GetAcidizerTags.cpp

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/*  SPDX-License-Identifier: GPL-2.0-or-later */
/*!********************************************************************
 
  Audacity: A Digital Audio Editor
 
  GetAcidizerTags.cpp
 
  Matthieu Hodgkinson
 
**********************************************************************/
#include "GetAcidizerTags.h"
#include "AcidizerTags.h"
 
#include <algorithm>
#include <array>
#include <cstring> // memset
#include <memory>
 
namespace LibImportExport
{
std::optional<LibFileFormats::AcidizerTags> GetAcidizerTags(
   SNDFILE& file, const std::vector<std::string>& trustedDistributors)
{
   SF_LOOP_INFO loopInfo;
   if (
      sf_command(&file, SFC_GET_LOOP_INFO, &loopInfo, sizeof(loopInfo)) ==
      SF_FALSE)
      return {};
 
   if (
      loopInfo.loop_mode == SF_LOOP_BACKWARD ||
      loopInfo.loop_mode == SF_LOOP_ALTERNATING)
      // Don't know what that is:
      return {};
 
   if (loopInfo.loop_mode == SF_LOOP_NONE)
      return LibFileFormats::AcidizerTags::OneShot {};
 
   if (loopInfo.num_beats != 0)
   {
      // Forward loop with number of beats set: all files like these I have seen
      // so far were correctly tagged.
      SF_INFO info;
      std::memset(&info, 0, sizeof(info));
      sf_command(&file, SFC_GET_CURRENT_SF_INFO, &info, sizeof(info));
      if (info.samplerate == 0 || info.frames == 0)
         return {};
      const auto duration = 1. * info.frames / info.samplerate;
      return LibFileFormats::AcidizerTags::Loop { 60. * loopInfo.num_beats /
                                                  duration };
   }
 
   // There is loop info, but in some unexpected combination. We don't trust it
   // unless it is from a trusted distributor.
   SF_CHUNK_INFO info;
   constexpr std::array<char, 4> listId = { 'L', 'I', 'S', 'T' };
   std::copy(listId.begin(), listId.end(), info.id);
   std::fill(info.id + sizeof(listId), info.id + sizeof(info.id), '\0');
   info.id_size = sizeof(listId);
   auto chunkIt = sf_get_chunk_iterator(&file, &info);
   while (chunkIt)
   {
      if (sf_get_chunk_size(chunkIt, &info) != SF_ERR_NO_ERROR)
         break;
      constexpr std::array<char, 4> INFO = { 'I', 'N', 'F', 'O' };
      constexpr std::array<char, 4> IDST = { 'I', 'D', 'S', 'T' };
      // Another 4 bytes after INFO and IDST that indicates the size of the data
      constexpr auto dataPos = sizeof(INFO) + sizeof(IDST) + 4;
      if (info.datalen < dataPos)
         // Not the expected data
         continue;
      const auto chars = std::make_unique<char[]>(info.datalen);
      info.data = chars.get();
      if (sf_get_chunk_data(chunkIt, &info) != SF_ERR_NO_ERROR)
         break;
      chunkIt = sf_next_chunk_iterator(chunkIt);
 
      auto pos = 0;
      const auto firstFour =
         std::string { chars.get() + pos, chars.get() + pos + sizeof(INFO) };
      if (firstFour != std::string { INFO.data(), INFO.size() })
         continue;
 
      pos += sizeof(INFO);
      const auto nextFour =
         std::string { chars.get() + pos, chars.get() + pos + sizeof(IDST) };
      if (nextFour != std::string { IDST.data(), IDST.size() })
         continue;
 
      // Ignore trailing nulls, which could be the result of byte-padding for
      // word alignment:
      const auto charsEnd = std::find_if(
         chars.get() + dataPos, chars.get() + info.datalen,
         [](const char c) { return c == '\0'; });
      const auto distributor = std::string { chars.get() + 12, charsEnd };
      const auto isTrusted =
         std::find(
            trustedDistributors.begin(), trustedDistributors.end(),
            distributor) != trustedDistributors.end();
      if (isTrusted)
         // Later we may want to get the key, too, but for now we're only
         // interested in BPM.
         return LibFileFormats::AcidizerTags::Loop { loopInfo.bpm };
   }
 
   // No luck:
   return {};
}
} // namespace LibImportExport