/*
 *  Copyright 2025 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */
#include "pc/codec_vendor.h"

#include <cstddef>
#include <map>
#include <optional>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>

#include "absl/algorithm/container.h"
#include "absl/strings/match.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/string_view.h"
#include "api/field_trials_view.h"
#include "api/media_types.h"
#include "api/payload_type.h"
#include "api/rtc_error.h"
#include "api/rtp_parameters.h"
#include "api/rtp_transceiver_direction.h"
#include "api/sequence_checker.h"
#include "call/payload_type.h"
#include "media/base/codec.h"
#include "media/base/codec_comparators.h"
#include "media/base/codec_list.h"
#include "media/base/media_constants.h"
#include "media/base/media_engine.h"
#include "media/base/sdp_video_format_utils.h"
#include "pc/media_options.h"
#include "pc/rtp_media_utils.h"
#include "pc/session_description.h"
#include "pc/typed_codec_vendor.h"
#include "pc/used_ids.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/string_encode.h"
#include "rtc_base/strings/string_builder.h"
#include "rtc_base/thread.h"

#ifdef RTC_ENABLE_H265
#include "api/video_codecs/h265_profile_tier_level.h"
#endif

namespace webrtc {
namespace {

bool IsRtxCodec(const RtpCodecCapability& capability) {
  return absl::EqualsIgnoreCase(capability.name, kRtxCodecName);
}

bool IsRedCodec(const RtpCodecCapability& capability) {
  return absl::EqualsIgnoreCase(capability.name, kRedCodecName);
}

bool IsComfortNoiseCodec(const Codec& codec) {
  return absl::EqualsIgnoreCase(codec.name, kComfortNoiseCodecName);
}

// Wrapper for FindMatchingCodecs that uses CodecList
std::optional<Codec> FindMatchingCodec(const CodecList& codecs1,
                                       const CodecList& codecs2,
                                       const Codec& codec_to_match) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  return FindMatchingCodec(codecs1.codecs(), codecs2.codecs(), codec_to_match);
}

void StripCNCodecs(CodecList& audio_codecs) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  std::erase_if(audio_codecs.writable_codecs(),
                [](const Codec& codec) { return IsComfortNoiseCodec(codec); });
}

bool IsMediaContentOfType(const ContentInfo* content, MediaType media_type) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  if (!content || !content->media_description()) {
    return false;
  }
  return content->media_description()->type() == media_type;
}
// Find the codec in `codec_list` that `rtx_codec` is associated with.
const Codec* GetAssociatedCodecForRtx(const CodecList& codec_list,
                                      const Codec& rtx_codec) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  std::string associated_pt_str;
  if (!rtx_codec.GetParam(kCodecParamAssociatedPayloadType,
                          &associated_pt_str)) {
    RTC_LOG(LS_WARNING) << "RTX codec " << rtx_codec.id
                        << " is missing an associated payload type.";
    return nullptr;
  }

  int associated_pt;
  if (!FromString(associated_pt_str, &associated_pt)) {
    RTC_LOG(LS_WARNING) << "Couldn't convert payload type " << associated_pt_str
                        << " of RTX codec " << rtx_codec.id
                        << " to an integer.";
    return nullptr;
  }

  // Find the associated codec for the RTX codec.
  const Codec* associated_codec =
      FindCodecById(codec_list.codecs(), associated_pt);
  if (!associated_codec) {
    RTC_LOG(LS_WARNING) << "Couldn't find associated codec with payload type "
                        << associated_pt << " for RTX codec " << rtx_codec.id
                        << ".";
  }
  return associated_codec;
}

// Find the codecs in `codec_list` that `red_codec` is associated with.
// Returns a vector of pointers to the codecs on success.
const RTCErrorOr<std::vector<const Codec*>> GetAssociatedCodecsForRed(
    const CodecList& codec_list,
    const Codec& red_codec) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  std::string fmtp;
  std::vector<const Codec*> codecs;
  if (!red_codec.GetParam(kCodecParamNotInNameValueFormat, &fmtp)) {
    // Don't log for video/RED where this is normal.
    if (red_codec.type == Codec::Type::kAudio) {
      RTC_LOG(LS_WARNING)
          << "RED codec " << red_codec
          << " is missing an associated payload type parameter.";
      // There are also tests that assume this behavior for audio, so don't
      // return an error here either.
    }
    return codecs;  // empty list
  }

  std::vector<absl::string_view> redundant_payloads = split(fmtp, '/');
  if (redundant_payloads.size() < 2) {
    return codecs;  // empty
  }
  for (size_t index = 0; index < redundant_payloads.size(); ++index) {
    absl::string_view associated_pt_str = redundant_payloads[index];
    int associated_pt;
    if (!FromString(associated_pt_str, &associated_pt)) {
      RTC_LOG(LS_WARNING) << "Couldn't convert payload type "
                          << associated_pt_str << " of RED codec " << red_codec
                          << " to an integer.";
      return RTCError(RTCErrorType::INTERNAL_ERROR,
                      "RED codec with non-integer argument");
    }

    // Find the associated codec for the RED codec.
    const Codec* associated_codec =
        FindCodecById(codec_list.codecs(), associated_pt);
    if (!associated_codec) {
      RTC_LOG(LS_WARNING) << "Couldn't find associated codec with payload type "
                          << associated_pt << " for RED codec " << red_codec
                          << ".";
      return RTCError(RTCErrorType::INTERNAL_ERROR,
                      "RED codec pointing to nonexistent PT");
    }
    codecs.push_back(associated_codec);
  }
  return codecs;
}

// Adds all codecs from `reference_codecs` to `offered_codecs` that don't
// already exist in `offered_codecs` and ensure the payload types don't
// collide.
RTCError MergeCodecs(const CodecList& reference_codecs,
                     absl::string_view mid,
                     CodecList& offered_codecs,
                     PayloadTypeSuggester& pt_suggester) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  // Add all new codecs that are not RTX/RED codecs.
  // The two-pass splitting of the loops means preferring payload types
  // of actual codecs with respect to collisions.
  for (const Codec& reference_codec : reference_codecs) {
    if (reference_codec.GetResiliencyType() != Codec::ResiliencyType::kRtx &&
        reference_codec.GetResiliencyType() != Codec::ResiliencyType::kRed &&
        !FindMatchingCodec(reference_codecs, offered_codecs, reference_codec)) {
      Codec codec = reference_codec;
      RTCErrorOr<PayloadType> suggestion =
          pt_suggester.SuggestPayloadType(mid, codec);
      if (!suggestion.ok()) {
        return suggestion.MoveError();
      }
      codec.id = suggestion.value();
      offered_codecs.PushIfNotPresent(codec);
    }
  }

  // Add all new RTX or RED codecs.
  for (const Codec& reference_codec : reference_codecs) {
    if (reference_codec.GetResiliencyType() == Codec::ResiliencyType::kRtx &&
        !FindMatchingCodec(reference_codecs, offered_codecs, reference_codec)) {
      Codec rtx_codec = reference_codec;
      const Codec* associated_codec =
          GetAssociatedCodecForRtx(reference_codecs, rtx_codec);
      if (!associated_codec) {
        continue;
      }
      // Find a codec in the offered list that matches the reference codec.
      // Its payload type may be different than the reference codec.
      std::optional<Codec> matching_codec = FindMatchingCodec(
          reference_codecs, offered_codecs, *associated_codec);
      if (!matching_codec) {
        RTC_LOG(LS_WARNING)
            << "Couldn't find matching " << associated_codec->name << " codec.";
        continue;
      }

      rtx_codec.params[kCodecParamAssociatedPayloadType] =
          absl::StrCat(matching_codec->id);
      RTCErrorOr<PayloadType> suggestion =
          pt_suggester.SuggestPayloadType(mid, rtx_codec);
      if (!suggestion.ok()) {
        return suggestion.MoveError();
      }
      rtx_codec.id = suggestion.value();
      offered_codecs.push_back(rtx_codec);
    } else if (reference_codec.GetResiliencyType() ==
                   Codec::ResiliencyType::kRed &&
               !FindMatchingCodec(reference_codecs, offered_codecs,
                                  reference_codec)) {
      Codec red_codec = reference_codec;
      RTCErrorOr<std::vector<const Codec*>> associated_codecs =
          GetAssociatedCodecsForRed(reference_codecs, red_codec);
      if (!associated_codecs.ok()) {
        return associated_codecs.MoveError();
      }
      if (associated_codecs.value().empty()) {
        // No parameter. Just blindly add the codec.
        // This is known to be used with video, but not with audio.
        if (red_codec.type == Codec::Type::kAudio) {
          RTC_LOG(LS_WARNING)
              << "RED audio codec with no associated codecs found: "
              << red_codec;
        }
        RTCErrorOr<PayloadType> suggestion =
            pt_suggester.SuggestPayloadType(mid, red_codec);
        if (!suggestion.ok()) {
          return suggestion.MoveError();
        }
        red_codec.id = suggestion.value();
        offered_codecs.PushIfNotPresent(red_codec);
        continue;
      }
      if (associated_codecs.value().size() < 2) {
        RTC_LOG(LS_WARNING)
            << "RED codec with only one valid associated codec ignored: "
            << red_codec;
        continue;
      }
      StringBuilder sb;
      for (const Codec* associated_codec : associated_codecs.value()) {
        std::optional<Codec> matching_codec = FindMatchingCodec(
            reference_codecs, offered_codecs, *associated_codec);
        if (!matching_codec) {
          // This should always succeed, because the associated codecs
          // were looked up in reference_codecs, and all reference
          // codecs were added in the first loop of the function.
          RTC_LOG(LS_WARNING) << "Couldn't find matching "
                              << associated_codec->name << " codec.";
          // TODO: https://issues.webrtc.org/455503439 - consider CHECK
          RTC_DCHECK_NOTREACHED();
          return RTCError(RTCErrorType::INTERNAL_ERROR,
                          "RED payload type lookup failed");
        }
        if (sb.size() > 0) {
          sb << "/";
        }
        sb << matching_codec->id;
      }
      red_codec.params[kCodecParamNotInNameValueFormat] = sb.Release();
      RTCErrorOr<PayloadType> suggestion =
          pt_suggester.SuggestPayloadType(mid, red_codec);
      if (!suggestion.ok()) {
        return suggestion.MoveError();
      }
      red_codec.id = suggestion.value();
      offered_codecs.push_back(red_codec);
    }
  }
  offered_codecs.CheckConsistency();

  return RTCError::OK();
}

// `codecs` is a full list of codecs with correct payload type mappings, which
// don't conflict with mappings of the other media type; `supported_codecs` is
// a list filtered for the media section`s direction but with default payload
// types.
// static
CodecList MatchCodecPreference(
    const std::vector<RtpCodecCapability>& codec_preferences,
    const CodecList& codecs,
    const CodecList& supported_codecs) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  CodecList filtered_codecs;
  bool want_rtx = false;
  bool want_red = false;

  for (const auto& codec_preference : codec_preferences) {
    if (IsRtxCodec(codec_preference)) {
      want_rtx = true;
    } else if (IsRedCodec(codec_preference)) {
      want_red = true;
    }
  }
  bool red_was_added = false;
  for (const auto& codec_preference : codec_preferences) {
    auto found_codec = absl::c_find_if(
        supported_codecs, [&codec_preference](const Codec& codec) {
          // We should not filter out the codec in |codec_preferences| if it
          // has a higher level than the codec in |supported_codecs|, as the
          // codec in |supported_codecs| may be only with lower level in
          // |send_codecs_| and |recv_codecs_| for the same codec.
          return IsSameRtpCodecIgnoringLevel(codec, codec_preference);
        });

    if (found_codec != supported_codecs.end()) {
      std::optional<Codec> found_codec_with_correct_pt =
          FindMatchingCodec(supported_codecs, codecs, *found_codec);
      if (found_codec_with_correct_pt) {
        // RED may already have been added if its primary codec is before RED
        // in the codec list.
        bool is_red_codec = found_codec_with_correct_pt->GetResiliencyType() ==
                            Codec::ResiliencyType::kRed;
        if (!is_red_codec || !red_was_added) {
          filtered_codecs.push_back(*found_codec_with_correct_pt);
          red_was_added = is_red_codec ? true : red_was_added;
        }
        std::string id = absl::StrCat(found_codec_with_correct_pt->id);
        // Search for the matching rtx or red codec.
        if (want_red || want_rtx) {
          for (const auto& codec : codecs) {
            if (want_rtx &&
                codec.GetResiliencyType() == Codec::ResiliencyType::kRtx) {
              const auto apt =
                  codec.params.find(kCodecParamAssociatedPayloadType);
              if (apt != codec.params.end() && apt->second == id) {
                filtered_codecs.push_back(codec);
                break;
              }
            } else if (want_red && codec.GetResiliencyType() ==
                                       Codec::ResiliencyType::kRed) {
              // For RED, do not insert the codec again if it was already
              // inserted. audio/red for opus gets enabled by having RED before
              // the primary codec.
              const auto fmtp =
                  codec.params.find(kCodecParamNotInNameValueFormat);
              if (fmtp != codec.params.end()) {
                std::vector<absl::string_view> redundant_payloads =
                    split(fmtp->second, '/');
                if (!redundant_payloads.empty() &&
                    redundant_payloads[0] == id) {
                  if (!red_was_added) {
                    filtered_codecs.push_back(codec);
                    red_was_added = true;
                  }
                  break;
                }
              }
            }
          }
        }
      }
    }
  }

  return filtered_codecs;
}

void NegotiatePacketization(const Codec& local_codec,
                            const Codec& remote_codec,
                            Codec* negotiated_codec) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  negotiated_codec->packetization =
      (local_codec.packetization == remote_codec.packetization)
          ? local_codec.packetization
          : std::nullopt;
}

#ifdef RTC_ENABLE_H265
void NegotiateTxMode(const Codec& local_codec,
                     const Codec& remote_codec,
                     Codec* negotiated_codec) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  negotiated_codec->tx_mode = (local_codec.tx_mode == remote_codec.tx_mode)
                                  ? local_codec.tx_mode
                                  : std::nullopt;
}
#endif

// For offer, negotiated codec must have the same level-id as that in
// |supported_codecs| with same profile.
void NegotiateVideoCodecLevelsForOffer(
    const MediaDescriptionOptions& media_description_options,
    const CodecList& supported_codecs,
    CodecList& filtered_codecs) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  if (filtered_codecs.empty() || supported_codecs.empty()) {
    return;
  }

  // TODO(http://crbugs.com/376306259): We should handle level-idx for AV1.
  // Ideally this should be done for all codecs, but RFCs of other codecs
  // do not clear define the expected behavior for the level in the offer.
#ifdef RTC_ENABLE_H265
  if (media_description_options.type == MediaType::VIDEO) {
    std::unordered_map<H265Profile, H265Level> supported_h265_profiles;
    // The assumption here is that H.265 codecs with the same profile and tier
    // are already with highest level for that profile in both
    // |supported_codecs| and |filtered_codecs|.
    for (const Codec& supported_codec : supported_codecs) {
      if (absl::EqualsIgnoreCase(supported_codec.name, kH265CodecName)) {
        std::optional<H265ProfileTierLevel> supported_ptl =
            ParseSdpForH265ProfileTierLevel(supported_codec.params);
        if (supported_ptl.has_value()) {
          supported_h265_profiles[supported_ptl->profile] =
              supported_ptl->level;
        }
      }
    }

    if (supported_h265_profiles.empty()) {
      return;
    }

    for (auto& filtered_codec : filtered_codecs) {
      if (absl::EqualsIgnoreCase(filtered_codec.name, kH265CodecName)) {
        std::optional<H265ProfileTierLevel> filtered_ptl =
            ParseSdpForH265ProfileTierLevel(filtered_codec.params);
        if (filtered_ptl.has_value()) {
          auto it = supported_h265_profiles.find(filtered_ptl->profile);

          if (it != supported_h265_profiles.end() &&
              filtered_ptl->level != it->second) {
            filtered_codec.params[kH265FmtpLevelId] =
                H265LevelToString(it->second);
          }
        }
      }
    }
  }
#endif
}

RTCError NegotiateCodecs(const CodecList& local_codecs,
                         const CodecList& offered_codecs,
                         CodecList& negotiated_codecs_out,
                         bool keep_offer_order) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  std::map<int, int> pt_mapping_table;
  // Since we build the negotiated codec list one entry at a time,
  // the list will have inconsistencies during building.
  std::vector<Codec> negotiated_codecs;
  for (const Codec& ours : local_codecs) {
    std::optional<Codec> theirs =
        FindMatchingCodec(local_codecs, offered_codecs, ours);
    // Note that we intentionally only find one matching codec for each of our
    // local codecs, in case the remote offer contains duplicate codecs.
    if (theirs) {
      Codec negotiated = ours;
      NegotiatePacketization(ours, *theirs, &negotiated);
      negotiated.IntersectFeedbackParams(*theirs);
      if (negotiated.GetResiliencyType() == Codec::ResiliencyType::kRtx) {
        // We support parsing the declarative rtx-time parameter.
        const auto rtx_time_it = theirs->params.find(kCodecParamRtxTime);
        if (rtx_time_it != theirs->params.end()) {
          negotiated.SetParam(kCodecParamRtxTime, rtx_time_it->second);
        }
      } else if (negotiated.GetResiliencyType() ==
                 Codec::ResiliencyType::kRed) {
        const auto red_it =
            theirs->params.find(kCodecParamNotInNameValueFormat);
        if (red_it != theirs->params.end()) {
          negotiated.SetParam(kCodecParamNotInNameValueFormat, red_it->second);
        }
      }
      if (absl::EqualsIgnoreCase(ours.name, kH264CodecName)) {
        H264GenerateProfileLevelIdForAnswer(ours.params, theirs->params,
                                            &negotiated.params);
      }
#ifdef RTC_ENABLE_H265
      if (absl::EqualsIgnoreCase(ours.name, kH265CodecName)) {
        H265GenerateProfileTierLevelForAnswer(ours.params, theirs->params,
                                              &negotiated.params);
        NegotiateTxMode(ours, *theirs, &negotiated);
      }
#endif
      // Use their ID, if available.
      pt_mapping_table.insert({negotiated.id, theirs->id});
      negotiated.id = theirs->id;
      negotiated.name = theirs->name;
      negotiated_codecs.push_back(std::move(negotiated));
    }
  }
  // Fix up apt parameters that point to other PTs.
  for (Codec& negotiated : negotiated_codecs) {
    if (negotiated.GetResiliencyType() == Codec::ResiliencyType::kRtx) {
      // Change the apt value according to the pt mapping table.
      // This avoids changing to apt values that don't exist any more.
      std::string apt_str;
      if (!negotiated.GetParam(kCodecParamAssociatedPayloadType, &apt_str)) {
        RTC_LOG(LS_WARNING) << "No apt value";
        continue;
      }
      int apt_value;
      if (!FromString(apt_str, &apt_value)) {
        RTC_LOG(LS_WARNING) << "Unconvertable apt value";
        continue;
      }
      if (pt_mapping_table.count(apt_value) != 1) {
        RTC_LOG(LS_WARNING) << "Unmapped apt value " << apt_value;
        continue;
      }
      negotiated.SetParam(kCodecParamAssociatedPayloadType,
                          pt_mapping_table.at(apt_value));
    }
  }
  if (keep_offer_order) {
    // RFC3264: Although the answerer MAY list the formats in their desired
    // order of preference, it is RECOMMENDED that unless there is a
    // specific reason, the answerer list formats in the same relative order
    // they were present in the offer.
    // This can be skipped when the transceiver has any codec preferences.
    std::unordered_map<int, int> payload_type_preferences;
    int preference = static_cast<int>(offered_codecs.size() + 1);
    for (const Codec& codec : offered_codecs) {
      payload_type_preferences[codec.id] = preference--;
    }
    absl::c_sort(negotiated_codecs, [&payload_type_preferences](
                                        const Codec& a, const Codec& b) {
      return payload_type_preferences[a.id] > payload_type_preferences[b.id];
    });
  }
  RTCErrorOr<CodecList> result = CodecList::Create(negotiated_codecs);
  if (!result.ok()) {
    return result.MoveError();
  }
  negotiated_codecs_out = result.MoveValue();
  return RTCError::OK();
}

// Update the ID fields of the codec vector.
// If any codec has an ID with value "kIdNotSet", use the payload type suggester
// to assign and record a payload type for it.
// If there is a RED codec without its fmtp parameter, give it the ID of the
// first OPUS codec in the codec list.
RTCError AssignCodecIdsAndLinkRed(PayloadTypeSuggester* pt_suggester,
                                  const std::string& mid,
                                  std::vector<Codec>& codecs) {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  int codec_payload_type = Codec::kIdNotSet;
  for (Codec& codec : codecs) {
    if (codec.id == PayloadType::NotSet()) {
      // Add payload types to codecs, if needed
      // This should only happen if WebRTC-PayloadTypesInTransport field trial
      // is enabled.
      RTC_CHECK(pt_suggester);
      auto result = pt_suggester->SuggestPayloadType(mid, codec);
      if (!result.ok()) {
        return result.error();
      }
      codec.id = result.value();
    }
    // record first Opus codec id
    if (absl::EqualsIgnoreCase(codec.name, kOpusCodecName) &&
        codec_payload_type == Codec::kIdNotSet) {
      codec_payload_type = codec.id.value();
    }
  }
  if (codec_payload_type != Codec::kIdNotSet) {
    for (Codec& codec : codecs) {
      if (codec.type == Codec::Type::kAudio &&
          absl::EqualsIgnoreCase(codec.name, kRedCodecName)) {
        if (codec.params.empty()) {
          StringBuilder param;
          param << codec_payload_type << "/" << codec_payload_type;
          codec.SetParam(kCodecParamNotInNameValueFormat, param.str());
        }
      }
    }
  }
  return RTCError::OK();
}

}  // namespace

// Exposed for testing
RTCError MergeCodecsForTesting(const CodecList& reference_codecs,
                               absl::string_view mid,
                               CodecList& offered_codecs,
                               PayloadTypeSuggester& pt_suggester) {
  return MergeCodecs(reference_codecs, mid, offered_codecs, pt_suggester);
}

RTCErrorOr<std::vector<Codec>> CodecVendor::GetNegotiatedCodecsForOffer(
    const MediaDescriptionOptions& media_description_options,
    const MediaSessionOptions& session_options,
    const ContentInfo* current_content,
    PayloadTypeSuggester& pt_suggester) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  CodecList codecs;
  std::string mid = media_description_options.mid;
  // If current content exists and is not being recycled, use its codecs.
  if (current_content && current_content->mid() == mid &&
      IsMediaContentOfType(current_content, media_description_options.type)) {
    RTCErrorOr<CodecList> checked_codec_list =
        CodecList::Create(current_content->media_description()->codecs());
    if (!checked_codec_list.ok()) {
      return checked_codec_list.MoveError();
    }
    // Use MergeCodecs in order to handle PT clashes.
    MergeCodecs(checked_codec_list.value(), mid, codecs, pt_suggester);
  }
  // Add our codecs that are not in the current description.
  if (media_description_options.type == MediaType::AUDIO) {
    MergeCodecs(audio_recv_codecs(), mid, codecs, pt_suggester);
    MergeCodecs(audio_send_codecs(), mid, codecs, pt_suggester);
  } else {
    MergeCodecs(video_recv_codecs(), mid, codecs, pt_suggester);
    MergeCodecs(video_send_codecs(), mid, codecs, pt_suggester);
  }
  CodecList filtered_codecs;
  CodecList supported_codecs =
      media_description_options.type == MediaType::AUDIO
          ? GetAudioCodecsForOffer(media_description_options.direction)
          : GetVideoCodecsForOffer(media_description_options.direction);

  if (media_description_options.codecs_to_include.empty()) {
    if (!media_description_options.codec_preferences.empty()) {
      // Add the codecs from the current transceiver's codec preferences.
      // They override any existing codecs from previous negotiations.
      filtered_codecs =
          MatchCodecPreference(media_description_options.codec_preferences,
                               codecs, supported_codecs);
    } else {
      // Add the codecs from current content if it exists and is not rejected
      // nor recycled.
      if (current_content && !current_content->rejected &&
          current_content->mid() == media_description_options.mid) {
        if (!IsMediaContentOfType(current_content,
                                  media_description_options.type)) {
          // Can happen if the remote side re-uses a MID while recycling.
          return LOG_ERROR(RTCError(RTCErrorType::INTERNAL_ERROR)
                           << "Media type for content with mid='"
                           << current_content->mid()
                           << "' does not match previous type.");
        }
        const MediaContentDescription* mcd =
            current_content->media_description();
        for (const Codec& codec : mcd->codecs()) {
          if (FindMatchingCodec(mcd->codecs(), codecs.codecs(), codec)) {
            filtered_codecs.push_back(codec);
          }
        }
      }
      // Note what PTs are already in use.
      UsedPayloadTypes
          used_pltypes;  // Used to avoid pt collisions in filtered_codecs
      for (auto& codec : filtered_codecs) {
        // Note: This may change PTs. Doing so woud indicate an error, but
        // UsedPayloadTypes doesn't offer a means to make the distinction.
        used_pltypes.FindAndSetIdUsed(&codec);
      }
      // Add other supported codecs.
      for (const Codec& codec : supported_codecs) {
        std::optional<Codec> found_codec =
            FindMatchingCodec(supported_codecs, codecs, codec);
        if (found_codec &&
            !FindMatchingCodec(supported_codecs, filtered_codecs, codec)) {
          // Use the `found_codec` from `codecs` because it has the
          // correctly mapped payload type (most of the time).
          if (media_description_options.type == MediaType::VIDEO &&
              found_codec->GetResiliencyType() == Codec::ResiliencyType::kRtx) {
            // For RTX we might need to adjust the apt parameter if we got a
            // remote offer without RTX for a codec for which we support RTX.
            // This is only done for video since we do not yet have rtx for
            // audio.
            auto referenced_codec =
                GetAssociatedCodecForRtx(supported_codecs, codec);
            RTC_DCHECK(referenced_codec);

            // Find the codec we should be referencing and point to it.
            std::optional<Codec> changed_referenced_codec = FindMatchingCodec(
                supported_codecs, filtered_codecs, *referenced_codec);
            if (changed_referenced_codec) {
              found_codec->SetParam(kCodecParamAssociatedPayloadType,
                                    changed_referenced_codec->id);
            }
          }
          // Quick fix for b/395077842: Remap the codec if it collides.
          used_pltypes.FindAndSetIdUsed(&(*found_codec));
          filtered_codecs.push_back(*found_codec);
        }
      }
    }

    if (media_description_options.type == MediaType::AUDIO &&
        !session_options.vad_enabled) {
      // If application doesn't want CN codecs in offer.
      StripCNCodecs(filtered_codecs);
    } else if (media_description_options.type == MediaType::VIDEO &&
               session_options.raw_packetization_for_video) {
      for (Codec& codec : filtered_codecs) {
        if (codec.IsMediaCodec()) {
          codec.packetization = kPacketizationParamRaw;
        }
      }
    }
    NegotiateVideoCodecLevelsForOffer(media_description_options,
                                      supported_codecs, filtered_codecs);
  } else {
    // media_description_options.codecs_to_include contains codecs
    // TODO: issues.webrtc.org/360058654 - figure out if this can be deleted.
    RTCErrorOr<CodecList> codecs_from_arg =
        CodecList::Create(media_description_options.codecs_to_include);
    if (!codecs_from_arg.ok()) {
      return codecs_from_arg.MoveError();
    }
    filtered_codecs = codecs_from_arg.MoveValue();
  }
  AssignCodecIdsAndLinkRed(&pt_suggester, mid,
                           filtered_codecs.writable_codecs());

  return filtered_codecs.codecs();
}

RTCErrorOr<Codecs> CodecVendor::GetNegotiatedCodecsForAnswer(
    const MediaDescriptionOptions& media_description_options,
    const MediaSessionOptions& session_options,
    RtpTransceiverDirection offer_rtd,
    RtpTransceiverDirection answer_rtd,
    const ContentInfo* current_content,
    const std::vector<Codec> codecs_from_offer,
    PayloadTypeSuggester& pt_suggester) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  CodecList codecs;
  std::string mid = media_description_options.mid;
  if (current_content && current_content->mid() == mid &&
      IsMediaContentOfType(current_content, media_description_options.type)) {
    RTCErrorOr<CodecList> checked_codec_list =
        CodecList::Create(current_content->media_description()->codecs());
    if (!checked_codec_list.ok()) {
      return checked_codec_list.MoveError();
    }
    MergeCodecs(checked_codec_list.value(), mid, codecs, pt_suggester);
  }
  // Add all our supported codecs
  if (media_description_options.type == MediaType::AUDIO) {
    MergeCodecs(audio_send_codecs(), mid, codecs, pt_suggester);
    MergeCodecs(audio_recv_codecs(), mid, codecs, pt_suggester);
  } else {
    MergeCodecs(video_send_codecs(), mid, codecs, pt_suggester);
    MergeCodecs(video_recv_codecs(), mid, codecs, pt_suggester);
  }
  CodecList filtered_codecs;
  CodecList negotiated_codecs;
  if (media_description_options.codecs_to_include.empty()) {
    const CodecList& supported_codecs =
        media_description_options.type == MediaType::AUDIO
            ? GetAudioCodecsForAnswer(offer_rtd, answer_rtd)
            : GetVideoCodecsForAnswer(offer_rtd, answer_rtd);
    if (!media_description_options.codec_preferences.empty()) {
      filtered_codecs =
          MatchCodecPreference(media_description_options.codec_preferences,
                               codecs, supported_codecs);
    } else {
      // Add the codecs from current content if it exists and is not rejected
      // nor recycled.
      if (current_content && !current_content->rejected &&
          current_content->mid() == media_description_options.mid) {
        if (!IsMediaContentOfType(current_content,
                                  media_description_options.type)) {
          // Can happen if the remote side re-uses a MID while recycling.
          return LOG_ERROR(RTCError(RTCErrorType::INTERNAL_ERROR)
                           << "Media type for content with mid='"
                           << current_content->mid()
                           << "' does not match previous type.");
        }
        const MediaContentDescription* mcd =
            current_content->media_description();
        for (const Codec& codec : mcd->codecs()) {
          if (std::optional<Codec> found_codec =
                  FindMatchingCodec(mcd->codecs(), codecs.codecs(), codec)) {
            filtered_codecs.push_back(*found_codec);
          }
        }
      }
      // Merge other_codecs into filtered_codecs, resolving PT conflicts.
      MergeCodecs(supported_codecs, mid, filtered_codecs, pt_suggester);
    }

    if (media_description_options.type == MediaType::AUDIO &&
        !session_options.vad_enabled) {
      // If application doesn't want CN codecs in offer.
      StripCNCodecs(filtered_codecs);
    } else if (media_description_options.type == MediaType::VIDEO &&
               session_options.raw_packetization_for_video) {
      for (Codec& codec : filtered_codecs) {
        if (codec.IsMediaCodec()) {
          codec.packetization = kPacketizationParamRaw;
        }
      }
    }
    // An offer is external data, so needs to be checked before use.
    auto checked_codecs_from_offer = CodecList::Create(codecs_from_offer);
    if (!checked_codecs_from_offer.ok()) {
      return checked_codecs_from_offer.MoveError();
    }
    NegotiateCodecs(filtered_codecs, checked_codecs_from_offer.value(),
                    negotiated_codecs,
                    media_description_options.codec_preferences.empty());
  } else {
    // media_description_options.codecs_to_include contains codecs
    RTCErrorOr<CodecList> codecs_from_arg =
        CodecList::Create(media_description_options.codecs_to_include);
    if (!codecs_from_arg.ok()) {
      return codecs_from_arg.MoveError();
    }
    negotiated_codecs = codecs_from_arg.MoveValue();
  }
  AssignCodecIdsAndLinkRed(&pt_suggester, media_description_options.mid,
                           negotiated_codecs.writable_codecs());
  return negotiated_codecs.codecs();
}

TypedCodecVendor InitTypedCodecVendor(const MediaEngineInterface* media_engine,
                                      MediaType media_type,
                                      bool is_sender,
                                      bool rtx_enabled,
                                      const FieldTrialsView& trials) {
  return media_engine ? TypedCodecVendor(media_engine, media_type, is_sender,
                                         rtx_enabled, trials)
                      : TypedCodecVendor();
}

CodecVendor::CodecVendor(const MediaEngineInterface* media_engine,
                         bool rtx_enabled,
                         const FieldTrialsView& trials)
    : audio_send_codecs_(InitTypedCodecVendor(media_engine,
                                              MediaType::AUDIO,
                                              /*is_sender=*/true,
                                              rtx_enabled,
                                              trials)),
      audio_recv_codecs_(InitTypedCodecVendor(media_engine,
                                              MediaType::AUDIO,
                                              /*is_sender=*/false,
                                              rtx_enabled,
                                              trials)),
      video_send_codecs_(InitTypedCodecVendor(media_engine,
                                              MediaType::VIDEO,
                                              /*is_sender=*/true,
                                              rtx_enabled,
                                              trials)),
      video_recv_codecs_(InitTypedCodecVendor(media_engine,
                                              MediaType::VIDEO,
                                              /*is_sender=*/false,
                                              rtx_enabled,
                                              trials)) {}

const CodecList& CodecVendor::audio_send_codecs() const {
  return audio_send_codecs_.codecs();
}

const CodecList& CodecVendor::audio_recv_codecs() const {
  return audio_recv_codecs_.codecs();
}

const CodecList& CodecVendor::video_send_codecs() const {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  return video_send_codecs_.codecs();
}

const CodecList& CodecVendor::video_recv_codecs() const {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  return video_recv_codecs_.codecs();
}

CodecList CodecVendor::GetVideoCodecsForOffer(
    const RtpTransceiverDirection& direction) const {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  switch (direction) {
    // If stream is inactive - generate list as if sendrecv.
    case RtpTransceiverDirection::kSendRecv:
    case RtpTransceiverDirection::kStopped:
    case RtpTransceiverDirection::kInactive:
      return video_sendrecv_codecs();
    case RtpTransceiverDirection::kSendOnly:
      return video_send_codecs_.codecs();
    case RtpTransceiverDirection::kRecvOnly:
      return video_recv_codecs_.codecs();
  }
  RTC_CHECK_NOTREACHED();
}

CodecList CodecVendor::GetVideoCodecsForAnswer(
    const RtpTransceiverDirection& offer,
    const RtpTransceiverDirection& answer) const {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  switch (answer) {
    // For inactive and sendrecv answers, generate lists as if we were to accept
    // the offer's direction. See RFC 3264 Section 6.1.
    case RtpTransceiverDirection::kSendRecv:
    case RtpTransceiverDirection::kStopped:
    case RtpTransceiverDirection::kInactive:
      return GetVideoCodecsForOffer(RtpTransceiverDirectionReversed(offer));
    case RtpTransceiverDirection::kSendOnly:
      return video_send_codecs_.codecs();
    case RtpTransceiverDirection::kRecvOnly:
      return video_recv_codecs_.codecs();
  }
  RTC_CHECK_NOTREACHED();
}

CodecList CodecVendor::GetAudioCodecsForOffer(
    const RtpTransceiverDirection& direction) const {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  switch (direction) {
    // If stream is inactive - generate list as if sendrecv.
    case RtpTransceiverDirection::kSendRecv:
    case RtpTransceiverDirection::kStopped:
    case RtpTransceiverDirection::kInactive:
      return audio_sendrecv_codecs();
    case RtpTransceiverDirection::kSendOnly:
      return audio_send_codecs_.codecs();
    case RtpTransceiverDirection::kRecvOnly:
      return audio_recv_codecs_.codecs();
  }
  RTC_CHECK_NOTREACHED();
}

CodecList CodecVendor::GetAudioCodecsForAnswer(
    const RtpTransceiverDirection& offer,
    const RtpTransceiverDirection& answer) const {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  switch (answer) {
    // For inactive and sendrecv answers, generate lists as if we were to accept
    // the offer's direction. See RFC 3264 Section 6.1.
    case RtpTransceiverDirection::kSendRecv:
    case RtpTransceiverDirection::kStopped:
    case RtpTransceiverDirection::kInactive:
      return GetAudioCodecsForOffer(RtpTransceiverDirectionReversed(offer));
    case RtpTransceiverDirection::kSendOnly:
      return audio_send_codecs_.codecs();
    case RtpTransceiverDirection::kRecvOnly:
      return audio_recv_codecs_.codecs();
  }
  RTC_CHECK_NOTREACHED();
}

CodecList CodecVendor::audio_sendrecv_codecs() const {
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  // Use NegotiateCodecs to merge our codec lists, since the operation is
  // essentially the same. Put send_codecs as the offered_codecs, which is the
  // order we'd like to follow. The reasoning is that encoding is usually more
  // expensive than decoding, and prioritizing a codec in the send list probably
  // means it's a codec we can handle efficiently.
  CodecList audio_sendrecv_codecs;
  auto error =
      NegotiateCodecs(audio_recv_codecs_.codecs(), audio_send_codecs_.codecs(),
                      audio_sendrecv_codecs, true);
  RTC_DCHECK(error.ok());
  return audio_sendrecv_codecs;
}

CodecList CodecVendor::video_sendrecv_codecs() const {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  // Use NegotiateCodecs to merge our codec lists, since the operation is
  // essentially the same. Put send_codecs as the offered_codecs, which is the
  // order we'd like to follow. The reasoning is that encoding is usually more
  // expensive than decoding, and prioritizing a codec in the send list probably
  // means it's a codec we can handle efficiently.
  // Also for the same profile of a codec, if there are different levels in the
  // send and receive codecs, |video_sendrecv_codecs| will contain the lower
  // level of the two for that profile.
  CodecList video_sendrecv_codecs;
  auto error =
      NegotiateCodecs(video_recv_codecs_.codecs(), video_send_codecs_.codecs(),
                      video_sendrecv_codecs, true);
  RTC_DCHECK(error.ok());
  return video_sendrecv_codecs;
}

void CodecVendor::ModifyVideoCodecs(
    const std::vector<std::pair<Codec, Codec>>& changes) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  RTC_DCHECK_DISALLOW_THREAD_BLOCKING_CALLS();
  // For each codec in the first element that occurs in our supported codecs,
  // replace it with the codec in the second element. Exact matches only.
  // Note: This needs further work to work with PT late assignment.
  for (const std::pair<Codec, Codec>& change : changes) {
    {
      CodecList send_codecs = video_send_codecs_.codecs();
      bool changed = false;
      for (Codec& codec : send_codecs.writable_codecs()) {
        if (codec == change.first) {
          codec = change.second;
          changed = true;
        }
      }
      if (changed) {
        video_send_codecs_ = TypedCodecVendor(std::move(send_codecs));
      }
    }
    {
      bool changed = false;
      CodecList recv_codecs = video_recv_codecs_.codecs();
      for (Codec& codec : recv_codecs.writable_codecs()) {
        if (codec == change.first) {
          codec = change.second;
          changed = true;
        }
      }
      if (changed) {
        video_recv_codecs_ = TypedCodecVendor(recv_codecs);
      }
    }
  }
}

}  // namespace webrtc