/*
* Copyright 2013 - 2014 Felix Müller
*
* This file is part of CodeQ Invest.
*
* CodeQ Invest 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.
*
* CodeQ Invest 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 CodeQ Invest. If not, see <http://www.gnu.org/licenses/>.
*/
package org.codeqinvest.codechanges;
import com.google.common.collect.Sets;
import org.codeqinvest.codechanges.scm.DailyCodeChurn;
import org.codeqinvest.codechanges.scm.factory.CodeChurnCalculatorFactory;
import org.joda.time.Days;
import org.joda.time.LocalDate;
import java.util.Collection;
import java.util.Comparator;
import java.util.SortedSet;
/**
* This {@code CodeChangeProbabilityCalculator} implementation uses
* historical scm data to calculate the probability. Exactly as
* {@code DefaultCodeChangeProbabilityCalculator}, it loads the past commit
* data for the last X days. But each code change from the past
* is weighted by an exponential formula.
*
* @author fmueller
*/
public class WeightedCodeChangeProbabilityCalculator extends AbstractCodeChangeProbabilityCalculator {
public WeightedCodeChangeProbabilityCalculator(CodeChurnCalculatorFactory codeChurnCalculatorFactory, LocalDate startDay, int days) {
super(codeChurnCalculatorFactory, startDay, days);
}
/**
* {@inheritDoc}
*/
@Override
protected double computeChangeProbability(int days, Collection<DailyCodeChurn> codeChurns) {
if (codeChurns.isEmpty()) {
return 0.0;
}
final double numberOfDays = days + 1;
final SortedSet<DailyCodeChurn> sortedCodeChurns = sortDescendingByDay(codeChurns);
final LocalDate startDay = sortedCodeChurns.first().getDay();
double changeProbability = 0.0;
for (DailyCodeChurn codeChurn : sortedCodeChurns) {
final int numberOfCurrentDay = Days.daysBetween(codeChurn.getDay(), startDay).getDays();
for (double churnProportion : codeChurn.getCodeChurnProportions()) {
final double weight = ((numberOfDays - numberOfCurrentDay) * Math.exp((days - numberOfCurrentDay) / numberOfDays)) / (numberOfDays * numberOfDays);
changeProbability += churnProportion * weight;
}
}
return changeProbability;
}
private SortedSet<DailyCodeChurn> sortDescendingByDay(Collection<DailyCodeChurn> codeChurns) {
SortedSet<DailyCodeChurn> sortedCodeChurn = Sets.newTreeSet(new Comparator<DailyCodeChurn>() {
@Override
public int compare(DailyCodeChurn codeChurn, DailyCodeChurn otherCodeChurn) {
return -1 * codeChurn.getDay().compareTo(otherCodeChurn.getDay());
}
});
sortedCodeChurn.addAll(codeChurns);
return sortedCodeChurn;
}
}