/*
 * This file is part of spark.
 *
 *  Copyright (c) lucko (Luck) <luck@lucko.me>
 *  Copyright (c) contributors
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package me.lucko.spark.common.util;

import me.lucko.spark.api.statistic.misc.DoubleAverageInfo;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Queue;

public class RollingAverage implements DoubleAverageInfo {

    private final Queue<BigDecimal> samples;
    private final int windowSize;
    private BigDecimal total = BigDecimal.ZERO;

    public RollingAverage(int windowSize) {
        this.windowSize = windowSize;
        this.samples = new ArrayDeque<>(this.windowSize + 1);
    }

    public int getSamples() {
        synchronized (this) {
            return this.samples.size();
        }
    }

    public void add(BigDecimal num) {
        synchronized (this) {
            this.total = this.total.add(num);
            this.samples.add(num);
            if (this.samples.size() > this.windowSize) {
                this.total = this.total.subtract(this.samples.remove());
            }
        }
    }

    @Override
    public double mean() {
        synchronized (this) {
            if (this.samples.isEmpty()) {
                return 0;
            }
            BigDecimal divisor = BigDecimal.valueOf(this.samples.size());
            return this.total.divide(divisor, 30, RoundingMode.HALF_UP).doubleValue();
        }
    }

    @Override
    public double max() {
        synchronized (this) {
            BigDecimal max = null;
            for (BigDecimal sample : this.samples) {
                if (max == null || sample.compareTo(max) > 0) {
                    max = sample;
                }
            }
            return max == null ? 0 : max.doubleValue();
        }
    }

    @Override
    public double min() {
        synchronized (this) {
            BigDecimal min = null;
            for (BigDecimal sample : this.samples) {
                if (min == null || sample.compareTo(min) < 0) {
                    min = sample;
                }
            }
            return min == null ? 0 : min.doubleValue();
        }
    }

    @Override
    public double percentile(double percentile) {
        if (percentile < 0 || percentile > 1) {
            throw new IllegalArgumentException("Invalid percentile " + percentile);
        }

        BigDecimal[] sortedSamples;
        synchronized (this) {
            if (this.samples.isEmpty()) {
                return 0;
            }
            sortedSamples = this.samples.toArray(new BigDecimal[0]);
        }
        Arrays.sort(sortedSamples);

        int rank = (int) Math.ceil(percentile * (sortedSamples.length - 1));
        return sortedSamples[rank].doubleValue();
    }

}