: filename_(config.filename()),

      watcher_(context.mainThreadDispatcher().createFilesystemWatcher()), api_(context.api()) {

  THROW_IF_NOT_OK(

      watcher_->addWatch(filename_, Filesystem::Watcher::Events::MovedTo, [this](uint32_t) {

        onFileChanged();

        return absl::OkStatus();

      }));

}

void InjectedResourceMonitor::onFileChanged() { file_changed_ = true; }

void InjectedResourceMonitor::updateResourceUsage(Server::ResourceUpdateCallbacks& callbacks) {

  if (file_changed_) {

    file_changed_ = false;

    TRY_ASSERT_MAIN_THREAD {

      auto file_or_error = api_.fileSystem().fileReadToEnd(filename_);

      THROW_IF_NOT_OK_REF(file_or_error.status());

      const std::string contents = file_or_error.value();

      double pressure;

      if (absl::SimpleAtod(contents, &pressure)) {

        if (pressure < 0 || pressure > 1) {

          throw EnvoyException("pressure out of range");

        }

        pressure_ = pressure;

        error_.reset();

      } else {

        throw EnvoyException("failed to parse injected resource pressure");

      }

    }

    END_TRY

    catch (const EnvoyException& error) {

      error_ = error;

      pressure_.reset();

    }

  }

  ASSERT(pressure_.has_value() != error_.has_value());

  if (pressure_.has_value()) {

    callbacks.onSuccess({*pressure_});

  } else {

    callbacks.onFailure(*error_);

  }

}