//+------------------------------------------------------------------+
//|                              OHLC_Append_Script.mq5               |
//| Read existing CSV, copy only NEW bars, append without rewrite     |
//+------------------------------------------------------------------+
#property strict
#property script_show_inputs

input string FileName = "XAUUSDm_PERIOD_M30_OHLC.csv"; // existing CSV

void OnStart()
  {
   string sym = _Symbol;
   ENUM_TIMEFRAMES tf = _Period;
   int digits = (int)SymbolInfoInteger(sym, SYMBOL_DIGITS);

   int totalBars = Bars(sym, tf);
   if(totalBars <= 0) { Print("No bars for ", sym); return; }

   // --- 1. Count existing data rows in CSV ---
   int existingRows = 0;
   int h = FileOpen(FileName, FILE_READ|FILE_CSV|FILE_ANSI, ',');
   if(h == INVALID_HANDLE)
     {
      // File doesn't exist yet — do full export
      FileClose(h);
      FullExport(sym, tf, digits, 0, totalBars);
      return;
     }

   // Count lines (skip header)
   while(!FileIsEnding(h))
     {
      string line = FileReadString(h);
      if(line != "Timestamp" && StringLen(line) > 10) existingRows++;
     }
   FileClose(h);

   // --- 2. If no new bars, exit ---
   int newBars = totalBars - existingRows;
   if(newBars <= 0)
     {
      PrintFormat("CSV is up to date. %d bars total, %d in file. Nothing to append.", totalBars, existingRows);
      return;
     }

   PrintFormat("Existing: %d rows | Total MT5 bars: %d | New: %d bars", existingRows, totalBars, newBars);

   // --- 3. Copy only new bars ---
   MqlRates r[];
   ArraySetAsSeries(r, true);
   int copied = CopyRates(sym, tf, 0, newBars, r);
   if(copied <= 0) { Print("CopyRates failed"); return; }

   // --- 4. Append to CSV (open for appending) ---
   int hOut = FileOpen(FileName, FILE_WRITE|FILE_READ|FILE_CSV|FILE_ANSI, ',');
   if(hOut == INVALID_HANDLE) { Print("Cannot open for append"); return; }

   // Seek to end of file
   FileSeek(hOut, 0, SEEK_END);

   // Write new bars in chronological order (oldest first)
   for(int i = copied - 1; i >= 0; i--)
     {
      FileWrite(hOut,
                TimeToString(r[i].time, TIME_DATE|TIME_MINUTES|TIME_SECONDS),
                DoubleToString(r[i].open,  digits),
                DoubleToString(r[i].high,  digits),
                DoubleToString(r[i].low,   digits),
                DoubleToString(r[i].close, digits),
                (long)r[i].tick_volume,
                (int)r[i].spread);
     }
   FileClose(hOut);
   PrintFormat("[OK] Appended %d new bars to %s", copied, FileName);
  }

void FullExport(string sym, ENUM_TIMEFRAMES tf, int digits, int start, int count)
  {
   MqlRates r[]; ArraySetAsSeries(r, true);
   int copied = CopyRates(sym, tf, start, count, r);
   if(copied <= 0) { Print("CopyRates failed"); return; }

   int h = FileOpen(FileName, FILE_WRITE|FILE_CSV|FILE_ANSI, ',');
   if(h == INVALID_HANDLE) { Print("Cannot create file"); return; }
   FileWrite(h, "Timestamp", "Open", "High", "Low", "Close", "TickVolume", "Spread");
   for(int i = copied - 1; i >= 0; i--)
     {
      FileWrite(h, TimeToString(r[i].time, TIME_DATE|TIME_MINUTES|TIME_SECONDS),
                DoubleToString(r[i].open,digits), DoubleToString(r[i].high,digits),
                DoubleToString(r[i].low,digits),  DoubleToString(r[i].close,digits),
                (long)r[i].tick_volume, (int)r[i].spread);
     }
   FileClose(h);
   PrintFormat("[OK] Created %s with %d bars", FileName, copied);
  }
//+------------------------------------------------------------------+