@Override
    public int compare(MetricData leftMetricData, MetricData rightMetricData) {
      Date leftMetricDataTimestamp = new Date(leftMetricData.getTimestamp());
      Date rightMetricDataTimestamp = new Date(rightMetricData.getTimestamp());

      return leftMetricDataTimestamp.compareTo(rightMetricDataTimestamp);
    }
  private List<Column> getChartColumns() {
    List<Column> chartColumns = new ArrayList<>(metricData.size());

    for (MetricData metricData : this.metricData) {
      MetricAvailability metricAvailability = MetricAvailability.from(metricData.getValue());

      float columnValue = getColumnValue(metricAvailability);
      int columnColor = getColumnColor(metricAvailability);

      chartColumns.add(
          new Column(Collections.singletonList(new SubcolumnValue(columnValue, columnColor))));
    }

    return chartColumns;
  }