From 70c7c82c5a73cb81bd65be4efb314252432de2c8 Mon Sep 17 00:00:00 2001
From: Markus Minichmayr <markus@minichmayr.net>
Date: Sat, 15 Feb 2025 16:03:16 +0100
Subject: [PATCH] Fix inverted limiting behavior of `BYMONTHDAY` (#730)

* Fix #728: wrong behavior of `BYMONTHDAY` limitting behaviour.

* Test: Add more test cases, i.e. covering BYYEARDAY, BYHOUR, BYMINUTE, BYSECOND limit behaviour.
---
 .../Calendars/Recurrence/RecurrenceTestCases.txt  | 15 +++++++++++++++
 Ical.Net/Evaluation/RecurrencePatternEvaluator.cs |  5 +++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Ical.Net.Tests/Calendars/Recurrence/RecurrenceTestCases.txt b/Ical.Net.Tests/Calendars/Recurrence/RecurrenceTestCases.txt
index 4b6c108c..d703b4e2 100644
--- a/Ical.Net.Tests/Calendars/Recurrence/RecurrenceTestCases.txt
+++ b/Ical.Net.Tests/Calendars/Recurrence/RecurrenceTestCases.txt
@@ -27,3 +27,18 @@ RRULE:FREQ=YEARLY;BYWEEKNO=1;BYDAY=MO,TU;INTERVAL=3;UNTIL=20320101
 DTSTART:20241231
 INSTANCES:20241231,20280103,20280104,20301230,20301231
 
+# BYMONTHDAY with limit behaviour; reproduces #728 as reported by pinkfloydx33
+RRULE:FREQ=DAILY;BYMONTHDAY=20,-2;UNTIL=20250401
+DTSTART:20250220
+INSTANCES:20250220,20250227,20250320,20250330
+
+# BYYEARDAY with limit behaviour; BYHOUR limit behaviour
+RRULE:FREQ=HOURLY;BYHOUR=0;BYYEARDAY=360,-2;UNTIL=20260101T000000
+DTSTART:20251220T000000
+INSTANCES:20251226T000000,20251230T000000
+
+# BYHOUR, BYMINUTE, BYSECOND limit behaviour
+# note that the max number of increments is 1000, so we can only observer a limited time span
+RRULE:FREQ=SECONDLY;BYHOUR=1,2;BYMINUTE=3,4,59;BYSECOND=5,6;UNTIL=20250216T020500
+DTSTART:20250216T015905
+INSTANCES:20250216T015905,20250216T015906,20250216T020305,20250216T020306,20250216T020405,20250216T020406
diff --git a/Ical.Net/Evaluation/RecurrencePatternEvaluator.cs b/Ical.Net/Evaluation/RecurrencePatternEvaluator.cs
index 39397d1c..d425f7bf 100644
--- a/Ical.Net/Evaluation/RecurrencePatternEvaluator.cs
+++ b/Ical.Net/Evaluation/RecurrencePatternEvaluator.cs
@@ -457,11 +457,12 @@ select monthDay > 0
             }
             return monthDayDates;
         }
+
         // Limit behavior
         for (var i = dates.Count - 1; i >= 0; i--)
         {
             var date = dates[i];
-            var keepDate = true;
+            var keepDate = false;
             for (var j = 0; j < pattern.ByMonthDay.Count; j++)
             {
                 var monthDay = pattern.ByMonthDay[j];
@@ -479,7 +480,7 @@ select monthDay > 0
 
                 if (newDate.Day.Equals(date.Day))
                 {
-                    keepDate = false;
+                    keepDate = true;
                     break;
                 }
             }