From 76011f6940144385b792039fdb9036711608cc7f Mon Sep 17 00:00:00 2001
From: Robert von Burg <eitch@eitchnet.ch>
Date: Fri, 2 Oct 2020 15:21:34 +0200
Subject: [PATCH] [Fix] Properly handle month periods in PeriodHelper

---
 .../li/strolch/utils/time/PeriodHelper.java   | 24 +++++++++++++++++++
 .../strolch/utils/time/PeriodHelperTest.java  | 23 ++++++++++++++++--
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/li.strolch.utils/src/main/java/li/strolch/utils/time/PeriodHelper.java b/li.strolch.utils/src/main/java/li/strolch/utils/time/PeriodHelper.java
index f58b9c5bf..e1e0446a2 100644
--- a/li.strolch.utils/src/main/java/li/strolch/utils/time/PeriodHelper.java
+++ b/li.strolch.utils/src/main/java/li/strolch/utils/time/PeriodHelper.java
@@ -9,6 +9,13 @@ import li.strolch.utils.dbc.DBC;
 
 public class PeriodHelper {
 
+	public static double monthsIn(PeriodDuration periodDuration) {
+		long hours = periodDuration.getDuration().toHours();
+		Period period = periodDuration.getPeriod();
+		long months = period.toTotalMonths();
+		return (months + (period.getDays() / 30.0) + (hours / 24.0 / 30.0));
+	}
+
 	public static double daysIn(PeriodDuration periodDuration) {
 		return (daysIn(periodDuration.getPeriod()) + (periodDuration.getDuration().toHours() / 24.0));
 	}
@@ -17,6 +24,10 @@ public class PeriodHelper {
 		return (period.getYears() * 365.0) + (period.getMonths() * 30.0) + period.getDays();
 	}
 
+	private static double monthsIn(Period period) {
+		return (period.getYears() * 12.0) + (period.getMonths());
+	}
+
 	/**
 	 * This special function allows us to shift a date by a multiple of the given {@link PeriodDuration} so that is
 	 * before the given to date. It does multiple tries to get as close as possible, due to the inexactness of 30 days
@@ -35,7 +46,20 @@ public class PeriodHelper {
 			PeriodDuration periodDuration) {
 		DBC.PRE.assertTrue("date must be before to!", date.isBefore(to));
 		DBC.PRE.assertFalse("period duration may not be null!", periodDuration.isZero());
+
+		// see if we need to shift by months
+		long monthsInPeriod = (long) monthsIn(periodDuration);
+		if (monthsInPeriod > 0) {
+			Period between = between(date.toLocalDate(), to.toLocalDate());
+			double monthsInBetween = monthsIn(between);
+			long shifts = (long) (monthsInBetween / monthsInPeriod);
+			if (shifts > 0) {
+				date = date.plusMonths(shifts);
+			}
+		}
+
 		Period between = between(date.toLocalDate(), to.toLocalDate());
+
 		double daysInBetween = daysIn(between);
 		double daysInPeriod = daysIn(periodDuration);
 		long shifts = (long) (daysInBetween / daysInPeriod);
diff --git a/li.strolch.utils/src/test/java/li/strolch/utils/time/PeriodHelperTest.java b/li.strolch.utils/src/test/java/li/strolch/utils/time/PeriodHelperTest.java
index 55c5676a1..7acfa4946 100644
--- a/li.strolch.utils/src/test/java/li/strolch/utils/time/PeriodHelperTest.java
+++ b/li.strolch.utils/src/test/java/li/strolch/utils/time/PeriodHelperTest.java
@@ -7,7 +7,6 @@ import static org.junit.Assert.assertTrue;
 
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
-import java.time.temporal.ChronoUnit;
 
 import org.junit.Test;
 
@@ -68,6 +67,26 @@ public class PeriodHelperTest {
 		assertEquals(30, daysIn(PeriodDuration.parse("P1M")), 0.0);
 	}
 
+	@Test
+	public void shouldCalcMonths1() {
+		assertEquals(1, monthsIn(PeriodDuration.parse("P1M")), 0.0);
+	}
+
+	@Test
+	public void shouldCalcMonths2() {
+		assertEquals(1, monthsIn(PeriodDuration.parse("P30D")), 0.0);
+	}
+
+	@Test
+	public void shouldCalcMonths3() {
+		assertEquals(2, monthsIn(PeriodDuration.parse("P60D")), 0.0);
+	}
+
+	@Test
+	public void shouldCalcMonths4() {
+		assertEquals(12, monthsIn(PeriodDuration.parse("P1Y")), 0.0);
+	}
+
 	@Test
 	public void shouldCalcShiftDays1() {
 		ZonedDateTime past = ZonedDateTime.now().minusDays(35);
@@ -83,7 +102,7 @@ public class PeriodHelperTest {
 	public void shouldCalcShiftDays2() {
 		ZonedDateTime past = ZonedDateTime
 				.parse("2007-12-03T10:15:30+01:00", DateTimeFormatter.ISO_OFFSET_DATE_TIME.withZone(systemDefault()));
-		ZonedDateTime now = ZonedDateTime.now().truncatedTo(ChronoUnit.DAYS);
+		ZonedDateTime now = ZonedDateTime.now();
 		PeriodDuration periodDuration = PeriodDuration.parse("P1M");
 		ZonedDateTime shiftedDate = shiftByMultipleOfPeriod(past, now, periodDuration);