// Snippet 3: one day of work per step, driven by a timer (TF_Engine.mqh and Tick_Forge.mq5)
bool CTFEngine::Step(CTFResult &res)
  {
   if(Done()) { res.ok = true; return true; }
   if((int)(GetTickCount() - m_ready_at) < 0) return true;      // symbol still settling
   datetime day = m_job.from + (datetime)m_i * 86400;
   bool ok = (m_job.mode == TF_MODE_TICKS ? WriteTicksDay(day, res) : WriteBarsChunk(day, day + 86400 - 60, res));
   if(!ok) return false;
   if(m_bad > 0) { res.err = "function produced an invalid price"; return false; }
   TF_Status(StringFormat("%s  day %d/%d   ticks %I64d   M1 bars %I64d", TimeToString(day, TIME_DATE), m_i + 1, m_days, res.ticks, res.bars));
   m_i++;
   if(Done()) res.ok = true;
   return true;
  }


void OnTimer()
  {
   if(g_dlg == NULL) return;
   g_dlg.Tick();                       // one day / one month of work per call, so the window stays responsive
   if(g_dlg.Closed()) ExpertRemove();
  }