Reopen "Fix DueDate.StringDate conversion to and from DateTime." (#41)

* Added FakeLocalTimeZone helper class.
The class is used to change the time zone of the tests upon initialization, and resets it back when disposed.

* Added more tests for DueDate model.
The added tests ensure consistency in StringDate property setter and getter.

* Changed date formatting in DueDate.StringDate property.
Date is now converted using the round-trip format without milliseconds.
Date is also no longer being converted to universal time before formatting.

* Made a simple change in floating due date test.
DateTimeKind is switched to Unspecified instead of Utc since the due date should be treated as floating.

* Fixed date convertion in `DueDate.StringDate` getter.
The fix reverts back to depending on `DueDate.Timezone` property to determine the conversion formatting.
However, it doesn't convert the `DueDate.Date` value to universal time unless the `DueDate` is intended to be fixed.

* Made a simple fix to the "fixed timezone" `DueDate` test.
Timezone info was missing for a fixed date.

* Fixed CreateNewItem_DueDateIsLocal_DueDateNotChanged test.
Since floating due dates are now converted to `Unspecified` date time, the method `ToLocalTime` is no longer used because it assumes the given date as `UTC`.

* Replaced DueDate public constructors with static methods.
Methods include detailed documentation comments.

* Removed redundant checks in DueDate.StringDate getter.
Static methods that are used to instantiate DueDates are now in charge of handling different kinds of dates.

* Updated tests with new DueDate static methods.

* Remove randomization in tests.
Fake time zone random selection is replaced by pre-determined custom offset.

* Remove unnecessary comments.

* Removed unnecessary SuppressFinalize call in DueDateTests.

src/Todoist.Net.Tests/Helpers/FakeLocalTimeZone.cs

@@ -0,0 +1,81 @@
+using System;
+using System.Reflection;
+
+namespace Todoist.Net.Tests.Helpers;
+
+/// <summary>
+/// A helper class that changes the local timezone to a fake timezone provided
+/// at initialization, and resets the original local timezone when disposed.
+/// </summary>
+/// <remarks>
+/// See this <see href="https://stackoverflow.com/questions/44413407/mock-the-country-timezone-you-are-running-unit-test-from">SO question</see> for more details.
+/// </remarks>
+public sealed class FakeLocalTimeZone : IDisposable
+{
+
+    /// <summary>
+    /// The fake time zone info that has been set as local.
+    /// </summary>
+    public TimeZoneInfo FakeTimeZoneInfo { get; }
+
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="FakeLocalTimeZone"/> class.
+    /// </summary>
+    private FakeLocalTimeZone(TimeZoneInfo fakeTimeZoneInfo)
+    {
+        FakeTimeZoneInfo = fakeTimeZoneInfo;
+
+        var info = typeof(TimeZoneInfo).GetField("s_cachedData", BindingFlags.NonPublic | BindingFlags.Static);
+        var cachedData = info.GetValue(null);
+
+        var field = cachedData.GetType().GetField("_localTimeZone",
+            BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Instance);
+
+        field.SetValue(cachedData, fakeTimeZoneInfo);
+    }
+
+    public void Dispose()
+    {
+        TimeZoneInfo.ClearCachedData();
+    }
+
+
+    /// <summary>
+    /// Changes the local time zone to the given <paramref name="fakeTimeZoneInfo"/>.
+    /// </summary>
+    /// <remarks>
+    /// Disposal of the returned object resets the local time zone to the original one.
+    /// </remarks>
+    /// <param name="fakeTimeZoneInfo">The time zone to set as local until disposal.</param>
+    /// <returns>
+    /// A <see cref="FakeLocalTimeZone"/> instance that represents the time zone change,
+    /// and used to reset it back to original at disposal.
+    /// </returns>
+    public static FakeLocalTimeZone ChangeLocalTimeZone(TimeZoneInfo fakeTimeZoneInfo)
+    {
+        return new FakeLocalTimeZone(fakeTimeZoneInfo);
+    }
+
+    /// <summary>
+    /// Changes the local time zone to a custom time zone with a <paramref name="baseUtcOffset"/>.
+    /// </summary>
+    /// <remarks>
+    /// Disposal of the returned object resets the local time zone to the original one.
+    /// </remarks>
+    /// <param name="baseUtcOffset">UTC offset of the custom time zone.</param>
+    /// <returns>
+    /// A <see cref="FakeLocalTimeZone"/> instance that represents the time zone change,
+    /// and used to reset it back to original at disposal.
+    /// </returns>
+    public static FakeLocalTimeZone ChangeLocalTimeZone(TimeSpan baseUtcOffset)
+    {
+        var fakeId = "Fake TimeZone";
+        var fakeDisplayName = $"(UTC+{baseUtcOffset:hh':'mm})";
+
+        var fakeTimeZoneInfo = TimeZoneInfo.CreateCustomTimeZone(fakeId, baseUtcOffset, fakeDisplayName, fakeDisplayName);
+
+        return new FakeLocalTimeZone(fakeTimeZoneInfo);
+    }
+
+}

src/Todoist.Net.Tests/Helpers/FakeLocalTimeZoneTests.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Linq;
+
+using Todoist.Net.Tests.Extensions;
+
+using Xunit;
+
+namespace Todoist.Net.Tests.Helpers;
+
+[Trait(Constants.TraitName, Constants.UnitTraitValue)]
+public class FakeLocalTimeZoneTests
+{
+
+    [Fact]
+    public void FakeLocalTimeZone_ShouldChangeLocalTimeZoneWithinScope_AndResetItBackOutsideScope()
+    {
+        var fakeTimeZoneOffset = TimeZoneInfo.Local.BaseUtcOffset + TimeSpan.FromHours(2);
+        var fakeLocalTimeZone = FakeLocalTimeZone.ChangeLocalTimeZone(fakeTimeZoneOffset);
+
+        using (fakeLocalTimeZone)
+        {
+            Assert.Equal(fakeLocalTimeZone.FakeTimeZoneInfo, TimeZoneInfo.Local);
+        }
+        Assert.NotEqual(fakeLocalTimeZone.FakeTimeZoneInfo, TimeZoneInfo.Local);
+    }
+
+}

src/Todoist.Net.Tests/Models/DueDateTests.cs

@@ -2,19 +2,35 @@
 
 using Todoist.Net.Models;
 using Todoist.Net.Tests.Extensions;
+using Todoist.Net.Tests.Helpers;
+
 using Xunit;
 
 namespace Todoist.Net.Tests.Models
 {
     [Trait(Constants.TraitName, Constants.UnitTraitValue)]
-    public class DueDateTests
+    public class DueDateTests : IDisposable
     {
+
+        private readonly FakeLocalTimeZone _fakeLocalTimeZone;
+
+        public DueDateTests()
+        {
+            _fakeLocalTimeZone = FakeLocalTimeZone.ChangeLocalTimeZone(TimeSpan.FromHours(5));
+        }
+
+        public void Dispose()
+        {
+            _fakeLocalTimeZone?.Dispose();
+        }
+
+
         [Fact]
         public void DateTimeAssignment_FullDayEvent_Success()
         {
-            var date = new DateTime(2018, 2, 5, 0, 0, 0, DateTimeKind.Utc);
+            var date = new DateTime(2018, 2, 5);
 
-            var dueDate = new DueDate(date, true);
+            var dueDate = DueDate.CreateFullDay(date);
 
             Assert.Equal("2018-02-05", dueDate.StringDate);
             Assert.True(dueDate.IsFullDay);
@@ -23,23 +39,65 @@ public void DateTimeAssignment_FullDayEvent_Success()
         [Fact]
         public void DateTimeAssignment_FloatingDueDateEvent_Success()
         {
-            var date = new DateTime(2018, 2, 5, 0, 0, 0, DateTimeKind.Utc);
+            var date = new DateTime(2018, 2, 5);
 
-            var dueDate = new DueDate(date);
+            var dueDate = DueDate.CreateFloating(date);
 
             Assert.Equal("2018-02-05T00:00:00", dueDate.StringDate);
             Assert.False(dueDate.IsFullDay);
         }
 
         [Fact]
-        public void DateTimeAssignment_FloatingDueDateWithTimezoneEvent_Success()
+        public void DateTimeAssignment_FixedTimeZoneDueDateEvent_Success()
         {
-            var date = new DateTime(2018, 2, 5, 0, 0, 0, DateTimeKind.Utc);
+            var date = new DateTime(2018, 2, 5);
 
-            var dueDate = new DueDate(date, false, "Asia/Jakarta");
+            var dueDate = DueDate.CreateFixedTimeZone(date, "Asia/Jakarta");
 
             Assert.Equal("2018-02-05T00:00:00Z", dueDate.StringDate);
             Assert.False(dueDate.IsFullDay);
         }
+
+
+        [Fact]
+        public void StringDateProperty_ShouldReturnExactAssignedValue_WhenValueIsFullDayDate()
+        {
+            var dueDate = new DueDate();
+            string initialValue = "2016-12-01";
+
+            dueDate.StringDate = initialValue;
+            string returnedValue = dueDate.StringDate;
+            dueDate.StringDate = returnedValue;
+
+            Assert.Equal(returnedValue, dueDate.StringDate);
+        }
+
+        [Fact]
+        public void StringDateProperty_ShouldReturnExactAssignedValue_WhenValueIsFloatingDate()
+        {
+            var dueDate = new DueDate();
+            string initialValue = "2016-12-03T12:00:00";
+
+            dueDate.StringDate = initialValue;
+            string returnedValue = dueDate.StringDate;
+            dueDate.StringDate = returnedValue;
+
+            Assert.Equal(returnedValue, dueDate.StringDate);
+        }
+
+        [Fact]
+        public void StringDateProperty_ShouldReturnExactAssignedValue_WhenValueIsFixedDate()
+        {
+            var dueDate = new DueDate();
+            string initialValue = "2016-12-06T13:00:00Z";
+
+            dueDate.StringDate = initialValue;
+            dueDate.Timezone = "Asia/Jakarta";
+
+            string returnedValue = dueDate.StringDate;
+            dueDate.StringDate = returnedValue;
+
+            Assert.Equal(returnedValue, dueDate.StringDate);
+        }
     }
 }

src/Todoist.Net.Tests/Services/ItemsServiceTests.cs

@@ -89,7 +89,7 @@ public void CreateItemClearDueDateAndDelete_Success()
         {
             var client = TodoistClientFactory.Create(_outputHelper);
 
-            var item = new Item("demo task") { DueDate = new DueDate("22 Dec 2021", language: Language.English) };
+            var item = new Item("demo task") { DueDate = DueDate.FromText("22 Dec 2021", Language.English) };
             client.Items.AddAsync(item).Wait();
 
             var itemInfo = client.Items.GetAsync(item.Id).Result;
@@ -113,7 +113,7 @@ public void CreateItem_InvalidPDueDate_ThrowsException()
         {
             var client = TodoistClientFactory.Create(_outputHelper);
             var item = new Item("bad task");
-            item.DueDate = new DueDate("Invalid date string");
+            item.DueDate = DueDate.FromText("Invalid date string");
 
             var aggregateException = Assert.ThrowsAsync<AggregateException>(
                 async () =>
@@ -133,7 +133,7 @@ public async Task MoveItemsToProject_Success()
             var item = new Item("demo task");
             client.Items.AddAsync(item).Wait();
 
-            item.DueDate = new DueDate("every fri");
+            item.DueDate = DueDate.FromText("every fri");
             await client.Items.UpdateAsync(item);
 
             var project = new Project(Guid.NewGuid().ToString());
@@ -162,7 +162,7 @@ public void QuickAddAsync_Success()
 
             Assert.NotNull(item);
 
-            client.Items.CompleteRecurringAsync(new CompleteRecurringItemArgument(item.Id, new DueDate(DateTime.UtcNow.AddMonths(1)))).Wait();
+            client.Items.CompleteRecurringAsync(new CompleteRecurringItemArgument(item.Id, DueDate.CreateFloating(DateTime.UtcNow.AddMonths(1)))).Wait();
             client.Items.CompleteRecurringAsync(item.Id).Wait();
 
             client.Items.DeleteAsync(item.Id).Wait();
@@ -189,12 +189,12 @@ public void CreateNewItem_DueDateIsLocal_DueDateNotChanged()
         {
             var client = TodoistClientFactory.Create(_outputHelper);
 
-            var item = new Item("New task") { DueDate = new DueDate(DateTime.Now.AddYears(1).Date) };
+            var item = new Item("New task") { DueDate = DueDate.CreateFloating(DateTime.Now.AddYears(1).Date) };
             var taskId = client.Items.AddAsync(item).Result;
 
             var itemInfo = client.Items.GetAsync(taskId).Result;
 
-            Assert.Equal(item.DueDate.Date, itemInfo.Item.DueDate.Date?.ToLocalTime());
+            Assert.Equal(item.DueDate.Date, itemInfo.Item.DueDate.Date);
 
             client.Items.DeleteAsync(item.Id).Wait();
         }
@@ -208,7 +208,7 @@ public void CreateItemClearDurationAndDelete_Success()
 
             var item = new Item("duration task")
             {
-                DueDate = new DueDate("22 Dec 2021 at 9:15", language: Language.English),
+                DueDate = DueDate.FromText("22 Dec 2021 at 9:15", Language.English),
                 Duration = new Duration(45, DurationUnit.Minute)
             };
             client.Items.AddAsync(item).Wait();

src/Todoist.Net.Tests/Services/ReminersServiceTests.cs

@@ -30,7 +30,7 @@ public async Task CreateDelete_Success()
 
             var itemId = await transaction.Items.AddAsync(new Item("Temp")).ConfigureAwait(false);
             var reminderId =
-                await transaction.Reminders.AddAsync(new Reminder(itemId) { DueDate = new DueDate(DateTime.UtcNow.AddDays(1)) }).ConfigureAwait(false);
+                await transaction.Reminders.AddAsync(new Reminder(itemId) { DueDate = DueDate.CreateFloating(DateTime.UtcNow.AddDays(1)) }).ConfigureAwait(false);
             await transaction.CommitAsync().ConfigureAwait(false);
 
             var reminders = await client.Reminders.GetAsync().ConfigureAwait(false);
@@ -50,7 +50,7 @@ public async Task AddRelativeReminder_Success()
 
             var item = new Item("Test")
             {
-                DueDate = new DueDate(DateTime.UtcNow.AddDays(1))
+                DueDate = DueDate.CreateFloating(DateTime.UtcNow.AddDays(1))
             };
 
             var taskId = await client.Items.AddAsync(item).ConfigureAwait(false);