package patternmatching;

import java.util.Arrays;
import java.util.stream.Collectors;

public final class Statistics {

    private final long[] data;
    private Double mean = null;
    private Double variance = null;

    private Statistics(long[] data) {
        this.data = data;
    }

    private double getMean() {
        if (mean == null) {
            mean = (double) Arrays.stream(data).sum() / data.length;
        }

        return mean;
    }

    private double getVariance() {
        if (variance == null) {
            final double mean = getMean();
            double temp = 0;
            for(double a : data) {
                temp += (a-mean)*(a-mean);
            }
            variance = temp/(data.length-1);
        }

        return variance;
    }

    private double getStddev() {
        return Math.sqrt(getVariance());
    }

    private double getMedian() {
        Arrays.sort(data);
        if (data.length % 2 == 0) return (data[(data.length / 2) - 1] + data[data.length / 2]) / 2.0;
        return data[data.length / 2];
    }

    static Statistics from(long[] data) {
        return new Statistics(data);
    }

    @Override
    public String toString() {
        return String.format(
                "mean=%.2fms stddev=%.2fms median=%.2fms",
                getMean()/1000,
                getStddev()/1000,
                getMedian()/1000
        );
    }

    String asCSv() {
        return Arrays.stream(data)
                .mapToObj(String::valueOf)
                .collect(Collectors.joining(","));
    }
}