code: #include "pch.h"
  #include "FileWatcher.h"
  
  std::optional<FILETIME> FileWatcher::MyFileTime()
  {
      HANDLE hFile = CreateFileW(m_path.c_str(), FILE_READ_ATTRIBUTES, FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, 0, nullptr);
      std::optional<FILETIME> result;
      if (hFile != INVALID_HANDLE_VALUE)
      {
          FILETIME lastWrite;
          if (GetFileTime(hFile, nullptr, nullptr, &lastWrite))
          {
              result = lastWrite;
          }
  
          CloseHandle(hFile);
      }
  
      return result;
  }
  
  void FileWatcher::Run()
  {
      while (1)
      {
          auto lastWrite = MyFileTime();
          if (!m_lastWrite.has_value())
          {
              m_lastWrite = lastWrite;
          }
          else if (lastWrite.has_value())
          {
              if (m_lastWrite->dwHighDateTime != lastWrite->dwHighDateTime ||
                  m_lastWrite->dwLowDateTime != lastWrite->dwLowDateTime)
              {
                  m_lastWrite = lastWrite;
                  m_callback();
              }
          }
  
          if (WaitForSingleObject(m_abortEvent, m_refreshPeriod) == WAIT_OBJECT_0)
          {
              return;
          }
      }
  }
  
  FileWatcher::FileWatcher(const std::wstring& path, std::function<void()> callback, DWORD refreshPeriod) :
      m_refreshPeriod(refreshPeriod),
      m_path(path),
      m_callback(callback)
  {
      m_abortEvent = CreateEventW(nullptr, TRUE, FALSE, nullptr);
      if (m_abortEvent)
      {
          m_thread = std::thread([this]() { Run(); });
      }
  }
  
  FileWatcher::~FileWatcher()
  {
      if (m_abortEvent)
      {
          SetEvent(m_abortEvent);
          m_thread.join();
          CloseHandle(m_abortEvent);
      }
  }
  