struct CryptomatteManifestReader {
  static constexpr int skip_whitespaces_len_(blender::StringRef ref)
  {
    int skip_len = 0;
    while (skip_len < ref.size()) {
      char front = ref[skip_len];
      if (!std::isspace<char>(front, std::locale::classic())) {
        break;
      }
      skip_len++;
    }
    return skip_len;
  }

  static constexpr blender::StringRef skip_whitespaces_(blender::StringRef ref)
  {
    return ref.drop_prefix(skip_whitespaces_len_(ref));
  }

  static constexpr int quoted_string_len_(blender::StringRef ref)
  {
    int len = 1;
    bool skip_next = false;
    while (len < ref.size()) {
      char current_char = ref[len];
      if (skip_next) {
        skip_next = false;
      }
      else {
        if (current_char == '\\') {
          skip_next = true;
        }
        if (current_char == '\"') {
          len += 1;
          break;
        }
      }
      len += 1;
    }
    return len;
  }

  static std::string unquote_(const blender::StringRef ref)
  {
    std::ostringstream stream;
    for (char c : ref) {
      if (c != '\\') {
        stream << c;
      }
    }
    return stream.str();
  }

  static uint32_t decode_hash_(const blender::StringRef ref)
  {
    uint32_t result;
    std::istringstream(ref) >> std::hex >> result;
    return result;
  }

  static bool parse(CryptomatteLayer &layer, blender::StringRefNull manifest)
  {
    StringRef ref = manifest;
    ref = skip_whitespaces_(ref);
    if (ref.is_empty() || ref.front() != '{') {
      return false;
    }
    ref = ref.drop_prefix(1);
    while (!ref.is_empty()) {
      char front = ref.front();

      if (front == '\"') {
        const int quoted_name_len = quoted_string_len_(ref);
        const int name_len = quoted_name_len - 2;
        std::string name = unquote_(ref.substr(1, name_len));
        ref = ref.drop_prefix(quoted_name_len);
        ref = skip_whitespaces_(ref);

        char colon = ref.front();
        if (colon != ':') {
          return false;
        }
        ref = ref.drop_prefix(1);
        ref = skip_whitespaces_(ref);

        if (ref.front() != '\"') {
          return false;
        }

        const int quoted_hash_len = quoted_string_len_(ref);
        const int hash_len = quoted_hash_len - 2;
        uint32_t hash = decode_hash_(ref.substr(1, hash_len));
        ref = ref.drop_prefix(quoted_hash_len);
        layer.add_hash(name, hash);
      }
      else if (front == ',') {
        ref = ref.drop_prefix(1);
      }
      else if (front == '}') {
        ref = ref.drop_prefix(1);
        ref = skip_whitespaces_(ref);
        break;
      }
      ref = skip_whitespaces_(ref);
    }

    if (!ref.is_empty()) {
      return false;
    }

    return true;
  }
};