*
 * @author Pete Gillin
 * @author Kevin Bourrillion
 * @since 20.0
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public final class StatsAccumulator {

  // These fields must satisfy the requirements of Stats' constructor as well as those of the stat
  // methods of this class.
  private long count = 0;

  private StatsAccumulator emptyAccumulator;
  private StatsAccumulator emptyAccumulatorByAddAllEmptyIterable;
  private StatsAccumulator emptyAccumulatorByAddAllEmptyStats;
  private StatsAccumulator oneValueAccumulator;
  private StatsAccumulator oneValueAccumulatorByAddAllEmptyStats;
  private StatsAccumulator twoValuesAccumulator;
  private StatsAccumulator twoValuesAccumulatorByAddAllStats;

    StatsAccumulator accumulator = new StatsAccumulator();
    accumulator.addAll(values);
    return accumulator.snapshot();
  }

  /**
   * Returns statistics over a dataset containing the given values.
   *
   * @param values a series of values
   */
  public static Stats of(double... values) {
    StatsAccumulator accumulator = new StatsAccumulator();

  private StatsAccumulator emptyAccumulator;
  private StatsAccumulator emptyAccumulatorByAddAllEmptyIterable;
  private StatsAccumulator emptyAccumulatorByAddAllEmptyStats;
  private StatsAccumulator oneValueAccumulator;
  private StatsAccumulator oneValueAccumulatorByAddAllEmptyStats;
  private StatsAccumulator twoValuesAccumulator;
  private StatsAccumulator twoValuesAccumulatorByAddAllStats;

  // These fields must satisfy the requirements of PairedStats' constructor as well as those of the
  // stat methods of this class.
  private final StatsAccumulator xStats = new StatsAccumulator();
  private final StatsAccumulator yStats = new StatsAccumulator();
  private double sumOfProductsOfDeltas = 0.0;

  /** Adds the given pair of values to the dataset. */
  public void add(double x, double y) {

    StatsAccumulator accumulator = new StatsAccumulator();
    accumulator.addAll(MANY_VALUES);
    Stats stats = accumulator.snapshot();
    accumulator.add(999.999); // should do nothing to the snapshot
    return stats;
  }

  private static Stats buildLongManyValuesStatsSnapshot() {
    StatsAccumulator accumulator = new StatsAccumulator();
    accumulator.addAll(LONG_MANY_VALUES);

    StatsAccumulator accumulator = new StatsAccumulator();
    accumulator.addAll(MANY_VALUES);
    Stats stats = accumulator.snapshot();
    accumulator.add(999.999); // should do nothing to the snapshot
    return stats;
  }

  private static Stats buildLongManyValuesStatsSnapshot() {
    StatsAccumulator accumulator = new StatsAccumulator();
    accumulator.addAll(LONG_MANY_VALUES);

    // For datasets of many double values created from an accumulator snapshot, we test many
    // combinations of finite and non-finite values:
    for (ManyValues values : ALL_MANY_VALUES) {
      StatsAccumulator accumulator = new StatsAccumulator();
      accumulator.addAll(values.asIterable());
      double min = accumulator.snapshot().min();
      if (values.hasAnyNaN()) {
        assertWithMessage("min of " + values).that(min).isNaN();

    // For datasets of many double values created from an accumulator snapshot, we test many
    // combinations of finite and non-finite values:
    for (ManyValues values : ALL_MANY_VALUES) {
      StatsAccumulator accumulator = new StatsAccumulator();
      accumulator.addAll(values.asIterable());
      double min = accumulator.snapshot().min();
      if (values.hasAnyNaN()) {
        assertWithMessage("min of " + values).that(min).isNaN();