/* Copyright (C) 2011, 2012, 2013 by Bundesanstalt für Gewässerkunde
 * Software engineering by Intevation GmbH
 *
 * This file is Free Software under the GNU AGPL (>=v3)
 * and comes with ABSOLUTELY NO WARRANTY! Check out the
 * documentation coming with Dive4Elements River for details.
 */

package org.dive4elements.river.artifacts.math;

import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

public class MovingAverage {

    public static double[][] simple(final double[][] values, final double radius) {
        final TreeMap<Double, Double> map = toMap(values);
        final int N = map.size();
        final double[] xs = new double[N];
        final double[] ys = new double[N];
        int ndx = 0;
        for (final double x : map.keySet()) {
            final SortedMap<Double, Double> range = map.subMap(x - radius, true, x + radius, true);
            double avg = 0d;
            for (final double v : range.values()) {
                avg += v;
            }
            avg /= range.size();
            xs[ndx] = x;
            ys[ndx] = avg;
            ndx++;
        }
        return new double[][] { xs, ys };
    }

    /** Build moving average over values. Weight them. */
    public static double[][] weighted(final double[][] values, final double radius) {
        final TreeMap<Double, Double> map = toMap(values);
        final int N = map.size();
        final double[] xs = new double[N];
        final double[] ys = new double[N];
        int ndx = 0;
        final double _1radius = 1d / radius;
        for (final double x : map.keySet()) {
            double avg = 0d;
            double weights = 0d;
            for (final Map.Entry<Double, Double> e : map.subMap(x - radius, false, x + radius, false).entrySet()) {
                final Double value = e.getValue();

                if (!value.isNaN()) {
                    final double weight = 1d - Math.abs(x - e.getKey()) * _1radius;
                    weights += weight;
                    avg += weight * value;
                }
            }

            avg /= weights;
            xs[ndx] = x;
            ys[ndx] = Double.isNaN(map.get(x)) ? Double.NaN : avg;
            ndx++;
        }
        return new double[][] { xs, ys };
    }

    /** From [x1,x2][y1,y2] makes {x1:y1,x2:y2}. Sorted by x! */
    private static TreeMap<Double, Double> toMap(final double[][] values) {
        final TreeMap<Double, Double> map = new TreeMap<>();
        final double[] xs = values[0];
        final double[] ys = values[1];
        for (int i = 0; i < xs.length; i++) {
            map.put(xs[i], ys[i]);
        }
        return map;
    }
}
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