Refactor CalDateTime and DateTimeSerializer

CalDateTime
* to use DateOnly and TimeOnly types
* Added SetValue(DateOnly date, TimeOnly? time, DateTimeKind kind) to set the value of the date and time properly.
* Refactored `ToString` overloads to convert the date and time to a string representation.
* marked some properties as obsolete.
* Updated related tests and methods to accommodate these changes.
* Increase code coverage > 90%

DateTimeSerializer
* Added validation in the `SerializeToString` method to ensure the TZID parameter is correctly handled based on whether the date-time is in UTC.
* Improved the Deserialize method to handle both full date-time and date-only strings, initializing the DateOnly and TimeOnly parts accordingly.
* Increase code coverage > 90%

Added new package reference `Portable.System.DateTimeOnly` for netstandard2.0 and netstandard2.1 for compatibility with net6.0 and later.

Fixes ical-org#630

Ical.Net.Tests/AlarmTest.cs

@@ -1,4 +1,4 @@
-using Ical.Net.DataTypes;
+using Ical.Net.DataTypes;
 using NUnit.Framework;
 using System;
 using System.Collections.Generic;

Ical.Net.Tests/CalDateTimeTests.cs

@@ -1,18 +1,19 @@
-using System.Collections.Generic;
-using System.Globalization;
-using Ical.Net.CalendarComponents;
+using Ical.Net.CalendarComponents;
 using Ical.Net.DataTypes;
 using NUnit.Framework;
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Drawing;
+using System.Globalization;
 
 namespace Ical.Net.Tests
 {
     public class CalDateTimeTests
     {
         private static readonly DateTime _now = DateTime.Now;
         private static readonly DateTime _later = _now.AddHours(1);
+
         private static CalendarEvent GetEventWithRecurrenceRules(string tzId)
         {
             var dailyForFiveDays = new RecurrencePattern(FrequencyType.Daily, 1)
@@ -34,7 +35,7 @@ private static CalendarEvent GetEventWithRecurrenceRules(string tzId)
         public void ToTimeZoneTests(CalendarEvent calendarEvent, string targetTimeZone)
         {
             var startAsUtc = calendarEvent.Start.AsUtc;
-            
+
             var convertedStart = calendarEvent.Start.ToTimeZone(targetTimeZone);
             var convertedAsUtc = convertedStart.AsUtc;
 
@@ -91,13 +92,15 @@ public static IEnumerable AsDateTimeOffsetTestCases()
             var convertedToNySummer = new CalDateTime(summerDate, "UTC");
             convertedToNySummer.TzId = nyTzId;
             yield return new TestCaseData(convertedToNySummer)
-                .SetName("Summer UTC DateTime converted to NY time zone by setting TzId returns a DateTimeOffset with UTC-4")
+                .SetName(
+                    "Summer UTC DateTime converted to NY time zone by setting TzId returns a DateTimeOffset with UTC-4")
                 .Returns(new DateTimeOffset(summerDate, nySummerOffset));
 
             var noTz = new CalDateTime(summerDate);
             var currentSystemOffset = TimeZoneInfo.Local.GetUtcOffset(summerDate);
             yield return new TestCaseData(noTz)
-                .SetName($"Summer DateTime with no time zone information returns the system-local's UTC offset ({currentSystemOffset})")
+                .SetName(
+                    $"Summer DateTime with no time zone information returns the system-local's UTC offset ({currentSystemOffset})")
                 .Returns(new DateTimeOffset(summerDate, currentSystemOffset));
         }
 
@@ -154,34 +157,70 @@ public static IEnumerable DateTimeKindOverrideTestCases()
         }
 
         [Test, TestCaseSource(nameof(ToStringTestCases))]
-        public string ToStringTests(DateTime localDateTime, string format, IFormatProvider formatProvider)
-            => new CalDateTime(localDateTime, "Pacific/Auckland").ToString(format, formatProvider);
+        public string ToStringTests(CalDateTime calDateTime, string format, IFormatProvider formatProvider)
+            => calDateTime.ToString(format, formatProvider);
 
-        public static IEnumerable<ITestCaseData> ToStringTestCases()
+        public static IEnumerable ToStringTestCases()
         {
-            yield return new TestCaseData(new DateTime(2022, 8, 30, 10, 30, 0), null, null)
-                .Returns($"{new DateTime(2022, 8, 30, 10, 30, 0)} Pacific/Auckland")
-                .SetName("Date and time with current culture formatting returns string using BCL current culture formatted date and time");
-
-            yield return new TestCaseData(new DateTime(2022, 8, 30), null, null)
-                .Returns($"{new DateTime(2022, 8, 30):d} Pacific/Auckland")
-                .SetName("Date only with current culture formatting returns string using BCL current culture formatted date");
-
-            yield return new TestCaseData(new DateTime(2022, 8, 30, 10, 30, 0), "o", null)
-                .Returns("2022-08-30T10:30:00.0000000+12:00 Pacific/Auckland")
-                .SetName("Date and time formatted using format string with no culture returns string using BCL formatter");
+            yield return new TestCaseData(new CalDateTime(2024, 8, 30, 10, 30, 0, tzId: "Pacific/Auckland"), "O", null)
+                .Returns("2024-08-30T10:30:00.0000000+12:00 Pacific/Auckland")
+                .SetName("Date and time with 'O' format arg, default culture");
+
+            yield return new TestCaseData(new CalDateTime(2024, 8, 30, tzId: "Pacific/Auckland"), "O", null)
+                .Returns("08/30/2024 Pacific/Auckland")
+                .SetName("Date only with 'O' format arg, default culture");
+
+            yield return new TestCaseData(new CalDateTime(2024, 8, 30, 10, 30, 0, tzId: "Pacific/Auckland"), "O",
+                    CultureInfo.GetCultureInfo("fr-FR"))
+                .Returns("2024-08-30T10:30:00.0000000+12:00 Pacific/Auckland")
+                .SetName("Date and time with 'O' format arg, French culture");
+
+            yield return new TestCaseData(new CalDateTime(2024, 8, 30, 10, 30, 0, tzId: "Pacific/Auckland"),
+                    "yyyy-MM-dd", CultureInfo.InvariantCulture)
+                .Returns("2024-08-30 Pacific/Auckland")
+                .SetName("Date and time with custom format, default culture");
+
+            yield return new TestCaseData(new CalDateTime(2024, 8, 30, 10, 30, 0, tzId: "Pacific/Auckland"),
+                    "MM/dd/yyyy HH:mm:ss", CultureInfo.GetCultureInfo("FR"))
+                .Returns("08/30/2024 10:30:00 Pacific/Auckland")
+                .SetName("Date and time with format and 'FR' CultureInfo");
+
+            yield return new TestCaseData(new CalDateTime(2024, 8, 30, tzId: "Pacific/Auckland"), null,
+                    CultureInfo.GetCultureInfo("IT"))
+                .Returns("30/08/2024 Pacific/Auckland")
+                .SetName("Date only with 'IT' CultureInfo and default format arg");
+        }
 
-            yield return new TestCaseData(new DateTime(2022, 8, 30), "o", null)
-                .Returns("2022-08-30T00:00:00.0000000+12:00 Pacific/Auckland")
-                .SetName("Date and time formatted using format string with no culture returns string using BCL formatter");
+        [Test]
+        public void Simple_PropertyAndMethod_Tests()
+        {
+            var dt = new DateTime(2025, 1, 2, 10, 20, 30, DateTimeKind.Utc);
+            var c = new CalDateTime(dt, tzId: "Europe/Berlin");
 
-            yield return new TestCaseData(new DateTime(2022, 8, 30, 10, 30, 0), null, CultureInfo.InvariantCulture)
-                .Returns("08/30/2022 10:30:00 Pacific/Auckland")
-                .SetName("Date and time with format provider");
+            var c2 = new CalDateTime(dt.Year, dt.Month, dt.Day, dt.Hour, dt.Minute, dt.Second, c.TzId, null);
+            var c3 = new CalDateTime(new DateOnly(dt.Year, dt.Month, dt.Day),
+                new TimeOnly(dt.Hour, dt.Minute, dt.Second), c.TzId);
 
-            yield return new TestCaseData(new DateTime(2022, 8, 30), null, CultureInfo.InvariantCulture)
-                .Returns("08/30/2022 Pacific/Auckland")
-                .SetName("Date only with current format provider");
+            Assert.Multiple(() =>
+            {
+                Assert.That(c2.Ticks, Is.EqualTo(c3.Ticks));
+                Assert.That(c2.TzId, Is.EqualTo(c3.TzId));
+                Assert.That(CalDateTime.UtcNow.Value.Kind, Is.EqualTo(DateTimeKind.Utc));
+                Assert.That(c.Millisecond, Is.EqualTo(0));
+                Assert.That(c.Ticks, Is.EqualTo(dt.Ticks));
+                Assert.That(c.DayOfYear, Is.EqualTo(dt.DayOfYear));
+                Assert.That(c.TimeOfDay, Is.EqualTo(dt.TimeOfDay));
+                Assert.That(c.Subtract(TimeSpan.FromSeconds(dt.Second)).Value.Second, Is.EqualTo(0));
+                Assert.That(c.AddYears(1).Value, Is.EqualTo(dt.AddYears(1)));
+                Assert.That(c.AddMonths(1).Value, Is.EqualTo(dt.AddMonths(1)));
+                Assert.That(c.AddMinutes(1).Value, Is.EqualTo(dt.AddMinutes(1)));
+                Assert.That(c.AddSeconds(15).Value, Is.EqualTo(dt.AddSeconds(15)));
+                Assert.That(c.AddMilliseconds(100).Value, Is.EqualTo(dt.AddMilliseconds(0))); // truncated
+                Assert.That(c.AddMilliseconds(1000).Value, Is.EqualTo(dt.AddMilliseconds(1000)));
+                Assert.That(c.AddTicks(1).Value, Is.EqualTo(dt.AddTicks(0))); // truncated
+                Assert.That(c.AddTicks(TimeSpan.FromMinutes(1).Ticks).Value, Is.EqualTo(dt.AddTicks(TimeSpan.FromMinutes(1).Ticks)));
+                Assert.That(c.ToString("dd.MM.yyyy"), Is.EqualTo("02.01.2025 Europe/Berlin"));
+            });
         }
     }
 }

Ical.Net.Tests/DeserializationTests.cs

@@ -448,22 +448,13 @@ public void Transparency2()
             Assert.That(evt.Transparency, Is.EqualTo(TransparencyType.Transparent));
         }
 
-        /// <summary>
-        /// Tests that DateTime values that are out-of-range are still parsed correctly
-        /// and set to the closest representable date/time in .NET.
-        /// </summary>
         [Test]
-        public void DateTime1()
+        public void DateTime1_Unrepresentable_DateTimeArgs_ShouldThrow()
         {
-            var iCal = Calendar.Load(IcsFiles.DateTime1);
-            Assert.That(iCal.Events, Has.Count.EqualTo(6));
-
-            var evt = iCal.Events["nc2o66s0u36iesitl2l0b8inn8@google.com"];
-            Assert.That(evt, Is.Not.Null);
-
-            // The "Created" date is out-of-bounds.  It should be coerced to the
-            // closest representable date/time.
-            Assert.That(evt.Created.Value, Is.EqualTo(DateTime.MinValue));
+            Assert.That(() =>
+            {
+                _ = Calendar.Load(IcsFiles.DateTime1);
+            }, Throws.Exception.TypeOf<ArgumentOutOfRangeException>());
         }
 
         [Test]

Ical.Net.Tests/RecurrenceTests.cs

@@ -2828,7 +2828,7 @@ public void UsHolidays()
         [TestCase("SECONDLY", 1, true)]
         [TestCase("MINUTELY", 60, true)]
         [TestCase("HOURLY", 3600, true)]
-        [TestCase("DAILY", 24*3600, false)]
+        [TestCase("DAILY", 24*3600, true)]
         public void Evaluate1(string freq, int secsPerInterval, bool hasTime)
         {
             Calendar cal = new Calendar();
@@ -2837,7 +2837,7 @@ public void Evaluate1(string freq, int secsPerInterval, bool hasTime)
             evt.Summary = "Event summary";
 
             // Start at midnight, UTC time
-            evt.Start = new CalDateTime(DateTime.SpecifyKind(DateTime.Today, DateTimeKind.Utc)) { HasTime = false };
+            evt.Start = new CalDateTime(DateTime.SpecifyKind(DateTime.Today, DateTimeKind.Utc)); // { HasTime = false };
 
             // This case (DTSTART of type DATE and FREQ=MINUTELY) is undefined in RFC 5545.
             // ical.net handles the case by pretending DTSTART has the time set to midnight.

Ical.Net.Tests/SimpleDeserializationTests.cs

@@ -451,22 +451,15 @@ public void Transparency2()
             Assert.That(evt.Transparency, Is.EqualTo(TransparencyType.Transparent));
         }
 
-        /// <summary>
-        /// Tests that DateTime values that are out-of-range are still parsed correctly
-        /// and set to the closest representable date/time in .NET.
-        /// </summary>
         [Test, Category("Deserialization")]
-        public void DateTime1()
+        public void DateTime1_Unrepresentable_DateTimeArgs_ShouldThrow()
         {
-            var iCal = SimpleDeserializer.Default.Deserialize(new StringReader(IcsFiles.DateTime1)).Cast<Calendar>().Single();
-            Assert.That(iCal.Events, Has.Count.EqualTo(6));
-
-            var evt = iCal.Events["nc2o66s0u36iesitl2l0b8inn8@google.com"];
-            Assert.That(evt, Is.Not.Null);
-
-            // The "Created" date is out-of-bounds.  It should be coerced to the
-            // closest representable date/time.
-            Assert.That(evt.Created.Value, Is.EqualTo(DateTime.MinValue));
+            Assert.That(() =>
+            {
+                _ = SimpleDeserializer.Default.Deserialize(new StringReader(IcsFiles.DateTime1))
+                    .Cast<Calendar>()
+                    .Single();
+            }, Throws.Exception.TypeOf<ArgumentOutOfRangeException>());
         }
 
         [Test, Category("Deserialization"), Ignore("Ignore until @thoemy commits the EventStatus.ics file")]

Ical.Net/CalendarComponents/CalendarEvent.cs

@@ -126,11 +126,37 @@ public virtual bool IsAllDay
                 // has a time value.
                 if (Start != null)
                 {
-                    Start.HasTime = !value;
+                    if (value)
+                    {
+                        // Ensure time part is not set
+                        var dt = new CalDateTime(Start);
+                        dt.SetValue(DateOnly.FromDateTime(Start.Value), null, Start.Value.Kind);
+                        Start = dt;
+                    }
+                    else
+                    {
+                        // Ensure time part is set
+                        var dt = new CalDateTime(Start);
+                        dt.SetValue(DateOnly.FromDateTime(Start.Value), TimeOnly.FromDateTime(Start.Value), Start.Value.Kind);
+                        Start = dt;
+                    }
                 }
                 if (End != null)
                 {
-                    End.HasTime = !value;
+                    if (value)
+                    {
+                        // Ensure time part is not set
+                        var dt = new CalDateTime(End);
+                        dt.SetValue(DateOnly.FromDateTime(End.Value), null, End.Value.Kind);
+                        End = dt;
+                    }
+                    else
+                    {
+                        // Ensure time part is set
+                        var dt = new CalDateTime(End);
+                        dt.SetValue(DateOnly.FromDateTime(End.Value), TimeOnly.FromDateTime(End.Value), End.Value.Kind);
+                        End = dt;
+                    }
                 }
 
                 if (value && Start != null && End != null && Equals(Start.Date, End.Date))

Ical.Net/CalendarComponents/VTimeZone.cs

@@ -1,4 +1,4 @@
-using Ical.Net.DataTypes;
+using Ical.Net.DataTypes;
 using Ical.Net.Proxies;
 using Ical.Net.Utility;
 using NodaTime;
@@ -177,7 +177,7 @@ private static VTimeZoneInfo CreateTimeZoneInfo(List<ZoneInterval> matchedInterv
             timeZoneInfo.TimeZoneName = oldestInterval.Name;
 
             var start = oldestInterval.IsoLocalStart.ToDateTimeUnspecified() + delta;
-            timeZoneInfo.Start = new CalDateTime(start) { HasTime = true };
+            timeZoneInfo.Start = new CalDateTime(start);
 
             if (isRRule)
             {
@@ -244,7 +244,6 @@ private static void PopulateTimeZoneInfoRecurrenceDates(VTimeZoneInfo tzi, List<
                     continue;
                 }
 
-                date.HasTime = true;
                 periodList.Add(date);
                 tzi.RecurrenceDates.Add(periodList);
             }