Update daily_file_sink.h

Relocate daily_filename_calculator

include/spdlog/sinks/daily_file_sink.h

@@ -19,27 +19,10 @@
 namespace spdlog {
 namespace sinks {
 
-/*
- * Generator of daily log file names in format basename.YYYY-MM-DD.ext
- */
-struct daily_filename_calculator
-{
-    // Create filename for the form basename.YYYY-MM-DD
-    static filename_t calc_filename(const filename_t &filename, const tm &now_tm)
-    {
-        filename_t basename, ext;
-        std::tie(basename, ext) = details::file_helper::split_by_extenstion(filename);
-        std::conditional<std::is_same<filename_t::value_type, char>::value, fmt::memory_buffer, fmt::wmemory_buffer>::type w;
-        fmt::format_to(
-            w, SPDLOG_FILENAME_T("{}_{:04d}-{:02d}-{:02d}{}"), basename, now_tm.tm_year + 1900, now_tm.tm_mon + 1, now_tm.tm_mday, ext);
-        return fmt::to_string(w);
-    }
-};
-
 /*
  * Rotating file sink based on date. rotates at midnight
  */
-template<typename Mutex, typename FileNameCalc = daily_filename_calculator>
+template<typename Mutex, typename FileNameCalc = details::filename_calculator>
 class daily_file_sink final : public base_sink<Mutex>
 {
 public: