avFrame->data,
      avFrame->linesize);
  TORCH_CHECK(status == outHeight_, "sws_scale failed");
  return avFrame;
}

torch::Tensor VideoEncoder::encodeToTensor() {
  TORCH_CHECK(
      avioContextHolder_ != nullptr,
      "Cannot encode to tensor, avio tensor context doesn't exist.");
  encode();
  auto avioToTensorContext =
      dynamic_cast<AVIOToTensorContext*>(avioContextHolder_.get());
  TORCH_CHECK(avioToTensorContext != nullptr, "Invalid AVIO context holder.");
  return avioToTensorContext->getOutputTensor();
}

void VideoEncoder::encodeFrame(
    AutoAVPacket& autoAVPacket,
    const UniqueAVFrame& avFrame) {
  auto status = avcodec_send_frame(avCodecContext_.get(), avFrame.get());
  TORCH_CHECK(
      status == AVSUCCESS,
      "Error while sending frame: ",
      getFFMPEGErrorStringFromErrorCode(status));

  while (status >= 0) {
    ReferenceAVPacket packet(autoAVPacket);
    status = avcodec_receive_packet(avCodecContext_.get(), packet.get());
    if (status == AVERROR(EAGAIN) || status == AVERROR_EOF) {
      if (status == AVERROR_EOF) {
        // Flush remaining buffered packets
        status = av_interleaved_write_frame(avFormatContext_.get(), nullptr);
        TORCH_CHECK(
            status == AVSUCCESS,
            "Failed to flush packet: ",
            getFFMPEGErrorStringFromErrorCode(status));
      }
      return;
    }
    TORCH_CHECK(
        status >= 0,
        "Error receiving packet: ",
        getFFMPEGErrorStringFromErrorCode(status));

    // The code below is borrowed from torchaudio:
    // https://github.com/pytorch/audio/blob/b6a3368a45aaafe05f1a6a9f10c68adc5e944d9e/src/libtorio/ffmpeg/stream_writer/encoder.cpp#L46
    // Setting packet->duration to 1 allows the last frame to be properly
    // encoded, and needs to be set before calling av_packet_rescale_ts.
    if (packet->duration == 0) {
      packet->duration = 1;
    }
    av_packet_rescale_ts(
        packet.get(), avCodecContext_->time_base, avStream_->time_base);
    packet->stream_index = avStream_->index;

    status = av_interleaved_write_frame(avFormatContext_.get(), packet.get());
    TORCH_CHECK(
        status == AVSUCCESS,
        "Error in av_interleaved_write_frame: ",
        getFFMPEGErrorStringFromErrorCode(status));
  }
}

void VideoEncoder::flushBuffers() {
  AutoAVPacket autoAVPacket;
  // Send null frame to signal end of input
  encodeFrame(autoAVPacket, UniqueAVFrame(nullptr));
}

} // namespace facebook::torchcodec