srecord noeq FollowTickerFile(File tickerFile) is AutoCloseable {
  settable int historyEntriesToGrab;
  settable int interval = 250;

  // internal, may change  
  TailFile tailFile;
  
  event historicLine(S line);
  event liveLine(S line);
  
  gettable volatile long liveTimestamp;
  gettable volatile S lastLiveLine;
  
  settable int maxLineLengthForTickerEntry = 200;
  
  bool started() { ret tailFile != null; }
  bool isLive() { ret liveTimestamp != 0; }

  void start {
    if (started()) ret;
    
    onLiveLine(line -> {
      lastLiveLine = line;
      liveTimestamp = now();
    });
    
    long fileSize = l(tickerFile);
    long start = max(0, fileSize-maxLineLengthForTickerEntry*historyEntriesToGrab);
    if (historyEntriesToGrab > 0) {
      S text = loadTextFilePart(tickerFile, start, fileSize);
      LS lastTickerLines = takeLast(historyEntriesToGrab, lines(text));

      for (line : lastTickerLines)
        historicLine(line);
    }
  
    makeTailFile(fileSize);
  }
  
  void makeTailFile {
    tailFile = tailFileLinewiseFromPosition(tickerFile, interval, fileSize, l1 liveLine);
  }
  
  close {
    dispose tailFile;
  }
  
  selfType onLine(IVF1<S> l) {
    onHistoricLine(l);
    ret onLiveLine(l);
  }
  
  toString {
    ret commaCombine(
      "FollowTickerFile",
      stringIf(started(), "started"),
      !isLive() ? null : "Last live line at " + formatLocalDateWithSeconds(liveTimestamp),
      tickerFile
    );
  }
}