// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "content/browser/speech/network_speech_recognition_engine_impl.h"

#include <algorithm>
#include <memory>
#include <string_view>
#include <vector>

#include "base/functional/bind.h"
#include "base/metrics/histogram_functions.h"
#include "base/numerics/byte_conversions.h"
#include "base/numerics/safe_conversions.h"
#include "base/rand_util.h"
#include "base/strings/escape.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "base/strings/utf_string_conversions.h"
#include "base/time/time.h"
#include "components/speech/audio_buffer.h"
#include "content/public/browser/google_streaming_api.pb.h"
#include "google_apis/google_api_keys.h"
#include "media/base/audio_timestamp_helper.h"
#include "media/mojo/mojom/speech_recognition_error.mojom.h"
#include "media/mojo/mojom/speech_recognition_result.mojom.h"
#include "mojo/public/c/system/types.h"
#include "mojo/public/cpp/bindings/receiver_set.h"
#include "net/base/load_flags.h"
#include "net/traffic_annotation/network_traffic_annotation.h"
#include "services/network/public/cpp/shared_url_loader_factory.h"

namespace content {
namespace {

const char kWebServiceBaseUrl[] =
    "https://www.google.com/speech-api/full-duplex/v1";
const char kDownstreamUrl[] = "/down?";
const char kUpstreamUrl[] = "/up?";

constexpr char kWebSpeechAudioDuration[] = "Accessibility.WebSpeech.Duration";

// Used to override |kWebServiceBaseUrl| when non-null, only set in tests.
const char* web_service_base_url_for_tests = nullptr;

// This matches the maximum maxAlternatives value supported by the server.
const uint32_t kMaxMaxAlternatives = 30;

// TODO(hans): Remove this and other logging when we don't need it anymore.
void DumpResponse(const std::string& response) {
  DVLOG(1) << "------------";
  proto::SpeechRecognitionEvent event;
  if (!event.ParseFromString(response)) {
    DVLOG(1) << "Parse failed!";
    return;
  }
  if (event.has_status()) {
    DVLOG(1) << "STATUS\t" << event.status();
  }
  if (event.has_endpoint()) {
    DVLOG(1) << "ENDPOINT\t" << event.endpoint();
  }
  for (int i = 0; i < event.result_size(); ++i) {
    DVLOG(1) << "RESULT #" << i << ":";
    const proto::SpeechRecognitionResult& res = event.result(i);
    if (res.has_final()) {
      DVLOG(1) << "  final:\t" << res.final();
    }
    if (res.has_stability()) {
      DVLOG(1) << "  STABILITY:\t" << res.stability();
    }
    for (int j = 0; j < res.alternative_size(); ++j) {
      const proto::SpeechRecognitionAlternative& alt = res.alternative(j);
      if (alt.has_confidence()) {
        DVLOG(1) << "    CONFIDENCE:\t" << alt.confidence();
      }
      if (alt.has_transcript()) {
        DVLOG(1) << "    TRANSCRIPT:\t" << alt.transcript();
      }
    }
  }
}

const int kDefaultConfigSampleRate = 8000;
const int kDefaultConfigBitsPerSample = 16;
const uint32_t kDefaultMaxHypotheses = 1;

}  // namespace

NetworkSpeechRecognitionEngineImpl::Config::Config()
    : max_hypotheses(kDefaultMaxHypotheses),
      audio_sample_rate(kDefaultConfigSampleRate),
      audio_num_bits_per_sample(kDefaultConfigBitsPerSample) {}

NetworkSpeechRecognitionEngineImpl::Config::~Config() = default;

const int NetworkSpeechRecognitionEngineImpl::kAudioPacketIntervalMs = 100;
const int NetworkSpeechRecognitionEngineImpl::kWebserviceStatusNoError = 0;
const int NetworkSpeechRecognitionEngineImpl::kWebserviceStatusErrorNoMatch = 5;

NetworkSpeechRecognitionEngineImpl::NetworkSpeechRecognitionEngineImpl(
    scoped_refptr<network::SharedURLLoaderFactory> shared_url_loader_factory)
    : shared_url_loader_factory_(std::move(shared_url_loader_factory)) {}

NetworkSpeechRecognitionEngineImpl::~NetworkSpeechRecognitionEngineImpl() {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
}

void NetworkSpeechRecognitionEngineImpl::set_web_service_base_url_for_tests(
    const char* base_url_for_tests) {
  web_service_base_url_for_tests = base_url_for_tests;
}

void NetworkSpeechRecognitionEngineImpl::SetConfig(const Config& config) {
  config_ = config;
}

bool NetworkSpeechRecognitionEngineImpl::IsRecognitionPending() const {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  return state_ != STATE_IDLE;
}

void NetworkSpeechRecognitionEngineImpl::StartRecognition() {
  upstream_audio_duration_ = base::TimeDelta();
  FSMEventArgs event_args(EVENT_START_RECOGNITION);
  DispatchEvent(event_args);
}

void NetworkSpeechRecognitionEngineImpl::UpdateRecognitionContext(
    const media::SpeechRecognitionRecognitionContext& recognition_context) {
  Abort(media::mojom::SpeechRecognitionErrorCode::kPhrasesNotSupported);
}

void NetworkSpeechRecognitionEngineImpl::EndRecognition() {
  base::UmaHistogramLongTimes100(kWebSpeechAudioDuration,
                                 upstream_audio_duration_);

  FSMEventArgs event_args(EVENT_END_RECOGNITION);
  DispatchEvent(event_args);
}

void NetworkSpeechRecognitionEngineImpl::TakeAudioChunk(
    const AudioChunk& data) {
  FSMEventArgs event_args(EVENT_AUDIO_CHUNK);
  event_args.audio_data = &data;
  DispatchEvent(event_args);
}

void NetworkSpeechRecognitionEngineImpl::AudioChunksEnded() {
  FSMEventArgs event_args(EVENT_AUDIO_CHUNKS_ENDED);
  DispatchEvent(event_args);
}

void NetworkSpeechRecognitionEngineImpl::OnUpstreamDataComplete(
    bool success,
    int response_code) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  DVLOG(1) << "Upstream complete success: " << success
           << " response_code: " << response_code;

  if (!success) {
    FSMEventArgs event_args(EVENT_UPSTREAM_ERROR);
    DispatchEvent(event_args);
    return;
  }

  // Do nothing on clean completion of upstream request.
}

void NetworkSpeechRecognitionEngineImpl::OnDownstreamDataReceived(
    std::string_view new_response_data) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  DVLOG(1) << "Downstream length: " << new_response_data.size();

  // The downstream response is organized in chunks, whose size is determined
  // by a 4 bytes prefix, transparently handled by the ChunkedByteBuffer class.
  // Such chunks are sent by the speech recognition webservice over the HTTP
  // downstream channel using HTTP chunked transfer (unrelated to our chunks).
  // This function is called every time an HTTP chunk is received by the
  // url fetcher. However there isn't any particular matching between our
  // protocol chunks and HTTP chunks, in the sense that a single HTTP chunk can
  // contain a portion of one chunk or even more chunks together.
  chunked_byte_buffer_.Append(new_response_data);

  // A single HTTP chunk can contain more than one data chunk, thus the while.
  while (chunked_byte_buffer_.HasChunks()) {
    FSMEventArgs event_args(EVENT_DOWNSTREAM_RESPONSE);
    event_args.response = chunked_byte_buffer_.PopChunk();
    DCHECK(event_args.response.get());
    DumpResponse(
        std::string(event_args.response->begin(), event_args.response->end()));
    DispatchEvent(event_args);
  }
}

void NetworkSpeechRecognitionEngineImpl::OnDownstreamDataComplete(
    bool success,
    int response_code) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);

  DVLOG(1) << "Downstream complete success: " << success
           << " response_code: " << response_code;

  if (!success) {
    FSMEventArgs event_args(EVENT_DOWNSTREAM_ERROR);
    DispatchEvent(event_args);
    return;
  }

  FSMEventArgs event_args(EVENT_DOWNSTREAM_CLOSED);
  DispatchEvent(event_args);
}

int NetworkSpeechRecognitionEngineImpl::GetDesiredAudioChunkDurationMs() const {
  return kAudioPacketIntervalMs;
}

// -----------------------  Core FSM implementation ---------------------------

void NetworkSpeechRecognitionEngineImpl::DispatchEvent(
    const FSMEventArgs& event_args) {
  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  DCHECK_LE(event_args.event, EVENT_MAX_VALUE);
  DCHECK_LE(state_, STATE_MAX_VALUE);

  // Event dispatching must be sequential, otherwise it will break all the rules
  // and the assumptions of the finite state automata model.
  DCHECK(!is_dispatching_event_);
  is_dispatching_event_ = true;

  state_ = ExecuteTransitionAndGetNextState(event_args);

  is_dispatching_event_ = false;
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::ExecuteTransitionAndGetNextState(
    const FSMEventArgs& event_args) {
  const FSMEvent event = event_args.event;
  switch (state_) {
    case STATE_IDLE:
      switch (event) {
        case EVENT_START_RECOGNITION:
          return ConnectBothStreams(event_args);
        case EVENT_END_RECOGNITION:
        // Note AUDIO_CHUNK and AUDIO_END events can remain enqueued in case of
        // abort, so we just silently drop them here.
        case EVENT_AUDIO_CHUNK:
        case EVENT_AUDIO_CHUNKS_ENDED:
        // DOWNSTREAM_CLOSED can be received if we end up here due to an error.
        case EVENT_DOWNSTREAM_CLOSED:
          return DoNothing(event_args);
        case EVENT_UPSTREAM_ERROR:
        case EVENT_DOWNSTREAM_ERROR:
        case EVENT_DOWNSTREAM_RESPONSE:
          return NotFeasible(event_args);
      }
      break;
    case STATE_BOTH_STREAMS_CONNECTED:
      switch (event) {
        case EVENT_AUDIO_CHUNK:
          return TransmitAudioUpstream(event_args);
        case EVENT_DOWNSTREAM_RESPONSE:
          return ProcessDownstreamResponse(event_args);
        case EVENT_AUDIO_CHUNKS_ENDED:
          return CloseUpstreamAndWaitForResults(event_args);
        case EVENT_END_RECOGNITION:
          return AbortSilently(event_args);
        case EVENT_UPSTREAM_ERROR:
        case EVENT_DOWNSTREAM_ERROR:
        case EVENT_DOWNSTREAM_CLOSED:
          return AbortWithError(event_args);
        case EVENT_START_RECOGNITION:
          return NotFeasible(event_args);
      }
      break;
    case STATE_WAITING_DOWNSTREAM_RESULTS:
      switch (event) {
        case EVENT_DOWNSTREAM_RESPONSE:
          return ProcessDownstreamResponse(event_args);
        case EVENT_DOWNSTREAM_CLOSED:
          return RaiseNoMatchErrorIfGotNoResults(event_args);
        case EVENT_END_RECOGNITION:
          return AbortSilently(event_args);
        case EVENT_UPSTREAM_ERROR:
        case EVENT_DOWNSTREAM_ERROR:
          return AbortWithError(event_args);
        case EVENT_START_RECOGNITION:
        case EVENT_AUDIO_CHUNK:
        case EVENT_AUDIO_CHUNKS_ENDED:
          return NotFeasible(event_args);
      }
      break;
  }
  return NotFeasible(event_args);
}

// ----------- Contract for all the FSM evolution functions below -------------
//  - Are guaranteed to be executed in the same thread (IO, except for tests);
//  - Are guaranteed to be not reentrant (themselves and each other);
//  - event_args members are guaranteed to be stable during the call;

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::ConnectBothStreams(const FSMEventArgs&) {
  DCHECK(!upstream_loader_.get());
  DCHECK(!downstream_loader_.get());

  encoder_ = std::make_unique<AudioEncoder>(config_.audio_sample_rate,
                                            config_.audio_num_bits_per_sample);
  DCHECK(encoder_.get());
  const std::string request_key = GenerateRequestKey();

  // Only use the framed post data format when a preamble needs to be logged.
  use_framed_post_data_ =
      (config_.preamble && !config_.preamble->sample_data.empty() &&
       !config_.auth_token.empty() && !config_.auth_scope.empty());
  if (use_framed_post_data_) {
    preamble_encoder_ = std::make_unique<AudioEncoder>(
        config_.preamble->sample_rate, config_.preamble->sample_depth * 8);
  }

  const char* web_service_base_url = !web_service_base_url_for_tests
                                         ? kWebServiceBaseUrl
                                         : web_service_base_url_for_tests;

  // Setup downstream fetcher.
  std::vector<std::string> downstream_args;
  downstream_args.push_back(
      "key=" + base::EscapeQueryParamValue(google_apis::GetAPIKey(), true));
  downstream_args.push_back("pair=" + request_key);
  downstream_args.push_back("output=pb");
  GURL downstream_url(std::string(web_service_base_url) +
                      std::string(kDownstreamUrl) +
                      base::JoinString(downstream_args, "&"));

  net::NetworkTrafficAnnotationTag downstream_traffic_annotation =
      net::DefineNetworkTrafficAnnotation("speech_recognition_downstream", R"(
        semantics {
          sender: "Speech Recognition"
          description:
            "Chrome provides translation from speech audio recorded with a "
            "microphone to text, by using the Google speech recognition web "
            "service. Audio is sent to Google's servers (upstream) and text is "
            "returned (downstream). This network request (downstream) sends an "
            "id for getting the text response. Then the (upstream) request "
            "sends the audio data along with the id. When the server has "
            "finished processing the audio data and produced a text response, "
            "it replies to this request."
          trigger:
            "The user chooses to start the recognition by clicking the "
            "microphone icon of the pages using Web SpeechRecognition API."
          internal {
            contacts {
              email: "chrome-media-ux@google.com"
            }
          }
          user_data {
            type: USER_CONTENT
          }
          data: "A unique random id for this speech recognition request."
          destination: GOOGLE_OWNED_SERVICE
          last_reviewed: "2024-2-21"
        }
        policy {
          cookies_allowed: NO
          setting:
            "The user must allow the browser to access the microphone in a "
            "permission prompt. This is set per site (hostname pattern). In "
            "the site settings menu, microphone access can be turned off "
            "for all sites and site specific settings can be changed."
          chrome_policy {
            AudioCaptureAllowed {
              policy_options {mode: MANDATORY}
              AudioCaptureAllowed: false
            }
          }
          chrome_policy {
            AudioCaptureAllowedUrls {
              policy_options {mode: MANDATORY}
              AudioCaptureAllowedUrls: {}
            }
          }
        })");
  auto downstream_request = std::make_unique<network::ResourceRequest>();
  downstream_request->credentials_mode = network::mojom::CredentialsMode::kOmit;
  downstream_request->url = downstream_url;
  downstream_loader_ = std::make_unique<speech::DownstreamLoader>(
      std::move(downstream_request), downstream_traffic_annotation,
      shared_url_loader_factory_.get(), this);

  // Setup upstream fetcher.
  // TODO(hans): Support for user-selected grammars.
  std::vector<std::string> upstream_args;
  upstream_args.push_back(
      "key=" + base::EscapeQueryParamValue(google_apis::GetAPIKey(), true));
  upstream_args.push_back("pair=" + request_key);
  upstream_args.push_back("output=pb");
  upstream_args.push_back("lang=" +
                          base::EscapeQueryParamValue(config_.language, true));
  upstream_args.push_back(config_.filter_profanities ? "pFilter=2"
                                                     : "pFilter=0");
  if (config_.max_hypotheses > 0U) {
    uint32_t max_alternatives =
        std::min(kMaxMaxAlternatives, config_.max_hypotheses);
    upstream_args.push_back("maxAlternatives=" +
                            base::NumberToString(max_alternatives));
  }
  upstream_args.push_back("app=chromium");
  for (const media::mojom::SpeechRecognitionGrammar& grammar :
       config_.grammars) {
    std::string grammar_value(base::NumberToString(grammar.weight) + ":" +
                              grammar.url.spec());
    upstream_args.push_back("grammar=" +
                            base::EscapeQueryParamValue(grammar_value, true));
  }
  if (config_.continuous) {
    upstream_args.push_back("continuous");
  } else {
    upstream_args.push_back("endpoint=1");
  }
  if (config_.interim_results) {
    upstream_args.push_back("interim");
  }
  if (!config_.auth_token.empty() && !config_.auth_scope.empty()) {
    upstream_args.push_back(
        "authScope=" + base::EscapeQueryParamValue(config_.auth_scope, true));
    upstream_args.push_back(
        "authToken=" + base::EscapeQueryParamValue(config_.auth_token, true));
  }
  if (use_framed_post_data_) {
    std::string audio_format;
    if (preamble_encoder_) {
      audio_format = preamble_encoder_->GetMimeType() + ",";
    }
    audio_format += encoder_->GetMimeType();
    upstream_args.push_back("audioFormat=" +
                            base::EscapeQueryParamValue(audio_format, true));
  }

  GURL upstream_url(std::string(web_service_base_url) +
                    std::string(kUpstreamUrl) +
                    base::JoinString(upstream_args, "&"));

  net::NetworkTrafficAnnotationTag upstream_traffic_annotation =
      net::DefineNetworkTrafficAnnotation("speech_recognition_upstream", R"(
        semantics {
          sender: "Speech Recognition"
          description:
            "Chrome provides translation from speech audio recorded with a "
            "microphone to text, by using the Google speech recognition web "
            "service. Audio is sent to Google's servers (upstream) and text is "
            "returned (downstream)."
          trigger:
            "The user chooses to start the recognition by clicking the "
            "microphone icon of the pages using Web SpeechRecognition API."
          internal {
            contacts {
              email: "chrome-media-ux@google.com"
            }
          }
          user_data {
            type: USER_CONTENT
          }
          data:
            "Audio recorded with the microphone, and the unique id of "
            "downstream speech recognition request."
          destination: GOOGLE_OWNED_SERVICE
          last_reviewed: "2024-2-21"
        }
        policy {
          cookies_allowed: NO
          setting:
            "The user must allow the browser to access the microphone in a "
            "permission prompt. This is set per site (hostname pattern). In "
            "the site settings menu, microphone access can be turned off "
            "for all sites and site specific settings can be changed."
          chrome_policy {
            AudioCaptureAllowed {
              policy_options {mode: MANDATORY}
              AudioCaptureAllowed: false
            }
          }
          chrome_policy {
            AudioCaptureAllowedUrls {
              policy_options {mode: MANDATORY}
              AudioCaptureAllowedUrls: {}
            }
          }
        })");

  auto upstream_request = std::make_unique<network::ResourceRequest>();
  upstream_request->url = upstream_url;
  upstream_request->method = "POST";
  upstream_request->referrer = GURL(config_.origin_url);
  upstream_request->credentials_mode = network::mojom::CredentialsMode::kOmit;
  if (use_framed_post_data_) {
    upstream_request->headers.SetHeader(net::HttpRequestHeaders::kContentType,
                                        "application/octet-stream");
  } else {
    upstream_request->headers.SetHeader(net::HttpRequestHeaders::kContentType,
                                        encoder_->GetMimeType());
  }

  upstream_loader_ = std::make_unique<speech::UpstreamLoader>(
      std::move(upstream_request), upstream_traffic_annotation,
      shared_url_loader_factory_.get(), this);

  if (preamble_encoder_) {
    // Encode and send preamble right away.
    scoped_refptr<AudioChunk> chunk = new AudioChunk(
        reinterpret_cast<const uint8_t*>(config_.preamble->sample_data.data()),
        config_.preamble->sample_data.size(), config_.preamble->sample_depth);
    preamble_encoder_->Encode(*chunk);
    preamble_encoder_->Flush();
    scoped_refptr<AudioChunk> encoded_data(
        preamble_encoder_->GetEncodedDataAndClear());
    UploadAudioChunk(encoded_data->AsString(), FRAME_PREAMBLE_AUDIO, false);
  }
  return STATE_BOTH_STREAMS_CONNECTED;
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::TransmitAudioUpstream(
    const FSMEventArgs& event_args) {
  DCHECK(upstream_loader_.get());
  DCHECK(event_args.audio_data.get());
  const AudioChunk& audio = *(event_args.audio_data.get());

  base::TimeDelta duration = media::AudioTimestampHelper::FramesToTime(
      audio.NumSamples(), config_.audio_sample_rate);
  upstream_audio_duration_ += duration;

  DCHECK_EQ(audio.bytes_per_sample(), config_.audio_num_bits_per_sample / 8);
  encoder_->Encode(audio);
  scoped_refptr<AudioChunk> encoded_data(encoder_->GetEncodedDataAndClear());
  UploadAudioChunk(encoded_data->AsString(), FRAME_RECOGNITION_AUDIO, false);
  return state_;
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::ProcessDownstreamResponse(
    const FSMEventArgs& event_args) {
  DCHECK(event_args.response.get());

  proto::SpeechRecognitionEvent ws_event;
  if (!ws_event.ParseFromString(std::string(event_args.response->begin(),
                                            event_args.response->end()))) {
    return AbortWithError(event_args);
  }

  if (ws_event.has_status()) {
    switch (ws_event.status()) {
      case proto::SpeechRecognitionEvent::STATUS_SUCCESS:
        break;
      case proto::SpeechRecognitionEvent::STATUS_NO_SPEECH:
        return Abort(media::mojom::SpeechRecognitionErrorCode::kNoSpeech);
      case proto::SpeechRecognitionEvent::STATUS_ABORTED:
        return Abort(media::mojom::SpeechRecognitionErrorCode::kAborted);
      case proto::SpeechRecognitionEvent::STATUS_AUDIO_CAPTURE:
        return Abort(media::mojom::SpeechRecognitionErrorCode::kAudioCapture);
      case proto::SpeechRecognitionEvent::STATUS_NETWORK:
        return Abort(media::mojom::SpeechRecognitionErrorCode::kNetwork);
      case proto::SpeechRecognitionEvent::STATUS_NOT_ALLOWED:
        return Abort(media::mojom::SpeechRecognitionErrorCode::kNotAllowed);
      case proto::SpeechRecognitionEvent::STATUS_SERVICE_NOT_ALLOWED:
        return Abort(
            media::mojom::SpeechRecognitionErrorCode::kServiceNotAllowed);
      case proto::SpeechRecognitionEvent::STATUS_BAD_GRAMMAR:
        return Abort(media::mojom::SpeechRecognitionErrorCode::kBadGrammar);
      case proto::SpeechRecognitionEvent::STATUS_LANGUAGE_NOT_SUPPORTED:
        return Abort(
            media::mojom::SpeechRecognitionErrorCode::kLanguageNotSupported);
    }
  }

  if (!config_.continuous && ws_event.has_endpoint() &&
      ws_event.endpoint() == proto::SpeechRecognitionEvent::END_OF_UTTERANCE) {
    delegate_->OnSpeechRecognitionEngineEndOfUtterance();
  }

  std::vector<media::mojom::WebSpeechRecognitionResultPtr> results;
  for (int i = 0; i < ws_event.result_size(); ++i) {
    const proto::SpeechRecognitionResult& ws_result = ws_event.result(i);
    results.push_back(media::mojom::WebSpeechRecognitionResult::New());
    media::mojom::WebSpeechRecognitionResultPtr& result = results.back();
    result->is_provisional = !(ws_result.has_final() && ws_result.final());

    if (!result->is_provisional) {
      got_last_definitive_result_ = true;
    }

    for (int j = 0; j < ws_result.alternative_size(); ++j) {
      const proto::SpeechRecognitionAlternative& ws_alternative =
          ws_result.alternative(j);
      media::mojom::SpeechRecognitionHypothesisPtr hypothesis =
          media::mojom::SpeechRecognitionHypothesis::New();
      if (ws_alternative.has_confidence()) {
        hypothesis->confidence = ws_alternative.confidence();
      } else if (ws_result.has_stability()) {
        hypothesis->confidence = ws_result.stability();
      }
      DCHECK(ws_alternative.has_transcript());
      // TODO(hans): Perhaps the transcript should be required in the proto?
      if (ws_alternative.has_transcript()) {
        hypothesis->utterance = base::UTF8ToUTF16(ws_alternative.transcript());
      }

      result->hypotheses.push_back(std::move(hypothesis));
    }
  }
  if (results.size()) {
    delegate_->OnSpeechRecognitionEngineResults(results);
  }

  return state_;
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::RaiseNoMatchErrorIfGotNoResults(
    const FSMEventArgs& event_args) {
  if (!got_last_definitive_result_) {
    // Provide an empty result to notify that recognition is ended with no
    // errors, yet neither any further results.
    delegate_->OnSpeechRecognitionEngineResults(
        std::vector<media::mojom::WebSpeechRecognitionResultPtr>());
  }
  return AbortSilently(event_args);
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::CloseUpstreamAndWaitForResults(
    const FSMEventArgs&) {
  DCHECK(upstream_loader_.get());
  DCHECK(encoder_.get());

  DVLOG(1) << "Closing upstream.";

  // The encoder requires a non-empty final buffer. So we encode a packet
  // of silence in case encoder had no data already.
  size_t sample_count =
      config_.audio_sample_rate * GetDesiredAudioChunkDurationMs() / 1000;
  scoped_refptr<AudioChunk> dummy_chunk = new AudioChunk(
      sample_count * sizeof(int16_t), encoder_->GetBitsPerSample() / 8);
  encoder_->Encode(*dummy_chunk.get());
  encoder_->Flush();
  scoped_refptr<AudioChunk> encoded_dummy_data =
      encoder_->GetEncodedDataAndClear();
  DCHECK(!encoded_dummy_data->IsEmpty());
  encoder_.reset();

  UploadAudioChunk(encoded_dummy_data->AsString(), FRAME_RECOGNITION_AUDIO,
                   true);
  got_last_definitive_result_ = false;
  return STATE_WAITING_DOWNSTREAM_RESULTS;
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::CloseDownstream(const FSMEventArgs&) {
  DCHECK(!upstream_loader_.get());
  DCHECK(downstream_loader_.get());

  DVLOG(1) << "Closing downstream.";
  downstream_loader_.reset();
  return STATE_IDLE;
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::AbortSilently(const FSMEventArgs&) {
  return Abort(media::mojom::SpeechRecognitionErrorCode::kNone);
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::AbortWithError(const FSMEventArgs&) {
  return Abort(media::mojom::SpeechRecognitionErrorCode::kNetwork);
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::Abort(
    media::mojom::SpeechRecognitionErrorCode error_code) {
  DVLOG(1) << "Aborting with error " << error_code;

  if (error_code != media::mojom::SpeechRecognitionErrorCode::kNone) {
    delegate_->OnSpeechRecognitionEngineError(
        media::mojom::SpeechRecognitionError(
            error_code, media::mojom::SpeechAudioErrorDetails::kNone));
  }
  downstream_loader_.reset();
  upstream_loader_.reset();
  encoder_.reset();
  return STATE_IDLE;
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::DoNothing(const FSMEventArgs&) {
  return state_;
}

NetworkSpeechRecognitionEngineImpl::FSMState
NetworkSpeechRecognitionEngineImpl::NotFeasible(
    const FSMEventArgs& event_args) {
  NOTREACHED() << "Unfeasible event " << event_args.event << " in state "
               << state_;
}

// TODO(primiano): Is there any utility in the codebase that already does this?
std::string NetworkSpeechRecognitionEngineImpl::GenerateRequestKey() const {
  const int64_t kKeepLowBytes = 0x00000000FFFFFFFFLL;
  const int64_t kKeepHighBytes = 0xFFFFFFFF00000000LL;

  // Just keep the least significant bits of timestamp, in order to reduce
  // probability of collisions.
  int64_t key = (base::Time::Now().ToInternalValue() & kKeepLowBytes) |
                (base::RandUint64() & kKeepHighBytes);
  return base::HexEncode(reinterpret_cast<void*>(&key), sizeof(key));
}

void NetworkSpeechRecognitionEngineImpl::UploadAudioChunk(
    const std::string& data,
    FrameType type,
    bool is_final) {
  if (use_framed_post_data_) {
    std::string frame(data.size() + 8u, char{0});
    auto frame_span = base::as_writable_byte_span(frame);
    frame_span.subspan<0u, 4u>().copy_from(
        base::U32ToBigEndian(static_cast<uint32_t>(data.size())));
    frame_span.subspan<4u, 4u>().copy_from(
        base::U32ToBigEndian(base::checked_cast<uint32_t>(type)));
    frame.replace(8u, data.size(), data);
    upstream_loader_->AppendChunkToUpload(frame, is_final);
  } else {
    upstream_loader_->AppendChunkToUpload(data, is_final);
  }
}

NetworkSpeechRecognitionEngineImpl::FSMEventArgs::FSMEventArgs(
    FSMEvent event_value)
    : event(event_value) {}

NetworkSpeechRecognitionEngineImpl::FSMEventArgs::~FSMEventArgs() = default;

}  // namespace content